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Recycling JBL 4647A cabs for 4pi? [message #71974]

Fri, 30 March 2012 18:31

dprice
Messages: 10
Registered: November 2009
Location: Florida

Chancellor

Wayne,

I picked up a pair of JBL 2226HPL that are loaded in JBL 4647A "subwoofer" cabinets. The 4647A is 5 cubic feet, tuned to 40 Hz. Simply turning them upside down and cutting in the horn makes for a pretty easy build.

http://www.jblpro.com/pub/cinema/4647a.pdf

Veneer and a grill can make it right spiffy looking.

My question is about how critical is for the baffle width, port location, and horn location to match the 4pi plans? Matching the horn location is easy. Plugging the 4 existing ports and installing a new one is not a big challenge...but no point in fixing it if it ain't broke. Baffle width is what it is. Reducing cabinet volume is easy enough...I forgot the 4pi specs....

I assume the easy answer is to locate the horn per plan and give it a listen. Modify the volume and tuning as desired...or go all the way and install a the new port.

Also is there any need to change the crossover to use the new H290C? I would be using the DE250.

Any other thoughts?

Thanks!

Don

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Re: Use the woofers, but scrap the box [message #71975 is a reply to message #71974]

Fri, 30 March 2012 19:42

Wayne Parham
Messages: 18678
Registered: January 2001

Illuminati (33rd Degree)

Honestly, I wouldn't go the fudge/fit route. I have spent a lot of time dialing in these designs and to modify them throws all that out the window. Box dimensions might seem trivial, but in a box this size, standing waves form in the lower midrange so port and woofer placement become important. It's not just a matter of Helmholtz tuning by way of volume and port. That's the fundamental mechanism, to be sure, but if you accidentally line up a pressure node with the port, you'll get some response ripple. So my suggestion is to scavange the woofers and get the right compression drivers, horns and crossovers to build the four π loudspeaker exactly as shown in the plans.

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Re: Recycling JBL 4647A cabs for 4pi? [message #71976 is a reply to message #71974]

Fri, 30 March 2012 19:51

Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA

Illuminati (2nd Degree)

You will enjoy the 2226 in a 4 or 5 cu ft cabinet with horn on top. A lot of us have done all sorts of variations on that theme and not surprisingly, it's the basic configuration of all Hi-Fi speakers going back to the 30's.

But....but.....the 4Pi is an entirely different sounding, more tonally neutral speaker than any Altec, Classic, Klipsch or other horn/bass reflex I've heard excepting the XLH 1812 which you can't buy and won't have room for.

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