1) Sound pressure level is a variance of air pressure around a norm, usually atmospheric.
Originally posted by Whip11:
Phew a lot of reading here.
I'm chiming in late but I have to say a few things.
1. I don't think sound pressure = air pressure
2. Given that I believe you use the air pressure to control certain aspects of you woofer loading.
3. so as to get the woofers to make the most violent sound pressure possible to equal Max SPL.
4. a focused sound wave would be more effective then one which is wide or multiple, because a focused wave will not cause sound cancellation like those other designs.
5. I learned that the air in the box of a ported enclosure was the spring and that the air in the port was the diaphragm and acted just like a passive radiator. And that air would move forward and backwards like a diaphragm, so that there wasn't any actual air really escaping from the box. But the air just in front of the port could be excited to move like the air coming off the woofer itself.
6. Finding the resonant Frequency and working with it to enhance your spl is better then working against it. (it's better to surf with the waves toward the shore then to fight paddling back out).
These are the principles I use for my spl installations
2) Air pressure is generally fixed, or quite close to fixed. Raising the air pressure would involve densifying the medium (more air) which would create a more efficient transfer of energy. Loading in horn or compression chamber does accomplish this.
3,4) The concept of focusing is very difficult for sound waves at low frequencies, because the wavelengths are SO long that any method of lensing requires either immense open space and construction or innumerable interference measurements
5) Energy flows downhill. If the air inside the port is compressed, then it gains potential energy. This energy will be lost in both directions from the point of compression continuously, therefore energy will radiate out of the box if the form of sound waves. The actual air in the port doesn't necessarily move all that much, although it is subject to the same rules of molecular motion and diffusion that it would be in an uncompressed state.
6) SPL is the measurement of pressure variance at a particular location. Resonating the entire mass of air within the cabin area requires very small cabin area coupled to very large radiators. Maximizing the pressure variation at the mic location is the key, and finding the frequency at which (for example) the roof of your car most readily couples the interior air to the exterior air is not necessarily conducive to a high variance at the mic.