Just about to go crazy with the dynamat on my doors, but at the same time i'm wondering if I should put a diffuser behind the speakers.

Is it worth spendng the extra considering it will have the dynamat in there? If so, what should I get?

I dont know the exact science behind it (thematt knows) but as far as I know, you would need about 30 cm worth of diffusion to actually make a difference, which is impossible unless your doors are huge... Hopefully thematt/pulse r or one of the other guys with more tech knowledge posts up...

It's one of those things that you do after you've done everything else.

Not saying you can't do it while it's all open. If it's cheap, it certainly won't hurt the sound.

I noticed a good improvement in midrange clarity with a diffuser 'pad' behind the door speaker.
I used the Jaycar 'premium acoustic foam' or such (see link below) which is cheap, and glued a square of foam onto the dynamat behind the speaker.

http://www.jaycar.com.au/productView.asp?ID=AX3656

one pair of tiles = two doors done

I might have to see what kind of clearance I have before I decide what i'll do.

Maybe it's something i'll do later, being a n00b and all.

The diffusion effect will only work on certain frequencies (what range it will work at is a function of how deep the ridges are). Most of the ones that will fit in the car will only work from ~ 800hz upwards.

Those ones pulse-R linked probably work at 400 and up, by the looks of them.

Aint nothing like searching to prevent me saying the same things over and over and over

Oh well, you get that.

These are totally difference acoustic responses. Diffusion, absorbtion. Diffusion - 'to spread out - to disperse'. Absorbtion - 'change of energy state by changing medium'.

Absorbing a backwave is related to power of the wave. More power, more absorbtion needed. Lower frequencies contain more relative power, and therefore need more 'hearty' mediums to absorb them. In car, mid/subbass (sub 400Hz) is simply too much to absorb in most cases (unless you use lead or other dense products).

Diffusion is a very specific science. In a car, aint no-one gonna be able to achieve it at higher wavelengths (lower frequencies) unless you abide by the basic scientific principles. Effective diffusion is related to quarter-wavelength principles, that simply state for a given frequency, the depth of the peak/valley needs to be minimum a quarter of the size of the wavelength to even begin to work. Therefore, for most diffusers, anything below ~700 to 800 Hz cannot be diffused.

If you look closely at anachoeic chambers, and some recording studios, you'll notice big foam inserts of the walls (proper ones anyway) that stick out about 1 meter. These are only effective down to around 150hz, so you can only imagine the effectiveness of your diffusers pads at those same frequencies (read: less then none).

Like Simon mentioned though, on the midranges, they work really really well. If you stop the backwave permeating through the cone during replay, it has a huge benefit through lower distortion levels, lower reverb, and clearer responses.

Absorbing a backwave though, is totally different to diffusing them. I'm still not sold on the Jaycar's, simply because they have the word 'absorbtion' in the name. Sure they may work good, but so does a wet sponge, and thats cheaper.

I just got the jaycar one because it's water resistant, flame retardant, slovent resistant (sort of ) and about the right size for inside a car door.

and it worked well.

Assuming you mean dynamat extreme, you're talking about an aluminium lining that will be covering the doors - not exactly reflection friendly, as sound waves will bounce off that aluminium lining like little kids off a trampoline...

Part of the idea behind diffuser pads is to help control those reflections - it's not a perfect solution, but it helps a little.

What's the Jaycar foam like with water getting in the door?

I've had no problems with water - the foam is glued to dynamat, so it's not going to rust out the door. I guess if it gets wet, it dries over time. as long as the shape is maintained, then functionally should be just fine.

I think I might give it a try with my Home project in a few months. Seems cheap enough, and looks fairly sturdy.

Simon are you using the 25mm or the 38mm pads?

the big 38 TEGBOY... it almost touches the window glass when I wind it down.

I figured as much. I tried the BIG boys in my car, they unfortunately do hit the glass. So I ended up using the SoundOff pads, which do fit.. only just.

Spray them with that stuff u waterproof shoes with.
I have the jaycar ones and i also found some stuff at clark rubber, its allot denser foam, almost closed cell foam.

hmmm I used deflex panels in both sub box and 8s box.

They claim they are as close as you can get to being a liquid while staying solid(they seem like jelly to me, which I guess makes their claim true)

My sub box had horrific resonances before I used them. I think they are *absorbing* energy, and so killing resonances.

Their shape is designed to disperse energy as well, so maybe they make the 8s *nicer* (to use pulse rs terminology lol) because they disperse, as well as absorb and so kill reflections back at speaker, as well as absorbing some of the energy, so it cant be reflected.

They definatly do something. My Alpine home speakers (yes you read that right...home) have egg shell type foam in there and they sound fkn awesome so dispersion is definatly something I think will work at higher freqs.


Anyway I thjink absorbtion of low freqs is definatly possibly and disperstion at higher is too and that they both are well worth pursuing
peace
Cyberpunky