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Quarter Wave/Transmission Line Enclosures

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    Quarter Wave/Transmission Line Enclosures

    So I have been researching what kind of box I want to build for my next subwoofer setup. I have done sealed and ported boxes before, which worked fine for their application, but I wanted to do something more involved and try to learn a thing or two on the way. So while researching I came across what some article called T-line, or Transmission line boxes. In the article it stated that this was the most efficient and accurate box to make, but due to their size it usually is not practical for use in cars. However, I am not trying to squeeze 13, 47" subs in the back. I would like a single or dual 10's, perhaps a 12 depending. So after hours of reading articles online and browsing several car audio forums, I decided to work out a design for a single 10" Rockford Fosgate P1. Took a while to get all the dimensions and parameters right, but I did it.

    Now, fast forward to today. I decide to consult a local car audio shop on my idea, as I purchase from them with some regularity, and he was vehemently opposed to the idea. First he said it would be too big, then that it has poor frequency range response, then that it would be heavy and cost me too much gas mileage.

    I say all of that to ask this question:

    What is your take/experience with Quarter wave/t-line enclosures?
    _C'est La Vie, C'est La Mort_

    #2
    They are extremely hard to design correctly.
    They have similar characteristics to folded horns which means they are very efficient (impedance transformers, not electrical).
    You'll have like a 2-3 cu ft enclosure for a single 10.
    I think they reduce excursion and increase mechanical power handling.
    Are you sure your calculations are correct? I'm sure the enclosures are very picky about minor miscalculations.
    That's all I remember: http://www.quarter-wave.com/
    Have fun

    YouTube Clicky!!

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      #3
      Well I think they are correct. Her is how I got my calculations:

      Port Area = Cone Surface area
      Port Length = Speed of Sound in fps ~ 1130 x the subwoofer's Fs(30hz) / 4 = 9.41 ft ~ 113"

      Port Dimensions = 16 x 3.75 x 113

      Then I would fill the chamber with the subwoofer with polyfill.

      Here is a rough idea of what I have so far.

      _C'est La Vie, C'est La Mort_

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        #4
        wait, why do you want to do a TL?

        YouTube Clicky!!

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          #5
          Something new, plus I read it was louder and had a more flat frequency range.
          _C'est La Vie, C'est La Mort_

          Comment


            #6
            I've read in the past that the T-line boxes are very clear in bass response, especially in a home theater setup where acoustics will be much better than in a car. I've never seen or experienced a T-Line box in a car so I don't know how the sound will be or if there will be a big difference between that and a ported/sealed box. The only T-line box I've seen was VERY long and used a single 8" subwoofer and sounded good in a movie room.

            It looks like you did your homework.
            Been a long time. Still alive...

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              #7
              I have watched a lot of videos on youtube, and read in forums where people used them in cars and were very pleased with the sound.

              I guess I could try a small scale test and build one for my home theater setup, and then throw it in my car and gauge the difference in sound. Now to find a good 8" sub...
              _C'est La Vie, C'est La Mort_

              Comment


                #8
                Louder than ported? Maybe, it depends on the design. I've looked at some of the theory behind it and the main goal is to reduce resonance, standing waves and flatten the impedance curve. These are good for sq.
                Honestly your design looks like a ported box tuned at 15 Hz, but I'm not well versed in TL box design. Most TL boxes I have seen people build have tapers to the port and yours is straight.

                YouTube Clicky!!

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                  #9
                  There are 3 basic types of "Transmission Line" boxes. I forget the names, but basically one the port gets smaller, one the port gets larger, and one stays the same. Now, this is all from my limited research. I am by no means saying this is the way it is, just what I have read from multiple sources. The true, plain Jane, transmission line box that I have been researching is a port where it maintains the same area as the cone surface area of the subwoofer.

                  Now as far as the "louder" comment I made, I meant to say louder across the frequency range, where a ported box may have a large spike at, say, 40hz, and a sealed box may have a more even response, but is considerably more quiet.
                  _C'est La Vie, C'est La Mort_

                  Comment


                    #10
                    I read that too. I think it was the "classical" design or something to that effect.
                    the TQWT are the ones with the tapered ports and can be considered horns.

                    I don't see a difference in a very low tuned ported box and a classical TL other than the stuffing. Either way your box looks like it will sound good even if it is a ported design.

                    YouTube Clicky!!

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                      #11
                      I hope so. It is gonna be huge for just a single 10" sub. Though I am considering different subs. I want to keep it in the 150-300w RMS power range. I would consider going down to an 8" sub, or two 6.5" subs. I don't care to rattle my car apart, just want to add a little depth to my music. I guess realistically I am open to anything, just want to do something creative.

                      Here is a design that would hang from the hat rack in the back of the car for two 6.5" Tang Band subs:

                      _C'est La Vie, C'est La Mort_

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