Audio to physical vibrations - design of the system

Hey,

I'm working on a project trying to produce physical vibrations using an analog signal from "music" files in the low 50-500 Hz range. I'm looking at 4-10 actuators to produce vibrations for a particular range of frequencies (ex one actuator for 50-100 Hz, another for 100-200 Hz, etc).

My current attempt has been to take the signal directly from an aux audio cable, amplify it, filter it using a 4th order filters and then present it to voice coil exciters, which actually vibrate at the frequency of the input signal. My knowledge of circuit design is limited and I simply copied an online 4th order circuit to create a low pass 300 Hz filter. My first question is, is it possible to design bandpass filters with a width of about 50 Hz or less? I've been told otherwise but I wanted to ask a larger audience.

Also, I'm trying to steer away from circuits and implement something in software so I can apply some more complex algorithms for the filtering. The voice coil exciters take in an analog "AC" signal, but I think I also have the option of using AC vibrating motors. I think the speed of an AC motor is proportional to the frequency of the signal so an AC motor should capture the information present in a band of frequencies as input. What can I use to output a bunch of analog signals carrying different bands of frequencies (analyzed and separated on a phone/computer/whatever) that would be used as input to these vibrating actuators?

Thanks for any help!

You might take a look at the [u]MSGEQ7[/u] chip. It's not going to give you the exact filtering you are looking for, but it will simplify things a LOT! (I have not used this chip myself.)

My first question is, is it possible to design bandpass filters with a width of about 50 Hz or less?

Sure! The bandwidth is related to the 'Q' of the filter, and it's related as a percentage of the center frequency. i.e. It's easy to make 100Hz filter with a width of 50Hz. A 10,000Hz filter with a 50Hz bandwidth is much more narrow and more complex (higher-order, higher Q).

I'm trying to steer away from circuits and implement something in software...

You're still going to need some hardware. If you are planning on using an Arduino, I'm not sure when you'll run out of processing power. I think running several DSP filters simultaneously could be an issue (in addition to other processing?). There are [u]FFT[/u] libraries for the Arduino, and that would essentially give you as many "filters" as you need. I'm not sure about the limitations of that either.

If you are planning on using a computer, more than 6 outputs (from a 5.1 channel soundcard) could be tricky. And, you'll have to know something about DSP programming as well as Windows audio programming.