My cabinet treatment project ... starting today

[TurboFC3S]

I have all my materials on-hand, getting ready right now to tear into my speakers and start the treatment. I think I have a good plan, but if anybody sees a flaw in my thinking, could you let me know before I get started

Speakers being worked - Wharfedale Pacific 40 mains, Pacific center, Pacific 30 rears.

Step one - I have 20 small bars of lead, each bar weighing 1 pound. I'll nail and glue about 5 pounds per cabinet to the bottom inside panel.

Step two - Paint the inside of the entire cabinet (including over the lead bars) with Noxudol 3101. It's a sound-deadening liquid, I like that it's water based - should be pretty easy on the woofers. Info - http://www.soundproofing.org/sales/liquid.htm

Step three - Oil-based non-drying modeling clay applied to the frames of the woofers, and applied to the inside of the cabinet - primarily the inside face which the woofers are screwed to and vertical faces in strips like rope caulk.

Step four - line as many inside walls as possible with a 1.5" closed cell polyethylene foam that is cut like you typically see with bass traps. I even have the sound absorption numbers for this foam:

125hz - .05
250hz - .06
500hz - .21
1000hz - .80
2000hz - .65
4000hz - .75
NRC - .45

Step five - .1" thick butyl rubber gasket tape as gaskets behind woofers and terminal cup.

So, am I nuts? My wife sure thinks so!

[wigginjs]

Why the lead bars?

[ShinOBIWAN]

Originally posted by m0tion
Why the lead bars?

Added mass.

Similar to the idea of filling your stand with sand or leadshot. I doubt that the lead bars will make much difference though, hope they do but can't see it anyway.

Also Turbo, have you considered that the closed cell foam will alter the internal volume of the cabinets? 1.5" all around will be quite significant too, expect the bass alignment to change.

Sounds like a fun project anyway and most changes should be reversible if its not to your liking.

[TurboFC3S]

Yes, the lead is just to add mass. I'm also making platforms which the speakers will rest on out of 1.5" thick maple, for more isolation (hopefully).

I know the foam will effectively change the internal volume, but since there is already a significant amount of polyfill in the chambers (came that way from the factory), it might not make much difference. But I'm confident that the closed cell acoustic foam cut in the triangle patterns will do more to reduce internal standing waves than polyfill ... and the speakers weakness has always been a slight hump around 1000hz (to my ears anyway). Since that's where the new foam is most effective, it might work out perfectly.

I wish I had all the equipment to really test before and after. Unfortunately it's just going to be a by ear test, and since I'll want so much for it to sound better after, who knows how accurate my perception will actually be. I doubt it can hurt though

[omni]

Turbo, I am wondering if the closed cell foam will serve to reduce effective volume in your cabinets. The polyfil, depending on what density it was originally stuffed, serves to increase the effective volume of the cabinet.......... Will the closed cell foam raise the Qtc of your system ? Bass may get boomy..........The lead will certainly reduce cabinet volume. Sounds like a tricky endeavor. I hope you hear what you are looking for.... Good luck man, I love experiments..........Respectfully.............Omni

[sreten]

Hi,

The foam should be open cell, closed cell is a waste of time,
and will drastically reduce internal volume, it will not fix what
you regard as internal standing waves, for this you need
decent grade open cell foam, commonly used as a mattress.



Not sure about the modelling clay, certainly sounds pointless
to try and attach after the liquid damping treatment, I would
not bother with it at all.

in the USA duct-seal appearstop be the stuff, use it to fill any
space between the magnet and the frame. You could apply
the liquid damping to the frames and also use it for the driver
gasket and the rear terminal gasket.

The lead in the base I'd simply press it into wet damping liquid
then apply more damping liquid, nails do not sound a good idea.

/sreten.

[planet10]

My initial reaction is that adding mass to the cabinet walls will lower the wall resonant frequency and increase box coloration.

Much more effective would be some edge on hardwood bracing (and these braced against the opposite wall).

dave

[planet10]

Originally posted by sreten
in the USA duct-seal appearstop be the stuff, use it to fill any
space between the magnet and the frame. You could apply
the liquid damping to the frames and also use it for the driver
gasket and the rear terminal gasket.

[wigginjs]

Originally posted by ShinOBIWAN

Added mass.

I figured as much, but it seems kind of silly to just dump them all in the bottom. It was my understanding that you would want that mass evenly distributed across the cabinet walls, for instance, lead sheets? Anyways, good luck, but I might try implementing one change at a time and seeing if I liked the result.

[TurboFC3S]

Originally posted by omni
Turbo, I am wondering if the closed cell foam will serve to reduce effective volume in your cabinets.

Originally posted by sreten
The foam should be open cell, closed cell is a waste of time,
and will drastically reduce internal volume, it will not fix what
you regard as internal standing waves, for this you need
decent grade open cell foam, commonly used as a mattress.

I know the thinking why people use open cell foam traditionally for this purpose, but don't know that I agree with it. I can't imagine sound 'bouncing' off closed cell and more than open cell ... and the foam I found has nice soundproofing qualities, better than any open cell I've seen.

But I want to make the right decision, if anybody has more to say about this please do so.

Not sure about the modelling clay, certainly sounds pointless
to try and attach after the liquid damping treatment, I would
not bother with it at all.[/B]

Well, I have to admit it wasn't my idea but that of others and has been used many times before.

http://www.meta-gizmo.com/Tri/secrettweak.html
http://r.duffy.home.att.net/dcm/
Jan 1982 edition of Audio Basics by Frank Van Alstine
... and many many other online resources I found

in the USA duct-seal appearstop be the stuff, use it to fill any
space between the magnet and the frame. You could apply
the liquid damping to the frames and also use it for the driver
gasket and the rear terminal gasket.

The lead in the base I'd simply press it into wet damping liquid
then apply more damping liquid, nails do not sound a good idea.[/B]

Duct seal IS butyl rubber ... I just wanted to for sure use the butyl rubber kind, not the cheaper hardening kind of duct seal.

Who knows if I'll nail the lead down, I don't think it'll matter how I attach it ... I just don't want the 1 pound bars to ever move.

Oh, and by the way ... a 1 pound bar of lead is tiny! They won't change the internal volume more than 1 or 2%.