I have been thinking over building two woofer cabinets with 2 woofer elements in each cabinet in a force cancellation setup fashion, which would become the bottom part, a foot stand sort of, for a complete stereo speakers set with mids and tweeters in their own cabinets on top of the woofer cabinets.
The 3 different main combination I have in mind are:
1. putting one element on each side (ie. X-axis)
2. one element on the front, the other on the rear (ie. Y-axis)
3. one on top and one on at the bottom (ie. Z-axis).
The cabinet dimensions aren't fixed but am visioning of a width almost equally the same as the depth but probably a bit less, the height though could be as much as roughly 2 times the width/depth, input on the WxDxH dimension ratios are however welcome.
Anyhow, my main question now pertains more to how the different mounting positions of the woofer elements (X, Y and Z axis) would interact and affect the room modes, ie. which would be more favorable for an even bass response and what are the cons, thoughts?
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EDIT: Clarification; In all 3 examples mentioned above, the two elements are supposed to be placed exactly on the same axis in opposite direction to each other, and preferably also mechanically coupled directly to each other, hence theoretically there should be a complete force cancellation in all 3 cases.
The 3 different main combination I have in mind are:
1. putting one element on each side (ie. X-axis)
2. one element on the front, the other on the rear (ie. Y-axis)
3. one on top and one on at the bottom (ie. Z-axis).
The cabinet dimensions aren't fixed but am visioning of a width almost equally the same as the depth but probably a bit less, the height though could be as much as roughly 2 times the width/depth, input on the WxDxH dimension ratios are however welcome.
Anyhow, my main question now pertains more to how the different mounting positions of the woofer elements (X, Y and Z axis) would interact and affect the room modes, ie. which would be more favorable for an even bass response and what are the cons, thoughts?
---
EDIT: Clarification; In all 3 examples mentioned above, the two elements are supposed to be placed exactly on the same axis in opposite direction to each other, and preferably also mechanically coupled directly to each other, hence theoretically there should be a complete force cancellation in all 3 cases.
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The X-over frequency isn't fixed yet but I'm imagining something like 150-200 Hz at most, or maybe even a bit lower, hmm.. I realize now that the mid, or perhaps more exactly I should call it mid-woofer, could potentially also contribute to room modes at lower frequencies... 
BTW, I couldn't attach a picture to my OP depicting the force cancellation, but here's a picture borrowed from Vivid's homepage.
link: Reaction Cancelling Compliant Mount
BTW, I couldn't attach a picture to my OP depicting the force cancellation, but here's a picture borrowed from Vivid's homepage.
link: Reaction Cancelling Compliant Mount
Attachments
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I built a set very similar to what you are describing with 2 CSS SDX10 per box. Performance was outstanding.
Mount the drivers on the side, a 90° turn of the box gives front & back. Side mounting, unless the box is way out from the wall (or way up in the air) is the only arrangement where the 2 woofers will get ~equal boundary loading. As radiation at these frequencies are omni-directional the direction makes little difference in that sense. And a recent FAST build where we let an associate go at that to design a passive XO, ended up with the side mounted woofers XOed up near 450 Hz — mind you much smaller woofers.
The only picture i have is of the push-push nature shown from inside:
We built the raw box out of well braced 15mm BB. You could easily pick up both boxes with two hands. Load the drivers in and each box was Good news a 2-man lift (or 1 guy with a strong back). They never got finished as Chris sold them to raise cash while i was in the hospital — the new owner raves over them.
I did a test with a mechanics stethoscope to check box resonances. I turned the system up to uncomfortably loud, then turned off the satellite amps and then added another 10 dB (bass amps were probably haevily clipping). I was able to get the top moving, alll the other panels were quiet. I figures a corian (or similar) top would fix that.
Good news — CSS is back in business under new ownership with SDX10s appearing again new years end, and i am already working on getting a new set for V2.
I did 2 plans for these, ended up building the smaller ones, i figure being sealed that i could EQ them to suit…sim-wise the larger box is closer to ideal Q.
http://www.planet10-hifi.com/downloads/TwinSDX10PPP-woof-230712.pdf
3d visuallization of the bigger box:
dave
Mount the drivers on the side, a 90° turn of the box gives front & back. Side mounting, unless the box is way out from the wall (or way up in the air) is the only arrangement where the 2 woofers will get ~equal boundary loading. As radiation at these frequencies are omni-directional the direction makes little difference in that sense. And a recent FAST build where we let an associate go at that to design a passive XO, ended up with the side mounted woofers XOed up near 450 Hz — mind you much smaller woofers.
The only picture i have is of the push-push nature shown from inside:
We built the raw box out of well braced 15mm BB. You could easily pick up both boxes with two hands. Load the drivers in and each box was Good news a 2-man lift (or 1 guy with a strong back). They never got finished as Chris sold them to raise cash while i was in the hospital — the new owner raves over them.
I did a test with a mechanics stethoscope to check box resonances. I turned the system up to uncomfortably loud, then turned off the satellite amps and then added another 10 dB (bass amps were probably haevily clipping). I was able to get the top moving, alll the other panels were quiet. I figures a corian (or similar) top would fix that.
Good news — CSS is back in business under new ownership with SDX10s appearing again new years end, and i am already working on getting a new set for V2.
I did 2 plans for these, ended up building the smaller ones, i figure being sealed that i could EQ them to suit…sim-wise the larger box is closer to ideal Q.
http://www.planet10-hifi.com/downloads/TwinSDX10PPP-woof-230712.pdf
3d visuallization of the bigger box:
dave
As long as the woofers are not spaced apart by a 'large' distance, all options are the same with regard to room modes: they are similar to having just one woofer. Mounting on top and bottom probably is the best option, as spacing is maximized and rooms generally are longer / wider than high. 'Large' is a bit vague, based on feeling I would say that distances smaller than one metre are not large.
Mounting on top / bottom has the drawback of cones sagging under gravity.
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Main question: room modes? Yes, different mountings irrelevant, best way to mitigate LF room modes are to dot subs around the room. Your crossover frequency is possibly a bit high though to make the subs mono.
Worth adding; my 1st thot experiments with push-psuh woofers (2009): toobz woofer
Meant to use 4 Perkins PR2 woofers which were designed to be bolted thru the pole-piece to the box — the plans were abandoned when he bought 2 of them back:
dave
Meant to use 4 Perkins PR2 woofers which were designed to be bolted thru the pole-piece to the box — the plans were abandoned when he bought 2 of them back:
dave
I love the idea of that force cancelling TL tube, got force cancelling IB (through wall) at the moment and wonder if TL would be an improvement
B139's this is a bit too tall for my room though http://p10hifi.net/TLS/downloads/PushPush-B139-TL-map-041107.pdf
There is a folded version. Modern woofers really outclass the B139 but they still have a special place for me. In my hifi store days i sold 100s of them — still, none of them have come back to me 🙁
dave
dave
They go low very easily and cleanly at moderate levels (which is all I need) in my IB. Have you heard either of those TL's? I also have a couple with rubbing voice coils I'm tempted to make into PR's.........
A friend built one of the straight ones (he shortened it a bit to fit the 8’ ceiling in his flat), the performace was impressive. We cut plywood for him to build an additional pair, don’t know whether he got that done.
My experiences with PR loaded woofers has never been positive.
dave
My experiences with PR loaded woofers has never been positive.
dave
I built a set very similar to what you are describing with 2 CSS SDX10 per box. Performance was outstanding.
Mount the drivers on the side, a 90° turn of the box gives front & back. Side mounting, unless the box is way out from the wall (or way up in the air) is the only arrangement where the 2 woofers will get ~equal boundary loading. As radiation at these frequencies are omni-directional the direction makes little difference in that sense. And a recent FAST build where we let an associate go at that to design a passive XO, ended up with the side mounted woofers XOed up near 450 Hz — mind you much smaller woofers.
The only picture i have is of the push-push nature shown from inside:
We built the raw box out of well braced 15mm BB. You could easily pick up both boxes with two hands. Load the drivers in and each box was Good news a 2-man lift (or 1 guy with a strong back). They never got finished as Chris sold them to raise cash while i was in the hospital — the new owner raves over them.
I did a test with a mechanics stethoscope to check box resonances. I turned the system up to uncomfortably loud, then turned off the satellite amps and then added another 10 dB (bass amps were probably haevily clipping). I was able to get the top moving, alll the other panels were quiet. I figures a corian (or similar) top would fix that.
Good news — CSS is back in business under new ownership with SDX10s appearing again new years end, and i am already working on getting a new set for V2.
I did 2 plans for these, ended up building the smaller ones, i figure being sealed that i could EQ them to suit…sim-wise the larger box is closer to ideal Q.
http://www.planet10-hifi.com/downloads/TwinSDX10PPP-woof-230712.pdf
3d visuallization of the bigger box:
dave
Thanks a lot Dave for your reply! Yes mounting side-side or front-rear is more or less a matter of turning the cabinets, actually I have already a pair of crappy fiberwood cabinets I put together on a whim long time ago of quit similar measurements as your bigger cabinet except they are shorter with 1m in height.
They are no beauties and not even painted nor veneered but I thought I would experiment with them as right now I have only one woofer element mounted in each cabinet, happening to have two spare woofer elements left over of same model thought I would like to try them in a FC setup.
One downside is that the TS parameters of the elements wouldn't be happy with the limited cabinet volume, so I thought I would maybe try some active analog filters built around some of the many op-amps DIY filters available to EQ boost the bass response, however my concerns are whether the Q would go up too much making the bass sounding "muddy", I am not sure if there are any ways to make an active analog filters allowing for a low total system Q, any thoughts on this?
BTW, they are sealed cabinets, the idea was already from the onset when I built them to go sealed instead of BR to get a more controlled bass behavior although the bass response wouldn't be as extended as with BR.
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Linkwitz Transform is specifically designed to make a too small sealed box act like it is much larger. The price is power & excursion needed.
dave
dave
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