10 replies to this topic

[heimerich]

Hi guys, i got a question and please help me. I'm working on a transmission line box for my IDMAX 12"... my friend sent me the blueprint and he said it was from Image Dynamics user in this forum... I'm trying to work on the box but it doesn't give enough information...

I need information about:
1. Where do i mount the subwoofer? Where do i have to make the hole? What is the measurement from the edges of the box?
2. I'm not too sure the gap between the braces...

So, please... anyone who has tried this box before, can you please provide me some help here? Or maybe IDMAX distributor...

[blanketman]

if you can send me the pic
i will look at it for you

[heimerich]

blanketman: thank you for your help... gimme your email address and i'll send it ASAP... thanks

[KDog]

You can' t build a transmissioin line in a car for a sub.

[Mr_Bob]

you CAN build one, but it'll be massive...
got a 4WD, wagon or a hatch which you're happy to convert to a 2 seater?

transmission line boxes look like a snail from the side profile.
the subwoofer gets mounted where the path is it's widest (beginning), and there's a port where the path is narrowest (end)
it can be a very difficult enlosure to tune, so i hope your designs are good.
i'm told you can modify it by adding dacron to reduce airflow in the path

[KDog]

Might want to check you math Mr Bob. Unless you have a semi trailer it aint going to work.

[Mr_Bob]

my calcs show about 220L if the TL assuming a frequency of 28Hz.
that's about 7.5cuft... it's doable, but as i said, you'll need a wagon or hatchback (converted to 2 seater)

what result did your Math get KDog?

[KDog]

The math of the box is fine.
You might want to check your theory on how a tranmssion line box actually works, unfortunately I don't have any links which you can read.

Basically tranmission lines don't work in a near field environment.

[Mr_Bob]

I agree with you on that point, however the imaging of subbass is not critical in a car environment, and at such low frequencies it's basically irrelevant anyway.
If he was building a TL for midrange drivers i'd say it's "near" impossible,
Mark Eldridge did it, but had to construct the TL's inside the engine bay of the 4Runner to make it work.
To my understanding:
The TL box works by slowing the rear soundwaves to a point where they are almost stationary.
This gives the benefits of a more bottom end, but doesn't reduce control on the cone like a ported enclosure can.
Although they're typically avoided due to size, weight and cost, IMO they're one of the better enclosure designs.

i don't reptend to understand all the ins and outs of such an enclosure, but if you're going to say it can't be done, you really should provide some evidence, or an explanation as to why it wont.

TL's are rarely used in car audio, and home/pa audio "gurus" don't understand how the car environment impacts audio. i wouldn't take their assumptions as gospel.

I'd be keen to give it a shot... maybe i should get a ute with a canopy and pull the rear window out

[KDog]

Your line of thinking is correct in how the box sort of works. They don't really slow the sound waves down they more or less make it so that it does not interact with other waves in the enclosure.
However the outside of the enclosure is also part of the box, without enough room outside of the enclosure you do not have a transmission line box. They are only a transmission line box when they are used in a far field environment, the near field is way too chaotic to contemplate listening to. There are lobes and troughs everywhere in the field.
It would be like eating blueberry pie without blueberry, its just a pie it aint blueberry.

[Volenti]

T-lines shouldn't be thought of as being something mystical or esoteric, it's just another enclosure type and can be used in an automotive environment just as readily as sealed or vented or bandpass.

One good thing about adapting a T-line for use in a car is the line length can be shortened considerably and still get very good results, I've built lines for 8" subs (JL8w-1) that were only a meter long (using pvc pipe) and yet still had flat in-car response down to 25hz.

For your 12'' I would try a tapered line, with the driver mounted at the very start of the line with the area of the line at that point being ~1.5* the cone area of the driver (~740cm2), use a line length of 1.7m with a taper down to 490cm2 at the end of the line. The entire line should be filled with dacron, right to the end, this is especially important in a folded line as it will damp a lot of unwanted resonance and noise caused by the folds in the line as well as smoothing the response somewhat.

Note that T-lines are just as sensitive to placement in the vehicle as any other enclosure type, treat them like a vented enclosure in this respect, give the open end enough clearance ect.

Good luck.