Correct Speaker Mounting

Rob Segal · From: New York NY

The Black Widow and the JBL D-130 place a cork gasket between the speaker frame and the cabinet sound board. This would seem to cause a dampening effect upon the sound output.....do we want this dampening, and why?

Donny Hinson · From: Glen Burnie, Md. U.S.A.

No, there's no "dampening" effect. Remember, the basket is still directly connected to the baffle through the mounting screws. The cork (or sometimes fiberboard is used) doesn't compress with the sound waves, and that's the only way it could dampen the sound. The gaskets merely allow there to be an airtight seal between the speaker and the baffle, and at the same time eliminate any chance of vibration (rattle) due to the warping of the baffle. Don't remove the gasket, or you'll be sorry later on!

Torquing the speaker properly is important to keep from warping the speaker basket. Install a speaker just like you would a wheel, torquing gradually, and torquing opposites to prevent warping. Do not over-torque! Use only enough torque to slightly compress the gasket.

Oh yeah, check the tightness of the screws every couple of years, too! You'd be surprised how many players had the speakers come loose while they were playing, and that ain't a good thing.

Jon Light (deceased) · From: Saugerties, NY

I just installed a pair of 10's in a pretty cool TubeWorks cab--it's a vertical V front with the top part open, the bottom part closed back. Jury's out on the sound but it sure thumps.
The speakers had gaskets for rear mounting but unfortunately the cab front mounts. As I tightened them in it really felt like I was having to over-torque them a bit in order to get them uniformly and firmly in place. I should have gotten or fabricated some kind of gasket but.....
Hope I didn't deform the basket.

Rob Segal · From: New York NY

Thanks guys. I've just built some open-back cabs and am wondering about these kind of issues.

Jon, what's an open V-front cab--closed back?

A soft gasket in the 'vibration chain' of a pedal steel would seem to be counterproductive, so I was guessing the soft gasket in the speaker sound chain would likewise be bad. However Donny, I see about the screws, they do provide a mechanical contact, though it's only one way--one more reason the screws must be tight, obviously.

I wonder who has extensively worked on open-back cab design?

Thanks again guys,

Rob

Jon Light (deceased) · From: Saugerties, NY

Hey Rob. It's a 2x10" cabinet with the speakers over/under instead of side by side (that's the vertical) and the top speaker baffle angled up a few degrees (that's the v front). And the clincher is that the bottom part of the cab is a closed box, the top half is open back. In theory it's the best of both worlds, I guess. Got it cheap on ebay a couple of years ago. The speakers aren't broken in yet so I'll reserve judgement. Plus I haven't tried it yet with the Dual Showman I hope to drive it with. With this particular cab the closed cab part cannot be opened from the rear---hence the speaker can only be front mounted which I did without a gasket. I just realized that I could have rear mounted the top one. But now that it's in there's no point.

Rob Segal · From: New York NY

....sounds interesting--and heavy! The cabs I made are dimensionally a cross between a Session 400 minus the amphead, and an Evans cabinet. This may have been a mistake, as they seem to be very warm and bottomy, though I can EQ it out.

I'm looking for crispness, no mud, but still bottom and fatness...impossible I suppose.....

David Deratany · From: Cape Cod Massachusetts

If by screws "one-way" you mean just screwed into the wood, you might consider using T-nuts, which I would take to be two-way, if I am understanding correctly. T-nuts allow for more secure and uniform tightening; and if you put a drop of LocTite on the threads, they will likely never vibrate loose.

Rob Segal · From: New York NY

Thanks.

By one-way I meant that, since the screw clamps the speaker frame against the sound board, with the compressable gasket in between, if the gasket shrinks, then firm mechanical contact between speaker frame and board is lost--because the head of the screw can only resist the frame's movement in one direction/way.

Loc-tite is good. I am using T-nuts.

Rob

Bob Hoffnar · From: Austin, Tx

Rob,

This cab is the best i have found:

Andy Marshall built it. Its tuned like a cello to my ear.

I got it from these guys:
www.thdelectronics.com/

I'll come by with it in the next week or so if you want.

Bob

BTW: Dan Tyack is all over the sound clips on the THD site.

[This message was edited by Bob Hoffnar on 30 November 2003 at 06:54 PM.]

Eric West · From: Portland, Oregon, USA, R.I.P.

Well Well Well.

I can answer your question in detail with correct information.

That cork "gasket" is not a gasket. It is slightly higher for BACK loaded speakers. This is done SPECIFICALLY for pressing the glued cone ito the basket assembly so as to hold it securely.

Here's how I know.

Mine just came unglued after 24 years. I took it off and found that about half of the cone was totally loose from the basket. I was mystified as to why nothing was holding it in except the glue.

I have one of the original Session 500s. The speaker is mounted with the cork "gasket" on the OUTSIDE of the cabinet. This left nothing holding the cone into the basket but the glue, which in my case only held for twenty years. ( sheesh...)

This is because there ISN't ROOM to back load the speaker in MY Session 500. I'd comfortably call it a Design Defect.

In my Nvl 400 the speaker IS back loaded because there IS room.

I am surprised the glue actually held it so long.

I tried super glueing it, but after this time the cone is warped somewhat and still buzzes in spite of cleaning and "repositioning"of the magnet. Basket time.

It should be like Mr Hinson said tightened incrementally like a head bolt pattern. I don't see that it would be able to be tightened down to compress the 3/32 or so or cork that I see sticking out "all the way" down to the cabinet, but it darn sure shouldn't be loose by any stretch. It's what holds the glued cone into the basket securely.

There you have it.

EJL

[This message was edited by Eric West on 30 November 2003 at 07:38 PM.]

Rob Segal · From: New York NY

Well. Eric, the gasket on the original jbl in my old session 400 is compressed to the extent that it no longer protrudes the 3/32 you refer to, and which I am familiar with because the other jbl I have, a recone, does protrude. I gues years of tightening have compressed it.

Hof, come buy with all your gear, call me. I'm in tone hell now, when only 2 weeks ago I was in tone heaven. All started when I tried some speaker cabs......

Eric West · From: Portland, Oregon, USA, R.I.P.

Well if the cone hasn't separated from the basket, I'd say there's a good chance it will stay that way..

Another one is tht "warpage" of the basket would have to be pretty pronouced to overcome the accordian edge of the cone. Care never hurts though.

In all the 24 years I completely powered the hell out of it this is the first time I noticed it. It was that way from the factory.

If anything, I bet a guy could cut sections out of a piece of thin cork gasket material from an auto parts store and super glue them on and snug it down in a case where it had gotten compressed. ( Leaving the old one on there of course.

I'm going shopping for another one tomorrow, and certainly a metal ring like I've seen on other front loaders.

Understand that it's something that Peavey in 1979 decided it wasn't critical enough to can shipping mine and redesigning it. They could have at least put a ring around it.

I wonder If my warrantee's up...

I thought I'd post the ser# but the plate is too worn out to read it. It's a good enough amp that I have no probs putting out the $ for another speaker, that's for sure.

EJL

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