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Old 6th February 2009, 11:25 AM   #121
el`Ol is offline el`Ol  Germany
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Quote:
Originally posted by Ziggy


KAPABOARD is made by the same people who make GATORFOAM - ALCAN COMPOSITES.There are a few varieties of this board but ......YES !!!........this material will be O.K to use.(

As already mentioned KAPA bloc is the one with resin cover.
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Old 6th February 2009, 11:52 AM   #122
APi is offline APi  Finland
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Quote:
Originally posted by Ziggy
APi : Great little invention. what you have is a distributed mode loudspeaker happening there.
Since I didn`t have piezos I tried with traditional voice coil if flexible foam (closed cell polystyrene) can be used. And it looks like the answer is yes: Material can also be flexible and a bit soft without loosing high frequency response.

I wish someone could try this also with piezos

The other thing why I did the experiment with a foam slice was to test if distributed mode loudspeaker can be less distributed:

You move just one end of the foam like line source and the foam act as a kind of one dimensional transmission line: Soft foam absorbs high frequencies before they reflect from the other end and mid frequencies can be matched by selecting right curvature and damping material at the points of attach. But even if material absorbs something it still makes some sound.
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Old 8th February 2009, 01:55 AM   #123
Ziggy is offline Ziggy  Australia
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Changed the speaker impedance setting on my amplifier to 6 ohms (didn't realise it had that option), so I wired up the panels for 5.4 ohms total impedance. A multimeter reading shows each panel at a DCR of 4.4 ohms, so I would presume that this is pretty close to 6 ohms as required.

RESULTS ON SOUND QUALITY? : after some sound pressure level readings compared directly to my two way horn system that are 103 db, I have approximately (this is with simple equipment and judgment by ear) 92db efficiency from the panels. Not bad at all.
The output is naturally much louder than my wiring mistake disaster previously.
Bass output has entered a new level - even deeper, richer and makes the overall sound fuller than they were (and that was fine already!).

So, I guess that's it. I have succeeded . The horns will be sold off from here on.

Basic summary of this whole experience and my recommendations and advice :

Don't disregard the NXT technology.........you will be very foolish to do so.

You MUST have a VERY LARGE suitable material as panels to obtain impressive bass, mids and highs.This is CRITICAL!

You MUST have multiple exciters(vertically and evenly spaced) to drive this size of panel and obtain the efficiency and reasonable power handling.

You MUST remove the exciters from their casings if you buy the ''Soundpads'' as your source for the exciters.

You MUST use the correct double sided adhesive tape to secure the exciter to your panel : 3M Adhesive Transfer Tape F9473PC.
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Old 9th February 2009, 12:01 PM   #124
APi is offline APi  Finland
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Quote:
Originally posted by Ziggy
You MUST have multiple exciters(vertically and evenly spaced) to drive this size of panel and obtain the efficiency and reasonable power handling.
Quote:
Originally posted by APi
You move just one end of the foam like line source and the foam act as a kind of one dimensional transmission line.
-> Line array proven to work best.
-> panel works as "one dimensional" transmission line having more controllable vibration modes.

Is there any change of building piezo (not voice coil) based continuous line source... not just an line array?
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Old 9th February 2009, 12:32 PM   #125
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I think you would have to add some mass to piezo drivers for them to work well. Otherwize you would mostly move the driver instead of the panel at lower fq.

It might be some mass balancing ideal between the panel mass and the counterweight (the magnets, in case of the exiters) .
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Old 9th February 2009, 01:24 PM   #126
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Ziggy,

Some problems I see.....

The exciters act much like a traditional point source at high frequencies. Since you have basically created a line source, the large spacing between the exciters is sure to create some combing effect.

You should really attach the back of the exciters to a solid object. This will help greatly in the lower frequencies. Not only will it help limit over-excursion, but it will also turn the panel into a more traditional linear driver at lower frequencies.

The plastic housing of the soundpads act as a mechanical high pass filter to limit low frequency excursion.
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Old 10th February 2009, 01:39 AM   #127
Ziggy is offline Ziggy  Australia
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theAnonymous1, yes, you are quite right and the rear brace will be used in the final assembly/frame.

Ran some test frequencies last night from 20hz - 20k and observed levels and panel behaviour.
Here are my findings :

The response at the low end of the scale before ''grounding the exciters'' as theAnonymous1 has stated, is approximately 3db down at 40hz. At the top end, I can hear the 16k cut off and then nothing at 20k (not bad for 52 years of age, eh?).

At 50hz, there is a strong vibrational rattle which I initially thought was an exciter problem or wire touching the panel. It's actually the panel itself and will cease rattling the moment both sides are gripped lightly with my fingers, or touched at the back near the middle exciter. Interesingly, I only notice this on one panel and not the other.
Then again, the two panels do not have their exciters mounted in exactly the same positions - quite the opposite in fact - they were just placed anywhere that looked like a straight line and roughly spaced away from each other as a quick test and have remained there since.
I would presume that this resonance is pretty close to the panel's actual resonant frequency at this point in time, and I expect it to shift or hopefully be a non issue once everything is mounted and suspended in a frame with rear bracing against the exciters.

I have received the adhesive mounting rings from NXT yesterday, so it's all accurate measuring and positioning from here on in.

Once again, the speed of drum rim shots, trumpet/brass blasts are so intense and dynamic, it's hard to believe that this level of performance is possible from NXT technology.

I only hope that nothing is lost in the sound quality department in the final steps of finishing off the panels.
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Old 11th February 2009, 08:02 PM   #128
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This project sounds interesting!

I don't think I have room for them, but the concept is fascinating.

They are fairly directional I assume?

Has anyone thought of a long, thin strip to make something more like a line array? That would lose the directionality without the 'combing' as I understand it.

For the high end, what about a silk dome tweeter crossed over to handle the highs? Or am I understanding the issue?

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Old 12th February 2009, 01:16 AM   #129
Ziggy is offline Ziggy  Australia
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jqwinner, they are definately NOT directional. They are diffuse bipolar radiators that can still produce a stunning stereo sound field.
Believe me, I have found no desire for any extra supplement to the highs - there are plenty of them and a dome tweeter or any tweeter for that fact would be pointless.
Can't say that combing is audible but may be there just the same.
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Old 12th February 2009, 02:06 AM   #130
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ziggy,

I don't want to thread-jack, but I have a quick question for you about gatorboard. Do you think it would be suitable as speaker enclosure material? I am attempting a mobile project which needs to remain extremely light, and I'm unsure if gatorboard would resonate poorly or would be too flimsy. Any idea on this?

Thanks!
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