Building a transducer Orchestra

Building a transducer Orchestra

For some time now I have been working with transducer speakers mounted on acoustic instruments as a kind of hybrid electroacoustic blend that bridges the different sonic realms of the virtual and invisible wall of loudspeaker sound and the physical and spatial reality of acoustic objects. But I had only used ad hoc arrangements of the different instruments needed for the musical experiment at hand. As the project developed, I wanted to create a more stable and well defined arrangement of instruments and speakers.

The instruments that had worked well as acoustic loudspeakers were mainly instruments where large surfaces or sound boxes are involved in creating or amplifying the sound of the instrument:  drums, stringed instruments, and cymbals.

I had also experimented with attaching exciters to other various instruments like the reed of a clarinet etc, but that seemed to work less well as wind instruments also need a stable air coloumn to amplify the sound properly. I did also look into other possible ways to set physical objects in motion, including solenoid acuators striking instruments, and inducing vibrations into strings by magnets like for instance Alvin Lucier did in his piece “Music On a Long Thin Wire” 1Alvin Lucier: Music on a Long Thin Wire, CD – Lovely Music #1011, where a combination of current and magnets is used to set a piano string into motion. But looking at the complexity of works like for instance the electromagnetic piano developed by Andrew McPherson2A. McPherson. Techniques and circuits for electromagnetic instrument actuation. Proc. New Interfaces for Musical Expression, Ann Arbor, MI, USA, 2012, 3http://www.eecs.qmul.ac.uk/~andrewm/mrp.html I decided to stick to the much simpler infrastructure of transducers for now. In addition, I did not want to get stuck building mechanical organs or other instruments when I had so many other things left to explore in my project. Also transducers are faster, have broad frequency response and can reproduce a wider range of sounds than both solenoid hammers and magnetized strings. I did also manage to achieve an alternatice string sounds by attaching some tiny transducers directly across several strings of a zither, which then sounded very different from just placing a transducer on the zither’s sound box.

To put it all together as a well defined “orchestra” I used the instrument categories above as sections of an orchestra (strings, drums, cymbals), assembling four different instrument members of the same kind in each group. That resulted in 12 outputs for these three groups of transducer instruments, in addition to one group of four loudspeakers, making it 16 outputs in total. With this setup it was easier to orchestrate ideas using one or more instrument group at a time or different combinations of groups. I made a software interface where I could pan a signal gradually between groups as well as between the instruments within the groups. I also added a function of automatic panning executable at each segment onset. This can be set in percentage so that 0% means that the pan position is static, anything <50% causes the signal to pan automatically within the current instrument group, and 50-100% would make it pan across all the outputs of all four groups.

I did not find any multichannel amplifier that would fit my purpose, so I assembled a 12 channel power amp in a 1U rack case, using six 2x50w stereo class-D amplifiers, and added separate volume controls for each output channel.

12x50W would mean a maximum power output of 600W, but I do not think I will ever have all 12 channels playing at full effect at the same time, so I decided that using two smaller 150w power supplies would probably be enough. The most powerfull transducers that I use are rated 40w but most are just 20w or 10w and many of the smaller ones are only 2w, so the transducers will probably burn out long before the power supply says goodbye.

References   [ + ]

1. Alvin Lucier: Music on a Long Thin Wire, CD – Lovely Music #1011
2. A. McPherson. Techniques and circuits for electromagnetic instrument actuation. Proc. New Interfaces for Musical Expression, Ann Arbor, MI, USA, 2012
3. http://www.eecs.qmul.ac.uk/~andrewm/mrp.html