An ideal pressure microphone responds only to sound pressure, with no regard for the

directional bearing of the sound source; as such, the microphone receives sound through a

single active opening. In reality, a pressure microphone exhibits some directionality along its

main axis at short wavelengths, due principally to diffraction effects. As we saw in Figure 2.12,

only as the received wavelength approaches the circumference of the microphone diaphragm

does the microphone begin to depart significantly from omnidirectional response. For many

studio-quality pressure microphones, this becomes significant above about 8 kHz.