# Dynamat in a speaker cab ????



## SG-Rocker (Dec 30, 2007)

I have a fair bit of Dynamat here left from a car audio install this summer and I was wondering what effect (good/bad) it would have if I used it inside speaker enclosure ? 

I have a Peavey Valve King 4X12. My only bone with it is that the cabinet is kind of hollowish when knocking on it. It doesn't buzz while playing or anything and it is very well constructed. I'm just curious if anyone has tried this. I think it might lend itself very well for more bottom end and a tighter overall sound, perfect for fast chugging palm muted a la Metallica and whatnot. My usual playing style is along the lines of AC/DC, Black Sabbath, Metallica, and includes Blue Rodeo and all point in between.

My guitar is a Epi G-400 that is am in the process of upgrading. I have Grover lockers in the mail and just installed the Seymour Duncan Blackouts.

Oh, FWIW the Valve King is loaded with unique 'Valve King Classic' edition speakers that have the baskets painted green. I'll admit that at first they are rather cold and sterile sounding but after a few good loud gigs they warm up and sound very close to the Greenbacks (which I imagine they are designed to emulate)


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## mrmatt1972 (Apr 3, 2008)

I once read a few books on speaker cabinet design. In the 50s and 60s Bell (telephone) labs basically wrote the book on speaker cab design. I forget the actual figure, but all 4x12 closed back cabinets suffer from the fact that there is just not enough air inside to act as a "spring" on the backs of the speakers. What I'm trying to get at is that yes, use the insulation. It basically increases the volume of your cabinet, which allows the speakers to move properly. Hence, better sound. If you don't like it, take it back out!

Matt


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## greco (Jul 15, 2007)

mrmatt1972 said:


> I once read a few books on speaker cabinet design. In the 50s and 60s Bell (telephone) labs basically wrote the book on speaker cab design. I forget the actual figure, but all 4x12 closed back cabinets suffer from the fact that there is just not enough air inside to act as a "spring" on the backs of the speakers. *What I'm trying to get at is that yes, use the insulation. It basically increases the volume of your cabinet, which allows the speakers to move properly. * Hence, better sound. If you don't like it, take it back out!
> 
> Matt


I don't get this statement (bolded) ...no offence intended, I just don't understand how adding material can increase volume.....unless/possibly...is the word volume is somehow referring to the volume/loudness of the cab?

Dave


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## SG-Rocker (Dec 30, 2007)

I can tell you how the stuff works in an automotive context.

Speakers produce sound through the conversion of electrical energy into mechanical energy (speraker excursion) which in tern generates sound energy. A by product of the mechanical action is vibration. A speaker is ideally mounted in a rigid material to minimize energy loss through vibration. Also the speaker enclosure will absorb the sound energy causing resonance which may or not produce a desired effect. The resonating effect is accomplished via a parasitic draw from the speaker's effective output.

In an automotive environment, acoustic chambering is far from ideal and the vehicle's primary composition of sheet metal lends to much undesireable parasitic losses. In such an application, sound deadening material (Dynamat, etc) is used to eliminate resonances and reduce the parasitic effect upon the speaker. This allows the speaker to become the primary sound source by eliminating secondary sources.

In a subwoofer application where frequencies commonly drop below 40 hz, the use of a sound deadening compound is used extensively to reduce resonant frequencies produced by the enclosure/cabinet. This reduces undesireable secondary frequency effects and detracts from the source. Also the sound deadener reduces the effective size of the enclosure while maintaining the benefits of the actual size.........

My brain hurts now lofu


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## greco (Jul 15, 2007)

Thanks for the detailed response...hope your brain is no longer in pain from the recent strain (poetic..huh)

I get all of what you are saying (VERY well written BTW) but I'm still missing the point that adding material to a finite volume can *increase * the total volume of the cabinet.

Am I thick as a brick ? (don't answer that ...LOL)

Cheers

Dave


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## SG-Rocker (Dec 30, 2007)

Well the dynamat will reduce the energy lost to the cabinet, henceforth making it louder in that it now projects more sound energy.

I'm giong to do it once I get my guitar back together. It will be a test of how much the actual cabinet contributes to the overall tone.


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## greco (Jul 15, 2007)

SG-Rocker said:


> Well the dynamat will reduce the energy lost to the cabinet, henceforth making it louder in that it now projects more sound energy.
> 
> I'm giong to do it once I get my guitar back together. It will be a test of how much the actual cabinet contributes to the overall tone.


Got it .....volume = louder, NOT volume = space inside the cab.

Cheers

Dave


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## mcgriff420 (Sep 30, 2008)

My two all time favorite 212's both had insulation/batting in them. Bogner OS212 and a 66' fender piggyback. I put some foam/sponge insulation in a 212 recto cab I had and it definitely helped get rid of some of the boxiness of the cab. I say do it, what do you have to lose except an hour.


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## hollowbody (Jan 15, 2008)

I understand why dynamat is used in cars, because in most cases, the speakers are loaded onto plastic baffles that reside in door panels, which don't weigh very much and can rattle around, but a decent 4x12 should weight enough that the speaker's movement should affect the cabinet too much, no?


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## SG-Rocker (Dec 30, 2007)

Well I got the sound deadener in....

Before:


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## SG-Rocker (Dec 30, 2007)

After:


























The verdict:

It's a little early to tell what effect this will have with my guitar as it's currently in pieces waiting parts from www.guitarpartscanada.com but I used my MP3 player into the low input jack as a before and after reference.

Before it was rather 'middy' in sound and overall undefined. I realize that these speakers are not voiced to produce home stereo sound. Anyway it used to have real clarity in the mid to low frequencies but stinging highs.

After it was much more balanced, the cabinet definitely vibrates A LOT less. I can play some bassy music and the cab will not resonate whereas it would before. Added weight is noticeable but manageable. If the MP3 test was any indicator of what I can expect with the guitar them I should be most satisfied.

I think low E palmed chugging will be much more gratifying.

I actually am surprised that no one in the metal crowd has ran a 4X12 cab with 2 normal 12" speakers and 2 12" automotive subwoofers using a passive crossover. The end result would be brutally heavy if it worked.


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## Bevo (Nov 24, 2006)

From my car audio days if we had an issue with the size of the speaker box we would add a type of batting ( not pink) to increase the air space behind the speaker...Almost the consistency of rock wool.

Depending on the amount as in pounds you added it increased the size by a set amount..Worked like a charm.
The idea is that it compresses or acts like a spring that works with the cone and air.
Contact you car audio guys for the material...stay away from Pink..

The subs in a cab does not work due to the frequency response and speed of the driver. I did give it a go and it was all mud... Tried it with my bass and if there was a crossover it would of added to it.

Plug your amp into your car and give it a go...just match up the impedence of your sub box and pull the car audio wire off..

Bev


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## sysexguy (Mar 5, 2006)

I redid the inside of my 70's B-15n bass amp with deflex panels per a suggestion by studio mod guru and Basson tech Jim Williams over on the gearslutz tech forum and I am very happy with the result, both when playing and when recording. Parts Connexion :smilie_flagge17:in Oakville has the deflex panels which started a very expensive habit for me (tweaks).

When the $$$ allows, a 4x12 will happen (deflex'ed)....maybe I'll get one of those Jarrah wood ones from down under......if there's only one winner (me) and the jackpot is 2+ weeks (BIG).....

Andy


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## mcgriff420 (Sep 30, 2008)

Cool, glad you went with baffling!

While I agree that 'bedroom metal' guys would see the merit in this for gargantuan 'guitar tones'....
I would submit that the cornerstone of my favorite 'Metal' bands is the consice thumping Bass and Drums....let them have their space! jus sayin..


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