Rotary Subwoofer Combines A Speaker Coil W/ a Fan

What happens when you combine a fan with a sub-woofer? Apparently, you get a high-efficiency ultra low hertz (3-5hz) rotary subwoofer!

First thing’s first, believe it or not, these things really do exist. [Chris] got the idea to build his own after seeing the TRW-17, a commercial offering of a rotary subwoofer.

The concept is pretty simple. If you use a giant subwoofer, you can get low frequency response, but it uses an immense amount of power to move a giant speaker coil. So what if you put something on a smaller speaker coil to increase airflow? Like, a fan or something?

The prototype [Chris] has rigged up is only a 300W amplifier (180W RMS), but as you can see in the following video, it literally shakes his house.

After posting the original test video he received a lot of questions about it, so he released another Q&A video:

47 thoughts on “Rotary Subwoofer Combines A Speaker Coil W/ a Fan

  1. I think it would work. On my Chrysler 200, if I leave one back window cracked open a little, the whole car resonates at around 7Hz from wind buffeting. It’s quite uncomfortable.

    1. think it? looks like he’s using one. a complete 5-blade assembly from swash plate and up..

      and his blades aren’t aligned… what a pain that’s gotta be with 5 different one’s to track..

    1. It’s a fan, where the blade angles are controlled by the sound source. At zero amplitude the blades are flat (no air motion). High amplitude deflects blades further, which pushes more air. By varying the degree of blade pulsing you can control amplitude… changing the rate at which you flip the blades can alter frequency.

      You have to be sitting in front of it for it to work. Sit behind it, and the amplitude is reversed.

      1. Or, actually in this case, he’s blowing into a semi-sealed room. So the overall room pressure climbs and falls based on the fan’s overall efficiency. The room leakage acts as a DC blocker : ) For really high efficiency, the blades should be able to swivel in reverse, effectively sucking air back out of the room!

      2. Having encountered the commercial one, it doesn’t actually work like that. The frequencies it can go down to are effectively below what we can truly hear. If you stand in front of it, it feels like any other fan really. It has to push air into a mostly sealed room for you to notice anything, as you’ll then ‘hear’ the sound as it changes the air pressure in the room. It’s below the frequencies we can truly hear, but at the same time it gives some things a much greater depth, as say the sound of a helicopter close by you don’t just hear but also feel as if you were standing right next to a real helicopter.
        They are seriously amazing speakers and can add a lot of depth to movies or music by adding in the sounds you can feel as if you were there.

    2. the subwoofer controls the pitch of the fan blades, so the blades are either pushing or pulling air, which is controlled by the subwoofer. think of the subwoofer acting as a solenoid that controls the fan pitch. Essentially it’s replicating what a speaker does (move air) but by using a much more efficient mechanism for moving air (a fan). Since the pitch of the blades can only be moved so fast, it’s only effective for low frequencies (mechanical mass, inertia, harmonics).

      The fan creates negative or positive air pressure depending on the pitch. Changing air pressure=sound.

  2. Since I was a kid I wanted to find a way of making something that had response this low, I thought of different ways of sealing environments, porting to the outside, everything.. nothing would do it… but this… this is brilliant!

  3. I’ve been a big fan of the rotary subwoofer since I first learned about it. The price however is very prohibitive! I am very interested in this project and may consider pursuing my own build of a rotary subwoofer.

  4. The blades on Eminent’s rotary subwoofer are specifically designed for the job; they are not standard pitch fan blades. It also uses a vector drive to very tightly control the speed of the motor to ensure that the output is as pure as possible. There is a reason that the original product costs $12K.

  5. the human hearing range covers about 20 octaves of frequency detection, this can easily be tested, take a frequency variable oscillator producing a square, pulse, triangle or ramp wave and run it through an ordinary amplifier and speaker, In frequencies above 20 HZ the waves sound more like a pitch and less like a tempo the higher they go, but it is not until they are in excess of about 300HZ that they lose all semblance of tempo and are heard only as pitch. Below 20 HZ the waves sound more like a tempo and less like a pitch the lower they go, but it is not until they are less then around 3HZ that they lose all semblance of pitch and sound only like tempo. The transitional range is approximatly between 3HZ and 300HZ, a range of over 6 octaves, 1/3rd of the entire 20 octave frequency detecting ability of the human ear.

  6. Oh noes. Do the neighbors laugh or complain about bangin me juilie? Oh I’m feeling all 7, 5 and 3 hurts. Did not enjoy. Unsure about how Zee Germans feelin bout this.

    1. That is a pretty odd argument. RMS power is a very useful calculation, and is a common standard used in many different industries. The idea that it “isn’t useful” because it isn’t equal to the heating power of a waveform is pretty much a non-sequitur.

  7. Forget dubstep, this is fanstep. A 1 horsepower 220 volt three phase motor can be bought pretty inexpensively, so can a 110 volt single phase to 220 volt three phase variable frequency drive.

    What I’d like to see someone try is a dual voice coil subwoofer using one coil as a shaping control with counter force to restrict over-driving and distortion from high power going through the other coil. Ie, when the sound signal hits maximum amplitude, apply a carefully shaped opposing signal to the other coil so the cone doesn’t overshoot.

    Should be possible with current electronics.

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