Interesting DIY rotary subwoofer project - Page 11 - AVS Forum | Home Theater Discussions And Reviews
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post #301 of 316 Old 08-22-2018, 03:42 PM
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Originally Posted by Steve Hanna View Post
I just stumbled on Chris Hudlin's YouTube videos concerning his DIY rotary subwoofer builds. He's building a few of these for customers now and he seems to be tweaking the design as he builds new units. If you build this, some parts might go out of production and you would need to find suitable alternatives. Not a deal breaker.
Interesting. I wonder if he has ran into patent issues now that he is making for other people. I'm going to have to catch up with his builds!
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post #302 of 316 Old 08-22-2018, 04:02 PM
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I thought about that too. As long as he doesn't build a factory, he's not a threat. These aren't that easy to build and implement. Looking at the TRW-17 blades, I imagine there was a lot of aerodynamic research done on that design that's lacking in the DIY versions. The baffle would take care of the mechanical noise on the DIY build. Getting everything perfectly balanced and linear isn't critical either as we can't even hear the 2nd and 3rd harmonics of the rotary unit and the rotational speed will limit higher order harmonics. You need a full 360 degree rotation to produce a complete sinusoidal pressure wave. I doubt we can feel infrasonic harmonic distortion. This isn't rocket science, but you'd better be a good mechanic and fabricator.

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post #303 of 316 Old 08-23-2018, 02:55 PM
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Quote:
Originally Posted by Steve Hanna View Post
You need a full 360 degree rotation to produce a complete sinusoidal pressure wave.


Seems to me that what's required is a back and forth change in blade position, and that the motor rotation is irrelevant.

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post #304 of 316 Old 08-23-2018, 03:40 PM
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Quote:
Originally Posted by noah katz View Post
Seems to me that what's required is a back and forth change in blade position, and that the motor rotation is irrelevant.
Pretty sure it's all covered in Chris Hudlin's YouTube videos.
I read and watched most of the build and the diy unit still requires periodic maintenance unless you have access to a metal lathe and milling machine to make it more robust! I'm still going to make one in the end regardless for my own interest. Chris seems to be a genuine nice bloke with no bull or excuses....

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post #305 of 316 Old 08-23-2018, 09:34 PM
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If I understood the explanation on the site, the rotation is constant, but the blade pitch determines the amplitude and polarity of the pressure wave. Pistonic diaphragms loose coupling as the frequency gets lower below resonance. The rotary subwoofer never does. As the frequency goes lower, there are more rotations per cycle and thus more displacement all the way down to DC.



https://www.soundandvision.com/conte...tary-subwoofer


http://www.rotarywoofer.com/
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post #306 of 316 Old 08-24-2018, 09:47 AM
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Quote:
Originally Posted by Steve Hanna View Post
If I understood the explanation on the site, the rotation is constant, but the blade pitch determines the amplitude and polarity of the pressure wave. Pistonic diaphragms loose coupling as the frequency gets lower below resonance. The rotary subwoofer never does. As the frequency goes lower, there are more rotations per cycle and thus more displacement all the way down to DC.



https://www.soundandvision.com/conte...tary-subwoofer


http://www.rotarywoofer.com/
Soooo, in theory would you be able to achieve greater "output" by having a variable speed motor to change (increase) the RPM of the fan itself?

Seems like a higher fan speed would put more resistance on the subwoofer voice coil and almost act as a more stiff spider, increasing the fs of the driver making it more difficult to reach those lower frequencies. Sound logical?

Very very interesting topic.

I feel like the new Tymphany Peerless 15" would be an EXCELLENT candidate for this application given it's huge voice coil, ultra high power handling and (borderline asinine) claimed cone travel. I wonder if 2" of pitch in both directions would be too much?
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post #307 of 316 Old 08-24-2018, 12:24 PM
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Higher rotation speed will increase the efficiency and allow higher frequencies, but then it puts more strain on the system and increases the mechanical noises. It shouldn't reduce the low frequency limit, but would increase the output. I don't know what xmax is needed for full travel, but the driver should have good motor strength and have a vent hole in the magnet large enough for the rotational motor shaft to pass through. Once the cone and surround are removed, the spider is the only suspension left and will allow more travel.


DIY Rotary Subwoofer guide by Chris Hudlin

https://drive.google.com/file/d/0BwC...FZSG1HVzA/view

Last edited by Steve Hanna; 08-24-2018 at 12:57 PM.
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post #308 of 316 Old 03-31-2019, 11:34 AM
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Bump... Any updates from the project builders? This is seriously exciting stuff!
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post #309 of 316 Old 03-31-2019, 11:47 AM
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i've followed this thread from inception, specifically for the DIY aspect.

Despite having read ALL the Tom Swift books, from the turn of the previous century, and the "gee-whiz" factor it can light up in a 10 y.o.

the availability of "better" DIY components seems to be stalled in R&D.

but knowing were the weak links are is also progress . .mol

If there were a good bullet proof plan . . why not?

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post #310 of 316 Old 03-31-2019, 12:58 PM
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Interesting build for sure. My friend who does car audio shows builds subs, he built mine for my home theater and designed the box. He sent me a pic of this new sub he is working on. Dual motor 15 inch sub pushing 1500 watts rms. He says:
Alot of people think motor Force is constant. But it's strongest when the coil is centered in the Gap. Further the coil goes, the lower the motor Force.
Also the assumption is centering the coil in the Gap is optimum. It actually isn't. May have 60% one way, 40% opposite.
So using a computer program I find the gap center where it's 50%\50%.
I do this with both coils. The other trick is because of this the motor Force increases with movement, inductance stays lower, and Zmax doesn't go up as high as a standard design.
In a standard design, the more the coil moves, the higher the resistance. But because one coil is leaving the other coil is entering.
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post #311 of 316 Old 03-31-2019, 01:03 PM
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Sorry forgot to post the pic
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post #312 of 316 Old 03-31-2019, 01:07 PM
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I'm hoping to have my proof of concept finished soon. Just finalizing the blade design and then need to test a new VFD. The first one I got was a dud.
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post #313 of 316 Old 03-31-2019, 01:08 PM
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not about the rotary but while this ^ is going "'around"

fire it up and get some measurements. .
TY

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post #314 of 316 Old 03-31-2019, 02:50 PM
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Quote:
Originally Posted by BllDo View Post
I'm hoping to have my proof of concept finished soon. Just finalizing the blade design and then need to test a new VFD. The first one I got was a dud.
Good to hear. I did plan on making one of Chris Hudlin's designs at some point but due to life I'll probably have to settle for the BOSS designs instead along with my other bass shakers. Due to my room size there is no room gain below 20hz which required me to boost the guts out of my DIY PR subs previously. It was still good but that natural feeling of the room flexing compared to bass shakers is hard to emulate!
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post #315 of 316 Old 05-30-2019, 06:03 AM
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OMG some of those videos drag @$$.

But this concept is seriously intriguing.

I would like to see a final working setup and what room volume(s) thrive under these conditions.

I'll bet if perfected, it nets an entire new blow your hair back experience. ( Perfect for the iFly training room, lol)

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post #316 of 316 Old 05-31-2019, 12:21 AM
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I can't stop thinking about the mechanics involved and what they sound like in person.

Basically...
It is very hard for me to even visualize proven speakers and how 35+ foot sound waves move around a room. Then you tell me how fast sound moves, it boggles my mind. Nothing helps me, not even tricks like the Schlieren Flow technique.

Anyone that has stood under a helicopter in idle knows that it is possible to rock your world using a simple spinning propeller but they are huge... And powerful.

I mean most of us can't even hear below 20hz. But like an elephant, we can still sense them in our own way. Using a Boss platform or bass shakers for tactile perception is freaking next level if you ask me, but since we are more connected than ever in the history time , I have to wonder if what the third level is!?

So stop reading stuff you knew in 3rd grade and get your savant butts back to work to unlock the ever growing mysteries of our amazing universe.

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