Piezos Pt 1 – General

Piezos, Piezo Sensors, Piezo Transducers, or Piezo Elements are small, cheap components that can be useful in several different ways to the electronic musician.  I had some ideas for ways I’d like to use them, and this series will describe some projects in which piezo elements were employed.

A transducer is a device which changes energy from one form to another – for example, tape heads and record pickup cartridges are transducers as they change magnetic signals on the tape or movement in the grooves of a record into electrical signals; microphones and speakers are transducers because in the first case they change movement in the air into electrical signals , or in the other they change electrical signals into movement in the air.

Piezo elements are transducers because they can transform physical movement into electrical signals like a pickup cartridge, or electrical signals into movement in the air like a speaker.  They do this not by sensing magnetic fields, like a tape head or guitar pickup, but by the movement of crystals, and this is what a piezo element has inside it.

Piezos work especially well when attached to something which will vibrate and produce electrical signals which can be amplified, or can amplify the vibration of signals fed into it.

In everyday life, they’re usually found in mobile phones, in buzzers or in place of speakers in smaller children’s toys.  This gives a clue as to the different ways in which they can be employed in electronic music circuits: as microphones, as speakers, or as triggers for switches.

Much of the information below was gleaned from Nic Collins’ book Handmade Electronic Music, and his series of videos on YouTube called Hack of the Month Club.

First of all, this is what piezo elements look like if you buy them from a components supplier, or take one out of a phone or musical toy:

or sometimes like this, if they come in the form of a sounder or buzzer – in this case, the element can be carefully removed from the plastic surround.

They vary in diameter from 10mm to 50mm.  I have used some of the smaller ones, but most of the ones I have are 18 or  20mm, and 27 or 35mm.

[Edit: I have usually got the best sound out of the larger diameter ones, so these are the ones I use for preference, unless space dictates a smaller one has to be employed.  This means I usually choose the 35mm, which cost quite a bit less than the 50mm ones; but I’ve occasionally used the 50mm ones for special purposes].

When I buy them, I prefer the ones with the leads already soldered on.  This saves a job – and it’s quite tricky to do the soldering effectively – and they’re still very cheap.  The last batch I bought worked out at about 12p each for the 35mm diameter ones, and just 6p each for the 18mm ones.

Perhaps the first piece of music to use transducers in its realisation was Cartridge Music by John Cage, composed and first performed in 1960. As described on the webite of the John Cage Trust: ‘The word ‘Cartridge’ in the title refers to the cartridge of phonographic pick-ups, into the aperture of which is fitted a needle. In Cartridge Music, the performer is instructed to insert all manner of unspecified small objects into the cartridge; prior performances have involved such items as pipe cleaners, matches, feathers, wires, etc. Furniture may be used as well, amplified via contact microphones. All sounds are to be amplified and are controlled by the performer(s).’

Another composer who famously used transducers was David Tudor. Tudor – who was closely associated with John Cage – created a piece called Rainforest – originally in the mid 1960’s, but it went through a number of changes during the rest of the decade as Tudor’s techniques and equipment developed. The piece was based on the idea of making objects other than speakers vibrate, picking up the sounds they made with microphones and then filtering and mixing the resultant sounds.

‘My piece Rainforest IV‘, Tudor explained, ‘was developed from ideas I had as early as 1965. The basic notion, which is a technical one, was the idea that the loudspeaker should have a voice which was unique and not just an instrument of reproduction, but as an instrument unto itself . . .’

‘. . . I eventually acquired some devices called audio transducers. They were first developed for the US Navy because they needed a device which could sound above and under the water simultaneously . . . I had them in 1968 when MC [choreographer Merce Cunningham] asked me for a dance score and I decided that I would try to do the sounding sculpture on a very small scale. I took these transducers and attached them to very small objects and then programmed them with signals from sound generators. The sound they produced was then picked up by phono cartridges and then sent to a large speaker system.’

‘Several different versions of this piece were produced. In 1973 I made Rainforest IV where the objects that the sounds are sent through are very large so that they have their own presence in space. I mean, they actually sound locally in the space where they are hanging as well as being supplemented by a loudspeaker system. The idea is that if you send sound through materials, the resonant nodes of the materials are released and those can be picked up by contact microphones or phono cartridges and those have a different kind of sound than the object does when you listen to it very close where it’s hanging. It becomes like a reflection and it makes, I thought, quite a harmonious and beautiful atmosphere, because wherever you move in the room, you have reminiscences of something you have heard at some other point in the space.’

(from An Interview with David Tudor by Teddy Hultberg in Dusseldorf, May 17-18, 1988, http://davidtudor.org/Articles/hultberg.html).

A reviewer present at a performance of Rainforest described the appearance and sound of the piece as follows: ‘The entire piece sounds at first like an ethereal insect chorus, but the layers gradually disperse into patterns of jagged counterpoint, which in the performance seemed to harmonize perfectly with the movements of the dancers . . .

‘Most of the sounds are created by sine tones being reverberated through a forest of suspended metal containers, pieces of junk that function as “biased” loudspeakers imparting their own timbral colouration to the sounds which pass through them. These sounds are picked up by contact microphones, fed back into Tudor’s mixing and filtering controls, and then recycled back into the expanding forest of increasingly hybrid noises. The array of metal containers usually fills an entire gallery, and spectators are invited to walk around and put their heads inside the containers.’

(Roger Sutherland, Musicworks, Number 75, Fall 1999, http://moderecords.com/catalog/064tudor.html)

Some modern performances of Cartridge Music will use piezo elements instead of cartridges, although this might be considered cheating. Piezos, on the other hand, are ideal for achieving the kinds of effects employed by Tudor in Rainforest, and the different projects I planned with them will hopefully cover these uses and more.

Part 2 of this series of articles is here.