Actually, the EPS cut with a heated thin wire. I've been to the factory many times.
Sure, EPS can be moulded, but the technology is too expensive to mould smaller items, extruding is much cheaper, at least that's what the people told me at the factory, when we were using a lot of polystyrene elements. Anyway, back to the topic, the EPS is open cell, that is, there is quite some air in it. Maybe that's why those who advocate using EPS for DMLs tell you to add watered down PVA to block the pores, at least the surface pores. XPS, on the other hand has a fully covered surface, straight from the factory. Also, its being said to sand and cover the front surface of the EPS panel, not all 6 surfaces. If you do that, it'd give a different sound effect. One can simply spray paint the surface from cans. EPS is cheap anyway, and sometimes free of charge.
If someone's interested, there's an offer right here of Yamaha's famous "elephant ears" Don't know, if this is off topic, though.
Hello Paul,
A mystery remains for me around EPS. It is a very attractive material because of the possible efficiency. The second side of the coin is its capacity to rich the high frequencies. The different theoritical papers predict a frequency cut off linked to the mechanical impedance versus the voice coil mass. It is something I have introduce in the material chart paper some weeks ago. For light material, this cut off might appear in the desired bandwidth. I think I have some indications in this way but not so many. If I try to summarize what I remember about EPS in the threads is there is a general recommendation for high density... but reports of success with moderate grades... Thickness is generally 20 or 25mm with some reports down to 5 or 6mm... I don't have in mind report of successful design from raw EPS. The general approach is to coat it with PVA. Coating it changes the resulting density, elasticity and damping. The difficulty is to appreciate what is needed, no data even like simple areal mass evaluation before and after coating are shared. I made tests with an easily available 15kg/m³ EPS but never get enough bandwidth (not coated enough?). Leob shown also frequency limitations (with no consequences in his PA application with EQ) 25kg/m³?. Recently, a Bertagny patent was posted, there are some indications of density in it.
If you can collect some data about density and elasticity (Young modulus), I can add that in the material chart.
Light and thin material seems to be a challenge (where is the limit in combination with the exciter that meets the FR target?).
Let see the other feedback you'll get to your question.
Christian
Thanks Christian.
I thought I had seen reports extolling the virtues of EPS, including HF performance.
Im going away for ~10 days holiday, so may not be on the forum for a bit.
Paul
Christian and Paul you may want to include the exciter performance in your thinking. Due to a rising inductance with frequency a review of frequency response for the majority of exciters show a falling response above 10k. In my experience without EQ this is a dominant trend. It isn’t difficult to correct this, and in reality there isn’t much information above 10k, mostly harmonics for a few instruments, so EQ is a good solution, but I am not sure materials performance alone defines > 10k.
Burnt
EPS is mostly sold according to compressive strength, that is, named that way, most popular at the construction material shops being EPS70 and EPS100. There might be EPS150 sometimes. Some knowledge here and here. Usually sold in packets. Loose sheets can be found sometimes at the shopping malls back areas, free of charge, or at construction sites.
So it's OK to boost with EQ? The videos I've watched advise on just cutting where too high.
Is it rising inductance, or do you mean rising impedance due to (constant) inductance? (jwL)
I have using the dayton thruster and with xps have falling response over 10k. Didn't expect much HF from such a large & heavy exciter. And yet, Typical Ben on YouTube with acrylic speakers, has a rising response above 10k. (See 7:30 minutes in)
Thruster spec sheet https://www.wagneronline.com.au/attachments/Audio-Speakers-PA/dayton/DAEX32EP-4.pdf
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In Australia there does not seem to he a rule, it can be sold by density or letter grade.
Its actually difficult to find a supplier selling small quantities cut to size. Many don't deal with the public at all, only distributors who mark up the product and don't stock the higher grades anyway, others have a minimum order of ~AU200, plus another ~AU100 for delivery
I found this table:
Nominal Densities vs compressive strength
EPS 70 15 kg/m³
EPS 100 20 kg/m³
EPS 150 25 kg/m³
EPS 200 30 kg/m³
EPS 250 35 kg/m³
Highest grade available in Australia is apparently X38 grade density 38kg/m3, compressive strength 270 kg/m3. Probably only available as a big slab.
Another site sells what they call low (13.5 kg/m³) medium (19 kg/m³) and high (24 kg/m³)
Another site gives letter designations apparently from an Australian standard.
L - 50 kPa
SL - 70
S - 85
M - 105
H - 135
VH - 165
Paul
You are correct I meant impedance, thank you for the catch. I have that exciter and it’s response falls from 5k and by 20k is 15dB down. Using EQ is perfectly acceptable in my view providing it is used with care and your amp and exciter can cope. EQ is used all the way through the recording chain so using it on your system at home is nothing special. Even direct to disk analogue recordings have EQ in the recording chain to correct cutter head error.
As for Acrylic I can’t comment as I have never tried it.
Burnt
Ask at the nearest construction site, they may have excess or damaged sheets. They usually have excess, for they have to buy in packets.
I do share burntcoils concerns about some exciter hf performance.
I have been surprised at some of the early roll off on certain materials.
I have shown that low grade EPS can reach above 10k when a little attention is paid to it.
But this hf is not necessarily produced all over the panel at the same high level.
I'd say most of my panels produce hf above 10k from around the central coil area.
Harder panels like plywood tend to radiate hf over 10k all over the panel, with my exciter that is.
I can alter the hf response in the central coil area with say my paper strips, but that does not alter the whole panel response , it stays the same, if I remember correctly?
A lot of papers seem to concentrate on the DML output and neglect the centrally radiated output.
Which can be considerable sometimes.
The smaller the panel becomes the more this central area dominates.
Steve.
Steve regarding harder materials like Plywood way back in this very long thread I posted measurements, just dB levels, from several points on a 1200 by 600 Poplar panel- centre, corners, mid points on long axis and short axis edges about 100 mm in. From memory output was within +/- 5dB across the panel using white noise. It might be interesting to repeat on EPS/XPs and others?
Burnt
I've been watching Ben's experiments for some time. His acrylic sheet gives very nice HF sounds. I also like the way he fixed the sheet to the frame. I've a feeling that if that sheet had been fixed to a box, maybe an open box, say, 8-10 cm deep, he might've got the bass too, that is, if the box is hung on to a wall. Did you catch form his videos what are the dimensions of that sheet, height, width and thickness?
+ @pway , @spedge
Many interesting things in those posts about HF behaviour.
About the existence of an HF cut in the driving force of the exciter, no doubt in my mind it exists (even if I haven't mentioned it). It is a low pass filter between the voice coil inductance and its resistance. Something like fc = R/2piL.
The highest is R high, L low. If we had 8 Ohms exciter with a 0.1mH inductance (lower value I know for L) : fc = 13kHz which becomes 6.5kHz (4Ohm, 0.1mH) and even about 2.2kHz for 4Ohm, 0.3mH.
Where it is not clear in my mind it is this effect is not visible with all the materials. I have in mind it is visible with PS, not with plywood, some material (acrylic?) are even said to have a rising FR. I have started some tests to see it but my test gear is not performing enough. The idea is to measure the current flowing through the exciter along with the SPL at 1m. This not so difficult in the principle by adding a small resistor (ie 0.15Ohm) in series with the exciter and sending it to a mic input with the right gain adjustment but my setup is too noisy for now. So seems another mechanism in the membrane is working that counteracts in certain case the inductance effect.
Above in frequency, other phenomena appear.
It is clear for me that something happens involving the voice coil mass and the material. I think I posted about that. There is an influence of the central moving mass which is easily visible with PS, not with plywood.
And you are right that how the waves are traveling should be added as the interest is the SPL at distance so the sum of the emission on the whole surface, this might be related to absorption of the energy in the material according to the frequency. If I have in mind papers speaking about the 2 first points, I don't remember for the last one... at least in papers about DML. There might be something in paper about music instrument.
To measure the signal at close distance is something I would like to do for different materials but it was more in the idea of evaluating the wave speed and the modes (see Eric's post). I was wondering if it is relevant in level (the mic is omni so, it catches also what is traveling in the air no?)
Christian
This is a EPS panel I found a couple of weeks ago in a skip.
It has been drying out after all the rain we have been having.
I was going to make two panels out of it to compare with the proplex.
But I think I might first glue the two halves together for a 127cmx55cm x35mm panel and see what I get.
It is not a high density EPS but it does have small tight beads.
If you zoom in you can see them.
It will be interesting to see what the hf will be on the raw panel and then with some of my tricks.
Will there be a difference?
What works on my 5mm EPS might not work on the 35mm.
I do have a 50mm panel in my loft but I felt that was a little excessive.
I intend to get back to my roots and build my final EPS panels, the ones I will use permanently in my room.
Steve.
It has been drying out after all the rain we have been having.
I was going to make two panels out of it to compare with the proplex.
But I think I might first glue the two halves together for a 127cmx55cm x35mm panel and see what I get.
It is not a high density EPS but it does have small tight beads.
If you zoom in you can see them.
It will be interesting to see what the hf will be on the raw panel and then with some of my tricks.
Will there be a difference?
What works on my 5mm EPS might not work on the 35mm.
I do have a 50mm panel in my loft but I felt that was a little excessive.
I intend to get back to my roots and build my final EPS panels, the ones I will use permanently in my room.
Steve.