Alan Carruth wrote:
in a bass reflex system the acoustic damping of the cone itself is high, and they add a lot of damping in the cabinet to flatten out the response of the Helmholtz mode.
The sound board is highly dampened. It works just like a speaker. The only difference is that a speaker is propagated (induced to move) electrically, and the soundboard is propagated mechanically.
Quote:
You do have to be careful to get the proper relationship between the various strong low-end resonances, such as the 'main top', 'main back', 'main air' (Helmholtz-type), and the 'first body mode (AKA the 'neck mode), to avoid problems of the 'wolf' type. Once you get up into the mid-range, say, above about 500-600 Hz, there is so much going on that you're in a 'resonance continuum', and the problem looks more like room acoustics than a speaker cab. An odd-shaped room, too, and one with walls that flex! It keeps it interesting.
You know, it's funny you mention a Helmholtz resonator here. As I've been pondering this effect for a few weeks now. The job of a Helmholtz resonator is to allow a broad band (full range) sound to go in, and not come back again. Just dissipates inside.
When you think about it. To the air inside the box, the sound hole IS A HELMHOLTZ RESONATOR. If it's working right, it will allow the air to move out of the box but won't allow it back in. Thus freeing up the box to reproduce the next sound. The box works just like a lung. Albeit, on a much smaller scale. It expands and contracts. When it's working properly (smoothly) it will do just that. But if it isn't, it will allow air to infiltrate back into the box when it contracts. Mixing with the sound presently trying to come out. Causing what we refer to in the recording industry as mud.
And you're right to point out that the lower frequencies are the ones which get the most benefit from this.
I really think this will work.
- Phil
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