Morning Cousin Cobber, i believe you will achieve better results if you copy the last part of your posting where you place the loudspeaker directly "under" a plate that contains sand or water..ive conducted some rough experiments using a 5 inch woofer at first i double spray coated it with a small spray can of clear top coat i brought at an auto place called repcos this the clear top coat you spray when you painted your car , anyhow the first experiment i used my second tesla 3,6,9 number based frequency generator and i put some water into the woofer since the clear top coat was well dried and water proofed the woofer , and ran through the frequencies to see what happens anyhow dident notice any patterns on the water at higher frequencies and using a woofer with 8 ohms impedance changes the intensity of the frequency sound compared to using a piezo speaker , anyhow not seeing any patterns in the water there was something i dident pay attention to but i changed to my first frequency generator and went through the frequencies when i got to one it created a pattern on the water that looked like it started at the center id say its a number not used much but seems to be the starting point number 1 then formed circles one around the other till it got to the middel this held for a short time before it changed by itself and then formed a pattern i cannot describe but caught on video and uploaded to YouTube, i then rotated the frequency know up to a higher frequency and again noticed nothing till i viewed the clear mirror like reflection on the surface of the water it was clear before but now distorted so im backed off that frequency till the mirrored reflection on the water was clear again then turned it back up to the frequency that was distorting again so i did this a few times and the results was the same and the water dident show any patterns that can be seen so i think its on a microscopic level and in the crystalline structure of the water was being altered so fine you cant see any patterns and yet my cam corder could not capture that on video so i can only see it with my the naked eyes when i view the mirrored surface of the water at an angle , so i backed off the frequency where the pattern in the water formed starting at what id say was circles in a circle before it formed an indescribable pattern and i then kept adding more and more water to see if it can still maintain that indescribable pattern and it seems to do it ok for such a small woofer , more experiments to do yet as ill need a few mirrors and some bits and peace's to see if it can change the reflected image at other certain frequencies and if it cant be filmed like before ill try the high speed video with slow motion replay to try bring out the unseen so you can capture it on video and ill try some laser reflections on that mirrored water see what it dose to that when its very flatt and still and mirrored while subjecting it to that high frequency again. so all up higher frequencies microscopically alters the crystalline structure of the surface of the water so fine you cant see any patterns but the change of reflections on the water from clear to distorted indicates some thing is going on, ive seen these video's on YouTube showing patterns forming in water and even sand when on top of a plate over a speaker but no reflections
dident use paint i used clear coat spray on varnish used on cars and i wanted the water to get the vibrational frequencies direct ill try the plate latter when i can find a right one to keep the water etc on and i need edges so it wont go off the plate, and ive successfully hacked 2 mirrors for my latter experiments using my frequencies for and im still wrapped on my discovery that on a microscopic level the crystalline structure of the waters top mirrored surface changes to a degree so much you cant see any patterns but the mirrored reflection changes instead and i cant capture that on camera but can see it with the naked eye very well when looking at it in an angleMorning Cousin Cobber, i believe you will achieve better results if you copy the last part of your posting where you place the loudspeaker directly "under" a plate that contains sand or water..
My thinking is if you place water directly onto a water proofed loudspeaker the weight of the water will decrease the ability of the loudspeaker to vibrate naturally...Also double spraying the loudspeaker with paint will diminish its ability to vibrate naturally ..
I believe your piezo loudspeakers will naturally produce more power (louder) when compared to 8 ohm woofer loudspeakers..the frequencies' from my frequency generators sound very loud when fed to a piezo speaker, but to an 8 ohms woofer the frequencies isn't the same loudness as the pizeos so they are less louder and i cant find any really big pizeos for the experiment may try something using the small pizeos