Installation project: coupling subwoofer speaker to material

[mcld]

Hi - I have a slightly unorthodox question which I hope you can help me with. I'm working on a kind of audio/visual project and we're planning to add an extra subwoofer to our sound system - but instead of using the speaker for actual subwoofer purposes, we want it to shake a fairly large piece of thin material (like silk), hanging up, so that you can literally see the sub-bass channel rippling through the material.

I've got a speaker and a driver, and what I want to know is: what do you think would be the best way to couple the speaker vibrations to the material? I could attach the speaker cone directly to the material, but alternatively I could (presumably) take the cone right off and attach the material directly to the coil.

What do you think?

Thanks in advance
Dan

 

[pinkmouse]

Cool idea.

Well, you will need a very high excursion woofer to make much of a movement in the material. If you are not bothered about the noise then just attach the cone directly to the fabric. Although the driver will be relatively quiet, (as it should have no baffle or enclosure), it will still make a perceptable noise. If you want a quieter method, you should remove the cone, (but leaving the spider) and attach the fabric to the voice coil. You will have to be careful not to drive the VC into over excursion as it will have no air loading, and you will need to tune the drive frequency for best effect, merely feeding it with the audio signal will likely produce unsatisfactory results.

 

[mcld]

Thanks pinkmouse, that all sounds like good advice.

I think I will take the cone off - don't really want much perceptible noise.

I have a plan for tuning the drive frequency. The audio is all coming from a computer, so I've written a little program to convert an audio stream into a single pure tone (a sine wave at the strongest frequency), and then shift it up/down in octave leaps until it's within the speaker's strongest range. That should give me the best chance of a visible wave, whatever the input...

 

[pinkmouse]

Sounds like you have thought this through fairly well. However, you might want to increase the frequency resolution of your program, the best frequency to energise the fabric might need to be tuned to 0.1Hz. You could also use the audio signal to drive the gate of a "ducking" compressor run from a signal generator.

 

[RHosch]

You might get better results attaching a horizontal rod to the VC after removing the coil. Hang the fabric from this rod. This will produce linear waves in the cloth instead of radially radiating waves... and will probably make a more consistent and noticeable visual effect.

 

[BassAwdyO]

I wouldnt detatch the cone if I were you. The surround and spider work together to center the coil in the gap, and without one, the coil might rub the sides of the gap. This could lead to premature failure of the speaker. What would be better instead would be to leave the full cone and attach a rod to the center of the cone. the rod would then be connected to the curtian. I wouldnt drive the speaker with anything but a passband of the signal being played because if the transducer produced any noticeable sound, it wouldnt be noticed due to the mains playing the same thing, but if it were playing something entirely different it would mess up the sound of what was being played. Try different passbands curtian tensions and curtian sizes to determine what is optimal in terms of visual effect. I'd really like to hear your results

 

[simon5]

You could cut a bunch of circular holes in the cone, symmetrically, so you can keep the surround intact and protect the driver. Then stiffen it up with glue or something. To see it moving, you better wait for the new HE18 from Stryke Audio.

 

[Mr Evil]

You don't need a high excursion driver. You can achieve any excursion you want using a mechanical transformer, i.e. a lever.

 

[BassAwdyO]

now wouldnt that be an idea for a speaker too. instead of needing big gaps or big coils we could simply us a high power coil with a small gap and small magnetic xmax. then use a lever system that would magnify that small xmax into a large xmax which the cone would perform. We'd need high BL, but that shouldnt be hard with a big magnet and small gap. especially if we squeeze alot of coil in the gap.

 

[Cal Weldon]

Would a Bass Shaker or two work?

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-027

Cal