| Help me troubleshoot freaky cabinet-tuning issue? [message #79934] |
Wed, 07 May 2014 20:16  |
Fritz Bogott
Messages: 4
Registered: July 2010
Location: Northfield, MN
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Esquire |
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I have a pair of JBL 2225Hs in 3ft3 3/4" MDF cabs tuned to 40Hz.
Using Room EQ Wizard as a real-time analyzer, I can see that one cabinet drops off sharply at 110Hz, the other at 60Hz. (I'm not moving the mic; it's sitting on a tripod about ten feet back and midway between the two cabs.) There shouldn't be a (major) directivity issue with mid-woofers, should there?
Swapping the drivers (oof, heavy) has no effect on this-- the 110Hz rolloff follows the cab not the driver.
In order to reduce the number of variables, I yanked the port tubes from both cabs. Weirdly, the rolloff points of both cabs did not change. (D'oh!) Still 60Hz and 110Hz. (Huh? I don't see how this can be possible?)
What's left to look at? As far as I can see, the cabs have identical cross-bracing and identical amounts and placement of R11 insulation. I sealed all the joints in both with silicone...
Ever run into anything like this before? Seems completely impossible / unbelievable to me. What should I look at next?
Thanks,
-Fritz
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