question about sound filter for my solo show

[Fedemuelas]

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 www.federicomuelas.com<p>I Have a problem with one of the pieces named “Dripping Sounds” and I wonder if anyone have an idea to overcome this problem.<p>Description of the piece “dripping sounds”<p>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. <p> 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.<p> 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. <p> 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.<p>Description of the circuit I have problems with in the piece:<p>-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<p>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.<p>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.<p>I would really appreciate any suggestion, you can e-mail me at [email protected]<p>Thanks a lot.<p>Federico Muelas

[Edd]

Ey Federico, que tal:<p>What you are doing sounds neat… and, oh yes, thank goodness for those grants.
It just seems that you are experiencing a light intensity swamping of the photocell /detector elements of the unit .
Typically the projected light level passing thru the fluid with no dye agent present would present the highest light level possible to the detector unit and set its benchmark of the highest output level experienced. Now if your detector receives the light that has been diminished by passing thru the dye medium, you are expecting an attenuation, in accordance to the dyes density/opacity. Therein, I believe, is your problem, you are expecting there to be quite a difference between the two extremes, whereas, in reality there is probably not enough diminishment of the light level reaching the detector.
Two methods come to mind initially, one of a mechano/optical solution and the other of an electronics nature.
I am thinking in the respect of the treatment of only one module/unit of your units infrastructure. Then you repeat the fix on all of the cells of the unit.
Since you are going to require the projected image at the highest level for the viewing audience, that variable must not be modified.
What I might suggest at first is the attenuation of the received light level at the photocell proper to “fool” the photocell and narrow out its response sensitivity curve.
Thinking in the availability of a proper attenuation medium, without having to obtain select pricey filter materiel from Edmund Scientific, etc. Find your closest auto tint shop and “acquire “ [FREE] some end of roll remnant remnants of different densities of grey. Now, you use as many layers at the face/front of the detector as necessary to diminish your detectors sensitivity down to the light level range that it is being subjected to.With main attention being to the full light level , as the muted light levels will just naturally fall into place.<p>If this optical solution didn’t fully acquire your optimal effect, the last aspect would be the incorporation of a sampling of the DC level out of the photocell (at the highest light level illumination) and then feeding this to one of the two inputs of a LM 339 I.C.’s linear comparator stage while its other input goes to a trimpot configured in a voltage divider bridge to adjust a variable DC reference/switching threshold for the unit. The output of the comparator feeds bias to either a bipolar or FET transistor utilized to shunt/mute the audio amp modules input to ground until that comparators set threshold level is tripped.
A functional operation would be the audio amp being normally muted , this with the illumination at its highest level (no dye attenuation) . As the dye permeates, the light level reaching the photocell would change, as would its output voltage , also the output voltage going to the comparators input would change accordingly. That is, until that voltage matches the level that is set up by the trimpot. That level you would manually set in as your desired light threshold that you want the unit to disable the muted audio and let the audio amp activate and pass on its tonal output.<p>73's de Edd
[email protected] ........(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs)<p>Well ,looks like Comcast’s on a roll ,minimal downtime lately !

It only took them 6 months.