Directional microphones roll off at 6dB per octave.
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A hearing aid directional microphone inherently rolls off low frequencies at a rate of 6 per octave due to the internal spacing subtraction between its dual ports, requiring specific frequency equalization to match an omnidirectional response. [1, 2]
Frequency Response and Equalization Mechanics
- Low-Frequency Roll-off: The subtraction process between the front and rear microphone elements inherently reduces low-frequency sensitivity, causing a 6 dB-per-octave slope where low-frequency sounds are attenuated. [1, 2, 3]
- Equalization Trade-off: Hearing aids apply internal amplification (equalization) to boost these low frequencies so the overall frequency response mimics an omnidirectional microphone. However, boosting low frequencies electronically also increases internal microphone noise. [1]
- High-Frequency Performance: Directional advantage is most prominent and stable in the mid-to-high frequency ranges (typically above 1,000 Hz), which are critical for consonant discrimination and speech understanding in noise. [1]
Factors Impacting Frequency and Directional Response
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