The loudspeakers are devices which are designed to reproduce the actual voice according to the voice frequency signals fed into it. The audible voice spectrum stretches from around 20Hz to 20 KHz and the interesting thing is that there is not loudspeaker design which can reproduce all these frequencies with the same effect. Hence there are different kinds of loudspeakers like Tweeters, Mid-range Speakers, Sub-Woofers and Woofers which can reproduce the voice in their own particular frequency bands only.
In an audio play back device, the entire audio signals are separated into different bands and applied to the corresponding type of loudspeaker. The Tweeters are normally fed with frequencies above 5 kHz, Mid-range speakers are fed with frequencies in the range of 300 Hz to 5 kHz, and Sub-Woofers with 300 Hz to 40 Hz and Woofers are fed with frequencies below 40 Hz.
Since the musical sound normally falls around the maximum frequency of 5 to 8 KHz, Tweeters are not so common in audio devices. For driving the Mid-range Speakers a high pass filter of cut-in frequency around 300 Hz is enough and for Woofers a Low pass filter with cut-off frequency around 40 Hz will suffice. Bass-beats of the songs appear in the Sub-Woofer range and a Band-pass filter can be used to separate out these frequencies from the entire audio signals. This project discusses the design and implementation of a Multiple Feed Back (MFB) Band pass filter for Sub-Woofer frequencies.
MFB Bandpass Filter Audio Sub-Woofer