question about sound filter for a solo show

Hi, My name is Federico Muelas, I�m an artist working with technology and I�m having a solo show in Barcelona at the end of the year titled �the sound of the chocolate smell� where I�m showing my recent installation pieces, you can check the info of the sound and more extended info about the piece at http://www.federicomuelas.com

I Have a problem with one of the pieces named �Dripping Sounds� and I wonder if anyone have an idea to overcome this problem.

Description of the piece �dripping sounds�

The "dripping machine" and the "sound Screen" are the two apparatus the installation is comprised of. The first one, constituted by A 0,22 gallons water container, a lighting and two lenses device, a ink dripping system and a microcontrolled flushing system, is in charge of the following three tasks; the optical projection of the enlarged image of the drop branching, the drops dispensation and the water renovation cycle of the liquid container where the ink is dripped. The second one translates the moving image projected over its surface into sound through the 20 photosensitive independent modules installed in its back face.

The modules, wired individually to 20 speakers encircling the screen, are distributed in an equidistant grid of five columns by four rows, each row comprises four elements connected in parallel; three individual modules and an electronic circuit that provides an exclusive sound. Having the same natural source, the five different sounds are modified in order to transform their pitch value, increasing vertically in a range from low frequency in the lower part of the screen to high in the upper one.

The photocapacitor installed in each module determines the variable volume of the sound it broadcasts through the speaker. The quantity of light this device receives is inversely correspondent to the volume of the wave it emits and viceversa.

Therefore the projected image of the drop, while it is growing and ascending from bottom to top (due to the image vertical flipping due to the combination of two concave lenses), activates the sensors installed over the screen and produces a sound that goes from low to high frequency values.

Description of the circuit I have problems with in the piece:

-A 20 seconds sound recording circuit sends a sound signal to a 1-watt amplifier. -The signal input of the 1-watt amplifier is connected to a photocell connected to ground that increases or decreases the incoming sound signal depending on the light it receiving. -The 1-watt amplifier is connected to a speaker that emits the sound

Description of the problem: -Supposedly the volume of the sound emitted by the speaker should be inversely proportional to intensity of light reaching the photocell. -Therefore when the photocell is receiving light the speaker shouldn�t emit any sound, but this doesn�t happen, there is always a sound in the background and since there are in the piece 20 of these circuits the sound is really annoying.

The solution I�m looking for: _What I need is to �cut� any sound emitted by the speaker under a determinate volume threshold, let�s say under 18 dB.

I would really appreciate any suggestion, you can e-mail me at d2ec@hotmail.com

Thanks a lot.

Federico Muelas

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