This month we hope to hear some vintage loudspeakers. Once again Eric will generously give us a glimpse and a listen from his fast growing collection. A pair of Altec -- Lansing A7 "Voice of the Theatre" loudspeakers and their domestic counterpart, the Altec Corona, will visit our listening room.
As of this writing one crossover is misbehaving, so our demo may be mono, but interesting nonetheless. The A7 (pictured here) is the smallest of a line of loudspeakers Altec produced for use in theatres, auditoriums and studios. It consists of a low frequency driver, type 803A, coupled to a short horn and rear loaded to a "bass reflex" enclosure. This is crossed over through a type 800E 800Hz crossover to a type 802 high frequency driver connected to a type 811 B multi-cellular horn baffle, which spreads the high frequencies horizontally over a 120 degree arc (and about 40 degrees vertically). The high frequency driver sits on top of the dark gray bass enclosure.
Maximum power handling is only about 30 Watts, but efficiency is around 110 dB SPL, so you can run them with very small amps. Eric and I listened to one of them with a Fisher 20A (6BQ5's PP at about 15W) in his garage with the door open and we found that they sounded plenty loud about 30 feet outside the door!
The crossover has quite a large range of adjustment and I think we ended up liking the neutral setting. Treble boost would really bring out that 'horn throat' hiss in recordings.
One thing is for sure. These babies do not simulate a point source unless you're over at the neighbor's. Standing inside the garage, one had the distinct impression of the two separate drivers. However when we stepped out to the 30 foot range things got a lot better.
For big orchestral recordings, standing at a distance and cranking it up really started to simulate the proper scale. Frequency response was not tubby as I expected. If anything there was a lack of bass at the bottom octave, but above that things are fairly smooth, as can be seen in the frequency response curve (below) I have scanned from Audio Cyclopedia. How'd you like to find one of those at a swap meet?
If you have a barn, old theatre, skating rink or other cavernous space, these could be a lot of fun. Pick up an old RCA capacitive video disk player and an Advent projection TV and call all your neighbors!