subwoofer making a crack sound

[Hostility]

SO recently got my home theatre set up, i have 2 dayton audio um-18 22 subs in 2 full marty boxes. powering them is a behringer ep4000, feeding the amp is a minidsp into a clean box pro.
Now i wanted to test some music out on it but when i turn them up my 1 seems to make a quick crack sound, its not crackling or popping, it sounds like a something cracks. hard to explain, i turned that one down and listened to the other and don't hear anything, it only does it on certain frequencies. The subs are not that old but I'm hoping the sub docent need repairs, was thinking of taking it out but other then a visual check not sure what to look for.

 

[WaynePflughaupt]

The EP4000 has a lot of dip switches on the back panel. Do you have them set right? Is the amp in stereo mode, parallel mode, or bridged?

You can take the minidsp and clean box out of the equation, one at a time, to see if one of them is the problem (you probably don’t need the clean box anyway).

If you pull the drivers of the boxes, put an ohm meter across the terminals and see if you get a reading. It should read roughly the impedance rating of the speaker (8 ohms, for instance). If you get no reading, the voice coil is blown and the speaker is toast. You might also try spreading your fingers evenly around the cone and gently pressing it in. If you hear a scratching sound, that’s another indication that the driver is toast.

Good luck, and get back to us.

Regards,
Wayne A. Pflughaupt

 

[Hostility]

i need the clean box pro as the minidsp doesn't output a high enough signal for the ep4000 to put out its full power. but ill try it again without the minidsp and clean box and see if it goes away. i tried pressing the sub in and out and no sound, smooth feeling, the rubber surround is good. i hope its just something else and not the sub. i haven't really pushed them since owning them. but ill check those few things out thanks

 

[shadyJ]

What frequencies does that cracking occur at? It could be that the driver is misaligned. That way it will act normally if you push it in and out gently, but when you start to give it some power, the former will be hitting something much sooner than it normally would. It could also be some clipping somewhere in the system. You need to examine every step of your gain stage to rule that out.

 

[Hostility]

I've never heard it before from previous setup. and I'm not sure what frequencies its at, i was just playing some music and heard it on a bunch of songs, subs are not being pushed really hard either when it does it. If it was the gain before the amp then shouldn't the other sub do it as they are running off the amp as 2 channels?

 

[shadyJ]

Sounds like clipping of some kind. It could be that one channel of the amp was damaged or is malfunctioning. Try swapping the sub channels. Reverse the subs to the other channels of the amp. If the popping noise follows the same driver, than it is a driver problem. If the popping stay on the same channel, than obviously it is a problem with the amplifier.

 

[Hostility]

So I had time to do some tests. I pulled subwoofer out and checked ohms on both coils. Everything looks fine. Spider cone tinsel leads are all ok. Looks brand new. So I put it back In with longer screws. Tested again. Same issue. Took the clean box pro out and still same issue. So I tested the other sub alone and no issue. So I then switched channels on the amp and tested the sub that makes the crack sound and again still does the sound. So now I'm confused. The box is glued and screwed so I don't know why the sub would make this sound. Also I've noticed the carbon fiber cone has the fibre hairs starting to poke out in both subs. I thought maybe the crack sound is the carbon fiber cracking but I'm lost now on what the issue is. I've barely used these

 

[TLS Guy]

So I had time to do some tests. I pulled subwoofer out and checked ohms on both coils. Everything looks fine. Spider cone tinsel leads are all ok. Looks brand new. So I put it back In with longer screws. Tested again. Same issue. Took the clean box pro out and still same issue. So I tested the other sub alone and no issue. So I then switched channels on the amp and tested the sub that makes the crack sound and again still does the sound. So now I'm confused. The box is glued and screwed so I don't know why the sub would make this sound. Also I've noticed the carbon fiber cone has the fibre hairs starting to poke out in both subs. I thought maybe the crack sound is the carbon fiber cracking but I'm lost now on what the issue is. I've barely used these

I doubt it is the cabinet, I would bet there is something wrong with that driver and it needs reconing.

You can confirm this by swapping drivers. I bet the fault will follow the driver.

I suspect there is something wrong with the suspension and or VC former.

The VC may too deep or not deep enough in the gap, or the former may have been damaged by over excursion and got caught on the pole piece.

If this fault follows the driver, you will have to take the driver apart and recone it. The issue is that you have to recone to isolate the problem.

 

[Hostility]

i did swap driver to a different channel on the amp and still same issue. Apparently this happens i guess with the dayton um18 subs as i guess their quality control is not the best. Ive contacted parts express to see about sending it back for a replacement.

Ive also noticed the carbon fibre cone has the fibres poking through, not sure if thats normal or not. both drivers are doing this. i guess i have to wait and see what parts express says. thanks

 

[TLS Guy]

i did swap driver to a different channel on the amp and still same issue. Apparently this happens i guess with the dayton um18 subs as i guess their quality control is not the best. Ive contacted parts express to see about sending it back for a replacement.

Ive also noticed the carbon fibre cone has the fibres poking through, not sure if thats normal or not. both drivers are doing this. i guess i have to wait and see what parts express says. thanks

I don't think the fibers coming through is a concern. They might be skimping on the polymer though!

There is clearly something wrong with the driver suspension and or voice coil though.

 

[Hostility]

Well I called them. Turns out I have to send it back to them for evaluation. So I pay for shipping from Canada back to us. Then if it's manufacturer defect they will ship me a new one. Again I'd have to pay shipping again. Not really happy about this. Sucks as I think it did this from the start

 

[TLS Guy]

Well I called them. Turns out I have to send it back to them for evaluation. So I pay for shipping from Canada back to us. Then if it's manufacturer defect they will ship me a new one. Again I'd have to pay shipping again. Not really happy about this. Sucks as I think it did this from the start

Well. I'm sure they do want it back. The most expensive part of a driver is the magnet and Chassis.

Either they or more likely Dayton will recone that driver. The cone and attached VC and suspension cost very little.

They won't know what the problem is until they remove the cone. If they determine it is abuse then I'm sure they will charge you for reconing.

 

[MrBoat]

Did you try taking the suspect driver and installing it in the other cabinet just for the heck of it? The reason I ask this is, I see some pretty precarious approaches with bracing, where some people use things like 2x2's, dowels etc. with coarse threaded screws into end grains and such without pilot (or proper sized) holes etc.

 

[mtrycrafts]

.... with coarse threaded screws into end grains and such without pilot (or proper sized) holes etc.

Don't think a pilot hole in end grain would help.

 

[MrBoat]

Don't think a pilot hole in end grain would help.

No, it wouldn't, ideally. It should be on the flat sawn, or, across the face grain on as much of a bias as possible. I see it done a lot though without any consideration of grain orientation, expansion/shrinkage etc. Screws driven from the outside of cabinets into end grain. If you have to do it, a pilot hole is likely the only way you might get away with it until the glue dries, and even then, the glue up needs to be optimal or some other mechanical joinery techniques employed.

I don't use solid wood 'cross' bracing or dowels. The OP may not have either. It was just a thought. I use more of an engineered approach where possible.

 

[Hostility]

i actually use dowels. it wasn't what i wanted to do, but i did it.. I screwed them in, with wood glue, then PL premium around the base of the dowels for extra strength, i took the sub out last week and checked for loose dowels but they are all tight. i also played the subwoofer out of the box and it made a weird vibration sound like the basket was vibrating, Not sure if i should try or not. Im trying to find a box to ship it back in as i just threw out the boxes a month ago. But i want to make sure the driver is the issue before i pay to send it back.

 

[MrBoat]

i actually use dowels. it wasn't what i wanted to do, but i did it.. I screwed them in, with wood glue, then PL premium around the base of the dowels for extra strength, i took the sub out last week and checked for loose dowels but they are all tight. i also played the subwoofer out of the box and it made a weird vibration sound like the basket was vibrating, Not sure if i should try or not. Im trying to find a box to ship it back in as i just threw out the boxes a month ago. But i want to make sure the driver is the issue before i pay to send it back.

No worries, or criticism intended, personally. I still would want to try it in the other box just to rule it out. And only because of the hassle with shipping it back and forth.

 

[Hostility]

Do you think playing the subwoofer outside the box is a good or bad idea to see if i can hear it make that crack sound? It doesn't take much to swap them, so i can try that also

 

[TLS Guy]

Do you think playing the subwoofer outside the box is a good or bad idea to see if i can hear it make that crack sound? It doesn't take much to swap them, so i can try that also

If that driver is not damaged now, it will be if you play it at power outside the box! Bad idea.

 

[MrBoat]

Do you think playing the subwoofer outside the box is a good or bad idea to see if i can hear it make that crack sound? It doesn't take much to swap them, so i can try that also

If you swap them in the boxes would do the same thing really and discount the cabinets as a problem at the same time.