Do the woofers on the shrill speaker put out any sound at all? Or do they and it's just a lot lower in output?

Thnx for responding Jeff!

The woofers both do produce sound. Volume is good but sound is shrill.

By the way, I found a lot of old foam sticking to the amp’s pcb. I cleaned that all using isopropyl. Unfortunately that made no difference. Any suggestions?

From what I've read here the foam can cause corrosion of the PCB traces and shorting or open circuits. Usually that causes the amp to just stop working, but I'm sure it can also cause other issues. I worry about this on my late 90's BL8000s but they so far work and I haven't gotten around to replacing the foam. Probably tempting fate.

Is the tweeter level right? That is, is the tweeter output on the shrill speaker about the same as on the good one? I usually test this by putting on pink noise, or tuning the FM tuner to inbetween a station with the muting turned off so you get the hiss. Easier to tell than with music. Also a good way to listen to the woofers on each speaker for tonal differences, that show up pretty well with the hiss of noise

I'm betting you'll need a service from someone who knows the amps, but it'd be good to diagnose it. Hopefully Dillen or one of our other experienced members will weigh in.

How old are your 8000s? Are the old enough that the two woofers are not hooked up the same, or the slightly later thru modern ones where both woofers output the same freq range? Could be damage to the electronic crossover, or even one woofer not working. Wish I could help more.

Thnx again Jeff!

• Tweeter level: this is the same.
• Woofers: this BeoLab 8000 set is a Mark I, Type 6801, serial no: 12543880. To my knowledge the woofers are hooked up differently; one to act as woofer, one to act for mid tones.

I did exchange the upper woofer speaker (mid tone speaker) for a different one, but that did not make a difference.

Hmmm. If I recall, wasn't one woofer run with a capacitor inline on the amp output? Could that have failed? Do you get sound out of both woofers? I could see it sounding shrill if one woofer that produced only bass was missing in action. Is it shrill as in a problem with frequency response, or is there distortion in the mix as well?

Interesting problem. You are getting sound out of the bass only woofer? Also, I believe that the 8000 is like the other Beolabs in that when you change a driver you need to readjust the output level to the speaker with the little trim adjustments. To make up for differences in the efficiency of different drivers. Could this be something relating to this?

Thanks again for sharing your suggestions Jeff.

I will look for the capacitor on the amp output connected to one of the woofers.
And also I will look for the little trim adjustments.

Concerning freq response and distortion, my response is based on the definition used by SoundGuys (https://soundguys.com/frequency-response-explained-16507/). 
What I notice is that both woofer speakers produce sound. In the Mark I series of the BeoLab 8000, the lowest positioned speaker is the bass speaker, and the speaker right above (which is physically the same as the lowest positioned speaker) is used for mid-tone.
What I think I hear is a non-flat freq. response, in which the 'low' seems not be amplified.

Does this info help you?

That could be either the amp, the ABL system, the driver itself, any of a number of issues. I guess if you swapped the drivers, temporarily, you could eliminate the actual driver. Say, from the upper to the lower one, or from one speaker to another. Try and remember where each one was originally or you'll need to rebalance the whole system. The service manuals are online here at Beoworld for silver or gold members. The manual should have instructions for setting levels for each speaker driver, I know the manual for the BL6000 I have does.

Kind of a head scratcher, I have been hoping one of our more hands on technical guys here like Martin or such would see this and chime in.

Another thought, have you switched the powerlink cables around so that the bad speaker is hooked up in place of the other channel? Swap L for R and all to make sure it's not a problem with the source unit, whatever that is (I use a BS9000).

Thnx for your thinking and suggestions again Jef, very much appreciated!

Drivers:

• I have changed the existing drivers from position (lower to upper and vice versa). Result; no difference.
• I changed drivers from a well sounding BeoLab 8000, into the shrill sounding unit. Result; they also sounded shrill.

I believe we can conclude that the problem is not in the drivers.

L & R channel switch:

I changed the Left channel to Right and vice versa, several times. And trying this with different kinds of music with bass. Result; it is very clear that in all situations, the same BeoLab unit keeps producing shrill sound.

Next

I am now going to check the capacitor (on the amp output connected to the lower woofer).