Coaxial Wedge Collaboration

Re: Coaxial Wedge Collaboration

Michael Smithers said:
This morning I removed the internal port tunnels. Only ~43mm of tunnel from the front support and front plywood remained.

The impedance trace showed a dip (and 0 degrees phase) at 57 Hz - finally.... (Updated CAD drawing attached.)

However bass reflex calculators all say that the port length should be closer to 92mm.

Could there be an effective lengthening of the port on the inside caused by two sides of the port continuing on? I.e. the cabinet floor and side-wall?

Thanks,
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When a port is located next to a wall/side the effective length is longer than the actual length. This is what you are seeing.

The actual effect depends on a number of factors-how close it is to the wall, the size of the port and so forth.
 
Re: Coaxial Wedge Collaboration

I finally got the BMS 12CN680 driver installed last Sunday. I also installed the crossover - I think the Curtis List - from Assistance Audio and a biamp switch. Sadly I haven't yet run it up to any significant level, but from brief listening, I must say I like the compression driver - smooth and clean.

6297898091_0e793d5804_z.jpg6298431460_932e0cced7_z.jpg

Next steps: grill and foam, plus a final coat of paint.
 
Re: Coaxial Wedge Collaboration

Man that's sexy! I've been wanting to build pretty much the same thing for a year or so now. Where can the x-over be had and about how much?
 
Re: Coaxial Wedge Collaboration

Michael Smithers said:
Yep, I thought it was something added by the North American distributor (with a hot glue gun) but the photo on the BMS website suggests BMS do it! :)
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Hello Michael, Bennett is talking about the foam you have added to the front of the cabinet.

We (the North American distributor) did add polyfill to the existing sweater that BMS has on the horn. (with a hot glue gun)
 
Re: Coaxial Wedge Collaboration

Here's a frequency response plot, 5' above the wedge and on axis. No grill. Systune (5.46s pink noise, approx 6ms window (due to the low ceiling in my garage) and Turkey 50% both ends, 1/12th octave smoothing) and a Behringer ECM8000 mic - not ideal, I know. Interestingly all the ripples above about 1kHz, including the peak at 16.3 kHz, match ripples in the frequency plots in the product data from BMS.
 

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Re: Coaxial Wedge Collaboration

Two custom grills finally arrived today. I figured I'd splurge rather than trying to cut up a larger sheet of circular perf'd steel (from, say, Penn Elcom) and making a hash of the edges. They're 2mm steel with a hex pattern. Here I've installed the first with 5mm of grill foam.
 
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Re: Coaxial Wedge Collaboration

John Halliburton said:
... but where on Earth did you find a shop that would only make two pieces?
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Thanks. Actually Googl'ing showed up a number of companies that do perf'd metal - circles and hex patterns. A few phone calls later, I found one that does small quantities. The grills look punched, not laser cut. I'm told laser cutting is more expensive, but there are some hacker spaces around with laser cutting gear.
 
Re: Coaxial Wedge Collaboration

Last night I did sound for a former Australian Idol finalist and her band. I gave her this (BMS based) wedge and the other band members got four JBL MRX512M's. (All monitors were on Lake Contour processors - HPF and limiters - and QSC PLX2 series amps.) Her mix was mostly her own vocal.

It's a subjective data point but after the show she said this wedge was the clearest she'd ever heard. (Since Idol she's done both larger festivals and very small gigs.) I think it's more a testament to BMS quality and the Curtis List crossover, than the cabinet design.

PC301913.jpg

With Bennet's move to B&C, I checked out their latest coaxials and there's a new 12" 12HCX76. It looks very similar to the BMS 12CN680. Has anyone heard it? A web search shows it to be about US$600.
 
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Re: Coaxial Wedge Collaboration

BTW: I'm having trouble with the grill foam separating from the grill. I originally used a fairly serious spray adhesive on the back of the grill then placed the grill on the foam and left it to dry with some gentle weight on top to keep everything flat.

Does anyone have better ideas? I've considered rolling glue onto the back of the grill first but I'm worried about glue seeping around to the front.

Best,
Michael
 
Re: Coaxial Wedge Collaboration

Michael Smithers said:
BTW: I'm having trouble with the grill foam separating from the grill. I originally used a fairly serious spray adhesive on the back of the grill then placed the grill on the foam and left it to dry with some gentle weight on top to keep everything flat.
Click to expand...


I suspect this is because the grill you chose has a LOT of open area compared to some of the grills I most often see. This leaves you with much less grill surface area for the foam to bind to. You can try re-spraying or gluing, but I have a feeling that this may be an ongoing problem if the wedge gets used a lot. In hindsight I would suggest a less porous grill or putting the foam on the outside.

Of course that's not helpful now.... all I might suggest now would be:

-re spray on an as-needed basis
-glue (choose carefully as some glues will eat the foam)
-try a slightly denser but thinner foam product which may give you marginally better contact with the grill with possibly less weight if made extra thin
-try to devise a couple of support rods behind the foam to keep it pressed to the grill
 
Re: Coaxial Wedge Collaboration

Michael Smithers said:
BTW: I'm having trouble with the grill foam separating from the grill. I originally used a fairly serious spray adhesive on the back of the grill then placed the grill on the foam and left it to dry with some gentle weight on top to keep everything flat.

Does anyone have better ideas? I've considered rolling glue onto the back of the grill first but I'm worried about glue seeping around to the front.

Best,
Michael
Click to expand...

Use grille cloth instead of foam (like Danley).
 
Re: Coaxial Wedge Collaboration

Michael Smithers said:
Thanks. Actually Googl'ing showed up a number of companies that do perf'd metal - circles and hex patterns. A few phone calls later, I found one that does small quantities. The grills look punched, not laser cut. I'm told laser cutting is more expensive, but there are some hacker spaces around with laser cutting gear.
Click to expand...

Hello. Ex-off-road truck enthusiast here. Australia , despite it's small population, has a very well-developed metalworking and fabrication industry, largely geared towards making small batches of tech-intensive products. I'm assuming Australias remote location, small population and need for specialized equipment in areas like farming, mining and remote travel largely supports this capability.

Edit: The comment was more directed towards JohnH than you, Michael. You are aware of this, I'm sure :)
 
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