Speaker membrane oscillating

[Danish Viking]

Hi members - am struggling with a strange behavior of my brand new B&W 805D3 Rear speakers. Just connected them to dedicated AMP (150W HOLFI - NB250 modified with lower effect). All speaker cables (4 seperate cables) are single wire with plenty space between them so no crosse over 'noise' possible. Changed wire between Main APM and Ream amp same results.

 

When playing (Pre-AMP output levels does not make any changes) following happens.

 

When looking closely at the membranes of each speaker in turn I can see that membrane slowly moves in and out about 1mm not related to the music being played but more like like an oscillating motion on top of the music it plays. 

 

Questing: What might be the root course of this problem?
- Speakers - brand new?
- Speaker wiring (unlikely)..?
- Amps?

 

NB! Front Speakers (B&W 802D) show no issues at all? 

 

Any suggestions to solve this mystery highly appreciated..?

[yamamoto2002]

Are you playing Vinyl? It seems the woofer excursion caused by warping of vinyl. Enabling subsonic filter of amplifier to eliminate the problem.

 

BTW digital signal processing is also possible, following is my software implementation of subsonic filter for PCM recorded vinyl sound data https://sourceforge.net/p/playpcmwin/code/HEAD/tree/PlayPcmWin/WWAudioFilterCore/SubsonicFilter.cs

[cjf]

On 10/5/2021 at 3:38 AM, Danish Viking said:

Hi members - am struggling with a strange behavior of my brand new B&W 805D3 Rear speakers. Just connected them to dedicated AMP (150W HOLFI - NB250 modified with lower effect). All speaker cables (4 seperate cables) are single wire with plenty space between them so no crosse over 'noise' possible. Changed wire between Main APM and Ream amp same results.

 

When playing (Pre-AMP output levels does not make any changes) following happens.

 

When looking closely at the membranes of each speaker in turn I can see that membrane slowly moves in and out about 1mm not related to the music being played but more like like an oscillating motion on top of the music it plays. 

 

Questing: What might be the root course of this problem?
- Speakers - brand new?
- Speaker wiring (unlikely)..?
- Amps?

 

NB! Front Speakers (B&W 802D) show no issues at all? 

 

Any suggestions to solve this mystery highly appreciated..?

Does the speaker have the same described motion without music playing?

 

If the issue described only happens with music playing then I would say it would be very hard to say if the motion of the driver is from musical content or some issue with the Amp. With the small driver two way speakers like the 805, the woofer has a whole lot of work to do when reproducing music. There could be lower bass notes coming thru that you cant hear but causing the woofer to perform work anyway.

 

Does anything sound "off" about the sound of the speaker? What happens if you hook up this same Amp to the front speakers? Do they now have the same described driver movements? If so, then my finger would point to the Amp being the culprit.

[Lone Mountain Audio]

This is not the speaker, speakers cant move without being told to do so from what's in front of them.  So either your turntable has warped record on it (which would reproduce that exact artifact as the warped record turns at 33 1/3 ) or an amp is oscillating very slowly.   Since its slow, its most likely turntable.  You could use a non warped record or a clamp to hold the warped record down and flatten it.  A 20Hz rumble filter could also "fix" it if this warped record is impossible to replace.  

 

Brad

[yamamoto2002]

I have 805S, predecessor of your speakers, and in the past I did an experiment to connect LR6 alkaline battery onto the speaker terminal. IIRC the woofer moved forward by 5mm or so. Therefore 1mm excursion should be no problem, for the applied power is way smaller than 1Watt.

[Danish Viking]

Hey Guys thanks for great inout. The movement of the membranes is less than 3mm and has no effect on the music qualify. Talked with the designer/creator of the AMP and SACD player - he said that challange with rear sound (5.1 and Art. made rear signal created front 'stereo signal' is that noise lvel is 85DB (better than turntable..but) wheras DB level on the front signal with the HOLFI NB250 (Improved) AMP is >= 105DB - noise could be filtered away, howvere that would have an impact on the sound quality (alwasy trade off's going on with HiFI I'm afraid)  - once again thanks for your great ideas.