*Help me diagnose this flatulent bass driver

[graham67]

Looking for some help on diagnosing this problem, on a Rogers LS2.

The first few seconds is a subsonic tone then I switch to a frequency sweep.

https://1drv.ms/v/s!AvReE5AaGPrehNNddC_fVKOXgWF0OA

In normal playing it sounds pretty decent and its*not immediately apparent something is wrong.

The other speaker doesn't exhibit any of this*vibration when playing the same tracks.

I can't detect any obvious air leak around the driver enclosure or cone but that isn't to say there isn't one*😉

Any advice much appreciated.*

Many thanks

Graham

[Eagle123]

Have u tried different amp and checked your connections

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[graham67]

Yes good suggestion sajid, and i have swapped speakers over and used in entirely different system but unfortunately the problem persists.

[walpurgis]

Not sure what we're supposed to be listening for.

[graham67]

Hi wal,
The other speaker doesnt make the same vibrations/chattering sound when playing the same low frequencies
I have made a recording of the good speaker using the same tracks. However if you play on a phone you may not hear anything as the freq will be too low to replay.

https://1drv.ms/v/s!AvReE5AaGPrehNRCvpJrL01uXBccFA

Many thanks
Graham

[Eagle123]

Hi did u look at the speaker mountings ... and if they fine then it be the crossover

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[graham67]

Ah interesting, was assuming it was a problem with the driver.
I was planning to swap the driver over so hopefully this will isolate it to the driver or crossover.
I will swap the drivers when I get the time.

[Pharos]

Put the speaker in question on the other amp channel to eliminate the amp.

Try gently moving the cone by hand with a very gentle bias towards the periphery around all 360 degrees to reveal any rubbing.

Use a sine sweep to reveal any loose parts on the cone/motor assembly.

[walpurgis]

Dennis is right. It's likely to be the voicecoil fouling in the magnet gap. The crossover is less likely to be the problem.

There are ways to deal with this, but you need to know what you're doing. Otherwise, a replacement driver is required, and they should be replaced in pairs.

[Lawrence001]

Actually I've solved this problem with two pairs of speakers in the past. The two probable reasons for this are that the coil has overheated and bubbled the varnish watch is now rubbing, or (less likely unless the driver has been opened) a small foreign object has got in the voice coil gap.

If you do the test above to confirm that there is some rubbing, then give it a minute of pushing on and out so the coil is gently rubbing and you rub a bit of the varnish off (or dislodge/rub away the foreign object). Try the speaker again, if not solved, repeat. You could try rubbing a bit harder this time but bear in mind it will increase the risk of damage to the voice coil. Patience is the watchword here.

There's a risk of damage to the voice coil but if you're going to replace it anyway there's no harm done.

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[graham67]

Hi Lawrence, interesting suggestion there. I will try it shortly.

with these drivers, it doesn't take much pressure on one side or the other to induce a scraping sound. The rubber surround is not very stiff.

[graham67]

BTW, by swap I just meant left to right. No chance of ordering replacement drivers for these polypropylene Rogers.
I may just put these aside with the hope of one day finding a used driver from another pair.

[Lawrence001]

Just listened to the recordings myself, not what I'm used to testing with so not sure how low the subsonic sweep is. Does it distort at any audible frequencies as that's what matters? I usually spot a problem in the bass on George Benson Give me the Night, not sure what it is with that track [emoji38]

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[graham67]

Hi Lawrence, the subsonic freq is very low, well below what the Rogers are capable of reproducing. On the good.speaker all.i can see is the cone vibrating but no obvious sound. ON On the bad speaker I can see the vibration and also hear the regular beat, beat, beat.
however after a few seconds I switch to a sweep that rises continuously and the vibration on the bad speaker is still obvious until the frequency gets high enough that the cones are not doing much. Its quite hard to pick up in general listening however the other speaker cone doesn't make the vibrating sound at all so there is obviously a problem that won't fix itself.