So finding space to practice a trumpet isn't easy. It is a very loud instrument. I'd read about people dressing a walk-in closet with acoustic materials but I didn't have a suitable closet. So...what about making a table-top version of a hat mute, a really solid box filled with absorbent material?
Turns out it works surprisingly well. It cut the volume way down, doesn't create the back pressure of a practice mute, and there's even space in there to slip a microphone. Oh, yeah; and the first time I tried it out was the first time I reached that G above High C.
Baltic birch ply (I had it on hand), Ultratouch denim insulation, wood glue.
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Step 1: Mock-up
I always do a mock-up when I can. This was done with black foam-core and gaffer's tape.
The design elements were to be the right height and the right angle so when sitting on a table I had in the shop it would be a comfortable height and angle to stick the trumpet into. The hole was cut just big enough that I could get a hand inside to practice plunger technique.
Step 2: Assembly
After figuring out the box and cutting all the pieces (I chose to cut bevels into several of the pieces to make a nicer look) I cut the insulation to size and glued it down. Almost any adhesive will work -- used to use Spray 77 for this task in a similar application.
The Baltic Birch is nominal 1/2" and quite dense. Possibly this would work just as well with thin cardboard, but my instinct says building it as solid as a speaker cabinet helps absorb the sound.
The Ultratouch is great stuff; it is at the hardware stores, absorbs as good as fiberglass but is safe to handle. You might get away with acoustic foam but I'm willing to bet the Ultratouch kills the high end that makes the trumpet so piercing to the neighbors.
I trimmed it just a little, slathered it all with wood glue and jammed it together. The insulation got caught in some of the joins but it all worked well enough.
And that's well, it!