DIY Rotary-Woofer (TRW-17 knockoff) - Please help

[Chester]

Hello, I am looking for people who have *in person* experienced a rotary woofer, or if there is anyone who knows anyone who has one in the Minnesota area; I realize this is a relatively rare item... I am in the beginning stages of researching to build one of my own and was wondering about a few things, particularly how much unwanted noise is produced by the fan blades? the

videos I have seen on youtube

videos I have seen on youtube

seem to have a lot of 'white noise'; presumably from the edge of the blade... I am thinking of ways this noise could be minimized, also I was thinking of making a shroud mechanism to also help reduce noise (think of a large diameter, short length, flared subwoofer port). Please give me your opinions and thoughts on the shroud idea and any ways of reducing the 'white noise' effect from the blades acting on the air; I was thinking that some sort of soft 'fluffy' attachment to the leading edge of the blade could help (think of a 'boa' like material, like what girls wrap around their necks, but very small diameter).

Thank you all for your input!

[Mike P.]

Just curious how you will make the blades oscillate?

[Chester]

I am going to do something similar to what the TRW-17 uses, basically a voice coil and magnet hooked to a push-rod system that will pivot the blades... I was thinking of using a neodymium magnet (to be on the interior), covered with Teflon to make it slide (instead of using a spider) and then have a voice coil over that

[Mike P.]

If you go ahead with this please keep us updated. It will definitely be interesting!

[Chester]

Right on, either way I will be doing some experiments, I probably make a '' prototype version first to get things figured out and then after that make a quality rotary woofer, as I said earlier, I would greatly appreciate a response from anyone who has seen or heard one of theses in person

[Ryan Anderson]

I'm guessing the guys that do the R&R, the engineers that design these, have been working on that... have you emails the company(s)?

I was going to start working on a pipe loaded with a heater fan from a car... the motor I had needed the Commutator's replaced as well as brushes... someday.

[Andysu]

I’m more curious like my cat is, just how fast does it react to the differences in low frequencies?

Is it fast?
It’s just about fast enough?
No it’s dead slower than snail?

Or use the fan with wind effects on films or when Ben Pinkwater gets diced up at the end in Terminal Velocity.Or even Alien 3 when that poor bugger gets thrown into a LARGE FAN by the alien.

See the fan as 101 uses thou I can only think of two uses for it. Cooling the flat down in the summertime or switching it ON to maximum and watching Flight of the Phoenix.

[Chester]

well from what I've read the fan rotates at 800 rpm; basically the faster the fan the more db (since there is more air pushed per cycle of the acoustic waveform due to the blades' longer 'cut' into the air)

EDIT: I would say how 'fast' it reacts to the changes in the sound would be dependent on how 'springy' the suspension is (how fast it wants to return to a resting state)... otherwise we are just dealing with pressure here; so the sound (pressure waves) should travel just as fast as any other sound (~1124 ft/s)

[Chester]

Ryan, you said you were going to start on a pipe loaded by a heater fan; are you talking about having a constant fan pressure (pitch) and modulating the airflow?... that is another solution to the problem I have been considering, perhaps for a 'smaller' portable solution

[Andysu]

Only downer is the silly size of the enclosure and I can see wife sharpening the axe in the shed.

I’ve noticed smaller fans the ones that go inside a pc tower can vibrate when the voltage is regulated. Maybe they can be attached to the inside of sofa on the wooden framing.

[Chester]

I'm 21 years old, not married so no worries on the WAF, I may use a pc fan for my trial build (the mini version to get the kinks figured out)

[Andysu]

Chester wrote:

Ryan, you said you were going to start on a pipe loaded by a heater fan; are you talking about having a constant fan pressure (pitch) and modulating the airflow?... that is another solution to the problem I have been considering, perhaps for a 'smaller' portable solution

That’s got me thinking “pipe”. No not smoking. What if the room had pipes going around in arc and the main (rotary fan sub) is placed in different part of the house so that it only blows mass air down though the pipes would that not work or would it have too much trade off in efficacy.

[Andysu]

Chester wrote:

I'm 21 years old, not married so no worries on the WAF, I may use a pc fan for my trial build (the mini version to get the kinks figured out)

I tried the same thing a few years ago. And with blade cut off it produced a different kind of vibration. I even attached or placed it underneath the seat on one of the seats feet and it was quite noticeable for tiny pc fan.

I just want know what device goes between the mechanism too regulate the flow of voltage as it has to be triggered off from the audio equipment to make it perform?

Also I’ve seen hard-drives being used on youtube as speaker. I wouldn’t have even thought possible. The one user removed the video after short while last or month before strange?

What about installing overhead in the ceiling providing there is enough space up there to work with. Who says it has to be placed on the floor next to the living room in spare good room that could be used for more practical means. The loft has bugger all up there apart from Spiderman.

[Chester]

well I was thinking about doing something like that; I wouldn't think it would hurt efficiency if the pipe had no resistance to the airflow... though it would add some delay: maybe some sort of furnace/ventilation system could be rigged up, better yet since it is a low pressure system, steel exhaust pipe (like a dryer vent hookup type thing but with a large diameter) may work, as long as there is no 'stretch' (so a fabric or tent material wouldn't work since the stretch in the material would allow the energy to transfer out around the pipe)

EDIT: but the main idea is to make a baffle board I can put in my doorway, if you have ever seen large 'rolling walls' in event centers and stuff, they usually have a bottom part that will push out and seal between the rooms, something similar to that on the edges would make it fit snug into a doorway so the room would be one side and the rest of the house (or outside if you use a window) would be the other side

[Chester]

in response to the pc fan (with the blades cut off) since you are looking for dc flow, if you were to use a rectifier you could get 'pulsed' ac (it would only 'flow' one direction, ex. 0 v to 1 v, then back to 0 again) but the frequency would be doubled if you used a full wave rectifier though i am not sure if you would only want 'taps', basically what you would be getting from a pulsed signal like i described

[Andysu]

I like the pipe idea. Using small dinky size room no bigger to swing a cat around would be fine.

I’m have some sceptical thinking at the moment don’t know why?

Also what is the average cost of this I read a few years ago it was silly price in the thousands and that is just not practical enough, it’s got to be cheap as chips.

One other important thing I’ve overlooked. What about stand waves does it suffer with standing wave issues? Also would it need equalizing?

[Chester]

hah you love cats dont you anyways, the cost *would* be ~$22-25,000, if I were to buy an installed system from the company that makes them; the cost to me, making it my self will hopefully be less than $1000... We shall see, I am probably going to have to get some parts laser cut and stuff but I know where I can get that done for a decent rate, the electric motor will definitely be the greatest expense as far as I can tell

[Ryan Anderson]

Chester wrote:

Ryan, you said you were going to start on a pipe loaded by a heater fan; are you talking about having a constant fan pressure (pitch) and modulating the airflow?... that is another solution to the problem I have been considering, perhaps for a 'smaller' portable solution

no, not at all. a DC motor can still be given an AC signal and it will oscillate, so long as there's not a circuit board. Take apart a DVD player, VCR, remote control car, or something with a small motor and hook it to your stereo and have some fun.

It's rough, but it's a bass line to play with, no pun intended

here's some vids I posted a while back


gets LOUD at :30 and distorted, turn your PC down!

http://www.youtube.com/user/kryptoni...35/O6nPm3uRDX4

http://www.youtube.com/user/kryptoni...37/I5_d2rSSyR0

not too interesting here, but 2 things to note: the low frequencies worked well...the 8Hz tone... and overall it favored moving one direction with the higher frequencies

http://www.youtube.com/user/kryptoni...36/eOkbHRdK2d0

Andysu wrote:

That’s got me thinking “pipe”. No not smoking. What if the room had pipes going around in arc and the main (rotary fan sub) is placed in different part of the house so that it only blows mass air down though the pipes would that not work or would it have too much trade off in efficacy.

how about placing the fan 1/3 to 1/5 the way into the pipe

[Chester]

I think I understand what you mean now: however I am looking to push air, not 'toggle' a motor, possibly the toggling system could work if the blades were mounted parallel to the axis of the motor shaft but I'm not really seeing that as pushing much air

[brandonnash]

This is a very cool idea. I just read this thread for the first time. I want to keep up on the progress of this one.
Posted via Mobile Device

[willy-be]

Chester wrote:

well from what I've read the fan rotates at 800 rpm; basically the faster the fan the more db (since there is more air pushed per cycle of the acoustic waveform due to the blades' longer 'cut' into the air)

It rotates at 300 RPM, using a 3 Phase 1/3rd HP motor.

I've 'heard' it and spoken to Bruce T about it.

There's a thread somewhere on DIYaudio forum about doing a DIY version

[Creative Sound]

Hi,

I heard this when Bruce introduced it a RMAF (not sure which year but I think 2005). It was in 2 rooms on a separate hotel floor and the rooms had a connecting door. The driver was mounted on a special baffle in the door and 1 room was the IB "behind" it and the other room was where the listeners were. I didn't get to hear any music or HT movie tracks but the tones played from 20 Hz down were impressive with everything vibrating. Suddenly (at 4 Hz) my friend had to leave as it was affecting his heart pacemaker!

One of the HT magazines also had some install notes but can't recall when or where. It would be of interest if someone developed something similar cheaper.

Bob

[Chester]

was there any noise from the blades you noticed?

also: is the thread you are talking about this one:http://www.diyaudio.com/forums/subwo...bwoofer-2.html ... they didn't seem to get very far (or at least did not post about it)

[willy-be]

Chester wrote:

was there any noise from the blades you noticed?

Sure the blades make noise. There's a loud 'fluttering' sound that varies according to frequency. This is the reason Bruce has the highly damped baffle/chamber between the sub and the room, it's used to absorb the mechanical noise caused by the operation of the blades.

[Chester]

Hmm, do you think the things I mentioned in my first post would help? some sort of shroud around the opening or something on the leading edge? perhaps I should talk to Bruce