New DIY double 15 bass/kick

Apr 4, 2017
24
3
3
#1
Hi everyone,

I'm currently working on a new cab that can be used as standalone for sub/bass with a BR 12/1.4 mid high.
As well as an low-mid extension for a horn loaded 12" with a 1.4" (mounted coaxial) ,on top an 18" tapped horn.

I like the TW audio B30 layout, and went that way. It looks like a tapped horn with "front" chamber configuration (correct me if I'm rong).
While knowing nothing about Hornresp, I started anyway, but I'm sure I made some mistakes.
I can post some info and pics tomorrow.

Dimensions would be: 571x571x750 (pretty close in external volume to the B30).
Extension down to +-45/50 Hz
Current driver: B&C 15NW76 (other options are possible)

So the main question is, how do I divide the cab in the right segments for hornresp.
3 segments or 4? etc.


I know this is not much info, but I'm working an a more detailed plan of approach.



Gr,

Stef
 
Aug 21, 2012
117
3
18
Aberdeen, Scotland
#2
Well, without knowing both the internal layout of the B30, and how closely you'll manage to stick to it, it'll be rather hard for anyone to tell you exactly how to model it.

I'll assume for the following that this layout is what you're tallking about however:



So, here's how Hornresp will interpret what you put in.

1: S1 is the area at the narrowest end of the horn.
2: S2 is the area at the point (nearest the throat) where the sound enters the horn. In the case of the B30, these are both at the same place, therefore you model them as being the same area with the smallest possible length between them, ie 0.1cm.
3: That therefore already uses up one segment, leaving you with only 2 left if you chose a 3 segment horn. However the last segment has to be used to designate the second entry point for sound from the other side of the driver entering the horn, so you'll have to use 4 segments.
3: S4 is the area where the other side of the driver sits in the horn, so that's the cross section though the horn at the centre of your driver.
4: That therefore means you only have one segment left free to use between the start of the horn and the inner end of the driver baffle - however if you're sticking to the B30-ish layout, you may have more than one angle to accommodate there. You will therefore need to combine 2 parts of your horn into one segment for the purposes of building your model. In order for the model to be representative when you do that, you'll need to make sure that those 2 parts have as consistent an expansion as possible so they can be merged without rendering the model un-representative.
5: Hornresp uses the "Throat Chamber" designation rather than "rear chamber" for any space between the driver and S1. You'll therefore need to leave the "rear chamber" fields blank.

In case all that text doesn't make sense, hopefully this image will:



I've used your suggested dimensions of 571h x 750d to get an idea of what the box will look like.
Even with 15mm plywood, you'll have to angle the driver baffles back further than the B30 to stop the magnets of the 2 drivers hitting each other.
That in turn means that getting to the back of the drivers to install their mounting bolts might be a bit awkward - I'd suggest you build a mockup out of any cheap material you can get before you go too far down the design route - the last thing you want is to come up with a brilliant idea in Hornresp that you just can't use once you've built it!

Hope this helps,
David.