Speaker Design…Waveguide, lets start from scratch……

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……

2D folded start from scratch 1

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…….

2D folded start from scratch 2

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)

2D folded start from scratch 3

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

2D folded start from scratch 3 - Copy

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

2D folded start from scratch 4

an improvement, we’re now

  • 355mm x 165mm x 110mm = 6.44 Liters – but an odd shape..

 

Four Folds

2D folded start from scratch 5

  • 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

 

2D folded start from scratch 6

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

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!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: