GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: Quick stuff jobPosted by jessie.dazzle on: 9/16/2010

Based on your claim that spray can foam takes time (days) to stabilize, it seems limiting the quantity used would be the right approach.

To do that you need to fill the majority of space with something solid.

The following might work for you:

Get some 1.5" thick foam insulation panels; usually blue or yellowish foam (available at Home Depot etc.). This foam is roughly equal in density to what you would get from spray can foam, and has similar physical properties and the two materials will easily bond.

Line the insides of the rear chambers with tape and protect drivers with a sac as in the photos you previously posted.

Spray a thin film of silicone on the taped inner surfaces of the chamber, but not on the sac. If you can't find silicone spray lubricant, use a petroleum-based spray lubricant such as WD40 (wipe off any excess). Better yet, use bees or carnauba wax in paste form, heated and applied with a cheap paint brush (heat it in a microwave oven).

Using a sharp knife (serrated works best) cut the foam boards into small, random chunks (like foam packing "peanuts"); max size 1 cubic inch (the smaller the better).

With chambers face down, spray in about an inch of spray can foam and immediately add cut pieces of the solid foam of a quantity that does not completely burry the spray foam. Push the pieces into the spray can foam before it sets. Add more "dry" foam pieces if necessary, submerging them below the spray foam as well. Spray in another inch of spary can foam and continue the process until the chamber is full.

Once set, the foam will have fairly uniform consistency and you can easily cut out what you don't need.

I have not tried this, but in theory it should work.

The silicone or petroleum lubricant or wax will allow you to more easily remove the foam in the event you need to access the driver.

What I don't like about it is the fact that the sac will be trapped, and any venting to the rear side of the membrane is not straight forward... You will need to carefully drill holes through the foam and sac so the driver can breath. The reason for not applying lubricant (mold release) to the sac is simply that you want the foam to stick to the sac doesn't rattle around between the foam and the basket. Obviously, you'll want to cut a hole in the sac to match the throat opening once the driver is mounted. It it were me, I'd consider not using a sac and protecting the rear of the driver with tape.

jd*

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