PIEZO NXT type panel

[mikadosan]

Filleting the corners (>R20) of the panel and filling the cavities of the honeycomb at the edges of the panel with some epoxy or similar will help this dramatically.

[mkstat]

Originally Posted by mikadosan

Filleting the corners (>R20) of the panel and filling the cavities of the honeycomb at the edges of the panel with some epoxy or similar will help this dramatically.

Hi Mikadosan!

I'm curious - what made the greater effect? rounding the corners or adding mass/damping at the edges?

I found out that the fibres of the glasfibre fabric of my honeycomb material are running all parallel to the sides of it (biaxial fabric). I thought about this and found out that the E-module in length/width direction has to be much higher than in diagonal direction (about 4 times).

In room acoustics axial modes have more energy than tangential modes.

So if I'm correct the axial modes are supported through the higher stiffness (more efficency) and the tangential modes are supressed (less efficiency from lower stiffness) /shifted (as the bending wave travels slower/ coincidence f is higher). The number of tangential modes for a given panel is substatialy higher than the number of axial ones.
I think that this is a hint to one of the reasons for the "foggy" sound character as it is much more difficult to acheive an even modal density over the lower frequency range just by optimizing lenght/width ratio. The axial and tangential modes do not blend in an even manner for a panel with optimum length/width ratio resulting in a bumpy frequency response and increased settling time.
Removing/rounding the corners seems to help to improve this shift of the tangential modes, leaving the problem of lower efficiency of the tangential modes compared to the axial ones.

Any thoughts about this?

[mikadosan]

Originally Posted by mkstat

Hi Mikadosan!

I'm curious - what made the greater effect? rounding the corners or adding mass/damping at the edges?

I found out that the fibres of the glasfibre fabric of my honeycomb material are running all parallel to the sides of it (biaxial fabric). I thought about this and found out that the E-module in length/width direction has to be much higher than in diagonal direction (about 4 times).

In room acoustics axial modes have more energy than tangential modes.

So if I'm correct the axial modes are supported through the higher stiffness (more efficency) and the tangential modes are supressed (less efficiency from lower stiffness) /shifted (as the bending wave travels slower/ coincidence f is higher). The number of tangential modes for a given panel is substatialy higher than the number of axial ones.
I think that this is a hint to one of the reasons for the "foggy" sound character as it is much more difficult to acheive an even modal density over the lower frequency range just by optimizing lenght/width ratio. The axial and tangential modes do not blend in an even manner for a panel with optimum length/width ratio resulting in a bumpy frequency response and increased settling time.
Removing/rounding the corners seems to help to improve this shift of the tangential modes, leaving the problem of lower efficiency of the tangential modes compared to the axial ones.

Any thoughts about this?

Hi,

In my prototype with the Nomex honeycomb with glassfiber skins (I quess it´s biaxial GF but the strands are arranged exactly vertically and horizontally) with the thickness of 6mm including the GF skins I found that rounding the corners has a dramatic effect in output and its clarity. If I remember correctly, at the moment there is a fillet with R30 in each corner and it works ok so far. It´s not perfect though but it works ok anyway...

In this prototype I´m using four (4) Dayton exciters per panel, arranged to a vertical array in the middle of the panel with even spacing between the exciters and the panel edges...

One problem in my first honeycomb proto is that the positioning of the excitrers is not perfect but I have been lazy and have not corrected it yet because I´m working on the other prototype panel at the moment - different material, different problems then...

I can recommend the rounding the corners anyway. It has surprisingly big effect to the overall balance of your panel then.

Best regards

-M

[mkstat]

Originally Posted by mikadosan

Hi,

In this prototype I´m using four (4) Dayton exciters per panel, arranged to a vertical array in the middle of the panel with even spacing between the exciters and the panel edges...

One problem in my first honeycomb proto is that the positioning of the excitrers is not perfect but I have been lazy and have not corrected it yet because I´m working on the other prototype panel at the moment - different material, different problems then...
-M

Which size do your panels have? Are they big ones like Podium? Do you use a back support for the exciters?

[mikadosan]

Originally Posted by mkstat

Which size do your panels have? Are they big ones like Podium? Do you use a back support for the exciters?

Hi mkstat,

Yes, I have a quite big panels. Not as big as Ziggy but they are in a size of average panel loudspeaker anyway. Pretty much like small or mid-sized Maggies, etc... It´s quite difficult get acceptable amount of lower freqs from a panel smaller than these. Of course, you can always use a sub or two to get some bottom though. But this is of course a bit different route then...

Small panels (with a proper material) has better hi freqs and bigger ones can fill the mid-freqs and bottom a bit more acceptable way then... combining these two would be an interesting project too...

-Mika

[jzagaja]

One picture tells everything

http://www.operesonore.it/gallery/la...ne-vela-13.jpg

[mikadosan]

Originally Posted by jzagaja

One picture tells everything

http://www.operesonore.it/gallery/la...ne-vela-13.jpg

Yep, pretty much like building an acoustical instrument then...

[el`Ol]

As suggested earlier I treated 50x50 cm 3-layer 3 mm balsa boards with hardwax oil and had the following result: The resonances are gone, but the sound is boring and muffled with massively reduced sensitivity. The damping seems to be a plague vs. cholera issue in DMLs. But the use of wood remains an interesting topic, e.g. the way Oliver Goebel does, with end grain balsa and epoxy/cloth cover layers.
esp@cenet — Bibliographic data
In the Visaton forum someone claims to have very good results with maple veneer.

[mikadosan]

Originally Posted by el`Ol

As suggested earlier I treated 50x50 cm 3-layer 3 mm balsa boards with hardwax oil and had the following result: The resonances are gone, but the sound is boring and muffled with massively reduced sensitivity. The damping seems to be a plague vs. cholera issue in DMLs. But the use of wood remains an interesting topic, e.g. the way Oliver Goebel does, with end grain balsa and epoxy/cloth cover layers.
esp@cenet — Bibliographic data
In the Visaton forum someone claims to have very good results with maple veneer.

Hi Oliver,

I have made a simple test with Finnish birch plywood in thicknesses 1,5mm and 3mm and the 1,5mm version sounded actually quite nice. It is heavy material if compared to the lightweight composites but in small thicknesses it works ok.

And if you think that you could treat it with some epoxy, hardwax oil, etc...it might be pretty nice. I did not spend too much time with it since it was a bit on the heavy side as a material then... Of course, in thickness of 1,5mm it´s not super heavy anyway... I might test it again with some "serious" listening and maybe even some measurements.

Biggest problem with this material is that it´s not very stiff. It is stiff if compared to veneers but if compared to some nice composite materials -its not. But if one could stiffen it with some proper material (epoxy, hardwax oil, lacquer, whatever) it might even work... I quess...

-M

[el`Ol]

I consider coating carbon fiber with hard wax oil.
Carbon-Platte, Abm.: 645 mm x 445 mm x 0,3 mm, EUR 36.10 --> www.carbonscout-shop.de
Arguments against?