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The ultimate enclosure for the box 18-500 8a
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Old Croc
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Joined: 26 December 2013
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Points: 2435 		Post Options Post Options   Thanks (0) Thanks(0)   Quote app Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2015 at 2:35am
Originally posted by _djk_ _djk_ wrote:

"Yeah I read that you suggest building the enclosure 4 x the Vas of the drivers"
 
That's not correct.
 
For a Qts=0.312 it is Qts^2 * Vas * 4.1
 
If the Qts is .3 vs .4 the cabinet will end up being about twice the size for the driver with the weaker motor (higher Qts).


So if the qts of the box 18-500 8a is 0.425 and Vas 208l the calculation looks like this:

0.425^2 x 208 x 4.1 = 154 approx

So the enclosure size should be twice that 308l ?
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Old Croc
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Joined: 23 November 2004
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The constant for a Qts=0.425 is more like 6 (rather than 4.1), so
 
.425^2 * 208 * 6 = 225L (per driver).
 
I would need to get out the LDC to check the exact value for the constant for that Qts, but I think 6 will be close. It may be possible to do a C6 alignment (like my B6 PPSL designs), with a small amount of ripple in the response. I will have to check that on a different computer at home (posting from work at the moment).
 
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Joined: 23 November 2004
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Points: 5992 		Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2015 at 7:04am
I ran some designs on this driver.
BB v6.0 suggested about 14.5 cu ft for a pair, and could be made to be 3dB down around 42.5hz.
 
An alternate design would be a C6 of 8 cu ft net tuned to 40hz with a Q=2 filter at 40hz. This would be 3dB down at 40hz. Two ports of about 50 sq in each by 12.5" long will be enough. A pair of these drivers will handle about 2KW before getting into excursion problems with this design.
 
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Originally posted by _djk_ _djk_ wrote:


I ran some designs on this driver.
BB v6.0 suggested about 14.5 cu ft for a pair, and could be made to be 3dB down around 42.5hz.
 
An alternate design would be a C6 of 8 cu ft net tuned to 40hz with a Q=2 filter at 40hz. This would be 3dB down at 40hz. Two ports of about 50 sq in each by 12.5" long will be enough. A pair of these drivers will handle about 2KW before getting into excursion problems with this design.
 

i wouldnt mond seeing the plan for that DJK.... iv always wanted a double 18" reflex and it sounds like you may have come up with a nice "little" box there. If you wouldnt mind sharing of course.
If it sounds like a gorilla is trying to escape, turn it down.
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Joined: 26 December 2013
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Points: 2435 		Post Options Post Options   Thanks (0) Thanks(0)   Quote app Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2015 at 8:34am
Originally posted by mini-mad mini-mad wrote:

Originally posted by _djk_ _djk_ wrote:


I ran some designs on this driver.
BB v6.0 suggested about 14.5 cu ft for a pair, and could be made to be 3dB down around 42.5hz.
 
An alternate design would be a C6 of 8 cu ft net tuned to 40hz with a Q=2 filter at 40hz. This would be 3dB down at 40hz. Two ports of about 50 sq in each by 12.5" long will be enough. A pair of these drivers will handle about 2KW before getting into excursion problems with this design.
 

i wouldnt mond seeing the plan for that DJK.... iv always wanted a double 18" reflex and it sounds like you may have come up with a nice "little" box there. If you wouldnt mind sharing of course.


Id like to see the plans too if possible! PM me if you want!Thumbs Up
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he's given you the info to start working on a plan..
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Points: 1924 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2015 at 3:43pm
Originally posted by _djk_ _djk_ wrote:

  a C6
 


thank you for your hints, and pardon my ignorance: what is C6 ?(I gather it's a specific alignment?) Can you point me to a good source of information?

best regards,

Bob
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" Can you point me to a good source of information?"
 
The LDC by Dickason
 
Loudspeaker Design Cookbook 7th Edition Book
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quote
Originally posted by _djk_ _djk_ wrote:

  a C6
 


thank you for your hints, and pardon my ignorance: what is C6 ?(I gather it's a specific alignment?) Can you point me to a good source of information?

best regards,

Bob

quote end

Hi Bob

It is electrically corrected reflex alignment. So generally in smaller enclosure one can have same low freq output with aid of eq (and low cut filtering to keep Xmax in control below box tuning).

one way of executing this By Mr Don Keele

http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20%281975-07%20AES%20Published%29%20-%20New%20Set%20of%20VB%20Alignments.pdf
torturing electrons since ......
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Points: 1924 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2015 at 10:04pm
Originally posted by _djk_ _djk_ wrote:

" Can you point me to a good source of information?"
 
The LDC by Dickason
 
Loudspeaker Design Cookbook 7th Edition Book


much obliged! Thumbs Up
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Joined: 26 December 2013
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Points: 2435 		Post Options Post Options   Thanks (0) Thanks(0)   Quote app Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2015 at 10:37pm
Originally posted by AndyWave AndyWave wrote:

quote
Originally posted by _djk_ _djk_ wrote:

  a C6
 


thank you for your hints, and pardon my ignorance: what is C6 ?(I gather it's a specific alignment?) Can you point me to a good source of information?

best regards,

Bob

quote end

Hi Bob

It is electrically corrected reflex alignment. So generally in smaller enclosure one can have same low freq output with aid of eq (and low cut filtering to keep Xmax in control below box tuning).

one way of executing this By Mr Don Keele

http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20%281975-07%20AES%20Published%29%20-%20New%20Set%20of%20VB%20Alignments.pdf



Thanks for the link! Thumbs Up
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Joined: 23 November 2004
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Points: 5992 		Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2015 at 2:38am
Don worked for EV, Klipsch, and JBL, he knows his stuff.

A PPSL cabinet for these would be about 24"H x 36"W x 30"D, with a plenum opening of about 9"W, and a shelf port on each side of the box about 2.375W X 12.5"D (I will see if I can make the ports bigger, this is the minimum suggested size).


Edited by _djk_ - 18 November 2015 at 4:21am
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