Help me fix this flatulent bass driver !

[graham67 691]

Hi,

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

[Jazid 334]

Sounds like a rubbing / bottoming out voicecoil on my phone, but I can't say I do subsonic sweeps on a phone more than once ever...!

Sent from my BLA-L09 using Tapatalk

[graham67 691]

Thanks James.  I can't hear any scraping when I depress the driver so bottoming seems a.likely explanation.  I assume this would only be solved by replacing the rubber surround?

[Jazid 334]

Hi Graham,
Best wait for those with more experience to help, I'm as much at sea as you are!

Sent from my BLA-L09 using Tapatalk

[Nopiano 2,375]

On 13/07/2020 at 21:43, graham67 said:

Thanks James.  I can't hear any scraping when I depress the driver so bottoming seems a.likely explanation.  I assume this would only be solved by replacing the rubber surround?

Depending which way you’re depressing the driver, there is an old trick that might work.  Some drivers sag after many years, due to gravity.  If you remove the four retaining screws and carefully rotate the drive unit by 180 degrees it might just fix it.  It is free too!  

[graham67 691]

Hehe yes tried his on my old rogers studio 1.  It worked for about an hour!!!

[graham67 691]

but I will flip the speaker upside down to see if it makes a difference

[wizmax 381]

Do you want to borrow another pair Graham?

[graham67 691]

Hi Robin very kind of you,  I have sent you pm 😀 

[graham67 691]

I had some time to experiment, so am now almost positive the rubber surround is, er, rogered.

Compared to the good driver, the noisy driver can be pushed in much easier, can be easily angled off centre to make contact with voice coil and the rubber distorts unevenly, unlike the good driver.

The driver looks like it was made by Kef, the basket and magnet appears very similar to the Falcon b110 reproduction  The rubber looks the same size though I have been informed it is not the same stiffness. So, I think the next step will be to attempt to find a b110 pattern rubber surround with a suitable stiffness.

If that fails, other option is to to try the Falcon b110 drivers in the LS2.

[steviep2024 80]

Hi Graham 

Use the b110 drivers but make sure you change both.

The Ls2 drivers are based on the b110 but have longer throw to accommodate being in ported cabinets.

Personally I'd switch to Monacor drivers and keep your Falcon b110 drivers as spares for your ls35a 

[greybeard 5,564]

Also the LS2 driver is Polypropylene and the B110 is bextrene. If you have not got this sorted, I think I may have a spare surround for an LS2, let me know.

[steviep2024 80]

Hi Greybird

I'm sure Graham will be over the moon

Top Man

[greybeard 5,564]

Found and posted the replacement today 

[deggie 671]

Top wamming Colin .........