> air pressure inside the cabinet keeps the speaker from moving as freely as it would in a ported or open back cabinet and makes the speaker that much less efficient
It's not that simple.
> college acoustics classes
Professors (who don't really do it) are often murky on details; what I find odd is that practicing professional speaker engineers don't really grok the Basic Principles. Don't need to: all the basics were worked-out 1927-1936, most useful speaker configurations were commercialized back then, all else has been details.
Re stiffness: take the shocks off your car. Stomp the bumper. A car bounces about 2 per second, 2Hz. This could be predicted if you knew the car mass and the spring stiffness.
Now grab the bumper and try to force the car to bounce 10 times a second. It will take real force. You are fighting the car mass. The faster you try to go, the harder you have to push.
Yes, the stiffness is still there. But when you shake a spring/mass system faster than natural frequency, the mass is the larger effect. If you get an octave above resonance, the mass is practically the only thing you fight. Double the spring stiffness, and it is still mostly mass.
Geetar speakers resonate near 100Hz. By 200Hz, the stiffness hardly matters, and we still have 200Hz-1,000Hz of good piston action. Things get messy past there, but one thing for sure: by 1KHz, the sound wave doesn't even reach the back of the cabinet in time to affect the cone. We are transitioning to wave-world, where wave effects will help or hurt depending on even or odd number of waves in the path.
Stiffness (suspension and box) shifts the resonance in frequency and height. A naked hi-fi speaker has a deep weak resonance. We put it in a box to bring resonance to Q=1 (neither weak nor strong) at whatever frequency that happens. Gitar speaker tradition is a fairly high ringy resonance, as-if a fairly small box (high stiffness) were built-in. Then large changes in box size give small changes in resonance. And the range an octave higher, even a half-octave higher, is just not affected by box stiffness. A big boomy or weak gutless bass resonance affects your perception of midrange, but the midrange itself is not much changed by the box.
If you were very desperate for BIG LOUD SOUND, to be sure all 3,000 in the crowd go home deaf, you know you want four or eight large cones (and maybe more than 18W?). Been there, done that, and know there is some market for less beastly sound to smaller crowds. And most cow-palaces now have OK PA systems, OK enough for the people who like mega-concerts.
As for 3dB: in most profitable venues, at max profit, most of the absorption is people. Hard tables, hard chairs, cheap or no carpet, low ceiling, no tapestries. But the fact is that you pack the room only rarely, and over half the time you play to a half-crowd or less. A half crowd absorbs 60% of a full crowd, so you need 2 or 3 dB less acoustic power. Do you normally count heads and then go home to find amp/speaker pair to suit exactly that size of crowd? No. You play what you got. Exact power is not critical.
Topic: Speaker effciency question.... (Read 9291 times)