@lewinskih01;By jove, I think you have it! 18" woofers have gained favour amongst OB enthusiasts because of their higher max-SPL characteristics in comparison to smaller woofers (and 15" for the same reason). Open baffle woofer design results in lower output relative to sealed and ported---using the same basic woofer (the woofer in the OB Sub is the same as that used in the F12, only electrically optimized for OB usage.), a characteristic cited against them by opponents of OB subs.
That criticism is justified and fair, but there is a solution, one employed by both Rythmik’s Brian Ding in the OB/Dipole Sub, and by Siegfried Linkwitz in his excellent OB/dipole loudspeakers: a dipole cancellation compensation circuit, which provides electronic boosting of the signal sent the woofer(s) at 6dB/octave below 100Hz. Problem solved! Or at least mitigated: even with that circuit, an OB does not produce as much output as a sealed or ported, fed the same amount of amplifier power. You can’t have it all! To get a slight increase in SPL, the 3-woofer OB Sub is offered. And one can of course stack multiple OB subs, using a separate plate amp for each OB Sub H-frame and it’s woofers.
Speaking of subs with 18" woofers: did you notice Rythmik now offers 18" sealed and ported models? Wow! The 15" models already produce a lot of max SPL, I can’t imagine the 18". And with servo-feedback!
Does your friend with the F8’s realize he owns collector items? Brian Ding discontinued the model (and no longer has the 8" woofer manufactured for him), which was popular for mid-bass use. A lot of audiophiles think smaller woofer = "faster" bass, but Ding insists his 12", 15", and 18" woofers are just as fast as the 8". What makes a sub sound "fast" is how quickly the driver stops and returns to "rest" after the signal stops; the Rythmik servo-feedback design provides stop-on-a-dime woofer control and sound quality.
As for OB sub-to-sidewall distance: Rejoice! Due to dipole cancellation on either side of the OB Sub frame (inherent in open baffle design, as described and explained in my earlier post), you may place the OB Sub right against the wall if you wish. Or lay it on the floor---there is no output on either side of the OB frame! As long as the sub fires down the length of the room, you’re good.
As for OB Sub to front wall (behind the Sub, not the listening position) distance: as with all dipoles, a minimum of 3’ is required, more encouraged. Of course, you may try different distances to optimize direct-to-reflected phase correlation and loudspeaker/sub blending, but the continuously-variable phase control (0-180 degrees phase rotation, creating 0-to-16ms delay) makes that unnecessary. But remember: a phase control can only delay the signal, not send it back in time. ;-)
That criticism is justified and fair, but there is a solution, one employed by both Rythmik’s Brian Ding in the OB/Dipole Sub, and by Siegfried Linkwitz in his excellent OB/dipole loudspeakers: a dipole cancellation compensation circuit, which provides electronic boosting of the signal sent the woofer(s) at 6dB/octave below 100Hz. Problem solved! Or at least mitigated: even with that circuit, an OB does not produce as much output as a sealed or ported, fed the same amount of amplifier power. You can’t have it all! To get a slight increase in SPL, the 3-woofer OB Sub is offered. And one can of course stack multiple OB subs, using a separate plate amp for each OB Sub H-frame and it’s woofers.
Speaking of subs with 18" woofers: did you notice Rythmik now offers 18" sealed and ported models? Wow! The 15" models already produce a lot of max SPL, I can’t imagine the 18". And with servo-feedback!
Does your friend with the F8’s realize he owns collector items? Brian Ding discontinued the model (and no longer has the 8" woofer manufactured for him), which was popular for mid-bass use. A lot of audiophiles think smaller woofer = "faster" bass, but Ding insists his 12", 15", and 18" woofers are just as fast as the 8". What makes a sub sound "fast" is how quickly the driver stops and returns to "rest" after the signal stops; the Rythmik servo-feedback design provides stop-on-a-dime woofer control and sound quality.
As for OB sub-to-sidewall distance: Rejoice! Due to dipole cancellation on either side of the OB Sub frame (inherent in open baffle design, as described and explained in my earlier post), you may place the OB Sub right against the wall if you wish. Or lay it on the floor---there is no output on either side of the OB frame! As long as the sub fires down the length of the room, you’re good.
As for OB Sub to front wall (behind the Sub, not the listening position) distance: as with all dipoles, a minimum of 3’ is required, more encouraged. Of course, you may try different distances to optimize direct-to-reflected phase correlation and loudspeaker/sub blending, but the continuously-variable phase control (0-180 degrees phase rotation, creating 0-to-16ms delay) makes that unnecessary. But remember: a phase control can only delay the signal, not send it back in time. ;-)