On March 20, 2007 at 12:19, Deafears said...
If a speaker, (i.e, 3 or 4 way) has a sensitivity of 101db,
1w @ 1m, am I to assume that all of the drivers in the
array are of this average efficiency, or does the box
contribute to this . I have looked for speakers with high
sensitivity ratings, and there are not that many to be
found, several woofers, at best?
I'll bite and actually give an answer.
If the speaker has a sensitivity of 101 db, a frequency is probably specified. It has been so long since this spec has been more than a yawn to me that I don't remember.
But let's say it's 101 dB, 1w, 1m @ 1kHz. First, plug up your ears with something at least as thick as overripe bananas before you test this.
The frequency response will be given as 1.8 Hz to 47.3 kHz +/- 17 dB, or something like that.
Maybe more like 20 Hz - 20 kHz +/- 3 dB. This spec includes the sum of what the box and the crossover and the speakers do with the voltages presented to them. One can presume that the +/- 3 dB figure uses 1 kHz as a reference, but it doesn't have to. If a speaker were dead flat (impossible) from 20 Hz to 20 kHz but had a rise of 6 dB at 1 kHz, and were specified with an efficiency of 101 dB at 1 kHz, well, that would mean that the speaker had an efficiency of 101 - 6 = 95 dB for its entire range except for that midrange bump. And dead flat with a 6 dB bump can be described as some level +/- 3 dB.
How do these high end
manufacturer's obtain these extremely efficient set-ups?
By making efficient woofers. Horns were developed to efficiently couple small high-frequency drivers to the air. If you had a tweeter with a 1" dome, that tweeter would put out more sound with a horn attached to it because the horn acts to make the transition much more efficient from a 1" circle of sound to a much larger area. In doing so, it makes the 1" driver sound like a horn. The simplest analog of this is a human voice shouting versus a human voice with a megaphone. The megaphone makes the voice louder but it does not sound the same.
It also seems that the passive crossovers found in most
would also negate some level of sensitivity.
Not in the frequencies that they are actually passing. A 1 mH coil offers an inductive reactance of about 0.12 ohms at 20 Hz, and that is hardly going to lower the volume of the woofer there. But at 1000 Hz, that coil offers about 6.3 ohms of inductive reactance, which will definitely lower the woofer output at that frequency...which should be handled by a midrange anyway, so it's not a frequency where the efficiency out of the woofer is paramount.
One of the most clever crossover designs I ever saw corrected for a sloped midrange response by being designed for slightly different frequency response than was actually desired; this crossover corrected and flattened the response curve of the midrange in the system. So the crossover introduced losses and created a flat curve in the process.
Efficiency isn't everything.
