Custom Stealth Box

new-yorker

Hi, How you doing all? I have minimal experience in the mobile industry, and i just got MECP Certified a week ago. I have done some custom projects though. Here is my plan:

a customer of mine wants me to build him a replica JL stealthbox for his 2000 Lincoln Navigator. Now for those who are familiar with these, in the '00 navigator, the center console between the two rear seats are used. i recommended him a Polkmomo mm2104 sub. Now I know with some fiberglass and MDF i can pull off this box. I want to make it so the sub is firing down, and i was thinking of doing a port to get more bass of it, because the customer likes hip hop & reggae. Any input from the experience folks if its a good idea to put the sub firing down, and do a port? Or just keep it sealed? I am a little shakey on how to put the port so it sounds good.

Thanks, any input is appreciated.

P.S. here is a link to how the JL stealthbox looks for the navigator:

http://mobile.jlaudio.com/products_stealthbox_detail.php?fit_id=1497

MacLeod

Congratulations on the MECP certification, thats outstanding!

In my humble opinion, the Momo subs sound better and work better in a sealed box. My 2104 is sealed and I love it.

Downfiring would not be a bad idea to add a litte extra output. You would lose a little clarity but I doubt he would notice, and if he's into rap I bet hed rather trade off a little clarity for a little extra output (not too many audiophiles listen to rap ).

new-yorker

Well it would sound better then what he has right now. He currently has a pre-fab box with some no name subs that he paid 150 bucks for, and his pioneer coaxials blew because they didnt have bass caps or crossovers on them. the guy who did his system did a very poor job. I gotta fix this crap.

btw, thank you, I went to Syntec technical school in NJ to get my MECP Bronze certification. In a few months, going to try for silver.

new-yorker

Hey MacLead, what kind of amp would you recommend? I was going to see if the guy wants a JL 500/1, because I like the technology involved in those amps. Anything you think is still reliable and good, and puts out the same amount of power RMS?

MacLeod

I think the 500/1 would be a little too much for a single 2104. That thing puts out over 600 watts and thats twice what the 2104 can handle and could easily shred a 300 watt 2104.

If you like JL the 250/1 would be a better match up.

Either way, I would find something in the 300-400 range and that would work well.

hellohello

well, since mac is here, i have a buffer on my opinions, he can disprove me if im wrong. I think the ports are supposed to be on the same side as the woofer, but in this case, i think the port would be better facing the passengers. That is unless Mac talked you out of it.

MacLeod

The ports do not have to be on the same side of the sub.

neomagus00

i agree with hellox2, the port(s) should point into the passenger cabin, if you do decide to go ported... the mm series are really built for sealed, but i don't see why they wouldn't do just fine in ported...

exalted512

right, ports do not have to be on the same side as subs. If ported out the passenger side, it would make it louder for the driver
-Cody

new-yorker

mac, i see what u saying about the 500/1 amp. i was going to use it, but just dont turn the gain all the way up, maybe just half way.

hellohello

oh, good thing i held off.

new-yorker

How big does the ports have to be? does Polk give port specs for their subs?

hellohello

http://www.diysubwoofers.org/portcal.htm
thats a more scientific approach...

new-yorker

i failed math in college, thats why i ended up at a technical school LOL

hellohello

yeah, i hear ya I failed college entirely. But to make a ported box sound good, it involves a lil math, u have to get the tuning right or itll sound like so much poo. A rule of thumb I THINK is that the ports diameter should be around .5 diameter of the woofer - 1" or in this case about 4"
(10"/2) - 1"= 4"
as for the length of the port, i have no idea.

new-yorker

hey you on AIM? i see ur AIM icon, i have AIM too.

hellohello

private message sent

neomagus00

try downloading 'unibox'... it's mostly self-explanatory, and it'll help you find the port specs you need - you already know the box volume (roughly, because you have to subtract the port's volume), all you need to do is find a balance between port length and size of the opening... a bigger opening affords less port noise, but requires the port to be longer... a lower tune also requires the port to be longer, but as you're doing a hiphop box, the tune can be relatively high - say 35 Hz - and still sound good...

new-yorker

35 hz? thats more like a frequency for a bandpass box. i thought a frequency for a ported box is usually around 55-65hz

MacLeod

Thats another reason I like sealed boxes. They require far less calculating and are much more forgiving of design or construction errors.

neomagus00

no, 55-65 will make it sound horrible and awful in too many ways to name... stick with sub-36 Hz for a ported box, because keep in mind you need a very steep highpass filter at or just below the tuning - that is, you lose all the bass below tuning, but you gain efficiency in the bass you do hear, it's a tradeoff...

new-yorker

no comprende

MacLeod

Yo quiro Taco Bell.

Thats Spanish for "use a sealed box"!

new-yorker

hahaha..Mac, u made my day :-)

hellohello

in the world of ported, the lower the frequency the better, thats the whole idea, to make the sub hit lower than it would sealed... joo 'no?

neomagus00

humm... to a point... a ported box with a tuning of zero hertz IS a sealed box (theoretically, of course)... as the tuning on the vented box drops, so does total output... the lower the tune, the less point there is in building the vent in the first place... this can be mitigated to a great extent by building a bigger box, but then transient response can suffer, plus you have a 6 cubic foot box to fit in your car somewhere... take, for example, SVS subwoofers... the lower their tune, the taller the cylinder gets, but it's still the same sub (those things is BIG, too)... so, for hiphop, which is mostly punchy, kick-in-the-gut bass, you don't really need the deep extension that a low tune provides, so you trade it off for either a louder box in a smaller space...

new-yorker

ight, I went to school for this stuff, and this is what I've learned. the human being can hear frequencies in the 20hz-20000khz range. a sealed box hits at between 75-85hz, a ported hits between 55-65hz, and a bandpass is around 40hhz and lower.
This stuff was on the MECP Test, and this is the knowledge i used to pass.

neomagus00

agreed, none of that is incorrect in the canonical sense... with the huge variety of boxes that could be built, though, you could get a sealed with a -3dB point of 60 Hz, a vented tune of 60 Hz, and a bandpass from 25-85 Hz, it's all in the specs of the box... the ranges you named are the vast majority, and for good reason - they tend to sound the best

and a ported box doesn't NECESSARILY peak at tuning, if that makes a difference...