buzz from driver - Did I over compress the gasket? - AVS Forum
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post #1 of 10 Old 06-16-2012, 09:34 PM - Thread Starter
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Greetings All:

This may be considered a nube problem, even though it is not my first build.

My new dual opposed Tempest 15 sealed sono-style sub has a resonant buzz at a consistent frequency when I sweep it. I can get up close to the drivers and both have a buzz which seems to come from the rims.

700

I used the Parts-Express Speaker Gasketing Tape 1/8" x 1/2" x 50 ft. Roll


Unlike how I would tighten the bolts on an engine valve cover gasket (ONLY snug plus some), I tightened the 8 nuts/driver with a nut driver, medium tight.

Did I over compress the gasket?
Any reports that the P-E sealing tape creates resonant buzzes? wink.gif

I know, I know, thin and lame...

I'm just looking for any other possibility than that I have to break two siliconed seals and redo the gasketing.

Some feedback from voices with experience would be appreciated, before I commit to surgery on my new baby! eek.gif

FWIW: the finish on the protube will be black burlap wrapped around the black cylinder area and polyurethaned.

TIA

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post #2 of 10 Old 06-16-2012, 10:28 PM
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Have you tried pressing various parts of the driver to see if it goes away? I don't see how making it TOO tight can cause it to rattle, maybe you didn't tighten it enough?

What about the threaded rods? Maybe they are vibrating and hitting against the hole...



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post #3 of 10 Old 06-17-2012, 10:55 AM - Thread Starter
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Quote:
Originally Posted by Mrkazador View Post

Have you tried pressing various parts of the driver to see if it goes away? I don't see how making it TOO tight can cause it to rattle, maybe you didn't tighten it enough?
What about the threaded rods? Maybe they are vibrating and hitting against the hole...

Thanks for the reply.

I did apply hand pressure to the drivers to help me locate the buzz; no amount of pressure anywhere muffled the resonant buzz. The buzz was fairly localized to the rims of the drivers.

As to how the gasket could be compressed too tightly: remove the gasket entirely and you WILL get a resonant buzz or two at the interface between the mounting plate and the driver rim.

The steel rods are around 39" long, and the range for the speed of sound in steel is between 9843 feet per second and 19686 feet per second, depending on grade and alloy.

This puts the first order longitudinal acoustic resonance for the rods into the following ranges:

@SOS=9843 feet per second
Full wave
9843/3.25 = 3028.61 Hz

Quarter wave
9843/13 = 757 Hz

@SOS=19686 feet per second
Full wave
19686/3.25 = 6057.23 Hz

Quarter wave
19686 /13 = 1514.30 Hz

These COULD be excited as harmonics of the sweep range I used (18-200Hz) but seems unlikely. Where the rods contact the driver mounting plates, I used thick neoprene washers between the steel washer and nuts and there are no other contact points, other than possibly the sides of the holes through the 1.5" thick mounting plates.

To eliminate this possibility I will temporarily remove the rods and test with low SPL tones. Since the only other force holding the mounting plates in place is a 360 degree silicone bead between the tube and the plates, I intend to keep the SPL low to avoid popping the plates off (or at least blowing the seals) when both driver’s cones move inward!

Process of elimination; I will test this and report.

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post #4 of 10 Old 06-21-2012, 12:13 PM - Thread Starter
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STILL LOOKING FOR ANYONE HAVING HAD THIS PROBLEM WITH DRIVER-TO-MOUNTING PLATE BUZZ TO CHIME IN, PLEASE!
Quote:
Originally Posted by robobob View Post

Thanks for the reply.
I did apply hand pressure to the drivers to help me locate the buzz; no amount of pressure anywhere muffled the resonant buzz. The buzz was fairly localized to the rims of the drivers.
As to how the gasket could be compressed too tightly: remove the gasket entirely and you WILL get a resonant buzz or two at the interface between the mounting plate and the driver rim.

Process of elimination; I will remove the allthread rods, retest and report.

OK, back with report as promised.

  1. Removed the allthread rods
  2. Filled through holes with rubber stoppers stuffed in as hard as I could then used duct tape to hold the stoppers in place
  3. Reswept and found the buzz still there, starting from around 90 and tapering off after 99 Hz, FWIW

This eliminates the rods as the cause of the buzz.

Curiously, this time I could dampen the buzz by about half by applying hard pressure on the driver rim, where, in my first test, BEFORE I removed the rods (and sweeping the sub RIGHT AFTER the first torque down on the sealing tape) applying pressure to the driver rim did NOT seem to have any effect!

This would seem to imply that I need to tighten down the drivers even MORE but that makes no sense. The nuts were tightened medium tight using a nut driver and I was worried that i was overtightening! Maybe using a socket set and ratchet instead would have given more accurate torque by feel?

Unless the neoprene foam sealing tape reforms a bit after first torque-down, which means definitely need to re-tighten.

I have to cut open the sub to redo the seals, with either looser or tighter torque on the mounting bolts; I just want to get it right this second time!

TIA

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post #5 of 10 Old 06-21-2012, 02:01 PM
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Maybe its something similar to this

http://www.hometheatershack.com/forums/creative-sound-solutions/52393-help-noisy-sonosub.html



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post #6 of 10 Old 06-21-2012, 02:13 PM - Thread Starter
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Quote:
Originally Posted by Mrkazador View Post

Maybe its something similar to this
http://www.hometheatershack.com/forums/creative-sound-solutions/52393-help-noisy-sonosub.html

Thanks for the reply.

I am using the Tempest Classic 15" driver, which is supposedly designed to handle being horizontally mounted. Both drivers make the same buzz at the same frequency range with both drivers tightened to the same torque. If I press down on the rims, the buzz is reduced.

The buzz is easy to localize to the rim of the driver so I THINK the problem is limited to the interface between the driver rim and the mounting plate.

I have used different sealing foam on previous builds; this my first experience with the P-E sealing tape. Before, I had to be careful not to overtighten the mounting hardware as the foam gaskets were not very dense.

The P-E sealing tape is more dense for the same thickness. If I had had on hand some of the other stuff (the kind recommended on Linkwitz' site) when I was loading the drivers, I would have stuck with what I know works!

I violated the Prime Directive: If it ain't broke, don't fix it!
eek.gif

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post #7 of 10 Old 06-22-2012, 11:15 AM - Thread Starter
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OK

I found a review on the P-E site which implies that I may need to crush the gasket even FURTHER. MUCH tighter than when using the vinyl foam sealing tape.

Sealing Tape Review

Cuts and forms to shape easily. It sticks well when you peel off the backing paper, but it easily removes from the speaker frame if you need to move it around a little. I found that an extra 1/4 in. at the end will give a tight boundary butting up to the starting point. Good results are achieved when tightening the gasket to approx 1/2 the original thickness. It does what it is intended to do.


I will cut open the sub, install fresh P-E sealing tape, Speaker Gasketing Tape 1/8" x 1/2" x 50 ft. Roll
and compress the tape to 1/16" thickness (1/2 the uncompressed height) .

Now that I know which frequency range to test for, I intend to try a sanity check on the driver-to-mounting-plate interface by sweeping the drivers BEFORE sealing the plates to the tube, to see if the resonant buzz at 90-99 Hz has been eliminated. Then silicone seal the plates to the tube and re-install the clamping rods.

Thanks to Mrkazador for responding!

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post #8 of 10 Old 06-22-2012, 12:02 PM
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Wait...how much is it compressed now? I usually go as hard as I can with my hand, worrying more about stripping the wood than about gasket tape compression. Tighten it down I say! smile.gif

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post #9 of 10 Old 06-22-2012, 12:32 PM - Thread Starter
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Quote:
Originally Posted by garciab View Post

Wait...how much is it compressed now? I usually go as hard as I can with my hand, worrying more about stripping the wood than about gasket tape compression. Tighten it down I say! smile.gif

Yeah, looks like I erred on the side of "too loose" with this thicker P-E sealing tape.

I tightened the nuts with a nut driver (screwdriver-like handle with a socket instead of blade or philips end), NOT a wrench or a ratchet and socket, which provide much more leverage of my muscular effort.

Using the nut driver, I tightened down pretty tight, but not maximum effort; from my use of the vinyl foam type sealing tape in the past, I was going for snug/super-snug, NOT batten-down-the-hatches tight.

Since the leverage factor of the nut driver is less, I have ended up on the side of "too loose" compression on the gasket tape.

I have an old automotive torque wrench around; I think I will at least use to make all the nuts the same tightness. I will note how much torque is required to compress the tape to 1/16".

The review I cited above PLUS your encouragement, gives me confidence that my sub surgery (required to remove the end mounting plates to get at the driver-mounting nuts) will finally result in a finished build!

Thanks for the reply!

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post #10 of 10 Old 06-22-2012, 01:21 PM
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I'll be checking in to see if that solves your problem. I haven't run sweeps on my subs in a long time, but I've never noticed any funny noises coming from them. I know sweeps are much better for finding these sort of noises though.

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