Dynamat sub box

MacLeod

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

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

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

Hmm...

Ill stick with Foam over both.

Foam rules.

MacLeod

Cheaper too!

VR3

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

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

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

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

ahh the voice of reason is back.

exalted512

Jstas wrote:

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

... 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

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

PoweredByDodge

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.