Topic: One of my lab cabs is creaking ? (Read 7042 times)

Alan Star · « **on:** January 03, 2006, 06:30:56 PM »

I have 2 at the moment and waiting till I find time and resources to build more, a friend (Clive Milne) built these ones, at the moment I run them side by side in the center with a pair of mackie sa1521's, one off to each side. Anyway, I have noticed the last couple times I have run them, after about 8 hours, as we are starting to get into the morning, 1 of them (the same one) starts to creak or distort and so I have to turn that one down, just wondering if anyone could help with troubleshooting suggestion to try and figure out why it's doing it ? On inspection of the drivers they seem fine ?

At the moment I am running each lab cabinet with a mackie m1400 (one amp per cab), so they are getting about 1000 watts each and am using the amps built in crossover (i think it says 67hz, the lower option anyway) and using the 35hz low cut filter.

Tom Manchester · « **Reply #1 on:** January 03, 2006, 11:23:04 PM »

Like a door creaking? The only time I have ever heard anything like that from a wood cabinet is when a joint is loose and 2 pieces of wood are rubbing. Make sure all of your screws are tight and joints glued.

Alan Star · « **Reply #2 on:** January 04, 2006, 12:46:47 AM »

thanks tom but actually maybe i could have described it better, I'm pretty sure all the timber joinery is tight. Although maybe it could be that, I'm not 100% sure but maybe it is a distortion from the speaker, I wonder if there is an air leak if it might cause that? Wonder why it seems fine when i first start them up and then only after a while do I start to hear the sound ?

Gary Perrett · « **Reply #3 on:** January 04, 2006, 10:26:13 AM »

Hi,
Its possible an air leak is happening as the chamber heats up, what was used to seal the wire holes?

You say you have inspected the drivers? Early runs of the Lab 12 had a glue issue and some of mine separated in spots where the cone meets the surround. Did you look through the wire mesh @ the voice coil. You should be able to see most of it with a good flashlight, and it should be a rich copper to a light brown color, not dark, or god forbid black Confused

Is there any sign of the surround touching the baffle plate (no discoloration/scratching on the surround)

Hows the gasket? they don't ususlly survive a removal of the driver.

Have you tried a DC resistance check of a warmed up driver VS a cool one?

Do you have the capability of running sweeps, as in a signal generator, or (but not the best way) a CD with low freq's that you could sweep through cold and after a good warmup? Are you using 'batting' in the chambers? if so try removing it.

Have you swapped amps to see if the sound follows the amp change.

That isn't much power for those, I use a QSC 4050 or Digam 5000 and the labs suck up all that power (well the Digam is plenty of amp actually, we ran 6 in stereo off 1 Digam 5000! you just wouldn't believe how loud it was... outdoors, you could FEEL them 1 mile away!)

My $.02
Gary

Alan Star · « **Reply #4 on:** January 07, 2006, 08:29:22 PM »

I drilled holes to feed the speaker wire through to the back and then forced construction adhesive into the holes and around the speaker wire, it's cured pretty hard and looks airtight.

Can't get a look at the voice coils through the mesh (perhaps with mirrors i might be able to ?), and don't want to take the drivers out for the reason that it will probably pull the gaskets off like you say. The cone seems to be well bonded to the suspension ring and moves in and out freely, feels nice and stiff.

Haven't tried a dc resisitance check once it's warmed up so will remember to do that next time if the problem persists.

I think what I will do is replace the wooden inspection covers with aluminium plate and see how that goes as it seems the distortion only occurs once things have heated up, maybe this will help.

Can't wait to get a few more of these boxes built but would like to sort out this problem first.

Thanks guys.

Alan Star · « **Reply #5 on:** February 19, 2006, 08:24:22 PM »

Problem persists, it's more like a flapping sound, didn't take too long for it to start this time and is not too easy to hear unless you get up close to the cabinet but is noticeable, so I am running one amp on full and having to turn one down to 2/3 rd's am thinking it's not an air leak as I imagine the drivers would be damaged if it was from what I understand ? I have a couple spare gaskets so am thinking to pull the drivers out and have more of a look at them and inside the cabinet ?

Gary Perrett · « **Reply #6 on:** February 19, 2006, 09:37:05 PM »

Ya ,do that.
Did you ever elimiate the amp by switching them out? I thought perhaps the amp might be clipping? Make SURE to get a DC resistance on both cabs, cool and warmed up. If the voice coil is compromised, as it heats up it may be shorting windings that cause the amp to see a much reduced resistance... -0- being a dead short. Kind of like taking a shorting bar and touching the lugs of the speaker jacks on the amp...

Make sure if you remove the drivers that the surround isn't touching the hole cut for the driver. Also make sure the gasket has a good sealing surface and(that a 'void'in the plywood) doesn't cause a leak.

When the speaker was built, were the seams of the "chamber casrefully inspected for potential leaks?

If you have the capability, you can monitor the amps current draw durring operation, and compare its draw to the one attached to the good speaker.

I use the wood covers but had to route out material behind the magnets to get sufficient clearance for cooling, and too make sure there would be no vibration when running.
Gary

Duane Massey · « **Reply #7 on:** February 20, 2006, 10:23:20 PM »

Not familar with the specific speaker, but I'd check the dust cover.

Alan Star · « **Reply #8 on:** February 20, 2006, 11:23:47 PM »

Have checked the dust covers and they seem pretty well sealed off. One thing I didn't pick up on before that I noticed last nite when i had a look is where the braces cross at the opening of the horn they are slightly loose, you canm move them a bit, I wouldn't have thought it would make that much noise but maybe thats what it is, will check it out tonight I think, as well as amp switching just to double check that.

Alan Star · « **Reply #9 on:** February 21, 2006, 09:01:00 AM »

Checked both amps with it and the other cab too, definately not the amp, its in the cabinet, mouth braces weren't moving, sound is coming from within, removed one driver, coil is original copper color, no discoloration, seemed well sealed, pushed other driver back, seems like plenty of pressure behind it so seems well sealed also. All the joinery seems rock solid. Didn't need voice coils to heat up to hear the distortion so I am figuring that it was always there but i didn't notice it straight away, you dont hear it so much untill you get up close or turn the amp up real loud ... and then it just sounds real dirty.

Not sure where to go from here except to try and replace the drivers ? ... but they seem fine ?

I'm sure they are wired in phase with eachother, unless the poles on the actual drivers are incorrect ? Would it sound distorted if they were out of phase with each other ?

Joe Jones · « **Reply #10 on:** February 21, 2006, 09:19:48 AM »

If the drivers were out of phase you'd get almost nothing from them. I'd test them out of the box, if there's a problem a 30Hz sine signal at 10 volts will point it out pretty quick. If it isn't the drivers then there's a leak in the box somewhere.

Dave Rickard · « **Reply #11 on:** February 21, 2006, 11:43:54 AM »

Low tech question:

Have you swapped drivers? Take the drivers (pair) from cabinet A and put them in cabinet B, and vice versa. Did the problem move with the drivers or stay with the woodwork?

If the problem moved with the drivers, swap only 1 this time and track the problem.

Joe Jones' test is worth trying too.

Dave

Dave

Gary Perrett · « **Reply #12 on:** February 21, 2006, 01:38:20 PM »

Is it possible one of the drivers is rattling against the cover plate?
I'd secure that mouth brace before doing anything else also.

P.S. those speakers have 2 dust caps, one under the other.

G

Antone Atmarama Bajor · « **Reply #13 on:** March 08, 2006, 02:46:08 PM »

I just posted about an issue I was having with binding posts having poor mechanical connection to coil lead tabs. I don't think it will make your cabs creak. But I was making mine make chunking/popping rattling noises.

I think I have another of them doing that in my BS-212's at high levels.

I found that using a right angle Philips on the screw cleared it up on one of them.

Now I have to experiment with the other that seems to make chunking under high power.

Does anyone know if the lab 12 driver audibly complains if you over excurd it?

Antone-

Wayne Parham · « **Reply #14 on:** March 08, 2006, 04:46:47 PM »

I think you smoked the driver(s). The voice coil has come unbound and started to buzz.

Look at this:

LAB12 Destructive Test

In that thread, you'll find destructive test results for a LAB12 driver. You'll also find out an easy thing you can do to prevent this in the future. One bolt-on part for each of the drivers conducts the heat from the pole piece to the outside covers.

A lot of heat is radiated from the voice coil into the pole pieces and magnet, and that heat re-radiates into the voice coil and bakes the glue. This is a pretty common faiulure mode for situations like you've described, extended use at high power levels.

The solution described is an easy and effective fix.

Wayne Parham · « **Reply #15 on:** March 08, 2006, 04:53:32 PM »

Over-excursion makes the driver sound like a jackhammer.

Alan Star · « **Reply #16 on:** March 08, 2006, 07:18:14 PM »

I am pretty sure the drivers are fine and haven't been overdriven, I have taken one out to inspect it and the voice coil doesn't look in the least bit burnt, and the cone moves in and out freely and feels nice and stiff. They have never been fed huge amounts of power either.

There are binding posts on the inspection plates which i dont use any more as I have routed the cables through to neutriks at the back of the speaker. I am getting some 6mm aluminium covers made up to replace the wood covers and am going to recess them into the timber so hopefully this will solve the problem. Antone, chunking/popping/rattling noises could easily describe how it sounds when turned up.

I agree with the suggestion of swapping drivers/cabinets until you isolate the problem but don't want to go through this process because the other cabinet is running fine and dont want to mess with it especially because when you take the driver out you have to replace the gasket and I don't have spare gaskets.

Thanks for your help / suggestions everyone, will post back here once I get these aluminium covers on and try it out again.

Antone Atmarama Bajor · « **Reply #17 on:** March 08, 2006, 09:08:09 PM »

Adam if you take the drives out again, also try running a LF signal though them. If you can hear the sound while they are free air, try tweaking on the binding post on the driver.

If its loose you can wiggle the post and it will make noise.

You maybe able to do this by simply running the cab with the access panel open since the lab12 binding posts will be exposed.

Antone-

Alan Star · « **Reply #18 on:** March 08, 2006, 09:14:32 PM »

Yes I did this running them in free air and one thing i did notice is that the wires that run from the binding posts on the speaker frame to the voice coil were slapping against the cone with the cone movement but I thought that couldn't possibly be making all that noise, anyway I twisted the binding posts a bit to try and get the wire to clear the cone.

Dave Rickard · « **Reply #19 on:** March 08, 2006, 11:44:32 PM »

Alan Star wrote on Wed, 08 March 2006 19:14

but I thought that couldn't possibly be making all that noise, anyway I twisted the binding posts a bit to try and get the wire to clear the cone.

Wouldn't the horn would amplify the lead slap as well as the program material? Some drivers have foam tape on the back of the cone to keep the leads quiet, others have sleeves for the leads.

Dave

Antone Atmarama Bajor · « **Reply #20 on:** March 09, 2006, 12:26:16 AM »

If you were able to twist the whole bracket that the coil lead is soldered to you should probably try tightening the its screw with a right angle philips driver. To ensure good mechanical connection.

Antone-

Alan Star · « **Reply #21 on:** March 23, 2006, 07:28:32 AM »

Well thanks everyone for your suggestions as I finally located the problem and it's pretty embarrassing considering how simple and obvious but rekon I at least owe it to post it here.

One of the sides had come loose at the bottom of the box, you couldnt see it easily and the main problem for me I found was that it wasn't easy to locate because I couldn't hear where it was coming from. In the end I worked my way around the box pushing down firmly on the edges until I noticed it stopped creaking. So have put some more screws in and that seemed to fix it.

So as you can probably imagine I am very relieved to finally get my sub back ! Thanks again guys, your help much appreciated.

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Author Topic: One of my lab cabs is creaking ? (Read 7042 times)