Quarter Wave / T-Line tutorial-UPDATED

[Stewie_21]

UPDATED with new pics, different subs, sorry about the wait people

Okay, some people will hate me for posting this, hopefully no one on the great world famous SMD forums :^ But I see alot of people asking about 1/4 wave T -line, Horn design/theory. All I ever see is people sending links, and thats all I ever did to, was send links- to confusing brain boggler websights. When honestly, 1/4 wave theory is easier than trying to calculate port dimension with no program. Anyone with simple 8th grade- no scratch that, 6th grade level math can calculate tline enclosure dimesnions.

Most websights say how Tlines are un-realistic for cars, yeah, a 15" with a 24hz Fs, is pretty unrealistic. But a 12" with a 40hz bass boost can be as small as a sql box, for the same subwoofer. 40hz quarter wavelength is only 7.06ft long (round to about 7ft) When 24hz is 11.77ft long, and then multiply that 11.77ft by the SD of the cone... Pretty damn big box Just 1 -15" tuned at 24hz will yeald about a 14+cf box. Maybe good for a large van, but definitley not a car.

Over the years I have learned tricks, and short cuts to tlines. I stick with tlines, because personally, its the Perfect box, for your sub. No more of that, "What box sounds best for my sub?" If you do a tline based on your subs Fs, That IS the perfect box POSSIBLE for that sub. Its in the environment that subwoofer is built for, with absolutley NO amplifier strain, yet huge db outputs. I still have never pwersonally ran over 500watts to a tline, yet I always stay in the low 140db-high 130s with awesome SQ. Another Main plus side to tlines are, there is no back presure to keep efficiency up, xmax up, and allows the subwoofer to stop on a dime, and start back up faster than sealed, or ported designs.

So, heres the formula, its simple, you would just need a pen , paper, and calculator. Quarter wave is all based on speed of sound, and length of the sound wave.

Sound travels at 1130ft / sec

to calculate length of Freq Devide 1130 / (freq) say 30hz

1130/ 30 = 37.66 ft long Full wave length But we need to devide this by 4- for 1/4 wave wich equals= 9.41ft long

Pretty long huh? And the worst part is, to have a true T-line, you need to keep the port/tunnel/line - a Line, that equals Cone area, or pretty close to it. If you have a 10" The average SD/Cone area is about 50-60sq inches (to find SD in inches, you measure the cone, by useing a tape measure, and measure from middle of surround, to middle of surround on opposite side) 10" is usually close to 9"- 8.5"-9". This is where Pie comes in 9"/2 = 4.5-------- 4.5"x 4.5"x 3.14" = 63.58sq"

That is your Port AREA ( usually round this number Down- say 60sq")

So, a Tline for a 10" with a Fs of 30hz, and a cone area of About 60sq inches, will be about 9.25ft-9.5ft long (rounded) Its okay to be a little off, because this is car audio tlines, the cars accoustics will not notice it, because of cabin gain. But, when building a t-line for a sub based on Fs, you need to keep in mind the speakers Qts, and Qms, they should be low for SQ, Qts of .40 and lower, and Qms of 7 and lower will work great. Qts is speakers total quality in Ratio to its electrical, and mechanical characteristics, Qms is the Mechanical ratio.

If you want to run a sub for more of a spl use, its better to run a woofer off of a Bass EQ/ Amp bass boost circuit/ Deck boost. But it cant be mixed frequecies, like a deck with a 60hz boost, and a amp with 40hz boost, you need to cancel 1 freq out, or level the 2 freq's (there will be cancelation, and the sub will sound like its being pushed to hard-boost for tline have to be close to the quarter wave of the box as possible) This allows you to use a shorter tline length, in comparison to the speakers natural Fs quarter wave length. But Tlines, with Low Q woofers, like .30 and lower, you will be amazed how low the subs will play, lower than the boxes quarter wave length- almost down to the next octave- Cleanly. So, your looking at about 20hz almost as loud as the subs 40hz peak tunning. (depending on cabin resonace of vehicle ofcourse)

So, enuff explained. Lets go over the math, because thats where people get stumped the most.... This box in the tutorial I made sunday, I kind of dont want to give away to much, the rest you guys need to learn first hand. And the camera ran out of batteries, and the sun was going down, I REALLY wanted to finish it before night fall. So SOME pics, towards the end are missing.

So, math--- Box is tuned to about 41hz. So... useing the formula up there^

6.89 feet long x's The combined cone area of these 2 12s, I needed to keep a Constant 160sq port, 6.89' long. This box is PB- 3/4" The customer isnt paying full amt for MDF- haha.. oh well, I braced it very well. Notice all the 45s, even seperateing the 2 woofers, that is to keep the air flowing Cleanly, so no turbulance effects sound, or spl, and again, Reinforces the box for strength. I even filled larger gaps with Bondo, and painted the inside with blue paint, to keep the box from absorbing to much moisture- I will resin it soon-where I can.

So, I started off with the wood cutting. I got all my basic cuts, then copied all the OD cuts with a router, so I dont screw up sealing joints later.

So i have a question. The way you explain the math is easy to understand accept one part i am confused on. I'm reallllllllllly wanting to experiment and build a t-line for a crappy old MTX sub i have laying around just to try this out. The part i didn't understand was where you used a 10" as an example. (So, a Tline for a 10" with a Fs of 30hz, and a cone area of About 60sq inches, will be about 9.25ft-9.5ft long (rounded)). How did you figure it would end up being 9.25-9.5ft long when just above this quoted text you mentioned a length of 9.41ft long?

Just curious. I've been building boxes, installing car audio for myself & friends off and on for the past 17yrs as a hobby dealing with mainly sealed enclosures and recently getting into ported, but i suck at math so i can never quite understand the MATH part of making the right box and getting the tuning Fq right.

Thanks, Jason

[STEvil]

If you cant do math how do you make sealed ones?

9.25-9.5 is a rough area if you want to aim a bit low or a bit high. 9.41 is the "exact" 30hz line.

[Stewie_21]

Was that really nesessary STEvil? I never said i CAN'T do math....i just said i suck at it. 12 x 12 x 12 = 1728....1728 / 1728 = 1ft cubed. Don't be a smart ass. It was just a simple question. Ya'll are supposed to be helpful here and answer or ask questions, not be rude.

[Chris Hammer]

Was that really nesessary STEvil? I never said i CAN'T do math....i just said i suck at it. 12 x 12 x 12 = 1728....1728 / 1728 = 1ft cubed. Don't be a smart ass. It was just a simple question. Ya'll are supposed to be helpful here and answer or ask questions, not be rude.

You answered your own question. 9.25-9.5 is range...covers every number in between...so 9.41 is in the range...so 9.41 is right? his math is dead on. Longer length, lower tuning. Shorter-higher tuning...so when aiming for 30hz you can have a little wiggle room so to speak. It might be hard to get exactly 9.41...but if you get 9.5 to work correctly and fit your space the difference is miniscule.

If I understood your question correctly. If not then IDK what you are asking.

[Stewie_21]

That's what i figured was 9.41ft being the target length but the 9.25-9.5ft being a range. That's all i was asking and you answered it. Thank you.

[kirill007]

i was looking at running either a soundqubed hdc 3.0 10 or an ssa icon 10

HDC 3.0 10:

QMS: 6.999

QTS: 0.355

FS: 41 Hz

ICON 10:

QMS: 5.5

QTS: 0.38

FS: 31.1 Hz

which one would perform better?

im looking for linear responce and good sq

The Icon will walk all over the HDC for linear response and sounding good.

It doesn't need a tline though, a simple ported box or sealed box will make it sound pretty amazing.

[1two3]

i was looking at running either a soundqubed hdc 3.0 10 or an ssa icon 10

HDC 3.0 10:

QMS: 6.999

QTS: 0.355

FS: 41 Hz

ICON 10:

QMS: 5.5

QTS: 0.38

FS: 31.1 Hz

which one would perform better?

im looking for linear responce and good sq

The Icon will walk all over the HDC for linear response and sounding good.

It doesn't need a tline though, a simple ported box or sealed box will make it sound pretty amazing.

I know but I'm dying to try a tline.

What makes u say the icon is better?

[Chris Hammer]

i was looking at running either a soundqubed hdc 3.0 10 or an ssa icon 10

HDC 3.0 10:

QMS: 6.999

QTS: 0.355

FS: 41 Hz

ICON 10:

QMS: 5.5

QTS: 0.38

FS: 31.1 Hz

which one would perform better?

im looking for linear responce and good sq

The Icon will walk all over the HDC for linear response and sounding good.

It doesn't need a tline though, a simple ported box or sealed box will make it sound pretty amazing.

I know but I'm dying to try a tline.

What makes u say the icon is better?

Just do the T-Line...and do the Icon. Be happy. Dont know why people in the Tline thread are telling someone to do a ported box. If you have the time/money/ and space and you feel like trying shit then do it. Dont get too caught up in all the specs on the subs, or exact line length. Every car is different and NOT a perfect environment for sound. My tline could smash the lows in my truck and I could throw in a different persons vehicle and the box suck. Just play with it have fun. Try some 6th orders too why youre at it. I am about to build a mini one for two 5.25" TangBands I have and put it in my truck.

[matt scarlett]

Dont get too caught up in all the specs on the subs, or exact line length

(away from subs for a sec) That's what I thought when i did my Alpine SPR69 project, and it was a absoltue disaster. I spoke to Alpine and the QTS was a bit higher than the (sometimes) suggested QTS of around 0.4 or 0.5. The Alpines QTS is 0.9

Alpine told me the 6x9's were suited to a 4 cubit ft enclosure.

[soBASED]

sooo, i'm back here agian, gonna build a dual t-line (hopefully) for 2 E8v3's but my question is, and i couldn't seem to find the answer... My subs depth is 5 1/8" or so, but my effective cone area is 30in^2 so if i did a port that 10"H x 3"W, i obviously dont have enough mounting depth, can i make an "air chamber" to mount the sub or would i need to just triple baffle the front? I've seen RAM Designs do a 8" in a t-line with an air chamber but not sure if this would change tuning?