The lower crossover point was dictated by the Linkwitz transform that compensated for the midrange closed box Fb and Q. It was the lowest it could go because the Qc/Qt ratio limited the Fc/Fb ratio. Besides, The P13WH, while wonderfully neutral was not the most dynamic driver at the low end. It worked just fine at 230.
IMO the major benefit of side-firing woofers is the opportunity to use them in opposed force-cancelling mode. It works spectacularly well in reducing box vibration. I recently needed a monitor for a home recording project and built a pair of compact mid-field monitors. I attempted a virtual point source performance by aligning the acoustic centres of the M-T-M front firing drivers with the pair of force cancelling side woofers. Crossover is 3 kHz for mid-tweeter and in the range 150-200 Hz for the bass-mid. The results exceeded my expectations. Bass is essentially flat in-room down to 50 Hz and falls off relatively slowly due to the sealed bass alignment and front wall re-inforcement. Since they are listened to only on axis at the one position, I am not concerned with off-axis behaviour much. Even so, there is nothing really concerning at say, 15 degrees off axis laterally.
I have noticed that these have been one of the best speakers I have built with regard to not exciting room modes. It takes much less than the usual positioning effort to get them to sound clean and tight. The M-T-M (D'Apollito) is known to have a restricted vertical window and the side firing woofers seem to similarly restrict bass propagated towards the side-walls. There is very little of the bass build-up out towards the side walls. The FR at the listening position is fine. I have used all SB Acoustics drivers, 1" ring-dome, 2x4" mid-range, 2x6" woofers. The very lowest octave is not as flat as with my bigger projects, ( 2x10" sealed box flat to 25Hz in my room), but for the intended use, these are just right. I always used sealed bass alignment and time-aligned Bessel active 3-way crossover for good transient performance. So, in general good for monitoring but maybe not for large group listening. As the Highlander says, "there can only be one"
I have noticed that these have been one of the best speakers I have built with regard to not exciting room modes. It takes much less than the usual positioning effort to get them to sound clean and tight. The M-T-M (D'Apollito) is known to have a restricted vertical window and the side firing woofers seem to similarly restrict bass propagated towards the side-walls. There is very little of the bass build-up out towards the side walls. The FR at the listening position is fine. I have used all SB Acoustics drivers, 1" ring-dome, 2x4" mid-range, 2x6" woofers. The very lowest octave is not as flat as with my bigger projects, ( 2x10" sealed box flat to 25Hz in my room), but for the intended use, these are just right. I always used sealed bass alignment and time-aligned Bessel active 3-way crossover for good transient performance. So, in general good for monitoring but maybe not for large group listening. As the Highlander says, "there can only be one"
Attachments
The four hex nuts next to the woofers connect the side baffle with 6mm threaded steel rod. I have toyed with idea of measuring the vibration with an accelerometer to set the tension optimally, but to be honest, the thread tension is not critical. I have always thought that it is the total baffle movement that needs cancelling, not only the magnet vibration. I can see some of the replies take this seriously with the extensive bracing.
The extent to which push-push drivers reduce vibration load to the box cannot be understated. We have found in practice that tight coupling of the magnets works pretty good, but using treaded rod to tie everything together is the next step. A thot experiment in did circa 2000 used that and a pair of woofers designed to be bolted thru the polepiece to the box, not a big step to bolt the 2 drivers together: toobz woofer
First time i have seen the pictures Chris posted, the last one only hints at how spectacular the veneer job on those was — note that these are 4 boxes, 2 woofers & 2 satellites. This design evolved into the Facets which were an ML-V to increase the height to allow the 3” FR to be “nestled” between 4 of the woofers push-push (one of those cabinets fairly straight forward to design but next to impossible to build).
note: these were bi-amped w 1st order PLLXO at 240 Hz
dave
First time i have seen the pictures Chris posted, the last one only hints at how spectacular the veneer job on those was — note that these are 4 boxes, 2 woofers & 2 satellites. This design evolved into the Facets which were an ML-V to increase the height to allow the 3” FR to be “nestled” between 4 of the woofers push-push (one of those cabinets fairly straight forward to design but next to impossible to build).
note: these were bi-amped w 1st order PLLXO at 240 Hz
dave
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