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Ground Control: Sun 31st May 2015

Maplin's Bone Conductor Transducer

This little critter is Maplin’s Bone Conductor Transducer offering for not so cheap at £9.99! [ Maplin ] It is a small, sturdy and relatively weighty device, due to a metal body housing two coils and a metal actuator. The metal plate photographed above in between the screws is a moving actuator, which induces vibration into any surface the device is pressed against or adhered to.

This device is essentially an incredibly tiny speaker rated at 1 Watt of Power. This power limits how much we can drive the speaker from the amplifier, and it means the transducer induces relatively tiny force into the surface it is pressed against. Depending on the surface of your choice, the transducer seems to be more effective when stuck against the jaw or ear bone, as it is advertised. But this doesn’t stop us from sticking it on any surface imaginable, and experimenting how effectively it conducts the sound into metal objects, wood, plastic or even glass.

It’s easy to drive this too hard as it requires little power. So some care is needed with the amount of amplification applied.


Using the Transducer as a Pickup

What’s more interesting though, is to use this transducer as a microphone instead of a speaker. By soldering the transducer to a Male XLR connector, I can plug this into the Mixer’s microphone input and put the Gain right up.

transducer pickup

This turns the little speaker into a microphone which pickups any vibrations from the surface it is stuck onto! I’ll put some recordings done using this method very soon. Although in contrast to a proper Guitar pickup, this has much lower sensitivity to the vibrations of a string or instrument body.



The Bone Conductor Transducer is much more rewarding perhaps to use as a movable pickup, in close proximity to a vibrating string or body. Otherwise, acquiring another unit of those to turn into headphones you can stick on your ear bones would definitely be an interesting endeavor; for any of the wild ones out there who want to try this crazy idea.


Ground Control 

At Hackoustic, we love Piezo discs. We use them in the Frame Project.  As Piezo discs are incredibly sensitive, high impedance components, it is important to provide adequate shielding from any external interference that may happen, as the signal goes from the piezo discs to the amplifier inputs. Hum noise is a big issue in the Audio world, especially when using Piezo discs and Guitar pickups.

This great PDF written by Bill Whitlock [ link ] sheds some light on the mysteries of the Hum, and how to get rid of it. This is especially useful when making your own DIY guitar or Piezo pickups. The first step is to use high performance shielded audio cables such as Belden’s 9259 Coaxial Cable. [ Farnell ] This will ensure no hum noise is picked up from the cable going from source to destination.

It is recommended to read the PDF to get an idea of this whole situation. Other solutions is to steer away from using mains power, and using batteries only at the amplification stage. Active DI boxes such as Behringer’s Ultra DI is an example.


Thank you for reading, and Good Luck in Your Projects! 

I hope this post has been some help. We’ll continue rummaging through Maplin’s goodies and Kits at the next meetups. For now, stay tuned, and get in touch.


In the true Tradition of Hackoustic, We leave you with is basically a Gigantic Industrial Sawblade, the Mother of All other Sawblades. (saving this one for a summer project, stay tuned in)



Tony Hardie-Bick: Sun 25th May 2014


Last meeting on Sun 25th marks one of our most successful meetings yet. It was overwhelming to witness such great attendance, with such a variety of people from different practices, ranging from visual artists and musicians to engineers and product designers. Below is an excerpt of the discussions that took place.

piezo impedance

Piezos are an essential tool to pick up surface vibrations, and here at Acoustic Hacking, we love them for their abundant availability, simplicity and versatility in a wide array of applications. As you can see, this simple circuit [drawn by Tony, a guest practitioner], may be needed to remove the ‘tinny’ sound, an issue commonly associated with piezo discs. The piezo-electric material has very high impedance, and this circuit is designed to match the impedance to mic level input on your mixer or audio interface.

Another tip is to use a shielded cable, to further prevent hum or electromagnetic interference being picked up along the cable.


Other discussions included how to design a ball for the blind. Some example of such a device/ball are photographed above, sitting on the table. The idea is to design a highly resonant structure embedded at the core of the foam ball. This structure can either be activated by movement of the ball, or possibly the vortexes of air can be harvested through the crevices of the ball to vibrate this ‘strucutre’; much like a whistle — example of whistle footballs commercially available.


Hacked Watkins Copicat Tape Echo by Tony Hardie-Bick

Quoting Tony from an email:

The machine is a Watkins Copicat Tape Echo, made in the 1970s and 80s, there were a number of slightly different designs, some with valves, some with variable tape speed, some using op-amps etc. My modification was to put the four playback heads at non-equal time differences along the tape, and to put two of them on a separate channel, to get an uneven stereo echo, which builds to create complex distorting stereo textures.

The thing that’s perhaps interesting, electro-acoustically, is the piezo mic on the tape arm, which picks up the sound of wheel-scratching and actual physical tape hiss, which can then be mixed in with the main signal, or just use on its own so the thing becomes an instrument in its own right.

The piezo idea was prompted by a performance in Vienna in 2011 by Martin Blazicek and Andras Blazsek. The performance can be viewed here.

Also I wanted to share this link as part of the discussion. This is Michael Vorveld, from Berlin, who I also saw in Vienna. He uses light bulbs in series with bimetallic strips to generate performances like this.

I think the sound also comes from piezos, picking up the vibrations from the bimetallic strips as they switch on and off.

The concept of using bimetallic strips is very interesting and unexplored, possibility to look into this in future workshops!


Again, huge thanks for the people who attended and contributed to the workshop this time. Please stay tuned here for an updated agenda for next meeting, and possibly another guest practitioner. The meetings are held last Sunday of the month, so ext meeting is going to be on:

June 29th 2014 at 7pm

It is a possibility workshops might be arranged in between those meetings, those will involve more making! this will also depend on people’s desires.

Any enquiries, please email acoustichacking@gmail.com