SQ JBL GTO-804 subwoofer transmission line enclosure.



A build last year for a JBL-GTO 804 8″ subwoofer, which is a little beast of a thing. The GTO 804 hits low enough on its own, but I wanted to push the limits a bit more, so I aimed at the JBL’s given FS figure of 29Hz. However, one doesn’t simply tune a box around a single Helmholtz resonance figure, you aim for a specific response or response curve. This was a transmission line built purely for SQ in mind. It hits low but I managed to design it to smooth out unwanted peaks in the response. Its not an SPL Monster, but it plays flat and hits low. Far better than your average 12″ pre-fab subwoofer enclosure from your local car audio shop, even though its only an 8″

39 x 12 x 10


7 thoughts on “SQ JBL GTO-804 subwoofer transmission line enclosure.

  1. Hi Matt i trust you are keeping well I am very interested in your design for the SQ TLine for the 8″ JBL it looks like you have put the dimensions down , would it be taking the piss if i asked you to share the build plan with me?

    I have 2 of these subs already and would really like to try your enclosure with them

    Kind Regards


  2. Matt,
    I think I can work most of it out with the given dimensions, except the length of the center board, and the thickness of the material used. I would really appreciate help with those. I am guessing either 1/2 or 3/4 inch mdf. I think this would make a great base to a console in a full size truck.
    Thanks for the help,

    • Sorry for the very late reply. Yes you could fit two JBL’s sub. Of course it all depends on what dimensions you have to work with, but your average baffle will be enough to fit 2 or 3 8″ subs.

  3. Matt,

    I emailed late last year about this build you did for the JBL GTO-804. The external box dimensions on your build were 39X12X10. What are the internal panel dimensions and placement locations? I would like to copy this build as I have one of these drivers that I want to use.

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