Quarter Wave / T-Line tutorial-UPDATED

[STEvil]

there will be minimal change due to the motor assembly, dont worry about having to do an air chamber.

[bigsausagepizza]

I just built a t-line for my subaru, this thread helped a ton

build: http://www.stevemeadedesigns.com/board/topic/180897-my-first-transmission-line-2008-subaru-wrx-sti/

[soBASED]

there will be minimal change due to the motor assembly, dont worry about having to do an air chamber.

Awesome, thanks a lot! Fairly soon ill be doing a t-line for a jbl Gt5-10 going in my buddies dodge ram 1500. Will post pics!

[tjennemann]

So just like school i am hoping someone can double check my math after reading just about every post in this topic.

I am going to run (2) DC lvl 3 12" subwoofers

Spec's for (1) subwoofer

(FS) frequency is 35.4 Hertz

(SD) Cone area 481cm^2 or 74.56in^2

So with the information above i have a 1/4" wave length of 7.51ft and a Port area of 74.51"

Now if i run (2) subs i still have a 1/4" wave length of 7.51ft does my port area change to 149.02" or will it stay at 74.51". i am assuming it is 149.02 since my cone area doubles running (2) subs

Now for the fun part. since i am a Mechanical Designer and use Autocad everyday these are the calculations i came up with to fit in the 37x30x15 space available.

for (1) sub the port area will be that will snake around for 7.5 feet will be 6"deep by 1'-0 3/4" tall giving me 75"

for (2) susb the port area will be that will snake around for 7.5 feet will be 11 1/2 "deep by 1'-1" tall giving me 149"

The reason i am questioning everything now is i discovered this website for a T-line build and the measurements are no were close to what i have previously calculated out

http://dbdynamixaudio.com/quarter-wave-flared-vent-t-line-horn-bass-reflex-enclosure-calculator/

[bbeljefe]

Line length would be 7.98' for 35.4Hz. Line area would be 149.12in² for two subs.

You can reduce the line area by as much as 40% if needed. In fact, A reduction in line area tends to give the driver(s) some acoustical suspension which of course, increases power handling. What you don't want to do is make the line area more than driver Sd, nor do you want the tuning to be higher than Fs. I've found that tuning below Fs improves performance and drastically improves low end response.

For the subs you have, I would tune at ~30-31Hz and I'd reduce line area by 10%. Especially if the specs you posted are manfacturer's published specs and not those you've derived through testing, because manufacturer's often publish before break in specs. After break in you can expect a 3-6Hz drop in Fs.

As for the calculator you linked to , I've seen it before and it doesn't make a lot of sense to me. But with that said, it's also not a calculator for a consistent area line.

[tjennemann]

double post by accident see below

[tjennemann]

well my fist mistake i noticed is i used the speed of sound as 1120. not 1130

now how did you come up with the 7.98'.

if i use the equation it is 1130/35.4 = 31.92 full wave length

then 31.64 / 4 = 7.91 then take off about 5% and you get 7.58

and i agree with the line area.

I know its all tweeking from there but its best to start with a good design and tweek, than a starting with the wrong box design.

Thanks for the help

Line length would be 7.98' for 35.4Hz. Line area would be 149.12in² for two subs.

You can reduce the line area by as much as 40% if needed. In fact, A reduction in line area tends to give the driver(s) some acoustical suspension which of course, increases power handling. What you don't want to do is make the line area more than driver Sd, nor do you want the tuning to be higher than Fs. I've found that tuning below Fs improves performance and drastically improves low end response.

For the subs you have, I would tune at ~30-31Hz and I'd reduce line area by 10%. Especially if the specs you posted are manfacturer's published specs and not those you've derived through testing, because manufacturer's often publish before break in specs. After break in you can expect a 3-6Hz drop in Fs.

As for the calculator you linked to , I've seen it before and it doesn't make a lot of sense to me. But with that said, it's also not a calculator for a consistent area line.

[bbeljefe]

I didn't take off 5% and I don't remember you saying you did either, although I could have missed that. Not that a 5% reduction will hurt anything but frankly, that's not a part of the equation. Done correctly, the equation works out to be 7.98.

You can reduce line area up to 40% although I've found that a 10% reduction works well.

[tjennemann]

thanks for the quick response. gives me a little more space. i will try and post up a design over the weekend when i get things thrown together in CADD

[bbeljefe]

Cool. I look forward to seeing it.