Re: No compromises front loaded double 18” cab
The B6 is basically a "too small" bass reflex needing a 6 dB LF boost to flatten out the response.
Turns out that my last cabinet re-build, cramming two 15" in a slot loaded push-pull arrangement in the the same box previously used for 2 Lab 12" (the design in the stickies in this DIY section) is "kinda" a B6 (QTS is too high), well more a B10...
http://www.diyaudio.com/forums/subwoofers/255010-compact-2x15-ppsl-using-dayton-pa385-8-drivers.html
To quote DJK:
"Take a driver with a Qts=0.312 and put it in a sealed box sized to make it a D2 alignment. Now vent it to Fs and it becomes an SBB4, with the best transient response of all the vented alignments. Now add a Q=2 high-pass filter at Fs, and you now have a B6. It still has the transient response of the SBB4 because the box volume and tuning have not changed, you have just applied some EQ, mechanically it is the same. Fb=Fs=Faux.
The Qts=0.312 is the intercept of two equations determining box size and low-frequency cut-off. The box size equation says that the size is proportional to the square of the Qts, so a Qts=0.3 can run in a box about half the size of a Qts=.4 driver. The problem is the bass response rolls off at a higher frequency the lower the Qts is. The two equations have an intercept at Qts=0.312, yielding the best bass extension and minimum box size, and allowing you to build a B6 alignment."
Higher-order bandpass boxes are different, there is no direct output of the driver, only output from 1 or more tuned resonant chambers.
Their bandwidth is limited, and the rapid phase change at the top of the bandpass does make alignment to the top cabinets "difficult".
Art
