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4Pi's and JBL 3678 looking for plans [message #67629] Sun, 15 May 2011 19:10 Go to next message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
hello.....Im looking to build a LCR set of speakers that will rival JBL 3678's
Are the 4Pis these speakers?
They will be used in a FIlm audio post facility
I have seen some pictures of differnt designs online that people are building
Looks like what im looking for.

thanks

Re: 4Pi's and JBL 3678 looking for plans [message #67630 is a reply to message #67629] Sun, 15 May 2011 19:20 Go to previous messageGo to next message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
I neglected to mention that the speakers need to be behind the screen so they cant be more then 12" deep.
They will also be tuned in the room by Dolby for film printmaster certification

thanks
Re: 4Pi's and JBL 3678 looking for plans [message #67642 is a reply to message #67630] Mon, 16 May 2011 10:06 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18783
Registered: January 2001
Illuminati (33rd Degree)

You've got mail!

One potential problem though, the speakers are 14" deep and cannot be made any smaller. The port is 10" long, and the wood thickness of the front and rear baffle takes up space too. So the port opening is as close to the rear baffle as it can be.

Re: 4Pi's and JBL 3678 looking for plans [message #67644 is a reply to message #67629] Mon, 16 May 2011 10:17 Go to previous messageGo to next message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
Can the cabinet be made taller with a larger diameter port?
Re: 4Pi's and JBL 3678 looking for plans [message #67646 is a reply to message #67644] Mon, 16 May 2011 10:27 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18783
Registered: January 2001
Illuminati (33rd Degree)

Well, of course, you can do a lot of things, but the real problem is that once you change dimensions of the box by any significant amount, you'll change where the standing waves line up in the box. You'll have to verify your changes with measurements.

One of the difficulties of designing high efficiency two-way speakers is the boxes are physically large, so standing waves line up in the lower midrange. Those are at a frequency that's tough to damp with insulation. You really have to position the woofer and port where response is best. The goal is to make sure a pressure node doesn't line up on the port or woofer.

Subwoofers are easy to tune because the wavelengths are so long. If there's no midrange presented to the woofer, you don't have to worry about internal standing waves, so modifications of layout and cabinet shape don't matter. But when you're making a high-efficiency speaker that uses a midwoofer, one that reproduces bass and midrange, this is a real consideration.

Re: 4Pi's and JBL 3678 looking for plans [message #67647 is a reply to message #67629] Mon, 16 May 2011 10:36 Go to previous messageGo to next message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
What do you think of JBL 3677 or 3678 lf cabinet designs?
Re: 4Pi's and JBL 3678 looking for plans [message #67648 is a reply to message #67647] Mon, 16 May 2011 10:41 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18783
Registered: January 2001
Illuminati (33rd Degree)

The low end is great, the top end sucks.

Re: 4Pi's and JBL 3678 looking for plans [message #67651 is a reply to message #67629] Mon, 16 May 2011 10:46 Go to previous messageGo to next message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
The cd horn top end or top end of the midwoofer?
Thanks for all the help btw.
Re: 4Pi's and JBL 3678 looking for plans [message #67655 is a reply to message #67651] Mon, 16 May 2011 13:59 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18783
Registered: January 2001
Illuminati (33rd Degree)

The horn is the weak link, not the midwoofer. That horn sounds artificial and "spitty". It's fine for prosound, but definitely not hi-fi.

Re: 4Pi's and JBL 3678 looking for plans [message #67656 is a reply to message #67629] Mon, 16 May 2011 14:01 Go to previous messageGo to previous message
diskeditor is currently offline  diskeditor
Messages: 7
Registered: May 2011
Esquire
i read a post about replacing the horn with a eminence horn and keeping the driver.....
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