AR LST-2's refurbished, but one now different from the other...

[Guest nweiler]

Hello group,

I've just had my vintage AR-Inc speakers overhauled by an experienced AR service/restore person.

The AR-3a's had woofer foam surrounds and rear level controls replaced. All drivers checked out OK and none were replaced.

The AR LST-2's (10" woofers) had woofer foam surrounds replaced. Just one tweeter and one midrange total was found to be bad, and replaced, but at this point I don't know which cabinet, or cabinets, have the 2 new drivers.

The 3a's sound fine -- no problems there.

The LST's however don't match regarding bass response. One sounds OK -- the other sounds weak & distant. The weak one is putting out a signal -- just nothing like the other. I'm testing with ear, using FM set to mono so the signal is the same, swinging the balance from one to the other while I listen. I've switched speaker outputs at the amp to eliminate that variable. Classical, jazz, and bass-boosted voice from my local jazz radio personality all sound solid on the good speaker -- weak on the questionable speaker. The mid's and highs seem equal, speaker to speaker.

I decided to put a digital multimeter on all 4 speakers. The AR-3a's each read 3 ohms, and the multimeter's continuity checker emits a continuous beep when the leads are attached. I guess this makes sense.

The LST's, however, don't match one another, as I thought they would. Each speaker has the front level control set to position #2, and changing these settings does not alter the following readings... the speaker in question, with the weak-sounding woofer, reads 10 ohms (continuity checker beeps), but the other speaker, the one with more bass response, reads 72 ohms! and does not set off the meter's continuity beeper! This seems strange.

Yes, I'll be contacting the fellow who did the work to see what he thinks, but I'd like to get some 2nd opinions in the meantime.

Any ideas on what could be going on?

Thanks very much,

Norm in NJ

[Carlspeak]

"....The LST's, however, don't match one another, as I thought they would. Each speaker has the front level control set to position #2, and changing these settings does not alter the following readings... the speaker in question, with the weak-sounding woofer, reads 10 ohms (continuity checker beeps), but the other speaker, the one with more bass response, reads 72 ohms! and does not set off the meter's continuity beeper! This seems strange.

Yes, I'll be contacting the fellow who did the work to see what he thinks, but I'd like to get some 2nd opinions in the meantime.

Any ideas on what could be going on?...."

Did you check the compliance of both woofers? Do both surrounds seem equally flexible?

Are you sure the bad sounding woofer has a good seal with the cabinet?

Is there any evidence of rubbing of the VC?

Also suggest you remove both woofers and re-check their DC impedence with your VOM. If they are different, then something went awry on one of the voice coils.

It's all about the music

Carl

Carl's Custom Loudspeakers

[onplane]

>Hello group,

>

>The LST's, however, don't match one another, as I thought they

>would. Each speaker has the front level control set to

>position #2, and changing these settings does not alter the

>following readings... the speaker in question, with the

>weak-sounding woofer, reads 10 ohms (continuity checker

>beeps), but the other speaker, the one with more bass

>response, reads 72 ohms! and does not set off the meter's

>continuity beeper! This seems strange.

>

>Any ideas on what could be going on?

>

>Thanks very much,

>Norm in NJ

>

Norm, something is clearly wrong as you should NOT be able to read any resistance on your LST's. The LST's have a bank of caps in series with everything and those caps should block any dc and any dc measurements.

Sounds like the caps are either shorted out, removed entirely or just by-passed in one of your speakers.

I'd open both boxes and look for the cap bank.

EDIT: Ooops, I just noticed you have LST-2's. If you have the autotransformer, then what I wrote above is corrent. If no autotransformer, then you won't have any cap bank ... sorry!

Regards,

Jerry