The pressure zone trap is a different type of sound trap than those mentioned. It uses lumped parameter acoustics while typical fuzz type absorption uses distributed parameter acoustics. Lumped parameter devices are designed like an electronic circuit with discrete items such as resistors, capacitors and inductors, and can be quite small; The distributed acoustic devices use the wave-guide approach to design and are sized directly to the wavelength of the note. For example: the pan pipe (¼ wavelength) and a soda bottle (lumped parameter) can both sound out the same note and equally loud, but the pan pipe will be many times longer than the soda bottle.
Improved Quarter-Wavelength Traps
Rather than a loosely packed fiberglass batt, which always settles, we can glue it to sheets of sound board which can be suspended by wires inside the closet. Nothing much new here; the same response curve as for the “ball-of fuzz” ¼ wavelength trap. The fiberglass does not settle out and so the trap keeps working for years.
Sympathetic Resonance Traps
The sympathetic resonance or panel trap is a creative cousin to the sound board and fiberglass trap. Often suspended in, supposedly, random overhead positions, these panels are each tuned by trimming to size and adding weights. Particular frequencies set these panels into sympathetic vibration motion, and the incident acoustic energy is converted to vibrating panel energy.
Dissipation of the energy occurs with the air moving back and forth across the face of the panel as it “twangs.” Its own internal friction also dampens its motion. These panels have to be ¼ wavelength in size, otherwise they would not be able to interact with the sound wave. An 8-by-8-foot panel would function at 40 Hz, if it was correctly tuned. Panel traps work best if aligned to meet the sound wave face on (like a ribbon mic) to engage action. The flat of the panel needs to face the wave front. Too often it is physically impossible to set up a real room with these panels because of size constraints.
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