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    Thread: How to make a transmission line enclosure in 4 easy steps !

    1. #1
      from dust to dust
      amangujral's Avatar
      Join Date
      May 2012

      Thumbs up How to make a transmission line enclosure in 4 easy steps !

      I had been driving from last 8 years now, car audio was very close to my heart, as i spent anywhere from 1:30 min to 2hrs daily back n forth from college. I did whatever i could with little or no money to upgrade and to customize my sound experience . From SQ to SPL , i did all . Now that i am finally an architect , i could spend more of my time at home for relaxing then worrying about my design to be submitted. I had gathered a lotta info in music to start carefully in my home audio project, i did some 4-5 custom builds while i was in college for home too but never to seriously and didnt had a lotta space in the room . Well you would know about the space issue , if ur a college student . . I tried sealed, ported, 6th order bandpass , dual chamber reflex , dual chamber dual reflex , horn loaded enclosers with drivers ranging from 10" to 3" full range drivers.

      I had the cdt audio sona pods installed in my room taking care of the 5.0 , they are 2" full range drivers , that go down to 200hz .Some of the best speakers i have heard within 1lakh range home theaters from brands like elac , wafedale, tannoy, polk audio and many more, yet costing 1/4th of those big brands. So i needed something that will take care of 30hz to 200hz , yet is punchy , musical and ca go down to 30hz . THIS WAS A BIG DECISION ! not many 8" -12" drivers go down to 200hz and roll off to a 6db slope beyond with a flat yet musical response , and those which are , costs a

      STEP 1
      : Decide the equipment !
      Not all spkrs/subs sounds sweet and comfortable in a t-line . not all spkrs/subs are designed to be used in t-line too. If you mates have a some understanding abt theil-small parameters, look at the Fs of the spkr/sub . That will tell you the tuning freq to use the thing at. The qts and qtc will tell you if the spkr/sub is suited for the t-line .

      Then there is the box rise !! this is a killer, lesson for some other day.

      I picked up a pair of CDT audio Qes 680 6.8" drivers . This is a amazing little puppy . awesome in vocals , yet a deadly sub-bass driver ! with a xmax of 15mm and xmech of whooping 25mm ! this small little driver will sure move lots of air . Also they fit the puzzle of a driver being musical, which can do vocals, yet acts like a sub .. all being inexpensive . People might think the efficiency is the drawback, but i have 1000watt rms at my stake for the subs alone !

      here are few specs for the same

      • Frequency response 10Hz-4000Hz
      • Power handling: 300Watt Pk.
      • Sensitivity: 84dB
      • Cone: Mid/Kevlar/Fiber glass
      • Magnet weight: 30 Oz
      • Voice coil: 38mm
      • Fs: 39Hz

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      STEP 2
      : Do lots of calculations.

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      from placement of driver to cancel 2nd and 4th order harmonics , to cross section of path, length of path , amount of stuffing needed and change in response due to stuffing .. and few more calculations causing high blood pressure.

      STEP 3
      : Get the sucker made !

      Just drafted some 3d looking drawings for carpenter understand the complexities, else they come up with a face so confused , which rivals that of viewers watching rahul dravid doing his tuk-tuk .

      Attachment 108970

      My friend own a interior firm, i usually get my wood work done at his workshop , they work with an accuracy of 0.5mm . Good enof for me !
      Got some 17mm grade-A mdf and started the work.

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      artists on work !

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      power saw : here we go

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      magic and its halfway done . .

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      a preview of box to be done , fixed the other panel for marking of mdf channel inside for screwing it up.

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      siliconed for no leaks.

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      anglular channels placed and wired in place.

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      and its standing on its feet for the very first time

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      siliconed again for the panel .

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      the final step : hole !

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      a little too small to fit .

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      My friend who own this interior firm thought he might give this a try .

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      4 : wait for the upgrades and review to follow , too tired to type more !'

      more to follow : how does it sound with no stuffing, little stuffing, lotta stuffing, acoustic foam and ANOTHER 6.8" DRIVER PLACED INTO SAME BOX !

    2. #2
      from dust to dust
      amangujral's Avatar
      Join Date
      May 2012

      missing attachment from step 3

      here an attachment of the box in 3d
      Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    3. #3


      Join Date
      Apr 2012
      New Delhi, India
      amangujral Awesome job, but your drawings have a big error that an architect like you can make but an ENGINEER like me will spot.... Im not telling you what it is though

      I got a chance to hear these a few days ago and i must say i was very impressed by their response. One would not imagine that its only a 6.8 inch driver playing!!!!

    4. #4


      Join Date
      Dec 2011
      Wow..you are the person who commented that you don't understand Hornresp!! In fact you don't need to!! you can do all the calculations that Hornresp does for yourself!! Hats off to you. So planning to put these TLs into your car


    5. #5
      from dust to dust
      amangujral's Avatar
      Join Date
      May 2012
      RodeoSport engineers always take orders from architects . So i dont mind making mistakes , its the engineer who gets yelled at ..
      Last edited by amangujral; 14th Oct 2012 at 21:05.

    6. #6
      from dust to dust
      amangujral's Avatar
      Join Date
      May 2012
      Quote Originally Posted by venki7744 View Post
      Wow..you are the person who commented that you don't understand Hornresp!! In fact you don't need to!! you can do all the calculations that Hornresp does for yourself!! Hats off to you. So planning to put these TLs into your car
      thanks venki , as mentioned , this is a home theater sub to go with rest of my equipment , but it was also build to test this sub in an car environment , specifically for car likes innova, scorpio , xylo etc.
      Last edited by amangujral; 14th Oct 2012 at 21:13.

    7. #7


      Join Date
      Apr 2012
      New Delhi, India
      amangujral bhai sahab, without an engineer, an architect is just like a kid with crayons can only make pretty drawings on paper

    8. #8
      Breaking Windshield !!!

      Join Date
      Feb 2011
      Aman very nicely done. Will surely want to audition the same !!! At one time few months back I was planning to make a T-Line for my SMD 18 inch sub for a Home Theater use but shelved the project because the enclosure was taking a huge space !!!

      A very nice write up for making T-Line enclosures !!!

      Taken from here -> Quarter Wave / T-Line tutorial-UPDATED - Subwoofers / Enclosures - SMD Forum

      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.

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