If using a single woofer to support the low-end under a small fullrange, what benefits or drawbacks are there to slot-load it?
In my theoretical configuration, I'd be using an 8" woofer, with whatever rear-chamber is appropriate for it. The front of the driver would be mounted in a slot perhaps a tad larger than its frame, say 9" x 9" in this case, with a uniform height of 1" or thereabout. The slot depth would likely dictate the maximum operational frequency for the woofer at a quarter-wavelength, so ~375Hz in this case, likely fine if the planned crossover is below this.
What I think is to be gained:
A slight lowering of Fs due to the air-load contained in the slot. It is not dramatic, but perhaps helpful if the woofer is significantly more efficient than the fullrange, say by 4 to 6dB. It could perhaps net me an f10 a few Hz lower for a given slope. Hornresp can simulate this to a certain extent.
It could also allow the fullrange to be mounted closer to the slot than it could be to a standard baffled woofer, thus raising the frequency below which both drivers become a quasi point-source. This might in turn facilitate crossover design. OTOH, perhaps it is pointless to have this be much higher the slot's QW resonance as mentioned earlier, as you'd want woofer output to be significantly down by this point. Close-mounted 3" + 8" drivers would already be "point-source" below ~600Hz if going by center-to-center distance. Cut this figure roughly in half if going to the extreme of furthest cone edges. Is this point moot?
Possible issues:
Assuming a crossover avoiding the slot resonances, I can't think of any major issue. Am I missing something obvious?
You usually see slot-loading being done with open-baffles, as it is an ergonomic way to arrange the several woofers often needed to produce useful SPL down low while keeping power handling up. The lowering of Fs is also likely a side-benefit there. Ripole "subwoofers" also seem to take this effect into account.
I'm almost constantly brewing potential projects and builds in my mind, especially if I have little or unused parts around. I have a pair of Peerless 830869 presently gathering dust, as well as Fostex FF85WK in so-so enclosures, seeing little use. They seem well-suited to be so matched IMO and I've never built a WAW. File under "More likely to become a build than scores of zany schemes found in the depths of this filing cabinet"...
In my theoretical configuration, I'd be using an 8" woofer, with whatever rear-chamber is appropriate for it. The front of the driver would be mounted in a slot perhaps a tad larger than its frame, say 9" x 9" in this case, with a uniform height of 1" or thereabout. The slot depth would likely dictate the maximum operational frequency for the woofer at a quarter-wavelength, so ~375Hz in this case, likely fine if the planned crossover is below this.
What I think is to be gained:
A slight lowering of Fs due to the air-load contained in the slot. It is not dramatic, but perhaps helpful if the woofer is significantly more efficient than the fullrange, say by 4 to 6dB. It could perhaps net me an f10 a few Hz lower for a given slope. Hornresp can simulate this to a certain extent.
It could also allow the fullrange to be mounted closer to the slot than it could be to a standard baffled woofer, thus raising the frequency below which both drivers become a quasi point-source. This might in turn facilitate crossover design. OTOH, perhaps it is pointless to have this be much higher the slot's QW resonance as mentioned earlier, as you'd want woofer output to be significantly down by this point. Close-mounted 3" + 8" drivers would already be "point-source" below ~600Hz if going by center-to-center distance. Cut this figure roughly in half if going to the extreme of furthest cone edges. Is this point moot?
Possible issues:
Assuming a crossover avoiding the slot resonances, I can't think of any major issue. Am I missing something obvious?
You usually see slot-loading being done with open-baffles, as it is an ergonomic way to arrange the several woofers often needed to produce useful SPL down low while keeping power handling up. The lowering of Fs is also likely a side-benefit there. Ripole "subwoofers" also seem to take this effect into account.
I'm almost constantly brewing potential projects and builds in my mind, especially if I have little or unused parts around. I have a pair of Peerless 830869 presently gathering dust, as well as Fostex FF85WK in so-so enclosures, seeing little use. They seem well-suited to be so matched IMO and I've never built a WAW. File under "More likely to become a build than scores of zany schemes found in the depths of this filing cabinet"...
The main benefit is a mechanical low-pass filter, so you can use a woofer with a 'spiky' top end without heroic measures in the crossover.(much like a bandpass sub)
A great way to use a larger woofer in a desktop speaker, but in a floorstander keep the slot by the floor(for boundary reinforcement), and put the widerange up where you like(again, if peaky up high on axis, lower to get off axis).
Remember when choosing height to calculate floor-bounce cancellation, to avoid or to use as part of the high-pass filter.
Good fun, allowing form to aid function.
A great way to use a larger woofer in a desktop speaker, but in a floorstander keep the slot by the floor(for boundary reinforcement), and put the widerange up where you like(again, if peaky up high on axis, lower to get off axis).
Remember when choosing height to calculate floor-bounce cancellation, to avoid or to use as part of the high-pass filter.
Good fun, allowing form to aid function.
Yes, the low-pass effect is another applicable contribution. 👍
I suppose implementing a side, rear or bottom firing slot could further tailor the effect to a specific design or application.
What if the slot was built with both ends open to the outside? Would the air-load effect on Fs be lessened? Would the slot's height need to be diminished to offset the otherwise larger opening? I am thinking of this so as to push up in frequency the first resonance, now essentially half-wave instead of quarter-wave. Does it make sense? It would not be so much to gain BW for the woofer as to push any slot peaking up in frequency and down in amplitude for a given electrical low-pass crossover.
I suppose implementing a side, rear or bottom firing slot could further tailor the effect to a specific design or application.
What if the slot was built with both ends open to the outside? Would the air-load effect on Fs be lessened? Would the slot's height need to be diminished to offset the otherwise larger opening? I am thinking of this so as to push up in frequency the first resonance, now essentially half-wave instead of quarter-wave. Does it make sense? It would not be so much to gain BW for the woofer as to push any slot peaking up in frequency and down in amplitude for a given electrical low-pass crossover.
A perimeter(or partial perimeter) slot acts as a slot of larger area.
At large amplitudes it will reduce pressure differentials around the cone.
The behavior will remain the same re: half-wave resonances(somewhat simple in a closed box, varying for a ported one).
At large amplitudes it will reduce pressure differentials around the cone.
The behavior will remain the same re: half-wave resonances(somewhat simple in a closed box, varying for a ported one).
+1 BP4 is best and why it's what the pioneers concluded to drive horns, ditto some of their early bass boxes before Thuras' reflex patent. 😉