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Old 25th October 2013, 05:48 AM   #1
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Default 18SW100 noise. Help identify (video inside)

Last week I noticed one of my drivers making noise. It still plays all bass/sub-bass notes, yet accompanied by this noise. It's quite noticeable at lower input drive levels and sometimes goes away during certain sine tests with varying input voltage.

Could it be a burned or misaligned vc? Blown? I'm unfamiliar with this noise, so I'm reaching out to you for advice.

VIDEO

Last edited by CRESCENDO; 25th October 2013 at 09:11 AM. Reason: more info in title
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Old 25th October 2013, 09:27 AM   #2
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Maybe some of this info will help:

I can also hear whatever is making noise when I manually pull up on the cone from its underside when connected to an amplifer that's turned on without signal present. It does not make the noise when the amp is off, nor when pressing down on the cone with the amp on or off. So, it only makes the sound when a powered up amplifier is connected and with positive cone movement (away from magnet). Makes me think VC related. Thoughts?
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Old 25th October 2013, 09:35 AM   #3
OMNIFEX is offline OMNIFEX  Jamaica
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The voice coil is rubbing, it is time to get it reconed.
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Old 25th October 2013, 09:53 AM   #4
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Thanks for the reply.

Assuming that's what was happening, I have since contacted a couple places regarding the price/availability of B&C's service kit. One of two places I contacted (loudspeakersplus.com) does re-cones in-house.

Has anyone attempted a re-cone on a B&C driver of this magnitude? Much different than any decent how-to videos would show?
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Old 25th October 2013, 04:08 PM   #5
OMNIFEX is offline OMNIFEX  Jamaica
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It depends on the kit. Some kits offer the voice coil attached to the cone, whereas, others will require a full assembly ( cone, spider, voice coil ) . Also, you need to take cost into factor. If you are planning to ship the speaker for repair, it may cost slightly less having it repaired (shipping plus repair) than buying a brand new speaker.

The last speaker I had reconed was 1994 so, I cannot tell you where the prices stand in this day and age. You live in the States so you can shop around for the best price if loudspeakerplus is too dear.
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Old 25th October 2013, 04:49 PM   #6
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Quote:
Originally Posted by CRESCENDO View Post
Could it be a burned or misaligned vc? Blown?
Sounds like some sloughed off windings dragging. Check the dc resistance.

If the voice coil former is Kapton, it could have developed some "heat blisters".
I successfully sanded off the blisters on an EVX 150A by removing the dust cap, then inserting emery cloth sandpaper in the gap and playing 20 Hz sine wave tones while holding the emery cloth. After blowing the dust out, and re-attaching the voice coil, the speaker worked fine.

Of course, if the voice coil is wound inside and out of the former, that procedure won't work.

Still, there is a chance that some crud melted and is in the gap, so worth a try to remove the dust cap and see if you can remove debris with compressed air or masking tape.
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Old 25th October 2013, 06:35 PM   #7
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That stinks. You'd expect some reliability with that kind of ($) driver.

Anyway, were these speakers under your watch at all times? Or were they out of your sight where someone could have abused them?
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Old 25th October 2013, 09:15 PM   #8
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Hi Art,

DC resistance: 5.5 ohms

Do you know of an appropriate how-to video for removing the dust cap or will most videos relate to this style driver?

Do you think it's weird the noise only happens during its positive stroke?


Hi m R g S r,

No, not at all times. I've come back to a heavily limiting amp rack (heavy limiting creates a lot of heat in the vc), but I don't blame anyone but myself. I could've been more clear of what I wanted from my partner and I could've made sure the DJ's levels were watched/controlled more carefully every night like we have for the last 6 years. I tell you, If there were 5 clip lights on a DJM-800, some "talent" still wouldn't have trouble lighting em all up (meaning, it sometimes takes a full half-turn of the DJ's channel gain knob to get em out of clip). Then again, we're not quite sure when this happened. We had been setting up this sub for our bi-weekly and the noise is kind of reminiscent of air coming through the handles on the bottom against the floor - so, we very well could've been using it like this for a while.

Last edited by CRESCENDO; 25th October 2013 at 09:19 PM.
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Old 26th October 2013, 01:01 AM   #9
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Quote:
Originally Posted by CRESCENDO View Post
Hi Art,

DC resistance: 5.5 ohms

Do you know of an appropriate how-to video for removing the dust cap or will most videos relate to this style driver?

Do you think it's weird the noise only happens during its positive stroke?
If the DC resistance is the same as other speakers of the same type, that is a good sign.

No videos I know of for removing dust caps, it just takes a steady hand and a sharp blade, an X-acto knife works well, and makes it easier to keep the blade parallel to the cone surface.
If the dust cap is glued with epoxy, it safer to cut it out above the glue line, but if you are confident cut it off below, it will be easier to re-use it.

If an upper portion of the voice coil has sloughed off, it may drag on the forward stroke and go back in place on the return stroke.

It might be possible to glue the windings back by inserting plastic shims in the gap and using a syringe to put some high temp epoxy on the loose winding- make sure the epoxy does not stick to the shim material.
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Old 26th October 2013, 01:14 AM   #10
sine143 is offline sine143  United States
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Crescendo, I do not know when you purchased these (or where), but this might be applicable to you (BEFORE YOU GO CUTTING THINGS)

http://www.parts-express.com/pedocs/...ranty-4458.pdf
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