T/S parameters on a beefed up Nightshade?

[CadillacMatt 31]

I'm thinking of designing a 4th order in my trunk for a D2 18" Nightshade, and after rooting around the web for a while I found some T/S parameters for the stock speaker, however, this speaker has been reconed with an extra stiff suspension built to handle about 3KW daily.

How would this affect the T/S numbers, if at all? The website I found here lists the Qts @ 0.44, the Vas @ 36.7 and an Fs of 38Hz.

Thanks!

Edited July 24, 2010 by CadillacMatt

[CadillacMatt 31]

Another thing I found strange is that when I plug those parameters into WinISD and several other box calculators for a 4th order, it gives ridiculously small enclosure recommendations like 2cuft sealed, 1cuft ported. I'm looking to design an enclosure with an S factor of about .6, a compromise between narrow and wide bandwidth (although I would prefer to have a somewhat wider passband at the expense of efficiency, especially one that would add greater low end extension). I realize that the smaller the enclosure the wider the passband but that would be an awfully small box!

Edited July 25, 2010 by CadillacMatt

[Impious 1,476]

I can't answer why, but the parameters listed on Db-r's page are completely different than those on Sundown's page. I'm not up to speed on all of the possible Nightshade revisions.

Anyways, an extra stiff suspension would mean Cms decreased. This decrease in Cms would increase Fs, increase Qts and decrease Vas. That's assuming everything else remained constant.

The reason for the super small enclosure suggestions is due to the extremely low Vas in the T/S parameters you are using. That Vas is absurdly small for an 18" driver.

[Duran 387]

It's normal for Nightshades to be in small enclosures

[CadillacMatt 31]

I can't answer why, but the parameters listed on Db-r's page are completely different than those on Sundown's page. I'm not up to speed on all of the possible Nightshade revisions.

Anyways, an extra stiff suspension would mean Cms decreased. This decrease in Cms would increase Fs, increase Qts and decrease Vas. That's assuming everything else remained constant.

The reason for the super small enclosure suggestions is due to the extremely low Vas in the T/S parameters you are using. That Vas is absurdly small for an 18" driver.

Thanks for taking the time to explain, it's helping me out as I've really been trying to tackle the details behind it all...

Well, just for giggles and to help myself learn I crunched the numbers for that off-the-shelf 18" Nightshade with the params listed on Sundown's page through the equations on DIYsubwoofer, and I got 1.16f³ for the vented chamber and 1.34ft³ for the sealed enclosure, a gain of 2.12dB, and a top freq of 62Hz... this is assuming an F1 lower dB of 30Hz, and an S Factor of 0.6.

I was also hoping you could help clarify things for me... when you plug a number for the lower cutoff into the equation it is likened to choosing a tuning for the box of a ported setup? Like a box that's tuned to 32Hz means the -3dB cutoff is at 32Hz? And as for the upper freq if my goal is to nail the lows on a daily setup, is that a good top end for a fairly wide passband and not a one note wonder?

And also, is there any way for me to determine the amount of Vas/Fs/Qts I should add or subtract based on the current info?

Thanks again for the help

Edited July 25, 2010 by CadillacMatt

[CadillacMatt 31]

Anybody?

[jonbearsmt 919]

bump?

[sundownz 197]

I don't have specs on hand for all the various spider configurations.