Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Alan Star]

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]

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]

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]

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 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]

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]

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]

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]

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

[Alan Star]

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]

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 ?