[OB_Newbie]

Hey Steve!  Thought you might have tried shellac at some point.  I treated 2x6 foot cardboard panels a few summers ago... even the inside flutes... what a pain... they still sit up in our spare room unused.  Almost didn't try DMLs thanks to that splendid experience with the cardboard.

Thanks for the kind words Sedge.  Yeah, wasn't sure how it would go honestly.  I knew it wouldn't be taken very seriously by the primary designers so very happy that it got even some semblance of traction.  We all have Ziggy to thank for introducing us and many others to the interesting and outstanding performance of these panels.  This is a good way of paying back that we have received... have much to pay back I would say.

[sedge]

 OB_newbie
I think ziggy heard something special and had to tell everyone about it and I believe that something special was the free edged floating panel,in all its different guises ,in the early days of using cc and plywood even I could hear that something special was going on,but he had the balls to stick his head above the parapet and start this and other threads  ,the down side is you can pick up a lot of flack hope I'm not worrying you OB ,but he carried on to the end,good on him!

The 12x10in x3mm panel coated in shellac feels to me as if it has hardened some more(boy , this stuff takes a long time to fully set) it's a few month's now,and I used a hand dryer at the time.
The panel still sounds a little over damped to me(lacking in some detail and air) but the sound is not so soft ,just enough to give it a little warmth,on the other hand the similar panel but with a pva coating on, has more detail and air but the sound is a little hollow sounding ,a bit too xps sounding,either I didn't sand it down enough or it needs another coat of pva,or other?
Odal3
You say we have not implemented the ply panel properly so have not heard them at their best,as you have thrown the gauntlet down,maybe you can show us how,I only say this because I feel the same way about my poly panels,at least as far as I know no one has implemented all of my mods,I'm not sure of what you have done and I suppose people are probably unsure of what I have done.
If you show me yours first,I'll show you mine  
Steve

[Odal3]

I would be more than happy too. But just to make it clear, I was joking with my comment  and hope it didn't come accross as critisism. If so I apologize. The nice and fun with audio and the panels is that there is not one perfect way to do it - only some ways are better and other are worse with different pros and cons including different rooms, systems and preferences. I especially like this thread where people freely post about their experiences and get positive and constructive feedback.

I actually have a newly sanded xps pannels and have coated one side with pva so far and I'm really looking forward to complete it to have a listen. I believe this will be the exact same setup as obnewbie since the panel is only 2 x 2 ft. Some of my previous xps experiments didn't work out to my liking since they came out too "hot" in the 4000- range (likely user error on my part) and wasnt super clear - not to mention curious kids fingers that liked to poke on the fragile panels.    I have even coated wood panels with pva glue.
I'm yet to try out your mod with thinning the area over the exciter.
Here's my favourite birch panel so far:
2 x 4 high quality birch ply. I start out with 1/4 thickness.
Brake all the edges so they don't splinter and round the four corners with a 4 to 6 cm radius.
Rough sand the front and back with a random orbital sander and apply the same technique of tapering the panels like they do on piano sound boards to better maintain the energy of the wave all the way out. In other words, sand much more on the ends and then work inwards to the middle. I sand it so I almost brake through the top layer of the ply on the end while the middle where the exciter will be mounted is just sanded smooth.
The edges are really important as you know and what I do is sand them a little bit sharp with a dull end if that makes sense. I'm using my hand orbital sander together with a hand rasp. Wish I had a router...  I like to get the edge curve smooth. I then
sand the panel  smooth down to 200 grit. As you can tell, it requires quite a bit of sanding.

I place thin and small nails on the two sides about 2 cm below from the rounded corner (approx 5 to 6cm from the top) to be able to hang them. This allows that nothing touches the front or back of the panels and they can move freely. This has worked out really well on wood but the nails keep slide out when I tried the same on xps.

I have used both 40W exciters as well as multiple low watt exciters placed in monacor 1 to 4 or other combinations. Using one high watt is my preference but multiple smaller ones works as well.

I have just recently been experimenting with treating the panels with stain or pva-water mix. Jury is still out on verdict. The one thing to be careful with if applying anything with water on ply is that it may warp.

What has not worked out so well: using thinner 1/8 plywood or oak plywood sounded horrible. The thinner birch ones were not rigid enough to support themselves and had a lot if self noise when listening to them.

Bigger panels produce impressive bass but they get really heavy. I never experienced that either low watt or more powerful exciters get warm when playing them as some of you have reported. Since the exciters are free mounted they move a lot when playing louder.

So instead of saying better or worse I would just call this is just another approach that works ok.

The bad things with wood is that they don't play as loud as the xps/eps panels but loud enough for me. When I'm in the basement with door closed my wife sometimes complain about the volume when she's on the second floor. The second thing that may be a deal breaker for some is the HF us not as good.

Looking forward to hear from all of you with ideas how to make the wood and xps panels even better!

[OB_Newbie]

I need to refresh my memory tonight but I believe they went away and smoothed the whole spectrum. Will check if I have some old measurement files - can't take any new ones because the exciters are off to be mounted up on my new thin and tall panels that will debut this weekend! 1.5 x 5 ft with the first one stained up to match my living room coffee table. Curious to see how the stain affected the sound. Hopefully not too bad. Would like the panel to go down to 100 so will see how it works.

Hey Odal, been meaning to ask how it's been going withn the narrow and tall panels?  Can't wait to see and hear what you think of them!

[OB_Newbie]

Combining some of the threads above on sound of ply and XPS. 

On my ply panels:
Odal is correct that I did not spend much time with the ply panels.  I had thin 1/8" ply as to not reduce sensitivity too much as my class D amps are low power.  Adding balsa just to the top (closest to the exciter) added very little weight and did improve the sound quite a bit.  1/8" is just to thin to on its own and not recommended even with the small 24"x30" panels.  What was left to do here was to treat with PVA, shellac or ??  This may have formed them up a bit and also improve the sound quality.  I wanted to like them very badly as they look great!  I still might build a finished panel just so I have some references to compare against.  These panels are cheap enough and easily moved around and stored when not in use.   

Sound quality of ply verses XPS:
This is REALLY subjective so take this into consideration but think its good to get something out there and in place and we can tweak and polish with more impressions from everyone.  This may be placebo effect at play but this is how the general sound is to me:

1. Oddly or NOT oddly enough; the *general* sound of the panel material is not notably different from when I simply rap on the panel material with my knuckles.  For instance, when I wrap on XPS it does indeed have a bit of a hollow sound as Sedge stated.  The sound seems to be absorbed by the XPS.  XPS certainly does have a coloration to it and have to think that the thicker the material the more coloration/hollow sounding the panel is.  I could hear less of the coloration with the smaller thinner panels I made (14.5"x12") but I was not and still not sure whether it was the small size or the thinner panel material.  But I did feel that there was less of the coloration that otherwise seems to cover the entire freq. spectrum.  So me, the more water:PVA the treatments the better it sounds; I have done a max coat of 2 but some with more PVA in it to make it more firm.  It is as if the firmer skin transfers more of the sound waves into the panel!?  This is based on early listening tests; seemed to sound a bit more more solid and less hollow and did have more air and detail as I added the second coat of PVA:water.

Now wondering... what if we tried laminated 2 (or more) thinner treated panels?  The dollar tree has the terrible paper faced panels for $1.  Now the thick paper face killed the sound for me but what if it was treated.  The paper would become quite hard.  You could remove the paper but that was a serious PITA so I'm inclined to treat it first pass and then evaluate.  Of course this only begs for a comparison of 1/2" XPS (or thinner) sanded, treated and laminated using PVA:water with probably more PVA.     

2. On ply, again, the knuckle test reveals the ply to be to dead sounding.  The wrap is not clear... it is a dull *thud* sound.  This is how they sounded to me.  To damped, lacking in detail and generally "flat" sounding for lack of a better term.  They lacked on overall detail but they did seem for retrieve more hall ambiance; that aspect was hard to describe.  But also mroe space around instruments it seemed.  I liked that aspect of it.  Also, the HF were lacking.  I did EQ them but when I try to flatten them they become for strident and loose some of that smoother sound quality.  A little EQ was an improvement but too much was not.  Frequency response was pretty smooth... that's a notable aspect.

Odal, any thoughts on improving the sound quality of the ply panels?  I am looking forward to your impressions of a treated ply panel.  Who is to say that ply can't be greatly improved by a new skin?

3. That comment from Podium (I also read the Podium review initially trying to glean insight into what the designer felt about DML and his specific design) about a panel must "ring like a bell".  My interpretation has been waned from time to time but what I believe he meant is that the sound should be clean and clear when you wrap it... clear as a bell.  The sound should be solid and transfer the strike across the panel cleanly.  This has shaped some of my comments above for sure.  It is a little strangle that he mentions wrapping the panel as well (or believe that was his statement... have to go back and reread).

Gotta run but wanted to get a start on some basic assessments about panel material "sound".  Don't be to harsh boys... just a start... looking forward to everyones own impressions and take on different materials.

[Odal3]

Great input - thanks for sharing! You captured a lot of good stuff.I like your knuckle test

 I havent had a chance to measure the panels or play them in my normal system yet but will hopefully some time this week.  So far so good but a sub us definetely needed. Btw: I use the TPA3116  amp board which is also a relatively low powered class D.

Question: is there a big difference  between treating both or only one side? Asking because I'm trying to decide if I should stain both front and back. It's currently only on the front and sides.

[OB_Newbie]

I have the TPA3116 too but haven't listened to it yet... looking forward to that.  Have the 2x8 watt Sure too and another 2x20? watt modded Sure (ver 1 of TPA3123 I think?) which has been my primary amp for the last 6 months+.  I really like Class D amps.  They have replaced a Denson Beat, NAD, Sumo and some various vintage Sansui and Sony amps.  Great sound for very little $$$.

I know the knuckle test sounds a bit odd but try it once and listen to the different panels... do you hear these basic signature in the output?  Might not have them explained well but I do hear similarities in the knuckle test and actual listening tests... at least with XPS and ply.

Boy, I would think that finish the front and back would be a positive improvement!?!  It makes such a big improvement on XPS... probably not to the same extent on ply but if I had to make a decision, I would finish both sides... especially if you hear sound quality improvements with the single finished side.

[sedge]

No problem Odal3 ,I was eager to hear if you had sorted out (my) main problems with the hard panels,the most obvious one being output,an exciter like Frank40s would sort that out straight away but at the time we only had low power models,so even if I managed to sort out the other problems I still wouldn't be able to use them in a practical system ,with the higher output xps I could instantly hear a way forward to an up and running system.

I agree with ON_newbie with regard to the knuckle test,but I would go one step further and use a hard object such as the head of a screwdriver,this produces a sort of clacking sound and if the exciter produced loud sound at this frequency it could set It off,I tried all sorts of damping but only managed to make the panel more insensitive and dull sounding
It's difficult to keep that lively sound with damping so I try to use as little as possible,or none.
Steve

[sedge]

Had another setback getting the 25mm good quality xps panels ,B+Q diy store are out of stock and don't know when they can get more ,hope they don't get the poorer quality stuff that wicks have.
The main problem with xps is the LF drum resonance ,but this is mainly only a problem on the much larger panels and then only if you intend to run them down to that fr.
With The ply and other harder panels these resonances are pushed higher up in the frequency band so are much harder to deal with,specially with the low powered exciters being pushed to third limits ,making things even worse .
The xps can have peaks and suckouts in the response above 10k ,I believe this to be the tin can affect ,from what I remember I thought the hf response on the ply panels was better,more efficient any,so I was a little surprised when low output in this area has been mentioned sometimes,this could be my bad memory so am tempted to get the 5x2ft panel from the loft and check,I'll wait and see what people think first.
I also seem to remember the panel didn't suffer from the same or as much room suck outs in the 100-300hz region as the xps?
Might get it down just to put my mind at rest.
So basically all types of panels have their individual problems ,then you add on the different size problems,then exciter position ,mounting,and so on.
It's a nightmare.
Steve

[Odal3]

It's a nightmare.

but that is also what makes it so addictive - the holy grail always feels to be around the corner.

I tried both the knuckle and screwdriver head test on the XPS and I hear what you mean. Not sure really what conlusions to draw. My birch panels sounds like, well, just like knocking on wood

Correction: My thinner panels are 1.25 ft wide and not 1.5 as I mentioned before. They measure kind of flat up to 10k before quickly dropping. Then I remembered that I only used the thick tape to mount the exciters so I took them off and re-glued them with gorilla wood glue and had them sit for a day. Mistake. Somehow this made the HF response worse and drop-out much earlier and the flat response were no longer flat.

I don't know if there is a diff vs XPS in 100-300hz, but panels larger than 2 x 4 stays pretty flat in my unfinished basement with concrete walls and floor.

I have had some panels stretching up much higher but I have always struggled with the HF on the wood (probably due to the thickness) and especially at distance. Seems like when I get the HF pretty good, somewhere else seems to suffer 

BTW: We have mainly been talking about frequency plots, but what other measurements do you guys do? Anything else that would be valuable to do when evaluating the panels? I'm new to measuring so I'm just learning as I go.

[ebonetti]

Good morning everyone,
in my opinion this could do the trick:
https://www.google.it/patents/US3767005
You could get the best of both worlds.

Brief introduction:
For two years now, I'm following this thread.
I'm a happy user of shellac treated CC panels.
One axis is stiffened by cardboard corrugation, the other by bending.
Similar to  this (not my work): http://www.diyaudio.com/forums/planars-exotics/133711-piezo-nxt-type-panel-58.html#post3154116
The bend is hold in place by the shellac.

[sedge]

Odal3
I have been trying to think of a better way to describe the sound and the best thing I can think of ,which is totally over exaggerated so please don't get offended,but I think gives an idea of what I mean.
When tap dancers place ply boards down on the floor to amplify their tapping and stamping,you are listening to the panel sound ,this is the clacking sound I was hearing ,if you played the sound of dancers tap dancing it would be phenomenal ,I think it was even worse on the smaller panels as this pushed the pitch up even higher,anyway as I said this is an over exaggeration ,but once I'd locked in to it, it became annoying!

I usually measure the panel response a foot or two in front of the panel to get an idea of what it is actually outputting,you can usually get very good 20hz to 20k responses depending on the panel in this area,then I measure the in room response to see how the room is screwing everything up,this can vary depending on the panel type and size and room,as I have said before ,you can be in the next room and the sound is fantastic,you could believe there is a live band in your front room,then you walk into the room and everything collapses because of the room cancellations in the 100hz to 400hz region.

One of my mods sorted out the hf problems above 10k on my 5mm panels ,near field ,but I never quite got around the implementing  this on a fully moded 25mm panel,am still trying to acquire some 25mm to test.
Steve

[sedge]

three pics of hardwood ply from the loft,3mmx6ftx2ft this pic 3inches from exciter area.

this pic 3ft in front of exciter area.notice the frequency between 40 hz and about 16k is almost all within +and - 2.5 db.

this pic about 15ft or so behind my listening seat

time getting them from the loft and up and running about 45mins ,didn't have a good exciter ready ,so used one with its foot missing ,stuck on with double sided tape, it fell off after 15mins so use this as a guide to the kind of response you could get,sounds pretty good to me but still can't get anywhere near decent volume as the exciter gets very hot.
as I said before this panel needs a much more powerful exciter,the hf would improve I'm sure if glued properly to the panel.

[sedge]

for interests sake ,this Is also a rigid panel called Aquapanel ,two layers of cement sandwiched between foam used for insulation in under floor heating ,efficiency is about the same as the ply panel,this too needs a more powerful exciter but as you can see has a large fr response with a higher hf response above 10k .
I have had this panel for about 5 years but have not used it because the exciter will melt if played loudly ,the sound is good like the ply panel as far as I can tell with the exciter used.
rigid panels don't seem to suffer the large suckouts in the 100hz to 400hz region as the light poly panels but to my ears sound a little restrained .
hope this is of some interest .
steve   

[sedge]

also the peek at 80hz drops  away when the panel is suspended(it was standing on the floor) the panel is a little expensive at 17 pounds for a 2ftx4ft x10mm sheet, I used plaster to fill in the holes caused by the thin cord that runs down and across the panel under the surface, but only in the exciter foot area.
steve   

[Odal3]

Been travelling so I haven't had a chance to reply yet. Thanks Steve for posting all the good info. I'm convincened that you must have the biggest DML panel collection of all of us. 

One of my mods sorted out the hf problems above 10k on my 5mm panels ,near field

Can you summarize the mods that you do again in addition to the PVA/glue mix? Do you do different ones for different materials?

[Odal3]

also the peek at 80hz drops  away when the panel is suspended(it was standing on the floor)

That's the double peak I also see when having the panels stand on the floor.

Thanks for posting all the plots. The slope of the drop in the HF is very similar to what I see as well. Untreated it normally drops around 10k but if treated can get up to around 16k. If exciter not  mounted properly it drops even sooner.

[dbishopbliss]

I've been travelling last week so I have no measurements, but before I left I shellac'd a 24x24x1 XPS panel.  The sound is much more natural and less boxy sounding.  There are two differences... the panel is leaning against a wall in my office instead of the frame away from the wall, I'm using a low wattage SET amplifier to drive it while it breaks in.  Measurements will come soon.

[OB_Newbie]

Thanks for the update dbishopbliss.  I assume this is compared to the untreated panel?

Sedge, can you elaborate on the sound of shellac now after a year of curing... comparing it to the PVA and water treatment?  Meant to ask... seems like shellac sounded better once fully cured?!? 

[snerdly]

In trying to read this entire thread ..I don't as if I've seen anything in detail about how these panel's would integrate with conventional speakers...
will they sound odd ..out of place? can anyone give an opinion on that?