[tommus]

I've been playing around with my stack of high-density EPS foam, 3/8" (9mm) thick.   
I made some 2x4 foot test panels, 2 exciters each, with the little Dayton 10w T-amp and was I very impressed.

I can offer a few ideas now:

Plastic resin (urea-formaldehyde) glue seems to be working well as a panel treatment.  This glue is the hardest drying stuff I have ever used.  It is a powder that you mix with water, it has the consistency of heavy cream when mixed up.  (The glue is nasty stuff as a powder, but does not fume when wet and is safe when dry) Diluted with extra H20 (1 part glue, 2 parts water, any more water and the mix separates) I rolled a very thin layer on the back of the EPS.  It seems to have a better HF response, but not by much, than just a bare panel, PVA glue or shellac.  Maybe worth trying on CC as well.  I haven't fully tested it for attaching the exciters but something that hard should transfer the HF quite well (if it doesn't crack).  I'll build up a small "pad" to spread the stress out and then glue the exciter foot on with a nice bead.

Next, I found some nylon/spandex fabric at the local fabric crafts store.  The stretchiest stuff in the place, used to make swimwear.  Cut into 3" strips, I have glued this to the edges of the panel (about 3/4" coverage from the edge) around the perimeter.  The glue I used is water-based tacky fabric glue.  Also there is glue made specially for foam board that is expensive but appears to be the same stuff.  Also there is something called "Weldbond" that also seems to be the same.  Dries clear and somewhat flexible.  The fabric is then stretched across a wooden frame and stapled, suspending the panel inside. The idea here is to damp the panel edge (apply extra coats of glue on the edge of the panel for more damping) but the stretchy fabric "gasket" lets the panel "dance" in the frame while supporting it.

So now it's time to make the big guys, a pair of 2x7 footers, 6 exciters each, the largest I can fit in my living room.  Before I commit, it sure would be nice to hear some details about Zygadr's latest and greatest, but hey, isn't it more fun if we all try playing the guessing game?

My guess is that Zygadr cut some of the EPS foam sheet into strips maybe 1" or 2" wide and glued them on edge to the perimeter of the panel, creating a light and stiff "torsion box" or "stressed skin" panel...
 

[hblester3]

Ok Ziggy you have again set the hook. I have chased panel materials and attached exciters coated CC ect and enjoyed the whole process. I use them in my classroom the the students are my test subjects. Younger ears better ears. We have also built the Peter Dainels Gainclone kit and the students can not believe the sound we get from our styrofoam speakers as they call them. Let the cat out of the bag as school will be out soon.

Thanks Hubert

[sedge]

Everyone
While doing the tests on the foamcore I noticed something strange about the hf.
I had noticed it before but had never really thought about what was going on.
I don’t know if the penny has finally dropped or if it’s a load of crap.
Near field test was done with the mic 10mm from the panel, this gave the best hf response ,say-25db at 13k or so.
But when I placed the mic on the floor say 2 to 3 meters in front of the panels,I noticed the overall hf had changed to the classic shape I have seen so many times before.
On my poly panels I would expect to see a sudden 5db or so drop at 10k and flat shelf from there on up to20k.
But what I noticed was that on the foamcore the flat shelf had appeared ,but it was only 20db down from the response below 10k and it was not sloping away.
This flat shelf from 10k to beyond 20k is still there when measured from the side of the panel .how much of this is from room reflections I don’t know.
So my point is this ,ok it’s beaming (slightly )from the centre but there must still be a low level of hf even at the outer edge of the panel.(I have measured this).
Is this combined low level output from a large 2x4ft panel(or 2x2.5ft foamcore)that is causing this flat 10k to 20 shelf(that’s a big tweeter!)
The level of the very flat response from10 to 20k off axis seems to depend on the panel but even with the bad foamcore panel(admittedly 20db down) it is still there!!
Ok so when you are measuring from the front (near field ) you are measuring the tweeter area beaming ,but when you move off axis and further back ,something else takes over(nxt,acoustic horn,whatever)
This does not change anything ,but it is nice to know it is there and is something else to take into consideration when measuring this panel type.
I am coming to the opinion that these panels radiate in so many ways it is hard to put a tag on them.
I am still trying to get my head round the fact that my 2ft wide panel is putting out a hell of a lot of deep LF,when it should be rolling off from 200HZ down(that is if it is working in piston mode as is stated by some?)
sedge
 



 

[zygadr]

All, as sedge has clearly indicated, the sound we are getting from these panels does not add up in the normal world of speaker performance.

I wish I had more knowledge on this technology, but when you read the white papers on it, your head nearly explodes from over complex information overload!!!

Now, despite my liking C.C. and having high hopes for it, even with a peizo assisting the h.f., the sound does not and can not match the VH grade EPS.

Now, I mentioned that I had found a way to stiffen the panels.........right?.Well, this was mentioned and discussed way back and I don't take any credit for it.
This should have been tried and done a long time ago

What's the secret?............................ADDING BRACES TO THE REAR OF THE PANEL

This can be done in a ''H'' configuration using specially cut pieces of EPS : 1-2 inch high strips positioned on each side(standing upright on their 10mm thick side)and then joined together with as many horizontal pieces as required.
Obviously, the exciters are between these cross braces and the wiring needs to be isolated from the EPS braces to avoid vibrations.

That's it!!!

[CLS]

Oh! that's actually very similar to 'the ugliest speaker'    It's horizontal ribs maintain the curve, while the camber forms the vertical strength to support itself up. 

And I'm wondering if it'd be better (or not) to locate the excitors at the xover nodes, where the structure should be stronger...

[zygadr]

There is NO curve to my panels..............I'll leave that to the ''ugliest speaker in the world''

''Crossover nodes''?????...............really????....................nonsense

[CLS]

Why?

I imagine the 'reinforced' portion (where ribs/braces are applied) on the entire panel would be more rigid, thus a faster medium for propagating sound waves. So, any excitment at the brace would be spreaded faster.

OTOH, when visualizing a pulse hammering at somewhere between the braces, the wave propagates along the surface and hits one of the brace. And then, the vibration on brace would run faster than the original. Two waves race against each other and probably some interfereces would happen.

No?   

[zygadr]

As bracing has added the very much required ''RIGID'' panel criteria (and it shows!!!!!.....audible!) :



 

Next to try : 20mm, 25mm, 30mm thick VH EPS !!!!!!!!!!!!!!!!

this is just the beginning.....................standby!

[sedge]

the 4x4ft panel with damage from windy car park

[sedge]

putting these pictures on just to see if I could remember how!!

[sedge]

zygadr

One good thing about gluing (what glue are you using?) on the poly bracing is that the bracing will become part of the radiating surface (as one) I have tried foam and other materials but they all killed the sound.
In a way I have tried these panels in the form of mouldings such as chill box lids container packaging 1x2ft or 2x2ft with an inch or two thicker on the sides but because of the size of the panels I don’t think it made much difference.
Just had an idea ,what if you had a brace of 2 or 3 inches depth  going down the centre of the panel ,with holes cut out for the exciters .
You could then possibly glue foam in between the exciter and the brace to help support and prevent sag and maybe give a little damping to the exciter body in the process.
I would have thought a light foam would be best to stop sound transferring to the poly.
If worried about heat ,spacers could be placed on the exciters.
Oh shit, I have really started rambling now! …….better sign off.

sedge

 

[zygadr]

sedge, the bracing you suggest could work, but I have found that a 10mm thick panel that's 6 x 3 foot needs to be cross braced as the sides bend also.
It actually bends in every direction at that size!! 

If anyone is considering gluing two thin sheets together to make a thick one..........don't!..........this doesn't work as the cavity and layer of glue between the two sheets kills the sound to a significant degree.

Remember that EPS has an interconnection of expanded beads when examined under magnification.
 It's this structure that is so efficient in transferring the sound at all frequencies from the rear of the panel to the front. Any interruption to this connection system and performance suffers.

Therefore, my next trials will be with much thicker sheets, still 6X3, but will be much more rigid.
Will the thicker and slightly heavier sheet affect the H.F or sound output?..........don't know.

I suspect that it may not cause any adverse results, only better ones!...........maybe?

Rigidity is FAR better than floppiness..........trust me.
Some extra mass will dampen the panel better?
Bass output could be more solid, even louder?
The panel can be made ''free standing'' with only a simple bottom support structure.

This week I will visit the store where I bought the 10mm thick sheets and do the ''scratch test'' to compare the different thicknesses and see what happens in that department.
If the H.F are still loud or even  louder(?)..............we may have a new breed of NXT panel here

[zygadr]

Ok Ziggy you have again set the hook. I have chased panel materials and attached exciters coated CC ect and enjoyed the whole process. I use them in my classroom the the students are my test subjects. Younger ears better ears. We have also built the Peter Dainels Gainclone kit and the students can not believe the sound we get from our styrofoam speakers as they call them. Let the cat out of the bag as school will be out soon.

Thanks Hubert

Hi Hubert, sorry for not replying earlier.
I'm glad to hear that you successfully made some NXT panel speakers and the students are enjoying them.
In fact, had you not built this and palced them in the class room, these younger folks would probably have never known of the NXT technology and what it can do!

Same goes for the Gainclone which works very well with the lightening speed of the panels

[sedge]

Zygadr
I have a 2inch thick panel 8x2 ft in the same material as my 1inch and have already tested it.
The sound was ok but not as good as the 1 inch thick.
Did not notice any LF improvement but then I was concentrating mainly on the mid and HF and would not really expect a single exciter to move a 8x2ft panel in piston mode while hanging off the back!
Even with the cc I proffered the sound of the thin 3mm to the thicker heavier 10 mm.
In trying to force the panel into piston mode at LF you will probably end up putting a strain on the all important mid and HF range.
Also in my post earlier I mentioned LF being produced by something other than piston mode, this is just a suspicion so far but is a possibility.
I would like to try a thinner panel in my material but that would mean a special order again (£) .I feel that a certain amount of flex ability IS necessary for these panels to perform as they do
But unless we try these things we well never find out, will we, I’ll keep my fingers crossed for you and hope for the best.

sedge

[pol_bct]

the 4x4ft panel with damage from windy car park

Hi SEDGE
when looking at  your panel, I think that  the flat shelf may comes from the thick panel
It could have some internal reflexions who kill large part of signal above the 1/4 or 1/2 wave length

POL

[hblester3]

Hi Zygadr

  A few quick questions
1. You are using the exciters free floating.
2. On your 6 x 3 panels how many exciters are using.
3. Are the exciters still even spaced down the center.
4. On your braces are the vertical braces close to the center or at 1/3rd or half way between the exciters and the edge.
5. The cross braces just between the exciters or also between exciters and the top and bottom of the panels.
 
Again loving this has been great just want to know what is working best for you. Will be waiting on the word on the thicker panels.

Thanks Hubert

[zygadr]

Hubert:
1 .yes............free floating exciters
2 .4 exciters
3. yes
4. half way between exciters and edge
5. top, bottom, and one in centre of panel.

Sedge, a 2 inch thick panel is WAY TOO THICK ............with lots of exciters even!

Pistonic movement of the panel MUST occur for any reasonable bass output.
Podium Sound's panels go pistonic also, but they split the frequencies with a crossover cap.

I am seriously considering 25 -30mm thick EPS in an 8 foot X 4 foot size, with six exciters!!!..........how does that sound????

[sedge]

Zygadr
I agree ,2 inch thick panels are way too thick,but it had to be tried.

Podium needs all those exciters to drive the heavy rigid panel into a piston motion but the mid and top end sound like NXT to me.
Podium also use the brace on the back of the exciters to force the panel into moving back and forth, pushing and pulling that mass of air in front and behind
Poly is very light but it still has to move that mass of air .
If you hold the panel in front of you and shake it back and forth you can feel the weight of the air bending the panel, this would be the same with cc or any other panel including podium panels ,but to a lesser extent with the podiums.
with my 2x4ft panels with single exciter (hanging off the back) and the exciter just gently buzzing away (this is loud)I have very good LF ,mids and HF.
So that is why I am a little unsure weather thickness and rigidity Is what we need (unless we are thinking of becoming a porn star that is ).
But unless we try these things we will never find out!(not the porn star bit)

Pol
The point I was making about the HF shelf above 10k was that it seems to be on all panel types including cc.
If you measure your panel from the side ,say 2 meters away,you will see a flat low level shelf  appear ,what level this is depends on the panel.
As I said it is not going to change anything but it is nice to know it is there(admittedly at a lower level) and radiating all over the room.

sedge   
   
   

[CLS]

As I visualize (imagine) the behavior of excitor and panel, maybe overly simlified -- that stone-ripple analogy...  I guess, the more rigid the "pond" (panel), the longer the excited wavelength (along the panel).

And then the air is excited by the 'waves' on the panel.

The bigger the waves on panel, the flatter the wavefront of the air -- because the air is pushed at the center first and then spread outward. So the radiation tends to be more long-throw and maintain its 'nearfield' effect in a larger range...  (No?)

But then it's against that almost-omni character, which I can't explain...

Ah~ it's all my own imagination. Please correct me if anything wrong.

http://paws.kettering.edu/~drussell/Demos/rad2/mdq.html


 

[zygadr]

I'll stress again from reading and remembering all that has been published on the panel ''requirements'' :

The panel MUST be ''rigid''.

If it flexes,(overly so) all the complex wave interactions that are supposed to happen in the DML principle..........doesn't............it's only half baked