21
Jan
18

Piezos Pt 3 – Amplifying and creating instruments

After preparing the discs and the buffer/amplifier in Part 2 of this series, I looked around for different instruments that could effectively be amplified and recorded with the use of piezo elements.

I also tried a few inexpensive commercial piezo contact mics, like these:

The top one (Cost: approx £1.50) has quite a large piezo disc inside a plastic cover and a sticky pad to fix it to the surface which is to be amplified; the bottom one (Cost: £1.25) is built into a (not-too-strong) plastic clip, with a foam pad to protect the disc.

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The more solidly the piezo is connected to the sound-producing surface, the better the sound obtained.  In other words, it’s best if the disc can be glued to the surface.  I did this with some of the non-valuable items:

However, I wasn’t keen on making this permanent addition to my instruments, and  looked for different ways of making temporary connections.  Each of these could be useful in different circumstances:

This double-sided tape is described as ‘removable’, and is less likely to damage either the piezo element or the instrument it’s stuck to, so is a good choice – although, at about £7.00, was rather expensive.   I hope to make use of it elsewhere in the house!  It’s also more suitable for a one-off performance or recording.  I’ve also read that Blu-Tac works in a similar way, although my experience is that it can leave marks; elsewhere I’ve read that insulating tape can be used – that might also be less sticky than conventional sellotape, but unlike the double sided tape, would have to go over the top of the piezo disc.

I also bought some clamps of different sorts:

The spring clips were very strong, so I would guess I’d have to be careful using them so as not to damage the piezos.  I have read of people using soft pads – made of felt or foam rubber, for  example – to put over the piezos when using them with strong clips.

In this way I had a variety of different methods of attaching the piezos to items I wanted to amplify or record.  The items themselves could be either acoustic instruments that just needed appropriately amplifying; or items that were not musical instruments, but which could be amplified – perhaps changing their sound, or revealing a hidden sound in the process – by attaching a piezo.

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As they are used to pick up sounds from vibrations in solid surfaces, the best acoustic instruments to work on would be those with sounding boards, such as guitars, zithers or other stringed instruments, several of which I had in my collection; as for non-musical instruments, this would be a matter of experimentation!  The advantage of using a piezo contact mic in these examples would be that, unlike a conventional microphone which picks up airborne sounds, the contact mic wouldn’t easily be affected by the nearby sounds of the player, other instruments, or external noises in the recording environment – e.g. traffic or the people next door.

First of all, the more conventional instruments.  These are just a few of the various things I tried the piezo mics with.  At the top are bells and a rainstick; at the bottom are a rattle (not perhaps, strictly speaking, an instrument!) and a zither.

The following sound file illustrates how these sounded:

In these experiments only the zither was recorded in stereo by using two piezos, but a stereo effect would certainly bring something to some of the others – for example the rainstick.

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Next, some uses of the piezos that created new instruments in themselves.  Both of these made sounds that, when picked up by the piezos were very different from the way they sounded in the room.

The first one uses a small snare – normally used for a snare drum.  This was purchased very cheaply (about £1.30) and attached to a wide, flat tin.  A 50mm piezo disc was superglued to the middle of the tin.

The second one is just a 50mm piezo disc with 4 lengths of piano wire soldered to it.  I’m not 100% certain of the diameter of the wire: it said ‘G0’  (i.e. ‘G zero’) on it, and was bought from a (classical) music shop about 30 years ago.  If it means Music Wire gauge 0, this would make it about 9mm, something like a thin top E guitar string, which is about what it seems to be.  The 4 lengths are approximately 6″, 9″, 12″ and 18″.

This sound file illustrates first the ‘snare’ instrument, then the ‘string’ instrument:

It’s surprising how different the sound through the piezo is, compared to the natural sound, especially the one with the soldered strings, which makes hardly any noise at all.  The small preamp also plays a part in preserving the lower frequency sounds.

The picture below shows, on the left, the three – I don’t know what to call them – strikers or activators, which I used to make the sounds from the snare instrument: the one on the left is a home made beater or mallet, made from a length of dowel and a wooden bead; the middle one is a wooden coffee stirrer, much more delicate; and the one on the right is a small cleaning brush.

Activators IMG_1281

It’s a good idea to make a collection of these if you’re going to make piezo instruments, as the way you interact with the instrument can make a big difference to how it sounds.  The picture on the right shows some more things I use, as well as pipe cleaners, fire-lighting spills and small emery boards.  This writer has a very impressive collection: https://skoglosa.wordpress.com/2015/05/06/contact-mic-guidelines/!

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The instruments required quite a bit of physical construction, since a framework was needed to support the sounding parts.  I bought some small square trays to serve as the bases, and cut lengths of 2x2cm wood for the uprights.

After glueing and screwing these together, I was able to attach the sounding parts:

The two on the right are the ones described earlier; the one on the left is simply a sandpaper disc with a 35mm piezo glued to the back.  The narrow space underneath the base can be seen in this picture.  The batteries and electronics would have to fit in this space.

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After the physical construction, it was time to add the electronics.  I’ll describe this in the next part of the series.

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