designing a box

[jrobie79]

picked up a 12" dual 2ohm VC sub. Fi SSD, was wondering if anyone had any ideas for designing the box for it. Im going to go ported and was wondering what I should tune it to based on the e30 cabin gain and what not. I already got the manufacturers recommended specs which are:

Ported box: 1.8 - 2.5 cu ft @ 33 Hz

however figuring our cars are different looking for something closer more specific to what would be best. Also I will be using a cylindrical port and dont really know how to figure out the tuning using that. are there any port length calculators out there on the web?\


sub specs are as follows:


Fs: 30.1 Hz
Re: 1.4 Ohms/coil
Qms: 7.65
Qes: .37
Qts: .36
Mms: 248g
Cms: 0.11mm/N
Sd: 480cm^2
Vas: 36.5
Spl: 86.1dB 1W/1m
Bl: 18.7 N/A
Xmax: 21mm
Rms: 800W
Sealed box: .7-1.2 cuft
Ported box: 1.8-2.5 cuft @ 33Hz
Sub OD: 12.500”
Cut ID: 11.125”
Mounting depth: 6.500”
Displacement: 0.14cuft

[Massive Lee]

You shoud tune your box to what the manufacturer recommends.

Port length calculator

http://www.psp-inc.com/tools.html

[jrobie79]

would you go with the 1.8 or 2.5 end of the spectrum of recommended size? just wanna get everything as close to ideal as i can before i start cutting wood.

thanks for that link, couldnt really find anything that good when i searched around different forums

[Massive Lee]

The bigger the box, the lower the frequency.

http://www.ajdesigner.com/phpsubwoofervented/box_tuning_frequency_equation.php

[StereoInstaller1]

Gotta love that: I do 2.0 cubic feet @32Hz as my standard E30 12" tuning.

What you guys seem to miss is that the box interacts with the cabin, and the woofer itself really does not affect the sound much at all, except in cases of really bad mis-match (Qts of .7 and a Fs of 60Hz? YUK!) the box interface does all the work.

Wanna make a huge difference, do 2) 4" ports. That is how I have mine set up, but with Aeroports. Port length is 30" IIRC.

If I can help, let me know.

Luke

[Massive Lee]

Wanna make a huge difference, do 2) 4" ports.

Eh, eh. I just made a prototype sub for home, using JBL's legendary 15" 2235h in a 6.9cf enclosure. I made two ports of different lengths to use alternatively, but never together. One port is tuned to 20Hz (driver Fs) and the other is tuned to 26Hz (enclosure resonance). Depending on material being played, I use one port or the other.

[jrobie79]

so two 4" inch ports each port is 30 inches long? can I use PVC for that? and if so can I use elbows to attain this length? or do I have to make the box 30+ inches wide from the skipass into the trunk?

I have 4 inch aeroports, but not the tube part, just the flared end, does PVC work for port tubes and should I use string to support the tube since PVC seems pretty beefy and with all the vibration might loosen itself?

gonna start doing math and figuring out the angle of the skipass wall with a bevel square tomorrow


edit

can either one of you guys recommend a good amp for that driver. I found a memphis 1000.1 for like 135 shipped. good deal?

[StereoInstaller1]

Eh, eh. I just made a prototype sub for home, using JBL's legendary 15" 2235h in a 6.9cf enclosure.

So what does that do to help this guy build a sub for his car?

[Massive Lee]

So what does that do to help this guy build a sub for his car?

I made two ports of different lengths to use alternatively, but never together. One port is tuned to 20Hz (driver Fs) and the other is tuned to 26Hz (enclosure resonance). Depending on material being played, I use one port or the other.

Which kinda answers the OP's question about how to tune the enclosure. He can try two different settings. But as the car's interior volume is pretty limited and not 20Hz-friendly (unless you run tons of drivers, and mega watts) I would simply tune to 30Hz, as suggested by the manufacturer. And if I had a late e30 with the ski pass, I wouldn't even build an enclosure. I would probably try to simply fit a pair of 10" drivers on a baffle, and screw the baffle on the ski pass opening, using the trunk as the enclosure.

BTW The membrane surface of two 10" is approximately equivalent to one-and-a-half 12", but with a more nimble/lighter/quicker diaphragm.

[jrobie79]

already bought the single Fi SSD, didnt even think to use the whole trunk as an enclosure, oh well, hopefully it turns out good. When calculating the size of the box, i know I have to factor in the displacement of the driver, do I have to do the same for the port tubes?

[StereoInstaller1]

Yes, you do. Anything inside the box needs to be accounted for.

Appropriate woofers for Infinite Baffle have a very high Qts (.7 or higher), a HUGE Xmax (25mm would help) and a fairly high Fs (over 30Hz, or the thing will flap like a bird) and your SSD is none of those.

So, are you looking to practice, make a whole bunch of different boxes and learn and stuff, or do you just wanna build one?

[jrobie79]

I just wanna build one, I am a carpenter so I'm gonna tackle this one on my own, already bought the woofer, still need an amp, but I can wait for the right deal for that. I just want this thing in before I take my car on a 2 day road trip in two weeks.

I just finished fiberglassing custom tweeter pods b/c I have a ton of that stuff and it wasnt worth it to me to buy stock tweeter sails, and I got my doors deadened and a bracket welded onto them with threaded holes to mount the speakers, so now I just got the box and tuning to do.

Thanks for all the help, seriously, I dunno what I'd do without this forum for the e30.

[Ssolidarity]

Maybe modeling it on WinISD will help out with how it will react with various ports and the size of the box

[jrobie79]

I tried, I lack the patience to learn how to use that program haha

[Ssolidarity]

haha. Well then I think www.sonicelectronix.com has good deals on amps