If the crests of the two waves rise at the same time and in the same place, the waves are said to be in phase and reinforce each other to produce a louder sound. This is called constructive interference. This occurs when the two sound sources are separated by exactly one full wavelength. (One wave has a leading edge of one wavelength, but both are in phase at the detector. Therefore this device's knowledge is that of the wavelength and frequency of sound, so it may be easy to determine its speed in based on the relationship v = f. Microphones produce a very small amount of current, which makes sense when you consider how light the moving parts need to be to accurately track sound waves, the signal must be amplified by a factor of over a thousand. Any electrical noise produced by the microphone will also be amplified, so even small amounts are intolerable. Dynamic microphones are essentially noise-free, but the electronic circuitry built into condenser types is a potential source of problems and must be carefully designed and constructed with premium materials