Cabinet damping for speakers - worthwhile tweak or no?

byteme · « **on:** 17 Apr 2003, 02:33 pm »

I recently upgraded my Polk RTA11t's to RTA11tl's by upgrading the tweeter and reworking the crossover with MUCH higher quality parts. I ordered everything from percy audio and at the time Michael recommended damping for the cabinet (which is MDF with little internal bracing). I didn't bother with it, but now I'm thinking maybe it would help. Has anyone used Deflex or Black Hole 5 or anything similar inside their cabinet? If I were to do this do I need to do the whole thing? Just the back or what?

Thanks!

Nelgan · « **Reply #1 on:** 17 Apr 2003, 02:38 pm »

This is one thing you'll have to experiment with. There is no one "right" answer. But I can't see how some measure of damping materials would not make some level of improvement. Start with basic materials like eggcrate foam or Acoustastuff. You may find the results to your liking. Another cheap way of deadening cabinet resonance is to use Parts Express vinyl damping sheets. If those materials don't yield positive results then try exotics stuff like BH5.

Darren Thomas · « **Reply #2 on:** 17 Apr 2003, 02:43 pm »

Much of the benefit would be if the cabinet isn't well braced. How large of a span is there without bracing? How thick is the cabinet material, what is the material? I've found that if the cabinet is made well with good bracing and the spans between bracing are minimal then damping doesn't make much difference. I guess in a way, you could say that a poor quality cabinet would benefit much more than a well constructed cabinet.

Darren

Carlman · « **Reply #3 on:** 17 Apr 2003, 03:01 pm »

Dampening helped a pair of speakers I had but, they were highly resonant. They were B&W minipods which were made of fiberglass. I used a black adhesive material on as much of the inside as possible. I can't remember what it was. I also replaced the wires.

In stock form it had an odd, wonky sort of sound with certain mid-bass frequencies. It was also a little too peaky and the imaging was poor. The dampening material definitely helped the imaging and toned them down a little. They weren't transformed into incredible speakers but, they definitely sounded better. The wires improved the detail but, the dampening helped the imaging and reduced bad sounds caused by the cabinets.

That's my non-technical answer... I've heard you can over do it.. some companies claim they depend on some resonance for the speakers to sound just right. Good luck!

byteme · « **Reply #4 on:** 18 Apr 2003, 12:22 am »

Ok, I opened one up and took some rough measurements. Overall outside cabinet size is 38"(H) x 10.5" (W) x 14" (D). Everything looks to be 1/2" MDF glued construction. There are three braces running up each side of the inside of the cabinet approx. 7" apart which are glued to the front, sides and back. There is one additional brace running from the middle front of the cabinet to the middle back about 12" down from the top (not touching the sides of the cabinet). There is already acoustastuff material behind the 3 active drivers (there are two passive radiators on the bottom of an MTM aligned top).

According to my calcs I'd need 3 sheets of 24"x27" black hole 5 or something similar. I don't know if this is a $150 experiment or not!

Nelgan · « **Reply #5 on:** 18 Apr 2003, 12:30 am »

Definitely not a $150 experiment! Try the Parts Express vinyl damping sheets. Way cheaper, and will probably have some effect on 1/2" MDF.

Darren Thomas · « **Reply #6 on:** 18 Apr 2003, 02:40 am »

Something to keep in mind. You don't need to cover the entire panels with the damping material, just a fair portion. So, say you had a 10" X 12" side that had no bracing...you could cut a 5" X 6" piece and center it effictively damping any vibration.

If it is constructed out of 1/2" MDF I'd say you stand a chance of benefiting from some form of damping though.

Darren

Tonto Yoder · « **Reply #7 on:** 18 Apr 2003, 09:08 am »

I'm just thinking aloud, but if the cabinet is opened up already, would it be wise to add some additional bracing????

BTW, here's Deflex link--
http://homepages.enterprise.net/smason/Pages/specdpfi.htm

Darren Thomas · « **Reply #8 on:** 18 Apr 2003, 01:36 pm »

Quote from: Tonto Yoder

I'm just thinking aloud, but if the cabinet is opened up already, would it be wise to add some additional bracing????

BTW, here's Deflex link--
http://homepages.enterprise.net/smason/Pages/specdpfi.htm

Not a bad idea but it would alter the internal volume of the enclosure which could have adverse affects.

Darren

byteme · « **Reply #9 on:** 18 Apr 2003, 04:07 pm »

Further bracing wouldn't really be an option, the driver holes aren't really big enough to work in there!

As for the Parts express damping material - is this what you are talking about?

http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=12580487&St=9436&St2=52219163&St3=70800827&DS_ID=3&Product_ID=15840&DID=7

http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=12580487&St=9436&St2=52219163&St3=70800827&DS_ID=3&Product_ID=7109&DID=7

Or would I be better off with Deflex? Oh, and if I were to do only certain panels of the box, am I better off doing it behind the drivers? Top and bottom of the cabinet?

markC · « **Reply #10 on:** 18 Apr 2003, 04:43 pm »

I should deffer this to someone more experienced, but, my experience is-behind the drivers, one side for sure and the top.

audiojerry · « **Reply #11 on:** 18 Apr 2003, 05:24 pm »

What amazing timing. I just spent 4 hours cutting and fitting adhesive backed vinyl damping sheets to some monitors last night. They are Italian made of solid mahogany on all sides with a brace running between the side panels in the middle. The woodwork is drop dead works of art, but I was annoyed by a ringing resonance, that I suspected was being caused by the solid wood panels. MDF is actually a better material.

Anyways, I added the damping with noticeable improvement, although I'm not entirely satisfied.

One point that should be made is the difference between damping the panels to help them from resonating, and using some sort of fill like wool or dacron to control internal sound wave distortions.

How a cabinet is damped and insulated can make a huge difference, and getting it right is very difficult.

TheChairGuy · « **Reply #12 on:** 18 Apr 2003, 05:29 pm »

<Definitely not a $150 experiment! Try the Parts Express vinyl damping sheets. Way cheaper, and will probably have some effect on 1/2" MDF.>
=============
I'm with Nelgan all the way on that as I don't think the Polk's are that expensive to start. The Parts Express vinyl damping is worthwhile stuff for something like $28.00 a good sized roll.

I have a cheapo Radio Shack LX-8 that I've modding on the cheap here...I liked their Linaeum tweeter and half decent Peerless woofer.

I rewired them internally, set on heavy stands with sand and are running them on active crossovers now...nothing, but nothing was as cost effective or as effective as $28.00 worth of Parts Express Vinyl Damping inside and out. Not even close the other mods were.

It's not that awful looking that you can't use it outside and it won't muck up internal dims as it's very thin. I have it on every wall of cabinet.

The Radio Shack uses 1/2" particleboard..how's that for crap! So, the damping was extra effective as it started out worse then your Polk's walls in MDF.

Enjoy -

byteme · « **Reply #13 on:** 18 Apr 2003, 06:21 pm »

I ordered enough of the Dayton Loudspeaker vinyl to do both for about $40 shipped. I'll let you know how it goes...

Tonto Yoder · « **Reply #14 on:** 18 Apr 2003, 10:13 pm »

Quote from: byteme

Further bracing wouldn't really be an option, the driver holes aren't really big enough to work in there!
?

I was thinking about just pouring wet cement through the driver holes--it'll level itself !!!!

But seriously, Michael Percy has that paint on stuff too--Soundcoat or something???? Dynamat makes a liquid too--Dynacoat I believe, about $30/gallon.

rosconey · « **Reply #15 on:** 18 Apr 2003, 10:21 pm »

i lined my speakers with porceline tile,they are dead

Tonto Yoder · « **Reply #16 on:** 18 Apr 2003, 11:08 pm »

Quote from: audiojerry

The woodwork is drop dead works of art, but I was annoyed by a ringing resonance, that I suspected was being caused by the solid wood panels. MDF is actually a better material.
How a cabinet is damped and insulated can make a huge difference, and getting it right is very difficult.

I can't remember the manufacturer now, but one speaker review made a big deal over a special kind of patented MDF: unlike your everyday Home Depot MDF, this had some tweaked adhesive holding all the wood bits together. It was a relatively expensive, well-known speaker but impossible to say how much the Mondo-MDF contributed.

bubba966 · « **Reply #17 on:** 18 Apr 2003, 11:12 pm »

Quote from: Tonto Yoder

I can't remember the manufacturer now, but one speaker review made a big deal over a special kind of patented MDF: unlike your everyday Home Depot MDF, this had some tweaked adhesive holding all the wood bits together. It was a relatively expensive, well-known speaker but impossible to say how much the Mondo-MDF contributed.

Were they using Rangerboard? I've used that in the past for projects. Nice in that it doesn't contain formaldahide (sp?), which is nasty to be breathing while working with it. Was quite a bit more expensive than standard MDF as I recall.

Tonto Yoder · « **Reply #18 on:** 18 Apr 2003, 11:38 pm »

bubba,
that "particular"

name doesn't ring a bell, but it may be something similar (or identical but w/ a different name). I made a half-hearted attempt to refresh my memory on the Stereophile, but the lights are out and the battery's gettin' weak. I'll post the name if it comes to me.
Tonto

bubba966 · « **Reply #19 on:** 19 Apr 2003, 12:43 am »

It's been 6 or 7 years since I've used any Rangerboard (haven't done much woodworking since then). It was stuff made up in Canada. Seem to recall that it machined a bit nicer than standard MDF, though I might not remember that quite right. But it was about 50% more expensive than standard MDF.