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fritzbogott
11-01-2010, 06:40 PM
I was driving my daughter to choir practice today, and I saw these out on the curb:

482734827448275

The former owner agreed that they were free for the taking.

They're covered with grey latex paint, and I discovered (aargh!) that isopropyl removes the paint but also dissolves the decals.

All three drivers have "Altec Lansing" (no Corporation, no Hollywood) in relief on the backs. I'm happy to open up the driver cases if I know what I'm measuring / looking for.

I need to get some big crossover caps to roll off the low end before I can test these, which means I'm doubly in suspense.

Where do I start?

Thanks a lot!

-Fritz

hmolwitz
11-01-2010, 08:58 PM
I always do it the other way around and regret it.
A nice set of drivers and horns perhaps a 203 and a pair of 805?
http://lansingheritage.org/images/altec/catalogs/1975-pro/page_8.jpg
http://lansingheritage.org/images/altec/catalogs/1975-pro/page_9.jpg


Very nice score, enjoy.

:bouncy:

Steve Schell
11-04-2010, 11:19 PM
I never seem to drive through the right neighborhoods. Great score! Looks like 1960s or 1970s Altec stuff, two 803A (or is it B?) horns and a 203B. These are 300Hz. cutoff horns (actually designed with a considerably lower yet flare constant), commonly used down to 500Hz. in higher power systems. For home use 300Hz. shouldn't be a problem and they sound glorious. The drivers are probably 288C or 288D, but it would be helpful to see the diaphragms under the rear covers. This is great equipment, commonly recycled out of commercial installations into very high performance audiophile home systems these days.

Since they were being given away the diaphragms might be toast, but Great Plains Audio in Oklahoma City can service the drivers. You can test the diaphragm voice coils for continuity with a 1.5V battery (an old worn out one is perfect) or by measuring at the terminals with an ohmmeter. If you connect an audio signal you will need to use a crossover network to keep low frequencies out of the driver. Don't sell this stuff without listening to it first; you will likely be shocked at how good it can sound.

fritzbogott
11-05-2010, 05:04 AM
Thanks for that extremely-detailed reply!

I verified (with a fistful of paralleled crossover caps and a low-power amp cranked way down) that all the drivers play music.

What crossover slope am I looking for if I'm going to cross at 300Hz?

(Now I have appropriate horns for those 71A amps I've been wanting to build!)

Thanks again,

-Fritz

spkrman57
11-05-2010, 08:16 AM
What crossover slope am I looking for if I'm going to cross at 300Hz?
(Now I have appropriate horns for those 71A amps I've been wanting to build!)
-Fritz

300hz at 12db/oct if the wattage is low, like 5 watts or less.

Tubes amps are best for these horns and drivers!

Ron

fritzbogott
11-05-2010, 08:36 AM
Now for some crossovers and bass bins.

Steve Schell
11-05-2010, 10:37 AM
The thing with the network is that we are trying to keep out-of-band low frequencies out of the high frequency driver. Below the range where the driver is well loaded by the horn, the diaphragm excursions become large, distortion high, and fatigue of the compliance can happen soon. Tom Danley once pointed out that a second order (12dB/oct.) filter is necessary just to keep excursions from increasing below the passband. In theory the diaphragm excursions quadruple with each halving of frequency, so a second order filter is necessary just to keep them constant, a higher order filter would have to be used to cause them to decrease.

Then there is the issue of polarity and the ability of the completed system to reassemble a complex waveform. Music signals are highly asymmetric, and imaging suffers greatly if the drivers are not all in the same polarity and proper alignment. Unfortunately a second order filter requires that the high and low drivers be connected in opposite polarity, a huge bummer. Usually I sneak by with first order filters, though a well implemented third order filter, which permits correct polarity hookup, might be a good choice. Jim Lansing had arrived at this solution in the last two way systems he built in the late 1940s.

fritzbogott
11-05-2010, 03:07 PM
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Progneta
11-08-2010, 06:42 PM
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fritzbogott
11-08-2010, 06:52 PM
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Steve Schell
11-08-2010, 10:49 PM
Fritzbogott, I think I still have three Altec 203 horns in my overhead storage. If you try your single and think that you'd like to hear them in stereo, I could probably be talked out of one pretty cheaply. I used 203, 803 and 1003 horns in my living room system years ago and the 203 was my favorite due to its narrow pattern.

fritzbogott
11-08-2010, 10:54 PM
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