Rotary Woofer facts

[bwraudio]

1. Response is from 25 hz to below 1 hz
2. High efficiency at very low frequencies
3. No equalization needed for response to below 1 hz
4. Has enough acoustic output to move an open door .5" between
1 and 5 hz
5. Transient response is near perfect
6. Requires very large enclosure to absorb fan noise
7. Infinite baffle enclosure to prevent front and back wave
cancellation (I use my entire basement of 2000 sq, ft.) The
smaller the back venting is the lower the efficiency (reduced
output)
8. Requires a low pass xover (recommended xover frequency
between 15 and 25 hz @ 18 db per octave (I use Marchand
Electronics rotary woofer controller which provides 200 watts
to pitch the fan blades, built-in adjustable xover from 15 to 25
hz, gain control, adjustable phase and damping.
9. Requires a motor controller to control the speed of the rotating
fan and maintains constant speed when the fan blades are being
pitched. This controller is used to set the speed of the rotary fan
to match the volume of one's room. My room is 29' long x 19'
wide x 11' high cathedral ceiling and I use considerably less
speed than the maximum.
10. The required opening into the room (minimum is 3' x 3') I use
4' x 4'
11. My enclosure is 8' long x 4' high x 4' wide and is braced completely
sealed. All inside surfaces are lined with 6" fiberglass
12. All the electronics; preamps, power amp that pitches the blades,
sources (Dacs, etc.) should have excellent very low frequency
response.
13. Produces very low bass utilizing low pressure (conventional subwoofers
utilize high pressure (cones move back and forth madly to produce
very low bass. The rotary woofer matches the air load (impedance)
Horn enclosures do the same to match impedance, but would require
an enormous enclosure.
14. One needs an additional 120 vac outlet for the fan motor and motor
controller.

[bwraudio]

Pictures show the rotary woofer up close, the large enclosure and
the 4' x 4' opening into the room Also the motor speed
controller

[bwraudio]

This is the Marchand Electronics rotary woofer controller. Also shown is my equipment cabinet that is mounted on a separate concrete foundation and is sand
filled to prevent vibrations to equipment. The lower one goes in frequency the better the isolation of all the equipment is needed. Attachment 1324Attachment 1325

[amirm]

Great write-up. Question. Is the air blowing through fiberglass in front of the blades? If so, is there something to catch the particles from going into the air? And how do you keep the fan noise from transmitting through that medium?

[bwraudio]

The fiberglass insulation is only on the inside surfaces of the enclosure, not in front of the blades. There is no problem with particles because the air is not being blown into the room, but the air pressure is going from positive to negative following the ac signal. Because the enclosure is both large and very absorptive in the inside, the noise from the fan is minimal,
and the speed that I set the rotary fan is far from the maximum. Also at the end of the enclosure (8'), the back wall further reduces the noise from the fan as the sound bends upward through more insulation. Some commercial installations don't use an enclosure to silence the sound of the rotating fan blades at all, but when one considers the size and distances of the buildings, the fan noise is not a concern.

[bwraudio]

Here is one of the installations that does not use an enclosure to silence the sound of the rotating fan blades, but just an infinite baffle to prevent cancellation of the low frequency sound.