Rotary Subwoofer inside Handheld Bluetooth Speaker (Will it work?) 

Nice idea in theory, unfortunately smaller volumes require higher static pressure from the "fan" to be effective, this is because the rotary subwoofer has to do a lot more compression. Awesome stuff nonetheless though!

Please try it again. Try to use flexture joints to reduce ratteling and to simplify assembling. Make blades fill surface of the speaker completely. To increase pressure you can use two cotrary rotating motors. Control signals should be synchronised, but phase should be tweaked, so they work in resonance.. It can be really interesting.

Smaller blades at a higher RPM might resist vibration distortions. Also the port is very restrictive. Been thinking of building rotary subs for years and trying to figure out a better way to interface the voice coil to the blades but have never got around to it. Subscribed!

If the fan is spinning clockwise like I think it is, then any little shove to the blade angle off center will result in the blades being slapped to their excursion limit. Basically, the pushing motor needs to RESIST the airflow effecting the blade angle. (Try running the motor CCW)

For a small size like this I think putting bearings on each blade to allow the pitch variation is a mistake. I think you'd get a much cleaner actuation and sound by using a compliant structure, a blade that just flexes back and forth instead of tilting. Actually that may be a good idea even for a large blade fan.

To fix the rattle you might look at RC car suspension parts. I believe they make tiny ball joints and linkages. Very cool project!

I think ideas like this (if perfected) could definitely make rotary subwoofers more popular

You should put the other drivers in two enclosed chambers to eliminate phase issues.

5:27 You have effectively simulated the sound of every jackass that drives by with a subwoofer in his car good job!

I've been building loudspeakers since the 80's, but never considered a spinning sub before and I think it's a great idea. A couple of thoughts (hopefully helpful ones!) Instead of a closed box. What about using the air behind the rotor by redirecting it to the front of the cabinet. Kind of a horn/ bass reflex hybrid that allows free air movement in front and behind the rotor. You might have to play with tuning a bit. I like the idea of a 3d printed cabinet. Adding dampening material, such as the asphalt material used to damp the noise in a car would help in vibration. Lastly, make the rotor as absolutely light and stiff as you possibly can. Of the two, stiffness is the more important. Everything that supports the rotor and motor should be as sound dead as possible. Be sure that no two parts meet that have the same natural frequency. Running the rotor with a belt rather than direct drive would be interesting, but probably a nightmare to package. I hope that I'm not just being Admiral Obvious here. I honestly love this idea. It may never be practical, but hey, I built a set of plasma tweeters with vents to the outside and ran them for months. So who cares about practical.

Really interesting. I was watching videos on rotary subs several years ago and there were only a few on RU-vid. Recently there seems to be a lot more people like yourself researching, building and experimenting. Eliminating rattle is important, it will be fascinating to see new techniques and different materials used in future.

Nathan, that was certainly worth a shot! Getting real bass out of a really small package has always been a challenge! Thanks for the video!

you really did great job making and testing rotary sub in actual use case scenario I appreciate your hardwork

I love that you took the time and tried it out. Was really curious my self if this in practice could work.

Thanks for the test ! much liked to see what it gives.

This NEEDS to be made and produced

I need a rotary subwoofer in my life. You've been my introduction to this idea. Thank you.

Excellent lesson. shows how rotary subwoofers' best application might certainly be in large scale low frequency reproduction of such displacement that with piston style drivers would not otherwise be practical.

You did a great job making everything and explaining everything

super cool to see someone make a tiny rotary sub for a bluetooth speaker :D

Loved that you played the music from Spirit: Stallion of the Cimarron! Great movie and great soundtrack.

That was honestly realy dope

This was sick, some further experimentation would definitely bring something more effective

Very cool project. Great work.

it will reduce distortion if you can make it a rubber busing instead of a bearing. Also, the paper clip rod must be tight. then check the xmax of the sub to make sure it wasn't bottoming out. iknow it would be difficult for the motor to work if is tight but it will sound good.

Awesome idea. Keep it up.

Awesome video, regardless of whether or not the rotary sub sounded better this project was a total success!

I'm excited to see someone working on rotary subwoofers.

New to the subject and you guys are blowing my mind🤯

I like the fact that you did this it was a great experiment and I learned more about rotary subs in you doing so. Seems that they require a much larger area of air movement...thank you foe the video! 👍👍

Keep up the great work!

U turned me on to something new ,thanks dude

That was a dope idea to try. Keep it up and don’t give up

Hey man great work! Would love to see a version 2 with all the things you learned on the way :)

What if you made the enclosure tube shaped, similar in design as the JBL Bluetooth speakers? Might have a different low frequency response. If you do design one like that I’d be interested in the outcome.

cool idea

thank you for putting in all your work, this video was most educational!

Very cool experiment. Rotary subs are so neat.

Might have to tune the port a bit for best accoustics. You want some restriction to generate a pressure differential, but you need it open enough that it doesn't overwhelm the fan and cause it to stall.

Creative idea! It sounds like the fan blades are hitting the shroud.

great job on the video.

I was thinking that . When I saw you video. Keep up the great work 👍

Interesting, I just learned rotary subs exist. Thank you for the info

Room for improvements. I see it has potential.

Hey man GREAT JOB. Keep up the good work

"And a couple of other parts." * Shows way more than the 2. Haha, nice exaggeration!

i really liked this video, thnak you

Nice 👍 you got some real creative engineering talent

This is becoming an incredible channel mate. Keep it up 🙏

Looks interesting

Sure, the fan thing shook the box more, but the sound quality wasn't nearly as clean. So there's that to consider too. It would definitely have to be tightened and/or otherwise cleaned up before it could be actually viable. Interesting idea, though!

What I really wanna know is would it be possible to make something like this using a turbine design instead of fans to have more pressure. Or maybe replace the blades entirely with an ionic thruster. I know Integza has been working on and made some neat designs for one, but if it were optimized to put out a lot of air, it might be a good idea to get rid of the fan noise and still be able to move air. Then again with all that being said, perhaps the sound of electricity zapping air would still defeat the purpose, but maybe it would help remove some mechanical components so less chance of mechanical failure. But I also am not sure if it would even move enough air to be worth the idea.

this is so genius bruh

This makes me wanna diy my own rotary

That was interesting.

I hope you try this again as well. I'm slowly gathering parts to try to turn a desktop computer fan into a small rotary sub and a couple of small speakers to my electric wheelchair for some rolling music. The way that I planned to mount it was similar to your box, but I was going to have a short pipe going through the middle of the box to leave the rotary open while providing backpressure for the cone speakers on either side. Getting to see this and a couple of your other builds has really helped me to work out what I need. Thank you.

wtf, amazing dude

Nice

I love the idea! I'm guessing more mass in the box itself and maybe a different motor might help reduce the rattling and other noise. Oh, and maybe some kind of flywheel ring around the rotary sub for stabilization

Incredible idea, i wonder if there exist a box configuration that would mimic an infinite baffle enough to be viable for this project? You are doing pioneering work sir. Thank you for all of your great videos.

Wider blades will control the air better. Narrow blades will allow air slippage. Have them nearly touch.

This is worth experimenting. Their has to be a efficiency range to doscover.

Transmission line is the way to go.

Cool idea. I think you would need machined parts and better airflow for this little one. I saw the double rotary you put in your laundry room window. You’re a badass man!

THATS SICK!!! It doesn't sound as good but my friend Trenton and I think it's a really cool thing you did. Even thoug the sound is that good. keep going dude this is awesome

Use a HHD motor and smaller blades or a larger casing don't forget silicone is your friend 😁

Haha test about subwoofer and suddenly hearing Run Free from Hans Zimmer. What a plot twist😂

Interesting! This is a great experiment. I wonder how you might be able to simulate an infinite baffle in a portable configuration.

Nice work, but it needs a larger air vent and stiffer construction. The thin walls will flex too much. Give it another shot.

Might need a small, wood or metal fan, brilliant idea

Very cool idea for miniaturizing this and getting the blades to pitch. Have you thought about implementing a small 100-size collective pitch rc helicopter swashplate and blade setup? Might be a little more accurate and easy to move.

Your box sound verry good with conventional speaker ,,.

Guess I would need to be there. sounds tinny

Could lubing the moving parts with a grease stop some of that rattling. It's not ideal considering it would grab the dust though

The rattling can be fixed, this concept idea should not be given up on. If there is a way, someone will make it possible. Rotary Subwoofer might have another good purpose as well, I wonder if it could keep open air flow in a open warehouse were there is no air conditioning?

Subscribed

Great idea. Keep refining it. I've only seen one rotary sub on the market (Eminent Technology TRW 17) for home hifi/theater use and I heard it costs about 25 grand installed. ...Ouch!

General rule of thumb. If you scale down a design you need tighter tolerances to an equal scale.

Keep it up! Your engineering skills are impressive. How many job offers have your had since your original post two weeks ago?

This is awesome but i had an idea could you just have the back open for an outdoor speaker?

So freakin cool. Could you explain infinite baffle?

Think maybe the fan is turning too many RPM's ? Might take care of some of the rattle.

It might be worth putting some sort of frequency splitter in there so the rotary sub is only handling frequencies below 20hz? It would probably sound dope with the native subwoofer and the addition of the rotary subwoofer!

alls i can think is like a engine or something with an imbalance could try some bushings and rubber spacers should deaden the vibrations in theory and maybe try a different blade design also maybe more air passages

Very interesting project. How would the Bluetooth speaker perform if there was a "tunnel" through the enclosure to hold the rotary sub?

Flip the rotary sub 180°. Basically inside out. Fan on the inside of the box and cd rom motor outside the box.

all you need is a good crossover to get rid of anything over 50hz. most people use them for 0hz-20hz and let other real woofers do the work as the fan blades are better for infra-sonics. these do not handle anything above 300hz at high gain/volume, and that is with the official ones that are like 12". you can barely turn them up if you have no crossover, as it makes the blades distort too much. also they require a sealed compression chamber, not a port. One last thing is that rotary subs are super efficient and if you have them hooked up to the same wattage as the other sub there is a good chance it was getting too much power. I just started the vid, havent seen if you addressed this yet. good luck!

Interesting! It sounds bad but at least it works. Keep going!

A small idea to get tid of fan noise is to put the entire assembly into a box and install a passive radiator in front of the fan. Idk whether it will work.

Wonder what would happen if you added a length of tube in front of / around the rotary sub, sort of turning it into a ducted fan

To add to my other comment, I think it’s a,axing you are doing this. I hope you keep it up because experimentation is the path to innovation. Also, if you can turn down gain and control the deflections of the blades better it could help reduce noise and allow small enclosures (relatively speaking)

Maybr try an extenal rotory sub using a blutooth sub as a base if its possible That way it can use the open baffle air

I would try a fan with 3 larger + deeper blades, rather than 5 small shallow blades, in addition to having a pass through pipe design, where you just put some metal screen material on the opened ends. I once bought these used Industrial fans, that were like 1" deep, with 3 blades. I believe their original use, was for the giant, original, HP Laserjet printers. They were VERY powerful, and very loud.. and created near hurricane level winds. I had put two of them in front of a cut up PC case... and it was pretty much overkill. I probably didnt even need my CPU cooling fans... because the amount of air those 2 industrial fans created... was astounding. But as said.. it came with a cost. The things were incredibly loud.. and being that they were AC... I couldnt control the speed (I never tried an in-line adjuster.. just wired them direct to the power cord) I believe those fans were 4" x 4" with a total of 1.5" depth. I have no idea what the RPM was.. but if memory serves correct... I think I was able to chop carrots with them. As for the blades themselves... take account for plastic stretching out, from rotational forces. You might have to increase the gap between the blades and the surround.. as well as add a bit more thickness and rigidity to the blades. Of course, certain plastics are less effected by rotational forces.. which is why those brown colored PC fans are able to preform much better than others (noctooah?). Because their plastic does not deform.. then can use less clearance between the blades and the housing.

Isobaric loading could help with space. And maybe play with blade shapes. How rattly are you largest ones?

have you thought of trying to make a centrifugal style rotary sub?

The problem for this mini sub is the tiny back enclosure, because if the little fan is successful at even generating 1 psi of pressure in the cabinet… Where is that pressure going to go but through the gaps in the blades of the fan, thereby neutralizing any pressure the blades pushed out or in. that’s why this works when it’s in a window because of very little blow-by or spillover pressure from either inside or outside. The smaller cabinet has to be pressure dissipative on the back side-down to the frequencies desired to be played, and timed to the enormously long wavelengths below 50hz. (100ft plus) It’s as though this design concept needs an indoor and outdoor separation just as hvac needs to discharge the heat to cool inside, and the two can’t share the same space… But people will still try to air condition their garage with a window a/c and no separator panel or wall. (Have seen it myself) But this is also this concepts limitation as to how loud it can create any sineuaoidal bass tones with any purity and intensity based on the action the pressure on the front or back of the fan blades it creates…makes a huge motivating force on the air to want to pass right back through the fan instead of out into the room with the listeners.

I would love to see a rotary inside a vehicle. Doesn't have to be big, something like a 4-6 inch. Get or borrow a SPL meter to see how many db's it makes

dayum if i could have one to see how is so diferent...

It would be interesting, how the fan speed affects the sound, less fan noise would be ideal. That rattle from loose fittings... well, you kinda can hear the bass. 🤭 It's still a neat consept, just keep working on it.

Hey, you could make it a portable window insert for demos.