May 6, 2016
The Garden of Earthly Delights listening room
now houses three different loudspeaker systems. These are the home designed and constructed Po Boy all horn system, the Beveridge
Model 2SW electrostats, and the Altec A7 Voice Of The Theatre system, modified to use a crossover originally designed and
implemented by the Frenchman Jean Hiraga, late in the last century, for use with his Altec A5 Voice of the theatre system.
All of these are marvelous systems. Lately I have been toying with the Altec A7 system, getting what seems to me to be fabulous
results. A now-extinct bias I had against vented loudspeakers interfered for years with any possibility that I might
end up with a pair of the Voice of the Theatre speakers. Sometimes my pre-conceived notions have really gotten in
In the photo above
one can see the in-room locations used for the Po Boy and Beveridge systems. These speakers work fine as stereo pairs
in these locations. The Altec A7 speakers are supported over carpet by plastic glides. The glides allow these 130 pound
speakers to be easily waltzed into position in front of the Po Boys, which turns out to be a great position to play them
from. Great sound stage.
In The Attic Subwoofer:
mouth of the Monster is shown in a photo above.
The Monster In The Attic mono subwoofer, which plays down to 20 Hz and up to 160 Hz, supports each of the
three loudspeaker systems now alternatively in use. The sub is played up to 160 Hz with all of the three speakers systems.
This works very well. There is never a sense of being able to locate the subwoofer, or a sense of confusion over the
location of bass instruments. And 20 Hz bass, when present on the program material, is marvelous. This subwoofer is driven
by an inexpensive 100 watt mono plate amp from Parts Express. Input to the plate amp is taken from the speaker system being
played. A pair of Altec Model 415 paper cone biflex drivers excite the 29 foot long bent sub-horn, which has mouth height
of 6 feet and a mouth width of 9.5 feet. The biflex drivers seems a strange choice, but I used what I had on hand, and
they work beautifully.
Po Boy System:
first system set up in the Garden, maybe 10 years ago, was the Po Boy horn system, which consists of a J shaped
70 Hz horn (j-horn) for the bass, a conical horn for the midrange, and a tractrix tweeter horn. This is a 16 ohm triamplified
system. Crossover points are 350 Hz between woofer and mid, and 6000 Hz between mid and tweeter.
The Po Boy system is triamplified. Electronic crossover and room equalization are
provided by a DEQX digital equalizer and crossover unit.
The woofer paper cone drivers are 8 inch units, two per channel, manufactured by B&C of Italy. The midrange phenolic
diaphragm compression drivers are RCA Model 9584A units manufactured by RCA for a couple of years around 1960 to complement
their theatre sound systems. The tweeter Mylar diaphragm compression drivers are by the German company BMS. This is a
very sweet sounding horn system, perhaps because there are no metal diaphragms.
The stereo amplifier for the woofers uses Sovtek
or Winged C 6550 tubes in push-pull. The Sovtek's do a very nuanced bass. The monoblock amplifiers for the mids use single Chinese
2A3C tubes operating single ended. The stereo amplifier for the tweeters uses single Amperex Bugle Boy EL84 tubes operating
To be continued
. . .
November 25, 2016 More about the Altec A7 and A5 Voice Of The Theater Speakers
So many projects, so little time. I've recently added a page to this site dedicated
to Altec A7. You might want to check it out at this link: