The hollow sound most probably comes from the thickness of the panel. The hum stops, when you fix the panel to a frame, that's why it stops when you hold the corners. If you have a piece of ply left, fix that piece to a frame with some soft double sided tape, and make a hole up to the last ply and paste the aluminium plate to it and check. Before making the hole, you might try just on the back of the panel to check the difference. Actually, thinner the panel, better the sound. Also, try with that additional ply panel, placing the Aiyima under the 6.5mm edge, right in the middle of that edge. (Like here I placed two of them under) Like to know your impressions.
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You can try and use some type of damping material for the edges like some weather foam tape.
I agree, the thickness could be contributing to the humm. And I agree about the sound quality improving as thickness is reduced - that is what I observed. Did not want to go much thinner than 3mm because of the structural integrity of the panels. They get skewed quite easily by changing moisture of the roomThe hollow sound most probably comes from the thickness of the panel. The hum stops, when you fix the panel to a frame, that's why it stops when you hold the corners. If you have a piece of ply left, fix that piece to a frame with some soft double sided tape, and make a hole up to the last ply and paste the aluminium plate to it and check. Before making the hole, you might try just on the back of the panel to check the difference. Actually, thinner the panel, better the sound. Also, try with that additional ply panel, placing the Aiyima under the 6.5mm edge, right in the middle of that edge. (Like here I placed two of them under) Like to know your impressions.
The placement of exciter right on the edge sounds interesting - I will test this as I have the chance and give feedback
I feel like the design that Leob presented for this PA system panels is the way to go - rigid frame that is enclosing the panel with soft foam clamping the long sides, really want to try this route for the next build
Sounds easy enough to try - I think I have some foam tape laying around at my workshop
When a question is not a question, I get lost...
When will you post results of an implementation of your ideas? pictures, selected material, FR, evaluation of the efficiency, of the directivity... is it sill spring as you mentionned if I remember well?
Ideas galore! Certain ideas can be tested at home, with things available at home. But to do some cutting, planning etc, etc I have to wait till late spring, when I can work in the unheated shed in the garden, that is in between gardening. There are 2 pairs of ears, musically trained, to give an opinion on whatever I make. My ears are not that good. It is no use taking any audio measurements in cluttered areas (as most do). Anyway, whatever that would be made has to be placed in the living room, that is has to be aesthetic. Atm, I find glass as the best as a panel, or but much better as a closed curved thing, such as a vase. It would be much easier to place the exciter under those 70cm tall glass vases and forget about any more experimenting. But, Joppe's vids are pulling me to try stretched mylar (or a silk saree) over rubber magnets. Or, maybe something like a rubanoide/DML, or even like a Telefunken Arcophon. (And here) Many ideas would come and go till late spring.
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That's typically the problem with such devices. When I shared my tentative of rubanoid like or Walsh like speaker I think I explained I made the choice not to enter in a endless trial an error process because the lack of any support or scientific background on them. I gave a chance to DML (flat one with the exciter behind) because of our community here, the existing scientific papers, the possibility to enter in a design process, the support of some measurements. Let us know your results.
I agree. Choice of frame material to your liking and away you go. With EPS of the proper thickness and the right exciter you can hardly miss.
You gave a chance to yourself, not to the loudspeaker, DML or otherwise.
There are patents, even some PhD thesis on DMLs, and some dead DML companies, and all what we have is an exciter stuck in the back of a panel. Atm, there's only one company producing such flat speaker, if I am not mistaken, is Amina Sound, who makes them for hotels and such like, where the guest doesn't give two hoots about the sound quality coming from the wall.
I have these Aiyima exciters, 20W 8Ohm, so I'd play with them, just because I have them. They are powerful, but I think a simple 3" full range driver with cut off cone would do better. These are sort of party gadgets, to be placed face down on a table or something.
On the question of audio measurements, I don't have any uncluttered rooms.
Thank you Paul for the link
For the ones who don't want to spend the hour on this video, I recommend the "Ohm's law" part starting at time 16mn or a bit after with the demo about the phase. We can probably make the connection with the diffuseness of the DML (IR in different direction are of low correlation = the phase relation of the frequency component is different according to the direction).
The part about the pitch is also interesting. It shows the phenomena known as the "missing fundamental" and also the existing pitch of sound without harmonic relation (chime). One important aspect coming from psychoacoustics and from the knowledge of the auditory system is that the frequency is a kind of carrier (like in radio transmission), not the message.
The brain is a correlation machine!
Steve I would consider ignoring attention seeking behaviour from people like this. There is zero useful content in their posts, and they post a lot.
Sure, you are very welcome!
Are your tall blondes sitting in the living room, or in the attic?
I have to agree with burntcoil, conversation that makes any sense is futile.
Steve.
Yes the fact that we are insensitive to the phase of the partials (freq components of a signal) suggests why it doesn’t matter that components come from different places on a panel. But we are sensitive to arrival time of well-correlated signals, and this can degrade the apparent quality of point-sources in small rooms, but DML speakers suffers less from this. The fact that we can also synthesise a perceived tone when there is no partial at that frequency might help to explain why DML speakers can sound amazing even though they have big resonances.
Also in the back of my mind is the question whether this resonant behaviour actually improves the perceived sound in some way via a psychoacoustic effect. Maybe we get more pleasure when our correlation circuits are working harder!
I did mention, a little further back in this thread, my thoughts and findings of why sometimes it is better to have the panel on its side.
Tectonic and other pro audio tend to have their panels on their side but I have never seen them say why.
Steve.