[sedge]

Ozzi
You lost me after "aims" ????
Life's too short to answer this.

Fidel coster
40 inches is into practically full range mode(depending on panel) and a poly panel will go as loud as you like with only a singe exciter.
Most panel types will go down to 300 hz, even small panels ,as long as they are not too flexible.
I have a 3mm ply wood panel smaller than this that has a sharp drop off below about 40hz, but needs more than the 10 watt exciter I use , that's if you want very loud volumes.
I haven't tried two 10 watt exciters on a rigid ply panel yet ,we will see.
Steve

[Fidel Costar]

New DML/ NXT type speakers from Monitor Audio (UK). No idea of their price. It would be interesting to know what exciters and what "flat, soft polymer membrane" they use.

https://ce-pro.eu/2017/01/monitor-audio-iv40-promises-high-performance-invisible-speaker/

[OZZIOZZI]

You lost me after "aims" ????
Life's too short to answer this.

I am sorry if my post was a bit long-winded and that you don't have time to offer a comment.  I was just trying to explain that maybe there is more than one way to approach the design of flat panel speakers and that DIYers are not subject to the same constraints as commercial manufacturers. Perhaps I should have made my point more succinctly.

Fidel, I agree that Monitor audio look interesting. What IS interesting is that they have removed the front panels, perhaps to show the exciters, which look pretty high powered with lots of heat sinking.

Cheers
Ozziozzi

[sedge]

Ozzi
I totally agree with everything you say in your last post.
In your previous post one of the things you mentioned was panel self noise,with light poly panels, just touching the panel with your fingers can change the sound.
To minimise self noise in a poly type panel I sand off the surface skin and apply a thin coat of diluted pva,I have tried thicker coatings and other types of coatings plus clamping ,weights ,you name it ,but the more you apply the deader it sounds,a totally dead panel sounds bad,to me anyway.
This is where I say the art of designing a panel is,in removing the self noise ,or any other problem,as much as possible without causing other problems in the panel.


Fidel coated
The monitor audio is supposed to be skimmed with plaster and even wallpapered over to make it disappear in the room,I have seen other manufacturers who do this ,can't remember the name .
The exciters look standard design types,like cone drivers.
Steve

[OZZIOZZI]

Just in case someone hasn't seen inside these things before.



Or another design



Inspiration for monitor audio IV40 perhaps



Or a homemade variant

[OZZIOZZI]

In wall NXT type panels from Amina









In this last one you can clearly see the aluminium honeycomb covered with thin material on both sides. I seem to remember from my browsing that there is foam rubber between the panel and its frame. The front is covered with paper similar to that used on the face of drywall or Gyprock wall cladding. This is designed to have a skim of less than 2mm of plaster to feather the panel into the wall so it is "invisible".

My first inspiration for building flat panels came when I saw and heard some flat foamboard lifesize cutout figures in a museum that delivered narration about different topics. I was impressed by the clarity of the spoken word. They were just like listening to someone speaking next to you and they were actual voices of well known people so it was easy to judge the quality of reproduction. I looked behind the figures and there was one exciter attached to each figure. I later asked a museum staffer about the display and he pointed me to the local distributor. At the time they were too expensive for experiments-- over a $100 each--so I lost interest, but they were great sounding. I think they were free-standing, attached only to a heavy base. You could have your own favorite politician delivering quotes all day

Ozziozzi

[sedge]

Patent  ep 1174001b1 is interesting ,I have used similar shapes in the centre  of the coil area,mainly concave ,to good results,it does help flatten peaks and troughs and can extend hf.
I first started doing this as I felt the 1 inch Poly panel was too thick in the exciter area ,thinning the panel in this area gave the panel a more intimate sound,as if you had a cone or concave tweeter in the exciter area.
I have also used this method on 5mm poly foam type's with good results .
They never say how these changes affect the sound, only how they change response plots,in The past I have made panels with smooth flat fr responses that sounded bad,I usually find trial and error the best way forward.
Steve

[sedge]

In my last post ,what I meant by bad,is that I had done everything to reduce the peaks and troughs ,and increased the response to almost fullrange ,minimized self noise to almost nothing .
Only to find on longer listening sessions that I had created a very boring sounding panel,not too dissimilar to a heavily doped cone type speaker in a box  .
Ok there are a lot of people out there that like that kind of  sound ,it can make certain types of music such as smooth jazz sound really good,but play anything with a bit of get up and go that's going to knock your socks off ,and you end up falling asleep,I'm not joking  .

As far as heavily damped panels plastered into walls and skimmed with plaster,and heavily damped picture panels in picture frames with pictures in front of them nailed to a wall ,what can I say,except that the sound from the panel will be compromised,not that they won't sound ok,just not as good as they could sound .
But if you have to make compromises ,I suppose it's an option.
Steve

[pol_bct]

As far as heavily damped panels plastered into walls and skimmed with plaster,and heavily damped picture panels in picture frames with pictures in front of them nailed to a wall ,what can I say,except that the sound from the panel will be compromised,not that they won't sound ok,just not as good as they could sound .

those kind of inwall panels are very good for the purpose of omni public adress & smooth background music, but have very few to do with HiFi music.
Only huge undamped panels come close to our area of interest.

POL

[sedge]

Pol
Huge free floating panels are amazingly good .
Oh to be single ,in a wood cabin in the wild 
When I finally clear my music room(junk room as my wife calls it) I will probably end up with large poly type panels.
It's great that the best is the easiest to make ,although it's not going to be as cheap and as easy to get as it used to be ,because the diy stores in the UK now only stock the lower grade eps
Steve

[pol_bct]

Huge free floating panels are amazingly good .
Oh to be single ,in a wood cabin in the wild 

When I get a set of fresh new panels, I want to try the pseudo infinite panel solution elaborated by the guys of Goebels loudspeakers

but still free floating and with rounded corners

POL

[OZZIOZZI]

Pol, it looks like the latest Goebel panels are covered with carbon fibre cloth. I came across this recipe for making balsa ply on an aeromodelling website. "Balsa Ply DIY in so far as the balsa ply, i like to use a 60/40 glue\water mix to make the firewalls. Make sure it is hot and work it into the wood then press it under some weight and allow it to dry for a few days so that all of the water evaporates.

For a firewall, ie: where the engine mounts, I like going 90 degree for the first three layers then at a 45 if i am making 5 layers. The epoxy is kind of passe, gorilla glue (amber type) offers far better results with a reduction in weight and possible complexity as if the epoxy is not mixed perfectly, it looses its efficacy. Gorilla glue can also enhance the joint with a little (and I mean a little) bit of moisture on the joints that are not quite tight . . . it foams and grabs the pores in the wood to hold it far better than epoxy.

I havent bought epoxy for building in a few years, gorilla glue has replaced it on almost every level with the exception of laminating or glassing. (I no longer use polyester resin because of the health issues and stench).

Re: Goebel clone panel. The epoxy is kind of passe, gorilla glue (amber type) offers far better results with a reduction in weight and possible complexity as if the epoxy is not mixed perfectly, it looses its efficacy. Gorilla glue can also enhance the joint with a little (and I mean a little) bit of moisture on the joints that are not quite tight . . . it foams and grabs the pores in the wood to hold it far better than epoxy.

I havent bought epoxy for building in a few years, gorilla glue has replaced it on almost every level with the exception of laminating or glassing. (I no longer use polyester resin because of the health issues and stench)."

I am currently preparing 2.5mm ply covered with 1:1 glue water mix to laminate ply with very thin polyester non-woven fabric. This dries clear and, hopefully, rigid enough. It is certainly very light and gives that "scratchy" sound of the poly panels when stroked with fingernail. I am working on 1ft X ~2ft panels. I plan that Goebel type edge treatment with slots filled with clear silicone for damping. I would like an outside frame for ease of mounting.

BTW, check that your glue is waterproof when dry if you live in a humid area. The foaming wood glues usually are as they react with the moisture in the wood to form their bond.

Let me know if you have any success with balsa wood. I suspect that Goebel panel's "exotic tropical wood" is just end-grain balsa sheets judging by the look of the end-grain on the surface, but that is hard to achieve without industrial equipment. You need to laminate square section beams and then cut thin slices. This is the same way people make butcher blocks or kitchen cutting boards, but usually with dense hardwoods for resistance to knives and meat cleavers.

Ozziozzi

[sedge]

Pol
By pseudo infinite baffle ,are they trying to minimise reflections from the edge to lessen the dml effect or are they trying to disperse the reflections to breakup standing waves ? Or something else?
What size and material are you thinking of using ?
Steve

[pol_bct]

Pol
By pseudo infinite baffle ,are they trying to minimise reflections from the edge to lessen the dml effect or are they trying to disperse the reflections to breakup standing waves ? Or something else?
What size and material are you thinking of using ?
Steve

ok,  By pseudo infinite baffle, I meant to mimic the edge cuts who are supposed to disperse the reflections & standing waves.
I had no intention to redo the special wood & coating & I_Dont_know_what_was_in_that_stuff....   

POL

[OZZIOZZI]

AFAIK from various reviews and Goebels own webpages, they have 9 layers on their panels. If you count the core that makes 4 layers each side. I think it goes in order
Epoxy resin
Either fibreglass or carbon fibre thin mat
Epoxy
Core of balsa
Epoxy
Thin mat
Epoxy

To give 7 layers. Then the whole thing is sealed in a thin but rigid bag of some sort of heat shrink material to give a shiny surface both sides, cooled and then the edges trimmed. I did see that they use a vacuum bag to laminate the first 7 layers.

The cuts around the edges are at 45degrees and 35degrees to the edge. I believe that this cut and filled (with siliconerubber) slots are to both damp the panel of unwanted resonances and to privide a compliant suspension. In cone driver terms this may lower the Fs of the panel below its operating range to prevent spurious rattles and buzzes. If I remember correctly the Goebel panels are high passed at about 170Hz and also have some sirt of linearizing (zoebel?) network and perhaps a peak removal trap although they ae very vague about the last two circuits.

I personally like the idea of the cuts and have already made a panel and filled the cuts with Clear roof and gutter Silicone. I plan to mount these panels in a baffle further suspended by foam rubber weather stripping to make a VERY compliant suspension. I'll report back how they sound once the silicone and the 1:1 glue water treatment on the ply has cured enough. I can take picture to show what I have done. I tried the bare, untreated ply and that sounded OK, but I suspect surface and edge treatment will help.

Cheers

Ozziozzi

[OZZIOZZI]

Complete 2.5mm plywood panel


Cuts around edge filled with silicone, not perfectly spaced, but maybe the randomness helps


Position of exciter 3/7 width 4/9 length as suggested by NXT


Exciter from Dayton



I have mainly been testing panel with 25W exciter driven by ~ 100W/ch receiver playing jazz piano and male vocal and cello and orchestra. Paul Grabovsky and Vince Jones "Provenance" album and "The Essential Yo-Yo Ma" CD. JS Bach's Jesu Joy of Man's Desiring sounds especially good on the ply panel. Little bit of buzzing on the lowest frequencies and really heavy piano crescendos, as I am running the panel fullrange with 3dB of bass boost at around 60Hz,  but the mids and treble are extended and convincing without distortion. BTW the exciter is not yet attached by glue and only has a couple of hours running time at fairly low voumes, so it may improve. Altogether I think this design is worth pursuing. I still have to build proper surrounds and foam edge mounting for panels to be incorporated in open baffle with helper woofer 31Hz to maybe 150-200Hz.

One question, does anyone have experience of using these exciters with and without a supporting spine holding the exciter? It has four mounting lugs which seem designed for mounting, but no instructions about mounting came with exciter.

[sedge]

Ozzi
The exciter looks like it might be a little heavy ,and might not be designed to support itself for long periods ,hence the mounting lugs.
Another problem you might have is the panel looks like it might have a bit of bowing ,ply tends to do this.
Using silicone as a filler between the exciter and a supporting spine might give a little support and a little flexibility in movement .
That is all I can think of at the moment,hopefully someone can come up with something a little better.
Steve

[OZZIOZZI]

The exciter looks like it might be a little heavy ,and might not be designed to support itself for long periods ,hence the mounting lugs.

Thats what I thought. I was looking at aluminium U channel with hole to accommodate magnet and metal surround and small self-tapping metal screws to hold exciter mounting lugs. Maybe damp channel so that it doesn't vibrate and become its own panel.  One worry is that some posters have reported that exciters DIE after mounting to a spine, altho that may be delicate low power exciters not designed for spine mounting.

Another problem you might have is the panel looks like it might have a bit of bowing ,ply tends to do this.

Yep ply is bowing and twisting a bit. It was almost flat until I applied 1:1 coating to both sides I was hoping that, when it is held in a frame it would flatten a bit, but that could be wishful thinking. While I was testing ply with exciter I put exciter down on a piece of polystyrene panel (ex broccoli box from supermarket !!! ) and it played a lot louder. I guess ply density is higher than XPS. Did you find the same result re efficiency? I may have to abandon thin ply because of this low efficiency despite ok sound. Fortunately the exciters I have are 24W so still a bit of headroom left., but I wonder when they start distorting from over-excursion or over-heating. At the levels I have been using magnet and metal frame do not even feel warm, but its hard to assess the voicecoil inside or movement of coil, spider or connecting wires to coil. Until they stop working !!!!!

Using silicone as a filler between the exciter and a supporting spine might give a little support and a little flexibility in movement .

This is possibly a good idea to mount semi- rigidly with some compliance to absorb any alignment problems between exciter and panel. Small rubber grommets either side of mounting lugs comes to mind. Have you ever seen inside vintage radios where speaker is mounted like that to prevent vibrations reaching metal chassis?

That is all I can think of at the moment,hopefully someone can come up with something a little better.

Yes lets hope so. BTW who was the poster who was making panels for wall mounting. He seems to have dropped off this thread. It looked as if he was using foam weather strip as edge surround for his hi- tech panels.

Thanks for suggestions

Ozziozzi

[Odal3]

Ozziozzi - nice job on the panels!

The exciter looks like it might be a little heavy ,and might not be designed to support itself for long periods ,hence the mounting lugs.

I have used that exciter for a long time on several different panels. I removed the adhesive tape and used glue instead to mount them unsupported on ply. Not a single one has fallen off, and I have never had any problem with heat even when playing loud.

I have had a few of the even heavier 40W exciters fall off when playing loud with deep bass, but never with the 24W ones.

I have never tried the silicon as a filler or other semi-rigid solutions so I can't comment on that (curious to see how it works out for you), but I had some problem with over-excursion when using a spine to support the exciters that eventually lead to the exciters fell off plus it didn't sound too good when it overextended. I never tried the spine with large wood panels but only with very small panels (think line-array using a couple of very small panels in a row) so maybe it would work better with larger panels that would require some more force to move.

While I was testing ply with exciter I put exciter down on a piece of polystyrene panel (ex broccoli box from supermarket !!! ) and it played a lot louder. I guess ply density is higher than XPS. Did you find the same result re efficiency?

Yes, using ply definitely reduces the efficiency a lot, but unless you want to play really loud it isn't really a problem. I like the character of the birch ply sound a lot so for me it is still really good (my preferred material). I use 1/4in which is thicker ply than you use. I found that the thinner ply warped and moved too much when playing loud.

Have fun and I'm looking forward to hear more about your panels!

[sedge]

Ozzi   Odal3
The problem I mentioned about the heavy exciter was to do with the spider suspension sagging over time ,causing the coil to rub.

Even with a low efficiency panel xo in the 150hz region should help greatly .
With large (6x2ft) ply panels the efficacy is very low,using single exciters fullrange will get very hot ,too ho to touch,and will eventually melt the coils ,using LF boost will only make things worse ,if your exciters are staying cool you should have no problems.
A free floating exciter ,will happily try and play sub sonic input,this will on loud music make the exciters bounce wildly ,and because of the imbalance of the exciter (cable and connecting area) the exciter will also have serious wobbling going on, xo at 150hz, there will be no problem.
Obviously mounting the exciter on a solid spine will sort out these problems.
Steve