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.
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.