First time sub - a couple of modeling/box questions

[whipdancer]

Howdy all!

I've been attempting to educate myself on how to build a subwoofer by reading through the forums and posts. I think I'm heading in the right direction, but I would like some feedback - just to make sure I am on the right path.

I'm using WinISD Pro Alpha (.050a7) to model my subs. The subs are MTX Thunder 4000, 12in, 8ohm.

Here are the specs:
Qts: 0.550
Vas: 111.1 l
Fs: 30.2 Hz
Le: 2.20 mH
Xmax: 8 mm
Dd: 25.9 cm
Sd: 525.5 cm^2
Re: 6.36 ohm

I've attached the WinISD graphic. On it are 3 boxes (6th order, 4th order, vented). I'm leaning toward the vented for simplicity. It is rather large (10 ft3), but this is simply a first try.

The drivers are just an old set of car subs that I have had forever. The only thing I would have to purchase will be the wood.

The vent in the image is a square vent that is only 0.89" in length. That's basically the thickness of the wood - am I reading that correctly?

Basically, am I modeling these subs correctly? Is there anything else I should do? Any advice would be definitely appreciated.

Thanks!

[Homeboydeluxe]

Hi there,

You need to check the "rear port-air velocity" tab and check its under around 17 meters per second ideally.

Also you need the check "cone excursion" tab, with only 8mm of travel, it will be exceeded very easily in 10 cubic feet, to stop this happening you need a high pass filter.

Maybe look at building two smaller 3 cubic foot boxes with a 4" round port and a higher tune 25-30Hz, see how that works out.

[whipdancer]

Originally Posted by Homeboydeluxe

Hi there,

You need to check the "rear port-air velocity" tab and check its under around 17 meters per second ideally.

Also you need the check "cone excursion" tab, with only 8mm of travel, it will be exceeded very easily in 10 cubic feet, to stop this happening you need a high pass filter.

Maybe look at building two smaller 3 cubic foot boxes with a 4" round port and a higher tune 25-30Hz, see how that works out.

There is a plot tab that has a "sound velocity" field - would that be the port velocity?

[Thawach]

whipdancer he meant this

[ontariomaximus]

with that highish Q I would strongly consider sealed

[whipdancer]

Thanks for the feedback! Much appreciated.

I found the graph for port velocity and cone excursion. Both are well within limits (see attached).

As for a sealed box, I'd be ok with that, except that I'm down 6db at 30Hz and down 10db at 20Hz. I'm under the impression that will not work very well for LFE from movies.

Anything else I should be considering (like maybe a good driver for my next try)?

Thanks again for all the help!

~Whip

[whipdancer]

Apparently my attachments didn't make it...

[GM]

Looks like a 1 W excursion/vent mach plot, so in the 'signal' tab, input your amp's power rating and/or driver's peak power rating in the 'system input power' window and watch the plots shoot up and vent size become unacceptably large unless you have < 100 W available.

Between the driver's relatively high Q and large vent required if a low tuning is used, morphing them into some type of TL or BLH is the traditional way to go low with such specs.

GM

[whipdancer]

Originally Posted by GM

Looks like a 1 W excursion/vent mach plot, so in the 'signal' tab, input your amp's power rating and/or driver's peak power rating in the 'system input power' window and watch the plots shoot up and vent size become unacceptably large unless you have < 100 W available.

Between the driver's relatively high Q and large vent required if a low tuning is used, morphing them into some type of TL or BLH is the traditional way to go low with such specs.

GM

Wow, that made a big difference. Basically at a 75w amp, i'm pushing the limits of excursion (and completely blowing past them at 19Hz). Thanks for pointing that out.

TL is transmission line? I'll need to search on that as I'm not familiar with much past the absolute basics.

What is BLH?

[GM]

Back Loaded Horn. The simple 'BIB' is one form: Bigger Is Better 'BIB' Cabinet Dimensions - ZillaSpeak

Most informative TL site AFAIK: Quarter Wavelength Loudspeaker Design

GM