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Old 5th December 2008, 02:03 AM   #11
Ziggy is offline Ziggy  Australia
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The Anonymous1, sorry to hear that you had little success with your NXT experiments.

Were you aware at the time that these exciters work best on ''floating panels''? Were you also aware that by using multiple exciters per panel brings you in to another dimension of possibilities and sound quality? Plus, what size panel were you experimenting on? if it was of small or medium size, you will have limited the bandwidth to just that size. A large panel 6 foot X 2 foot will be a different ball game for certain.

You speak of corrugated cardboard as the best sound you obtained. There are many coatings that can be applied to this : dope used in model aircraft for example will strengthen the cardboard significantly without adding too much more mass. However, what it will also do is BRIDGE the front and back laminates through the corrugation enabling a much more efficient transfer of energy(IN PARTICULAR THOSE BLOODY HIGH FREQUENCIES THAT ARE LOST THROUGH THE TRANSMISSION OF VIBRATIONS WITH OTHER MATERIALS SUCH AS FOAM CORE, COREFLUTE AND RELATED ''SOFT'' MATERIALS).

Even plain thin foam can be epoxy coated and hardened with a special type designed primarily for foam!

Reading up on Shelly Katz's PODIUM LOUDSPEAKERS, he reveals that the panel material's best and most appropriate quality is that it ''rings like a bell !!
Foam core, coreflute and cardboard don't do this. I'm not saying that I will find something that does, even though this exact material can be obtained (at large cost), only that common materials can be inproved dramatically with ''coatings'' that will stiffen, harden and perhaps''ring''to suit the purpose required

I intend to suspend this SPECIALLY PREPARED panel as free floating as possible within a simple wooden frame and will be using Sonic Impact's ''SOUND PADS'' as the initial exciters - 2 per panel, LARGE PANELS in stereo mode.

The plan is to use as many as 6 exciters per panel, offset from the middle point of the panel. In other words, the exciters will run down the exact center of the panel but none of the exciters will be touching the middle position of the panel height.

Ed, thanks for your encouragement. I would only be pursuing this method after realising that simple piezo cones taped to the back of resonant panels actually does work in creating a DISTRIBUTED MODE LOUDSPEAKER The fact that they are piezos limits their low end response of course, but what happens upwards is VERY interesting and warrants further investigation.

Summing all this up, the panel will need to be reasonable ''thin'' and ''treated/coated'' and ''stiffened'' as much as possible.
It will also need to be ''LARGE'' with mutiple exciters

I do have a sound pressure level meter and a tone generator so I can roughly measure the response - crude, but will give us some idea on what's happening frequency wise.
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Old 8th December 2008, 04:37 AM   #12
Ziggy is offline Ziggy  Australia
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Old 8th December 2008, 04:38 AM   #13
Ziggy is offline Ziggy  Australia
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Old 8th December 2008, 04:40 AM   #14
Ziggy is offline Ziggy  Australia
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Old 8th December 2008, 04:42 AM   #15
Ziggy is offline Ziggy  Australia
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Old 8th December 2008, 04:56 AM   #16
Ziggy is offline Ziggy  Australia
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As you can see, it's a crude and simple set up .....but hey, it works as a mid/tweeter panel surprisingly well. BUT.......to get the required output from piezos you MUST HAVE TRANSFORMERS!.
I'll post a picture of one that I have been using. There are also two larger and even more efficient one's that I haven't tried yet.

the Sonic Impact ''SOUND PADS'' have just arrived according to my wife!.............I'm gonna have me some fun tonight!!!.........
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Old 8th December 2008, 04:59 AM   #17
Ziggy is offline Ziggy  Australia
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Apologies for the ''rough as guts'' photography - they were very rushed with my daughter's point and shoot digital camera.
As a professional photographer, I allways blame the equipment
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Old 8th December 2008, 05:53 AM   #18
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Ziggy,

The largest panels I tried were about 5' x 3' and used two of the exciters out of the same SI SoundPads you just received.

As you stated about the panel material, the highs are what lacked the most. There were also multiple unwanted resonances.

My panels were secured to a frame at the top and bottom by means of thick expanded foam "tape". The back of the exciters were securely attached to a beam that ran vertically to the top and bottom frame portion. This method provided much better low end output over just having the motor of the exciter unsecured.

All in all it made plenty of "noise" suitable for not so critical listening. It's not something I cared to listen to for too long though.
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Old 8th December 2008, 06:17 AM   #19
Ziggy is offline Ziggy  Australia
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TheAnonymous1, sounds like I am thinking along the same path as you have already gone down.
So, where to go from here?

I was thinking of suspending the panels using ''bias tape'' from fabric shops as suspension corners for the panel?
The use of a piezo DMA as depicted in my photos will sort out the high frequencies with a simple cap. crossover, but may impart some directionality to the sound, even when mounted at the back of the panel.

A few important questions if you don't mind :
What was causing the resonances? The panel? Frame? Were the resonances present on all materials (foam core, coreflute, corrugated cardboard?). Was there any one panel material that resonated the least? How thick were the panels?
I'm wondering if the size and thickness plays an important part in resonances and the supression of high frequencies?

If you read the reviews on the PODIUM 0.5 AND PODIUM 1 panels on 6 moons reviews, there may be some worthy experimenting on these strange ''black spots'' that the designer uses(and this has been employed by other compamies using the NXT panels) to ''TUNE''? the sound. Perhaps he's tuning OUT the resonances?
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Old 8th December 2008, 05:23 PM   #20
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I bet the "Spots" are some kind of damping.

To That end, you could try butyl rubber cut from bicycle inner tube material for a surround. It can be glued with contact cement, and it would offer a lossy edge termination if that was desirable.

Just a thought.

Ed
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