Dynamat sub box [Archive]

new-yorker

11-26-2005, 04:30 AM

Would it be a good idea to dynamat the inside of a box..preferrably a sealed box? any opinions? i know MDF lets air leaked out because its wood, well compressed saw dust. I am thinking the dynamat will help.

1996blackmax

11-26-2005, 04:59 AM

If the box is properly sealed it should not leak air.

swerve

11-26-2005, 11:15 AM

no - there is a huge discussion about this somewhere... i'd have to hunt it down.

hellohello

11-26-2005, 01:02 PM

if ur worried about the mdf leaking air, put a couple coats of a sealer/paint on the inside, dynamat will still have gaps/seams, and its hella expensive

VR3

11-26-2005, 01:45 PM

Dynamat will make the woofer think the enclosure is bigger than it actually is. This may be in ur favor or against it.

Just use caulk or a liquid nail of some sort and put it on the inner seams and take your finger and run over it... this "seals" it...

skydeaner

11-26-2005, 04:59 PM

Fiberglass resin coating the entire inside of the box works awesome. Make sure it is dry before you put the subs in.

VR3

11-26-2005, 05:34 PM

Do you folks use multiple pieces of MDF per panel?

Why would you need to coat the entire panel?

1996blackmax

11-26-2005, 05:38 PM

VR3

11-26-2005, 07:33 PM

No...

Dynamat absorbs vibrations...

IE: Slows them down.

Polyfill slows them down, just not as much...

So Dynamat... Foam... - all they do is dampen things... and inside the enclosure would make the woofer think it is bigger.

Anything spongey/absorbant inside an enclosure acts as a "insulation"

If hes talking about doing the outside of the box... I say sure... but why? Whats the point...

Adequate bracing would be much more effective...

exalted512

11-26-2005, 08:12 PM

the only thing dynamat will do is absorb vibrations from your box rattling. It will not make the box think its bigger. It will actually hurt your sq due to its outside barrier. You want something more along the lines of ensolite or the foam second skin makes. If your worried about your box leaking air through the wood, dont. The only place it would leak is where the sides meet. You can slap some resin on to stop that...or seal it with gorilla glue.
-Cody

VR3

11-26-2005, 10:01 PM

"Would it be a good idea to dynamat the inside of a box"

The way he wants to use it. It will add volume to the box.

audiobliss

11-26-2005, 10:33 PM

It will add volume to the box itself, meaning the box's materials. However, it will reduce the volume in the box. It makes perfect sense to me that it would act much like polyfil, slow the backwave, and so make the sub act like it's in a bigger box.

swerve

11-26-2005, 10:48 PM

just someone hunt down the old thread. we've argued about this before!

audiobliss

11-26-2005, 10:58 PM

I know it's fun to re-read old arguments, but it's more fun to make them again!! :D:D

neomagus00

11-26-2005, 11:55 PM

well, i see where vr3thingy is coming from... to a sound wave, dynamat and polyfill do exactly the same thing, slow it down, so in this particular sense, i'd say they're identical... now, how much dynamat you need to equal 1 pound of polyfill, that i have no idea... and yeah, putting a layer of dynamat inside a box would decrease its volume, by a very little bit, but the acoustic effect would be much larger than the physical effect...

one of the reasons mdf is used is because it is inherently resistant to vibration and resonance, so dynamatting the inside to get rid of such things shouldn't be necessary... sealing the inside using the caulk-and-finger along each seam is a good idea... i'm not sure why you'd resin the entire inside of a panel, but i don't see a problem with it as long as you let it get completely dry...

and vr3... no, we don't generally use multiple pieces per panel, unless it's a wicked huge sub and it needs a double layer on the front to mount onto...

VR3

11-27-2005, 12:21 AM

I have used multiple pieces per panel before... :p

I like to use foam on the inside of my enclosures... instead of Polyfill...

It helps dampen the panel and increases the volume a lil bit - but I think its important to have something in there to dampen the backwave from the driver to... (learned that one from Russ)

http://eandr.biz/AS/Projects/Jigsaw/EarlyConstruct2.jpg

Uses a total of 12 panels (not counting the top and bottom cap)

Here is how I seal the inside...
http://eandr.biz/AS/Projects/Jigsaw/JIGAmpMountInternal.jpg

new-yorker

11-27-2005, 02:01 AM

For some time now, I have used Wood Putty to seal up the inside of a box. does anyone agree wit me that wood putty is very effective?

swerve

11-27-2005, 02:04 AM

I've always used liquid nails...

audiobliss

11-27-2005, 02:06 AM

I don't see why wood putty or liquid nails wouldn't work.

swerve

11-27-2005, 02:14 AM

That's just how I do it.

Man Juice works best though

MacLeod

11-27-2005, 10:08 PM

Its not a terrible idea to use Dynamat on the box to add mass to it which would make it more rigid. I had a severe space problem with mine so I had to use 1/2" birch plywood to get the volume I needed to fit in the space I had. I was concerned about the box flexing so I covered the outside with Dynamat simply to make it a little more rigid.

If you dont have a space issue tho it would be stupid to do this cause all youd have to do is use thicker wood.

Bottom line: Its not a bad idea to use Dynamat and it wont hurt anything. The only benefit from it is it will add mass and density to your box but you could use thicker wood and get the same results for about $100 less.

VR3

11-27-2005, 11:41 PM

I wouldnt use wood puddy to seal a box...

Wood puddy as a tendency to shrink and crack - even if it says it dosnt.

For instance... wood puddy dries VERY hard and can be knocked out of place on a surface its not dug into... it just dosnt leave "intact" to a flat surface... its meant to fill in holes.

Liquid nail gets in there... and it sticks and will last a long time and you can count on it to stay.

Just use liquid nail...

Caulk gun - 3 bucks... tube of caulk... 1 buck... sealed box... priceless

PS: Make sure you let the caulk fully dry and no "smell" is left behind... if you put the driver in there and its a sealed enclosure, the acid content from the glue will eat away at the driver materials...

exalted512

11-28-2005, 12:40 AM

dynamat DOES NOT SLOW DOWN WAVES IN THE BOX
that is all...if you want to know why, use your common sense, if you still cant figure it out, ill let you know
-Cody

VR3

11-28-2005, 01:24 AM

How can dynamat... INSIDE of a box... a "dampening" material (which eliminates/slows down sound waves) NOT double as a polyfill material when placed INSIDE a box... NOT OUTSIDE... but INSIDE (just incase you arnt getting what I am saying)...

Inner...Within...Inside The Woofers Container...Inside The Boomers Crate... WITHIN...INNER... Ya know... INSIDE... slowing down the waves directly before hitting the outside walls... taking away mass from the box - but adding much more in theory...

Explain to me how it dosnt work that way... INSIDE the box. Not outside the box. BUT INSIDE.

swerve

11-28-2005, 01:41 AM

It doesn't work. a marine biologist told me this afternoon.

lackeyb

11-28-2005, 03:28 AM

If your looking to have a sealed box, use the liquid nails or wood glue and a nail gun or wood screws. Then give the box a coat of fiberglass resin, mixed according to directions of course. Let the box cure and dry without the speaker, I'd give it at least a day. The fumes some of these products give off when curing can eat away the surrounds of your speaker. If your really going for airtight you should think about a gasket of some kind between the basket and the enclosure.

As for dynamat vs polyfill vs foam. Take your pick. Since the enclosure is sealed and you don't have to worry about blowing fibers everywhere I would recommend a half fill of loose polyfill. Better yet try your options out and see which one works better with the acoustics of your box and car. The speaker makes an wave in front and an identical but 180 degrees out of phase signal in the back. So if these wave mix you get a significant cancelling out a lot of your bass. The effect your enclosure is trying to achieve is to cancel out the wave created from the back of the speaker cone and provide air suspension to the woofer. See what fits in the budget and test them out if you can, they should give a similiar effect but your ear may like one better than the other and in the end that's what matters.

PoweredByDodge

11-28-2005, 10:58 AM

RE - Wood putty.
-------------------------------------
Junk dude. As stated above, it'll shrink, crack, etc. It's meant for finishing cabinets and stuff, not sealing anything. 100% silicone caulk to seal the corners up. Don't worry about anything else. If you're overly insane, as stated above you can do it up with an ENAMEL based paint.

RE - dynamat inside box
--------------------------------------
No opinion - never tried it, probably never will. I'd be worried that it would fall off the insides of the box. If i wanted to make a box "bigger" i would simply use polyfill or foam... or just straight up make it bigger.

As far as what dynamat does... I am not so sure it 'slows down' waves as it absorbs vibration (waves). absorbtion and "slowing down" are two different things. absorbing a wave in a box i THINK (am no where near sure) would just keep it from rattling. I dunno - freaky ****.

RE - Box building
---------------------------

I hate MDF - i have never used a more ****ty material in my life. Jstas said a long time ago that if i ever made a box out of cabinet grade birch ply that i would never go back - and he was very correct. joints should be coated with carpenter's wood glue prior to being nail-gunned or wood-screwed in place. If you're lazy like I get most times, you can just screw the bastard together with screws every 4 inches and then caulk the **** outa the seams inside. Glue gets too messy for me, however, glue is the proper way to do it.

exalted512

11-28-2005, 02:05 PM

exalted512

11-28-2005, 02:06 PM

heres a hint:
http://secondskinaudio.com/products/products_detail.php?productid=1

they both use the same type of material in their shielding
-Cody

audiobliss

11-28-2005, 02:51 PM

Good point, Cody.

Also, I hadn't thought about the dynamat absorbing the waves more than slowing them down. Good point, PWD.

VR3

11-28-2005, 03:03 PM

I still am not convinced... ;)

I like MDF...

I however do NOT like Particle Board

Atleast when you know how to work with it.

Plywood is stronger, thats for sure.

Why do people consider Birch Plywood to be Baltic Birch Plywood? Birch plywood is a common plywood... it cant be the same???

MDF is fun... (before I sanded it)

http://eandr.biz/AS/Projects/DTBP10B/VersionTwo/ASBP10Bfinishpart1Ver2.jpg

MacLeod

11-28-2005, 04:57 PM

Dynamat works by adding mass to whatever its applied to thus making it more rigid and less likely to vibrate. Slowing down waves ala pollyfill is totally different and not something Dynamat would do.

VR3

11-28-2005, 05:02 PM

Absorbing... Slowing Down... sounds the same.

Sounds like Dynamat would make the enclosure seem HUGE... it just dosnt make sense... sorry... will have to explain in-depth.

MacLeod

11-28-2005, 05:11 PM

It doesnt slow down waves and it doesnt absorb waves. It adds mass to the surface its applied to, thats all. Maybe since its softer than the wood it could possibly slow down the waves a tiny bit but it wouldnt be near enough to warrant spending $75 in Dynamat when $1 of polyfill wouldve done a better job.

VR3

11-28-2005, 05:17 PM

Hmm...

Ill stick with Foam over both.

Foam rules.

MacLeod

11-28-2005, 05:18 PM

Cheaper too! ;)

VR3

11-28-2005, 05:21 PM

Not nessicarially.

I like the Sonic Barrier stuff PE sells. Very dense stuff... (and kind of expensive)

Just to give you an idea how dense the 3/4" sheet is... you cant squeeze it together... it leaves about 1/8" - it has a 3 layer type deal... a soft, then harder bottom...

I plan to get a 1" thick pad for my current speaker - it dosnt have that hard bottom layer so it wont be as dense...

I like foam better because it damps the panel and does what polyfill does...

PoweredByDodge

11-28-2005, 05:46 PM

what in the HELL is that structure for ??? is that a speaker cabinet half done? or a book case or what ?? that is GIGANTIC!

Baltic Birch is just that -- from i dunno, um, the baltics? It's imported I believe... but that's not really the point. When somebody says "Baltic Birch Ply" they mean "marine grade ply" --- it holds up to water and the elements like a champ. Cabinet grade baltic birch ply will run you between 75 and 100 bucks a sheet depending where you buy it from... regular cabinet grade birch ply is almost as good for what we car audio nuts do because - hell - we're not in water! - and that's about 40 to 60 bucks a sheet. well worth it in my opinion... at least until i get a table saw and a brad nailer (already have the air compressor! hehehe)... then i will investigate the goodness of high density fiberboard... yes high density - its "tighter" than MDF (medium density) - but it's not as available as MDF -- you can get MDF at any home depot - but HDF usually has to be gotten from a mom and pop type lumber yard or somethin like that -- it's not a "normal item" at superstores. It's cheaper than the birch ply... about 25 to 30 bucks a sheet... and i would like to play around with it and see if i like it as a compromise.

VR3

11-28-2005, 06:00 PM

My Definitives use Medite (for the front and back). which is a type of HDF wood - its stronger and uses different glue.

Those "large" speakers are towers, that are not done. lol

I still gotta put the front and back on them...

Jstas

11-28-2005, 06:22 PM

Wow.

Wood Putty is meant for covering blemishes, knicks, mistakes and other marks in wood where there is material missing. It dries hard and porous so it will accept stains and paint the same way natural wood will. It is not good for sealing anything because it will dry, crack and separate. It's a filler, not a sealer.

Liquid nails is glue and like all glues, it will shrink as it dries. This causes gaps which turn into air leaks. If you want to seal the inside of an enclosure, silicone caulking is what you should be using. Clear RTV sealant will work too. These will remain soft and pliable when dry and will not dry out and crack like the glues and fillers will. Gorilla Glue will seal also but you need to use more than is necessary to ensure proper sealing.

My boxes are built with seams being glued with either regular old Elmer's Wood Glue or Gorilla Glue. They are then either screwed or nailed together depending on the size of the speaker and the kind of load being put on the box. The inside joints get a bead of silicone run along them and the a nice finger slide to stuff it all down in the joints. I have had no leaks at all and construction is solid. My boxes usually outlast the speakers that are mounted in them. Oh yeah, I use cabinet grade plywood...no voids, sonically dead. It's expensive but it works so damn nicely!

Birch veneer plywood and Baltic Birch Plywood are not very different. I'm pretty sure that Baltic Birch plywood is called Baltic Birch because the veneer is birch from a species of Birch tree native to the Baltic region of eastern Europe. It's not necessarily wood from that area, just wood from that kind of tree.

The grades are different though. Straight up birch veneer plywood is usually a cabinet grade and not suitable for a marine use. That is because the glues are water soluable and therefore inappropriate for use in exposed conditions where moisture is a problem. Baltic Birch is also avialable in a cabinet grade but is most commonly found in marine grade plywoods. The marine grade uses glues that will not deteriorate in the weather or UV light. Cabinet grade doesn't have these abilities and is meant for indoor use only. Which is better? For speakers, cabinet grade. You get teh same voidless benefit of marine grade but with glues and materials that are not only easier on the pocketbook but less likely to have odors or other chemicals that can be harmful to poeple. Also, you can get a better veneer on cabinet grade plywood that is more suitable to a finished product and not a constructon material. If you are covering in carpet or other covering, it's not a big deal. However, I have to really question the benefits of marine grade wood over cabinet/furniture grade. Mainly becaus ethe cost can almost double when you hit the marine grade stuff and your sonic and construction benefits are nil. They are structurally similar with strengths and properties being very similar. The only benefit is weather resistance. If it is going inside a car or a house, that is not necessarily and issue and shouldn't justify doubling your materials cost.

As far as Dynamat inside the box, bad idea. It is meant to absord vibrations of physical structures, not dampen sound waves. Because of that, it is heavy and dense. It also has a relativly thick layer of aluminum on it. This doesn't "slow down" sound waves. It stops them and any vibrations that the stuff it is attached to may encounter. It is a bad idea inside the sub box because it doesn't do anything to stop standing waves, since the surface is metal and quite smooth, it reflects much more readily than wood will and it usually does it more directly. The vibration absorbtion doesn't benefit any either because it totally destroys the backwave and can slow it down so much that it kills the phase and sends everything out of whack. That results in cancelled frequencies and a ton of standing waves. Add to that the fact that it reduces the internal volume of the enclosure and artificially truncates the frequency response of the enclosure. It's a bad idea overall.

A properly built sub box needs no internal dampening. However, teh real world gets in the way and it isn't always possible to compromise and get the size you want. If you have to use dampening, polyfil will work best. The spray on foams will work too but can cost more to apply. Don't Dynamat the inside or outside of the box. Inside, it will cause problems, outside, you get no benefit whatsoever. Dynamat is not a sound deadener, it is a vibration dampener. Different ideas.

PoweredByDodge

11-28-2005, 07:13 PM

ahh the voice of reason is back. :)

exalted512

11-28-2005, 08:20 PM

It also has a relativly thick layer of aluminum on it. This doesn't "slow down" sound waves...
since the surface is metal and quite smooth, it reflects much more readily than wood will and it usually does it more directly

we have a winner!!! Finally, someone with some common sense and knows how to use it!

Dynamat is backed with a nice, shiny, reflective, FOIL shielding. It doesnt stop, slowdown, whatever--any sound waves, it reflects then 10x better than MDF. Reflection=bad. Poly fill is the cheap way out, foam is the best.

I wouldnt really think it would do too much to the outside of the box besides a minimal difference as far as mass loading goes. You would be better off making sure everything is sealed in the box, then coat it with a few layers of resin. That would make it much more study than dynamat, minimal amount of air space lost, and cost a lot less. Drawback: you have to wait a day before you can put a sub in it.
-Cody

PoweredByDodge

11-28-2005, 08:31 PM

... i'm the guy who dumps the sub in while the caulk is still wet ... or if its a painted box, while that's still wet too -- i've got the painty finger print on subs to prove it.

heXtant

11-29-2005, 09:47 PM

wow. i like these forums. i learn more and more every time i read a post :p. ..i just use liquid nails.. works good for me :x

PoweredByDodge

11-29-2005, 09:50 PM

in between boards, yes, it is great stuff - like or better than wood glue. but that's between two pieces you are going to nail or screw together. the LN or even glue will shrink up and crack when you go to seal corners with it - best use a silicone caulk than to have your box end up leaky once it's in the vehicle -- then you have to take the speaker out and re-seal it - gets annoying as hell.