Yes. The air cannot move out of the way fast enough so it builds up. This is the cause of pressure. The pressure causes it to move and it travels as a wave.
Yes it would, of course. I had in mind something much smaller though.
PS my comment about edge diffraction is of course wrong - the bending wave doesn’t need to reach the edge for the sound wave to continue 😬
Btw, did you ever write your recommendations for tap testing procedure in one document? I did a bit of tapping last night, and will get more serious today. Reading the tap-test thread, you used fem by trial and error to get the best fit, correct? I have a few different sizes, and thicknesses, so should be instructive.
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Actually pond waves do carry on for a large distance, but they get smaller and smaller mainly bc their energy is spread over a larger front. Regarding your remarks about waves on eps, if you had a very large sheet of eps, the pond wave analogy works pretty well I think. It’s resilient and elastic, it will not crease or wrinkle. On any finite size of panel, you do indeed get stable interference patterns of bending waves, just as with water. These are the modes shapes we have discussed on the forum.
Indigestion is better, thanks. But now I’m afraid that the Channel-billed Cuckoo has joined the Koel for the first time this year, for a rousing morning chorus. Look them up on YouTube if you want to hear two exceedingly noisy birds 😳
I'll have to look and see if there are one or two particular posts which give a good summary, if I don't find it, I'll just write you something new.
Note that there are two different ways that I use the tap test. One is to estimate the elastic moduli of a panel material. For that I use a rectangular panel of virtually any reasonable size and with free edges (at least as close as I can get anyway). And for that, yes, I basically use FEM by trial and error to get the best fit between the measured natural frequencies and the model's predictions. It would be trivial to write a little excel spreadsheet or whatever to pick subsequent trial values of the estimated elastic moduli, and the second guess would be virtually dead on. But I kind of enjoy the trial and error method. It also helps that my FEM models only take about 10 seconds to run. If they took longer I'd probably make the calculations rather than just guessing.
The second way I use the tap test is to determine the natural frequencies (and the associated mode shapes) of a panel that is sized and mounted with a particular design objective in mind. It also gives me qualitative indication of the amount of damping achieved by the constructed panel. In this case the role of the FEM is that it tells me the likely mode shape for a particular natural frequency. If the frequency in question disappears from the RTA response whenever I tap on a predicted nodal area, and reappears whenever I tap on an antinode, then I know I've got the correct modal shape nailed down.
It's possible to combine both of these. That is, estimate the elastic properties by tapping on any mounted speaker instead of a free panel. But then you have to understand your boundary conditions well, and your model has to be able to handle more complex boundary conditions. That introduces a lot more uncertainty. So for base property determination, I much prefer the free panel method.
Eric
Did a new test yesterday. I put my exciter (DEAX25HFE-4) on the top of my bourbon bottle and played one of my favorites (Dire Straights, Telegraph Road). Fortuitously, the top of the bottle had a nice flat surface of the perfect diameter for the exciter. When the bottle was (nearly) full, the sound wasn't great. Low efficiency and very biased to high frequency. Luckily, the exciter has a little hole, so I was able to pour out the bourbon little by little. By the time the bottle was empty, it sounded great!
I did some REW frequency measurements, but curiously, they were almost identical full and empty. Can't explain. Is anybody willing to verify these results with their own tests?
Eric
I did some REW frequency measurements, but curiously, they were almost identical full and empty. Can't explain. Is anybody willing to verify these results with their own tests?
Eric
Eric.
The closest I came to a panel similar to the Goebel panel was my large aluminium panels.
The two very thin sheets of aluminium glued together with a spray mount had a lot of self damping.
It was also very flexible.
I had to make the panel smaller as there was not a lot of dml going on.
Goebel uses 9 layers with a mesh webbing plus lots of different edge damping , his panels are a lot smaller.
I called the aluminium sheets, lossy, because I was getting very little reflections from the edges.
Most of the sound stayed within the central area.
The large panel was heavy and hard to drive, the small aluminium panel worked quite well.
Steve.
The closest I came to a panel similar to the Goebel panel was my large aluminium panels.
The two very thin sheets of aluminium glued together with a spray mount had a lot of self damping.
It was also very flexible.
I had to make the panel smaller as there was not a lot of dml going on.
Goebel uses 9 layers with a mesh webbing plus lots of different edge damping , his panels are a lot smaller.
I called the aluminium sheets, lossy, because I was getting very little reflections from the edges.
Most of the sound stayed within the central area.
The large panel was heavy and hard to drive, the small aluminium panel worked quite well.
Steve.
If I emptied a bottle of Bourbon like that anything would sound good 🤪😵💫
Steve.
Steve.
Now there is a problem that deserves serious, extended consideration. I have a litre each of gin, Campari and Martini Rosso for Christmas Negronis, but the science cannot wait…
Yep - They're in my new area (Samford Valley QLD) in strength also - noisy, noisy, noisy
Sometimes joined by Kookaburras to make a trio.
Interestingly, we've noticed that unlike most areas, here the birds are quite noisy all night long...they must be tired out by daylight.
Eucy
Hello
yes, the panel is a 50x 40 mm carbon - nomex
the thickness of the carbon is 0.3mm on both sides and the total is about 3.7mm, sounds good but sadly the issues with that rattle delayed actual tech testing, the system is made up of 4 exciters from the new dayton line that have screwable support, compared to the previous one it has a real full 100Hz and where before the other exciters had extreme effectiveness around 160-200 with this exciter everything has dropped to around 100Hz. At 200Hz I don't even hear a hole but definitely subdued. In essence it seems to work well, slight attenuation on the treble compared to previous exciters due to the screw adapter.
The wooden frame is provisional only to understand how to connect it to the panel and where to obtain maximum performance. In fact it is 1 cm larger than the panel just to allow me to understand how to connect it. The carbon panel therefore apparently works well, but having not tried it I cannot compare it with the various panels used by other users. The reason I started with carbon is if I was using tecton I think it was best for pro use so I wasn't interested in skimping on that. Now I'm hoping to fix this damn magnet weight problem to really see results, but first I need to figure out how to secure the panel to the frame and what thickness and material is best to use.
Guys sorry for the english translated with google
sorry 50x40 cm thickness 3,6mm approx . the total weight of the carbon skins is 1500g/m2
Edge transfer of sound waves/vibrations through the mouth of the bottle, which in turn moves through practically at 90 degrees from the neck to the shoulders of the bottle and to the somewhat flatter surfaces, if there were any. Any idea how the waves took took the turns (direction)?
Not so bad down this way (Lower Blue Mountains). It's pretty cool this year, so I think they're less active. Really wanted to sleep this morning though, and it chose just the right time to sit outside and serenade me.
I remember a patent saying the main point of a DML is its aperture (finite size) not the modes. I have to say that I haven't understood for now... I'll try to find it tonight.
Christian
The big question is... Will a 21yr single malt have superior sound to a 5yr blended whisky...?? 😜🤔🤭
Eucy