I can't be certain at this point but I used contact adhesive for both so I would say its worth exploring. My brother's build is captured in the Tall Story build notes Christian has added to his Wiki. It also has a good HF extension although the Snow White build was a touch better.
I can't detect any subjective difference between an EQ'd response on my hanging panels and the natural response of the recent builds. Without EQ the hanging panels, which are Birch ply without edge damping, lose some "air" and "sparkle".
I can't detect any subjective difference between an EQ'd response on my hanging panels and the natural response of the recent builds. Without EQ the hanging panels, which are Birch ply without edge damping, lose some "air" and "sparkle".
I get heaps of volume from my 20w 25SHF exciters... But they also have a slightly higher BL than the 40w Thrusters
Eucy
Christian..As I recall from my lost sweep recordings, the hf response of the Blackwood was pretty good .. I'll check it again... It was the low efficiency that made me put it aside in favour of the more lively Poplar
I've also tried light and cheap 3mm ply from the local building supply store with poor hf results...I considered possible causes to be
1/ Soft and low quality core material...air gaps slowing transmission speed? Low compression strength damping through panel transmission?
2/The glue material and thickness
Generally, I found that you can tell the likely hf performance by tap testing - as per guitar building. If it sounds dead under tap testing it's most likely to be a poor candidate for DML use. Tap testing led me to Poplar. Birch was somewhere in the middle of the pack of results.
Eucy
Hi Earbourne
I wanted the Blackwood for the same aesthetic reasons. It's a very good quality ply... Quite stiff and "true".
Needs a fair bit of power to get the required volume... That's why I didn't use it in the end.
Poplar on the other hand is quite floppy and needs some attention/treatment/detailing to keep it flat, although Burnt obviously didn't find that an issue.
I'd caution against trying to veneer the Poplar...I feel fairly certain that the extra mass of the veneer and importantly the glue layer will kill the effectiveness of the Poplar. However, that said, if be interested in the results of you do try it
Keep us posted
Cheers and best of luck
Eucy
@Earborne 963Hz
Uh oh... That sounds a lot like what I purchased for the 24"x96" DML build. It is 'hardwood' three-ply plywood, 1/8" thick (1/8" = ~3.2mm), bought from a U.S. chain store (Home Depot); it is from Indonesia according to the label and is definitely not quite heirloom furniture quality. I have been unable to identify the wood species.
This is the edge/end of two stacked pieces. Does this look familiar? At any rate I'll 'tap test' it tomorrow and see what it sounds like.
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Hi Deude...
Hmm... It doesn't look great does it.. On first sight I wouldn't be holding high hopes for that material.
Looks to me like it could be what is termed 'overlay grade' ply meant to be a surfaced with a paper or vinyl facing and used in the RV industry etc as lining. Lightweight, cheap, and definitely non-structural
The faces could be Meranti which is a soft hardwood, and the core is likely to be Falcata. I believe the core will control the performance of this panel. I don't know if anyone's tested this material but it's very light and will be soft..
Only time and testing will tell... If possible I'd buy a real Poplar piece and compare with this material through testing before the final build.
Cheers
Eucy
Luan is another name for Meranti, or vice versa ... That'd be the face material with the Falcata (Albasia) core... Pretty certain but....not 100%
https://www.google.com/url?sa=t&sou...YQFnoECBAQAQ&usg=AOvVaw2BA-Pk6DoLX-wBCBs_2sZR
Look forward to the test results
Eucy
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So here is what I came up with...
density = 447 kg/m^3 (on the light side but reasonable - falcata is very low density, like balsa, and the center layer is most of the volume)
E = 13.5 GPa (on the higher side for woods, something like 10% moisture content birch?)
Density should be fairly accurate. E is estimated (crudely) using a free-free beam frequency equation and then looking for a mode (octave multiple of the calculated fundamental) that matches what I measured. The fact this is a composite of different woods throws off the property estimations versus actuals of course. But, overall, this looks like it has good effective stiffness for its effective density. Damping is another question but I am not set up to measure that.
MathCAD worksheet
density = 447 kg/m^3 (on the light side but reasonable - falcata is very low density, like balsa, and the center layer is most of the volume)
E = 13.5 GPa (on the higher side for woods, something like 10% moisture content birch?)
Density should be fairly accurate. E is estimated (crudely) using a free-free beam frequency equation and then looking for a mode (octave multiple of the calculated fundamental) that matches what I measured. The fact this is a composite of different woods throws off the property estimations versus actuals of course. But, overall, this looks like it has good effective stiffness for its effective density. Damping is another question but I am not set up to measure that.
MathCAD worksheet
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Ok... Luan has a density of around 705 kg/m3. If the faces are about 0.4mm each as suggested previously, then the faces contribute 0.56kg/m2.
Working backwards leads to a core mass of 1.43 kg/m2 , and for a 2.4mm thickness gives a density of 361 kg/m3, very close to the Falcata density of around 320 kg/m3.
QED...?? maybe
Eucy
Deude,
Using the natural frequencies of the beam or panel is a great way to determine the elastic modulus (or moduli). But how did you measure the natural frequency you measured and how did you determine that it was the 16th mode? You may have seen in the other thread that it is not to hard to measure the natural frequencies with a frequency analyzer and a microphone. But, be careful in your calculation of elastic modulus. unlike the natural frequencies of tensioned strings, the natural frequencies are not integer multiples of the fundamental. Rather, they are a rather inharmonic series of overtones, as in the table below. You can actually use the irregular spacing to help figure out which modes you are observing, since adjacent modes should have a ratio that is unique to their mode orders.
Eric
I used a cell phone app RTA and multiple measurements with a peak hold to check repeatability. The pitfall then would be the integer multiple harmonics.
I am taking additional measurements using a cantilever mode (and equation), and plucking the unsupported end, using the same RTA, but so far the results are not reasonable. So there is some measurement uncertainty here.
I also tried simply supported beam deflection measurements but the problem is my Mitutoyo runout indicator has a lot of stiction force compared to the beam deflection load and thus I cannot get a good measurement.
So, I am at the point where I am inclined to build and test since I do not want to get mired down in characterization testing. It seems like others have reported good results with 3mm Luan type ply so I do not think I am doomed necessarily.
I am taking additional measurements using a cantilever mode (and equation), and plucking the unsupported end, using the same RTA, but so far the results are not reasonable. So there is some measurement uncertainty here.
I also tried simply supported beam deflection measurements but the problem is my Mitutoyo runout indicator has a lot of stiction force compared to the beam deflection load and thus I cannot get a good measurement.
So, I am at the point where I am inclined to build and test since I do not want to get mired down in characterization testing. It seems like others have reported good results with 3mm Luan type ply so I do not think I am doomed necessarily.
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Here is the thread Eric refered (and opened) to : Application of Impulse Excitation for DML Design and Analysis