Transducers / Exciter Speaker

I saw this video from a nicola ratti performance https://www.youtube.com/watch?v=v7DDDeK4Xjg (it starts at 1:08) he seems to use an audio transducer (actually the opposite of a contact mic) on a string instrument, not to capture the sound but to trigger it. I wonder if anyone has any recommendations on this.

3 Likes

You can find relatively cheap audio transducers for very little money (look for Dayton Audio’s Exciters). I used them a lot for various projects, last time was to make a plate reverb, they work really well for the price.
I can’t really see how Nicola Ratti is using it in this video though, it looks as if it’s directly in contact with the strings…

You can actually use a piezo disc as a transducer (just add an audio transformer to adjust impedance on the output of a small amp), it can work pretty well, depending on the surface it’s attached to, I used it on some resonant objects for a sound installation two years ago. Nicolas Collins explains it in his book “Handmade Electronic Music” :
http://www.nicolascollins.com/handmade.htm (he also explains you can use small motors, vibrators from cell phones etc.).

If you want to work with strings though you might want to drive an induction coil and use a small neodyme magnet to create an electromagnetic field and drive the string/object present in between. It’s the same principe as an eBow, but an eBow works by feed backing an electromagnetic pickup and driver, here you can send whatever signal you want in the string. Be careful though you need to match your impedances and maybe add a fixed resistor depending on the power of the amplifier you use.
I learned these techniques during a workshop with media/sound artist Aernoudt Jacobs, but my notes with the technical details are far away from me right now.

Lastly, if you’re into Eurorack, take a look at Pulplogics’ DRVAC Tile : http://pulplogic.com/product/drvac/

10 Likes

Found these a couple links downstream from the DRVAC tile:
http://www.ebay.ca/itm/Tectonic-Elements-TEAX11C005-32-11mm-Exciter-32-Ohms-/221568881926?hash=item339688d506:g:bE4AAOSwDN1UMt~c
looks like a decent little part for building plate reverbs or driven resonators. Guess it should also work in reverse as a coil-based contact mic…

yes, this looks interesting. also good way to expereiment with plate reverb. ÂŁ18 postage to the UK! not as cheap as it first looks.

You can do some really cool stuff with exciters. We did this project a couple of years ago, where we used a string quartet as loudspeakers/resonators, working with the strings’ sympathetic resonations: http://www.kvsu.net/projects/acousmatic-strings/
The sounds were all generated with c-sound and processed via modular synths, then sent to the exciters.

8 Likes

great stuff.Did you use bone conducting exciters for that project?

thanks! We used some really crappy exciters. Actually… the whole idea came after building the exciter-speaker kit from Technology Will Save Us and we ended up using for of the exciters that came with the kit, though we replaced the amps with better ones.
We did start to experiment with more high-quality exciters, we also tested some of the big ones for bass (which is a bit of an issue with the smaller ones).
Aren’t “bone conducting” exciters just a kind of brand name of the Dayton Audio ones? Or is it a specific technology type of?

Been wondering about exciter drive for the lazy DIY-er. What did you use?

My current solution to (basically) this problem is to create a circuit where a unity-gain op-amp closes it’s feedback loop around a bipolar class A-B. Prob not the cheapest way to do it, but actually can be a decent way to drive small voice coils (< 10W) right down to DC with surprising fidelity.

Seen this design disastrously oscillate though when another guy tried to copy my protoboard hack with like 10dB of gain in the loop, mind you!

We used some PWM (T class ) amps. Not the best audio quality (but a lot better than the TWSU ones), but small, affordable and powerful enough.
We used one amp for every exciter

I am beginning work on an installation piece where I hope to make 6 singing dangling objects. I still need to experiment with what objects I would use, but I’m imagining big aluminum sheets or thin wood panels or found shapes.

Anyways, I’m hoping to test out a setup of:

6 separate output channels from k-mix
—> 3 small stereo class d amps
—> 6 exciters attached to objects
powered by this one power supply

I was wondering if @papernoise, @rick_monster or anyone with experience in this area could let me know if i’m making a silly mistake. Would this setup work? I’m mostly unsure of the power supply and amp/speaker pairing…like can that power three amps sufficiently? I’m not very experienced with diy power and speaker stuff. I can make custom cables (ie. two 1/4" to stereo 1/8" for two channels kmix to one amp)

Also, I don’t really know what to expect in terms of volume and frequency range, but I don’t think it needs to be amazing. I just want to make sure it is somewhat loud and somewhat good fidelity I guess.

Thanks in advance for any help!

Also, @papernoise, the kvsu piece is really lovely. Great job with that! I’m kinda ripping your ideas…

2 Likes

class D amps is exactly what we had used with the exciters. Commercial class D amps are usually stereo so I don’t see the big problem with attaching two exciters to each. But of course this depends on the actual exciter.
Not really an expert but the amps are rated for less than the speaker, which should be safe, the problem is usually when you have an amp which is too powerful for the speaker.
If you want to go with a switching PSU for this maybe look at Meanwell, while they are not made for audio they seem to work ok for most applications. The only thing to keep an eye on is how much current the whole system will draw, 480W seems overkill, but you should ask somebody who knows more about this than I do.
From a more safety-related point of view you’d certainly be better off using 3 12V bricks instead of an open frame thing like this.
For the Acousmatic Strings thing we used amps with an enclosure, and these came with their own brick. These are often sold as a low-cost music amp solution and will not be much more expensive than the more DIY solution you found.

Hehe no problem, keep me updated I’m really curious to see what you make with this!

A question to the community: Are you all ok if I split this topic into a “exciter speaker” one? This doesn’t have much to do with contact mics anymore…

1 Like

Thanks for the reply!

I’m going to look into those things and get back to ya. For now, I’d be happy with a new thread. I aaaalmost did it for that post :grimacing:

Okay, so after reevaluating, I came up with this shopping list:

6 of these exciters
3 of these amps

much more simple…the lepai amp looks good, but do you happen to know what you used if its better? From what I can tell, this amp is 20W and the exciter is 24W so it will be a little underpowered. maybe that is fine since any more would approach more speaker distortion?

2 Likes

Forgot to add one thing. I’d like to encourage you to try out different exciters before committing to one solution. We made the error to not do that beforehand, and it would have totally be worth the extra work in retrospect. So, get a bunch of them, try them out, see how they behave and sound. Not all exciters will work the same.

1 Like

When you’re talking about amplifying multiple singing dangling objects and working with exciters it sounds like you’re making a version of David Tudor’s Rainforest IV. I imagine you’re aware but just in case not, worth looking into the beauty of that piece that has been presented many many times
http://www.getty.edu/research/tools/guides_bibliographies/david_tudor/av/rainforest.html

8 Likes

This sounds really cool. Excited to check out the show!

1 Like

I’ve been meaning to update my work in progress, but post opening, here are some photos of my installation utilizing transducers on objects. thx @papernoise @stephenvit and @sns for the wonderful information.

Today, I am performing the 6 channels of audio with precomposed and improvisatory textures. If you’re in Austin, TX stop by today between 11-6p.

If anyone is interested I can add some more info about my setup. its pretty fun :slight_smile:

Uploading: IMG_0276.JPG… Uploading: IMG_0278.JPG…

3 Likes

Something went wrong with the image upload.

A dad in New England makes DIY transducer speakers with “flat frequency response”, wired in serial without a crossover. Says they cost ~ $45 each including mounting hardware, which consists of hooks and plastic fishing line. A good set of studio monitor speakers that don’t consume much interior space are missing from my setup. Perhaps this is the answer?

He mentions they bottom out around 120 Hz so a subwoofer with a crossover would be useful to get a full spectrum. The part where he mounts the transducer and counter weights to remove material resonance is particularly interesting.

4 Likes

at 14:30 in the video…stoic…15:30…ok I’ll move a lil’ bit.
edited to say, this video is super interesting. This dad from New England is the cool science teacher I never had.