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Author Topic: Looking for plans for dual 18 cab for JBL 2241H drivers  (Read 11974 times)

David Morison

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #20 on: November 08, 2014, 09:02:49 am »

Thank you David for making me use my brain. I believe Win ISD is working for me now. Maybe you could do me a favor and confirm my results.
 With 2 2241 drivers in a 17.255 ft3 box, for a tuning freq. of 30 hz, a single vent 5x18" should be 6.89" deep and will give me a vent mach of .11.

My version of WinISD (version 0.7.0.9) gives a fractionally longer vent for that config, (7.72"). I'm not sure where that difference is coming from - I don't recall port calculations changing between any of the older versions of the program I've used in the past. Have you perhaps selected "2 flanged ends" rather than the default "1"?

If anything, I'd go with the shorter of the 2 anyway, as I think 30Hz is a little low for these drivers. In common with large box sizes, low tunings allow the speaker to run out of excursion more easily, so a slightly higher tuning will help mitigate that.

Vent airspeed is dependent on power applied, I'm getting a max of 37.8ms-1 (that's your Mach 0.11) at full program power, but you'd be so far over Xmax at that power level that I don't think any air noise would matter - distortion would already be through the roof anyway.

At the 40V input I mentioned earlier, excursion is only a little over Xmax (8mm vs 7.6) and vent airspeed is 19.5ms-1 or Mach 0.56, which should be perfectly fine.

Cheers,
D.
« Last Edit: November 08, 2014, 09:32:43 am by David Morison »
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Mike Holtzinger

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #21 on: November 08, 2014, 01:36:17 pm »

My only option for ports are square or round so I changed the tuning to 35hz and my 5.5"x18" vent length is now 3.77. No flare is available. BTW, my WinIsd free version is 0.44.
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David Morison

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #22 on: November 09, 2014, 09:51:36 am »

My only option for ports are square or round so I changed the tuning to 35hz and my 5.5"x18" vent length is now 3.77. No flare is available. BTW, my WinIsd free version is 0.44.

OK, maybe the older versions of WinISD do calculate vent length differently then.
I've checked using formulae published here and here and those both agree with WinISD 0.7.0.9.

For your latest iteration this gives a target length of 4.35", so not too big a difference.

I'd definitely agree with keeping the tuning frequency up at 35+Hz, that helps avoid the worst losses of headroom from running out of excursion.

D.
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Mike Holtzinger

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #23 on: November 10, 2014, 01:22:38 pm »

As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?
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Spenser Hamilton

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #24 on: November 10, 2014, 01:29:54 pm »

As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?

If I am picturing it correctly, the extensions will effect port tuning, it will likely take a physical build to determine how much,
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David Morison

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #25 on: November 10, 2014, 02:51:27 pm »

As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?

I'd agree with Spenser, it'll probably take building and measuring to be sure.
My hunch is that it'll fall somewhere in between the tuning you would achieve without those extensions and that which would come from having all 4 sides of the vent extended.
I'd be very tempted to just extend the short sides as well to make everything match as long as that's physically possible. That also means the vent takes up a bit less room in the cabinet, essentially by pulling the whole thing forward by that amount.

David.
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Mike Holtzinger

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #26 on: November 11, 2014, 10:23:42 am »

So I'm going to extend the port outside of the cab to the baffle and I've figured approximately .65sf for the internal bracing which will bring my port length to 4.5". I think I'm ready to start cutting!
 Thanks for all the help!
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David Morison

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #27 on: November 11, 2014, 03:17:02 pm »

So I'm going to extend the port outside of the cab to the baffle and I've figured approximately .65sf for the internal bracing which will bring my port length to 4.5". I think I'm ready to start cutting!
 Thanks for all the help!

Nice one, good luck!
D.
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Mike Holtzinger

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #28 on: November 29, 2014, 01:23:37 pm »

 What material and how much should I use for dampening on the inside? I know the stuff JBL uses is like a flexible 1" thick yellow fiberglass that isn't available at Home Depot.
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Jim McKeveny

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Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #29 on: December 10, 2014, 08:40:24 am »

Most manufacturers have moved away from fiberglass based products to polyester. It is easier on the the assemblers - and us - over the long run. Convoluted foam is also a choice.

"Typical" padding in a VLF box reduces internal reflections up the frequency range that may present themselves at the vent or even through the cone. Kind of a "hamburger helper".

"Overstuffing" can change response.


All of that said...Owens Corning 703 semi-rigid is a top quality product for this app.
« Last Edit: December 10, 2014, 09:06:17 am by Jim McKeveny »
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ProSoundWeb Community

Re: Looking for plans for dual 18 cab for JBL 2241H drivers
« Reply #29 on: December 10, 2014, 08:40:24 am »


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