Has anyone placed a audio signal controlled fan outside a ported sub ?

[DJDestiny]

Typically i was either expecting a squirrel cage fan ...
But is it any useful ?
I was thinking about rotary woofers and this idea came out ...

[john dozier]

WTF?

[simon7000]

In some pro gear there are fans used to cool the voice coils. In others the port air movement is used to cool the built in amplifier.

In Danley stuff a motor is used to drive the piston directly.

The problem with using a fan to increase velocity is it is not bi-directional and relatively slow.

[kenpeter]

You mean like a fast butterfly valve after a squirrel cage vented from outside?
Servomotor from a hard drive comes to mind... But maybe thats only so fast
cause its not moving anything heavy... Would 3 or 4 inch valve be too much?

If the butterfly was at the inlet, the motor might speed up slightly during
rarifications and store energy that could be let out during pressurizations.
If so, motor might have to be run on DC to avoid IMD with powerline.

Whats the "ported sub" for? Trying to acoustically filter away the fan noises?
Trying to accumulate a volume of pressurized air from the fan with butterfly
at the exit port instead?

[DJDestiny]

I was saying the fan is on the vent itself , to enhance the amount of air in puts out , i'm talking about a amplified line signal to the fan
Yeah , i could try a 30k rpm motor , might be possible , will it be possible for that thing to handle 12kHz ?
Or i could make a 6th bandpass order box and stuff the sub there , the exhaust squirrel cage fan on one side , and a 30krpm intake fan .
Those PC varieties that put out lots of wind @ 12VDC , 0.53A . ( Mine's about 73CFM )
Is it possible for those DC fans to run with AC ?

[cbdb]

How does a fan push-pull the air? It just pushes it. You might be able to make a sound by adjusting the push ( modulate the fan speed by the signal ) but it would probably be noisey low bandwidth and very inefficient.

[DJDestiny]

Originally Posted by cbdb

How does a fan push-pull the air? It just pushes it. You might be able to make a sound by adjusting the push ( modulate the fan speed by the signal ) but it would probably be noisey low bandwidth and very inefficient.

My goal is not the sound , but because subbies operate mostly at the low-end spectrum , and it is mostly felt .
My thought was more air = more bass .
Regarding your push pull thing , i use a 6th order bandpass something like this dual port thing .

[revboden]

Originally Posted by DJDestiny

My goal is not the sound , but because subbies operate mostly at the low-end spectrum , and it is mostly felt .
My thought was more air = more bass .
Regarding your push pull thing , i use a 6th order bandpass something like this dual port thing .

more air = sub operating below tuning frequency= not good.

sorry, i should clarify. When you feel a subwoofer blowing air out the port, it is operating below it's tuning frequency and is not making bass with all that air movement.

[head_unit]

Originally Posted by revboden

more air = sub operating below tuning frequency= not good.

sorry, i should clarify. When you feel a subwoofer blowing air out the port, it is operating below it's tuning frequency and is not making bass with all that air movement.

Mmmm, well, sometimes, but not all the time. If you drive the ported box with a sine wave right at the port tuning frequency, it should make a LOT of bass with a lot of air movement. More of the bass output from concert arrays comes from the port than the cone. In a perfect system, the woofer would nearly stop moving.

Now, if you're talking about some tiny "ported" satellite which is probably tuned well above real bass frequencies, then you'll get a lot of exactly what you describe: poof poof poof with little bass sound. I remember a guy in college with some little Polks trying to play the heartbeat on Dark Side Of The Moon-his woofers just bottom with a lot of noisy port chuffing. I stuffed the ports shut for him, and he was a lot happier.

[head_unit]

DJDestiny, a fan driving the bass needs to make the output track the input signal. So you can't just have a fan blow more air from the port, that won't work.

Tom Danley once showed me an array that WAS using a fan as a direct air source. Actually a whole cascade of I think it was 15 horsepower (!!) industrial fans, blowing air in a kind of circle/torus. Then he had giant flaps which would disturb the airstream into a horn throat. This made something like 170 dB at 3 Hz, so if you want to scare your neighbors into thinking "The Big One" has arrived, get out your saw and start cuttin'

See p. 1328 of

which I stumbled on in a thread about rotary woofers (following Danley also):
http://www.avsforum.com/avs-vb/showt...1301446&page=5