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Old 19th December 2008, 03:28 AM   #41
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Just go with the thinnest 5-layer you can find. Thin double sided tape was used for my experiments, but I would have used CA (super glue) if I was going to make it permanent.

I can't remember how the little carboard disk was attached to the black platic ring on the voice coil.

I took a look at those podium speakers. I see the whole panel is free floating at the edges, the panel being suspended down the middle by the array of exciters. That would be impossible to do with only one or two exciters and a large panel.
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Old 19th December 2008, 05:03 AM   #42
Ziggy is offline Ziggy  Australia
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O.K......will do.

I presume the plastic ring is attached with double sided tape also. We'll have to wait and see when I dismantle one.

I know what you mean about the way the PODIUM speakers are built altough I think you'll find that the corners are held by some kind of white gooey rubber like substance according to the review on 6 Moons where they watched as a panel was repaired by Shelly Katz, the designer.He mentions his never ending search for sticky materials before the right one was found(marketing hype?)

A floating panel is still what it is though and that's why I am intent on using multiple NXT motors to drive a large panel - it's the only way to approximate this design and get enough power handling and sensitivity.

Don't know where this will all lead to but I'll give it my best shot.

By the way, the other 4 pairs have arrived today, which will make it 6 drivers per panel, so, obtaining the panels cut to size will be the next step.

I live close by to a ''composite materials'' supplier and guess what.......he can supply NOMEX HONEYCOMB sheets and will laminate anything you want to it. Estimate so far is about $500 Aust. for (2X) 6 foot x 2 foot sheets. That's a lot to spend without much more experimentation though

Checked out a rubber goods supplier today - man!.........there is a multitude of rubber sheeting, strips tapes to choose from. There will surely be something there to suspend the panel with.
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Old 19th December 2008, 08:37 AM   #43
el`Ol is offline el`Ol  Germany
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Why not try paper honeycomb first (like Podiumsound and most other NXT speakers do) to have a reference?
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Old 20th December 2008, 07:58 AM   #44
Ziggy is offline Ziggy  Australia
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elOL, the honeycomb material is very expensive. Not sure if they have any off cuts, but I'll try during my holiday break early in January.
The other thing is, you have to specify what you want ''laminated'' to it, so off cuts may not be suitable in some or any of the samples.
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Old 20th December 2008, 04:41 PM   #45
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Ziggy,

Thanks for keeping us posted I have a suggestion for panel material, but cannot find a trade name for the stuff. Anyhow, my wife came home the other day with some packing board from the post office. It seems to be a laminate styrofoam core faced by paper/cellulose. This is a very stiff material for its weight - semingly a good candidate for distributed mode projects.

Cheers,

Ed
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Old 21st December 2008, 05:59 AM   #46
Ziggy is offline Ziggy  Australia
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WOW!...........great stuff Ed!
It could be foamcore but who knows?
Foamcore is one material I have not tried yet.
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Old 22nd December 2008, 05:58 AM   #47
Ziggy is offline Ziggy  Australia
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Update...........bought a plastic jar of SHELLAC FLAKES from the local hardware store (Bunnings for all you Aussies out there).
I will try the mix on some nomal 5mm thick corrugated cardboard scrap to see what happens.

The recipe for shellac ''varnish'' needs an 8 hour dissolving of the flakes in spirits.

Should be interesting as shellac is bug s**t (of all things !). It dries super fast and cures rock hard I believe.

This I presume will take the cardboard panels to a noticeably different performance level....it has to, as cardboard is essentially made from glued paper and is soft if anything - not ideal for NXT applications.

Here's an intersting fact : honeycomb nomex is also made of paper that's dipped in resin to harden and strengthen it so I think I'm on the right path with the shellac coated corrugated cardboard laminate.

The idea of using the honeycomb structure in DML's is due to the vibrations being able to travel in all directions due to the connections of the honeycomb cells........similar to the corrugated waves in cardboard laminates but maybe not as efficiently.

As many audiophiles believe that paper is the best sounding speaker driver material, being made of natural materials, the ''bug doo -doo'' infused card board is as natural as you can get I suppose
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Old 22nd December 2008, 03:40 PM   #48
el`Ol is offline el`Ol  Germany
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I just tried a piezo on cardboard and I find at higher levels it doesnīt differ much from what I have heard in stinking basement discos in my youth.
What I have to admit is that transparency is much better than the Podium Sound speaker I heard at the Highend in Munich this year. In fact together with Rethm (Lowther) it had the worst transparency I experienced at the show. Itīs a shame that non of those NXT guys with their 1000 patents had the idea of using piezos for the top octave.
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Old 23rd December 2008, 02:35 AM   #49
Ziggy is offline Ziggy  Australia
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Must confess I haven't had much experience during my youth with ''stinking basement discos'' LOL !!

elOL, don't get confused between what is mainly high frequencies from a piezo on cardboard and transparency. The piezos can and will produce some good sounds in their limited range. Overdrive them and they will sound terrible.

I too have thought about using piezos as tweeters with the NXT panel drivers but don't feel that this is necessary in my listening room which is very large and live sounding. As a matter of fact, I have noticed some important facts that have emerged over the last few weeks of experimentation :

1. The NXT drivers are beginning to sound better and better each day and I can only (even though I'm not a great believer) attribute this to'' BREAK - IN '' which is at about 30 hours of use in total at the moment according to my rough calculations.

2. On the subject of transparency, this is what I have noticed more than anything else.........some recordings that have background shuffling, coughing and other noises are more pronounced now than ever. Sometimes they jump out at you quite unexpectedly. I have never experienced this as much with any other speaker over here , even with the large compression driver horns that I have at the moment.

I'm not trying to defend the Podium speakers and have never heard them (and probably never will), but I have heard some NXT small panels linked to small subs and can't say that their top end was anything to rave on about - quite the opposite in fact.

Some of these panels had METAL SHEETS on the fronts of the panel material
How in the hell is that going to assist in the high frequencies ? Sure it will stiffen the panel, but at what cost to the audio spectrum and sensitivity?

My purpose to this thread has been to demonstrate that DML's can and do work and by the looks of it, a ''podiumclone'' LOL is within our reach and cheap to build. No, you won't need a piezo as a tweeter, it will be a crossoverless true ''full range'' driver, I hope

elOL, if you found the Lowther based Rethm's lacked transparency, I suggest you have the wax removed from your ears.
With the Podium's sound, they are very contraversial in their high frequency delivery as I have discovered in my tests. As stated before, the high frequencies/transparency are all there in more than adequate amounts, it's just that they are presented to the listener in a different way.

I can move the one and only summed mono panel I have just a couple of feet in, out, left or right and the sound changes ( but not like a typical direct radiator speaker ).

What you heard at the show may well have sounded bad if the room acoustics and set up was not ideal. There is no doubt about that.

I can only hope that my continued experimentation ends up being a useable DIY product.
So far, it's a pure joy to listen to music through this prototype, even in mono, and not noticing driver material differences, crossover points, coloration etc. They just play music. Music you can listen to all day
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Old 23rd December 2008, 07:49 AM   #50
el`Ol is offline el`Ol  Germany
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Quote:
Originally posted by Ziggy

2. On the subject of transparency, this is what I have noticed more than anything else.........some recordings that have background shuffling, coughing and other noises are more pronounced now than ever. Sometimes they jump out at you quite unexpectedly. I have never experienced this as much with any other speaker over here , even with the large compression driver horns that I have at the moment.


elOL, if you found the Lowther based Rethm's lacked transparency, I suggest you have the wax removed from your ears.


Maybe we are talking apples and oranges. With lacking tranparency I donīt mean the number of perceived events (the Lowthers are really good in this respect) but some kind of fog that lifts when you enter a room with conventional speakers. The Geobel NXT speaker is much better in this respect, as in others, but has limited SPL
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