[oldschoolVlad]

Sorry that I misunderstood your question marks, Rob, no offence… 
Thanks for your notice of a single exciter, certainly will make a comparison of the one- and multi exciter setup. My plans was multi exciter so far. The only well known problem is the low output level. Looks like we have a dead end here. It seems, there is no extremely powerful exciter available on the market. DIY?...

[oldschoolVlad]

...BTW, in DML simulation 2 times BL increase gives +3dB in SPL, similar as for the cone speakers arrays.
1 exciter = XdB; 2 exciters = X+3dB; 4 exciters = X+6dB etc....

[zygadr]

No problem at all Vlad. Don'get me wrong, there is a lot of black art at work with this technology that is just waiting to catch you out!
You are correct with the fact that these exciters do not have enough power handling for some of the better sounding materials unfortunately.

I am fearful that the only way back to what was useable for high levels of sound would NOW be - 8 x the 40w drivers I have mentioned in my latest posts, lined up in a vertical array as before on "white Gatorboard"???........oh, no....... NOT AGAIN.  

Forum member "Scorpion" ........if you are monitoring this forum, you are the only forum member who had previously heard my first, black Gatorboard panels........please comment!

Rob.

[zygadr]

Sorry guys, I don't know if I can pursue this any longer.

Yes........we can build a loudspeaker using this technology that can equal and play as loud as a Quad ESL 53, but I don't have the time and money to spend on the newer, more poweful( debatable) exciters that as an Australian, with the dollar so low at present, it does not warrant further disappointment for a most probable small gain in performance for a large outlay.

By all means carry on guys.........I'm sure that the more knowledgeable as well as the die hard experimenters out there will come up with something.

Good luck to all.

Rob.

[gragra]

Hi to all, I'm new.

I think birch plywood is the best choice (very clean sound).
I will try to build the diy exciter that mr Pulverrostmannen has shown on youtube ("Home made vibration speaker"  www.youtube.com/watch?v=-Jvosadq2ao).
Maybe it is more powerful...
Bye

[oldschoolVlad]

QUAD ESL = Göbels = 86dB of sensitivity. On my simulation 2mm thick plywood with 8 conventional exciters will have the same sensitivity. As for me, I think I’ll be able to live with it… 

[zygadr]

Good luck to you Vlad.
According to my calculations, your wiring configuration/ sensitivity figure rating iis unfortunately far from correct!

I have specifications of many and most of the standard exciters supplied to me from NXT and China (Billion Sound) and if you have properly wired "8 " exciters on a panel, you should be closer to 90db at minimum"............86db is equivalent to many of the single exciters mounted on their own on a single panel.

Suggest you recalculate your proposed sensitivity using multiple exciters - you are far from the mark.

I can quite clearly recall the huge difference in using 8 exciters as opposed to 2 or 4 compared to 8 .
Please do not get me wrong - I do not mean to correct you in a "know it all manner", but "I have been there and done that!"

[sedge]

a lot of the more powerful exciters seem to be based on shakers which could work well with heavy panel types.
the low power exciters we are using benefit from a light panel such as poly foam or eps ,with the coil directly attached to the panel any small amount of power applied to the exciter produces vast amounts of sound with no over heating (they run cold)I have destroyed a few on heavy panels .
using multiple exciters is not an option for me for the same reasons described by zygadr , I restrict the LF to 40 or so HZ to protect the mid and hf from large coil movements on loud close mic placement or electronic bass ,I leave that to the LF driver.
over the years I have found poly panels to sound better than all the other panels I have tried(and I have tried many types and shapes ), but only if used properly.
for me this is a finished project and only needs me to make up my mind as to what size and what it looks like.

steve

[zygadr]

sedge, when you say poly ''used properly'', what exactly do you mean?. I am sure that there are many out there (including myself) that have ditched or shelved the poly idea due to less than ideal sound balance.

Rob.

[oldschoolVlad]

Jesus..........just look at that.....at the bottom....

http://science.wonderhowto.com/how-to/make-paper-plate-speaker-actually-works-for-under-1-0141522/

....Guys, I feel now an irresistable desire to play with those wires and magnets...
Ziggy, I swear now I'll find a way how build an ultimate exciter to drive the plywood... 
A fast look on the market gives me all I need - a lot of cheap chinese neodymium discs and rings. And large steel washers. As for the voice coil, I wound some to repair, isn't a problem. The theory of the perfect driver is simple: the voice coil must be single layered and a whole one must be placed in magnetic flux as stronger as possible. Ok, let’s go….

[sedge]

zygadr
I have never ditched my poly panels but have over the years improved the sound of them.
foamcore and gatorfoam are both light panels but with heavy paper damping ,these to me are over damped ,the only way to make the foamcore sound good is to strip the paper off and that is a messy job ,believe me .
I have used heavy damping on panels and cured the problems but the sound was never good ,the panels just sounded soft and slow ,nice for smooth jazz but not much else.
I also do not intend to use the panels below say 40 or  100HZ depending on size or panel responce ,using the exciter below  this can be very destructive to the exciter and panel ,let alone to the sound (how many subwoofer  units do you know that play up to 20k)
there was a track on batman forever in the 20 to 30HZ region that made my large panels start walking across the room ,I had to turn it off before they self destructed .
you mentioned the sound balance of poly panels ,this I was trying to explain was not just the panels but the room responce ,then you suddenly announced that you had binned your eps panels with pleasure !!!!!!!!!! ? and gone back to cc?I cannot help with the heavier panels as they have a differant set of problems,as do very rigid panels.
the coating I do use on the panel is heavily watered down and so when the water evaporates you are only left with a trace on the panel.
steve

[zygadr]

Thanks for your reply sedge.
Yes, I have swapped and changed panel materials quite a lot lately. Hope I haven't confused too many people in the process of doing so. My reason is that each material has it's own set of advantages as well as disadvantages.

So what do you coat your poly/eps panels with if you don't mind me asking?

[zygadr]

Have just spent the rest of the day reading technical papers on DML/BWL papers....................what a pack of dumbos!!!!!!!
What we have learnt in actual experimentation and implementation makes these ''experts'' look like geek fools!!!!................they are so far behind the eight ball that it is truly laughable

What, according to them, will not work...................DOES!!!!!!!..........................SUCH IS THE POWER OF THE DIY ARMY!!!!!

[zygadr]

sedge, is there a reason why two forum members including myself have asked what you use as a coating for the poly panels and have been ignored (perhaps) ?

[jeffac]

Only reason I can see is that the EPS coating method is here already, just buried due to being posted a few years back.

From memory and the posts quoted:

PVA glue:water diluted 1:1, thin coat applied on the VH-EPS panel back (exciter side) only. This dries to an imperceptibly thin film, as sedge has specified in various posts (unless he's now discovered some improved patent-pending concoction ) I applied 2 x thin coats to my 10 mm thick 196 cm x 76 cm VH-EPS panels back in 2010 that I still use and that sound very detailed but natural enough to me warmed up by 4 x Eminence Alpha 15A H-frames augmenting bass up to ~250 Hz. Mini-DSP used to low-pass the H-frames, panels playing full-range.

cheers.. jeffac

hi zygadr
you can vastly improve the sound of your panels with a very light coating of pva but it has to be done in a certain way.I mentioned this some years back on this forum but no one seems to have given it much thought,I have an old 40 cm vh xps testpanel in my loft ,I could get it down and test it for you,or do you have any scrap panels you can test yourself and compair with the untreated panels ,the test panel does not have to be the same size as the db output and sound  will be very similar above say at least 200HZ if a 40cm panel is used if my memory serves me well.
using any poly panel or foam panel without a light coating will have a lot of self noise will tend to be over bright and have a tendency to sound hard at times,vh xps is no exception.
Steve

GIANT KILLER PANELS PART TWO.  (in the music room ,no one can hear you scream…………….with joy!)

Since building the first 18 inch wide panel with one exciter, I have made two further panels, one 2ft and one 4ft wide, all 4ft high and 25mm thick, using two exciters per panel.
The t-amp I was using is rated at 8 watts at 8 ohms, if that.
This drove my hifi News test cd with the  sound of BIG BEN striking twelve, to realistic levels,I kid you not! Plus the lovely sound of the clockworks clinking and clonking as clear as a bell…..ha ha .
I am sure the neighbours loved it as much as I did.
So I think I can safely say that these panels are very, very efficient.

To make these panels is very easy, and only takes an hour or two If using a hair-dryer,but the hf will not be good until the glue hardens,  this takes at least 24 hours, so be patient.
You could do as I do ,and just hang them from a stand ( cheap up lighters, in my case -best sound for me so far), but if you mount the panel  in any other way you must make sure you do not restrict the panel movement in any way, or else you will lose dbs and alter fr. So take care.
The glue I have used for the panels is nothing special. It is just that I had a gallon lying around and it sounded good on other panels as damping.
The 2ft by 4ft is probably the easiest size to work on and you can easily cut an 8ft by 4ft sheet into four to fit in the car,if using a van or lorry 8ft by 4ft max !!!I would love to try this and could use it as a projector screen  with a higher quality polystyrene. The panels do not shake around as my metal panels used to - its just a thought,so far!
 To damp the panels I used a 50 50 mix of water and pva mixed in a 1 lb (400grm or so?) jam-jar ,this should do 2 panels, a thin a coating as possible so the panel is just wetted, if you use too much glue you could over damp the panel but if it is still under damped you can add another thin coat.
If you are doing this on the kitchen table be warned glue will seep through in places .
The panels should be damped on one side only!!! And this is the side the exciters will be glued on, you can use a hair dryer to dry this coat, 15 mins or so,  and when dry, its  time to glue the exciters on.
I used undiluted pva for the exciters, using a match-stick to apply the glue onto the foot. Try to get a nice mound of glue on the base and also dab the sides of the foot. Make sure none goes into the voice coil.
Just remembered that I used sand-paper to take the shine off the exciter foot and hopefully give a little adhesion.
I also applied a thin coating of undiluted glue about 3 inches in diameter around the fixing position. Not sure if this helped in any way but that’s what I did.
Also using the match-stick, build up a small mound of undiluted glue around the area that the foot will come into contact with the panel. The glue will shrink and hopefully this will help fill the gaps.
You could use the hair-dryer to start the drying process on the panel and the exciter, before sticking them together.
Using glue that does not shrink,  so as to fill in the gaps could be an idea at a later date but the sound would have to be checked.
I also placed a little bit of weight on the exciter to give a good bond, enough to push the exciter foot into the panel without damaging the voice coil.

Dry the glue using a hair-dryer, waving it around from all sides.  The exciter will eventually get hot ,very hot,  but don’t worry.. If you are a little worried that the panel is getting too hot,  you could always leave it to dry over night instead, its just that I only had a couple of hours till dinner and my wife had a gun at my head!
So if you have to move them after a couple of hours keep them somewhere with a flat surface and leave them to dry overnight ,you can wire them up ready but they will not sound good until the glue hardens, probably after a day or two.
If you are using two exciters I found it better to have the connections facing each other (on the inside) but it’s your choice.
While I think about it I hope every one has removed the horrible plastic casing with those stick on wobbly feet, if not you have got problems!
AS for the position of the exciters ,I used a one third up from the bottom  and a one third down from the top in a centre line, other spacing’s could give a better sound ,or maybe  not.
But this position sounded superb so it’s a good start.

Also I rounded off the corners of an experimental panel which I had used to trial the damping
But can’t say that I heard a lot of difference, my mind was on other things at the time and now they are lying on the chair with the exciters ripped off but hopefully I can try again at a later date.   
 
sedge

[zygadr]

Many thanks jeffac  for taking the time to post sedge's posts from the past  .........how one forgets after 102 pages!! .
I have a couple of medium sized VH EPS sheets left and will do a test to compare a treated panel with a standard one.

[sedge]

thanks jeffac
patent -pending ,that sounds fun,not as much fun as nailing my head to a table
for years I have coated my panels with pva, but in the last year I have changed the method, which has altered my understanding of the panel
I need to sit at the computer and try to explain why and how I think it works.
there Is a lot going on in my life at the moment ,basically  I picked the wrong time to announce it
so please forgive me for being a bit slow,
rob ,if you can wait till I get it all written down on word and in my head, you can try the new mods I have mad and see what you think?
sorry once again.
steve

[jeffac]

thanks jeffac
patent -pending ,that sounds fun,not as much fun as nailing my head to a table
for years I have coated my panels with pva, but in the last year I have changed the method, which has altered my understanding of the panel

No worries guys, I knew this info was here somewhere.
I got 8 x VH-EPS sheets cut at the time and still have 6 untouched, plus spare el-cheapo but good exciters, so........ sneak some time to draft that patent app sedge.. 

cheers.. jeffac

[sedge]

Hello all
There is something I should say from the start, although I have used  pva to damp the self- noise of the panel I do not regard it as  panel  damping, to me it is the opposite.
I always felt that a very light coat helped  the sound propagate from the exciter  across the back of  the panel  ,this was my main objective ,the fact that it damped the self- noise was a bonus (this was the same when I was testing  cc as well).
We must not forget that we are dealing with two surfaces the back exciter side and the front surface (plus the four sides which can also affect the sound)I was reading some tech papers a couple of days ago and they called the surfaces skins ,this I hope will help to explain my next step .
Coating The eps panels was no problem but when I tried to coat my new foam panels with watered down  pva the skin was waterproof ,so I started to scuff the skin with sand paper to give the pva a grip ,well I got a bit carried away and took all of the skin off on the exciter side  ,the pva went on perfectly  and I just placed the exciter in the 2/5ths position as per parts express info.
It sounded ok but with too much self-noise , I taped the back exciter skin  and it sounded fine but when I taped the front skin the self- noise was there  .Next step take off the front skin and sides,this had the effect softening the sound and was stopping the sound propagate across the surface ,when I coated a 3inch area around  the exciter  it sounded like a point source ,I expanded this area 3ins at a time slowly moving into dml ,this could be another way of tuning the panel?
In the end I ended up with a panel with the offending  skins taken off and replaced with pva skins,so far I have left the last 2in of the outside of the panel un-coated ,back and front,the idea is to help stop reflections from the sides without applying damping! also I'm not using pva to damp the noisy skin,the pva is the skin and it sounds very nice too.
As I said before in another post I did try a 40cm vh eps 10mm thick panel the same as your panels (rob)but a small panel  of vh eps is very rigid and has a lot of energy to dissipate ,a large panel should be more flexible and help absorb the energy,I would probably have used another coat of pva for  the small panel but as I said  this panel was a few years old and I'm afraid it has the exciter in the middle of the panel which was obviously making things even worse ,but having said all that it still gave a good performance , as you can see in the pics in my gallery the panel is usable down to 40HZ with the help of a LF driver to fill in up to 300 or so HZ to beyond 20K,well I think that's not bad, anyway!
We now have an eps or foam panel that does not have the eps or foam sound ,it now sounds like pva              I had to be the first to say it as I know someone will,but to me the panel sounds very natural and the instruments  and voices sound so real, I could listen to them forever and a day ,if my wife would let me!
Before I go (to bed)I would also like to make a further  observation on the comment made by rob on the ideal sound balance of these panels ,when I use my ears to blend the tls with the sound of the   panels below 300 or so HZ I find the mic in the room is telling me I have overshot by 3to 5 db,when I compare the sound to my headphones It sounds pretty much identical ,I did try once to make the panel sound like my TLs but by the time I lowered the detail to match the TLs I had almost turned them off.this reminds me of the problem I always seem to have with ribbon tweeters ,I presume that the response is flat ,I have never measured any ,the detail is fantastic ,but its like having a search light shining in your face ,where is the rest or the sound to match it?
My ears are telling me that there is more going on in the sound from the panels than the mic is picking up ,so I blend the sound using my ears.    Steve.

ps
my next patent app errrrrr mod  :scratch:is the inner part of the exciter ring area .costs nothing adds no weights.

[zygadr]

Well done Steve...........................I take my hat off to you!!

Have you tried Shellac as a coating?

Rob.