As for the third strategy I'm curious what will happen if you take such a foam:
http://apama.pl/APAMA FOTOS/PANEL STT7.5.200/STT7.5.200-1.JPG
spray with a stiff resin and excite transversely and longitudinally.
http://apama.pl/APAMA FOTOS/PANEL STT7.5.200/STT7.5.200-1.JPG
spray with a stiff resin and excite transversely and longitudinally.
Hi,
for me the link does not work, could you post a picture please ?
Maybe there was a misunderstanding concerning my former
post:
I do not think that it is very useful to increase modal density
at low frequencies by searching for materials only.
I'd like to do it by design ...
But i am curious concerning that foam ...
for me the link does not work, could you post a picture please ?
Maybe there was a misunderstanding concerning my former
post:
I do not think that it is very useful to increase modal density
at low frequencies by searching for materials only.
I'd like to do it by design ...
But i am curious concerning that foam ...
The idea is as follows - generate longitudinal waves like in yours plus transverse and if they are shorter than panel dimension then radiation like above fc occurs. Below bending waves are excited on pyramids - "wide coincidence region". Radiation will be efficient but the question is if f0 are not higher than in a plain membrane.
Attachments
I mean the torsion motion on the edges, radiation below coincidence. You can check it with your transducer just compare curved membrane with a flat one. Curved will be more efficient. Bending waves forms around exciter and edges so more "knees" you have more the longitudinal waves are transformed into bending transverse waves.
jzagaja said:
Do you mean the large scale curvature, like in my tranducer or
do you mean the "small scale" curvature introduced by
pyramids (crumbles, ripples) on a structured surface ?
My transducer has both, but the "small scale" curvature (ripples)
is small against bending wave length ( at least up to the mid
frequency range).
What about "fractal folded" strucure ...
Of cause the structure below is not fractal enough
By that you introduce
- larger surface
- length of possible propagation paths increases and is
randomly "smeared" over neighboured paths
- stiffness, mass and speed of bending waves will vary regionally
and is path dependent, thereby varying along each single path.
I think this is what i have already to some extent in my
transducer, although it is not really "fractal".
Of cause the structure below is not fractal enough
By that you introduce
- larger surface
- length of possible propagation paths increases and is
randomly "smeared" over neighboured paths
- stiffness, mass and speed of bending waves will vary regionally
and is path dependent, thereby varying along each single path.
I think this is what i have already to some extent in my
transducer, although it is not really "fractal".
Attachments
Any change in curvature, bending stiffness generate bending waves. Please have a look again (page 14+):
http://www.wikipatents.com/gb/2400264.html
http://www.wikipatents.com/gb/2400264.html
That is understood, but i thought we were discussing
- how to increase modal density by structure (not overall size)
- some idea of "broadband" coincidence
???
Your foam with pyramids was an attempt to go into that
direction. I just tried to understand your idea, while finding it
interesting ...
I am currently thinking about a different approach to
increase modal density in the lower frequency range of a
DML, which does not necessarily imply curvature of any scale.
- how to increase modal density by structure (not overall size)
- some idea of "broadband" coincidence
???
Your foam with pyramids was an attempt to go into that
direction. I just tried to understand your idea, while finding it
interesting ...
I am currently thinking about a different approach to
increase modal density in the lower frequency range of a
DML, which does not necessarily imply curvature of any scale.
I just got my 50x100 cm Balsa board (3x1mm). http://www.balsabar-shop.de/
Compared to the Rohacell board with about the same mass per surface it has better transparency (comparable with a conventional speaker) and sounds much more "alive". Neutrality is also better. In fact I could live with it very well if there were not these nasty resonances.
The choice between more or less damped material seems to be like the choice between plague and cholera.
In an old thread there was mentioned a DML design software from NXT (unfortunately with dongle and I don´t know the price). Does anybody know whether there is an alternativ now?
Compared to the Rohacell board with about the same mass per surface it has better transparency (comparable with a conventional speaker) and sounds much more "alive". Neutrality is also better. In fact I could live with it very well if there were not these nasty resonances.
The choice between more or less damped material seems to be like the choice between plague and cholera.
In an old thread there was mentioned a DML design software from NXT (unfortunately with dongle and I don´t know the price). Does anybody know whether there is an alternativ now?
I have been using polyueretane "foam" from a spraycan to make some panels for my planar speaker. I was wondering if it could be used to make your own "panels",may be with a piece of wood to atack the exiter to,and some paper as surface. The polyeuretane expands after a while , so you have to make a fixture.
Hope you understand it.
![URL]](/community/proxy.php?image=http%3A%2F%2F%5BURL%3Dhttp%3A%2F%2Fimg29.imageshack.us%2Fi%2Fbillede064.jpg%2F%5D%5BIMGDEAD%5Dhttp%3A%2F%2Fimg29.imageshack.us%2Fimg29%2F8647%2Fbillede064.jpg%5B%2FIMGDEAD%5D%5B%2FURL%5D&hash=7169b70619a1a97d1eb0acf70387cd3a)
Hope you understand it.
Panels go down below 100Hz with a volume velocity I suppose. Disc bender seems to have higher fundamental resonance. Anyone already used Chladni patterns for n=0,1,2,3... modes to find excitation area? This is a nice violin makers technique and could work as well as FEM simulations. Impedance and capacitance for piezo is high, resulting efficiency rather low. Time to wind tranny.
Hi all,
> It all makes sense now when you realise that the PODIUM speakers mount their drivers down the centre line of the panel width. Also noticeable from the photos on 6 moons , and as mentioned before, no one driver is positioned at the EXACT CENTRE of the panel - important?....yes, I think so.
Ziggy , I dont know if you are still on this job
but the picture shows clearly that transducers are exactly on the center line. I have done some tests, only this central position give the maximum bass extension. And if the motors were aligned on the short axe of panel, instead of the long one, this would extend again bass response. (plain 1/4 wave excitation)
POL
> It all makes sense now when you realise that the PODIUM speakers mount their drivers down the centre line of the panel width. Also noticeable from the photos on 6 moons , and as mentioned before, no one driver is positioned at the EXACT CENTRE of the panel - important?....yes, I think so.
Ziggy , I dont know if you are still on this job
but the picture shows clearly that transducers are exactly on the center line. I have done some tests, only this central position give the maximum bass extension. And if the motors were aligned on the short axe of panel, instead of the long one, this would extend again bass response. (plain 1/4 wave excitation)
POL
Attachments
>> Originally posted by WrineX
> then they sound incredible and the next day they suck. day after they sound superb again.
Hello
yes, this is true, because the sound relie only on the quality and state of the material used for the panel. It may change greatly with hygrometric and electrostatic state of this membrane. I use a stereo set of 2x8 DAEX25 on a 1m panel (inline source), sound can goes up and down from incredible to awfull in less than one hour. Especially if there are more than 1 person in the room or if the panel has been manipulated.
POL
> then they sound incredible and the next day they suck. day after they sound superb again.
Hello
yes, this is true, because the sound relie only on the quality and state of the material used for the panel. It may change greatly with hygrometric and electrostatic state of this membrane. I use a stereo set of 2x8 DAEX25 on a 1m panel (inline source), sound can goes up and down from incredible to awfull in less than one hour. Especially if there are more than 1 person in the room or if the panel has been manipulated.
POL
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