I want to split an audio signal into 5 bands by frequency range (top and bottom can be low-pass and high-pass) and send these into speakers with moderate power, say 10 watts. I can use amplified speakers if a
5-way audio amp gets complicated.
This is not for quality audio, but for educational demo purposes, so I don't need an even response and distortion is okay. I'm really looking for the sharpest cut-offs I can get, in as simple a box as I can build. Can anyone suggest how to accomplish this?
I haven't made many coils before (rather embarassing for a ham op), but I'm fine with simpler circuits. I found a post about an IC that might do the trick, but I'm doubting it'll handle audio frequencies.
One good resource is Don Lancaster's "Active Filter Cookbook". You will not need any inductors (one of the virtues of active filters), but you will need some matched components. Look at "equal component Sallen-Key" designs. These avoid the need to have 2 different specific capacitors in each stage to control Q and frequency. Instead, you use 2 equal-value caps, and equal-value Rs, and you adjust Q with a separate gain factor. Stability is alleged to be poorer than the unequal Sallen-Key, but IMHO that's more than compensated by the ease of correct tuning in the first place.
You will have to make some tradeoffs between complexity, sharpness of slopes, and passband ripple.
Also, with only 5 bands to cover the audio range, the bands will be too wide to use classical bandpass fitler stages. You will need to create each band from a separate high- and low-pass stage, or a chain of simple bandpass filters summed together.
In fact, you may find it simpler to change your design to use more than 5 bands, just to allow simpler bandpass stages. (They should be well under an octave to use bandpass stages. Narrower allows sharper tuning.)
You will come to appreciate why designers prefer to make filters like this digitally. One A/D and DSP chip, and you can generate any combination of filters and slopes with perfect stability and no parts tolerances. You can use FFTs (a whole bunch of simple bandpass filters, equally spaced) or Finite Impulse Response (delay line with summed weighted taps) or even the trickier Infinite Impulse Reponse types (like analog filters) to create fitlers for this job.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
Amplified speakers would be the way to go. Implementation can then be by 5 off, passive or active filters. For passive component simplicity, would suggest for the HP, LP and 3 bandpasses, '3nd order' Butterworth responses. Simplest is a passive, standard LC design (HP,LP,BP's using say, 1000ohm source and termination resistances). To avoid the ballache of hand winding, then use of Toko style inductors would be preferable. Needs in total, 11 inductors and 13 capacitors. For demo purposes the roll-offs are quite fast with a nice flat response over each pass band. T'other method is to use 5 active filters. As a minimum, would need a total of 5 opamps. 27 resistors and 18 capacitors. The HP and LP are standard 3rd order Butterworth design but the 3 bandpasses (2nd order this time) use a jiggery pokery component arrangement to give a wide flat top response using a single opamp. (My "service" supplier of 6 years has ditched A.B.S.E. so I can't post an example circuit). 'Wannadoo' is a just a cabal of f***** useless management wankers. regards john
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