Speaker Enclosure Design….


Task – Create a pipe of 8.5cm diameter and 72cm in length in Fusion! and fit it into as small an enclosure as possible

The 85mm Diameter transmission pipe will set the dimensions for the enclosure width,

The sketch above shows a single fold of the pipe, The length is half of the 180mm needed as I’ll be rotating these and joining them to make the 3D sketch to form the pipe.

The purple line shows the path that the centre of the pipe will follow

The red dotted line shows the path that the outside of the pipe will follow

I’ve allowed a 1cm ‘seperation’ between the folds – this should ensure that when the enclosure is 3D printed, there’ll be plenty of stiffness

– Right now, the only dimension that i’m not sure of is the 90cm part….lets work on that

The audio path consists of 4 straight parts and 3 curved parts.

folded 2.PNG

The length of the Purple curved parts from the first drawing is easy enough.

Circumference – 2 x π x r
We only need 1/2 the curcumference (as one fold is 1/2 a circle)
Radius here is (42.5 + 42.5 + 10)/2 = 47.5
Circumference of the full circle = 2 x π x 47.5 = 298.45
Half of that is 149.225…..Lets call it 150mm
we have 3 folds = 3 x 150mm = 450mm length
we need a total of 720mm length
720 – 450 = 270mm
we have 4 straight lengths of
270 / 4 = 67.5mm
So, our completed sketch should look something like……….



D’oh! – Need to adjust that pipe length a little to take into account the radius of the bend!

That bottom ‘port’ pipe end – shown in yellow will be need flush with the outer side of the box – so in effect my transmission line will now be longer than intended…

I need to reduce the lengths of the straight parts a bit

Radius of bend = 47.5mm, Add the 10mm for the box thickness (may reduce that later) – I need to allow for an extra 57.5mm for that bottom part.

I’ll also need to allow for the speaker……


Speaker mounting depth is 47.61mm. The enclosure’s going to be 10mm thick which means the back of the speaker will sit 37.61mm into the enclosure….

Looking at the top part – where the speaker will go, we know it’s 57.5mm ‘short’

Questions……..Cavity / transmission line


Does this mean that I need to allow another 57.5mm – short – 10mm thickness  – 37.61 speaker = 9.69mm?

actually – do I need to allow a cavity behind the speaker in a transmission line? (probably), if so, how much.

and that raises another question – Volume of the transmission line? does this have an effect on the response (probably) – I know that larger speaker enclosures make for more bass…..

I guess i’ll be iterating a little with the prints………..

For now, i’ll ignore the speaker cavity and revise the line length a little


we have 3 folds = 3 x 150mm = 450mm length
we need a total of 720mm length
720 – 450 = 270mm
one quarter has 57.5mm longer…
So, 270mm – 57.5mm = 212.5mm
we have 4 straight lengths of
212.5 / 4 = 53.125mm
Lets reduce that 67.5mm to 53.125mm…call it 53mm


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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