[zygadr]

Sedge and all.
There seems to be an anomaly between what you and others have as " roughy cut VH grade EPS "  

The two pieces I have here are actually off cuts from two full size 8X4 sheets. There is no way that these surfaces have a rough texture that needs sanding!, let alone coating with watered down PVA glue.  The surface of these two pieces as well as the the others before it came from the same batch of sheets (that I binned in frustration while moving house    )!!!!!! The surfaces have the feel of very fine sand paper......not rough at all!
As I have mentioned before, it seems that once the exciters have broken in, there is a quantum leap in sound quality!
Now, this breakin period can be likened to Black Gate capacitors.....a statement that I laughed at until it happened to me some 70 Hours of playing time later in another electronics project some time back !!!
Please don't get me wrong...........I am not trying to discredit the experimental results and conclusions of others, but beware of of your VH EPS supplier !

[sedge]

Zygadr
I feel you might have misunderstood the point of the pva , I used to coat the panels in the pva to help damp the plasticy sound produced by the hard surface of the eps ,nothing to do with its roughness .
The idea now ,is to remove the plasticy sounding surface and replace it with a good sounding surface ,that is all.
What you wish to coat the surface with is up to you(pva shellac or what ever) I just find the sound of pva to be very natural and helps the panel to disappear because of the lack of self noise.I also use pva to glue the exciters on.
Once again I hope this clears up this misunderstanding .
Steve.

[j gale]

Hi Just to add a little. The plasticky surface we are talking about is a result of heat in the cutting process. EPS is manufactured in large blocks and is cut to size and thickness by hot wires 400-800 degrees.(Google it) Those hot wires leave a plastic skin on the surface that doesn't,t sound good. I believe that when we listen to our panels we are primarily listening to the surface. If that skin is 1.sanded off the panel sounds natural. 2.If coated with Pva IT is slightly damped, sounds better still. 3. If coated with shellac even better. (Mother of tone) It is amazing how much better EPS sounds when the skin is gone.  Yes it makes a mess. I have not worried about surface smoothness and just take my sander to it with coarse sandpaper. Shellac gives it a hard surface. I don't know if another coat will be better or worse. I am also guessing that as the shellac gets harder over time it will get better still.

[Odal3]

Are you using a power sander? I wasnt even able to hand sand the panels I have even with a light touch using 200 paper so I suspect we are talking about different versions of EPS. 

Btw: borrowed a microphone for measurements so will do some experimenting over the Holidays.

[j gale]

Yes a power sander. If your EPS is falling apart that easily that's not normal. I rounded off the edges on mine with my sander too and a few beads broke loose as well but not too bad. Since EPS is so cheap get some from another source. Here in Canada we have 2 grades that are easily available, the basic white and a green tinged one with smaller beads that's a little harder. If you can't get decent stuff I would suggest trying the extruded stuff which also needs to be sanded as well. Like Sedge said before sounds very similar. In the past I tried several thicknesses of both the extruded and EPS and always ended up rejecting it because of what I call a plastic sound. Getting rid of the skin makes it acceptable and opens up options for adding better sounding skins EG shellac.

[zygadr]

Thanks sedge and j gale.
I fully understand what you are saying, but still suspect that the EPS over here in Australia is somewhat different to what you describe j gale.
However, I will eventually try sanding the surface of my 6X2  20mm panels and probably coat them with shellac.

j gale.......what cut do you use for your shellac? Also, what do you use to glue your exciters with?.......VHB or PVA.........or something else?

Finally, my son works and lives in Canada (Toronto).........where do you reside if you don't mind me asking?

Rob.

[j gale]

Hi Rob, Your son and I are about 3,000 miles apart. I live on the West coast near Victoria BC. Perhaps you could experiment with smaller pieces of EPS to compare a sanded and or coated piece to one not altered to see what you hear. Both sides and edges too need to be sanded. Being as lazy as I am I just buy shellac already prepared in a can. The brand is Zinsser sold in Canada and the US. It's described as a 3lb cut. I gather that if buying it already prepared you should pay attention to date of manufacture.Too old is not good. One nice feature of the shellac is the way you can prepare the site of your exciter with a little circle of a thicker coat and make it smooth for a good bond.  After reading what Sedge said about gluing exciters on with PVA glue I tried that using his method (3" circle of fairly heavy coat, heat glued on exciter and wait 24 hrs) It worked well. I have since used the VHB tape as well. I have both the recommended 3MF9473 PC and a thinner one F9469 which I prefer (much thinner and has never let go) If you have the patience for the glue it is certainly cheaper. I don't notice a sonic difference. For now I like the convenience of the tape.

[zygadr]

Thanks  j gale.
Looks like I have some experimenting to do..........no probs..........it's all fun!!!!

As a lead up to Christmas, can I wish you all a safe merry holiday season and thank you all for your fantastic input to one of the greatest threads on any audio forum.

I hope that I have managed to enable as many as possible to build a panel speaker that only dreams are made of.
We can grab anything stiff and light, place one or more exciters on the panel in the exact location and have sound that rivals the electrostats and the magneplanars at a low cost that is near on ridiculous!

Best wishes to all...........and I can't wait to see what the new year brings to this forum!!!!!   

[Odal3]

Happy Holidays to all of you as well

[OB_Newbie]

First off... Happy Holidays to all!

I finally put together some DML panels and can see why you guys are excited (couldn't resist) about these panels!! I split up into 2 posts to make it a little more manageable...

PART 1

System
- Fairly small listening room about 12 X 14.
- System : Vintage Sony CDP-C77ES, Behringer DEQ2496 Ultracurve Pro for crossover and EQ duties.  Parts Express TPA3122 Class D amp with upgraded resistors and Wima caps.
- Bass duties handled by dual 10 MCM's per OB panel driven by 200watt Jung plate amps with 6 db boost.  Flat to 35Hz.
- DML panel of 1inch thick, 24x24 pink XPS (high density?) found at Lowes, Menards, etc. Sanded and treated with 1 coat/each side with 1:1 water|white glue.  Exciters are the Dayton Audio DAEX25FHE-4 High Efficiency 25mm Exciter 24W 4 Ohm - 1 per panel 2/5ths from top and left per PE lit.  Panels rest on old cane seat high-back chairs.  They positioned 7+ feet apart CTC at a listening distance of 6-7 feet.
- Have them crossed around 200Hz to the bass bins to increase the output and keep the self noise more tolerable (they are a bit noisy otherwise at even moderate levels. Also EQed by boosting the HF and a bit off BBC dip to flatten out a hump in that range.
- Have only 30 hours on the panels so still plenty of breaking to go so improvements to come I'm sure.

[OB_Newbie]

PART 2...

General observation
The good
- High efficiency. Notably more efficient than the Tang Band W4-1879's I have in the OB panels at the moment.  I'd estimate 90+ db!   
- The panels really do a nice job on percussion and plucked strings.  Bongo drums are very realistic.. You can hear the reverb inside of the bongos... really nice.  Almost on par and very similar to my vintage Philips 8" full-rangers in OB.  Ambiance, and space around instruments... not quite at the level of the Philips but still breaking in and can't wait to see how they open up over the next few days.
- Dynamics are really good… speed and attack is just fantastic… as good as the best traditional dynamic speakers I’ve heard… in OB of course and considerably better than any boxed speaker.  Surely will sound better when the panels are quieted from improved dampening and more break-in time.

The bad
- The panels seem to be pretty well damped right out of the gate but can surely be improved (the XPS I’m using is really good it seems) .  I can hear only slight resonances during passages that go from very quiet to very loud passages, many instances on Muddy Waters Folk Singer for instance.  This is at fairly loud levels so somewhat understandable considering they have only been treated with PVA.  Surprised how good they sound with minimal panel prep. 
- There is also a general high pitch haze that over lays much music.  Might be related to the first bullet.  When I listen to the panel close-up I hear that same type of high pitch coming out of the edges of the panels, wrapping around to the front or back the high pitch is not noticeable but is still present at all times it seems.  Going to try felt on the edges tomorrow.  Any other suggestions would be appreciated.
- Most troublesome, the general presentation is kind of flat and slightly veiled.  It’s like the sound is coming from the backside of the panel.  Adele’s voice is diffused and coming from a large area... not pin-point like my Tang Bands.  Flipping the panel around seems to slightly improve the sound (maybe!?) but still have the sensation that the sound is emanating from the backside of the panel.  This, I think, is the aspect that leads folks to not enjoying DML panels?!?!  It’s difficult going from my Tang Bands that image so well.  Wonder if this is a function of a wide panel?  Would a thinner (and possibly taller for more output) panel improve this aspect or some other panel size/thickness?!?  Do you guys hear this?  Do you get used to it?  Especially noticeable on close mic'ed (sp) recordings.  Recordings in more open spaces recorded at a distance fair much better… just don’t notice it as much.  Small recording spaces just don’t seem “there”,  is fuzzy and lacks image definition!?  What do you guys think?? 

Can anything be done to reduce this effect? 

Bottom line   
If I can get rid of this “diffused, the sound is coming from behind the speakers), these panels would be absolute leading edge and for flippin’ PEANUTS!  Even if this haze is still present, for the money it’s hard to beat these panels.  The exciters and panels cost less than $30… less than just the crossover components of a traditional 2-way monitor speaker!!!  ABSOLUTELY CRAZY!!!

I’m pretty pumped and having so much fun listening to these so far!  What can I do next to improve the sound?!?  You guys have years of experience and I know that I’m at the beginning of the journey but hope you guys can help the process along as you guys have certainly been there and done that!

Any ideas to improve would be greatly appreciated!!
 
Thanks,
Rich

[zygadr]

OB Newbie, firstly, don't think for a second that a DML will act like laser beam death rays at high frequencies and provide pseudo acoustic imaging tricks that so many audiophiles just can't live without despite all their direct radiator shortcomings.

I find it strange that your attempt at DML 's produces a sound that is ''veiled'' (??????) and ''flat'' (?????). There is something amiss there as DML's are the opposite to this in my opinion.
Also, you are using a SQUARE (  ) panel that is very thick and run by a more or less average exciter.........probably not a good match? Your room size, together with their positioning within that room,  will also have a great effect on how these panels work.

 You say your panel material is pink, and others have mentioned blue?? .
 I came across the light blue stuff recently at the foam supplier and can say that it is definitely NOT the same stuff as VH GRADE EPS that I have been using (it was named ''XPS :  SOVIRA BLUE''???.  I don't know if this other stuff is what is causing anomalies out there, but I wouldn't be surprised. It is definitely NOT ''EPS''.

By the way, the sound DOES come from the back of the panel.......it is supposed to and is what contributes to the magic of panel speakers.OB speakers that are primarily forward firing, are a different ball game, so forget about comparing the two systems and concentrate on improving the DML's.

Once again on the subject of wide versus narrow panels to improve imaging.................you are not dealing with shoe box speakers on stands............the width of the panels do not act in this way (thank God! ).

May I suggest you read ALL of the reviews found on the Podium website(as well as comments throughout this thread) so that you can fully understand that the DML is the only speaker type that can do what other speakers, including panel types, just can not. This is especially evident when compared to the sound of live music, which is what we audiophiles strive for.

Rob.

[Odal3]

OB Newbie

It's fun, isn't it? I'm new to it as well but here are some thoughts.

Are you using the Owens Corning Foamular insulating sheeting boards with the pink panter? I picked up the the 1/2" thickness R-3.0 from Home Depot labeled XPS insulation, film-faced insulating sheeting a few weeks ago. I havent had a chance to prep one with pva yet as many in the thread recommends, but after I read your note I tried just hand holding one exciter to the board. Keep in mind that the one I have hasn't been cut down in size yet so its 8 x 4ft. And yes, I also hear the hazy and flat sound you describe, which is very different from the clear and "vivid" sound I hear using birch plywood. I also want to get the good EPS sound I'm reading about so I'm curious to follow your efforts to see if similar boards can easily be bought in the US as well. 

Using other panel materials I have found that I like slightly larger boards to get some lower frequencies. My 4x3ft panels go to about 60Hz before dropping, but unfortunately only 12k on the high end. Maybe it will be better once I run only 1 exciter vs four. I really  wanted a square panel to work out for the look, but it didn't work out for me.

I like to get the panels off the ground and put two spikes (=nail with round head toward floor/stand) to allow them to move more freely and still support the weight. I found this to sound better in my set-up vs standing straight with the whole bottom edge on the on floor/stand. I also have velcro on the back of one of the exciters holding it in place on the panel stand. The only problem is if the music has really deep bass I get too much vibration so I need to put in a high pass filter. Btw: Anyone has some good tips what's the easiest way is to put in a high pass filter?

I like the stereo image better if I step back a little bit from the panels- maybe 12ft (haven't measured) and have the panels toed in just slightly (not much at all)

[xit]

Hi OB newbie

I hear the same as you in the bads, but is it not the DML that sounds this way ?
If you want to stop theses panel sing from the rear, you can maybe damp it with some acoustic foam
(like the one for speakers) but i think you'll probably loose some output SPL

Here's some explanations from the creator of the podium sound panels:

"Natural sound manifests two types of sound-waves: binaurally correlated and binaurally de-correlated waves. Binaurally correlated soundwaves are highly coherent, and among other things, permit us to determine where a sound source is located. Binaurally de-correlated soundwaves are highly incoherent, and among other things, permit us to estimate our distance from the source, or the nature and size of an acoustic space. The main problem with loudspeakers is their inability to propagate sound with both wave-types. This is an engineered limitation inherent in the mechanical nature of the devices themselves. Conventional cone loudspeakers propagate longitudinal waves. Longitudinal waves are highly coherent and binaurally correlated. Resonating DML type loudspeakers are transverse wave loudspeakers. Transverse sound waves are highly incoherent and binaurally decorrelated. It is simply impossible to propagate transverse waves with a conventional loudspeaker and conversely, it is impossible to propagate longitudinal waves with a resonating panel loudspeaker. No amount of DSP, loudspeaker placement, room treatment or other adjustments will change this simple fact. To reproduce natural sound, both types of loudspeakers are required.
Layered Sound is the term used to describe the process of combining a conventional and a distributed mode loudspeaker, to produce the same audio signal. This combination, when used in the correct configuration, delivers to the listener sound that is clear, spacious, better imaged and more pleasant to listen to

The correct balance between direct and reflected sound is very desirable. When we listen to acoustic instruments in a concert space, we hear a blend of direct and reflected sounds. This combination creates the immersive effect we all enjoy and instinctively recognize as a natural sound. Unfortunately, conventional loudspeakers do not provide good reflected sound due to destructive interference and DM loudspeakers do not provide good direct sound due to their diffuse nature of transmitting sound. Not every loudspeaker is ideal for generating both direct and reflected sounds. However, conventional loudspeakers are well suited for direct sound and Distributed Mode loudspeakers are well suited for reflected sound. By combining these speaker designs according to the principles of Layered Sound, air disturbance patterns are created that physically emulate the sound waves of acoustic instruments, a natural sound. As a result, Layered Sound provides smooth diffusion, clarity and depth in any size room."


so for him,

with our brain and ears,
DML is useful to know the position in depth of a source in a room and give the room infos
pistonic speakers are useful to know the panoramic position of it in the room


hope this helps

[zygadr]

Hi OB newbie

I hear the same as you in the bads, but is it not the DML that sounds this way ?
If you want to stop theses panel sing from the rear, you can maybe damp it with some acoustic foam
(like the one for speakers) but i think you'll probably loose some output SPL

Here's some explanations from the creator of the podium sound panels:

"Natural sound manifests two types of sound-waves: binaurally correlated and binaurally de-correlated waves. Binaurally correlated soundwaves are highly coherent, and among other things, permit us to determine where a sound source is located. Binaurally de-correlated soundwaves are highly incoherent, and among other things, permit us to estimate our distance from the source, or the nature and size of an acoustic space. The main problem with loudspeakers is their inability to propagate sound with both wave-types. This is an engineered limitation inherent in the mechanical nature of the devices themselves. Conventional cone loudspeakers propagate longitudinal waves. Longitudinal waves are highly coherent and binaurally correlated. Resonating DML type loudspeakers are transverse wave loudspeakers. Transverse sound waves are highly incoherent and binaurally decorrelated. It is simply impossible to propagate transverse waves with a conventional loudspeaker and conversely, it is impossible to propagate longitudinal waves with a resonating panel loudspeaker. No amount of DSP, loudspeaker placement, room treatment or other adjustments will change this simple fact. To reproduce natural sound, both types of loudspeakers are required.
Layered Sound is the term used to describe the process of combining a conventional and a distributed mode loudspeaker, to produce the same audio signal. This combination, when used in the correct configuration, delivers to the listener sound that is clear, spacious, better imaged and more pleasant to listen to

The correct balance between direct and reflected sound is very desirable. When we listen to acoustic instruments in a concert space, we hear a blend of direct and reflected sounds. This combination creates the immersive effect we all enjoy and instinctively recognize as a natural sound. Unfortunately, conventional loudspeakers do not provide good reflected sound due to destructive interference and DM loudspeakers do not provide good direct sound due to their diffuse nature of transmitting sound. Not every loudspeaker is ideal for generating both direct and reflected sounds. However, conventional loudspeakers are well suited for direct sound and Distributed Mode loudspeakers are well suited for reflected sound. By combining these speaker designs according to the principles of Layered Sound, air disturbance patterns are created that physically emulate the sound waves of acoustic instruments, a natural sound. As a result, Layered Sound provides smooth diffusion, clarity and depth in any size room."


so for him,

with our brain and ears,
DML is useful to know the position in depth of a source in a room and give the room infos
pistonic speakers are useful to know the panoramic position of it in the room


hope this helps

Yes, ............but as far as I know, Podium have never released a "layered sound" loudspeaker.As a guess, they probably had significant trouble making it work due to the two totally opposite technologies and the sound they produce.

Having attended numerous symphonic concerts, I have never noticed "imaging" as a real event occurring on stage. What I have noticed is the diffuse and homogenous sound field with lots of reflected energy (I actually heard the Tuba notes reflecting off the concert hall roof!!!)and some direct sound..........very similar to the effect of a DML in action.

[j gale]

+1.  So called pin point imaging that some are so fond of is unnatural.It is never heard in live or real music. Having said that I can understand the fondness for it. I like the effect too, but since it is not natural we should not be critical of the panels for not giving us this unnatural feature. If we are honestly looking for close to a real listening experience the DML panels come closest and with the greatest clarity. How the reflected sound is managed becomes very important. My own room is long and fairly narrow. With the panels toed in about 45 degrees about 30" from the back wall (closest edge) and about 18" from the side walls I get a strong centre image. A vocalist sounds very real. My room is fairly lively. I realize that  reflected sound is dominant in producing the experience, but then it is at a live event too. Coming from monkey coffins or horns the panels take time to get used to. I think it takes time to let go of the flaws that we are used to. With the panels I find that I listen to the music instead of listening to speakers. When properly set up the panels are almost unnoticed. Sedge mentioned a difference in presentation between small panels and larger ones. In my opinion 2'x4' is about the smallest size that is useful and then only if something else handles bass. The bigger the panel the more realistic the listening experience. Playing with panels smaller than 2'x4' is a waste of time--again my opinion.

[OB_Newbie]

OB Newbie

It's fun, isn't it? I'm new to it as well but here are some thoughts.

Hey Odal,
Yeah man... I was up late last night (move the panels downstairs way from the family sleeping so I could get more listening time into the wee hours of the morning.  Lots of fun for sure... still hard to believe that such good sound can come from $10 of insulation and $16 in exciters... CRAZY!!

Are you using the Owens Corning Foamular insulating sheeting boards with the pink panter? I picked up the the 1/2" thickness R-3.0 from Home Depot labeled XPS insulation, film-faced insulating sheeting a few weeks ago. I havent had a chance to prep one with pva yet as many in the thread recommends, but after I read your note I tried just hand holding one exciter to the board. Keep in mind that the one I have hasn't been cut down in size yet so its 8 x 4ft. And yes, I also hear the hazy and flat sound you describe, which is very different from the clear and "vivid" sound I hear using birch plywood. I also want to get the good EPS sound I'm reading about so I'm curious to follow your efforts to see if similar boards can easily be bought in the US as well. 

To me honest, I can't say for sure about the 24in x 24in and 1 in thick panels I'm listening to right now is Owens-Corning XPS.  I went yesterday and bought the 3/4in 4x8ft panel of Owens-Corning XPS and just assume that the smaller panels are the same... I took the sticker off right away when I purchased them so only assuming.  But they look and feel like the O-C XPS.  I'll look next time I go to Home Depot and report back to verify.

I don't think I can blame the XPS panels for the haze.  I was not clear about the "haze".  So here goes :
 - 1. The minute I started to listening to the panel there was a different "tone" to the overall sound... hate to use audiophile speak but it would likely be considered as sounding "veiled". not crystal clear and or immediate.   
-  2. Listening to the side of the panels, I hear a higher pitched tone coming from the panel pretty clearly, no bass at all.  When I first started listening to the panels it seemed like I could hear that same "tone" covering the entire soundscape... but I am doubting it now.  This is likely due to the null in the dipole radiation pattern where the front and back lobes for the figure 8 pattern.  Please scratch this notion... want to listen more but I have a hard time saying that this is responsible for the "haze".

"Good" EPS.  I bought the cheap 3/4in, 14 1/2in X 48in white EPS panels from Home Depot first but they are floppy and seem low quality.    I sanded and prepped with Sedge's 1:1 water and white glue but they didn't sound good at all.  Even when you just run your fingers across the panel you hear a really terrible scratchy sound... finger nails on chalkboard.  I just listened to them standing up against a chair with no other dampening (or my boys holding them in free air for me to listen... they LOVED that).  They might be made to sound good with a real frame around them for dampening but it just seems hard to believe with all the crunchy self noise but who knows.   

I'll be on the hunt for better, higher quality EPS but I was just amazed to hear how good the O-C XPS sounded with just Sedge's coating and propped up on a high-back chair.  I was listening at some pretty loud levels and the panel was moving around on the chair and they were only playing above 225Hz!!!!!  I did a quick RTA on them and they play pretty flat to 15K and only needed a 4.5db boost to be flat to 20K!  Not bad right!?!  I personally think they just need a little tweaking... can't get it right from the start... where is the fun in that!!!   

 
Using other panel materials I have found that I like slightly larger boards to get some lower frequencies. My 4x3ft panels go to about 60Hz before dropping, but unfortunately only 12k on the high end. Maybe it will be better once I run only 1 exciter vs four. I really  wanted a square panel to work out for the look, but it didn't work out for me.

Yeah, the 24x24 panels were handy and just a quick test to see how the XPS sounded after the crap cheapo EPS board listening session.  Have to go large for a full-range panel.  But I also wanted to hear how a smaller panel as Sedge commented that the panel sizes and shapes all had a similar sound and since I am not running them full-range (planning on running my OB bass panels end-state) it was a place to start.  Sedge also made a comment about the smaller panels sounding more point source like.  A large panel should act very much like a line array and sound like a giant pair of headphones.  Not that it is bad (I have the parts for a OB line array using the PE buyout Fountek 3 in full-ranger), but wanted to start small and see what can be done to integrate the DML panel and OB subs in a reasonable sized speaker.

I like to get the panels off the ground and put two spikes (=nail with round head toward floor/stand) to allow them to move more freely and still support the weight. I found this to sound better in my set-up vs standing straight with the whole bottom edge on the on floor/stand. I also have velcro on the back of one of the exciters holding it in place on the panel stand. The only problem is if the music has really deep bass I get too much vibration so I need to put in a high pass filter.

I have my panels on a chair so my ears are about 2/3 up the panel high... can't see over the panels.  Like you, I got vibration when there was a lot of bass so the best I got out of it was a sock about 5 in. from each corner.  I was able to play louder and cleaner with a little loss in high-frequencies.  I also put a thin rubber band on the chair back where the panel met the high-back.  That reduced panel vibrating against the wood chair back. 

Btw: Anyone has some good tips what's the easiest way is to put in a high pass filter?

You could just buy some cheap capacitors for a 6db slope and test by ear to get what you want.  But might be best to pick up a pair of Harrison Labs electronic x-overs if you know the target x-over freq (less then $30 at PE).  That will get you a steeper 12db slope and is cheaper than buying caps and coils.  If you can get impedance and freq. response graphs you could easily model the Xover and expected results.  I really like Jeff Bagby's Passive Crossover Designer (PCD).  VERY accurate and little learning curve if you have background in XO design.  Highly recommended!

I like the stereo image better if I step back a little bit from the panels- maybe 12ft (haven't measured) and have the panels toed in just slightly (not much at all)

Yeah, when I moved them downstairs to the large living room the sound improved.  They need more space than my Open Baffle panels!!!  Arg.

[OB_Newbie]

Hi OB newbie

I hear the same as you in the bads, but is it not the DML that sounds this way ?
If you want to stop theses panel sing from the rear, you can maybe damp it with some acoustic foam
(like the one for speakers) but i think you'll probably loose some output SPL

Here's some explanations from the creator of the podium sound panels:

"Natural sound manifests two types of sound-waves: binaurally correlated and binaurally de-correlated waves. Binaurally correlated soundwaves are highly coherent, and among other things, permit us to determine where a sound source is located. Binaurally de-correlated soundwaves are highly incoherent, and among other things, permit us to estimate our distance from the source, or the nature and size of an acoustic space. The main problem with loudspeakers is their inability to propagate sound with both wave-types. This is an engineered limitation inherent in the mechanical nature of the devices themselves. Conventional cone loudspeakers propagate longitudinal waves. Longitudinal waves are highly coherent and binaurally correlated. Resonating DML type loudspeakers are transverse wave loudspeakers. Transverse sound waves are highly incoherent and binaurally decorrelated. It is simply impossible to propagate transverse waves with a conventional loudspeaker and conversely, it is impossible to propagate longitudinal waves with a resonating panel loudspeaker. No amount of DSP, loudspeaker placement, room treatment or other adjustments will change this simple fact. To reproduce natural sound, both types of loudspeakers are required.
Layered Sound is the term used to describe the process of combining a conventional and a distributed mode loudspeaker, to produce the same audio signal. This combination, when used in the correct configuration, delivers to the listener sound that is clear, spacious, better imaged and more pleasant to listen to

The correct balance between direct and reflected sound is very desirable. When we listen to acoustic instruments in a concert space, we hear a blend of direct and reflected sounds. This combination creates the immersive effect we all enjoy and instinctively recognize as a natural sound. Unfortunately, conventional loudspeakers do not provide good reflected sound due to destructive interference and DM loudspeakers do not provide good direct sound due to their diffuse nature of transmitting sound. Not every loudspeaker is ideal for generating both direct and reflected sounds. However, conventional loudspeakers are well suited for direct sound and Distributed Mode loudspeakers are well suited for reflected sound. By combining these speaker designs according to the principles of Layered Sound, air disturbance patterns are created that physically emulate the sound waves of acoustic instruments, a natural sound. As a result, Layered Sound provides smooth diffusion, clarity and depth in any size room."


so for him,

with our brain and ears,
DML is useful to know the position in depth of a source in a room and give the room infos
pistonic speakers are useful to know the panoramic position of it in the room


hope this helps

Thanks for the post XIT!  I listen to OB panels and enjoy the reverberant nature of a dipole speaker.  What I hear *seems* to be different and related to the "veiled" sound I hear.  Its like the sound originates from behind the panel... like the exciter is the sound source and trying to play the music through the panel and is slightly muffled in the process.  So I thought that if I flipped the speaker and have the exciter in the front facing me it would get rid of this effect and make the sound more live and less veiled.  But when I flipped them they sounded almost the same!!  Sound still seemed to originate at the rear of the panel.   A slight improvement possible as the exciter is receiving the signal and is responsible for transferring the signal to the panel.  But this is only a very slight improvement and doesn't really change the "veiled" sound characteristic. 

BTW - I do have to say that after listening to the panels for a few days now I don't hear that veiled sound as much as I sit, listen and type tonight.  This is not uncommon... you adjust to tonal differences over time.  If I went back to my open baffles for some time (or any other speaker) and came back again to the DML's I would hear the differences and have to get adjusted again.  I want to validate that but right now I'm immersed in panel sound.    

[Odal3]

Got a couple off home improvement projects I need to complete before experimenting more with the panels. I still suspect the muffled sound you are hearing is the xps board you are using. I wonder if some shellac or something similar would help. ?? At least that is what I will try when I have a chance.

[OB_Newbie]

+1.  So called pin point imaging that some are so fond of is unnatural.It is never heard in live or real music. Having said that I can understand the fondness for it. I like the effect too, but since it is not natural we should not be critical of the panels for not giving us this unnatural feature. If we are honestly looking for close to a real listening experience the DML panels come closest and with the greatest clarity. How the reflected sound is managed becomes very important. My own room is long and fairly narrow. With the panels toed in about 45 degrees about 30" from the back wall (closest edge) and about 18" from the side walls I get a strong centre image. A vocalist sounds very real. My room is fairly lively. I realize that  reflected sound is dominant in producing the experience, but then it is at a live event too. Coming from monkey coffins or horns the panels take time to get used to. I think it takes time to let go of the flaws that we are used to. With the panels I find that I listen to the music instead of listening to speakers. When properly set up the panels are almost unnoticed. Sedge mentioned a difference in presentation between small panels and larger ones. In my opinion 2'x4' is about the smallest size that is useful and then only if something else handles bass. The bigger the panel the more realistic the listening experience. Playing with panels smaller than 2'x4' is a waste of time--again my opinion.

Hey Rob and JGale,
Been listening to the panels and still really enjoying them... moving them downstairs last night to listen while the family slept made for a noticeable improvement (listening to them full-range at the moment).  The panels seem to need even more space than open baffles with traditional dynamic loudspeakers.  Tonight the panels seem to be really opening up and are more clear and even more dynamic.  Its still really early to make judgments but am using the forum to capture the process as I progress... hope you don't mind.  There are probably others that are following along and experimenting as well and might be experiencing and wondering about the same things (did I do something wrong or is this a DML panel at play).  Like Odal3 said... its fun... REALLY enjoy listening to these panels!!!           

On imaging, I guess it depends on the venue and how the performance is recorded.  I don't listen to much classic music these days but can certainly agree that listening to symphonic music from many rows back (or first row for that matter) will be hard to make out the composition of musicians in the soundscape with such a huge venue and mix of direct and reflected sound. 

But for small venues with sparse instruments... imaging is very real.  Now I'm going out on a limb here, but using the opening track on Cowboy Junkies Trinity Session as an example, I believe the bass player is to the right of Margo a few feet behind her and keeping time with his feet (picked up by the mic through the old wood plank floor).  The drummer to her left and further back than the bass.. 6-7, 8 feet?!?  I can hear the heat register to the far back of the church 30-40 feet?!?  This makes up the original acoustic space and recreated by the recording.  Its not too complicated honestly, its just being able to tell where the musicians were positioned in the recording... that's all.  Some recordings its easy to tell, others is very difficult or NOT possible (thanks electronically composed pop music).  As listeners we don't have a clue to the recording venue.  But on good recordings I can hear the acoustic space when its well recorded and reproduced by my audio system.  To me its an enjoyable part of the listening experience.  Whether the recording captured it accurately or not, what is reproduced in my system adds to the realism of music playback.

Some folks might not enjoy or care as much for that particular characteristic and that is perfectly fine.  Be it the music that he/she listens to or what can be reproduced by their audio system or the information recorded on the CD or LP.  SOOOoooooo many trade-offs and design decisions to find the sound that is most enjoyable for that particular listener.  That is why we all tinker with DIY audio.    

Like I said, lots more music to listen to too get better acquainted with these panels.  its early to make judgments and really understand the capabilities and design decisions that can be made.

For instance, has anyone tried making single exciter, smaller panels; say 3 - 24in x 24in panels ( ) stacked to make a combined 2 ft x 6 ft panel?  Then EQ the bass (and treble) to get a decently flat response similar to Rodger Russel's line array using small Vifa full-range speakers?  The increased surface area should provide a panel that doesn't need to be excited as much, increase in sensitivity and power handling while still maintaining a single exciter to single panel configuration?  Should be even MORE dynamic and clear with the increased surface area and number of exciters.  A DML stack might begin to behave more like a line array but reading others comments about sounding like a big set of headphones and the sound seemingly carrying longer distances (with less loss in dB) are common characteristics of traditional line array config.  I picked up full sheet of XPS and had it cut into 2 - 2 ft. by 6 ft. panels and going to try that first but kinda pumped to try a stacked array of panels.  I have a feeling that it will enjoy improved dynamics, speed and effortlessness of a common line array.  This hobby is soooo addicting...