Transmission Line box

[fritosaregood 0]

I just finished a build on a trans line box, Its a 1/4 wave 33 hz. But i thought i had read some where that 1/2 wave trans lines were better, but impractical for space. so i thought i would make a box with a 1/4 wave at 33 for daily and 1/2 wave at 66 for comps, but from testin the box in my house the box getts really quiet after about 40-45(guesstimation) when using a reasonce test song,

so was my idea of a dual purpose box dumb.. and are the only good trans line boxes 1/4 wave boxes?

[95Honda 486]

How long is your line?

Did you use any stuffing?

Did you measure impedance?

What cross-area did you terminate with?

[fritosaregood 0]

How long is your line?

Did you use any stuffing?

Did you measure impedance?

What cross-area did you terminate with?

the line is 106"

I didnt know i needed stuffing.

after i posted i read about the impedances.. put idk how it measured it..its a dual 2 ohm sub it that means anythin

as for the cross area at the end... because of space its not a true trans line(its in the trunk of a honda accord) but the port is 2.25"x14.5" the whole way with the openin firing 90degrees to the sub..

im findin the trans lines are gettin harder that i once thought they were

here is a pic

http://www.geocities.com/fritosaregood/PA050137.JPG

[95Honda 486]

Actually, you didn't built a transmission line. With the size of that rear chamber and the the size of the line, you ended up with a very low tuned ported box.

The line needs to be roughly the Sd of the driver. The rear chamber needs to be as small as possible, idealy it should just be the begining of the line. Most TLs use stuffing to flatten the impedance/behave appropriately.

[fritosaregood 0]

Actually, you didn't built a transmission line. With the size of that rear chamber and the the size of the line, you ended up with a very low tuned ported box.

The line needs to be roughly the Sd of the driver. The rear chamber needs to be as small as possible, idealy it should just be the begining of the line. Most TLs use stuffing to flatten the impedance/behave appropriately.

yea.. it definately hits the lows

I am using and Audiopulse Axis 15. its Sd is 0.082m^2. so are you sayin the cross area of the port/line needs to be 0.082m^s.

and if i got a True trans line box would i be able to have it play music at 33hz tune and also use 66hz tune for comps?

Also can you explain the impedence part.

here is a pic of the next box i want to build for theater system in my room. Its just a rough drawin i just made in paint. would this be a trans line.. and which box would be better? the right most one is and its basic 3-D look

http://www.geocities.com/fritosaregood/new_box_design2.bmp

[JimJ 11]

and if i got a True trans line box would i be able to have it play music at 33hz tune and also use 66hz tune for comps?

No. The best way to do that would be a traditional ported enclosure with a removable port insert for changing the tuning.

I'm a big fan of TL's, but trunks and SPL are two things I'd say they don't do very well, if at all

[fritosaregood 0]

and if i got a True trans line box would i be able to have it play music at 33hz tune and also use 66hz tune for comps?

No. The best way to do that would be a traditional ported enclosure with a removable port insert for changing the tuning.

I'm a big fan of TL's, but trunks and SPL are two things I'd say they don't do very well, if at all

I originally planned to just switch out ports, but i thought id give the Tline a try.

.But i thought Tlines had more db output than a regular ported box

[fritosaregood 0]

i just estimated the tunin with winisd box designer.. its 21hz..reall low

[Duran 387]

and if i got a True trans line box would i be able to have it play music at 33hz tune and also use 66hz tune for comps?

No. The best way to do that would be a traditional ported enclosure with a removable port insert for changing the tuning.

I'm a big fan of TL's, but trunks and SPL are two things I'd say they don't do very well, if at all

I originally planned to just switch out ports, but i thought id give the Tline a try.

.But i thought Tlines had more db output than a regular ported box

Well they wont if you build them wrong. At a comp a while back, there was a guy there with 2 older Rockford 12"s in a T-Line box with 2000 RMS on tap, he burped a 127.X.

[95Honda 486]

Yes, a true T-line should at least have the line equal to Sd at the termination point. It isn't practicale to start with Sd because unless you are using a tube, it is impossible. This is why they are tapered to a point, usually they start out at 1.25X Sd and terminate right around Sd.

T-lines don't have tuning, in fact they are very non-resonant. They have a cutoff frequency that is determained by line length and stuffing density. 6 feet of length gets you roughly around 30Hz or a little lower. The stuffing supposedly manipulates air velocity in the line and dampens resonance, usually you stuff heavily at the beginning of the line (1lb per ft3) and gradually taper to little or no stuffing the last foot or so. You stuff accordingly to smooth the impednace plot.

I have built maybe 10 T-lines, all have been stuffed with Dacron or Acustastuff, every one I have seen is also stuffed. Most modeling uses stuffing.

A port calculation has nothing to do with a T-line.

T-lines are not for SPL. If someone has a T-line for SPL, 99% it isn't a T-line. They are non-peaky (little ripple) by nature and will not exploit the driver with huge Fr peaks if done correctly.

A perfect texbook T-line would be you woofer attached to the end of a 6-8' piece of 15" diameter sonotube with about 6-7 pillows worth of stuffing inside, maybe this will help you visualize what a T-line really is, and why they are impractical in a car if they are true T-lines...

Hope this helps...

[///M5 2,833]

Definitely not something for your trunk. If you drove a school bus perhaps, but for your goals it isn't the right style of enclosure.

[fritosaregood 0]

ok, thanks for clearin up some things, but i have one more question.

There is another box i have seen built called a tapped horn. is this just a variation of a T line

[fritosaregood 0]

A perfect texbook T-line would be you woofer attached to the end of a 6-8' piece of 15" diameter sonotube with about 6-7 pillows worth of stuffing inside, maybe this will help you visualize what a T-line really is, and why they are impractical in a car if they are true T-lines...

Hope this helps...

would this 6' tube be straight or would it have a u-bend so it would terminate in the same direction of the woofer

[JimJ 11]

ok, thanks for clearin up some things, but i have one more question.

There is another box i have seen built called a tapped horn. is this just a variation of a T line

Sounds like a marketing term for some kind of horn, which is not a T-line.

would this 6' tube be straight or would it have a u-bend so it would terminate in the same direction of the woofer

It depends, I've seen lines that end up in the same direction or are straight, all depends on where they're going.

[fritosaregood 0]

ok, thanks for clearin up some things, but i have one more question.

There is another box i have seen built called a tapped horn. is this just a variation of a T line

Sounds like a marketing term for some kind of horn, which is not a T-line.

here is the site.. it seems to use alot of the principles of a T-line.. or i could be wrong

http://www.cowanaudio.com/th.html

[JimJ 11]

Interesting, reminds me of a BIB with the driver going the opposite direction

It's still not a transmission line.

[95Honda 486]

They are actually using horn loading, this is different method than a T-line. A horn acts like an acoustic transformer (sort of) by effectively coupling the acoustic output of the driver to the air very efficiently in the passband, or at least above cutoff. Horns are not very forgiving as far as design execution, but if done well are much more efficient than a T-line. A T-line on the other hand is much more forgiving as far as design and construction goes, is usually less efficient and is easier to achieve a lower cutoff with less ripple than a horn.....

[fritosaregood 0]

I must have done something right with this box. i was showin it to some ppl at college today and was playin a sweep from 10 to 100 hz, and around 25~30 my passenger seat was movin back and forth about 1.5 to 2 inches. way better than my last box which had close to the same port area i think.

I am goin to a comp this saturday so ill post some numbers from it soon. the last box hit 146.0 im hopin more with this one but this box is tuned lower.

[fritosaregood 0]

I went to the comp, after my runs I realized I forgot to turn my eq setting back to the louder bass, but it did a 144.1 at 40 hz. i think it did a 137.7 at 25hz. Im pretty sure i coulda got more out of it, but ill have to wait to see