Although I really enjoy to see how this project evolves and how quickly expert help is offered, I think you are getting a bit off-course by not prioritizing more important elements than an acoustic variometer system at this stage in your project.
Like I tried to explain before, if your model sinks twice as fast when it's airspeed is doubled, no useful information is given by any system measuring vertical movement. It would be the same as displaying the airspeed on a scale indicating vertical speed. Since this lineair relation between horizontal and vertical speed would not be realistic in any case, I think you should think of implementing realstic polars first before trying to measure vertical speeds at all, even in a world without natural sources of lift.
First make sure your glider behaves realisticly in laboratory conditions, which means only a single airspeed will give the best glide ratio. Notice that speed for the minimum sink is not the speed for the best glide ratio. The speed for minimum sink would give the longest flight duration, not the furthest possible distance which can be flown with any given altitude.
The next step would be to implemend sources of lift. Once you got that sorted (and like you have been warned before, this is going to be the hard part), you can think of how to measure these vertical air movements. Variometers in gliders are not constructed to measure the vertical speed of a glider. They measure the vertical speed of the airmass in which the glider happens to be.
When you got a system in place to measure it, only then it's time to think of an user interface to communicate this information like a speaker system which make sounds with varying pitch. I really doubt whether you will ever get good results if you reverse this proces like you seem to do now.
I've been flying gliders for many years. Myself, as well as many other glider pilots, do not use the acoustic vario or at least set the volume to hardly-audible or zero. The reason is simple: Every instrument and especially a vario-meter system, has a certain delay before they indicate proper values. Air movement has to be measured, usually by an airflow in some tube, and this measurement has to be transported using a mechanical system to some instrument housing gears before a needle moves or a speaker makes a sound. This delay could be as short as a few hundred miliseconds or even shorter, but it's still way too long when centering thermals.
There is a much better way to know when you have encountered lift. A glider's airspeed increases when entering zones of rising air. You can feel the g-force easily. Also, because generated lift increases quadratic with speed, the wings will make crackling noises. So you already have two sources of information on the movement of the airmass without delay and without the need to glance at an instrument panel. There is really no need for a fancy acoustic vario.
