Is my woofer toast?

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byoung

Well-known member
Joined
Jul 16, 2006
Messages
125
Location
San Gabriel Valley, CA
So I've got some weirdness going on in one of my studio monitors that has me a little frazzled. It's a pair of dynaudio bm6a's and they have never given me issues before, and I've always treated well. I was giving a tr808 a run for it's money today when I noticed that the right cabinet was 'rattling' with low frequencies, sort of a screw was loose int the cabinet sort of buzz/rattle, picture on the wall rattle. I inspected it visually and even got out an allen wrench to make sure all screws were solid. Everything checked out, so I listened to it and it sounds like it's most apparent at the rear where the bass port is. I switched speakers l/r and it still had the rattle while the other remained clean.

I finally ran a sine wave through them and below about 100hz the one speaker/cabinet starts to make this noisy rattle, when I get to about 60hz one has tight clean bass the other has a little less bass but a sort of pink noise behind it. I have heard you can check for a bad voice coil if you gently and evenly press on the woofer, so I did that(even though I cringed the entire time), but it was super smooth. So now I'm not sure what to think, it seems fine until you get below 100hz. So I don't know if a blown speaker would react this way, since I've never blown one or if it might be something in the electronics/amp possibly? Anybody have any suggestions before I go out and buy a replacement woofer?
 
First you gotta be careful putting pure sine into speakers at higher levels.  They don't like it much.  Use sine gently to find buzzing.
There are a few things with any active speaker.  There are all sorts of mechanical issues that can cause a buzz or rattle.  I have gone through Genelec 1031 speakers with all sorts of mechanical fixes to get rid of buzzy guts.
One thing to test is the throw of the woofer.  Gently push it in, touching it towards the center, and feel for any scratching.  Look at the surround for any slit.  Get the buzzing happening, gently just barely there, and see if you can apply pressure to any part of the cone to stop the buzz.  Any of those three would indicate blown woof.  The coil can go bad, the spider can rip, or the surround can fart.
Your next test is to swap the woofers- which cabinet is buzzing then?  If the buzz stays with the cab, then check anything mechanical.  If it moves, look at the woof and sometimes you can glue a ripped spider or surround.  Otherwise, buy a PAIR of new woofs and install them.  Save your good used woof for the next time you kick an 808.
Mike
 
Well I'm pretty certain I found the cause of the issue I am having. I pulled the amp off the back of the speakers, and there are a few holes on the inside compartment which allow the speaker wires to pass through. In the cabinet that is having issues, air is blowing through these holes, and in the good cabinet it's not. I used some putty to cover the holes so I could test it and it seems to be fine now.

Now I need a permanent fix, I'm figuring some silicone in the holes should fix the problem. I really wanted to pull the woofer and do it from the inside but I can't get the woofer out, maybe I'm not pulling hard enough, but I also don't want to damage anything, or maybe there is some trick to removing it? I've also just read that silicone fumes can eat the rubber surround of the speaker, so I'm hesitant to fill the holes with the woofer still in there. Any thoughts?
 
byoung said:
I've also just read that silicone fumes can eat the rubber surround of the speaker, so I'm hesitant to fill the holes with the woofer still in there. Any thoughts?
It's possible that acetic acid fumes from acetoxy silicone might damage rubber. You can get non-acetoxy silicone if you're worried about it. I used the acetoxy kind for exactly this purpose in a sub bass and haven't noticed any damage to the rubber (neoprene I think) cone surrounds.
 
Hi,

I was looking at someone's BM6A MK-I pair when I noticed that when pumping up the volume to a noticeably high level,
there's a rattle sound which comes from the cabinet itself. That specific unit's amp has been repaired before. Could it be that it has the same issue going inside ? I want to buy them but not sure it doesn't has a defect...
 
Not necessarily suggesting it's the case here, but in my experience, when I've come across the same phenomenon, it was either due to the port coming loose or the foam surround starting to perish, thus making the voice coil chatter against the magnet assembly (the latter being a less-than-desirable situation). So, if you're getting rattling from 808 kick drums, these are a couple of avenues worth exploring.

Justin
 
byoung said:
Well I'm pretty certain I found the cause of the issue I am having. I pulled the amp off the back of the speakers, and there are a few holes on the inside compartment which allow the speaker wires to pass through. In the cabinet that is having issues, air is blowing through these holes, and in the good cabinet it's not. I used some putty to cover the holes so I could test it and it seems to be fine now.

Now I need a permanent fix.
Use BluTak.  Speaker Manufacturers use this.
 
hi, I have had this EXACT same problem. rattling inside one of the BM6A speaker boxes.

I finally tracked down the problem. Firstly, you should unblock those holes that you plugged up! they were the holes to let the bass waves flow out of the rear bass port, the thin slit that runs along the top of the BM6As.

the problem is...that over time as the speakers amps run for periods of time, it slowly damages the FAKE PLASTIC WOOD COVERING inside the top slit port. The plastic cover falls down, and flaps and rattles in the breeze! its a design fault.

take a torch, shine in deep into the top slit port on the back and you will see the plastic fake covering hanging down and blocking the port. and it will be flapping around in there when the bass is up!

take a look at my attachment pic. you need to use some pliers, pull the plastic covering out (I also used a thin screwdriver to help twist enough of it to grab)...pull it outwards and then just cut it off with a pair of sissors.

problem solved! this drove me nuts for ages. I was worried I had blown a woofer as well. phew!! I imagine as the other BM6's in the world clock over hours of use that this problem will become more and more widespread.

I hope this helps someone out there one day!!

Cheers :)
Blackout
 

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Hi blackout, I think you missed here, this topic is from 3 or 4 years ago.

Still,  welcome to the forum! Enjoy.

JS
 
Old topic or not -Blackout's post may prove invaluable to someone in the *future*.  Thanks for sharing!

We had a similar problem with an ATC 25 here.  Turns out the port has a tube which connects to the plastic port opening and the tube had come off and started flapping around...
 
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