New BassChat 8"Cab design

[djk]

1 minute ago, Phil Starr said:

Hi David, to keep the same tuning you only have to match the area of the round port and keep the same length. Those are the only two numbers that matter. I keep using the drainpipe because it's simpler for most people. if you can calculate pi r^2 that will be ok, but if you are forming a port then it would be better to make it slightly bigger to reduce potential wind noise in the port. I've had a look and something 8x5cm inside measurements and 11.4cm long would work. You can change the shape so long as you keep to 40cm^2 area

Phil, many thanks for the help, it's much appreciated.

 

As I said, for me as I have the ply and no drain pipe it might be simpler.

 

I've now loaded the driver into the cabinet as it is and at low volumes it sound great, although I only completed this today and have only had the chance to try it with my Ashdown Rootmaster 800 (at low volume). I'm ging to see how it sound with the TC Electronic amp later this week. Still waiting for the grill to arrive too.

 

I have a ruminate over which path to take regarding the port and let you know the results.

 

I really appreciate all the work and support you and the others involved in the development of the BC cabinets, thank you.

 

Regards

David

 

 

[Mottlefeeder]

37 minutes ago, Phil Starr said:

Hi David, to keep the same tuning you only have to match the area of the round port and keep the same length. Those are the only two numbers that matter. I keep using the drainpipe because it's simpler for most people. if you can calculate pi r^2 that will be ok, but if you are forming a port then it would be better to make it slightly bigger to reduce potential wind noise in the port. I've had a look and something 8x5cm inside measurements and 11.4cm long would work. You can change the shape so long as you keep to 40cm^2 area

Phil,

Just for my education: changing the port size changes the available internal volume of the cab - what sort of % change in cab volume would start to be audible / ring alarm bells for you?

(Another) David

[Phil Starr]

7 hours ago, Mottlefeeder said:

Phil,

Just for my education: changing the port size changes the available internal volume of the cab - what sort of % change in cab volume would start to be audible / ring alarm bells for you?

(Another) David

That's a great question and I had to think about the answer. Part of this is that I rely on experience, I've spent a lot of time building and modifying cabs. When I build pairs of cabs I'll often try modifications on one cab and then A/B them next to each other so you do get an instinct about small changes

 

The first thing is that the efffects are slight. First of all most of the 'sound' of the speakers is what goes on above 200Hz and the box modelling is about the response of the true low end below that frequency. The other David has tried the cab out as a sealed cab andit 'works' and it probably sounds OK, even though he will get 3db of boost of the low end with a port plus a lower roll of frequency.

 

Secondly the calculations give incredibly percise answers but in real life it's a bit messier. Manufacturing tolerances mean measured speakers vary and the published figures I use can't always be trusted. Thre are always air losses from a cab which are allowed for in the calculations but I use a 'standard' value of Ql=0.7 which is middle of the bell curve. Importantly I then build the cab so ay significant error would show up. I'ver no control over how accurately people build the cab so calculating port sizes to 3 decimal places doesn't make much sense. You can build the cab successfully even if you make small mistakes, which should be reassuring

 

Anyway I've looked at the responses with the same tuning and the box sizes increased and decreased by 10% but tuned to the same frequency.  This is the box you are all building with the Fane in blue. You can see that increasing the cab by 10% (red) gives you a bit more bass but reducing the cab 10% makes a smaller difference. The red trace gives 1db extra at 60Hz and you'd hear that with the cabs next to each other but only just. You wouldn't be able to detect the difference with the smaller cab in this case. This is a 2l shift in volume and the increase in port size is only 0.2l so insignificant. It looks like my instincts were good in this case, Phew

 

 

 

[rwillett]

Finally have finished all the routing for Speakon connectors and handles.

 

 

 

 

Sides, top and bottom already glued,  Now doing front and rear glueing and clamping.

 

 

 

Next steps tomorrow, let the glue cure overnight, a bit of filler (ahem), sanding down, put a 6mm curve on the edges with the router, two layers of smooth Armacab on all external surfaces, one top layer of textured Armacab but masking off any rebated areas, measure for black 3d printed corners, print them overnight as eight hours , assemble all and test for Sunday (hopefully).