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In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project
Post Subject: Rear chamber (fixed volume)Posted by jessie.dazzle on: 2/26/2009
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JP,
Start with a rear chamer having a volume a bit larger than you think you will really need (calculate rear chamber volume to get you in the ball park; for this you will need the driver's tech data).
From there you can tune the chamber volume by introducing solid objects (closed-cell foam, blocks of wood, whatever) to the rear chamber.
The "stuffing" could end up quite close to the rear surfaces of the driver, so some shaping may be required (in your case, I would do some temp volume research using modeling clay, then, once the correct volume has been determined, make a removable hard part from wood).
Also, see Romy's post detailing the Haskins technique using expanding insulation faom (though the spray foam does not set up as rigidly as pre-cast polyeurethane modeling foam).
With any of these solutions, adjusting chamber volume will not be as convenient as turning a threaded shaft, but once the correct volume is found, you're done.
Making a pair of adjustable chambers as I did takes a week end (and that's once you have all the materials). I did it this way because I wanted to use these horns before finishing work on the larger 40Hz horns, and also because I know I will not stay in this house.
Keep things air tight.
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