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Filters

Filters. Definition: A filter is a frequency selective system that allows energy at certain frequencies and attenuates the rest. Filters. Parameters: Center frequency (resonant frequency) Lower cutoff frequency (half power point or 3 dB down from center frequency).

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Filters

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  1. Filters • Definition: A filter is a frequency selective system that allows energy at certain frequencies and attenuates the rest.

  2. Filters • Parameters: • Center frequency (resonant frequency) • Lower cutoff frequency (half power point or 3 dB down from center frequency). • Higher cutoff frequency (half power point or 3 dB down from center frequency). • Bandwidth (high cutoff - low cutoff) • Slope as measured in dB per octave attenuation.

  3. Types of Filters • High Pass Filter

  4. Types of Filters • Low Pass Filter

  5. Types of Filters • Band Pass Filter

  6. Types of Filters • Gap Filter (aka band reject or notch filter)

  7. Determining Slope of Filter • From the high or low frequency cutoff determine the dB attenuation per octave. • e.g., octaves of 1kHz would be 2, 4, 8kHz, etc.

  8. Determining Slope of Filter • For example….. • If the peak intensity is 50 dB at 1kHz, is 46 dB at 2kHz, and 42 dB at 4kHz, what is the slope? • If the peak intensity is 40 dB at 500 Hz, is 28 dB at 250 Hz, and 16 dB at 125 Hz, what is the slope?

  9. System tuning of filters • Narrowly tuned system - very narrow bandwidth • E.g., tuning forks, strings on musical instruments, etc. • Minimal resistance - low damping • Efficient generators of sound.

  10. System tuning of filters • Broadly tuned system - very broad bandwidth • E.g., diaphragms of microphones, headphones, loudspeakers, and auditory system, etc. • High resistance - high damping • Efficient transducers of sound.

  11. Summary

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