I was comparing the Performance Series system with the Synthesis 4 system, which is basicly the Performance Series, upgraded to THX and made in wall. I noticed that the subs used in the Synthesis 4 are perfect cubes-can anyone say standing waves? The subs that go with the Performance Series have non-equal dimensions.
The cube is pretty small. The crossover frequency is 24 dB/octave, variable from 50 to 150 Hz. I guess JBL feels the standing wave modes aren't a show stopper in this particular instance, being sufficiently attenuated.
The transducer in that little cube is quite expensive.
I'd like to be able to do an A-B comparision between the Performance and the Synthesis 4, with the Performance connected to a Lexicon MC-12.
I've always had thoughts of inwall speakers leaving something to be desired. But I do like the idea of the Synthesis 4 surrounds being able to be configured a multitude of ways.
There is a dealer/installer in Reno that told me he's going to be moving into a larger store front and is going to have a Performance Series system set up. I've been wanting to audition those for 2 years.
Please post your "review" here on the forum after you get a chance to hear the installers new setup. Thanks.
MBB
Well, just doing some basic math, it doesn't seem that ANY dimension in a sub THAT small, is going to have any standing wave effect. The wavelengths are simply TOO LONG!
To have a standing wave, you have to have a coherent, near-parallel pair of opposing walls, a half-wave-length (or multiples of a half-wave, in lesser strength of formation, ie, they're not as strong as the 'fundamental') apart.
With the crossover at 150 Hz (worst-case), and 24 dB/oct, the ABSOLUTE highest frequency that you should have to think about, would be 300 Hz or lower. In theory, 300 Hz should be at least 21 dB down... that's like, 1% of the broadband output.
For a 300 Hz wave, the wavelength is about 3.3 feet; a half wave is about 1.66 feet, or about 20 inches. This means, that the "cube" would have to be 20 inches on a side, for a wave to be able to be set up inside of the box.
For a 150 Hz standing wave, it'd take a 40 inch spacing (ie a 40" cube)... that would be a RATHER HUGE cube, to get any appreciable effect at the frequencies involved here...
Personally, knowing that it'll be a RARE occurance that any crossover frequency over 100 Hz will be used, I'd be inclined to totally ignore the cabinet dimensions, for something this small. As long as it's built airtight and free of vibration, it could be pretty much any shape you want...
Regards,
Gordon.
Exactly what I always say. If it's a sub it's playing low freqeuncies and I noticed as a briefly read that it uses a 24dB/octave crossover. It probably wont be playing much over 100hz and since ithats nowhere near midrange frequencies.. no standing waves!Originally posted by GordonW
The wavelengths are simply TOO LONG!
Mike
You guys have the right idea. You might wish to look at it from the perspective of the actual standing wave frequency of the cube in question, which is a given. Like I said, it isn't a show stopper in this instance, being sufficiently attenuated.
MJC:
I'm in Reno, what dealer!?
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