"Eintönen" - "soundin" with low power audio equippment

Equipment:

Computer

battery powered Lenovo Thinkpad with 9cells plus extra Accu 6cells

Audiointerface

ESI Maya USB 4 channel in and 4 channel out on line level

Microphone

sound core TetraMic Ambisonics microphone. 1st order, 4 channels

Speaker

Tetrahedral speaker with 4 speaker each 40W/8Ohm

Amplifier

4 channel Class-D amplifier TK2050 Tripath Audio Amplifier, with 50W@8Ohm

Microphone Preamplifier

Tascam DR-680 with Sound-core adapter

Battery

recharbable sealed lead acid battery: 12V/12Ah

Piece

"Impulse Response" is an experimental piece, programmed in PureData, which plays a short impulse and calculates an score out of it, controlling the recording and play back of 24 Sample buffers with each 10 second, so the resonant frequencies of the dome and speaker/microphone position will be play back. The amplitude was controlled manually and adjusted to the noise level of the audience.

power supply

As an power supply one 12V/12AH battery was used and played for 12 hours. With measurement of current and Voltage, a constant current of 0,3A was needed for the amplifier, 0.4A for the recorder with microphone amplifiers. The computer was powered on old Accumulators and had to be recharged after 4 hours with a second battery. Peak power needed by the amplifier has been 1.2A if playing with lower frequencies, but on average not more than 1A was needed. So even after the performance there was still 12,4V on the battery.

This shows that concert can be done with small batteries in the sound dome.

Result

As as result, it could be shown, that playing with low power speaker, even four, is loud enough in the very reverberant room to play a piece for about 150 visitor in the 320 m2 room and 200 m3 volume, whereby the composition is clearly heard, even when a lot of people are talking. If there are less people in the room, smaller amplifications could be used to get an sound-level over 90dBA, when no frequencies below 150Hz are relevant.

Therefore the construction of an low-energy ambisonics system can be done with less then 100W amplifier power, but using 400W peak would sound nicer on impulse charakteristics.