Woofer driver vibration problem ?

[KolfMAKER]

Issue
When playing music there seems something wrong with the representation of bass by the two drivers for mid and bass. When it happens, the vibration sounds like there is something loose or damaged in the driver (foam ring, cone, dust cap). The vibration does not occur at low(est) volumes, but it starts to be hearable at medium volumes (and gets awful at higher volumes).

These BeoLab 8000’s have serial numbers in the 1072 xxxx. These speakers had foam rot which has now been removed. All PCBs have been cleaned thoroughly. I have installed 1 bypass in the power supply section towards the relay.
There was also quite a bit of foam rot sticking to the head side of PCB02 and PCB04. This has also been cleaned. I have not found any damaged copper traces (I hope I did not miss that).

One speaker was free of vibrations for a while, after everything been cleaned and PCB04 had been placed back after cleaning. But the vibrations were there again the next day.

Music (with bass) tested:

1. Vail Johnson – Bass solo (Spotify link): Though there is some dominant bass (bass guitar) in this song, the described vibration issue does not occur. OK
2. Coldplay – Magic (Spotify link): Immediately from the beginning of the song, the vibration can clearly be heard. The vibration follows the kick drum instrument. NOT OK
3. Bass test 20 Hz (Spotify link): In this song, there is an electronically generated low sound. For instance, starting at the beginning at 8 seconds in the song. Here the vibration is quite heavy. NOT OK

I focussed on testing with ‘Coldplay Magic’, I consider this is a common song with no tricked bass instrument. And as the song makes the vibration yes/no hearable at different volume levels.

Physical check
I checked the speaker drivers on any damage or loose parts for: foam ring, cone, dust cap. After removing them from the panel, I also checked looking at the backside of the drivers. Result: no damage or loose parts found.

Comparison test: How

• I played Coldplay Magic on 3 different sets of BeoLab 8000.
• I changed the two speaker drivers between the sets used in the test. BeoLab Set 1Set is the set where the issue started. I used BeoLab Set 2 as a reference, because I did not have the vibration issue on this set.
• Source: iPhone 12 with Spotify, connected via Lightning to RCA cable, to the RCA input of the BeoLab.
• Measuring: Spotify has 16 volume steps. I measured 4 points: a) at what highest volume step level there was no vibration, b) at what volume step level the vibration starts, c) at what level it gets clearly hearable, d) at what level it mis absolutely bad.

Comparison test: Results

Please, have a look at the table attached with the test measuring results.

The woofer drivers clearly had issues in the BeoLab set 1 (as I noticed the issue with this set). But when I put these woofer drivers in BeoLab set 2, I also heard & measured the vibration issue. In fact the measurement with these drivers in set 1 and set 2 are almost the same.

I also wanted to know what would happen when I would put the woofer drivers of set 2 (the no-issue set) into set 1 (the set with issues). Result: the ‘good’ woofer drivers, performed bad in set 1. Actually the measurement is about the same as with the ‘bad’ woofer drivers that are originally with set 1.

As a reference, I also measured in Set 2, with its own woofer drivers. Result: far better than any other combination tested. (Confirming this is a good set, without the vibration issues)

Question

First I thought it’s the woofer drivers of BeoLab set 1 that caused the problem. Cause if they perform bad in a ‘bad’ BeoLab 1 set, but also in a ‘good’ BeoLab 2 set, it could be damage somewhere to the driver.

But I was surprised to find that the ‘good’ woofer drivers from the ‘good’ BeoLab 2 set, performed bad in the ‘bad’ BeoLab set 1.

1. A bit confusing now, because is this problem a combination of bad woofer drivers with a problem on the amplifier/cross-over filter side?
2. So, what could be wrong here and what should I check?

Any advice is welcome!

 

Attached:

• Pictures of the ‘bad’ drivers from BeoLab set 1, after I removed them from the panel to have a visual check.

 

 

[spassmaker]

Hi

Did you  replace the foam and gaskets? Could be airventilation caused by gaps between the amp module speaker module or top module with pipe.

May be that a PCB is ratteling  because of a missing screw or a broken screwpost. Often the screwpost break while tightening the boards or handling, or screw isn’t fully tightened.

Why the ratteling sometimes is audible and sometimes not is quite a mystery.

did you crosscheck the”bad” woofers in the”good” speaker set? For me it’s a bit confusing how you did the test ;-))

If you push gently the bad woofers is there any scratchy feeling?

Try to test the woofers out of the speaker with reduced volume and listen to the bad ones and good ones > any difference?

Good luck

Christian

 

[KolfMAKER]

Thanks for your input Christian!

Interesting remarks you made. Especially the air ventilation triggered me. So I now changed two things since last time:

• I cleaned away every tiny bit of the left glue of the old gasket. To make sure the whole surface is smooth and straight.
• I placed brand new foam (original B&O, placement according to B&O instruction).

Result: Happy that I can say that the bad vibrations are gone. Just one remark about that. I have played a list of songs with a bit more heavy and low bass tones. All play well, but only one song keeps disturbing me a bit: Coldplay with Magic. Still, in the first part of the song, the vibration can be heard when the kick drum comes in. But the effect is much less than before, and only at high volume (75% or up). Maybe it is in the song.

 

Your questions

• Did you crosscheck the”bad” woofers in the”good” speaker set? > Yes, the so-called bad woofers did well in the ‘good’ speaker set.
• If you push gently the bad woofers is there any scratchy feeling? > There is no scratchy feeling or noise.

 

Question to you

• What kind of material do you use for the gasket?

(share a link if you can)

[Author]

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