Tuning freq. for sub box build.

[svn2002s]

So, I am building a box with the ports facing up just under the factory speakers are (rear shelf). I have an M3 rear bench seat and not planning on removing foam.
The sub I'm using (10in JL Audio) comes with some parameters for a ported box (Box Volume and port area/length). If you plug those parameters in a tuning formula. it works out to 30hz.
So the Q? is : Is this freq. arbitrary? or you could go 25 or 35? Is there such thing as max. efficiency on subs? Why not 35 instead of 30 (maybe my ears are shot and can hear crap below 40, maybe I hate all the booming shit).
Luke... time to shine..
Will post build for all cheapskates that won't buy from Luke.

[Jean]

To put it shortly, it's not arbitrary, t/s parameters describe what the sub is like on paper and what the optimal sub box should be.

http://en.wikipedia.org/wiki/Thiele/Small

http://diyaudioprojects.com/Technical/Thiele-Small-Parameters/

Good reading - http://www.amazon.com/gp/product/188...SIN=1882580478

[StereoInstaller1]

Yeah, basically there is an assload of breathing room if the box's basic size is in the ballpark.

I wish I had an article that was published back in the early 80's. Audio guys were pretentious fucks back then, too. The only difference is that manufacturers really had to prove their shit worked, because the magazines actually showed the facts, not just pure hyperbole as they do today.

Richard Clark (I think? brain is old) used to do a column randomly in one of those rags. He did an assload of testing all kinds of enclosures in and out of the car. He found that changing the tuning frequency as much as 10Hz had very little effect on actual in-car frequency response, but power handling changed quite a bit.

We are talking a 2 or 3db change in frequency response, in an environment which can inherently have peaks and dips as much as 25db...who gives a shit about 2db?

If you do, you are gonna have to tune it out electronically anyway, so the idea is to get it as close as you can, mechanically. That is why I use a fairly high tuning of 35Hz, and ask you to find a woofer that has Qtc of less than .4 and a Fs under 30Hz, hopefully lower than that.

I port higher because it works so well in this car. If the woofer is less "peaky" (Qtc under .4) and does it lower, the box can play pretty low. I do not know of anyone who has done any frequency measurements, and believe me, when I can do FFT waterfall plots as part of a design, they won't be $180 anymore...

[svn2002s]

Good to hear that I won't compromise sound too much. @ 30 HZ the port length is too long. I need to increase the tuning freq in order to get a smaller port length that can fit in the box. (4 inches on top might be too much due to box design).

[StereoInstaller1]

So you are planning on building something like my V2 box?

[svn2002s]

Never seen your V2 box. I'm just planning something similar to yours but with the ports facing up. I don't want to fuck up my rear seat by removing foam. It might create an indentation later. It's already done and paid for. The fabric is NLA. I will follow your advise and put a little more power to the sub. and try to get trough the thick foam.

[svn2002s]

Is V2 some sort of Version 2 of your famous box?
Just building something like yours (trapezoidal shape) front face in angle parallel to back seat.

[StereoInstaller1]

V1s vent through the stock speaker hole: V2s need to have 2 holes cut.

Here is an old tutorial from a couple years ago: http://www.r3vlimited.com/board/show...ttcrack&page=2

[svn2002s]

Good stuff as usual, how do you like the sound?

[StereoInstaller1]

The V2, or the V1? It (the V2 "keep your rear speakers" stuff) all started with James Crivellones "all ADS" car (with an Exile woofer, thank god) and it is pretty stunning IMO. I think about 2 dozen have gone out. Soon I am gonna swap the wifes car to a 10 from a 12, I think they are 90% as good unless you listen exclusively to rap.

They make the same bass of course.

Having rear speakers does make the car sound "bigger", but if you don't have adjustabilty to turn the gain WAY down on the rears, you aren't gonna be happy.

[svn2002s]

I'm going with no speakers in the back and components on the door. 2 amps 10 in. sub. All JL Audio and an Alpine deck until I get a cd43.

[StereoInstaller1]

Cool. Post some pics when you are done.