Maybe this belongs over on the Planars & Exotics, but I have been wondering if anyone has ever looked into the concept of a large flat panel subwoofer?
Something along the lines of of a home made DML speaker, which are typically made with a treated foam panel attached to cheap sound exciters. The threads I have seen on these look promising enough to want to give it a try. Anyways my thought is to attach a rigid foam board or similar (probably 4'x4' or larger) to 2 or 4 cheap woofers and to see what happens.
I am only concerned about response below 100 Hz for the time being. I was thinking a driver similar to these :6-1/2" Poly Cone Midbass Woofer 4 Ohm . Yes, those are the cheapest woofers that PE carries lol. I would make a simple frame to attach the drivers to a wall directly, and then figure out a way to attach the foam panel to the cone directly. The extra weight of the foam should drop the Fs pretty low, so hopefully they are not too inefficient down low where I am hoping they will work, plus you have a massive diaphragm working in your favor.
Anyways, I was just wondering what everyone's thoughts were on something like this? I think it would be worth the $30 as an experiment. Hopefully it will at least work well enough in the garage to support the bottom end of the open baffle Pioneer BOFU speakers that I am playing with in there. Thanks for looking and any thoughts.
Something along the lines of of a home made DML speaker, which are typically made with a treated foam panel attached to cheap sound exciters. The threads I have seen on these look promising enough to want to give it a try. Anyways my thought is to attach a rigid foam board or similar (probably 4'x4' or larger) to 2 or 4 cheap woofers and to see what happens.
I am only concerned about response below 100 Hz for the time being. I was thinking a driver similar to these :6-1/2" Poly Cone Midbass Woofer 4 Ohm . Yes, those are the cheapest woofers that PE carries lol. I would make a simple frame to attach the drivers to a wall directly, and then figure out a way to attach the foam panel to the cone directly. The extra weight of the foam should drop the Fs pretty low, so hopefully they are not too inefficient down low where I am hoping they will work, plus you have a massive diaphragm working in your favor.
Anyways, I was just wondering what everyone's thoughts were on something like this? I think it would be worth the $30 as an experiment. Hopefully it will at least work well enough in the garage to support the bottom end of the open baffle Pioneer BOFU speakers that I am playing with in there. Thanks for looking and any thoughts.
Might want to look here:
http://www.diyaudio.com/forums/full-range/272576-study-dmls-full-range-speaker.html
http://www.diyaudio.com/forums/full-range/272576-study-dmls-full-range-speaker.html
I heard of someone using bicycle inner tubes as the surround. IIRC, making sure the weight of the foam doesn't pull the VCs out of alignment was the biggest challenge.
That said, I'm interested in this. I think that, if you kept the cone of the drivers and attached the board near the dustcap, you could get a useful amount of support. It'd have to be infinite baffle though, right?
Chris
That said, I'm interested in this. I think that, if you kept the cone of the drivers and attached the board near the dustcap, you could get a useful amount of support. It'd have to be infinite baffle though, right?
Chris
Wow...definitely going to be doing some reading. I am hoping with designing this to be used for bass only I can bypass many of the complications with material choice that the full range guys face.
As long as the material does not ring or resonate on its own at low frequencies I should have a good selection of materials that I can play with. Corrugated plastic sheets might be a good option, especially if they were layered together so that the corrugations are 90 degrees from each other. Maybe with a thin foam (.5"?) layer sandwiched between to dampen resonance and to stiffen it without adding much mass. Balsa ribs could be sandwiched in there too of needed.
Realistically what would my weight limit of the diaphragm be before 4-6 cheap woofers cannot support it any more? In my mind the thing that would make drivers not want to function properly is any twisting on them. I think that if the drivers are attached to a rigid frame, and the cones are attached to the hopefully rigid diaphragm, then there will only be force pulling down on the spiders and surrounds, which hopefully they will tolerate. I was thinking a round plastic ring could be epoxied into the cone, and then that could be epoxied to the diaphragm. Maybe an upside down cup of some sort could be attached to the cone, which would allow the diaphragm to be bolted or unbolted from the driver to allow experimentation.
If the diaphragm gets too heavy it could be neutrally supported from the top with fishing line or from the bottom with soft foam or an air cushion. Obviously this would kill HF response, but remember at this point I am only envisioning this as a subwoofer.
As far as enclosure type, to start it would probably be an open baffle with dampening material surrounding the edges / lining the back of the "chamber" to minimize phase cancellation. I am hoping that in a finished version of this, the enclosure would only be the size of the depth required (call it 6" for easy math) and essentially the width and height of the diaphragm. With my dream 4'x8' diaphragm that would give you a 16 ft^3 cabinet. That should be more that enough considering that the diaphram would have a Sd of 4,608 in^2 (46,800 cm^2), so the driver will not have to move much to make sound. At least that is the hope and theory behind this. Giving up extrusion for massive surface area.
Any ideas on how to model this in HornResp or WinISD before I order up anything? Going to see what I can do on my own with my limited knowledge. Any suggestions on drivers? The surplus ones are cheap enough that I can buy a pile of them and not feel bad if I destroy them.
As long as the material does not ring or resonate on its own at low frequencies I should have a good selection of materials that I can play with. Corrugated plastic sheets might be a good option, especially if they were layered together so that the corrugations are 90 degrees from each other. Maybe with a thin foam (.5"?) layer sandwiched between to dampen resonance and to stiffen it without adding much mass. Balsa ribs could be sandwiched in there too of needed.
Realistically what would my weight limit of the diaphragm be before 4-6 cheap woofers cannot support it any more? In my mind the thing that would make drivers not want to function properly is any twisting on them. I think that if the drivers are attached to a rigid frame, and the cones are attached to the hopefully rigid diaphragm, then there will only be force pulling down on the spiders and surrounds, which hopefully they will tolerate. I was thinking a round plastic ring could be epoxied into the cone, and then that could be epoxied to the diaphragm. Maybe an upside down cup of some sort could be attached to the cone, which would allow the diaphragm to be bolted or unbolted from the driver to allow experimentation.
If the diaphragm gets too heavy it could be neutrally supported from the top with fishing line or from the bottom with soft foam or an air cushion. Obviously this would kill HF response, but remember at this point I am only envisioning this as a subwoofer.
As far as enclosure type, to start it would probably be an open baffle with dampening material surrounding the edges / lining the back of the "chamber" to minimize phase cancellation. I am hoping that in a finished version of this, the enclosure would only be the size of the depth required (call it 6" for easy math) and essentially the width and height of the diaphragm. With my dream 4'x8' diaphragm that would give you a 16 ft^3 cabinet. That should be more that enough considering that the diaphram would have a Sd of 4,608 in^2 (46,800 cm^2), so the driver will not have to move much to make sound. At least that is the hope and theory behind this. Giving up extrusion for massive surface area.
Any ideas on how to model this in HornResp or WinISD before I order up anything? Going to see what I can do on my own with my limited knowledge. Any suggestions on drivers? The surplus ones are cheap enough that I can buy a pile of them and not feel bad if I destroy them.
What about using a inner tube like they suggest to mount a piece of heavier board right in front of the drivers in a sealed enclosure. The air pressure from the drivers will drive the board. Physically attaching them will lead to failure in my mind.
That should sufficiently lower the fs.
Also the radiation to the rear of the drivers will also be "slower" due to the fact that that they will need to suck the board back.
One thing to watch out for though. You are indirectly weighting the drivers.
With a open enclosure at the back you are going to Xmas the drivers out very quickly. Even before achieving usable SPL levels.
However a rear sealed enclosure even a small one will deliver really deep lows with that heavy board at the front.
If you want the look of just a panel then a option is to cut a hole through the wall and have the box on the other side. The hole will just be your blow/suck port to move the board.
That should sufficiently lower the fs.
Also the radiation to the rear of the drivers will also be "slower" due to the fact that that they will need to suck the board back.
One thing to watch out for though. You are indirectly weighting the drivers.
With a open enclosure at the back you are going to Xmas the drivers out very quickly. Even before achieving usable SPL levels.
However a rear sealed enclosure even a small one will deliver really deep lows with that heavy board at the front.
If you want the look of just a panel then a option is to cut a hole through the wall and have the box on the other side. The hole will just be your blow/suck port to move the board.
I'm with you on the inner tube thing, and think it might be worth a shot. My main concern, is wouldn't it mostly just act like a passive radiator? As in will only want to work at its resonant frequency? I see the driving it with air part...but the air will also want to act as a cushion between the too and dampen things somewhat. I could see this leading to poor transient response as well as having a pretty narrow range it operates in.
I do have a coupe B&C 18TBX100 subs sitting back at home that I could try it with sometime. I could block off the port in their current enclosures and put a 20" bike tube on the baffle, and play with some different diaphragms. The cool thing would be that you could change the air pressure to change the tuning on the fly. I could imagine them driving a large diaphragm at low frequencies pretty nicely.
I did order up 4 of those cheap drivers last night, and we have plenty of different materials at work to make a diaphragm out of. I will probably play with this mounted right to the studs in my garage for now, driven off of an active crossover and amp from my old FOH setup.
Another thought I had was to rigidly mount the drivers, suspend the diaphragm right in front of them with fishing line, and then glue semi rigid foam between the driver and diaphragm. If done right this would allow the speaker to drive the diaphragm, but allow some misalignment, and not make the diaphragm pull down on the drivers. It could even be an aluminum pushrod, leaving the drivers as linear servos.
I do have a coupe B&C 18TBX100 subs sitting back at home that I could try it with sometime. I could block off the port in their current enclosures and put a 20" bike tube on the baffle, and play with some different diaphragms. The cool thing would be that you could change the air pressure to change the tuning on the fly. I could imagine them driving a large diaphragm at low frequencies pretty nicely.
I did order up 4 of those cheap drivers last night, and we have plenty of different materials at work to make a diaphragm out of. I will probably play with this mounted right to the studs in my garage for now, driven off of an active crossover and amp from my old FOH setup.
Another thought I had was to rigidly mount the drivers, suspend the diaphragm right in front of them with fishing line, and then glue semi rigid foam between the driver and diaphragm. If done right this would allow the speaker to drive the diaphragm, but allow some misalignment, and not make the diaphragm pull down on the drivers. It could even be an aluminum pushrod, leaving the drivers as linear servos.
Almost like a passive radiator. But more like a isobaric setup without the front driver firing. It will still move along with the second woofer because of the air pressure but the total weight for the driver would be doubled. Lowering the FS considerably.
Those B&C drivers in a hidden enclosure behind the wall could work really well.
Let us know what your testing reveals.
Those B&C drivers in a hidden enclosure behind the wall could work really well.
Let us know what your testing reveals.
Ohm done it. 18" was pushing 21 or 24" membrane.
I was thinking to try 4x10" put them in push-pull position from two sides and large membrane between.
Attachments
While reading this thread, the first thing that I picture is one or more cheap sound exciters mounted to one of those "half saucer snow toys" you know the round parabolic sleds that were always Aluminum in the 60's when they first came out but are now usually plastic.
I'm not exactly sure how to seal the OD of it to a baffle, be it an OB or some sort of box but with the correct size bicycle inner tubes, unbroken rings of rubber could be glued between the saucer and the baffle.
Several of these, mounted in a wall would be quite interesting, and may work best if low passed below 60 Hz, maybe even 40 Hz to fill in missing lows.
For that matter, what would happen if you mounted exciters directly to the inside of your walls.
I built my entire upstairs (bedrooms and baths) using 1/2" 5 ply roofing under the drywall with insulation in the walls both between rooms and between rooms and the hallways.
I did this for racking strength, thermal insulation and acoustical insulation (privacy).
What if I had installed a whole bunch of exciters to the plywood. It has the drywall glued to it Hmmm...
Well, just dreaming of what could have been.[/dream]
Dave
I'm not exactly sure how to seal the OD of it to a baffle, be it an OB or some sort of box but with the correct size bicycle inner tubes, unbroken rings of rubber could be glued between the saucer and the baffle.
Several of these, mounted in a wall would be quite interesting, and may work best if low passed below 60 Hz, maybe even 40 Hz to fill in missing lows.
For that matter, what would happen if you mounted exciters directly to the inside of your walls.
I built my entire upstairs (bedrooms and baths) using 1/2" 5 ply roofing under the drywall with insulation in the walls both between rooms and between rooms and the hallways.
I did this for racking strength, thermal insulation and acoustical insulation (privacy).
What if I had installed a whole bunch of exciters to the plywood. It has the drywall glued to it Hmmm...
Well, just dreaming of what could have been.[/dream]
Dave
You could always glue exciters to the outside of the drywall and give it a shot. I think what you will find is that the drywall is too heavy to excite at low frequencies, plus it is screwed into your studs which will only dampen it even more. Plus you have all the insulation behind which will kill the HF. Back when I was doing live events I had always heard that drywall resonates at 8 kHz, which I tend to believe because if you got into a room with lots of drywall you would find yourself getting lots of feedback at around 8 kHz. Maybe someone else can chime in on this.
I think for now I am going to try to directly power the diaphragm by attaching it to the driver directly. I am afraid that using an air cushion to drive the diaphragm will cause delay issues as well as phase shift as you come in and out of resonance.
I think for it to work effectively you would want a pretty large driver, and then surround the driver with a bike tube just larger than the driver. Glue the tube to the baffle and the diaphragm and put probably just a couple PSI in it. You would also need to have the outside frame set just right to let the diaphragm have equal displacement froward and backwards. Maybe a matched tube mounted to a very minimal frame up front to make its movement linear. Push-pull configuration as mentioned?
For this to work I think it is going to have to be able to move some air...not just vibrate with a few little exciters. Punch you in the chest and knock stuff off the shelf type of bass. But maybe I am just dreaming 🙂 . I just have it in my head that a massive diaphragm moving even just a few millimeters will do this for me.
Given that I will (hopefully) not need much movement out of this, and its large size I think that that greatly simplifies the overall design as far as a surround is concerned. Now yes, a rigid diaphragm that could move freely would be sweet, but I'm not sure is is realistic it this point. It would be pretty heavy, and rely on exotic materials making it pretty expensive.
If I go a full 4'x8' , and have a semi flexible diaphragm I think I can get away with constraining the outside of it to a certain degree. Imagine a simple frame the same size as the diaphragm right behind it with foam weatherstripping or light rubber (vacuum line) between the two. Then have a same size clamp plate on the outside with the same foam / rubber treatment between them. Then tack the top two corners in loosely with wood screws or glue the top to the foam /rubber to hold it from falling down.
Now it is loosely clamped between foam / rubber, which should seal it acoustically, but still allow it to move back and forth as well as in and out as the diaphragm flexes slightly. If you tighten it too much it will start to tighten up and raise the resonant frequency, which could be used for in room tuning.
Given that basic layout I want to try a .062" thick sheet of LDPE (Low Density Polyethylene) as the diaphragm or at least the backbone of it. For the sake of packaging simplicity for now it will mount vertically on the back wall of the garage, using the studs as the basis of the frame. The drivers will mount on their own mini baffles so I can position them between studs and play with positioning relatively quickly. Any ideas on layout? All 4 right down the center spaced a foot apart? Or maybe drive the corners of a 2'x4' rectangle?
Lastly any good ideas on coupling the drivers to the diaphragm? Right now I am leaning towards cardboard shipping tubes glued to both the cone and the diaphragm.
I think for now I am going to try to directly power the diaphragm by attaching it to the driver directly. I am afraid that using an air cushion to drive the diaphragm will cause delay issues as well as phase shift as you come in and out of resonance.
I think for it to work effectively you would want a pretty large driver, and then surround the driver with a bike tube just larger than the driver. Glue the tube to the baffle and the diaphragm and put probably just a couple PSI in it. You would also need to have the outside frame set just right to let the diaphragm have equal displacement froward and backwards. Maybe a matched tube mounted to a very minimal frame up front to make its movement linear. Push-pull configuration as mentioned?
For this to work I think it is going to have to be able to move some air...not just vibrate with a few little exciters. Punch you in the chest and knock stuff off the shelf type of bass. But maybe I am just dreaming 🙂 . I just have it in my head that a massive diaphragm moving even just a few millimeters will do this for me.
Given that I will (hopefully) not need much movement out of this, and its large size I think that that greatly simplifies the overall design as far as a surround is concerned. Now yes, a rigid diaphragm that could move freely would be sweet, but I'm not sure is is realistic it this point. It would be pretty heavy, and rely on exotic materials making it pretty expensive.
If I go a full 4'x8' , and have a semi flexible diaphragm I think I can get away with constraining the outside of it to a certain degree. Imagine a simple frame the same size as the diaphragm right behind it with foam weatherstripping or light rubber (vacuum line) between the two. Then have a same size clamp plate on the outside with the same foam / rubber treatment between them. Then tack the top two corners in loosely with wood screws or glue the top to the foam /rubber to hold it from falling down.
Now it is loosely clamped between foam / rubber, which should seal it acoustically, but still allow it to move back and forth as well as in and out as the diaphragm flexes slightly. If you tighten it too much it will start to tighten up and raise the resonant frequency, which could be used for in room tuning.
Given that basic layout I want to try a .062" thick sheet of LDPE (Low Density Polyethylene) as the diaphragm or at least the backbone of it. For the sake of packaging simplicity for now it will mount vertically on the back wall of the garage, using the studs as the basis of the frame. The drivers will mount on their own mini baffles so I can position them between studs and play with positioning relatively quickly. Any ideas on layout? All 4 right down the center spaced a foot apart? Or maybe drive the corners of a 2'x4' rectangle?
Lastly any good ideas on coupling the drivers to the diaphragm? Right now I am leaning towards cardboard shipping tubes glued to both the cone and the diaphragm.
Been thinking about the same for a while, using a honeycomb panel, about 3/4 - 1" thick. Using 1 mm thick or less (airplane grade) Baltic birch for the panel and bicycle tube for the suspension.
Thought about using bass shakers instead of exciters for more excursion or sacrificing an 15" - 18" woofer.
Johan
Thought about using bass shakers instead of exciters for more excursion or sacrificing an 15" - 18" woofer.
Johan
If you dont mind, how were you going to construct the honeycomb panel? Does anyone know exactly how the bass shakers work? Is it basically a voice coil attached to a weight? I had considered them too...that would make things really simple.
Rynothealbino,
The bass shakers have a massive magnetically suspended piston slug moving in a cylinder, the "equal and opposite reaction" of the moving slug is transmitted to the exterior housing. That attached housing is great for tactile shaking, not good for driving a lightweight large membrane pushing air.
The difficulties you face with a flat panel sub woofer are the same as any woofer, making the moving membrane as light and stiff as possible, while retaining precise voice coil alignment in the magnetic gap. The magnetic gap must be as narrow as possible to be efficient, while the voice coil must be thick (and heavy) enough to handle the current required to move the mass of the membrane.
Although a square membrane has more moving area than a circle of the same width, a circular cone shaped membrane is quite strong in comparison, requiring less mass. Although honeycomb panels have a good strength to weight ratio, after addressing the reinforcement needed at the attachment points of the surround, voice coil and spider(s), the weight advantage diminishes, while the problem of making a linear high excursion suspension with a square driver is far more difficult than with a round one.
Although in theory multiple distributed drive units on a membrane could be advantageous, the difficulties described above will unfortunately insure your B&C 18" drivers will (far) outperform multiple cheap drive units attached to a large membrane.
Art
Hi,
The problem with using high Q drivers to drive a panel is even higher Q.
Open baffle up to a Q of 2 can work, each driver would need to see
about 3 times its own cone mass, doubling Q and halving Fs.
Expanded Polystyrene and kitchen foil is an old but good idea.
rgds, sreten.
The problem with using high Q drivers to drive a panel is even higher Q.
Open baffle up to a Q of 2 can work, each driver would need to see
about 3 times its own cone mass, doubling Q and halving Fs.
Expanded Polystyrene and kitchen foil is an old but good idea.
rgds, sreten.
.... and one interesting answer is electrostatic loudspeaker. Which is the answer to a lot of quality sound-making questions.
With all the extraordinary huffing-and-puffing in this thread, you could go to the same effort* and make a giant ESL. No problem in theory, eh.
The famous Dayton-Wright ESL panel was enclosed in a meter-square steel box with mylar covering the whole front and back, which is larger than the ESL membrane. The insides were filled with a welding gas called by its friends, SH6 or something like that which is far heavier than air. Impedance matching.
Being full-range, DW didn't go for broke on the bass. The box resonance is around 45 Hz but you could go lower if you were only interested in bass. The sound is exceptionally good, of course.
For those of us who are negative on boxy sound, the DW box is different in that the essential working parts aren't trafficking in the resonances.
Ben
*OK, 100X the effort
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So I managed to find a little time to play with this during the weekend. I made a simple open baffle roughly 2'x3' and mounted the 4 drivers a few inches apart in the center. Running open baffle the drivers just start to become audible around 50 Hz or higher. and were overall very quiet even with your head right in front of them.
I then cut out the top 1" or so of 4 foam coffee cups and used weatherstripping adhesive to glue them to the cones. Then I glued a piece of corrugated plastic (same size as baffle) to the cups. I tacked the 4 corners in with wood screws careful to let the diaphram "float" and not push the drivers in and out. I then set my crossover to 100 Hz, cranked the amp and set to chasing down the parts of the diaphragm that were floating in the breeze.
I never could get the diaphragm to quit buzzing, but I was able to put out audible bass down to 30 Hz or so. Still not very loud, but audible at least. Strictly judging by how easily the drivers were driven to clipping, I would say the resonant frequency was around 20 Hz. Despite the problems I had, a few times I could get the panel to just sing and crank out the tunes at certain frequencies.
At one point I unhooked 3 of the drivers and left only one running, and notices I didn't lose that much output. That being said, I think the next direction would be for each driver to have its own diaphragm or to mount the drivers much farther apart. A real suspension system would help greatly, as I ended up stuffing the edges with blankets to get them to stop buzzing. At this point rubber hose or foam would be a huge upgrade in the surround department. As far as damping the rest of the panel, balsa spars epoxied to the baffle or 1/2-1" thick foam glued to the front would do wonders.
So in conclusion for now, I think the idea holds some promise, but I didn't see anything that blew me away so far. I figure I will play with this and see if I can get it to quit buzzing like crazy. If that works and I still think the idea holds promise I will build 4 units each with one driver in them and see what they will do.
I then cut out the top 1" or so of 4 foam coffee cups and used weatherstripping adhesive to glue them to the cones. Then I glued a piece of corrugated plastic (same size as baffle) to the cups. I tacked the 4 corners in with wood screws careful to let the diaphram "float" and not push the drivers in and out. I then set my crossover to 100 Hz, cranked the amp and set to chasing down the parts of the diaphragm that were floating in the breeze.
I never could get the diaphragm to quit buzzing, but I was able to put out audible bass down to 30 Hz or so. Still not very loud, but audible at least. Strictly judging by how easily the drivers were driven to clipping, I would say the resonant frequency was around 20 Hz. Despite the problems I had, a few times I could get the panel to just sing and crank out the tunes at certain frequencies.
At one point I unhooked 3 of the drivers and left only one running, and notices I didn't lose that much output. That being said, I think the next direction would be for each driver to have its own diaphragm or to mount the drivers much farther apart. A real suspension system would help greatly, as I ended up stuffing the edges with blankets to get them to stop buzzing. At this point rubber hose or foam would be a huge upgrade in the surround department. As far as damping the rest of the panel, balsa spars epoxied to the baffle or 1/2-1" thick foam glued to the front would do wonders.
So in conclusion for now, I think the idea holds some promise, but I didn't see anything that blew me away so far. I figure I will play with this and see if I can get it to quit buzzing like crazy. If that works and I still think the idea holds promise I will build 4 units each with one driver in them and see what they will do.
Basically 2 sheets of 1 mm Baltic air plane grade birch (which is 3-layer, and usually the cheapest). A ring, that's the same thickness as the honeycomb, made from spruce, poplar or any other light weight ply (300 - 450 kg/m^3). The inner diameter of the ring about 2 cm smaller as the outer diameter.
For a 26" disc this would work out to be less then 750 gram. For PA-drivers 500 - 600 gram would be the equivalent weight for such an Sd (assuming the Xmax would be 8 mm or more. For high excursion 10", 12" or 15" drivers used at home 750 gram is on the low side.
The trick with the bass shakers would be to turn it into a moving magnet type transducer. With the housing mounted stationary and the moving part of the shaker attached to the cone.
Best regards Johan
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