Thank you BurntCoil!
Spedge - very nice recording, what was your panel again?
I found this site that seems reasonable. It has balsa wood core panels, PET foam, but most interesting a flexible balsa wood panel. I will probably end up buying both the balsa wood, the flexible version and the birch ply since that has the best reviews so far. The flexible balsa wood will either be great because it would act with the best properties of balsa wood and canvas or it will just fail haha.
Shop Composite Core Materials Online | CoreLite Composites
Spedge - very nice recording, what was your panel again?
I found this site that seems reasonable. It has balsa wood core panels, PET foam, but most interesting a flexible balsa wood panel. I will probably end up buying both the balsa wood, the flexible version and the birch ply since that has the best reviews so far. The flexible balsa wood will either be great because it would act with the best properties of balsa wood and canvas or it will just fail haha.
Shop Composite Core Materials Online | CoreLite Composites
I wonder if you cut a slit in a pool noodle and slide it onto the edges, if that would help with these “edge reflections”?
Hey Burnt, I thought I read elsewhere that your French panels were 1/4”, but see here that they might 1/8”.
Could you confirm? I have a fantasy of recreating your French Setup
Hi CovidCrazy,
The French panels are 4mm thick, not 3mm. My bad.
The French ply we get here is Poplar, not Birch, much to my surprise. This may account for its better performance as Poplar is lighter than Birch.
Poplar is 0.35 – 0.5 kg/m3
Birch is 0.67 kg/m3
But the Birch ply in Ealing panels sound great so I am sure you won't be disappointed. I run both with IB subs crossing over at 200Hz and eq to flatten the FR response.
Have fun
Burnt
The French panels are 4mm thick, not 3mm. My bad.
The French ply we get here is Poplar, not Birch, much to my surprise. This may account for its better performance as Poplar is lighter than Birch.
Poplar is 0.35 – 0.5 kg/m3
Birch is 0.67 kg/m3
But the Birch ply in Ealing panels sound great so I am sure you won't be disappointed. I run both with IB subs crossing over at 200Hz and eq to flatten the FR response.
Have fun
Burnt
Reflection.
A lot of people seem to be very worried about reflections, reflections are a friend or dml .
If you are trying to get rid of a bad sound by damping,then there is something fundamentally wrong with the panel.
And If you are trying to extend the lower frequency response with damping and clamping you will always find that the midrange and above will suffer,there is no free lunch.
1 You should always start with a good exciter .
2Then look at how and where you are attaching and gluing the exciter.
3 the panel material is very important .
4 panel size v flexibility .
5 distortions in the centre area of the exciter within the coil area ,very important ,the tin can effect.
6 panel thickness can be a problem.
7 panel shape to help break up large panel LF standing waves plus exciter placement.
8 try to let the panel freely vibrate,for the best sound, anything more like restricting the
panel is less.
9 the use of a light coating on light panel materials to help the propagation of sound across the panel as with my eps panels , has the added advantage of minimising self noise,it was never ment to dampen the panel, but to replace the poor sounding eps skin.
If all of these things are done well you shouldn't need to do anything else.
Working from the point of view that you have to clamp and damp a panel ,then try to sort out these things afterwards just doesn't make sense to me, the damage has already been done!
I really do like the sound of eps , it's my favourite of the bought panel materials, but there are other thinner but not as light materials that are readily available and sometimes free,that will do far better than the very expensive hi tech materials on offer.
Alius 123 .
The rigid balsa wood panels would be my best choice, 20 dollars for two 24x24inch x1/4 panels seems a good price+ delivery?
You can cut the panel so as not to have any waste and also not have parallel sides,I love win win situations,this works for eps panels too.
Let me know if you want further information , that's if you buy them.
Steve
A lot of people seem to be very worried about reflections, reflections are a friend or dml .
If you are trying to get rid of a bad sound by damping,then there is something fundamentally wrong with the panel.
And If you are trying to extend the lower frequency response with damping and clamping you will always find that the midrange and above will suffer,there is no free lunch.
1 You should always start with a good exciter .
2Then look at how and where you are attaching and gluing the exciter.
3 the panel material is very important .
4 panel size v flexibility .
5 distortions in the centre area of the exciter within the coil area ,very important ,the tin can effect.
6 panel thickness can be a problem.
7 panel shape to help break up large panel LF standing waves plus exciter placement.
8 try to let the panel freely vibrate,for the best sound, anything more like restricting the
panel is less.
9 the use of a light coating on light panel materials to help the propagation of sound across the panel as with my eps panels , has the added advantage of minimising self noise,it was never ment to dampen the panel, but to replace the poor sounding eps skin.
If all of these things are done well you shouldn't need to do anything else.
Working from the point of view that you have to clamp and damp a panel ,then try to sort out these things afterwards just doesn't make sense to me, the damage has already been done!
I really do like the sound of eps , it's my favourite of the bought panel materials, but there are other thinner but not as light materials that are readily available and sometimes free,that will do far better than the very expensive hi tech materials on offer.
Alius 123 .
The rigid balsa wood panels would be my best choice, 20 dollars for two 24x24inch x1/4 panels seems a good price+ delivery?
You can cut the panel so as not to have any waste and also not have parallel sides,I love win win situations,this works for eps panels too.
Let me know if you want further information , that's if you buy them.
Steve
Thank you so much Burnt!
A question to pick your brain as an “arch grand daddy” of this topic if I may:
Have you heard of anybody putting two exciters wired out of phase with each other at the exact same location on opposite sides of a long thin free floating plywood panel ala your Tall Story dimensions?
Is this crazy? Would it just be better to put them on different panels or the same panel on the same side?
I’m asking about this because of some points made earlier in the thread about the most effective transfer of energy from the exciter to the panel.
Could this approach somehow mimic the benefits of a spine holding the exciter in place?
Where I live it is very difficult to get materials, so I have to map moves out well in advance of buying anything.
Spedge, love the break down you provided. Thanks for the input. Still trying to figure out what type of panel I want. It’s more convenient to be able to go to Lowe’s or Home Depot than buy online with shipping and delivery time. It’s crazy just with how many options there are,it definitely makes it more difficult to choose, but there’s no way to know till you dive in and experience yourself.
I am far from being an arch grandaddy, I only came across DML’s last summer when my Electrostatics decided they were going to sulk because I had moved them to France and they didn’t like it hear. I have posted a lot in that time though
Yes the principle of out of phase and 180 degree coupled exciters has been tried with no reported benefit. This doesn’t surprise me as the total output from the panel is a combination of the early signal from the panel at the exciter plus the output from the rest of the panel. There is a paper on that by Farad Azima with a nice image of the outputs as simulated. However, having said that you might want to try it as a test before you finalise your build? Many of us have discovered that the claimed state of the art isn’t complete with some variations on the published approaches giving helpful results. In my case long tall panels working much better than they should.
Burnt
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Steve, can you elaborate on this distortion? Is it a particular resonant frequency that can be measured? Do you hear it with certain instruments or vocals?
Thanks, Dave
True, but virtually the only plywood that's the same species for all the plies is birch. Birch is kind of special that way. The core layers of most plywoods are not the same as the face layers. Rather, they are likely whatever is cheapest in the region they are made. So while birch is all birch, "Poplar" ply most likely has Poplar skins and some other unspecified core.
The birch plies I have are about .65 g/cc. The "Poplar" is have is about 0.52 g/cc. So the difference in density between birch ply and "poplar" ply is not as much as it ought to be, based on the density of true poplar.
So Poplar ply is lighter than birch, but not by as much as you might expect.
Eric
For about $20, it's a small risk, but I wouldn't waste it on the "flexible" balsa. This stuff is made for making curved panels with fiberglass skins. If it works "as is" you will have invented a different type of speaker panel, not a dml.
I have tried their 3/8" end grain balsa. If I bought more I'd try the thinner 1/4" instead. I must add that the balsa panels I got from corelite were on the heavy side, based on my expectations for balsa. Mine were close to 0.29 g/cc. I expected more like 0.20 g/cc. But to be fair, they don't specify a target density, so I can't say it was out of spec.
Eric
That is true for certain, but just to give you a slightly different perspective:
1. start with a good panel material.
2. put the exciter(s) near the middle of the panel.
3.Many of the Parts Express exciters over $10 are okay. Some are a little better.
4. Stiff, light panels are more efficient, but may need to be larger to reach low frequencies.
5. Sometimes there is a tin can effect at frequencies that you can hear only if you are under 25.
6. See 4.
7. Don't bother with rounded corners or angled sides, unless you prefer how they look. They will slightly change the fundamental frequency, but won't reduce reflections. Plus, reflections are what makes it a DML.
8. Attach your panel to a rigid frame around most of the perimeter with a soft foam. This will increase the output for low frequency. If you plan to cross to a sub below 200 Hz, it may not matter.
9. Use an inexpensive underlayment plywood,if you like, sand it, stain it and coat it with polyurethane. Or not.
Oh contraire Msr Eric. But don’t worry, the French have been driving Brits nuts for centuries by being different
https://www.joubert-group.com/en/joubert-gamme-326-joubert-poply.html
https://www.joubert-group.com/en/joubert-gamme-326-joubert-poply.html
Intaud.
Yes you can hear and measure the noise ,in the old days I used a very small 2mm blob of blu- tack in the centre of the exciter to tame the peaks and troughs.
The problem with the ring or coil exciter is not with the outwards radiation, but the inwards radiation.
If you can imagine the coil at low frequencies mostly acting like a piston ,but then as the frequency gets higher the coil radiates inwards.
I've tried to think of an analogy and the only one I can think of at the moment is ,if you can imagine the coil with hundreds of little guns pointing into the centre of the ring ,and all these guns are firing into the centre at the same time,as you can imagine ,I hope, it is going to get pretty messy at the centre point when they all collide ,but does it all stop there?the frequencies do collide and try to carry on to the opposite side , causing distortions, cancellations and peaks, similar to the combing effect from having two exciters or drive units in close proximity,but because this is all happening within such a small space within the ring ,the sound is very harsh and messy ,this is what I call the tin can effect,it is not used as a derogatory term but to describe the uncontrolled noise.this harsh sound will not just effect bats.
It spreads through the frequencies causing all sorts of problems,the blu-tack does dampen the problem but as you might know I'm not keen on damping,it does soften the sound a bit.
But please do give blu-tack a try it's cheep and won't damage your panels,you don't need large amounts ,just 2 or 3mm should do .
Burntcoil.
Do you have your measuring equipment with you in France,if your panels give a good response over 10k within the exciter area ,you could do some tests and a few very cheap tricks to improve performance,it doesn't just effect the performance above 10k but helps to see the big overall picture.
If you are interested please let me know.
Steve
Yes you can hear and measure the noise ,in the old days I used a very small 2mm blob of blu- tack in the centre of the exciter to tame the peaks and troughs.
The problem with the ring or coil exciter is not with the outwards radiation, but the inwards radiation.
If you can imagine the coil at low frequencies mostly acting like a piston ,but then as the frequency gets higher the coil radiates inwards.
I've tried to think of an analogy and the only one I can think of at the moment is ,if you can imagine the coil with hundreds of little guns pointing into the centre of the ring ,and all these guns are firing into the centre at the same time,as you can imagine ,I hope, it is going to get pretty messy at the centre point when they all collide ,but does it all stop there?the frequencies do collide and try to carry on to the opposite side , causing distortions, cancellations and peaks, similar to the combing effect from having two exciters or drive units in close proximity,but because this is all happening within such a small space within the ring ,the sound is very harsh and messy ,this is what I call the tin can effect,it is not used as a derogatory term but to describe the uncontrolled noise.this harsh sound will not just effect bats.
It spreads through the frequencies causing all sorts of problems,the blu-tack does dampen the problem but as you might know I'm not keen on damping,it does soften the sound a bit.
But please do give blu-tack a try it's cheep and won't damage your panels,you don't need large amounts ,just 2 or 3mm should do .
Burntcoil.
Do you have your measuring equipment with you in France,if your panels give a good response over 10k within the exciter area ,you could do some tests and a few very cheap tricks to improve performance,it doesn't just effect the performance above 10k but helps to see the big overall picture.
If you are interested please let me know.
Steve
Oh contraire Msr Eric. But don’t worry, the French have been driving Brits nuts for centuries by being different
https://www.joubert-group.com/en/joubert-gamme-326-joubert-poply.html
Poply, cool. I stand corrected. That looks like good stuff. I've never seen that here. We just get thin poplar skins with a mystery core.
Eric
Vive le France! You might get some in the US soon Eric, Poplar is farmed as a sustainable source over here and is gaining in popularity.
Hi Steve,
Yes I do have my gear in France now. I was planning a lot of experiments with panel designs but the shut-down has put that on hold as I can't get new material. I would be very interested in anything that can be applied to my first panels, thank you! I get a linear response to 10k when eq'd though, it falls away gently from 8k without EQ. I don't know if that would effect anything?
Burnt
Hello,
Has anyone determine the predominate wave i.e. Stoneley wave or Scholte wave? These waves have a exponential decay from the exciter which would lessen the reflection at any boundary condition. I see this decrease in amplitude when I use a laser reflection off a small mirror place on the panel. The further away from the exciter the less the amplitude until the piston effect kicks in about 160-150 Hz. The problem I see with current models is it assumes a homogenous material and most panels that the DML community is using is not homogenous. So I don't see reflections playing a major roll what am I missing??
Cheers
Steve
Has anyone determine the predominate wave i.e. Stoneley wave or Scholte wave? These waves have a exponential decay from the exciter which would lessen the reflection at any boundary condition. I see this decrease in amplitude when I use a laser reflection off a small mirror place on the panel. The further away from the exciter the less the amplitude until the piston effect kicks in about 160-150 Hz. The problem I see with current models is it assumes a homogenous material and most panels that the DML community is using is not homogenous. So I don't see reflections playing a major roll what am I missing??
Cheers
Steve