I should be able to report soon on how well or badly this works.
Almost completed two combination subs/stands for standmount speakers. Subs are dual 10s per side, sealed (2nd-order bass cutoff), confirmed anechoic 40 Hz f3 cuttoff (30 Hz f3 w/ average boundary effects, confirmed in two seperate rooms). As confirmed in prior enclosures & by NHT founder Ken Kantor's custom software, these particular 10s require only .75cf sealed ea. 1.5cf for dual 10s yields a solid enclosure w/ moderate weight, expense, & volume (all 1.25" MDF + full-length window brace + dual 10s + BH5/Soundcoat/cork lining estimated 85-90 lbs per sub/stand-SWEET). 10s only about 84.5 dB each confirmed, but 4 = over 90 dB, plenty w/ one ubiquitous PE table-top 1000W amp/parametric eq/active xo set at estimated 55-60 Hz.
The sub/stands will be mirror images, one 10" fires forward while the other side-fires; so far, so normal, right? Here's the twist: toward the goal of minimizing this room's already well controlled bass modes, ONE of the sub/stands will be swiveled around 180 degrees vs. the other. E.g: L speaker stays stationary while the R speaker is swiveled 180-degrees. Picture this overhead view: L speaker 10s fire forward & rightward, R speaker 10s fire rearward & rightward. Stooopid, right? Maybe yes, meybe no...
Wavelengths below 55-60 Hz are long enough to mask the different pathlengths to the ear. The room is symmetrical (benefits mid/treble) & almost 27' front-to-back. The front wall to speaker baffle spacing is over 6', consistent w/ Yoav Geva of YG Acoustics' principal mandating long spacing to the front wall for any rear-firing woofer. (It's interesting that since my rave YG reviews, several professoinal testers have echoed most or all of my comments; Yoav's an interesting, bright & energetic designer. Yes, the speakers are ultra-expensive but apparently worth it: 2-way mini speaker to 40 Hz is $17k/pair. At RMAF make sure you take the shuttle bus to YG's factory; you won't believe your ears.)
All 10s are sited close to the floor; it's good for the common first boundary to be one of the two largest (floor & ceiling share this characteristic). But look at how each of the four 10s has a different pathlength to the first vertical wall in its direct forward path.
L speaker
Forward 10" woofer: estimated 23' to the first vertical wall in its direct path
Right-side 10" woofer: about 12'
R speaker
Rearward 10" woofer: about 6+'
Right-side 10" woofer: about 3.5'
I'm hoping/predicting the above will smooth/average the bass modes. The worse case is for a potential neutral effect caused, again, by the long wavelengths.
If it does work, it should be a common feature either w/ fullrange speakers having built-in powered subs or seperate outboard powered multiple subs. Symmetricaly sited L/R sub drivers below approximately 70 Hz is apparently always only bad & never good. This is counter-intuitive to most, who would probably disaprove on first site of such non-symmetrical arrays (along these lines I will install a "dummy" grill on the front of the rear-firing sub; at least the fronts of the two subs will look symmetrical; the sides will look non-symmetrical as will the rear-firing woofer viewed from the back).
Neighbor Duke LeJeune (
www.AudioKinesis.com) makes a nice, interesting sub system aimed at Quad/Maggie owners: four seperate 1cf sub enclosures (each reflex-loaded single-6.5") powered by one PE amp/xo. The four subs are carefully sited in the room in a maximum non-symmetrical pattern. The target is each woofer having a different boundary spacing, exactly as it should be for maximum speed, smoothness & musicality resulting from maximum bass mode averaging. This is consistent w/ the demands of the owners of good 'stats/ribbons, explaining why they usually go sub-less: better to go without than to add sloggy/tubby bass modal problems inherent in most rooms. Is it a coincidence that Bob Carver is now working on a new sub system w/ a large quantity of tiny subs placed throughout the room in a maximum non-symmetrical pattern? Do you know something about this that physicist Bob Carver doesn't?
At the least, w/ a reflex loaded speaker, it would appear to be always only a good thing if the two speakers' ports or passive radiators were sited in a non-symmetrical non-mirror image array. But this will probably never occur in a production speaker, for purely marketing &/or esthetic reasons that are only counter-productive to better performance: form hurting function, not good.
The only known exception where symmetry may be preferred is true corner loading. In corner loading almost all output is boundary generated while direct output is minimized, damping the interaction & distortion between these two competing signals (normally extensive eq is required for flat FR & time-alignment is required w/ the mains).
