Hey all,
probably a long shot but - Years ago, I remember reading in a magazine about a particular type of foam-like material that could be used to make a large speaker work in an enclosure *far* too small for it. Eg. a 15" subwoofer in a rectangular 0.5 cu ft. box with 5 mdf sides, and this foam mounted as a very large port (sandwiched between two sheets of aluminium mesh) as the sixth side.

I saw (and heard) this once in a vehicle - was very impressed! It was in a demo vehicle - possibly installed by a Bruno Bacari(?) IIRC. I used to do serious car audio comps a few years ago and this car stuck in my mind, simply because of the truly unique subwoofer enclosures.

It was made by the same people who make dynamat if I remember correctly - called something along the lines of anechoic or anerobic foam.

Does anyone know if it still exists, what it is (was) called, and a possible source for it?

Googled a bit but had little success. Always helps if you have a clue :nuts:

Cheers
Heath Young

dacron :)

Also called innerbond at Jaycar etc... To make it effective you need to fill the entire box with it, not just the lining... Here's a detailed explanation

Quote Someguy "here's the theory and the facts--------in an acoustic suspension system the cone motion is primarily controlled by the air spring behind the cone------this spring is the trapped air in the box and since air is a compressible gas it actually makes a fairly linear spring compared to most mechanical springs-------hence the inherent low distortion of most sealed box designs----------we all should know that when a gas is compressed it heats up------we should also know that when it is rarified (expanded) it cools---------as a speaker compresses the air in a box there is a temperature rise in the gas-------when the speaker moves outward the heat is removed from the gas to the same degree (boyles law tells us that there is a direct relationship between pressure, temperature and volume of a gas)--------this constant rise and falling of temperature occurs whenever thhe speaker moves--------since this system constantly rises and falls in temperature strictly due to gas volume no real energy is lost------when energy is contained in a system and only converted it is considered to be adiabatic---------this is a mechanical pure reactance----ie a perfect spring (no such thing exists but for simplicity we will assume it does)-------remember that if we had a perfect spring and exerted 10 lbs of force to compress it the spring would exert 10 lbs of force back till it was relaxed----------since temp, volume and pressure of a gas are directly related, the spring action controlling the speaker movement is clearly defined----------now if we introduce a way for energy to be removed from the system things change--------if we introduce stuffing we are actually adding resistive losses--------as air moves through the stuffing it suffers resistive losses that produce heat-------unlike the heat that results from compressing air this heat is not recovered when the speaker reverses direction-------this heat is dissipated in the stuffing--------since some of the energy is lost this means that there is less spring power to move against the speaker when it moves---------this means that the speaker "thinks" the box is bigger since the air seems to be a weaker spring----------a system that loses energy permanently to resistive elements is know as an isothermal one-----------now the real issue is not if the theory is correct since it is clearly scientific and beyond question----------i see it as more like the amp sq issue--------we know we can measure differences but can we really hear them???---------it is easy to demonstrate that stuffing a box will lower the resonant frequency a few hertz----------but like the amp issue it is really thin ice to claim to be able to hear it in most cases--------is that a reason not to do it????-------not at all------any real improvement that can be supported by scientific evidence that is as cheap as a few oz of fabric just make a lot of sense--------but don't expect miracles..........RC"

So it'll help, but who knows how much.
~$5 m^2 at Spotlight
Hope it helps...

Peace

Tim

Unfortunatly no - see my crappy drawing. The grey is the 18mm mdf box, the red is the mystery material, sandwiched between two sheets of aluminum mesh.

It actually forms one of the sides (usually the rear) of the enclosure, and allows a large speaker to be used in an impossibly small box.

It works by mimicing the damping effect of a large sealed enclosure by allowing some air to pass through, and back again, so there is some damping of the subwoofer cone, rather than just freeair.

It has also been used by placing it across the front of a subwoofer, with no enclosure, but only for smaller subs like 8" - allows a non-freeair sub to be used as freeair - very weird, very cool stuff.

In case anyone wonders what I want this for - I am looking to use the subwoofer mounting in the rear parcel shelf - mainly because of the weight of the 15" subwoofer and box - and I have to carry a lot of $hit in the car with my job.

Cheers
Heath Young

I re-read your reply - adiabatic foam rings a bell now...

Hmmmm....

Seems that everyone uses it as a damper inside the box, much like dacron/innerbond etc.

Will have to see if I can find the article now :redface:

Cheers
Heath Young

Ah k. Damn, i dunno about mounting a 15" on the parcel shelf...
There's space for an 8" there, would require a fair bit of cutting otherwise.

Make sure you seal off the boot as much as possible... Consider mdf over the entire backseat and sides and making a huge ass box that doubles as a boot??

Just a thought

Let us know how it goes...

The parcel tray apparently had a cutout space (that was held in with screws in the earlier 3rd gens, but is solid metal that has to be cut) for a 10" subwoofer - I don't think a 15" subwoofer would go anywhere near fitting! :shock:

A 10" subwoofer mounted freeair could sound OK, but I think it would require a shvitload of sound deadener to stop the parcel tray vibrating. I do have a 12" Kicker Freeair comp subwoofer, I was thinking of mounting in the ski-hole - wouldn't weigh much, and would take up very little room.

However, I did fit a 15" into the parcel tray of my old Saab 900 turbo - there was no metal in the parcel tray, was just thin MDF.

Cheers
Heath Young

hey guys, i know this forum is real old but i jsut finished the box for my sub and realised i didn't have foam in it (my old one did)
does anyone know if "adiabatic foam" as written above is what you need? or is it worth it. i always thought it was to minimize vibration within the box or to soak up any moisture that forms.

thanks guys in advance :)

Don't really see the need for it, I don't use it. Anything that has the possibility of coming loose and finding its way inside the motor of a subwoofer I wouldn't want to put in a box :P

But hey that's coming from a shops perspective, the only phone call I want to hear about a woofer is how good it is, not that its not working :P

Cheap and easy way is Poly-fill, find it at your local lincraft or spotlight store.

Not sure on other foams, just prefer to build a bigger box :P

Cheap and easy way is Poly-fill, find it at your local lincraft or spotlight store.

Not sure on other foams, just prefer to build a bigger box :P

thats it, nothing will beat the right size box!

Sometimes its unavoidable.

Hence why my box is stuffed with Poly-fill, but all good.

thats it, nothing will beat the right size box!

No replacement for displacement :D