Hi Christian
If I can be permitted to respond, Eric and I discussed this at some length a long time ago.. We have differing approaches to this, I favour the grain running in the long direction, with the anisotropy being more balanced by the shorter lateral width. I was looking at achieving the lowest possible fundamental which I believe needs the lateral and longitudinal stiffnesses to be balanced as much as possible
Eric favours cross wise which he believes provides more even mode spacing (as I recall), so different aims, but I think he was also using 5 ply which has reduced anisotropy???.
No doubt he'll jump in here
Different strokes for different folks.
Maybe we need a duel, panels at twenty paces 🤭
Eucy
Yes
I doubt 1.5 mm would be stable under vibration at normal panel dimensions but it's worth a try .. May need to be treated more like a membrane in terms of mounting
I tested Sassafras...I tested most of their samples. I also ranked them... Just have to find it all again 😖☹️
I'm living between 2 states at the moment so life's a bit chaotic
My gut feeling is that the core is at fault here...
Ditto... Try listening along the edges of the panel to try and tell how the sound is travelling through the panel
Why aren't you trying the exciter on the top of the horizontal panel??
Core again?
You may have to bite the bullet and try a different ply material
Regards
Eucy
That looks more like an attempt to do away with the depth of a conventional woofer than true DML to me. The forerunner of DML was a military speaker. Not clear if that was use of some panel in a vehicle or a separate easily installed item with good sound reproduction capabilities.
The Yamaha set up might relate to a youtube video where some one converts a wider range speaker to an exciter and makes a glass table produce music 😉 providing a weight is placed on it to tension the glass. Yamaha may have hooked up something similar to a diaphragm. A kef b139 uses some sort of foam plate.
So the panel is about 15ft^2. Has anybody looked at using the same panel area with different aspect ratios? Dayton suggest taller aspect ratios can be used but suggest this arrangement. They don't mention a max.
A ratio of 1,25 against your 3,8, Good, bad or doesn't matter?
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That is what I am doing (of course) as it is the easiest way. Exciter on top, moving around the panel listening/measuring for changes. However, the SQ UNDER the panel, with the exciter ON TOP of the panel, is significantly different.
Fair question. There are a few here who deviated from that ratio, and in one of the papers and/or one of the participants here tested multiple ratios and found that the higher aspect ratios tend to work at least as well if not better. BurntCoil's 'Tall Blondes' are high aspect for example at ~3.8 IIRC.
So a bit more quick testing this morning...
At first l gave everything a listen before starting modifications so my memorized basis of comparison was fresh. Distribution throughout the panel was better than I remembered. I started by removing almost all of the full edge damping with a few pieces left of random lengths in random locations (see below). This as expected increased the SPL considerably and the sound was distributed more throughout the panel. I also added the sound absorbing panels shown in both images which seemed to improve the aforementioned discrepancy of above vs. below response. The panels are 2" x 24" x 48" Corning 703 covered with foam triangle baffles.
Then I added a second exciter wired in series. The bottom exciter in the image is in the 2/5 position in length and width. The upper exciter started in the 2/5 position (opposite side) and then was shifted to a position that gave a bit more low end extension. This as one would expect increased the spread of the sound across the panel. The placements look strange in the photo just because of the perspective.
At first l gave everything a listen before starting modifications so my memorized basis of comparison was fresh. Distribution throughout the panel was better than I remembered. I started by removing almost all of the full edge damping with a few pieces left of random lengths in random locations (see below). This as expected increased the SPL considerably and the sound was distributed more throughout the panel. I also added the sound absorbing panels shown in both images which seemed to improve the aforementioned discrepancy of above vs. below response. The panels are 2" x 24" x 48" Corning 703 covered with foam triangle baffles.
Then I added a second exciter wired in series. The bottom exciter in the image is in the 2/5 position in length and width. The upper exciter started in the 2/5 position (opposite side) and then was shifted to a position that gave a bit more low end extension. This as one would expect increased the spread of the sound across the panel. The placements look strange in the photo just because of the perspective.
Before I commit to the plywood I think I will try EPS in the same size just to hear the difference. One panel of EPS is cheap enough to try out. The problem however is so far I can only find 1/2" or 2" thick panels locally which is considerably off from the 1" thickness I want to try.
Go with the 1/2". You'll be amazed at the efficiency EPS is gonna' have compared to ply. You could even make the panel half that size for the same output. Be sure to apply a thin coat of 50/50 wood glue to water.
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Standard EPS with density aound 15kg/m³ is said not dense enough for DML application. 25kg/m³ more suitable (see Audiofanzy, Leob or Spedge posts). If you go for it, tell us about HF.
For the oter tests you did, have you some possibility to post FR?
According to the Owens Corning datasheet the standard 'Foamular 150' is 20.8 kg/m^3 and the 'Foamular 250' is 24.8 kg/m^3. The local big box stores carry the Foamular 150 with 1/2" in unscored, and 1" and 2" in scored. Due to the size of my frame (2' x 8'), and the fact that Tech Ingredients had good results with 1.5" foam in a 2' x 4' panel (albeit free hanging) I am inclined to go thicker than 1/2".
Right now all the measurements are qualitative. I have not been performing REW sine sweep testing etc. yet though I am getting set up for it.
Right now all the measurements are qualitative. I have not been performing REW sine sweep testing etc. yet though I am getting set up for it.
I had a look to the specifications. Not found the density... but it is XPS (eXtruded) no? not EPS (Expanded)?
They are foams - the main difference,
There appear to be 2 grades around in the UK used for insulation so I'd guess it's easily found elsewhere. Pink - sometimes paper backed and blue. The paper backing appears to be used to help prevent damage which suggests the pink is less dense than blue.
and this: "They are foams - the main difference"
I can't believe people here haven't even read the thread enough to know the difference between EPS and XPS. This site has turned to crap... to put it mildly.
OK who was it here that tried EPS or XPS panels sandwiched in Luan (3mm hardwood faced plywood)? I cannot find it, even using google externally and the site's search engine.
So I made a side stop at the hardware store this afternoon, specifically Home Depot, who carries 4'x8' sheets of 3mm and 5mm Luan type ply, as well as Foamular (XPS) and R-Max (EPS) both in several different thicknesses (1/4" 1/2" 3/4" 1"). I conducted a highly scientific transient test by pulling panels from the shelf and rapping on them repeatedly with my knuckles while suspending them in the air with a Heisenberg two-finger grip.
The XPS and EPS both ring like crazy. My highly trained assistant (my teenage daughter) and I could both hear the ring clearly which lasted about 576.3 ms as measured by an atomic clock that had been calibrated at NIST only a few hours before. The EPS had a significantly higher 1st mode frequency than the XPS for a given thickness; however that could have been due to the thin aluminum face sheets on the EPS as compared to the XPS with no face sheets.
The ply panels only rung about 1/4 of that or less. I came very close to buying a 5mm panel to try out (current panel is 3mm ply) but it would not fit in my car. Maybe I will go back tomorrow with the truck. I was not tempted to get EPS or XPS.
So to summarize... Foam be ringin' like a mofo. Ply be dead like Tupac. Those are both scientific terms. These properties appear to be consistent with a lot of the results reported here like efficiency, sound quality, and frequency range; ply damps much more than EPS or XPS foam, but ply is not nearly as stiff per unit volume as EPS or XPS.
I am surprised that a Luan/foam/Luan composite does not work well (reportedly) since it would be very stiff for its weight (like foam) yet provide significant damping (like Luan). That is why I ask in my post above about that particular test since I would like to compare notes. It seems like a 3mm-0.5"-3mm sandwich of carefully bonded ply-foam-ply would work at least acceptably and would definitely be less expensive than a more exotic ply like carbon fiber/nomex honeycomb core/carbon fiber.
The XPS and EPS both ring like crazy. My highly trained assistant (my teenage daughter) and I could both hear the ring clearly which lasted about 576.3 ms as measured by an atomic clock that had been calibrated at NIST only a few hours before. The EPS had a significantly higher 1st mode frequency than the XPS for a given thickness; however that could have been due to the thin aluminum face sheets on the EPS as compared to the XPS with no face sheets.
The ply panels only rung about 1/4 of that or less. I came very close to buying a 5mm panel to try out (current panel is 3mm ply) but it would not fit in my car. Maybe I will go back tomorrow with the truck. I was not tempted to get EPS or XPS.
So to summarize... Foam be ringin' like a mofo. Ply be dead like Tupac. Those are both scientific terms. These properties appear to be consistent with a lot of the results reported here like efficiency, sound quality, and frequency range; ply damps much more than EPS or XPS foam, but ply is not nearly as stiff per unit volume as EPS or XPS.
I am surprised that a Luan/foam/Luan composite does not work well (reportedly) since it would be very stiff for its weight (like foam) yet provide significant damping (like Luan). That is why I ask in my post above about that particular test since I would like to compare notes. It seems like a 3mm-0.5"-3mm sandwich of carefully bonded ply-foam-ply would work at least acceptably and would definitely be less expensive than a more exotic ply like carbon fiber/nomex honeycomb core/carbon fiber.
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👍👍👍😃🤭
Not even for a (more scientific) try??
I think that combo would be deader than Tupac as well...It doesn't take much to deaden XPS hence the watered down PVA used by many. To date, I can't find non-commercial quantities of high density EPS here so I haven't tried it...I will keep looking just to tick that box. I have tried XPS and it is certainly LOUD.
Going back to basics though, development of low frequencies is favoured by more mass in a panel, so having a very light panel encourages HF over LF. A balance has therefore to be struck unless separate HF and LF panels are used.
It would be useful to see side by side sweep tests of XPS and EPS sheets instead of just subjective comments on each..I don't think anyone's done that???
Eucy