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 (link): Though there is some dominant bass (bass guitar) in this song, the described vibration issue does not occur. OK
2. Coldplay – Magic (): Immediately from the beginning of the song, the vibration can clearly be heard. The vibration follows the kick drum instrument. NOT OK
link
3. Bass test 20 Hz (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) Login to view image 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.

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