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[thomasrchapman]

Hi guy and gals! 

I have a 21" active Cerwin Vega Stroker subwoofer.  It has been in storage at a friends and when I picked it up and tested it, it sounds raspy at low volume. It still has plenty of punch and the level of bass being produced at higher volume is no issue.  It's not that the sound is distorted or flat or anything less than ok but it sounds like a sub trying to do mid range and doing it very badly. 

I have tried adjusting the parametric EQ and phase adjustment on the back to no avail. It has an automatic low pass filter to remove the higher frequencies.  It used to sound fine but something seems to have changed but it's not a setting that I can alter. 

I don't think I should take the back off as the amp etc will be very heavy and I don't think it is user serviceable. 

Is this something that you have come across before or could shed any light on? 

Regrettably, I am unable to ship to the UK for repair because the size and weight of the unit means that the shipping from the Isle of Man to the UK will be circa £500, which is the approx value of the unit.   A link to the sub can be found here http://www.totalsounds.co.uk/cerwin-vega-cva-121-21-active-sub-woofer-p-1799.html?gclid=CLPZqpDdu80CFXMz0wodJW8DMg

There are people on the IoM here that are competent to undertake minor repairs to pro audio equipment but if anyone has any suggestions they would be very gratefully received. 

Many thanks!  Tom Chapman

[Cailen Waddell]

Is it a rubbing sound?  Almost scratchy?


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[Tim McCulloch]

In storage?  Heat/humidity?

I'm suspecting cone/coil suspension sagging.

Lay the sub so the cone faces up (whatever cabinet orientation that might require) and try your low level test again.  If the scraping sound is lessened my hypothesis might be right

If you can remove the speaker you can do the gently-press-around-the-cone test as listen/feel for the scraping.  If the scraping is consistent regardless of physical orientation there's a good chance the voice coil has been damaged or the sub has been dropped, shifting the magnet's pole piece inside the voice coil.  The other possibility is too much heat leading to a partial unwinding of the voice coil.

If the pole piece is decentered the woofer is toast.  I'm not aware of any facility that will demag the motor, recenter the pole piece and then remagnetize the motor, and then recone the frame/motor.  The labor costs involved will exceed the price of replacing the woofer.

With the woofer removed from the cabinet, and using an external amp and signal generator you can "sweep" the woofer, too.  You want to use a known, external source of amplification to rule out a problem with the Vega's amp.

[thomasrchapman]

Is it a rubbing sound?  Almost scratchy?


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No, I wouldn't describe it as rubbing or scratchy.  I guess it sounds like the mid range of the track being heavily EQd and put through a slight distortion but the sound is drowned out when the volume is turned up and the thunder kicks in. 

[Rob Spence]

No, I wouldn't describe it as rubbing or scratchy.  I guess it sounds like the mid range of the track being heavily EQd and put through a slight distortion but the sound is drowned out when the volume is turned up and the thunder kicks in.

Any chance a critter got in while it was in storage?


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[thomasrchapman]

In storage?  Heat/humidity?

I'm suspecting cone/coil suspension sagging.

Lay the sub so the cone faces up (whatever cabinet orientation that might require) and try your low level test again.  If the scraping sound is lessened my hypothesis might be right

If you can remove the speaker you can do the gently-press-around-the-cone test as listen/feel for the scraping.  If the scraping is consistent regardless of physical orientation there's a good chance the voice coil has been damaged or the sub has been dropped, shifting the magnet's pole piece inside the voice coil.  The other possibility is too much heat leading to a partial unwinding of the voice coil.

If the pole piece is decentered the woofer is toast.  I'm not aware of any facility that will demag the motor, recenter the pole piece and then remagnetize the motor, and then recone the frame/motor.  The labor costs involved will exceed the price of replacing the woofer.

With the woofer removed from the cabinet, and using an external amp and signal generator you can "sweep" the woofer, too.  You want to use a known, external source of amplification to rule out a problem with the Vega's amp.

It was stored in a friends office out of direct sunlight.  I don't think it has been exposed to heat or humidity. 
Thanks for the reply, that is really helpful.  I will try lying it down or upside down and see if it changes anything.  I guess I can take the grill off the front as well for a prod about!

[Tim McCulloch]

It was stored in a friends office out of direct sunlight.  I don't think it has been exposed to heat or humidity. 
Thanks for the reply, that is really helpful.  I will try lying it down or upside down and see if it changes anything.  I guess I can take the grill off the front as well for a prod about!

Your up-thread description of "raspy" makes me wonder about the amp module, as that description doesn't give me the feeling the problem is mechanical, but the mechanical problems are the easiest to sort out.

Here's another suggestion:  can you borrow an unpowered sub (or any LF speaker)?  If so, connect it to the Vega's amp and see if the noise is still there.

[David Allred]

Your up-thread description of "raspy" makes me wonder about the amp module, as that description doesn't give me the feeling the problem is mechanical, but the mechanical problems are the easiest to sort out.

Here's another suggestion:  can you borrow an unpowered sub (or any LF speaker)?  If so, connect it to the Vega's amp and see if the noise is still there.

Do you have a driverack or other DSP to send a filtered signal to the amp?  Say, LPF @ 100 or so?  That would be easier than hauling a sub box around.

[Ivan Beaver]

If you don't have a generator to sweep with, try this.

Remove the driver from the cabinet.

Try to put equal pressure on the cone and move it in and out and see if you hear a rubbing.

There could be some trash in the gap causing the problem.

The FIRST thing to do is to divide and conquer.

Is it the driver or the amp?

Until you know that-there are all sorts of different possible problems

[duane massey]

Also, check the dust cap.

[ProSoundWeb Community]