Altec A7 Voice of the Theatre Loudspeaker Adventures
About the Speakers:
For one in interested in the Altec Lansing Voice of the Theatre speakers it would be beneficial to read a wonderful article by John Stronczer from Sound Practices on his experience with A5 speakers using a crossover circuit designed by French audio legend Jean Hiraga. I have heard at length the A5 and the A7 loudspeakers with Hiraga circuit crossover networks. While both the A5 and the A7 are wonderful sounding loudspeakers, my preference lies with the A7, which in my experience sounds better, creates a better sound stage, and which tends to be less expensive on the used market.
For one in interested in the Altec Lansing Voice of the Theatre speakers it would be beneficial to read a wonderful article by John Stronczer from Sound Practices on his experience with A5 speakers using a crossover circuit designed by French audio legend Jean Hiraga. I have heard at length the A5 and the A7 loudspeakers with Hiraga circuit crossover networks. While both the A5 and the A7 are wonderful sounding loudspeakers, my preference lies with the A7, which in my experience sounds better, creates a better sound stage, and which tends to be less expensive on the used market.
This page is about a pair of Altec Lansing A7-500-8 Voice Of The Theatre Speakers I set up in the Pete Riggle Audio listening room, known as The Garden of Earthly Delights. The speakers were built by Altec Lansing in November of 1976. I am told that they spent many years in a church in Montana hanging up in the ceiling space. These are two-way speakers with crossover at 500 Hz. This particular pair uses model 828B cabinets with a utility gray finish, model 416-8B Alnico woofers, model 511B sectoral tweeter horns, and model 802-8D alnico magnet drivers. The speakers came with model N501-8A crossovers. I left the original crossover networks in place, but play the speakers with crossovers built from a schematic originating with French audio legend Jean Hiraga. More later about Messr. Hiraga and his crossover network design. Considering the age of the speakers, they are relatively blemish free. I recently touched up a few wear spots with interior latex paint matched to the original paint by the folks at Home Depot. The match is perfect. As audio equipment goes, these speakers can be a fantastic bargain. In my room the speakers play a band width from 42 Hz to 12 kHz. With my big horn subwoofer the band width is 20 Hz to 12 kHz.
These Speakers are Wonderful:
Perhaps the first thing you should know about the A7 speakers is how wonderful they are when outfitted with a crossover using the Hiraga schematic, and using crossover capacitors of high quality. The reflex loaded bass goes adequately deep with rich timbre and beautiful midbass. I augment the bass with a giant subwoofer horn located in a loft above and behind the listening room. The subwoofer helps in subtle ways, but the bass of the Altec A7 speakers is quite good on its own. I had expected that the aluminum tweeter diaphragm would result in shouty highs. Nothing could be further from the truth. The tweeters provide a very smooth top end, ranging from 500 Hz to about 12 kHz. This is an unusually wide bandwidth, about 4-1/2 octaves, almost half of the audio spectrum. With the Hiraga crossover circuit and top performing capacitors, the overall sound has a directness, immediacy, timbre, authority, nuance, ease and musicality that engage the listener, and don't let go. Further, these speakers are capable of producing a big sound stage with great width, depth, nuance, localization of instruments and voices and a great sense of space. The Altec Lansing people knew what they were doing. If the products had been sold with good crossover networks, they would have been even more revered than they are today, and the ebay prices would be out of this world. Perhaps the large size of the boxes and the utilitarian look has suppressed audiophile enthusiasm. Mama may not like these speakers.
Perhaps the first thing you should know about the A7 speakers is how wonderful they are when outfitted with a crossover using the Hiraga schematic, and using crossover capacitors of high quality. The reflex loaded bass goes adequately deep with rich timbre and beautiful midbass. I augment the bass with a giant subwoofer horn located in a loft above and behind the listening room. The subwoofer helps in subtle ways, but the bass of the Altec A7 speakers is quite good on its own. I had expected that the aluminum tweeter diaphragm would result in shouty highs. Nothing could be further from the truth. The tweeters provide a very smooth top end, ranging from 500 Hz to about 12 kHz. This is an unusually wide bandwidth, about 4-1/2 octaves, almost half of the audio spectrum. With the Hiraga crossover circuit and top performing capacitors, the overall sound has a directness, immediacy, timbre, authority, nuance, ease and musicality that engage the listener, and don't let go. Further, these speakers are capable of producing a big sound stage with great width, depth, nuance, localization of instruments and voices and a great sense of space. The Altec Lansing people knew what they were doing. If the products had been sold with good crossover networks, they would have been even more revered than they are today, and the ebay prices would be out of this world. Perhaps the large size of the boxes and the utilitarian look has suppressed audiophile enthusiasm. Mama may not like these speakers.
The Size of the A7 Speakers:
The A7 speakers are large, with a height of 56 inches, a width of 30 inches, and a depth of 24 inches. The A5 speakers use a comparable bass box but are a little taller because the tweeters are taller.The most common finish is a utility gray with no grill over the front of the woofer box, and with the large 500 Hz tweeter horn exposed atop the cabinet. As woodworking goes, it would be relatively straightforward to build a shell around each speaker with two sides, a top, and a grill, turning them into furniture. My wing-man Stephaen tells me that I exaggerate the ease with which tasks can be accomplished.
The A7 Speakers In Small Rooms:
There is a prevailing myth that the A7 speakers do not work in small rooms and that the listener(s) need to be far away from the speakers in order for the woofer and tweeter to blend. Do not believe it. I have my pair set up with 9.5 feet between the centers of the speakers, and 9.5 feet from the front plane of the speakers to the listener's ears.
Jeff Day's A5 and A7 Speakers:
I have been aware of the Altec Lansing Voice Of The Theatre speakers for years. I enjoyed them at the movies when I was young. A friend had a beautiful pair with furniture finish and grills when I was in my twenties. A mono VOTT unit played in the classroom when I took a music appreciation class at the University of Washington in 1961. But for many reasons it never occurred to me to try a pair. Then I heard a pair of A7 VOTT speakers last year in a very small room in the home of friend, audio reviewer, and audio blogger Jeff Day. You can find Jeff at http://positive-feedback.com and at his audio blog jeffsplace.positive-feedback.com/
Jeff's A7 speakers were originally built up by Altec Lansing as a furniture pair for Leopold Stokowski, who worked with Altec on some of the first public live vrs. recorded performances at Carnegie Hall. The Stokowski A7 speakers are gorgeous, and look deceptively small in the small room Jeff uses them in. Jeff is the third owner. Even in the small room, and even with the stock crossover units (which leave much to be desired) I could hear the promise of these speakers.
Jeff also has a pair of Altec A5 speakers. The bass cabinets of the A5 speakers are the same size as the A7 cabinets, but the A5 use different components than the A7. The woofers of the A5 use more massive magnets than the woofers of the A7. Jeff's A5 tweeter uses cellular horns (an array of many small exponential horns), versus the sectoral horns of the A7 tweeters. Jeff's A5 speakers use the Altec 1005 horns, which have two rows of 5 cells, one above the other. The tweeter compression drivers of the A5 are more massive than the compression drivers of the A7. With a Hiraga network in place, and some fine tuning, Jeff has his A5 units sounding mighty wonderful. I would compare the A5 and A7 speakers (using the Hiraga crossover circuit and top performance capacitors) to chocolate. The A5 would be very dark chocolate. The A7 would be medium dark chocolate. Although the A5 components are more expensive than the A7 components, I somehow prefer the A7. Jeff doesn't have to worry about that. He has both.
I modelled Jeff's A5 speakers using the Spice electric circuit analysis program and provided the results to Jeff. Jeff discussed his experience with the A5 speakers in the following link. Jeff included my crossover calculations in his discussion.
https://jeffsplace.positive-feedback.com/the-altec-a5-voice-of-the-theatre-project-wow/
The Sound of the A7:
So how will I describe the A7 speakers as set up in my Garden of Earthly Delights listening room: full bodied, rich, directly engaging, punchy, present, immediate, smooth, sweet, musical, articulate, and nuanced, with a big sound stage, pin point localization of instruments, and lots of space. The sound stage lies well behind the loudspeakers. That is what I hear. I can't speak for others. However my wing man, Stephaen, who does not often throw bouquets at audio systems, said quietly the other day as we were listening "those are good loudspeakers, Petie." If you can get out here to Eastern Washington State, give me a call, and I will give you a demo.
Power Amplifiers:
Driving the Altec speakers I have tried 30 wpc triode wired 6550 push-pull power amps, 15 wpc ultralinear Heathkit UA2 power amps with EL84 tubes, and McIntosh MC30 power amps with 6L6 tubes. The Macs sounded better than the Heathkits, which sounded better than the triode wired 6550 amps. More recently I have been using the 15 wpc Guilty Pleasure 845 integrated amps I designed and built from scratch 20 years ago. The Guilty Pleasure 845 integrated amp provides body,musicality, and separation of voices exceeding other amps I have tried, including several other 845 amps. The gain tubes are Sylvania 12SN7 tubes. The cathode follower driver tubes are GE 6AU5GT. It is surprising how much of the wonderful body of this amp is attributable to the 6AU5GT cathode follower.
The A7 speakers are large, with a height of 56 inches, a width of 30 inches, and a depth of 24 inches. The A5 speakers use a comparable bass box but are a little taller because the tweeters are taller.The most common finish is a utility gray with no grill over the front of the woofer box, and with the large 500 Hz tweeter horn exposed atop the cabinet. As woodworking goes, it would be relatively straightforward to build a shell around each speaker with two sides, a top, and a grill, turning them into furniture. My wing-man Stephaen tells me that I exaggerate the ease with which tasks can be accomplished.
The A7 Speakers In Small Rooms:
There is a prevailing myth that the A7 speakers do not work in small rooms and that the listener(s) need to be far away from the speakers in order for the woofer and tweeter to blend. Do not believe it. I have my pair set up with 9.5 feet between the centers of the speakers, and 9.5 feet from the front plane of the speakers to the listener's ears.
Jeff Day's A5 and A7 Speakers:
I have been aware of the Altec Lansing Voice Of The Theatre speakers for years. I enjoyed them at the movies when I was young. A friend had a beautiful pair with furniture finish and grills when I was in my twenties. A mono VOTT unit played in the classroom when I took a music appreciation class at the University of Washington in 1961. But for many reasons it never occurred to me to try a pair. Then I heard a pair of A7 VOTT speakers last year in a very small room in the home of friend, audio reviewer, and audio blogger Jeff Day. You can find Jeff at http://positive-feedback.com and at his audio blog jeffsplace.positive-feedback.com/
Jeff's A7 speakers were originally built up by Altec Lansing as a furniture pair for Leopold Stokowski, who worked with Altec on some of the first public live vrs. recorded performances at Carnegie Hall. The Stokowski A7 speakers are gorgeous, and look deceptively small in the small room Jeff uses them in. Jeff is the third owner. Even in the small room, and even with the stock crossover units (which leave much to be desired) I could hear the promise of these speakers.
Jeff also has a pair of Altec A5 speakers. The bass cabinets of the A5 speakers are the same size as the A7 cabinets, but the A5 use different components than the A7. The woofers of the A5 use more massive magnets than the woofers of the A7. Jeff's A5 tweeter uses cellular horns (an array of many small exponential horns), versus the sectoral horns of the A7 tweeters. Jeff's A5 speakers use the Altec 1005 horns, which have two rows of 5 cells, one above the other. The tweeter compression drivers of the A5 are more massive than the compression drivers of the A7. With a Hiraga network in place, and some fine tuning, Jeff has his A5 units sounding mighty wonderful. I would compare the A5 and A7 speakers (using the Hiraga crossover circuit and top performance capacitors) to chocolate. The A5 would be very dark chocolate. The A7 would be medium dark chocolate. Although the A5 components are more expensive than the A7 components, I somehow prefer the A7. Jeff doesn't have to worry about that. He has both.
I modelled Jeff's A5 speakers using the Spice electric circuit analysis program and provided the results to Jeff. Jeff discussed his experience with the A5 speakers in the following link. Jeff included my crossover calculations in his discussion.
https://jeffsplace.positive-feedback.com/the-altec-a5-voice-of-the-theatre-project-wow/
The Sound of the A7:
So how will I describe the A7 speakers as set up in my Garden of Earthly Delights listening room: full bodied, rich, directly engaging, punchy, present, immediate, smooth, sweet, musical, articulate, and nuanced, with a big sound stage, pin point localization of instruments, and lots of space. The sound stage lies well behind the loudspeakers. That is what I hear. I can't speak for others. However my wing man, Stephaen, who does not often throw bouquets at audio systems, said quietly the other day as we were listening "those are good loudspeakers, Petie." If you can get out here to Eastern Washington State, give me a call, and I will give you a demo.
Power Amplifiers:
Driving the Altec speakers I have tried 30 wpc triode wired 6550 push-pull power amps, 15 wpc ultralinear Heathkit UA2 power amps with EL84 tubes, and McIntosh MC30 power amps with 6L6 tubes. The Macs sounded better than the Heathkits, which sounded better than the triode wired 6550 amps. More recently I have been using the 15 wpc Guilty Pleasure 845 integrated amps I designed and built from scratch 20 years ago. The Guilty Pleasure 845 integrated amp provides body,musicality, and separation of voices exceeding other amps I have tried, including several other 845 amps. The gain tubes are Sylvania 12SN7 tubes. The cathode follower driver tubes are GE 6AU5GT. It is surprising how much of the wonderful body of this amp is attributable to the 6AU5GT cathode follower.
Sound Pressure Measurements:
Gary Ford, a very competent sound systems professional living out our way, is good at speaker measurements. Gary dropped by recently and did a measurement of the Altec A7 speakers in the Garden of Earthly Delights. I knew that these speakers sounded good, but did not know how they might measure. From the listening position they measured very well indeed, with and without the giant horn subwoofer in operation. The frequency response was from the low forties to about 12 kHz without the subwoofer. The drivers for this measurement are the 416-8B 8 Ohm alnico magnet woofer, the 802-8D 8 Ohm alnico magnet compression driver, and a pair of Altec 415 biflex drivers for the subwoofer horn. Why use a wide range driver for a subwoofer? It was what we had on hand when the woofer was built. The measured system frequency response with the subwoofer engaged is from the 20 to 12 kHz with the subwoofer. From about 50 Hz to 12 kHz the response drops in an almost straight line on a log-log frequency response graph (the so called Bode diagram we audiophiles see so often), falling about 1.38 dB per octave.The L-pad setting for the tweeter is the one that makes the speaker sound best. I asked Gary about the gradually falling response. He advised that a smoothly falling response makes for good listenable sound and is targeted by some sound reinforcement professionals.
My experience has also been that a smoothly falling response, or at least a wide band reduction of frequencies centered on about 3 or 4 kHz, makes a system sound lovely. By wide band, I mean the output might start falling at 700 Hz, reaching a trough of maybe 4 dB at 3.5 kHz, gradually returning to the baseline at 9 or 10 kHz. Every effort I have made at flat loudspeaker response equalization has ended in disaster. Gary's measurements were another learning experience for me, reinforcing observations I had made before (about the desirability of having the system response fall with increasing frequency), but about which I was tentative.
Above 10 kHz the Hiraga network provides a rising drive signal to the tweeter, which might add a little extension to the tweeter output at these frequencies. Looking at the smoothed frequency response plot below, and noticing the shelving of frequencies above the 500 Hz. crossover point, one might suspect that raising the tweeter level about 3 dB would give a better result. It certainly would provide a flatter measurement. However the system sounds best with the tweeter set where it is. If one were a hound for bright high frequencies, it might make sense to turn the tweeter up just a little.
On a different point, the rising output of the subwoofer at very low frequencies helps deal a blow to the Fletcher-Munson effect without exciting boom frequencies in the 50 Hz range.
The A7 response curve immediately below is taken at the listening sweet spot with a pair of A7 speakers in the Garden of Earthly Delights with the big horn subwoofer (29 feet long, mouth dimensions 9.5 feet wide by 6 feet high) playing.
Gary Ford, a very competent sound systems professional living out our way, is good at speaker measurements. Gary dropped by recently and did a measurement of the Altec A7 speakers in the Garden of Earthly Delights. I knew that these speakers sounded good, but did not know how they might measure. From the listening position they measured very well indeed, with and without the giant horn subwoofer in operation. The frequency response was from the low forties to about 12 kHz without the subwoofer. The drivers for this measurement are the 416-8B 8 Ohm alnico magnet woofer, the 802-8D 8 Ohm alnico magnet compression driver, and a pair of Altec 415 biflex drivers for the subwoofer horn. Why use a wide range driver for a subwoofer? It was what we had on hand when the woofer was built. The measured system frequency response with the subwoofer engaged is from the 20 to 12 kHz with the subwoofer. From about 50 Hz to 12 kHz the response drops in an almost straight line on a log-log frequency response graph (the so called Bode diagram we audiophiles see so often), falling about 1.38 dB per octave.The L-pad setting for the tweeter is the one that makes the speaker sound best. I asked Gary about the gradually falling response. He advised that a smoothly falling response makes for good listenable sound and is targeted by some sound reinforcement professionals.
My experience has also been that a smoothly falling response, or at least a wide band reduction of frequencies centered on about 3 or 4 kHz, makes a system sound lovely. By wide band, I mean the output might start falling at 700 Hz, reaching a trough of maybe 4 dB at 3.5 kHz, gradually returning to the baseline at 9 or 10 kHz. Every effort I have made at flat loudspeaker response equalization has ended in disaster. Gary's measurements were another learning experience for me, reinforcing observations I had made before (about the desirability of having the system response fall with increasing frequency), but about which I was tentative.
Above 10 kHz the Hiraga network provides a rising drive signal to the tweeter, which might add a little extension to the tweeter output at these frequencies. Looking at the smoothed frequency response plot below, and noticing the shelving of frequencies above the 500 Hz. crossover point, one might suspect that raising the tweeter level about 3 dB would give a better result. It certainly would provide a flatter measurement. However the system sounds best with the tweeter set where it is. If one were a hound for bright high frequencies, it might make sense to turn the tweeter up just a little.
On a different point, the rising output of the subwoofer at very low frequencies helps deal a blow to the Fletcher-Munson effect without exciting boom frequencies in the 50 Hz range.
The A7 response curve immediately below is taken at the listening sweet spot with a pair of A7 speakers in the Garden of Earthly Delights with the big horn subwoofer (29 feet long, mouth dimensions 9.5 feet wide by 6 feet high) playing.
Alternative Compression Drivers for the A7 speakers:
My 8 Ohm Altec A7-500-8 speakers came with Altec 802-8D one-inch compression drivers for the 511 tweeter horns. I have been very happy with the 802-8D drivers. I had an extended opportunity to try Altec 802-8G one-inch compression drivers and found them to be less musical than the 8D version. The 8G version is more extended on the high end; however this advantage did not convince me to adopt the 8G version. The overall musicality of the 8D version won out.
The rear face of the compression driver phase plugs is a convex spherical sector matching the concave curvature of the aluminum diaphragm it faces. Whereas the 8D version uses an older style steel spherical sector phase plug with concentric circular slots, the 8G version uses the plastic Tangerine phase plug, which has radial slots. The Tangerine phase plug is so named because it is made from orange plastic about the color of a tangerine, and because the radial slots make the phase plug appear like a peeled tangerine viewed on axis.
Recently I have had an extended opportunity to play the one-inch Radian 475PB compression drivers in place of the Altec 802-8D. I find the Radian drivers quite musical. They are relatively inexpensive. The Radian drivers are a touch smoother and warmer than the Altec drivers. The Altec drivers are a touch more incisive and leaner than the Radian drivers, allowing the listener to listen a bit deeper into the music. Through the Altec 511 horn the sense of space is comparable between the Radian 475PB and Altec 802D drivers. Both drivers give the listener much to love. Different listeners might reasonably choose different drivers. The impressions given in this paragraph are those of myself and a trusted member of my listening panel. We independently arrived at the same conclusions.
Some, and perhaps all, Radian compression driver diaphragms use a Mylar surround. This is different than most Altec compression driver diaphragms which have tangentially pleated aluminum surrounds stamped integrally with the dome of the diaphragm. It is my understanding that Radian diaphragms were inspired by Emilar diaphragms. Emilar split off from Altec with his own ideas about compression driver design. Altec made some polymer surround diaphragms called Symbiotic, which in principle are similar in concept to the Emilar and and Radian diaphragms. I have not heard Symbiotic diaphragms. In my early musings I was concerned that aluminum surrounds would not provide sufficient damping to the diaphragm, and might suffer from resonances. In the intervening years I have been favorably impressed by the 802 drivers. Experience with the Radian Mylar edged diaphragms tends to ever-so-slightly confirm my early musings regarding possible benefits of a polymer surround.
If I had studied the specifications and the response curve of the Radian 475PB drivers before I tried them on loan I would not have given them a try. The specified low frequency limit is 800 Hz. The recommended protective filter is 12 dB/octave at 1200 Hz or 24 dB/octave at 800 Hz. The response curve shows the output falling at 24 dB/octave below 750 Hz. The resonant frequency is 750 Hz. All that said, in non-professional use, there has been no sign of distress with the 525 Hz cutoff frequency of the Hiraga network, and there is no obvious sonic deficiency. To the contrary, the Radian drivers provided a very desirable sound. Looking at the data and knowing the 12 dB slope woofer above 585 Hz (determined by the crossover low pass filter), I suspect the combined response curve of the 416 woofer and the 511 horn with the Radian driver to be approximately level where the woofer crosses over to the tweeter.
Whereas the Altec 802 drivers use audiophile approved Alnico magnets, the Radian 475PB drivers use Ferrite V. On the subject of Alnico vrs. Ferrite V, I hear no advantage either way. The Radian magnets want to grab any close-by iron or steel. I have purchased an aluminum 7/16" spanner to use when mounting the Radian drivers.
Here is a link to data for the Radian 475PB drivers:
My 8 Ohm Altec A7-500-8 speakers came with Altec 802-8D one-inch compression drivers for the 511 tweeter horns. I have been very happy with the 802-8D drivers. I had an extended opportunity to try Altec 802-8G one-inch compression drivers and found them to be less musical than the 8D version. The 8G version is more extended on the high end; however this advantage did not convince me to adopt the 8G version. The overall musicality of the 8D version won out.
The rear face of the compression driver phase plugs is a convex spherical sector matching the concave curvature of the aluminum diaphragm it faces. Whereas the 8D version uses an older style steel spherical sector phase plug with concentric circular slots, the 8G version uses the plastic Tangerine phase plug, which has radial slots. The Tangerine phase plug is so named because it is made from orange plastic about the color of a tangerine, and because the radial slots make the phase plug appear like a peeled tangerine viewed on axis.
Recently I have had an extended opportunity to play the one-inch Radian 475PB compression drivers in place of the Altec 802-8D. I find the Radian drivers quite musical. They are relatively inexpensive. The Radian drivers are a touch smoother and warmer than the Altec drivers. The Altec drivers are a touch more incisive and leaner than the Radian drivers, allowing the listener to listen a bit deeper into the music. Through the Altec 511 horn the sense of space is comparable between the Radian 475PB and Altec 802D drivers. Both drivers give the listener much to love. Different listeners might reasonably choose different drivers. The impressions given in this paragraph are those of myself and a trusted member of my listening panel. We independently arrived at the same conclusions.
Some, and perhaps all, Radian compression driver diaphragms use a Mylar surround. This is different than most Altec compression driver diaphragms which have tangentially pleated aluminum surrounds stamped integrally with the dome of the diaphragm. It is my understanding that Radian diaphragms were inspired by Emilar diaphragms. Emilar split off from Altec with his own ideas about compression driver design. Altec made some polymer surround diaphragms called Symbiotic, which in principle are similar in concept to the Emilar and and Radian diaphragms. I have not heard Symbiotic diaphragms. In my early musings I was concerned that aluminum surrounds would not provide sufficient damping to the diaphragm, and might suffer from resonances. In the intervening years I have been favorably impressed by the 802 drivers. Experience with the Radian Mylar edged diaphragms tends to ever-so-slightly confirm my early musings regarding possible benefits of a polymer surround.
If I had studied the specifications and the response curve of the Radian 475PB drivers before I tried them on loan I would not have given them a try. The specified low frequency limit is 800 Hz. The recommended protective filter is 12 dB/octave at 1200 Hz or 24 dB/octave at 800 Hz. The response curve shows the output falling at 24 dB/octave below 750 Hz. The resonant frequency is 750 Hz. All that said, in non-professional use, there has been no sign of distress with the 525 Hz cutoff frequency of the Hiraga network, and there is no obvious sonic deficiency. To the contrary, the Radian drivers provided a very desirable sound. Looking at the data and knowing the 12 dB slope woofer above 585 Hz (determined by the crossover low pass filter), I suspect the combined response curve of the 416 woofer and the 511 horn with the Radian driver to be approximately level where the woofer crosses over to the tweeter.
Whereas the Altec 802 drivers use audiophile approved Alnico magnets, the Radian 475PB drivers use Ferrite V. On the subject of Alnico vrs. Ferrite V, I hear no advantage either way. The Radian magnets want to grab any close-by iron or steel. I have purchased an aluminum 7/16" spanner to use when mounting the Radian drivers.
Here is a link to data for the Radian 475PB drivers:
Reduce the Reflex Port Area:
Vented enclosures like the bass box of the A5 and A7 speakers need to have the correct vent area. The factory provided area of 208 square inches for the bass box port of the A5 and A7 speakers is too large for best results. With the large area the bass was boomy and poorly defined.
An article on the A5 by John Stronczer suggested that it might be desirable to reduce the port area. My first attempt at reducing the port area was accomplished by inserting an 8-1/8 inch by 17.5 inch board of 3/4 inch plywood into the center of the slot provided by the factory. This left two 34 square inch vents, one on each side of the plywood board. The board was friction fit into place using card stock shims as required.This gave a very nice bass response with which I was quite satisfied for an extended period.
A timeworn methodology for adjusting vent area is to do woofer-in-box electrical impedance sweeps, adjusting the port area to achieve two roughly equal impedance bumps. This was done for me by Gary Ford, mentioned above. With the vent at either the original 208 square inches or at 64 square inches we found only one impedance bump . Reducing the port area of the A7 speaker to 34 square inches resulted in two roughly equal impedance bumps. My initial impression on selected pieces of music was that 34 square inches of port in each box was preferable to 68 square inches. More recently I happened to be playing a succession of pieces, all with a lot of very low bass material. What I heard was disturbing. Even with the big horn subwoofer turned off, I was hearing some of what I can only call grotesque bass undertones. Upon opening up the port area to the previous value of 64 square inches, the bass returned to a very pleasant presentation on all the material that I played. So we are back at 64 square inches, and very pleased. With good crossovers and the right setup, the A7-500 speakers are really wonderful. They are completely non-clinical, with a big full rich bottom end, lots of nuance and inner detail, good localization of performers, big space, and a really musical presentation.
Praise for the Altec Lansing A5 and A7 speakers:
To back up my praise for the Altec Lansing A5 and A7 loudspeakers, let me suggest that you read an article authored by John Stronczer of Bel Canto Design. The article was published in Positive Feedback some years ago. John set up a version of the A5 based on communication with Jean Hiraga. The following URL will get you to the article: http://wajonaudio.webs.com/Voice%20of%20the%20theatre.pdf
Also, wajonaudio has a nice article on the A7:
http://wajonaudio.webs.com/RETURN%20of%20a%20LEGEND%20-%20ALTEC%20A7%20Speaker-System.htm
These articles express the respect the authors have for the A5 and A7 speakers.
About Jean Hiraga:
Looking for biographical info on Jean Hiraga turned up an excerpt from an article by the redoubtable Lynn Olson. I encourage you to read the article:
http://www.nutshellhifi.com/library/europe3.html
Here is the excerpt selected from Lynn Olson's article:
"Jean Hiraga, long-time editor of "Revue du Son", gave a truly inspiring talk and musical presentation - a highlight not just of this show, but any show. Why? Jean Hiraga, son of a Japanese father and a French mother, was in a unique position to bridge the European and Japanese world of audio, speaking both languages fluently, and with a deeply felt attachment to the art and craft of high-fidelity sound. He was exposed to Japanese triode culture in the mid-Sixties - twenty-five years before the American triode revival in the early Nineties - and brought it back to Europe."
"He wrote some of the first articles analyzing the desirable harmonic characteristics of direct-heated triodes, and is directly responsible for introducing the sound of DHTs to France, Italy, in time, the rest of Europe, and finally, to the English-speaking audio world. Without Mr. Hiraga, there would have been no Sound Practices magazine, no VSAC, and no ETF - the English-speaking audio world would be nothing but high-watt mainstream and home-theater equipment. Fortunately for music lovers everywhere, events took a different course."
About Crossovers for the A5 and A7:
A circuit by Hiraga for a crossover for A5 speakers with the 8 ohm drivers is included in John Stronczer's article. John also shows a crossover for A5 speakers with 16 ohm drivers. Neither of these schematics shows an L-pad for the tweeter, which has turned out to be a necessity for my A7 speakers and for Jeff's A5 speakers.
When faced with the need for improved crossovers it occurred to me that the notch filter Hiraga included in his A5 crossover would possibly be a welcome addition to many 2 way speaker systems, which often are too hot in the 900 Hz to 9 kHz range addressed by the notch filter. So I decided to try the Hiraga's circuit (designed for the A5 speakers) on my A7 speakers, using component values specified by Hiraga. Here is the circuit for 8 Ohm speakers, with the L-pad included. The image may be difficult to read, so here are the values: In the low and high pass branch the inductors are 3.3 mH. The capacitor in the low pass circuit is 36 uF (40 uF works equally well). The capacitor in the high pass circuit is 19 uF (20 uF works equally well). The notch filter inductor is 3.3 mH in series with a 50 Ohm resistor. The notch filter capacitor is 1.7 uF (2 uF works equally well). The notch filter resistor is 12 Ohms. The resistors to ground are 70 Ohms and 5 Ohms. The L-pad is 8 ohms.
This circuit, typical of second order crossovers, connects the tweeter out of phase with the woofer. Note that the amplifier positive terminal is connected to L-pad terminal 3. The compression driver negative terminal goes to L-pad terminal 2. The amplifier negative terminal is connected to the crossover ground bus which is connected to L-pad terminal 1 and the compression driver positive terminal.
How to determine the positive terminal of an 802 driver?
For the 802-8D compression driver the + terminal is the one marked with the number 2. Looking at the rear of the compression driver with the terminals at the top, the + terminal is on the right. Mark it with some red tape or paint. I notice that for the later 802-8G driver the + terminal is marked in red, and located the same as for the 802-8D driver. On the Lansing Heritage Site one of the forum members, jimd, has the following advice:
"In the case of Altec cone drivers marked with terminals marked 1 and 2, 1 is hot as the magnet is behind the cone.In the case of the 802 and other "inside out" type HF drivers, where the builders routed the sound output through the magnetic assembly, the magnet is in front of the diaphragm instead of behind it like conventional drivers. Therefore, to get positive pressure at the exit of the Altec HF driver, one must apply positive voltage to terminal 2. Confusing? Yes. It was really nice when they went to Red or + on the hot terminals."
For a 16 Ohm crossover, double the values of the inductors, resistors, and L-pad, and halve the value of the capacitors.
The Hiraga Circuit as Modified by Pete Riggle:
The circuit shown below, based on Hiraga's 8 Ohm crossover circuit, includes the tweeter L-pad, not included in Hiraga's original circuit diagram, and two switches not included in Hiraga's original circuit diagram. With both switches open the notch filter resistance is 12 ohms (the sum of 6 ohms, 3 ohms, and 3 ohms). This provides a 4 dB deep Hiraga notch, which starts somewhere around 1 kHz, deepens to a maximum at 3.5 kHz, and ends some where around 9 kHz. If one of the switches is closed, the notch filter resistance becomes 9 ohms, which provides a 2 dB deep Hiraga notch. If both switches are closed the notch filter resistance becomes 6 ohms, which eliminates the Hiraga notch. For the past few years this figure has had an error in the L-pad connections. As of 7/16/20 this error has been corrected.
Vented enclosures like the bass box of the A5 and A7 speakers need to have the correct vent area. The factory provided area of 208 square inches for the bass box port of the A5 and A7 speakers is too large for best results. With the large area the bass was boomy and poorly defined.
An article on the A5 by John Stronczer suggested that it might be desirable to reduce the port area. My first attempt at reducing the port area was accomplished by inserting an 8-1/8 inch by 17.5 inch board of 3/4 inch plywood into the center of the slot provided by the factory. This left two 34 square inch vents, one on each side of the plywood board. The board was friction fit into place using card stock shims as required.This gave a very nice bass response with which I was quite satisfied for an extended period.
A timeworn methodology for adjusting vent area is to do woofer-in-box electrical impedance sweeps, adjusting the port area to achieve two roughly equal impedance bumps. This was done for me by Gary Ford, mentioned above. With the vent at either the original 208 square inches or at 64 square inches we found only one impedance bump . Reducing the port area of the A7 speaker to 34 square inches resulted in two roughly equal impedance bumps. My initial impression on selected pieces of music was that 34 square inches of port in each box was preferable to 68 square inches. More recently I happened to be playing a succession of pieces, all with a lot of very low bass material. What I heard was disturbing. Even with the big horn subwoofer turned off, I was hearing some of what I can only call grotesque bass undertones. Upon opening up the port area to the previous value of 64 square inches, the bass returned to a very pleasant presentation on all the material that I played. So we are back at 64 square inches, and very pleased. With good crossovers and the right setup, the A7-500 speakers are really wonderful. They are completely non-clinical, with a big full rich bottom end, lots of nuance and inner detail, good localization of performers, big space, and a really musical presentation.
Praise for the Altec Lansing A5 and A7 speakers:
To back up my praise for the Altec Lansing A5 and A7 loudspeakers, let me suggest that you read an article authored by John Stronczer of Bel Canto Design. The article was published in Positive Feedback some years ago. John set up a version of the A5 based on communication with Jean Hiraga. The following URL will get you to the article: http://wajonaudio.webs.com/Voice%20of%20the%20theatre.pdf
Also, wajonaudio has a nice article on the A7:
http://wajonaudio.webs.com/RETURN%20of%20a%20LEGEND%20-%20ALTEC%20A7%20Speaker-System.htm
These articles express the respect the authors have for the A5 and A7 speakers.
About Jean Hiraga:
Looking for biographical info on Jean Hiraga turned up an excerpt from an article by the redoubtable Lynn Olson. I encourage you to read the article:
http://www.nutshellhifi.com/library/europe3.html
Here is the excerpt selected from Lynn Olson's article:
"Jean Hiraga, long-time editor of "Revue du Son", gave a truly inspiring talk and musical presentation - a highlight not just of this show, but any show. Why? Jean Hiraga, son of a Japanese father and a French mother, was in a unique position to bridge the European and Japanese world of audio, speaking both languages fluently, and with a deeply felt attachment to the art and craft of high-fidelity sound. He was exposed to Japanese triode culture in the mid-Sixties - twenty-five years before the American triode revival in the early Nineties - and brought it back to Europe."
"He wrote some of the first articles analyzing the desirable harmonic characteristics of direct-heated triodes, and is directly responsible for introducing the sound of DHTs to France, Italy, in time, the rest of Europe, and finally, to the English-speaking audio world. Without Mr. Hiraga, there would have been no Sound Practices magazine, no VSAC, and no ETF - the English-speaking audio world would be nothing but high-watt mainstream and home-theater equipment. Fortunately for music lovers everywhere, events took a different course."
About Crossovers for the A5 and A7:
A circuit by Hiraga for a crossover for A5 speakers with the 8 ohm drivers is included in John Stronczer's article. John also shows a crossover for A5 speakers with 16 ohm drivers. Neither of these schematics shows an L-pad for the tweeter, which has turned out to be a necessity for my A7 speakers and for Jeff's A5 speakers.
When faced with the need for improved crossovers it occurred to me that the notch filter Hiraga included in his A5 crossover would possibly be a welcome addition to many 2 way speaker systems, which often are too hot in the 900 Hz to 9 kHz range addressed by the notch filter. So I decided to try the Hiraga's circuit (designed for the A5 speakers) on my A7 speakers, using component values specified by Hiraga. Here is the circuit for 8 Ohm speakers, with the L-pad included. The image may be difficult to read, so here are the values: In the low and high pass branch the inductors are 3.3 mH. The capacitor in the low pass circuit is 36 uF (40 uF works equally well). The capacitor in the high pass circuit is 19 uF (20 uF works equally well). The notch filter inductor is 3.3 mH in series with a 50 Ohm resistor. The notch filter capacitor is 1.7 uF (2 uF works equally well). The notch filter resistor is 12 Ohms. The resistors to ground are 70 Ohms and 5 Ohms. The L-pad is 8 ohms.
This circuit, typical of second order crossovers, connects the tweeter out of phase with the woofer. Note that the amplifier positive terminal is connected to L-pad terminal 3. The compression driver negative terminal goes to L-pad terminal 2. The amplifier negative terminal is connected to the crossover ground bus which is connected to L-pad terminal 1 and the compression driver positive terminal.
How to determine the positive terminal of an 802 driver?
For the 802-8D compression driver the + terminal is the one marked with the number 2. Looking at the rear of the compression driver with the terminals at the top, the + terminal is on the right. Mark it with some red tape or paint. I notice that for the later 802-8G driver the + terminal is marked in red, and located the same as for the 802-8D driver. On the Lansing Heritage Site one of the forum members, jimd, has the following advice:
"In the case of Altec cone drivers marked with terminals marked 1 and 2, 1 is hot as the magnet is behind the cone.In the case of the 802 and other "inside out" type HF drivers, where the builders routed the sound output through the magnetic assembly, the magnet is in front of the diaphragm instead of behind it like conventional drivers. Therefore, to get positive pressure at the exit of the Altec HF driver, one must apply positive voltage to terminal 2. Confusing? Yes. It was really nice when they went to Red or + on the hot terminals."
For a 16 Ohm crossover, double the values of the inductors, resistors, and L-pad, and halve the value of the capacitors.
The Hiraga Circuit as Modified by Pete Riggle:
The circuit shown below, based on Hiraga's 8 Ohm crossover circuit, includes the tweeter L-pad, not included in Hiraga's original circuit diagram, and two switches not included in Hiraga's original circuit diagram. With both switches open the notch filter resistance is 12 ohms (the sum of 6 ohms, 3 ohms, and 3 ohms). This provides a 4 dB deep Hiraga notch, which starts somewhere around 1 kHz, deepens to a maximum at 3.5 kHz, and ends some where around 9 kHz. If one of the switches is closed, the notch filter resistance becomes 9 ohms, which provides a 2 dB deep Hiraga notch. If both switches are closed the notch filter resistance becomes 6 ohms, which eliminates the Hiraga notch. For the past few years this figure has had an error in the L-pad connections. As of 7/16/20 this error has been corrected.
The calculated electrical response of the Hiraga 8 Ohm crossover into 8 ohm electrical loads is shown in the Bode diagram below, with a correction to match the sensitivities of the woofer and the tweeter (like using an L-pad on real speakers). These results were calculated using the Spice electrical circuit analysis program. Pure resistance, inductance and capacitance were assumed. Response curves were also calculated adding parasitic inductance to the crossover resistance values and adding measured speaker driver inductance values to the load resistance values. The difference between the response curves with and without the inductance corrections was small. These are the speaker response curves we would expect for perfect speakers when driven by the Hiraga circuit through a perfect power amplifier. What is the point of all this? We want to know the contribution to frequency response attributable to the crossover network.
Crossover Capacitors:
Not all capacitors are created equal. Good capacitors are the key to good crossover networks. To get wonderful sound the capacitors need to deliver wonderful sound. They need to sound musical. Capacitors are often the weakest link in an audio component. On the basis of listening tests of capacitors using my Altec A7 speakers in the Garden of Earthly Delights, I have laid in a stock of high performance capacitors oil capacitors which I sell as Pete Riggle Personally Selected Loudspeaker Crossover Capacitors (active link). My Spice program calculations show that +/- 15% deviation in capacitance from the values shown on the schematic has little effect on the calculated crossover response. Don't be afraid to round up or down a little as needed to obtain capacitors to do the job. I will mention here that for the notch filter capacitors in his Altec A5 speakers Jeff Day has tried Dueland Cast capacitors with tin plated copper plates. Jeff is quite pleased with the resulting sound. These capacitors are very expensive, and out of range for most of us. Not to worry. I must say that I am more than happy with the oil capacitors that I use and sell.
Low Pass Crossover Inductors:
For inductors for the low pass branch of the crossovers I suggest the lowest DC resistance air core inductors you can afford. I like the ERSE Super Q inductors which have grain oriented silicon steel cores. For the low pass branch of the A7 speakers, lower DC Resistance (DCR) of the inductor is better. Low resistance in the low pass inductor limits degradation of woofer electro-dynamic damping. Arguments are made that air core inductors sound better than
For his A5 Hiraga type crossovers Jeff Day used identical air core inductors in the low pass, high pass, and notch filter locations and got nice results. It is worth mentioning that the slightly greater DC resistance of the air core inductor in the low pass location of the A5 crossover might not be detrimental. It is possible that the driver of the A5 has too much magnet for best bass response, which can be offset by a little more DC resistance in the inductor.
High Pass Crossover Inductors:
Low DCR is unimportant in the high pass branch. Electrical response calculations made with the Spice program show that a modest amount of DCR (an ohm or two) does cause a reduction in the slope of the high pass filter. This is not a concern, because the reduction in slope occurs at a frequency much lower than the crossover point, and at a level of attenuation where the benefits of slope are no longer important. So save a bunch of money and use 18 gage wire.
It is preferable to use air core inductors for the main inductor and the notch filter inductor of the high pass branch.
Notch Filter Inductors:
It is practical to use a fairly high resistance notch filter inductor, using the electrical resistance of the inductor wire as part of the 50 or 100 ohms in series with the inductor (for 8 ohm or 16 ohm crossovers, respectively). I buy spools of 24 gage copper magnet wire from Remington on eBay. I randomly level wind these inductors by hand on wood bobbins handmade in my wood shop. The core has a diameter of 1.5 inches and a length of 1 inch. The end plates are 3/16 inch or 1/4 inch plywood cut 2.5 inches square. Each end plate is glued on with white glue and clamped with two small brass screws (do not use steel). I temporarily provide the bobbin with an axial screw and nut, and spin the bobbin with a slow electric drill in one hand, level winding the wire with the other hand. The DCR for a 6.6 mH inductor is about 5.5 ohms (which ends up in series with a 95 or 100 ohm resistor). The DCR for a 3.3 mH inductor is about 3.5 ohms (which end up in series with a 47 or 50 ohm resistor).
If you have or buy inductors with higher inductance than required, it makes perfect sense to unwind the inductor until it measures the required value. If, for example, you need a 3.3 mH inductor, but can buy only 4.0, it makes perfect sense to buy the 4.0 and unwind it to 3.3 mH. Low cost capacitance/inductance meters are available; check on ebay. As you unwind the inductor, leave the loose wire coming off the inductor intact. The loose wire will not have significant inductance. When the inductance meter gives you the desired value, cut the wire a little long and secure it.
Sources of Inductors:
Check with Parts Express, partsexpress.com , and ERSE, erseaudio.com.
Crossover Resistors:
You will want to use wire-wound power resistors with a power rating of 5 or 10 watts. These resistors come in a number of varieties. The type with the metal heat sink are convenient to mount, but are expensive. The glossy brown ceramic type such as the Ohmite resistors are pretty. I have gotten spectacularly good sound using the least expensive power resistor type, which is the cement wire wound resistor in the rectangular ceramic box.
Sources of Power Resistors:
Cement wire wound resistors in 5 or 10 watt power ratings will generally suffice. I normally use 10 watt values. It is not easy to find a catalog with organized results for easy shopping. ERSE (erse.com) was at one time a good source, and may be again in the future. Currently Digi-Key electronics sells Yageo cement resistors, available in many values. However the catalog is not organized by resistor value, making it time consuming to assemble an order.
Sources of L-pads:
I have had fine success with inexpensive L-pads out of my parts box. For my crossover products I use the 100 watt units sold by Parts Express. These work well. The slightly less expensive 50 watt units sold by Parts Express should also work well and be a safe bet.
Building Crossovers:
First let me advise you that building crossovers is quite a bit more time consuming than you would imagine from just looking at the schematic.
If you are not interested in constructing your own crossovers, I can build them for you (active link). Also, a different crossover construction method than shown below is available at the link.
The following discussion may be helpful to those planning to build their own crossover boards. I recommend using 3/4 inch plywood to mount the components. More recently I have been adding a front and rear panel of 1/4 inch plywood or masonite to the 3/4 inch plywood mounting board. I put the controls on the front panel and the amplifier and speaker terminals on the rear panel. Click here (active link) to see image of crossovers built in this alternative way.
Shown below, are layouts and photos of crossover networks designed and fabricated for Jeff Day's A5 Voice Of The Theatre speakers.
Let us start with the first image. I put Jeff's crossovers on two boards; one board is for the low pass network; one is for the high pass network. I separated the low and high pass networks onto two boards so that the boards can hide behind the tweeter horn, one on each side of the tweeter support stand. In the image below you see one completed set of boards, and one set not yet populated:
The images below show the low and high pass boards individually:
Not all capacitors are created equal. Good capacitors are the key to good crossover networks. To get wonderful sound the capacitors need to deliver wonderful sound. They need to sound musical. Capacitors are often the weakest link in an audio component. On the basis of listening tests of capacitors using my Altec A7 speakers in the Garden of Earthly Delights, I have laid in a stock of high performance capacitors oil capacitors which I sell as Pete Riggle Personally Selected Loudspeaker Crossover Capacitors (active link). My Spice program calculations show that +/- 15% deviation in capacitance from the values shown on the schematic has little effect on the calculated crossover response. Don't be afraid to round up or down a little as needed to obtain capacitors to do the job. I will mention here that for the notch filter capacitors in his Altec A5 speakers Jeff Day has tried Dueland Cast capacitors with tin plated copper plates. Jeff is quite pleased with the resulting sound. These capacitors are very expensive, and out of range for most of us. Not to worry. I must say that I am more than happy with the oil capacitors that I use and sell.
Low Pass Crossover Inductors:
For inductors for the low pass branch of the crossovers I suggest the lowest DC resistance air core inductors you can afford. I like the ERSE Super Q inductors which have grain oriented silicon steel cores. For the low pass branch of the A7 speakers, lower DC Resistance (DCR) of the inductor is better. Low resistance in the low pass inductor limits degradation of woofer electro-dynamic damping. Arguments are made that air core inductors sound better than
For his A5 Hiraga type crossovers Jeff Day used identical air core inductors in the low pass, high pass, and notch filter locations and got nice results. It is worth mentioning that the slightly greater DC resistance of the air core inductor in the low pass location of the A5 crossover might not be detrimental. It is possible that the driver of the A5 has too much magnet for best bass response, which can be offset by a little more DC resistance in the inductor.
High Pass Crossover Inductors:
Low DCR is unimportant in the high pass branch. Electrical response calculations made with the Spice program show that a modest amount of DCR (an ohm or two) does cause a reduction in the slope of the high pass filter. This is not a concern, because the reduction in slope occurs at a frequency much lower than the crossover point, and at a level of attenuation where the benefits of slope are no longer important. So save a bunch of money and use 18 gage wire.
It is preferable to use air core inductors for the main inductor and the notch filter inductor of the high pass branch.
Notch Filter Inductors:
It is practical to use a fairly high resistance notch filter inductor, using the electrical resistance of the inductor wire as part of the 50 or 100 ohms in series with the inductor (for 8 ohm or 16 ohm crossovers, respectively). I buy spools of 24 gage copper magnet wire from Remington on eBay. I randomly level wind these inductors by hand on wood bobbins handmade in my wood shop. The core has a diameter of 1.5 inches and a length of 1 inch. The end plates are 3/16 inch or 1/4 inch plywood cut 2.5 inches square. Each end plate is glued on with white glue and clamped with two small brass screws (do not use steel). I temporarily provide the bobbin with an axial screw and nut, and spin the bobbin with a slow electric drill in one hand, level winding the wire with the other hand. The DCR for a 6.6 mH inductor is about 5.5 ohms (which ends up in series with a 95 or 100 ohm resistor). The DCR for a 3.3 mH inductor is about 3.5 ohms (which end up in series with a 47 or 50 ohm resistor).
If you have or buy inductors with higher inductance than required, it makes perfect sense to unwind the inductor until it measures the required value. If, for example, you need a 3.3 mH inductor, but can buy only 4.0, it makes perfect sense to buy the 4.0 and unwind it to 3.3 mH. Low cost capacitance/inductance meters are available; check on ebay. As you unwind the inductor, leave the loose wire coming off the inductor intact. The loose wire will not have significant inductance. When the inductance meter gives you the desired value, cut the wire a little long and secure it.
Sources of Inductors:
Check with Parts Express, partsexpress.com , and ERSE, erseaudio.com.
Crossover Resistors:
You will want to use wire-wound power resistors with a power rating of 5 or 10 watts. These resistors come in a number of varieties. The type with the metal heat sink are convenient to mount, but are expensive. The glossy brown ceramic type such as the Ohmite resistors are pretty. I have gotten spectacularly good sound using the least expensive power resistor type, which is the cement wire wound resistor in the rectangular ceramic box.
Sources of Power Resistors:
Cement wire wound resistors in 5 or 10 watt power ratings will generally suffice. I normally use 10 watt values. It is not easy to find a catalog with organized results for easy shopping. ERSE (erse.com) was at one time a good source, and may be again in the future. Currently Digi-Key electronics sells Yageo cement resistors, available in many values. However the catalog is not organized by resistor value, making it time consuming to assemble an order.
Sources of L-pads:
I have had fine success with inexpensive L-pads out of my parts box. For my crossover products I use the 100 watt units sold by Parts Express. These work well. The slightly less expensive 50 watt units sold by Parts Express should also work well and be a safe bet.
Building Crossovers:
First let me advise you that building crossovers is quite a bit more time consuming than you would imagine from just looking at the schematic.
If you are not interested in constructing your own crossovers, I can build them for you (active link). Also, a different crossover construction method than shown below is available at the link.
The following discussion may be helpful to those planning to build their own crossover boards. I recommend using 3/4 inch plywood to mount the components. More recently I have been adding a front and rear panel of 1/4 inch plywood or masonite to the 3/4 inch plywood mounting board. I put the controls on the front panel and the amplifier and speaker terminals on the rear panel. Click here (active link) to see image of crossovers built in this alternative way.
Shown below, are layouts and photos of crossover networks designed and fabricated for Jeff Day's A5 Voice Of The Theatre speakers.
Let us start with the first image. I put Jeff's crossovers on two boards; one board is for the low pass network; one is for the high pass network. I separated the low and high pass networks onto two boards so that the boards can hide behind the tweeter horn, one on each side of the tweeter support stand. In the image below you see one completed set of boards, and one set not yet populated:
The images below show the low and high pass boards individually:
The images below show the low and high pass boards individually:
I set Jeff's boards up so that any component can be removed and replaced without soldering. This makes it convenient if one wants to try different components. In the above two images you can see that the chokes are strapped down with zip ties which run through holes in the board. For Jeff's boards I chose to secure the capacitors to blocks screwed to the board from below with drywall screws.
Note that I put the input and output terminals on the same end of each board. This makes for tidy wire runs into and out of the crossover board, but causes the layout of the components to appear very different from the layout of the schematic, which can be confusing when trying to follow the circuit on the board.
I used terminal lugs provided to me by Jeff (see the images above). These are nice looking lugs, which allow through wires; but they suffer from limited throat capacity, which is a problem. I recommend using lugs like the ones shown in the image below. The lugs in the image below have a large throat. They are designed with a tongue and a collar. The tongue can be screwed to the crossover board with a No. 8 or No 10 pan head wood screw with a length of 3/4 inch. You could use 1/2 inch screws if you can not find 3/4 inch screws. The collar encircles the tongue and has a set screw has a set screw that presses the tongue against the bottom of the collar. These lugs are designed to have the wires enter below the tongue. Running the wires below the tongue prevents the user from using a through wire. If the user wishes to use a through wire (sometimes I use No. 12 solid wire, from Romex house wiring, as a bus bar), one could run the through wire(s) above the tongue. I purchased these lugs from Home Depot, at a price of $1.97 USD per pair. Lugs like those in the image below are also available from McMaster Carr, but at a higher price. The disadvantage of the big box store is that they may not have enough terminals on the shelf to meet your needs.
Note that I put the input and output terminals on the same end of each board. This makes for tidy wire runs into and out of the crossover board, but causes the layout of the components to appear very different from the layout of the schematic, which can be confusing when trying to follow the circuit on the board.
I used terminal lugs provided to me by Jeff (see the images above). These are nice looking lugs, which allow through wires; but they suffer from limited throat capacity, which is a problem. I recommend using lugs like the ones shown in the image below. The lugs in the image below have a large throat. They are designed with a tongue and a collar. The tongue can be screwed to the crossover board with a No. 8 or No 10 pan head wood screw with a length of 3/4 inch. You could use 1/2 inch screws if you can not find 3/4 inch screws. The collar encircles the tongue and has a set screw has a set screw that presses the tongue against the bottom of the collar. These lugs are designed to have the wires enter below the tongue. Running the wires below the tongue prevents the user from using a through wire. If the user wishes to use a through wire (sometimes I use No. 12 solid wire, from Romex house wiring, as a bus bar), one could run the through wire(s) above the tongue. I purchased these lugs from Home Depot, at a price of $1.97 USD per pair. Lugs like those in the image below are also available from McMaster Carr, but at a higher price. The disadvantage of the big box store is that they may not have enough terminals on the shelf to meet your needs.
Attached below are crude layouts of the crossovers I built for Jeff Day:
A couple of things worth mentioning:
Jeff's high pass crossover has a potentiometer used as a variable resistor in series with two 10 ohm resistors to allow him to fine tune the nominal 24 ohm resistor in the Hiraga notch filter. As you can see in one of the photographs, my technique for mounting potentiometers and L-pads is to cut wood strips to go across the top of the potentiometer and L-pad. Each wood strip is about 3/4" wide and 1/4 inch thick, and long enough to clear the body of the device. I drill a hole in the center of the strip to clear the shaft bushing, and drill a hole at each end to accept drywall screws long enough to do the job. Note that I made dials out of file card stock to indicate the settings of the potentiometer and the L-pad. I glued the dials to the top of the wood strip. More recently I have been building Hiraga circuit networks, and also Altec N800 circuit networks on 11 inch wide by 12 inch front-to-rear 3/4 inch thick plywood. I have been adding 3/16" or 1/4" thick front and rear panels (11 inches wide by 5.5 inches high) of plywood or acrylic. The front panel is used to mount the L-pad(s) and switches. The rear panel is used to mount the amplifier and speaker terminals.
Changes to my Altec A7 Speakers:
Subsequent To the discussion above I have stiffened the front panel of my A7 speakers. The front panel of my cabinets was a bit flexible. I made a strongback from doubled up layers of 3/4" plywood, which I front mounted to the original panel. This change did improve the quality of the bass.
Another change I made was the relatively inexpensive addition of tweeters intended to be helpful in support of the higher frequencies. I am cautious about calling these tweeters super-tweeters, but I am using them in that role. In general, I have found it difficult to find any tweeter that does not beam pretty badly above 10 kHz. The background is that I got an email from audio friend Steve Schell about the Harmon/JBL/Selenium ST400-BLK ring radiator tweeters. At the time Steve felt he liked these tweeters as well as the expensive JBL 075 tweeters, and possibly better. These tweeters have phenolic diaphragms. They have a sensitivity perfectly matched to my 511 horns with the 802-8D compression drivers. In my system the sensitivity match eliminated the need to pad down the Selenium tweeters. Steve is one of the originators of the JBL Heritage web site, and a partner in Cogent True to Life Loudspeakers. Steve tried these for a system he put together for a friend or family member and was impressed. He was kind enough to tell me about them. Long story short: They add a nice touch of air and space to my A7 system. I paid $126 for the pair, purchased from Parts Express, shipping included. More recently they have been available from Amazon for $130 per pair, shipping included. I located these tweeters to be time aligned with the 511 tweeter horns. I have a 2 uF capacitor in series with each tweeter, providing a high pass response 3 dB down at about 10 kHz.
The image below shows the front panel reinforcement and the Selenium tweeters.
Jeff's high pass crossover has a potentiometer used as a variable resistor in series with two 10 ohm resistors to allow him to fine tune the nominal 24 ohm resistor in the Hiraga notch filter. As you can see in one of the photographs, my technique for mounting potentiometers and L-pads is to cut wood strips to go across the top of the potentiometer and L-pad. Each wood strip is about 3/4" wide and 1/4 inch thick, and long enough to clear the body of the device. I drill a hole in the center of the strip to clear the shaft bushing, and drill a hole at each end to accept drywall screws long enough to do the job. Note that I made dials out of file card stock to indicate the settings of the potentiometer and the L-pad. I glued the dials to the top of the wood strip. More recently I have been building Hiraga circuit networks, and also Altec N800 circuit networks on 11 inch wide by 12 inch front-to-rear 3/4 inch thick plywood. I have been adding 3/16" or 1/4" thick front and rear panels (11 inches wide by 5.5 inches high) of plywood or acrylic. The front panel is used to mount the L-pad(s) and switches. The rear panel is used to mount the amplifier and speaker terminals.
Changes to my Altec A7 Speakers:
Subsequent To the discussion above I have stiffened the front panel of my A7 speakers. The front panel of my cabinets was a bit flexible. I made a strongback from doubled up layers of 3/4" plywood, which I front mounted to the original panel. This change did improve the quality of the bass.
Another change I made was the relatively inexpensive addition of tweeters intended to be helpful in support of the higher frequencies. I am cautious about calling these tweeters super-tweeters, but I am using them in that role. In general, I have found it difficult to find any tweeter that does not beam pretty badly above 10 kHz. The background is that I got an email from audio friend Steve Schell about the Harmon/JBL/Selenium ST400-BLK ring radiator tweeters. At the time Steve felt he liked these tweeters as well as the expensive JBL 075 tweeters, and possibly better. These tweeters have phenolic diaphragms. They have a sensitivity perfectly matched to my 511 horns with the 802-8D compression drivers. In my system the sensitivity match eliminated the need to pad down the Selenium tweeters. Steve is one of the originators of the JBL Heritage web site, and a partner in Cogent True to Life Loudspeakers. Steve tried these for a system he put together for a friend or family member and was impressed. He was kind enough to tell me about them. Long story short: They add a nice touch of air and space to my A7 system. I paid $126 for the pair, purchased from Parts Express, shipping included. More recently they have been available from Amazon for $130 per pair, shipping included. I located these tweeters to be time aligned with the 511 tweeter horns. I have a 2 uF capacitor in series with each tweeter, providing a high pass response 3 dB down at about 10 kHz.
The image below shows the front panel reinforcement and the Selenium tweeters.
First Order Crossover Tried:
Another thing I tried was use of first order Butterworth 500 Hz crossovers. I found the sound of the first order crossovers to be very good, but not as musical as the Hiraga crossovers. The first order crossovers provided greater clarity and articulation (good for my old-man ears) and a great deal of space. Into resistive loads the first order Butterworth filter provides an electrical response that is flat and has no phase shift. I was concerned that I might damage the Altec compression drivers by using a first order network. At first I fused the tweeters with a fast blow 1 amp fuse, but had no fuse failures and eventually removed the fuses. It is worth keeping in mind that Altec needed second order networks to fill large auditoriums with sound without damaging tweeters. This seems to be a non-problem in domestic applications. A 40 uF capacitor and a 2.5 mH inductor will give an approximately Butterworth crossover at about 500 Hz for 8 ohm speakers. But read on.
First Order Crossovers Rejected:
I played my system with the first order crossovers for about 6 month. I found myself fascinated by the clarity, detail, and imaging, but never got happy with the music. I was gobsmacked by the loveliness of the music when I went back to the Hiraga second order crossovers, which remain in the system to this day.
Another thing I tried was use of first order Butterworth 500 Hz crossovers. I found the sound of the first order crossovers to be very good, but not as musical as the Hiraga crossovers. The first order crossovers provided greater clarity and articulation (good for my old-man ears) and a great deal of space. Into resistive loads the first order Butterworth filter provides an electrical response that is flat and has no phase shift. I was concerned that I might damage the Altec compression drivers by using a first order network. At first I fused the tweeters with a fast blow 1 amp fuse, but had no fuse failures and eventually removed the fuses. It is worth keeping in mind that Altec needed second order networks to fill large auditoriums with sound without damaging tweeters. This seems to be a non-problem in domestic applications. A 40 uF capacitor and a 2.5 mH inductor will give an approximately Butterworth crossover at about 500 Hz for 8 ohm speakers. But read on.
First Order Crossovers Rejected:
I played my system with the first order crossovers for about 6 month. I found myself fascinated by the clarity, detail, and imaging, but never got happy with the music. I was gobsmacked by the loveliness of the music when I went back to the Hiraga second order crossovers, which remain in the system to this day.
Pete Riggle Audio
2112 S. Olympia Street, Kennewick WA 99337, USA
shop phone: 509 582 4548 email: peteriggle@msn.com
VTAF™ Trademarked. U.S.Patent No. 7630288.
Website content Copyright © 2021 Pete Riggle Audio, All Rights Reserved.
2112 S. Olympia Street, Kennewick WA 99337, USA
shop phone: 509 582 4548 email: peteriggle@msn.com
VTAF™ Trademarked. U.S.Patent No. 7630288.
Website content Copyright © 2021 Pete Riggle Audio, All Rights Reserved.