Cerberus sub port change help

[timznidar]

I built a cerberus sub with some small recommended mods. It's a 12" cube (3/4" mdf) rather than a 11". The thing i need help with is I'm going to a 2" port rather than the 1.5" but I need to figure out the exact length. I've already got a 90 degree elbow since i'm pretty sure it's going to be long enough that it'll need it. I tried Unibox but got somewhat lost. Anyone want to help me out?

[Chris Roemer]

> I built a cerberus sub with some small
> recommended mods. It's a 12" cube
> (3/4" mdf) rather than a 11". The
> thing i need help with is I'm going to a
> 2" port rather than the 1.5" but I
> need to figure out the exact length. I've
> already got a 90 degree elbow since i'm
> pretty sure it's going to be long enough
> that it'll need it. I tried Unibox but got
> somewhat lost. Anyone want to help me out?

My best guess would be to shoot for a length of 10-1/2". You MIGHT be getting an F3 3-4 Hz lower than the original design, but Roman already had oversized his box (as much as he thought he should) to get the EBS alignment. Your bottom end will have a definate "rise" in response just before rolloff. It looks like you'll lose SPL (slightly) above 50 Hz, with basically the same output at 50 Hz, then maybe an additional dB at 40, and possibly +2dB at 30.

Chris

[timznidar]

> My best guess would be to shoot for a length
> of 10-1/2". You MIGHT be getting an F3
> 3-4 Hz lower than the original design, but
> Roman already had oversized his box (as much
> as he thought he should) to get the EBS
> alignment. Your bottom end will have a
> definate "rise" in response just
> before rolloff. It looks like you'll lose
> SPL (slightly) above 50 Hz, with basically
> the same output at 50 Hz, then maybe an
> additional dB at 40, and possibly +2dB at
> 30.

> Chris

Hey thanks. What did you use to model that?

[Chris Roemer]

> Hey thanks. What did you use to model that?

WinISD beta <A HREF="http://www.linearteam.org">www.linearteam.org</A> running both PE's T/S parms as well as the ones Roman quoted. I also assumed that .08 cf would be taken up inside your box by the amp, driver, and vent. This is what Roman used, although your vent should take up more volume, making the actual box smaller, which forces the port to get longer to achieve the same tuning, which makes it take up more volume, which makes the actual box smaller, which forces the . . .

Maybe you'd be better off to shoot for 11" or 11-1/2" right away! ;-)

[Wolf]

I went ahead and modeled it in Unibox since I had the time, and I'm mailing you the database file for the driver in question.
Wolf

[romanbednarek]

> WinISD beta <A HREF="http://www.linearteam.org">www.linearteam.org</A> running
> both PE's T/S parms as well as the ones
> Roman quoted. I also assumed that .08 cf
> would be taken up inside your box by the
> amp, driver, and vent. This is what Roman
> used, although your vent should take up more
> volume, making the actual box smaller, which
> forces the port to get longer to achieve the
> same tuning, which makes it take up more
> volume, which makes the actual box smaller,
> which forces the . . .

> Maybe you'd be better off to shoot for
> 11" or 11-1/2" right away! ;-)

I just want to note that the Cerberus TB woofer has mutated quite a bit over the years with different suffixes in the model name and different T/S parameters. My enclosure was designed around the earliest model but turned out to work fairly well with later models although the bass response changed.