Finally – A Fully Parametric Transmission Line….

1 - Final Parametric - 1

Doesn’t look like much but this is the culmination of several days of cursing & Learning!

This enclosure (pictured sideways here) dynamically changes its height and depth depending on the speaker SD and the enclosure width you chose.

You can alter the following parameters , I’ve set the above to be the number in Brackets for my PS95-8.

  • Speaker Outer Diameter (about 100mm)
  • Speaker Mounting Cutout (about 80mm)
  • Speaker Mounting Depth (about 60mm)
  • Speaker SD – 28.8
    • This parameter is the key one for determining the dimensions of the enclosure
  • Speaker Diameter – 60mm
    • (calculated from SD)
  • Guide Width – 110 mm
    • This is the width of the speaker, less two wall thickness
  • Tolerance – 0.5mm
    • When joining the two ‘sides’ to the central part, this sets the small amount of free play you’ll have to be able to join them all up nicely
  • waveguide Correction – 10mm to 140mm – This sets the height of the exit port, which alters the waveguide length, allowing some tuning to happen.

How it works

SD gives the surface area needed for a waveguide. Any Waveguide should have the same area as the speaker.

  • Here I’m using a rectangular waveguide
  • I’m going to use the entire width of the speaker as the waveguide and just bolt some sides on to seal the guide up
  • SD = 28.8 which gives a diameter of 60mm which is the area of the cone
    • A = πr = 28.27cm2
    • The Rectangular waveguide also needs an area of at least 28.27cm2
  • my speaker is 140mm wide, less two wall widths (10mm each) gives a width of 120cm
    • Area of a rectangle = X x Y = 28.72 cm2
    • 28.27cm2 = 120mm x ?
    • ? = 2827/120 = 23.5 mm
  • So, that gives us an enclosure waveguide / port width and height of
    • 120mm x 23.5mm

Some Pictures

The above pictures show a couple of black blocks that represent my existing speakers. I’ve changed the parameters which shows how much the enclosure changes


And some pictures of the internals

The two black blocks are the size of my existing speakers, see the caption on each image but you can see how much the box changes in size when you change the parameters!


All that’s left now is figuring out the cable routing and mounting the speaker terminals!


Author: Bleugh

Early Fourties, Wife, two kids in primary school. Both of us work full time...5 years now we’ve been Back in Blighty after a decade away...It's a new country for everyone! Still finding time to tinker!

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