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Author Topic: Refurbishing Altec Voice of the Theater Speakers? Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 12-22-2002 10:35 AM                     JBL is actually the oddity...I don't know of any other manufacturers that had a positive on red causing an inward cone motion. Steve  |  IP: Logged System Notices Forum Watchdog / Soup Nazi Posts: 215 Registered: Apr 2004 posted 08-30-2009 07:12 PM                 It has been 2443 days since the last post.  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 08-30-2009 07:12 PM                     I have just lost the horn in my center voice of the theater Altec Lansing speaker The torn diaphragm has 391911 written on it and the driver is 288 c 24 ohms which i am learning is no longer supported or available. What is my best move at this point to get this horn singing again?  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 08-30-2009 08:31 PM                     Victor, I might have a diaphragm that would work..but I think it's a 16ohm part. If so , you could add an 8 ohm, 50 watt resistor in series to get close to the original 24ohms (crudely). I will check later tonight...  |  IP: Logged Jake Spell Master Film Handler Posts: 294 From: Johns Island SC Registered: May 2009 posted 08-30-2009 09:51 PM                     This might be of some help Great Planes Audio These are the same guys who used to make Altec speakers. My dad has gotten some stuff from them with good results.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-30-2009 10:19 PM                       You don't really need to worry about getting back to the original impedance. 16 ohms will works just fine. The part is still made. Any good dealer can get you one.  |  IP: Logged Jeremy Weigel Phenomenal Film Handler Posts: 1062 From: Edmond, OK, USA Registered: Mar 2007 posted 08-30-2009 11:02 PM                     quote: Steve Guttag Altec had an outward cone motion when a positive voltage was applied to the "+" terminal. JBL drivers were just the opposite. A few years ago while checking phase on all of our speakers I came across a JBL 18" sub that pushed the cone out. So I checked the wiring on the terminals first and all was good. So I then pulled the speaker to check the connections inside and found everything just fine. I then thought that maybe somewhere between the booth and the screen they must have had a splice wired wrong, so I took a short piece of cable and connected it directly to the cone and the cone still pushed out. I figured they must have wound the coil differently at the factory and went ahead and reversed the wires in the cabinet. That auditorium sounds a lot better now that both subs are in phase. What prompted me to check phase in the first place was that I was replacing all of our surround woofers (the foam had begun to rot) and noticed the (+) and (-)'s weren't connected correctly and decided to check phase and found a lot of mis-wiring of the surrounds. Now that was a pain in the ass to correct and the kicker is that it was that way for almost 16 years.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 08-31-2009 05:35 PM                     Victor, I have those diaphragms available. I have two that I am sure are good, PM me if you want them. They are Altec part # 23834 They are for a 288 driver, not sure if the 288c is that different. Perhaps Sam or Steve Guttag can verify...  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-01-2009 12:54 AM                     Sam is partially correct. If the system has a passive crossover and is expecting a 24-Ohm impedance, then you will alter the crossover frequency by not using the correct part. If it is an active crossover system (bi-amped) then you have many choices...including going down to 8-Ohms for better power efficiency from modern amps. The correct part for the 288C is the 20221...it is the 24-Ohm version. Please note, if you have an original diaphragm still, then you will also need a diaphragm kit. The original diaphragms (made before 1983) used a Bakelite ring...modern ones use a plastic ring and use much shorter screws. Another key difference is the older ones used screw terminals on the diaphragm, the current ones use push on connectors. We stock the 20221 as well as all of the other current Altec diaphragms (sorry, no Symbiotiks...except maybe one or two of the ones for the 808/908 series). Note too, if this is a bi-amp situation, one can also move up to the 299/399 series of Pascalite diaphragms. They handle double the power and are aluminum so they retain the same sound. I've found they have a slightly reduced upper frequency response above 16KHz.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 09-01-2009 01:49 PM                     From Steve's post it looks like the ones I have will work, as they are the late models with push-ons, and the 20221 is listed on the box as the 24 ohm replacement. Mine are the 23834 16 ohm replacements and as Steve noted if you have passive crossovers the impedance mismatch will alter the response. Hey Steve, what the hell is the "Symbiotic" model all about? It is listed on one of the boxes here as being for the 291 driver..what's it made of that's so special?  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 09-01-2009 03:50 PM                     Thanks everyone! We are using a passive crossover I am not sure how old the blown diaphragm is but it uses screws for the terminals. Does that mean i will need a kit along with this newer diaphragm and is the altered responce something we can fix with eq or...  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-01-2009 07:04 PM                     Tony, The Symbiotik was Altec's answer to higher power handling but at the cost of frequency response (at the high end). Instead of pleated aluminum for a compliance, it used something like mylar. Note, the 288, 291, 299, 399 all use the same motor so the diaphragms are interchangeable. The Pascalite series essentially made the Symbiotiks obsolete. The Pascalite have the same power handling as the Symbiotiks but with almost the same frequency response of the aluminums. This applies to the 1.4" 200/300 series as well as the 1" 800/900 series. Note, the 290, is NOT in the same series as the other 200s...it uses a phenolic diaphragm and I believe the spacings are different. As to the frequency differences based on impedance mismatch, no you can't EQ that out. It isn't an EQ thing, it is a crossover thing. You are going to shift the actual crossover point away from 500Hz...on the upside, I believe it will shift up...closer to 750Hz...on the down side, you will develop a hole at the 500Hz crossover point. Merely applying boost in the EQ will induce phase anomalies. Your choices for a good result are, get the proper diaphragm, change the crossover to one that wants the 16-Ohm HF and the proper LF for your system (probably 8-Ohm), use autoformers to get the impedance correct, upgrade to a bi-amped system. The cheapest solution, for sure, is to just replace the diaphragm with one of the same impedance. Not to worry, the 20221 IS available as are the conversion kits (non-ferrous short screws with 90-degree push crimp terminals). We stock this stuff as I suspect other as well. Steve  |  IP: Logged Jarret Chessell Master Film Handler Posts: 288 From: London, Ontario, Canada Registered: Jan 2009 posted 09-05-2009 04:21 PM                     I just put a meter across the toasted diaphragm, I got a measure of 10 ohms of resistance. Would it be fair to assume that it really is more like 8ohms and that someone has already replaced the crossover and replaced a previous diaphragm? Speakers aren't my forté (I specialize in Megan Fox). Victor and I will try to get a picture up so that hopefully someone can better identify what's going on.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-05-2009 06:18 PM                     You can't use an Ohm meter (resistance) to read impedance. It will give you a ball park though. Typical impedance curves have the value decrease as it approaches "DC". It is possible someone has put in a 16-Ohm diaphragm or it may be a low reading 24-Ohm one. Remember, its impedance is important at frequencies ABOVE 500Hz on a diaphragm, not anywhere near DC. Odds are, the crossover was not changed to suit the diaphragm...but we can get to the bottom of that...what model crossover do you have? Steve  |  IP: Logged Jarret Chessell Master Film Handler Posts: 288 From: London, Ontario, Canada Registered: Jan 2009 posted 09-05-2009 11:37 PM                     We'll unhook the screen and get back there tomorrow and get model numbers and pictures up. Out of personal curiosity... say we took a diaphragm like this one, attached a frequency generator running at 500Hz, measured the potential difference across the diaphragm, and put it in line with an ammeter... would I be able to use Vrms/I=R to get a more accurate impedance measure? I really should brush up my knowledge in this area, I do find it very interesting.  |  IP: Logged

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