View Full Version : Altec 9815-8a need help
11-15-2009, 04:14 PM
Hi Guys - I would like advice on my newly veneered 9815s that sound good in the mid range but dont seem to have any real top or bottom. These were acquired very second hand and tatty a while ago and they now look more domestically acceptable since I recovered them with some black walnut.
I have never had the luxury of hearing Altecs in England (very rare here) so dont know what the normal sound should be like. Currently using EAR 859 valve amp to power them, volume seems ok but all mid range which is very sweet and with impact but I assume there should be a lot more, even with a 46hz bottom.
I am also assuming the crossover components are past their best and before I pull out the woofers would like to know what components to get in to at least restore performance to stock or a bit better.
Any help with schematic or any other advice would be gratefully received. I am impressed with them and want more !
11-15-2009, 07:02 PM
Humm , that's definately an obscure speaker . Looking at the component line-up / I can see why you are excited about it's potential .
Here's the pdf for the similar ( but earlier ) 9812-8A. (http://www.altecpro.com/pdfs/vintage/SpeakerAndMics/systems/9812-8A%20Speaker%20System.pdf) Check out the published response curve ( mostly all midrange ) .
From the published response of the 9812 ( & your own observation ) these were designed as general purpose sound reinforcement boxes / and as such / the crossovers are presently voiced ( EQed ) for maximum midrange output .
Unless you can find someone local to redesign the existing crossover / I think you're sort of stuck with it's "forward voicing" .
FWIW, having the schematic for the existing crossover won't really help you much since ( IMO ) you need to start from scratch ( crossover wise ) if you want to turn your 9815 into something a bit more hifi . The drivers ( & horn ) ought to be able to deliver something a bit more hifi, if the crossover is redesigned ( by someone with access to the right equipment & access to your speakers .
<> Earl K
ps; The easiest & fastest way to test the potential of the inherent components is by biamping these speakers ( bypass the internal crossover ) with ( even an inexpensive Behringer ) 2 -way crossover . These crossovers all have sweepable crossover points / plus an HF boost circuit ( to compensate for HF attenuation from the constant directivety horn ).
11-16-2009, 01:44 PM
Thanks for the thoughts Earl.
I have attached an up to date pdf for the M500/9815. It isnt as bad as the earlier version you found - 20khz to 46hz with current Great Plains drivers. In view of the better specs, perhaps it might just need the crossover updated ? Jeff
11-16-2009, 01:56 PM
Thanks Jeff for the pdf .
- Is there an attenuator for the horn circuit within the crossover ?
- After perusing the data sheet, it's clear to me that the horn ( in the 1K to 10K region ) needs to be turned down/"padded" to match the woofer level ( & perhaps, a tad bit more ) . That'll be a more hifi sounding curve .
- Then the speaker will have a sensitivety in the low 90s .
11-16-2009, 02:06 PM
Here is one of them ...
11-16-2009, 02:12 PM
There is only a button on the outside. I will have to pull the woofer out to have a proper look at the crossover.
Like you say it would be better to pull the whole thing out and make separate connections on the back of the cabinet so I can play with the crossover or go active long term. Not so original but that is not really a consideration. Jeff
11-16-2009, 02:25 PM
Very Nice :thmbsup:
You've done a great job at refurbishing those .
- I'd suggest making copious notes about the wiring inside the box / then yank the crossovers out so that you can take many detailed pictures of them .
- You could take the crossovers to someone ( if you can't do this yourself ) who can trace out the circuit ( & commit the parts values to paper ).
- Once you have a schematic in hand , it'll be easier to suggest changes to the network to tame that midrange .
11-16-2009, 02:58 PM
Thanks for your generous help. I will get on to it ....
Best regards Jeff
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