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Old 6th November 2008, 09:26 AM   #1
CLS is offline CLS  Taiwan
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Join Date: Jun 2005
Location: Taiwan
Question Bass Effeciency, Driver, Tuning, etc.

Derived from this, I'm somewhat confused by the efficiency of MB and Bass drivers in the band between the very bottom to about 200Hz.

According to the basic physics, electric current push the motor, then the diaphragm, finally air, thus the sound pressure we hear or feel. While in all those datasheets and other measurements, (except for few exceptions) we can see almost all speakers have resonant peak(s) in the impedance graphs.

Now, because of the impedance is very high, so "normal" constant voltage amplifier can only deliver a fraction of power compared to the "nominal rating". Meantime, the woofer is moving mostly on its own! -- by some kinds of resonances of its own or the 'tuning'. So, even though a powerful pro style woofer has very strong motor, say, BL of more than 20TM and low Re, but still has so less control at these resonant peaks -- so little current flows through the motor, thus produce so little force.

I think of several things:

1. The famous article by Mr. Nelson Pass on the current output amplifier and full range drivers -- what a brilliant and elegant way of dealing with the 'problems'! But there must be some reasons that constant voltage amps dominate the market for all these years. Why?

2. How about the highly damped tuning, like TL or AP? They have much lower impedance peaks than most other boxes. So, this means more current is allowed to flow through the voice coil, thus more input power. But, are they any more efficient than other boxes? In a TL, maybe we can say yes. It is indeed more efficient in the lower bass! In an AP, it seems not much gain and puts itself in between sealed and vented. So where's the current and power go? Damping materials? Or, the areas under the impedance graphs of an AP and sealed are actually the same? So, their average consumed power is actually very close or simply identical?

3. Other than acoustic gain (e.g., horn), how can we effectively increase the bass efficiency? As said above, the low endˇ¦s resonances seem dominate the overall behavior of bass. Raising the strength of motor makes a more damped (i.e., tight and less in quantity) response before pumping more air. So we're trapped in the dilemma here. Where would be the way out? Lighter cone? More compliant suspension? (But I see an opposite trend.)

Or, do I worry too much about the impedance peaks? But, they are actually there, sometimes tens of, sometimes hundreds of ohms! ˇ§Normalˇ¨ amps just let go, I imagine. Itˇ¦s kind of frustrating thinking all these, and I got so many question marks here....


Thanks for reading. And any comments are appreciated.
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