The Physics of Parabolic Microphones: Frequency Dependence of Gain
16 days ago
- #parabolic-microphones
- #acoustics
- #wave-physics
- Parabolic microphones use large dishes to capture faint sounds by focusing them to a central point, similar to how telescopes focus light.
- Early adoption of parabolic microphones included recording bird sounds, with a 32-inch dish first used to capture avian vocalizations.
- Parabolic microphones favor high frequencies, resulting in a 'tinny' sound quality, while low frequencies are not amplified below a cutoff frequency.
- The cutoff frequency for a parabolic dish is determined by the formula f_c = V / (2a), where V is the speed of sound and a is the dish diameter.
- Gain in parabolic microphones increases by 6 dB per octave for frequencies above the cutoff, due to the relationship between wavelength and dish aperture.
- Reciprocity in wave physics allows parabolic dishes to function similarly whether used to focus incoming waves or emit collimated beams.
- Diffraction effects at the dish aperture influence performance, with smaller wavelengths (higher frequencies) experiencing less diffraction and higher gain.
- The focusing capability of a parabolic dish relies on its shape reflecting parallel waves to a single focal point, ensuring constructive interference.
- Interference and diffraction principles explain why parabolic dishes lose effectiveness when the wavelength exceeds the dish diameter.
- The gain of a parabolic microphone is proportional to the square of the ratio of dish diameter to wavelength, favoring higher frequencies.