[DanTheMan]

Whyis it that so many conversations in audio these days are gravitating towards Bras and Pantyhose?

Dan

[jeffac]

Whyis it that so many conversations in audio these days are gravitating towards Bras and Pantyhose?

Completely appropriate here as Bra's are essential to reducing the long term effects of gravity on our favourite play things  aa  ... that's NXT panels of course 

magnetic levitation

spine exciter mounting - good idea not to remove that cushioned double sided tape fixed to the back of those cheap PE exciters just yet.

cheers.. jeffac

Hmmmmm... Reply #666 - Lucky me 

[mkstat]

To get access to the DML skript you will need a NXT licence.

This was a little bit hasty - look at page 10.

http://www.randteam.de/_Docs/Aes104%20Distributed%20Mode%20Loudspeaker%20simulation%20model.pdf

 

Paste it into AkAbak - Oh there is an error - 3rd line - Bs (for Bending stiffness) instead of B
 
-m

[jeffac]

Stupid here has just disassembled 2 piezo tweeters and forgotten to mark + and -.  One wire is attached to the ceramic disk edge, the other is attached further in and looped over the edge. Lesson learned, play with one at time.  Anyone tell me which is which.

Ta.. jeffac

[sedge]

Jeffac
If you want to be sure of the polarity you can make a little seesaw out of paper ,if you make its length about 8 ins or more and the pivot about an inch or less  from the speaker end,  attach short end to speaker cone ,any small movement back or forward of the cone will make a large movement at the other end .use small AA battery  to get +or ? [not sure if one 1.5volt is enough ] hope this makes sense.
sedge

[sedge]

jeffac
just thought, this is a piezo oops , won't work probably
very high resistance at low fr.bigger battery ?

[zobsky]

jeffac
just thought, this is a piezo oops , won't work probably
very high resistance at low fr.bigger battery ?

Exactly,

Measuring mic setup would be best, but if that's not possible, ...
try and compare concurrently played test tones with a known tweeter  at normal and reverse phase with test tones.

[sedge]

There is Something I have been meaning to ask for some time now ,has anyone noticed that If you toe the panels inward ,sometimes quite heavily,[even tried facing the panels at each other] you seem to get an almost 3D  effect .
I am not sure If this is because of my long thin room or if it has the same effect in larger rooms ?
It makes you feel like you can walk through the image, as if there is more depth.
With the panels facing strait forwards they still sound good but it is more like a wall of sound [I think this is partly what I was hearing when I heard the podiums] which can sound a bit odd.
I did not try this With the small panels, say down to A4 size ,as the panels seem to give good ambience already.
This is also quite good for me as it makes the panels narrower and deeper ,so that I can have a bigger panel.
On normal speakers toeing in seems to [IMO]give a more central image .
If anyone can at sometime let me know if they can hear the same [or not ] It could be helpful , thanks.
I could just be going mad [who said that]?

[zobsky]

There is Something I have been meaning to ask for some time now ,has anyone noticed that If you toe the panels inward ,sometimes quite heavily,[even tried facing the panels at each other] you seem to get an almost 3D  effect .
I am not sure If this is because of my long thin room or if it has the same effect in larger rooms ?
It makes you feel like you can walk through the image, as if there is more depth.
With the panels facing strait forwards they still sound good but it is more like a wall of sound [I think this is partly what I was hearing when I heard the podiums] which can sound a bit odd.
I did not try this With the small panels, say down to A4 size ,as the panels seem to give good ambience already.
This is also quite good for me as it makes the panels narrower and deeper ,so that I can have a bigger panel.
On normal speakers toeing in seems to [IMO]give a more central image .
If anyone can at sometime let me know if they can hear the same [or not ] It could be helpful , thanks.
I could just be going mad [who said that]?

probably some dipole cancellation causing the ambience (though I'm not sure that this design is pure dipole / bipole)

[jeffac]

Thanks guys,

Based on this schematic it seems the wire to piezo bimorph edge will be the (-) and the wire attached internally and wrapped around the edge will be the (+)

sledge,
You've been thinking what I've been thinking regarding 'fun' panel placement experiments. I remember reading somewhere where a guy with cheap multi-driver and very narrow tower-type  home theatre speakers couldn't believe the holographic sound field that he could generate by placing the speakers about 1/3 way into a rectangular room with them directly facing each other, with the seating position about 2/3 of the way back.

Like in this doodle and something definity worth playing with.
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I've been getting a similar holographic effect by listening near field to my dinky cardboard test panels which have wings \__/.    I have 2 large corrugated cardboard pieces that I'm going to test curved, as this really aids vertical rigidity, and they might stand up by themselves. (Don't fry me about affects on bass, I know there probably will be but it's early days for me and I'm just trying to get a feel for how these things work.) 

cheers.. jeffac

[zobsky]

Can anyone comment on the sound of (say) two 2 x 3 panels vs one 2 x 6 panels on a single channel. I ask because it's going to be hard for me to acquire large pieces of gatorfoam. At least the smaller pieces can be shipped with no difficulty.

[usp1]

"cardboard test panels which have wings \__/"

Thats the test panel I used (made from science project display) and it was interesting how the sound stage changes when you move the wings closer or farther apart. I never thought of placing them face to face...hmmm maybe I will experiment this weekend if I get a chance.

[usp1]

Can anyone comment on the sound of (say) two 2 x 3 panels vs one 2 x 6 panels on a single channel. I ask because it's going to be hard for me to acquire large pieces of gatorfoam. At least the smaller pieces can be shipped with no difficulty.

Contact a local sign maker. They will often be willing to sell you a sheet of gatorfoam and they will cut it for you at no extra cost. That way you can go pick them up. My panels are 2X4...I got 4 panels out of a single sheet of GF for about $60. If I understand correctly the larger panels add more bass. With two exciters I can get from about 100hz - 13khz. Adding extra exciters seems to reduce the top end a bit but gives more SPL.

[captainjack115]

Can anyone comment on the sound of (say) two 2 x 3 panels vs one 2 x 6 panels on a single channel. I ask because it's going to be hard for me to acquire large pieces of gatorfoam. At least the smaller pieces can be shipped with no difficulty.

[/b]

My feeling is they would have to be seamed together in a way that would allow them to work as one large 2X6 panel. (Tricky)
The bending waves need to expand across one large panel to radiate lower frequencies.

Jack

[captainjack115]

Can anyone comment on the sound of (say) two 2 x 3 panels vs one 2 x 6 panels on a single channel. I ask because it's going to be hard for me to acquire large pieces of gatorfoam. At least the smaller pieces can be shipped with no difficulty.

[/b]



My feeling is they would have to be seamed together in a way that would allow them to work as one large 2X6 panel. (Tricky)
The bending waves need to expand across one large panel to radiate lower frequencies.

Jack

Addendum

I'm playing with a pair of 20" X 30" foam core panels.
Placing my microphone from my spectrum analyzer at my listening position, 16 feet away from the speakers yields usable bass in the low 30 Hertz range.

Placing the panels on the floor produces a strong peak in the 60 to 120 Hertz range. Getting the panels off the floor and rounding the corners flattens the peak. I will be doing larger panels soon with more exciters. Loudness with two exciters is quite ample. Eight exciters per channel will allow more power handling and increased sensitivity. It should be quite enough for most sane people.

Jack

[jeffac]

I can confirm the bad news, called the local distrubutor of Re-board here today and yep, only 10 mm 2440 x 1220 sheets currently available, and must purchase in packs of 6 at about $75AUS a sheet. Sample pieces only in the order of 10 x 15 cm so too small to be useful for testing. Bugger. 

Folk in the US, Bio-board that I posted a link to previously looks to be similar to Re-board and might be worth a phone call.
http://www.lairdplastics.com/content/view/495/

Piezo cone/exciter HF enhancement 

Well I've just added a 'smaller type' piezo cone as desrcibed by Ziggy to one of my small cardboard panels with a single PE exciter, parallel connection, correct polarity now I think I know which wire is which. Not that the panels were lacking much in the way of HF beforehand but anyway, Ziggy's description of what they add is pretty much spot on. Quite some added HF to the panel front but more still rear firing as might be expected. Too much HF tilt with a single exciter but that's good to clearly hear what the piezo cone is doing. The added HF energy certainly adds sparkle/vibrancy and the extra rear HF energy adds to the reflected response energy. A few more exciters on a panel displaying early HF roll off and I'd expect a piezo exciter to blend in and boost HF seamlessly.

Higher SPLs and it buzz's with nasty distortion, but I only taped the come edges to the panel with masking tape and proper mounting of the complete cone face with 3M VHB tape or similar would probably fix this to at least some degree. I'll attach the other piezo to the other panel when I get a sec to see whether I get the same buzzing or have a dud. 

cheers.. jeffac

[zobsky]

If you can't get Gatorfoam, use corrugated cardboard.......it's better than nothing, or, trying to piece together smaller panels.

I wasn't contemplating piecing / duct taping together smaller panels. Rather I was considering using multiple panels per channel, each within their own (sub)frame.

[sedge]

Jeffac
What If you cut a hole in the panel so that the lip of the back of the  peizo can be glued to the front of the panel so that it is forward facing, this would make the peizo part of the front surface[nxt], radiating frequencies cleanly across the surface [no trying to penetrate through two surfaces and foam core ] ,hopefully this would sound cleaner from the front and louder .
You could then reduce the volume to the peizo to blend in ,this would also reduce distortion as the peizo would not have to work so hard .
If I had a gatorfoam panel and felt it needed  the extra hf  this is probably the way I would do it .it would also blend in very well with the black panels
On the other hand it might just sound like shit.
All the best .
sedge

[jeffac]

What If you cut a hole in the panel so that the lip of the back of the  peizo can be glued to the front of the panel so that it is forward facing, this would make the peizo part of the front surface[nxt], radiating frequencies cleanly across the surface [no trying to penetrate through two surfaces and foam core ] ,hopefully this would sound cleaner from the front and louder .

Hi Sledge,

Tested.  And with a small piezo cone attached to 2 mm plastic lined (rear) cardboaord, this produces crystal clear, silky smooth and dynamic HF.  No buzzing either even at extreme SPLs.  The only engineering problem is the very shallow depth of the small (~1 3/8" dia.) piezo cone and the large-ish ceramic bimorph. On 2 mm cardboard there is enough space between the cone and panel for rear firing HF but on 6 mm Gatorfoam, there wouldn't be. Maybe with the larger 2" piezo mentioned by Ziggy, this would be OK.

Is there much involvement of the panel front? Hard to tell but I don't think so there's not much vibrational energy happening that I can detect just by touching it.

Does it rock my boat? I can't believe the HF clarity and energy and musical aliveness that this brings with it. Please .... someone else confirm this and that I'm not just an excitable boy.  aa

a few pics
The line across the cardboard is due to one side being coated with a single application of tung oil to test as a stiffener
And laugh all you like at the dinky panels , but they are teaching me heaps. I quite like them now and beleive it or not, for what they are and their <$15 cost, they sound great. 






cheers..jeffac

[cometarossa]

Hello,
I'm going to copy the podium system.
So i need some information about the materials used in that setup.
I know there is a honeycomb panel made of Nomex but i'm wondering about the thickness...
then there is a mylar sandwich protecting the nomex honeycomb right?
even here i wish to know the thickness of the mylar.
I do not want to seem arrogant cause of this  you guys are fantastic and you are working well, very well.
I'm learning a lot from your mistakes and your successes, but I would overcome this stage and use the finest materials to get as close as possible to a hi-end results.
many thanks to all

p.s.
clearly once assembled the panel, will explore the position of the exciters!