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Old 1st May 2009, 01:58 AM   #201
Ziggy is offline Ziggy  Australia
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Well, as I said before, I don't give up easy on experiments even though I stated that this one was dead

I have discovered some interesting facts that may have misled my conclusive last official post on the performance of the panels

The buzzes and rattles were not the actual panel assembly - they were that damned wiring that interconnects all the drivers!
How could I have missed this MOST IMPORTANT aspect??

I came across this realisation when I had one of the panels in my study at the far end of the room, hooked up to a cheap Kenwood receiver, playing FM radio.
I heard the buzzes in one particular jazz recording that had great lows coming through. Walked up to the panel and suddenly noticed that I had not taken in to consideration that even floppy(but not touching the panel normally) wires would oscillate violently until they hit the panel!
On top of that, some wires were buzzing and rattling against the exciters also.

Had a private email from a New Zealand guy that threw some light on the dampening/mounting of the panels and how to retain output levels. So, there is more work to be done.

In the area of the reproduction of highs - in my study, no problem, lots of highs, even bright but this is a totally different sized room and the panels were just thrown in for fun.

Since then, I have discovered that they will vary their output including the high frequencies like night and day depending on where they are positioned in a particular room.
I read in many reviews that the Podium speakers are VERY sensitive to placement but never really paid any attention to this - I should have.

Another scary find - it's true, they are music dependant and WILL show up what's being fed to them down the line.On some recordings, the highs sound absolutely fantastic - classical string sections sound amazing. Yet, in other recordings,that had normal sounding highs on my horn system(if a bit lite on), the highs are simply awful - go figure

Where to from here?.............more experimenting, positioning,research and possibly trying some different panel materials as suggested by el'OL.
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Old 2nd May 2009, 02:32 PM   #202
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i was about to buy the exciter, now i don't know what to do but i' very very happy to see you keep experimenting!

about the honeycomb panels, is it the internal structure of the material or just the surface? if so maybe it can be done diy from the kind of panels you are alredy using...
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Old 2nd May 2009, 04:47 PM   #203
aczern is offline aczern  Poland
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Where to buy over the Internet transducers for DML?
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Old 2nd May 2009, 04:53 PM   #204
el`Ol is offline el`Ol  Germany
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Quote:
Originally posted by aczern
Where to buy over the Internet transducers for DML?
http://www.intertechnik.de/index.htm...&artnr=1381991
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Old 3rd May 2009, 01:10 AM   #205
Ziggy is offline Ziggy  Australia
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The honeycomb panels have many open sections just like honeycomb from bees wax.The material is phenolic resin coated paper formed in to a honeycomb pattern.
This structure is then covered in a strong plastic/mylar and in some variations, fiberglass and aluminum.

So, it's not really something that is easy to DIY. The Gatorfoam can not be modified to anything like this.
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Old 3rd May 2009, 01:20 AM   #206
Ziggy is offline Ziggy  Australia
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Thanks for that link el'OL. Here's another:


http://www.parts-express.com/pe/show...number=300-375
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Old 5th May 2009, 08:05 AM   #207
Ziggy is offline Ziggy  Australia
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Looking back on this thread and visiting the the sites of some commercial offerings, I have a strong temptation to try 1/4 inch thick (or less) planks of balsa wood.

The idea is to join these end to end, side by side, in effect making a large lightweight sheet to form a panel for the exciters.

As far as information on this technology goes, it seems that any soft medium whether it be whole, in the middle of or laminated to, will stuff up the high frequencies.Then there is the problem of rigidity - any lack of, and the output takes a dive,so too if mass or weight is excessive.

Simple rules?......YES...........BUT,..........how to overcome them with a DIY alternative? Making a honeycomb, phenolic coated fine paper structure is obviously beyond a home build.

A large balsa wood sheet made from numerous sections can also be strengthened with cross beams at the rear of the structure and still not interfere with the exciter positioning.

Anyone care to comment?
Perhaps the total weight may end up being too high?
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Old 5th May 2009, 10:56 AM   #208
jzagaja is offline jzagaja  Poland
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I was experimenting with aluminium+PU (3mm thick) and hard PVC+PU (25m thick), aerial density 5600-5800 g/m2, piezoelectric exciter. Aluminum was much quieter so young modulus has stronger influence on efficiency as impedance of plate, Zm = 8.sqrt(B.mu). Can you confirm?
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Old 6th May 2009, 08:19 AM   #209
Ziggy is offline Ziggy  Australia
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Sorry, I don't quite understand. If you mean the heavier or greater the mass of the panel = less output/sensitivity, then yes, I confirm this from my findings.

The material needs to be very light but stiff. ........easier said than done(unless you spend big bucks on the honeycomb panels which defeats the purpose of the whole effort).
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Old 6th May 2009, 09:43 AM   #210
jzagaja is offline jzagaja  Poland
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We use stiffer plate for low critical frequency. In my example softer plate (PVC+PUR plate) is 0,086 kg and heavier and much stiffer aluminum (Alucobond) is 0,13 kg but difference in sound output is large. As mu at around 5,6 kg/m2 is too high then which material is cheap, light and stiff enough? What about balsa wood? Goebel says critical frequency being 600Hz. Here in Poland double side vakuum aramid honeycomb plate 2500x1250x15mm costs EUR 225,00.
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