20 cm x 20 cm x 25.3 cm = 10,120 cm3 = which is 10.12 Liters ..roughly a 22cm cube
Ok, Designing a conventional enclosure would get us a volume of a less
Looking at this website – http://www.bcae1.com/spboxad2.htm
and plumbing in a few numbers gets us a volume of 6.357 Liters for a ported enclosure
Working backwards, that 6.357 liters gets us dimensions of 15 w x 15 w x 28.5 d (ish), or alternatley a roughly a 19cm cube……a 3cm per side reduction……
So, lets see just how small we could get ‘sensibly’ –
The speaker outside physical diameter is 98.2mm – lets call it 10cm. That’s going to drive the outer dimensions of the speaker…….
The speaker ‘cutout’ is 76.8mm – lets call that 80mm
I’ll use walls of 1.5cm thickness for rigidity (may change this later)
Speaker diameter = 6cm – that’s a surface area of 28cm2
One dimension of our rectangular waveguide is 8cm. lets call that width
8cm width x ? cm Height = 28cm2
28/8 = height =
That gives us waveguide of 8cm x 3.5cm……..
Working with the above gives us the following minimal enclosure dimensions……
This comfortably sets the minimum Front width of the speaker to 110mm. It could go to 100mm but it’ll look a little better with a few mm either side….
And, the length – we’d figured out earlier that the waveguide needed to be 72cm in length
Lets add the speaker mounting depth – roughly 5cm…….
This tube takes up a volume of ……
- 770 long x110 high x 110mm wide = 9.32 Liters
That’s no good!, the length and height will be set by how many times we can fold that guide over……..
Half of 72cm is 36cm – should be easy enough?
err, Nope, allowing 50mm for speaker depth and another 35mm for a coupling chamber (I have no idea if this is needed or not , but it seems sensible that there’s some cavity behind the speaker to allow airflow)
By folding in half, we get an enclosure that’s
- 475mm long and 115mm high x 110mm wide = 6 Liters volume taken up
BUT…something is a little amiss…
Note the path followed
add up the path lengths – we get roughly 342 + 50 + 310 + 32 = 732mm – a small increase in intended length due to the bend. That’ll lower the resonance of the tube so we’ll need to watch how many turns are used
Lets fold 3 times to get that length down
720mm / 3 = 240mm line
an improvement, we’re now
- 355mm x 165mm x 110mm = 6.44 Liters – but an odd shape..
- 295mm deep x 215mm tall x 110mm wide = 6.98 Liters and a good shape –
- How long is the TL?
- 162.5+50+130+50+130+50+262.5 = 835mm..
That’s 115mm longer than needed……
That’s OK, we have 4 channels, lets reduce them all equally in length to make it all shorter….
we need to reduce the overall speaker length by 28.75mm
Better – Volume =
- 266.25mm x 214mm x 110mm = 6.27 Liters –
TL Length =
- 133.5+50+101.25+50+101.25+50+233.75= 719.75
We’ll call this REV 1