Lowpass or Bandpass????

[soundNERD]

i am working on a sub amp and need to build the crossover for it.

i was originally planning on building a low pass that crosses over at 50hz, but then thought, i can't hear below 20Hz and the speaker can't produce much less than 30Hz, so why not make a bandpass 50hz - 30hz, that would protect the speaker from dangerous low frequencies and reduce distortion since all power of the amp would be used to amplify only bass notes between 30 and 50hz, right?

if so, how would i go about building a variable bandpass that varies between 30-50hz to 30-100hz?

[soundNERD]

anybody???

[planet10]

Originally posted by soundNERD
if so, how would i go about building a variable bandpass that varies between 30-50hz to 30-100hz?

Probably makes sense to cascade a 30 hz hi-pass with a variable 50-100 Hz lo-pass.

dave

[soundNERD]

but do you think this is a better solution than just a lowpass?

[officeboy]

I think that would work pretty good. I know you can build a variable lowpass. Building a variable high pass might be a little harder, but you could always just set it at 20hz and forget it.
Of course you might want to go even less that that (10 would work well), since with a 2nd order crossover at 20hz you will be down 3db @20hz and almost 1db down at 30hz and that combined with the natural roll off of your box might not work to get you much deep bass.
I’m in the middle of making a plate amp for a sub project I have, and it’s all going pretty well. I still haven’t completed my circuit, but I’m getting close to being able to hook it all up for testing.

You can find a few pictures at my website, and I’ve done my best to document design procedures in this thread here.
Sub plate amp design

[pk386]

What is the amp going to be used for? Movies or music.

If it's going to be used as a home theater sub I'd say the lower cut off frequency shoud be 10-15hz. This is cause some moives have this effect for the rumble not the sound.

If it's going to be used for music I'd say 20-30hz.

or designe a variable one and adjust to what you like....

[planet10]

The disadvantage of the bandpass is an extra op-amp in the signal path and more complexity... with vinyl it would be a real good thing, with digital not as necessary... a good compromize might be to just put an input coupling cap in the circuit that gives you a 1st order hi-pass at 10-20 Hz.

dave

[jleaman]

If this help.. My old band pass subwoofer kill my other one... spec's are


kicker OLD worn out comp C10 in a band pass box with about 80watt into it.
then a USD 15" C Pro Subwoofer paid about 800$ for it.. and i played with tons of boxes..

The winner the 30$ subwoofer The kicker in the band pass.. It was loud and efficient