I’m guesing you haven’t grasped the concept.
Yiou fold the baffle so that you can fit a push-puh pair of drivers. There will be a cavity resonance. Output nearfiekld will be increases omewhat near the cavity mouth, farfield will be as if the drivers were on a flat baffle. But with much less flapping of the OB. Wire the drivers to push the air in the direction of the arrows.
Second is how i plan on doing it.
dave
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I do not grasp it, not yet, so thanks for helping. I appreciate it.
So in that first drawing (the top one of your two there), the drivers are magnet to magnet. Opposite directions but same polarity wiring, so this will cancel vibration force on the baffle right? The output far field, despite being 90 degrees off axis from the face of the drivers will have normal output because of the cavity? And the cavity itself will cause a spike near field (which can be smoothed out with DSP)? Magnet to magnet, is there a space there to allow the vent poles to breathe? And finally, can that be reversed so that the driver cones face each other into that cavity and the magnets are hidden?
Thanks for taking the time. 🙂
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Some reading, I found some info that I'm trying to work through. But basically we're talking about these I think?
Source:
https://www.hifizine.com/2012/12/subwoofer-origami/
Very best,
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Yes, energy flowing from the driver ractive force is dramatically reduced, making it much less likely that the bass drivers will excite baffle resonances. If executed well all greatly stiffen the baffle.
The “spike” caued by the cavity is 1/ a suckout that will limit the HF. The maller the cavity the higher that frequency.
I like magnet to magnet but if take more care to couple the woofers mechanically. And X’s OBs mount them push-pull to reduce second harmonic distortion, useful with cheap drivers. One generally likes to avoid the basket and magnets as the primary radiation source, hence Linkwitz’s arrangement.
The W-Bin is my upper sketch with wings. That further limits bass extention on the top. I’d be tempted to boffle something like that.
dave
The “spike” caued by the cavity is 1/ a suckout that will limit the HF. The maller the cavity the higher that frequency.
I like magnet to magnet but if take more care to couple the woofers mechanically. And X’s OBs mount them push-pull to reduce second harmonic distortion, useful with cheap drivers. One generally likes to avoid the basket and magnets as the primary radiation source, hence Linkwitz’s arrangement.
The W-Bin is my upper sketch with wings. That further limits bass extention on the top. I’d be tempted to boffle something like that.
dave
Thanks Dave, I will explore this further.
I like the idea of the slot and using 8 x 12" woofers and making a lovely tall pine baffle with it and maybe add wings so it's more like the W above for added stability/rigidity on the base.
I take it that the slot allows a build up of pressure that loads the drivers, like adding mass, so it lowers Fs and we get a bit more extension and output and shapes it better for bass I think if I understand this?
I only care about up to about 100hz at best on this, as I will crossover somewhere below that or around there, and as low as possible within reason (I don't want to have to high pass it and keep whatever is in the recording to any frequency down there).
I love the idea of a monolith.
I just wish I could get the vibration cancellation so its a dead tower for vibration...
Very best,
Hrm,
Reading more about this slot concept. The 1/3rd area slot relative to the combined area of the two cones, isn't really explained where this area is to be maintained. Is it the dimensions of the slot completely as in all sides or more like port dimensions and just represents the opening dimensions of the slot? Or does it include the depth of the slot? Confusing as this could be so many things.
It's interesting and I have the drivers, so it's just some scrap plywood to test and see how it sounds and behaves. I'm curious. It would allow for beautiful hardwood towers without seeing drivers, look classy. Just curious how low it can get and what the output is like.
So for example if two 12"s is 113 square inches of area x 2, or 226 square inches summed, then 1/3rd of that is around 74.5 square inches for the slot. But not sure how to use that 74.5 square inches for the slot size other than at least the width of the slot, but then what about the depth? And can I scale this to 8 drivers in the slot and if so, how to relate the slot dimensions to that area, or if you just consider it pairs for that and just scale in pairs (it seems?).
I like the idea of being able to compactly fill a small area with lots of fairly inexpensive drivers and use height to get the surface, less floor space.
Very best,
Reading more about this slot concept. The 1/3rd area slot relative to the combined area of the two cones, isn't really explained where this area is to be maintained. Is it the dimensions of the slot completely as in all sides or more like port dimensions and just represents the opening dimensions of the slot? Or does it include the depth of the slot? Confusing as this could be so many things.
It's interesting and I have the drivers, so it's just some scrap plywood to test and see how it sounds and behaves. I'm curious. It would allow for beautiful hardwood towers without seeing drivers, look classy. Just curious how low it can get and what the output is like.
So for example if two 12"s is 113 square inches of area x 2, or 226 square inches summed, then 1/3rd of that is around 74.5 square inches for the slot. But not sure how to use that 74.5 square inches for the slot size other than at least the width of the slot, but then what about the depth? And can I scale this to 8 drivers in the slot and if so, how to relate the slot dimensions to that area, or if you just consider it pairs for that and just scale in pairs (it seems?).
I like the idea of being able to compactly fill a small area with lots of fairly inexpensive drivers and use height to get the surface, less floor space.
Very best,
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Can anyone confirm the following?
Assuming slot loaded open baffle with 12" drivers. I'm just wrapping my head around the slot size. From what I've read, I'm keeping the depth of the slot minimal. The cavity itself is limited to just the two drivers. Each slot is separate cavity so that the cavity itself isn't larger which will have impact. A single 12" driver's cone area is 113 square inches. Two of these is 226 square inches. The slot has to be at least 12" tall to allow the drivers themselves, and about 12" depth to minimize the cavity, so that just leaves the width of the slot to figure. I've read two things, one just calculated one cone area of one driver for the 1/3rd area slot dimension. Another document said to use combined cone are of both drivers. One 12" driver's 113 square inches has a 1/3rd area of 37.3 square inches. So if the slot height is 12" then the slot width would be 3.1 inches. Or, if it's correct to use two cone areas summed, we have 226 square inches of total cone area, and 1/3rd of that is 74.5 square inches. So keeping a 12" height still on the slot, the new slot width becomes 6.2 inches. That seems really wide for this. So that's why I'm asking to confirm.
Then in theory this can be scaled from 2 pairs to any number of pairs really, individual slots.
I see some with magnet to cone (but wired in phase so they both push air out of the slot together on positive signal). And I see some with cone to cone doing the same thing. I see some comments about magnet to cone being asymmetrical and that being better for some artifact stuff. But it seems as long as the drivers are squeezing out of the slot together, it will work at the basic level before any tweaks.
In this configuration I still get vibration cancellation too.
Does this sound appropriate so far?
Do I have to isolate each slot? Or can I do one big continuous slot if I don't care about anything above 200hz?
Thanks for everyone's time and contribution so far, it's been super helpful!
Very best,
Assuming slot loaded open baffle with 12" drivers. I'm just wrapping my head around the slot size. From what I've read, I'm keeping the depth of the slot minimal. The cavity itself is limited to just the two drivers. Each slot is separate cavity so that the cavity itself isn't larger which will have impact. A single 12" driver's cone area is 113 square inches. Two of these is 226 square inches. The slot has to be at least 12" tall to allow the drivers themselves, and about 12" depth to minimize the cavity, so that just leaves the width of the slot to figure. I've read two things, one just calculated one cone area of one driver for the 1/3rd area slot dimension. Another document said to use combined cone are of both drivers. One 12" driver's 113 square inches has a 1/3rd area of 37.3 square inches. So if the slot height is 12" then the slot width would be 3.1 inches. Or, if it's correct to use two cone areas summed, we have 226 square inches of total cone area, and 1/3rd of that is 74.5 square inches. So keeping a 12" height still on the slot, the new slot width becomes 6.2 inches. That seems really wide for this. So that's why I'm asking to confirm.
Then in theory this can be scaled from 2 pairs to any number of pairs really, individual slots.
I see some with magnet to cone (but wired in phase so they both push air out of the slot together on positive signal). And I see some with cone to cone doing the same thing. I see some comments about magnet to cone being asymmetrical and that being better for some artifact stuff. But it seems as long as the drivers are squeezing out of the slot together, it will work at the basic level before any tweaks.
In this configuration I still get vibration cancellation too.
Does this sound appropriate so far?
Do I have to isolate each slot? Or can I do one big continuous slot if I don't care about anything above 200hz?
Thanks for everyone's time and contribution so far, it's been super helpful!
Very best,
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More slot volume will increase the cavity resonance peak amplitude.
Wired in opposite polarity so they both push air out of the slot together..
The slot can be continuous.
The slot depth's 1/4 wavelength resonant peak affects response both above and below 200Hz.
Thanks 🙂
A continuous slot will be easier for the initial build and testing. I'll try it out.
I really only care about 100hz, to 200hz max on bandwidth on the upper side. I guess I need to find out how to simulate the slot width for that cavity resonance value and what it will be and if I can just cut it out with a low pass filter or not. It will have full active DSP available to it. No passive crossover, so I can shape it however.
Very best,
If the woofers are mounted push-pull then yes
If mounted push-pushl then wire in-phase.
Has nothing to do with the nature of the baffle.
dave
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Ok, I re-read the Pass article and coming up with a better plan of things.
The last thing I really want to learn to do is I've seen some mention of Horn Resp simulating the slot loaded cavity to sort of adjust the slot to the drivers being used. I like this idea better than the rule of thumb 33% of the piston area. I'd rather get it closer to the driver's behavior.
Anyone have link or source for horn resp for slot cavity simulation?
Until I figure that part out, looks like I'll do a continuous slot with 8 x 12" drivers in cone to cone pairs wired in phase. Piston area is around 10" on the drivers (250mm), so 78 square inches of piston area, vs the full flange to flange area of a 12" being 113 square inches. So if I use the actual piston area of one driver, I'm at 25 square inches as 1/3rd the area and the slot height would be that of the piston again, so 10" x 2.5" basically I'm thinking. And then scale it to four of those as one big long slot.
But, It would be fun to simulate it with the actual driver T&S in horn resp to get an idea of whether there's a better width on the slot to use, vs this guestimate.
Very best,
The last thing I really want to learn to do is I've seen some mention of Horn Resp simulating the slot loaded cavity to sort of adjust the slot to the drivers being used. I like this idea better than the rule of thumb 33% of the piston area. I'd rather get it closer to the driver's behavior.
Anyone have link or source for horn resp for slot cavity simulation?
Until I figure that part out, looks like I'll do a continuous slot with 8 x 12" drivers in cone to cone pairs wired in phase. Piston area is around 10" on the drivers (250mm), so 78 square inches of piston area, vs the full flange to flange area of a 12" being 113 square inches. So if I use the actual piston area of one driver, I'm at 25 square inches as 1/3rd the area and the slot height would be that of the piston again, so 10" x 2.5" basically I'm thinking. And then scale it to four of those as one big long slot.
But, It would be fun to simulate it with the actual driver T&S in horn resp to get an idea of whether there's a better width on the slot to use, vs this guestimate.
Very best,
Hrm, or if it cannot be simulated properly, maybe at least some basic calcs to help guide the slot width based on specific drivers? Any ideas?
Very best,
Very best,
The smaller the cavity, the higher the cavity resonance. With a 100 Hz XO you don’t have to fret much.
You want to build something like this?
I would put the woofers as close together (magnet-to-magnet) as any vents allow. The blue triangles are meant to represtn deflectors at the back of the slots that decrese the cavity volume. Bracing not shown,
The cavity resonance that represents the folded over ends will likely be a greater issue — the woofer miodule makes those ncavities smaller.
If you want an idea of where the resonaces will occur i believ Martin King covers the subject in one of his papers, and i would be surprised if there isn’t something onthe linkwitz site.
And now to throw something completely different, at a fairly recent European Triode Festival a “Heil Woofer” was demonstrated. I could find no pictures or info. I would be ssurprised if there was not someone here who attended and can tell us more.
Same idea, i think, as this one, but a different folding.
dave
Thanks Dave,
Yes, I'm interested in something like that. I may try magnet to magnet or cone to cone. From reading it seems magnet to magnet is useful just because of the volume displacement to reduce cavity volume. The deflector idea is good to help reduce volume in addition in either arrangement. Personally I don't care to see the magnets and don't want to see wires in the slot, so from an aesthetic point of view, cone to cone looks nicer to me. But I'm open to both options really and can try both honestly, plywood is cheap.
And yes, truly interested in just using this for sub woofer duty. I like the ideas of how it works in terms of being similar to line array, compact, lots of woofers in a much more compact space, opposed for vibration suppression, and able to present a large baffle face that can be done in lovely hardwood so its an attractive piece and not a "big speaker" so to speak.
I'll try to find some info in the King/Linkwitz papers. If the issues are going to be over 100~200hz, then it won't matter to me, but I like to learn stuff so that I know why, etc, when I can. Bit by bit. It starts with questions of course. Read. More questions...
I was mainly looking for ways to calculate or think of the cavity in terms of what the size of the cavity would do if I made it wider, less wide, etc, on the output and response shape, or if it wouldn't do anything and only effect resonance, etc, etc. My main goal would be to go with the width that allows the best lowest frequency output, ok to give up everything above 100hz.
Very best,
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Thanks, that's a good point. So I will need to isolate the pairs or at least isolate group of 4 to keep the slot cavities smaller. 34" will be too short for 8x 12" drivers, as I need around 50~55 inches for that (I've done 4x 12's on 55" baffle and it fits close but is pretty doable). So 34" will clearly be too short. I'll break it up into two 24" slots. Thanks!
So, the line resonance of the cavity would be from the middle of the cavity and up one side to the opening as a distance, and that's the quarter wavelength, so the full wavelength is 4x that. So if it were 12 inches depth and 2.5" wide, it would be 12+1.25" = 13.25" length x 4 = 53 inches = 223hz or so. So well above my operating bandwidth. And to keep it an octave higher, I can low pass it at 100hz basically. Sound right?
Very best,
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Hrm, I'm confused on this one. A brace horizontally between each woofer and basically through the entire length of the slot? Is that what you meant? To reduce cavity volume?
Makes me wonder, if that's the case, why not just reduce the cavity width in general to limit the volume, which would also decrease the quarter wavelength of the cavity for the line resonance.
Very best,