Sound Localization

This is the code i am currently employing however i am fairly sure my coefficient is completely wrong. I understand it should have a relation to the distance of the microphones but not sure how to calculate or determine what this should be. Do I need to workout what the average time it would take for the sound to travel the distance between them and use that as the coefficient?

I have tried a few completely random values for this but as im sure you can guess had no positive results.

float coefficient = 400;
float soundAngleY = srvoPosn[y];
soundAngleY = asin (coefficient * summa / 2048.0) * 180.0 / PI;