Design ported cab to compensate for BS?

[krips]

I was just thinking the other day, would it be practical to design a cab that was intentionally large/tuned high instead of building BSC into the XO?

[Tyson]

Something like this?

http://www.troelsgravesen.dk/PMS_Kari.htm

[krips]

Thanks for the reply. I'm not sure I explained my question very well. What I meant was....can you create a hump in the response in order to compensate for baffle bass rolloff? Without having the wide baffle.

[evilskillit]

I doubt that, otherwise somebody would have done it right now. I think part of the problem is that on a narrow baffle you start rolling off in the upper 100s. I forget how high but its like 500hz or above. Where as most ports generally boost a fairly small range, I don't think its possible to tune ports to have a wide enough output bandwidth to evenly compensate for baffle step loss. I'm sure someone who knows more than I do and can throw around some real numbers will chime in. But I'm betting thats the case.

[cjd]

BSC can reach up to 1kHz... that is a tough assignment for a port.

So, the answer is, not really something to try. Port output at 1kHZ won't sound so clear.

[penngray]

I doubt that, otherwise somebody would have done it right now. I think part of the problem is that on a narrow baffle you start rolling off in the upper 100s. I forget how high but its like 500hz or above. Where as most ports generally boost a fairly small range, I don't think its possible to tune ports to have a wide enough output bandwidth to evenly compensate for baffle step loss. I'm sure someone who knows more than I do and can throw around some real numbers will chime in. But I'm betting thats the case.

Im confused, I think the wider the baffle the lower the diffraction and drop in response.

narrow baffles roll off in the upper 100s?

Never mind, you did say 500Hz

[penngray]

http://www.trueaudio.com/st_diff1.htm

So using the formula

my baffle is 16" and my BDS F3 = 4560/16 = 275Hz... So I need a Shelf filter of 6dB to offset that drop.

A narrow baffle like an 8" one should have an F3 around 570Hz.


btw, a 1KHz BDS would be a 4.56" baffle.

This is pretty cool though because the smaller the baffle the higher the F3 and you can eliminated by using a crossover and a mid range driver.

[Dennis H]

The F3 from the baffle width calc is the center frequency but BSC is a gradual slope that extends well above and below there. See Murphy's pic with the F3 at 1K. There's really no need to calculate it if you have measurements. Just EQ the measured response flat in the crossover.