A Study of DMLs as a Full Range Speaker

Andre Bellwood.
Thank you.
It was that sort of setup I was thinking of for the proplex, not 5000watts 😃
My friend does those sort of gigs but mainly with acoustic guitar.
I was wondering whether I might make him some panels.
Steve.
The setup I'm aiming for will eventually be a small 1,000W system driving 2 x 250W panels and a 500W sub, and should be able to deliver 120db peak SPL, ideal for a one-man setup or a small folk band indoors. I'd suggest double that for a rock band with live drums and bass playing through the P.A.

I suspect that Proplex is not Polycarb but Polypropylene, the same stuff they use to make Corflute/Correx signboards etc. Unfortunately it's at the bottom of my pile of tested, parametrised and discarded samples. It's just way too dense and far too highly damped to be of any use for my application IF it's the stuff I'm thinking of.
But I'd be interested if you can get me material properties on Proplex (density, shear modulus, Young's modulus, tensile strength, etc etc) or maybe point me at a supplier who would submit these details. I have tried to Google it, but have found some wholly unrelated answers.
Cheers,
A.
 
I was not getting as much HF as what I was getting mids.
+ @spedge
As far as remember, this is an open topic on EPS. Several of us faced the lack of HF with EPS. I am currently in the opinion that the EPS we had is to light, not stiff enough; a too low mechanical impedance that leads to a high pass filter with the mass of the voice coil. the only way I see as a counter measure is to increase the stiffness and the weight by the quantity of PVA coating... and starting from a not too light EPS. I would appreciate to have figures about that.
Christian
 
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+ @spedge
As far as remember, this is an open topic on EPS. Several of us faced the lack of HF with EPS. I am currently in the opinion that the EPS we had is to light, not stiff enough; a too low mechanical impedance that leads to a high pass filter with the mass of the voice coil. the only way I see as a counter measure is to increase the stiffness and the weight by the quantity of PVA coating... and starting from a not too light EPS. I would appreciate to have figures about that.
Christian
Hi Christian,
I suspect the EPS is too soft to transmit vibration from a back surface to a front surface. So it does not matter how stiff we make those surfaces (I used Kevlar and UHMWP!) and it does not matter how strong or heavy the panel is, but if the core is too soft, then HF cannot "penetrate" from driver on the back to acoustic radiation on the front.
I did try to reduce this effect by using hard pucks in the EPS, but it made little difference. Maybe they are too small?

I keep denying it, but the solution seems to be 2mm honeycomb panels with CF(?) skins... Eish.
 
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I suspect the EPS is too soft to transmit vibration from a back surface to a front surface. So it does not matter how stiff we make those surfaces (I used Kevlar and UHMWP!) and it does not matter how strong or heavy the panel is, but if the core is too soft, then HF cannot "penetrate" from driver on the back to acoustic radiation on the front.
What if you connect the coil former/bobbin of the exciter to the front of the panel by a connector, through the EPS panel from the back? The connector could be a flat one, or an extension to the coil former/bobbin. This video and this might point to the idea.
 
NXT quote,
Sounding boards are, of course, very well-known for stringed musical instruments such as pianos and the violin family. The making of successful such sounding boards is very old, and they are invariably held effectively rigidly at edges and/or clamped medially.
meaning that DM panels should be held effectively rigidly at edges and/or clamped medially.

Indeed, affording simpler alternatives to traditional sounding boards, particularly of calculated and orderly design as herein, is seen as an aspect of this invention.
NXT states.
 
Hi Christian,
I suspect the EPS is too soft to transmit vibration from a back surface to a front surface. So it does not matter how stiff we make those surfaces (I used Kevlar and UHMWP!) and it does not matter how strong or heavy the panel is, but if the core is too soft, then HF cannot "penetrate" from driver on the back to acoustic radiation on the front.
I did try to reduce this effect by using hard pucks in the EPS, but it made little difference. Maybe they are too small?

I keep denying it, but the solution seems to be 2mm honeycomb panels with CF(?) skins... Eish.
If this is the case, that there is a lack of transfer of energy from back to front, then there should be a difference in frequency response comparing back and front. I’m Assuming that the exciter is directly connected to backside and thus inducing waves in the panel.
’Thomas
 

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Proplex is PP

HomopolCopolym
Density/ kgm-3905905
Price / Tonne/ £680620
Tensile Strength/ Mpa3325
Tensile Modulus/ Gpa1.41.0
Elongation at Break/ %150300
Hardness/ Rockwell "R" Scale9080
Notched Izod Impact/ kJm-10.070.1
Thanks BC,
Given those numbers (just by density alone,) Proplex is as suspected: too heavy for decent efficiency. I will have to quadruple the size of my amps to get the same SPLs.
 
If this is the case, that there is a lack of transfer of energy from back to front, then there should be a difference in frequency response comparing back and front. I’m Assuming that the exciter is directly connected to backside and thus inducing waves in the panel.
’Thomas
Thanks Thomas,
I do recall doing "back-side" tests a while ago, and noting that the FR definitely goes higher than front side. I'll do the same tests on these panels today and see if I pick up anything note-worthy.
 
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Andre bellwood.
Proplex is a heavy duty floor protector and able to withstand high impact.
I think it is polypropylene ,the sample was sent to me by JohnnoG after it had been used to protect his flooring.
There are a few dents in it but it still works fine.
I have also made recordings of these panels with my 10watt exciters.
Steve.
It is indeed polypropylene - the polycarbonate twin cell is a different animal - much stiffer and more glass like.

Australian proplex is marketed as corflute and is not heavy, at least in the 5mm thickness I have which weighs 890 gsm versus 1400 gsm for 3mm poplar ply

https://corex.com.au/product/corflute/


Eucy
 
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