[Arny Krueger]

"John Atkinson" wrote
in message
ups.com
Arny Krueger wrote:
"John Atkinson" wrote
in message
ps.com
Harmonics visible on the spectrum analyzer were in the
few per cent.

If it can do say 120 dB @ 10% THD, why don't they say
it?

I have no idea. You should ask Bruce Thigpen at Eminent
Technolog, Mr. Krueger. I am only reporting what I
witnessed.

Unh, it was a rhetorical question.

And remember, this is with _one_ drive-unit and 30W
of amplification. No reason (other than financial) to
use multiple units.

The 30 watt number is misleading.

No, this was the rated power of the audio amplifier being
used to modulate the fan blades' angle of attack.

Next time John, try reading a bit further before jumping to a questionable
conclusion.

This is a speaker driver that works on the principle of
modulation.

That is correct. That is what I discussed in my Show blog
entries to which I gave the URLS earlier.

Which means that unlike most speakers, the devices power input is not taken
entirely from the amplifier.

I see no specification for the power input to the
motor that provides the airflow that is modulated.

I don't see that it matters, as long as it has sufficient
torque/motive force. You can see from the photo that
a small electric motor, perhaps a couple of HP, rotates
the blades.

If the motor is really a 2 hp motor, then it needs special wiring of one
kind or another. That is unless the 2 HP rating is made up out of the same
kind of whole cloth as is used with vacuum cleaner motors.

If the pictures I've seen are any indication, the motor might develop 1/2 hp
if it spun at 1725 rpm, which it doesn't. I seem to recall that its actual
speed is 800 rpm, so it might be rated at 1/4 hp.

All things considered, I would expect this woofer to generate more spurious
noises given as a percentage, when operating at low levels. IOW, the largest
source of spurious responses would be turbulence generated by the fan
blades, which is always spinning. It would not be classic IM or THD but
rather modulation distortion plus an increase in background noise.