Veleric.
Let's take the ohm Walsh bending wave drive unit for instance.
This uses the primary bending wave to produce sound in the cone ,the last thing they want is that wave being reflected back up into the cone .
So they heavily damp the end of the cone to stop the reflections.
Standard cone drive units have the same issues as they only want pistonic movement, so they also use damping in the form of a roll surround and other forms of damping.
Gobel uses the same sort of damping and more to prevent the same reflections which would set up standing waves in the panel (DML).
Without these reflections distributed modes cannot be set up, like the stone in the pond the ripples will just continue on outwards .
Obviously the damping does not stop all of the reflections but it does reduce it considerably.
BMR is pretty much the same but is pushed more into pistonic mode.
They all use primary bending waves but restrict the distributed modes in varying degrees.
I have always thought that the combination of all three ,pistonic,primary bending wave, and dml are all important for the best possible sounding panel.
All types of light and heavy panels have differing degrees of these three combinations, they are not all the same.
I like the sound of free floating dml panels ,adding damping of any sort just makes them sound dead to me, boring would be a better word.
Steve.
Let's take the ohm Walsh bending wave drive unit for instance.
This uses the primary bending wave to produce sound in the cone ,the last thing they want is that wave being reflected back up into the cone .
So they heavily damp the end of the cone to stop the reflections.
Standard cone drive units have the same issues as they only want pistonic movement, so they also use damping in the form of a roll surround and other forms of damping.
Gobel uses the same sort of damping and more to prevent the same reflections which would set up standing waves in the panel (DML).
Without these reflections distributed modes cannot be set up, like the stone in the pond the ripples will just continue on outwards .
Obviously the damping does not stop all of the reflections but it does reduce it considerably.
BMR is pretty much the same but is pushed more into pistonic mode.
They all use primary bending waves but restrict the distributed modes in varying degrees.
I have always thought that the combination of all three ,pistonic,primary bending wave, and dml are all important for the best possible sounding panel.
All types of light and heavy panels have differing degrees of these three combinations, they are not all the same.
I like the sound of free floating dml panels ,adding damping of any sort just makes them sound dead to me, boring would be a better word.
Steve.
Steve,
There's no doubt that it's possible to design a radiator (cone/panel) that's virtually anywhere along the continuum from fully pistonic to fully resonant. But the focus of of this thread is flat panels of moderate size (generally over one square foot). Such panels would certainly be mainly resonant, rather than pistonic, over the vast bulk of the audible frequency range.
I accept that you may think that you prefer the sound of free floating, undamped panels. But I wonder if your preference is based on objective evidence or preconceived notions. Plastics like PS (and PS foam) have substantial internal damping. And I suspect that the primary effect (if any) of adding PVA coatings is to add to that damping. PVA has a lower Tg than PS, and hence likely a higher damping factor at room temperature.
If you truly prefer undamped panels, solid aluminum sheet should be much better. Metals like aluminum have orders of magnitude less internal damping than plastics like PS. True, solid metals have low radiation efficiency (B/mu^3 is pretty low), but at least they avoid the costs of damping.
Eric
There's no doubt that it's possible to design a radiator (cone/panel) that's virtually anywhere along the continuum from fully pistonic to fully resonant. But the focus of of this thread is flat panels of moderate size (generally over one square foot). Such panels would certainly be mainly resonant, rather than pistonic, over the vast bulk of the audible frequency range.
I accept that you may think that you prefer the sound of free floating, undamped panels. But I wonder if your preference is based on objective evidence or preconceived notions. Plastics like PS (and PS foam) have substantial internal damping. And I suspect that the primary effect (if any) of adding PVA coatings is to add to that damping. PVA has a lower Tg than PS, and hence likely a higher damping factor at room temperature.
If you truly prefer undamped panels, solid aluminum sheet should be much better. Metals like aluminum have orders of magnitude less internal damping than plastics like PS. True, solid metals have low radiation efficiency (B/mu^3 is pretty low), but at least they avoid the costs of damping.
Eric
Veleric.
As much as I find patents interesting, I find then not very helpful in finding a good sounding panel material.
For me it is all about the sound.
Most materials sound bad and should be avoided, it is as simple as that.
As for the 50x50 mix of pva I use on my eps panels, many,many times I have said it is not used as a damping layer , it replaces the poor sounding eps surface.
The weight of the panel is changed very little once all the water has evaporated.
I do use pva on the 1mm veneer panel and on my card panels to help increase rigidity to stop excessive flexing (buzzing)at low frequencies and I believe it also helps reduce the self noise .
I have also been using epoxy on my 5mm xps panels to increase rigidity to help the propagation of the sound across the panel with nice sounding results.
Clamping an eps panel for instance , to subdue a peak for instance , causes problems that cannot be corrected.
I have made panels from 4inches to 7 feet , they are all free floating dml in varying degrees , except for my very rigidly mounted 3mm ply panels and the canvas ply panels which are both full range to about 40hz ,not that I would use them down to this frequency if driving a room.
I suppose it is down to what sort of sound you like ,some like a warm cosy sound or a bright dynamic sound, ect, I myself prefer a natural sounding panel that I can see but not hear, only the music.
I'd thought many years ago that I had come very close using my standard loudspeakers ,that was until I heard dml,and that was when I was using corrugated cardboard !!
I can't thank ziggy enough for pointing me in the right direction.
R.I.P.
Steve.
As much as I find patents interesting, I find then not very helpful in finding a good sounding panel material.
For me it is all about the sound.
Most materials sound bad and should be avoided, it is as simple as that.
As for the 50x50 mix of pva I use on my eps panels, many,many times I have said it is not used as a damping layer , it replaces the poor sounding eps surface.
The weight of the panel is changed very little once all the water has evaporated.
I do use pva on the 1mm veneer panel and on my card panels to help increase rigidity to stop excessive flexing (buzzing)at low frequencies and I believe it also helps reduce the self noise .
I have also been using epoxy on my 5mm xps panels to increase rigidity to help the propagation of the sound across the panel with nice sounding results.
Clamping an eps panel for instance , to subdue a peak for instance , causes problems that cannot be corrected.
I have made panels from 4inches to 7 feet , they are all free floating dml in varying degrees , except for my very rigidly mounted 3mm ply panels and the canvas ply panels which are both full range to about 40hz ,not that I would use them down to this frequency if driving a room.
I suppose it is down to what sort of sound you like ,some like a warm cosy sound or a bright dynamic sound, ect, I myself prefer a natural sounding panel that I can see but not hear, only the music.
I'd thought many years ago that I had come very close using my standard loudspeakers ,that was until I heard dml,and that was when I was using corrugated cardboard !!
I can't thank ziggy enough for pointing me in the right direction.
R.I.P.
Steve.
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When I say the Goebel patent is "bad" I certainly do not mean throw the baby out with the bathwater!
The reason I am so interested by this is because they have implemented DML in a very expensive, high end speaker. Although I have never heard them, I highly doubt the speakers are anything other than exceptional. They have thrown many hours of development into this so I would expect the end result to be outstanding.
What I mean by "bad" is that some of the explanations in the patent make little scientific sense. Patents, unlike peer reviewed journal papers, do not need to be sound scientifically, they just need to be unique. The explanation of the "acoustic lens" in particular made me scratch my head.
I wondered if I had it right that this lens was on the back of the speaker and not the front. Pictures of the speaker clearly show carbon fibre on the front which is not obscured by any lens.
Anyway I think this is sorted out by a paper I found which can be downloaded here but I have also attached if the link goes bad. (Zenker et al)
The summary of this paper is that they have a DML of unspecified construction materials which has a "separation plate" mounted only about 1cm behind the panel. This is comparable in distance to Goebel's "acoustic lens". They also share other similar characteristics. In particular both have a large cutout located centrally.
Zenker et al modelled this construction very accurately using finite element analysis software. Read the paper for details. The intention was to prevent standing wave nulls which caused frequency response dips of up to 25dB. The large central space in the separation plate minimised air stiffness behind the panel at the fundamental resonance antinode. Elsewhere it effectively suppressed nulls at other resonance modes. The end result was a much flatter frequency response.
I believe Goebel just found the same result by trial and error and attributed it to an acoustic lens rather than altering the panel's standing wave profile. Of course I could be wrong and it may have been lost in the translation.
Anyway this is another piece of the puzzle. I think the following are super important:
1) panel materials (some degree of damping is necessary IMHO)
2) boundary conditions (how the sides are mounted - I will probably use butyl to damp)
3) exciter position (maybe central not so bad)
4) use of an enclosure (I probably will)
5) use of a separation plate (the salt/sugar method can be used to work out where holes should be placed)
I don't want to criticise others for not following a similar path. We all have our own methods but this will be mine.
EDIT:
My current plan is just to make a 2.0 system with bass driver (eg. Anarchy 704) to 300-1000 Hz or so and DML panels to handle the rest. It just seems too problematic to make a FAST type system with subwoofer as the panels need to be too large to get anywhere close to a reasonable crossover frequency (~150Hz)
The reason I am so interested by this is because they have implemented DML in a very expensive, high end speaker. Although I have never heard them, I highly doubt the speakers are anything other than exceptional. They have thrown many hours of development into this so I would expect the end result to be outstanding.
What I mean by "bad" is that some of the explanations in the patent make little scientific sense. Patents, unlike peer reviewed journal papers, do not need to be sound scientifically, they just need to be unique. The explanation of the "acoustic lens" in particular made me scratch my head.
I wondered if I had it right that this lens was on the back of the speaker and not the front. Pictures of the speaker clearly show carbon fibre on the front which is not obscured by any lens.
Anyway I think this is sorted out by a paper I found which can be downloaded here but I have also attached if the link goes bad. (Zenker et al)
The summary of this paper is that they have a DML of unspecified construction materials which has a "separation plate" mounted only about 1cm behind the panel. This is comparable in distance to Goebel's "acoustic lens". They also share other similar characteristics. In particular both have a large cutout located centrally.
Zenker et al modelled this construction very accurately using finite element analysis software. Read the paper for details. The intention was to prevent standing wave nulls which caused frequency response dips of up to 25dB. The large central space in the separation plate minimised air stiffness behind the panel at the fundamental resonance antinode. Elsewhere it effectively suppressed nulls at other resonance modes. The end result was a much flatter frequency response.
I believe Goebel just found the same result by trial and error and attributed it to an acoustic lens rather than altering the panel's standing wave profile. Of course I could be wrong and it may have been lost in the translation.
Anyway this is another piece of the puzzle. I think the following are super important:
1) panel materials (some degree of damping is necessary IMHO)
2) boundary conditions (how the sides are mounted - I will probably use butyl to damp)
3) exciter position (maybe central not so bad)
4) use of an enclosure (I probably will)
5) use of a separation plate (the salt/sugar method can be used to work out where holes should be placed)
I don't want to criticise others for not following a similar path. We all have our own methods but this will be mine.
EDIT:
My current plan is just to make a 2.0 system with bass driver (eg. Anarchy 704) to 300-1000 Hz or so and DML panels to handle the rest. It just seems too problematic to make a FAST type system with subwoofer as the panels need to be too large to get anywhere close to a reasonable crossover frequency (~150Hz)
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tsardoz,
I agree for sure with 1,2 and 3 on your list.
Concerning 3, you should read this if you have not already:
(PDF) Optimized Exciter Positioning Based on Radiated Sound Power of a Flat Panel Loudspeaker
Sorry if it's something you already referenced previously. My interpretation (colored by my own experience) is that the best exciter position does not follow simple rules (i.e 2/5, or 40% rule) like many want to believe. Zenker shows that the best position may be close (or far) from the 40/40 position, and depends greatly on panel size. While the paper doesn't prove it, it seems likely that the ideal position also depends strongly on the panel aspect ratio, as well as the degree of anisotropy of the panel, and on the boundary conditions, and on and on. And what if you use 2 (or more) exciters?
For me, the lesson is this: lacking the ability to run simulations, the best approach is simply to experiment with different positions and see what works best for your panel, in your chosen mounting configuration. You may not find the true optimum location, but at least you won't pick an absolute crap position, simply because you decided to use some comforting "rule of thumb". And yeah, one of the interesting things Zenker shows is that the often maligned center location is actually better than the 40/40 position in 2 of his three examples.
Regarding your number 4 (using an enclosure), I actually kind of enjoy hearing radiation from the back, since it's novel compared to conventional speakers. Is there a journal article or other good source that has convinced you that there is an advantage to be gained with an enclosure? If so, I'd be interested to read it.
Regarding 5 (separation plate) maybe. Your post made me re-read Zenker's paper. He picked a configuration that had particularly large peaks and dips. I wonder if such an approach is worth the effort for a configuration with more typical peaks and dips.
The thing that struck me the most in this article is actually figures 7a and 12a. I always assumed that the contribution of the fundamental mode of vibration (Mode 1) would be limited to the frequency range near to the associated frequency (i.e. the fundamental frequency). But if (big if) I am correctly interpreting the article, those figures suggest that Mode 1 contributes over a much broader range than I expected, and apparently contributes the most to sound pressure up to at least 1000Hz (the farthest his plots go) in his example, where the fundamental is only 52 Hz.
Interestingly, he suggests at the end of the article that the separation plate concept could work without a full enclosure.
Eric
I agree for sure with 1,2 and 3 on your list.
Concerning 3, you should read this if you have not already:
(PDF) Optimized Exciter Positioning Based on Radiated Sound Power of a Flat Panel Loudspeaker
Sorry if it's something you already referenced previously. My interpretation (colored by my own experience) is that the best exciter position does not follow simple rules (i.e 2/5, or 40% rule) like many want to believe. Zenker shows that the best position may be close (or far) from the 40/40 position, and depends greatly on panel size. While the paper doesn't prove it, it seems likely that the ideal position also depends strongly on the panel aspect ratio, as well as the degree of anisotropy of the panel, and on the boundary conditions, and on and on. And what if you use 2 (or more) exciters?
For me, the lesson is this: lacking the ability to run simulations, the best approach is simply to experiment with different positions and see what works best for your panel, in your chosen mounting configuration. You may not find the true optimum location, but at least you won't pick an absolute crap position, simply because you decided to use some comforting "rule of thumb". And yeah, one of the interesting things Zenker shows is that the often maligned center location is actually better than the 40/40 position in 2 of his three examples.
Regarding your number 4 (using an enclosure), I actually kind of enjoy hearing radiation from the back, since it's novel compared to conventional speakers. Is there a journal article or other good source that has convinced you that there is an advantage to be gained with an enclosure? If so, I'd be interested to read it.
Regarding 5 (separation plate) maybe. Your post made me re-read Zenker's paper. He picked a configuration that had particularly large peaks and dips. I wonder if such an approach is worth the effort for a configuration with more typical peaks and dips.
The thing that struck me the most in this article is actually figures 7a and 12a. I always assumed that the contribution of the fundamental mode of vibration (Mode 1) would be limited to the frequency range near to the associated frequency (i.e. the fundamental frequency). But if (big if) I am correctly interpreting the article, those figures suggest that Mode 1 contributes over a much broader range than I expected, and apparently contributes the most to sound pressure up to at least 1000Hz (the farthest his plots go) in his example, where the fundamental is only 52 Hz.
Interestingly, he suggests at the end of the article that the separation plate concept could work without a full enclosure.
Eric
tsardoz,
How have you come to this conclusion? How small do you need your panels to be?
My plywood panels (16" x 23") have a fundamental frequency in the neighborhood of 50 Hz, and work fine with my sub using a crossover frequency of 160 Hz. If I let the Yamaha YPAO system set the crossover automatically, it actually sets the crossover even lower, at maybe 100 or 120 Hz IIRC. And I don't think my plywood panels are particularly unusual in terms of reaching low. I think a 150 Hz crossover in a FAST system with panels and a sub is easily achievable.
Gobel thought so too, right?
Eric
Eric
Steve,
I sure agree with all of that.
But my suggestion is this: the PVA will do whatever it actually does, regardless of what it is you intend for it to do. So saying that it's not used as a damping layer, doesn't mean that it isn't. And I can't help but wonder if the reason it seems to improve the poor sounding surface of EPS, and stop the buzzing of card, and reduce self noise, as you say, isn't actually be because it actually adds some damping, even if that is not your intention.
What are those problems?
Eric
Eric.
Removing a few grams of the eps surface and replacing it with a few grams of pva does not dampen the sound of the panel, unless of course you increase the coatings or use neat pva.
This will start to dampen , soften the panel sound, this would be a matter of taste of course.
Some like heavily doped cones and some do not,it's the same old story.
Once a panel or cone for that matter , is over damped ,the damage is done(in my opinion) ,as you can guess I'm not too keen on over damped cones either.
So you can imagine my horror if someone suggested that I nailed wood and rubber to say a delicate lowther drive unit in an attempt to smooth the response
On very light eps (the lower grades) the pva does actually improve the response (output)across the panel , so saying it's damping the panel would be a little misleading ?
We are talking about very light and delicate sounding panels here ,that even lightly touching the panel with your fingers will alter the sound.
Clamping and heavily damping an eps panel (and any other light panel or cone for that matter )will destroy that light and delicate sound .
Heavier panels like my large rigidly clamped 3mm ply panels are a different story , and I use different methods to increase the performance(to my ears anyway).
Steve.
Removing a few grams of the eps surface and replacing it with a few grams of pva does not dampen the sound of the panel, unless of course you increase the coatings or use neat pva.
This will start to dampen , soften the panel sound, this would be a matter of taste of course.
Some like heavily doped cones and some do not,it's the same old story.
Once a panel or cone for that matter , is over damped ,the damage is done(in my opinion) ,as you can guess I'm not too keen on over damped cones either.
So you can imagine my horror if someone suggested that I nailed wood and rubber to say a delicate lowther drive unit in an attempt to smooth the response
On very light eps (the lower grades) the pva does actually improve the response (output)across the panel , so saying it's damping the panel would be a little misleading ?
We are talking about very light and delicate sounding panels here ,that even lightly touching the panel with your fingers will alter the sound.
Clamping and heavily damping an eps panel (and any other light panel or cone for that matter )will destroy that light and delicate sound .
Heavier panels like my large rigidly clamped 3mm ply panels are a different story , and I use different methods to increase the performance(to my ears anyway).
Steve.
Here's a good paper for those interested in the effects of boundary conditions (i.e. hanging from strings vs. in a frame), and damping, on radiation efficiency of a rectangular plate (i.e. DML/bending wave). Purely theoretical (no actual measurements) unfortunately, but still quite interesting.
https://eprints.soton.ac.uk/369232/1/Eprints.pdf
Regarding boundary conditions, it concludes:
In general, the comparison among FFFF, SSSS, and CCCC boundary conditions suggests that the
radiation efficiency increases, on average, with an increasing amount of constraint, even though at
some single frequencies an opposite trend can be found.
Here FFFF means free on all four side (i.e. hanging from strings) and is the least constrained, CCCC is clamped on all four sides and is the most constrained. SSSS is "simply" supported (i.e. hinged) on all four sides, and is between the two extremes.
The paper also shows how higher internal damping increases radiation efficiency from the panel's fundamental frequency (f0) up to the coincidence frequency (fc), which is a large part of the frequency range of interest (if not the entire range).
Eric
https://eprints.soton.ac.uk/369232/1/Eprints.pdf
Regarding boundary conditions, it concludes:
In general, the comparison among FFFF, SSSS, and CCCC boundary conditions suggests that the
radiation efficiency increases, on average, with an increasing amount of constraint, even though at
some single frequencies an opposite trend can be found.
Here FFFF means free on all four side (i.e. hanging from strings) and is the least constrained, CCCC is clamped on all four sides and is the most constrained. SSSS is "simply" supported (i.e. hinged) on all four sides, and is between the two extremes.
The paper also shows how higher internal damping increases radiation efficiency from the panel's fundamental frequency (f0) up to the coincidence frequency (fc), which is a large part of the frequency range of interest (if not the entire range).
Eric
Steve,
You seem to define damping as reduced output.
And sure, if you coat a panel with some heavy compound (damping or otherwise), it will reduce the output.
But pure damping, either via a damping material in the surround at the panel perimeter only, or via selection of a panel material with higher internal damping (i.e wood, plastic, or fiber epoxy composite rather than steel or aluminum), need not reduce the output. Rather, as shown by the paper in my previous post, damping should increase, rather than decrease, output.
And yes, it seems counter-intuitive at first. But if you consider that with undamped standing waves, antiphase areas of the panel will cause destructive interference and minimize output. But damping reduces the amplitude of the antiphase vibrations, and hence reduces the interference and increases net output. At least that's how I understand it.
So, no, it's not misleading to suggest that something that increases output is damping. Rather, the fact that something increases output might actually be considered evidence of damping.
Eric
It seems that everyone is stuck with using a standard vioce coil around a pole piece.Perhaps we should look at alternative ways to excite material beyond the same way a cone is excited.
The sound characteristics are different than a cone so why shouldn't the motor be different too? Or perhaps use a standard motor design and "Edge Excite" a material and control resonance and response via width and length. (Think exciting a triangle at one point) Damp the edges and frequency finds it's own "Sweet Spot"..
My theroy is.. Why shake a rug in the center or at any point beyond an edge? All sound pressure is moving in one direction, away from the source, which reduces interfering waves coming from behind...
I played with this and it does have merit. I just wanted to throw another brain fart out there and let ya run with it..
The sound characteristics are different than a cone so why shouldn't the motor be different too? Or perhaps use a standard motor design and "Edge Excite" a material and control resonance and response via width and length. (Think exciting a triangle at one point) Damp the edges and frequency finds it's own "Sweet Spot"..
My theroy is.. Why shake a rug in the center or at any point beyond an edge? All sound pressure is moving in one direction, away from the source, which reduces interfering waves coming from behind...
I played with this and it does have merit. I just wanted to throw another brain fart out there and let ya run with it..
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Plywood DML ? could it work - YouTube
This looks interesting but a lot of hard work ?
Piezoelectric drivers are getting more powerful ,but need special amps ?
There is bending foil as well ?
coils are ok if you sort out the problems first.
Steve.
This looks interesting but a lot of hard work ?
Piezoelectric drivers are getting more powerful ,but need special amps ?
There is bending foil as well ?
coils are ok if you sort out the problems first.
Steve.
Personally, I believe there is inertia loss and "colorization" added to the sound at the connection point of the voice coil to whatever material. The true full spectrum of sound the voice coil is obviously capable of reproducing always must travel through some sort of adhesive material and never is a true part of the material being excited. Not to mention the fact of only exciting one surface of the material at a very small spot...
Way back in time, I was messing around in my normal out of the box mode, using a bottom of a beer can as a concave tweeter mounted in a foam panel. The voice coil was connected to the can bottom in the center BUT the can part was connected to the foam panel and excited both surfaces, front and rear, or per se.. The whole panel and not just relying on one point on one surface to transfer energy. My thought was the aluminum would be more reactive to high frequency and still transfer inertia frequencys to the panel with a more substantial connection..
Isn't aluminum used as a voice coil former..? Just sayin'..
Way back in time, I was messing around in my normal out of the box mode, using a bottom of a beer can as a concave tweeter mounted in a foam panel. The voice coil was connected to the can bottom in the center BUT the can part was connected to the foam panel and excited both surfaces, front and rear, or per se.. The whole panel and not just relying on one point on one surface to transfer energy. My thought was the aluminum would be more reactive to high frequency and still transfer inertia frequencys to the panel with a more substantial connection..
Isn't aluminum used as a voice coil former..? Just sayin'..
Hi guys, new member here, experimenting with panels and different combination to eliminate that echo-y sound coming from the foam panels. Currently using plywoood for left channel and foam for right channel to cover all range but it still seems a bit fishy. As i understand correctly the best combination is to glue a piece of plywood on the back of the foam panel to eliminate that problem and add a spine to support the exciter?
Can you guys help me summarize the best combination for the best possible sound I can get out of these babies?
P.s. i also read somewhere that using cones can eliminate that echo.
Can you guys help me summarize the best combination for the best possible sound I can get out of these babies?
P.s. i also read somewhere that using cones can eliminate that echo.
Hi Spedge,
Yes, i mean hollow, as if i'm hearing the vocals/music coming from a tunnel.
I've tried both xps and eps, 1 inch and 1 and a half inch thick. 40x50cm and with both rounded and non rounded corners. I've tried plywood too, and that solves most of the hollowness but it's still there, so i try to combine both. What's your suggestion in improving this?
Yes, i mean hollow, as if i'm hearing the vocals/music coming from a tunnel.
I've tried both xps and eps, 1 inch and 1 and a half inch thick. 40x50cm and with both rounded and non rounded corners. I've tried plywood too, and that solves most of the hollowness but it's still there, so i try to combine both. What's your suggestion in improving this?
The same is with the wooden board, they sound a bit hollow, much less than the foam, but still noticeable. I have 3d printed a whizzer cone and will try to glue it onto my wood panel to test out the speech crispness as i feel like it will crisp it out and be less hollow, although counter intuitive to the whizzer use. Since a whizzer is used for higher frequency response, logically it will smooth out the speech since it will counter the lower frequency dip in efficiency. Will test and post results. So far the panels sound good and i always adjust the balance to be 65% wood panel and 35% foam panel just because the foam panel is louder and this balances things out.
First post and i would like to applaud this thread, a very interesting read. our family decided to do craft swaps for xmas and i drew my younger step son. In his 30's but younger . After spending some time i decided to do DML speakers for his gift. i went with 2'x2' 1/4 inch acrylic. i know the square form has resonance issues but i decided to give it a shot. i wonder if anyone has tried piercing the flat panel...with small plastic tubes, or metal tubes or even nails? i see the weight and spedge's tacky glue methods to change the sound/resonance problems but an actual pierced addition of metal or plastic might offer a breakdown of the resonance spots and add an upper range "tweeter". i suppose punching a hole in the panel could change the whole way the panel responds too. Another thought that i had while reading through this tome was lead. Has anyone tried using lead in a sheet, perhaps for bass, or in panel damping work? Anyway thx folks for this amazing work u all have done.
. After spending some time i decided to do DML speakers for his gift. i went with 2'x2' 1/4 inch acrylic. i know the square form has resonance issues but i decided to give it a shot. i wonder if anyone has tried piercing the flat panel...with small plastic tubes, or metal tubes or even nails? i see the weight and spedge's tacky glue methods to change the sound/resonance problems but an actual pierced addition of metal or plastic might offer a breakdown of the resonance spots and add an upper range "tweeter". i suppose punching a hole in the panel could change the whole way the panel responds too. Another thought that i had while reading through this tome was lead. Has anyone tried using lead in a sheet, perhaps for bass, or in panel damping work? Anyway thx folks for this amazing work u all have done.