PIEZO NXT type panel

[jzagaja]

And how it looks like.

[jzagaja]

Obstructions and supports increase the radiation efficiency for f < fc according to Equations 9.3 and 9.5

http://books.google.pl/books?id=hVPP...F43WzASxsKDxBg

It was proven on the red trace.

[Ziggy]

I'm not in to technical response curves as such, but I can see that 2 piezos in phase increase output at their most efficient frequencies?In my experience, as more exciters were used, the sound got better and better - it's as simple as that.
To this day, I find no abnormal resonances (but the panels are still not properly mounted and supported - that may be another story?).

Also, according to your set up, you must NEVER place an exciter in the exact middle of a panel, be it round, square or rectangular. I read this on some NXT application notes somewhere a while back.This may be the reason for some of the resonant peaks?

I have never taken most people's suggestions seriously on using push pull exciters. Your response and experiment proves this - well done!

[jzagaja]

I couldn't find decent prise for laminated aramid honeycomb. I think we should focus on paper honeycomb and HSPE (high-stiffness-polyethylene). It has better efficiency than carbon fibers, under tension even more that was proven by Skalmierski on the formnats spectra.

[Ziggy]

There is no decent price for this material. I have checked and it is pure robbery - extremely overpriced for what it is(especially in large sizes, plus enormous shipping charges unless you live next door to the factory that makes it).

That's why I use Gatorfoam. NXT have used it in some of their products and have advised me directly of this fact. So, for the little gain that will be obtained from using the honeycomb panel - it's NOT worth it

[jzagaja]

Ziggy have you already asked NXT for piezo exciter suggestion? Don't know if that super strong and expensive actuators are better than cheap buzzers (unimorphs). Dr Harris couldn't tell me but he gave me CSD of BMR driver. Looks interesting - there peaks that don't decay like in pistonic or DML panels.

[Ziggy]

jzagaja, the pistonic exciters are FAR SUPERIOR to any Piezo. I know, I've been there and done that as you will find at the beginning of this thread and what followed on from there.

As an example, I tried a piezo on my panels as an addition to the pistonic NXT exciters. The result sound wise?............the piezo could not penetrate the highs through the panels where the NXT exciters could (much better).Secondly, with Piezo's you will never obtain any bass or low notes - it's not physically possible.
This is mainly due(besides the small size and limited movement) to the fact that you must have an exciter that is capable of providing a strong vibrational force or push to ''excite'' the panel material.

Any audible peaks that occur can be tuned out with suspension or added dampening(as you have found) with rubber disks etc. as NXT and Podium Sound do in their products. I have not found that this is of any great concern at this stage, but will be visiting this area when the completion stage is near.

Piezos are o.k as DML's when attached to small panels such as notebook computer screens and cell phones - that's it, unfortunately

I would love to see a 10 inch diameter piezo with a few small hard feet that attach to any resonant lightweight panel - now that would be interesting!!!

[jzagaja]

Ziggy there are piezos with a displacement >2.5mm and fs<100Hz.

[Ziggy]

jzagaja, yes, but........they do not have the same driving ''force'' as do the piston drivers. This is a physical/mechanical ''push'' with weight behind it - something that only a voice coil and strong magnetic field can do effectively to make a DML produce enough sound level.

For example : hit a bell with a hammer
now hit it with a small stick of balsa wood..................what happens?

You must see a raw exciter, hold it(but only briefly)in your hand with a signal applied and place it against various objects....even on top of your head...LOL!

The thing can really VIBRATE - STRONGLY with great intensity. A Piezo will only buzz in comparison.

[jzagaja]

But have you tried those expensive stripe actuators?