[sedge]

Ob_newbie
For quick testing I use 1inch masking tap to suspend the panels at one central point,but for long term listening I use  1in by about 4inches old foam dish sponges which are softer than New ones (starting to sound a bit weird now)they glue on easily with pva ,this way does not adversely effect the sound quality or impede the movement but best of all ,it will not buzz or transfer the vibrations to make something else buzz,I eventually intend to build an adjustable support which clamps on to the foam for easy changing of the panels.
At the moment ,anything under 5ft I hang from some old uplighters I have,in the past I have used  foam to hold an 8ft panel between the floor and ceiling,had to use bluetak to stop them walking across the room.
At the moment the 5ft 6in panel is sitting on a small dish sponge and resting slightly back on another at the very top ,no buzzing or noises so far heard,the panel moves freely .
Zegadr used to like the large panels(vh xps)but I don't remember him ever using any form of suspension?
If you freely hang the exciter on the panel and then freely suspend the panel you should end up with a panel that outputs down to 20hz and below,this will not play loudly so close mic or electronic bass will need support from an extra LF unite, for natural acoustics switching in and out the LF driver makes little difference.(if I remember rightly).
Using EQ to boost the LF on loud electronic bass or close mic music will cause the exciter to bounce around heavily and overheat,the panel will also visibly shake ,this shaking can be heard as a rustling sound ,so please everyone keep your exciters and the panels within their limits for good sound and longevity.
Steve
PS
From experience ,using a LF unit such as TLS OR whatever ,in the 300HZ or so down helps the panel drive the room in its most week area(this is if you are using a low powered 20watt or so exciter) using a large and powerful exciter could help fill in this area but with added mounting and other such problems.

[OB_Newbie]

Hey Sedge, old foam... wasn't expecting THAT!   

The issue I had with the large unsuspended panels where, what you called, a drum resonance.  I had mine sitting on socks and leaning against a high-back chair with large rubber bands so thought that more suspension may be needed given what I had experienced with my only large pair of panels?!?

I'm not a huge fan of DML bass at this point but based on at least 1 of the white papers the lack of suspension causes the large dip followed by the high peek so there is some interest in using suspension to even out some of the low frequencies.  I am concerned about the impact on the sound quality with more suspension.  From my experience, with adding suspension I felt that there was a loss of "air" and detail.  I have run my open baffle bass bins with my panels but for the large panels I want to try to create a more full-range panel with no additional LF assistance and a bit more suspension to smooth the low frequencies.

In regard to EQ, I think its important to point out that EQ is best used to even the response.  This has been the best improvement I have had with my panels.  In all cases, the low frequencies are cut sharply (24dB) at 40Hz on my largest panels; higher on small panels of course.  This is on XPS but I also thought that it improved birch panels as well; especially to boost high frequencies otherwise ply is more smooth than XPS.

[sedge]

OB_newbie
I wouldn't want you to think I'm tight,and that I only use the old washing up pads because when the other half throws them in the bin they are FREE 
The very large panels do suffer from panel resonance in the lower end ,a CHEAP  trick I tried some years ago was to glue a piece of wood down the centre of the lower half of the panel probably no more than 18 inches long ,I had the idea of using this as a mounting point clamped to the floor.
If I remember right  it didn't effect the sound of the panel too badly as the rest of the panel was free floating,I didn't follow this up as I wasn't that interested in a 8x3ft panel in my small room ,small panels don't seem to suffer from this problem.
It's just a thought but it might do the job of damping the resonance on very large panels without interfering with the overall sound too much ?
Steve

[sedge]

OB_newbie
Have to say that all the white papers I have read so far ,although interesting have not mentioned much about how to achieve the best sound quality,it's usually more about exciting as many nodes as possible to produce as much sound (noise) as possible !
Clamping the panel in a frame (nxt) sort of amplifies the nodes ,adding weights to the panel changes the shape of the node pattern ,adding a roll surround dampens the panel and lowers reflections (nodes).
All of these things have a knock on effect a sort of catch 22 situation,large panels have their problems ,small panels have different problems ,different size panels give different room responses ,moving the panel to another room can totally change the sound.I could go on ,but will leave it there for now as it will only give me a headache.

So far ,for me anyway,the best sounding panel is the free floating poly type panel,with a little help from my TLS to fill in any dips in the room response below 300hz,although I do have the equipment to EQ the panels I must say I have not found it necessary.
The slight mods I do use on the panels,don't have bad knock on effects,if they did I wouldn't use them.

Using multiple panels per channel could help fill in the dips ,especially if you had different exciter positions on the panels, to spread the nodes on the panel and in the room,cancelling the cancellations (which is basically what I am doing with the TLSs).
I've got to the stage now where I just don't want to do any more testing of panels,all I want to do is set up my final system and listen to music,as I'm typing this I'm thinking of other ideas 
Steve

[Odal3]

I also find that the bigger panels move more and requires some more work to not color the sound. Suspending them has worked the best for me. I put two nails in the side abut 5cm from the top so nothing touches the front or back side. I attach a wire to the nails so the panel can move freely in all directions. This is building on the idea of the paper we discussed a while ago with all the theoretical models.

If standing on the floor is a must, the solution I use is putting two nails with rounded heads on the bottom to allow some movement. The round nail heads stands on cedar blocks with moongel underneath.

The difference you see in the LF is huge using these methods  (in particular the suspended) and it really takes out some of the big peaks and dips. If I just have the panels standing on the floor with nothing underneath the frequency response below 100hz has two large peaks and two lare dips.

[OB_Newbie]

OB_newbie
I wouldn't want you to think I'm tight,and that I only use the old washing up pads because when the other half throws them in the bin they are FREE 
The very large panels do suffer from panel resonance in the lower end ,a CHEAP  trick I tried some years ago was to glue a piece of wood down the centre of the lower half of the panel probably no more than 18 inches long ,I had the idea of using this as a mounting point clamped to the floor.
If I remember right  it didn't effect the sound of the panel too badly as the rest of the panel was free floating,I didn't follow this up as I wasn't that interested in a 8x3ft panel in my small room ,small panels don't seem to suffer from this problem.
It's just a thought but it might do the job of damping the resonance on very large panels without interfering with the overall sound too much ?
Steve

Ha, loved this post!  Coming from a guy who uses old athletic socks to rest my panels on I ought to have no opinion.  The used foam pads seem better than my old socks!!

I have to think over the suspension options.  I have seen different foam material used... the thick foam that is used to isolate water pipes and even the foam used in swim noodles that kids use so this seems like a popular material as it damps the panel as opposed to Velcro or felt that suspends the panel but not really damp it!? 

So for me... if you want a bit more dampening, it seems you might want to use foam or some other similar material.  If a builder wants a little less damping use Velcro or some other similar material (stretchy would seem to be best).  Case in point, light string would offer little to no damping while wider pieces of foam top and bottom (dare even sides) provide the most damping yes?!?

[OB_Newbie]

OB_newbie
Have to say that all the white papers I have read so far ,although interesting have not mentioned much about how to achieve the best sound quality,it's usually more about exciting as many nodes as possible to produce as much sound (noise) as possible !
Clamping the panel in a frame (nxt) sort of amplifies the nodes ,adding weights to the panel changes the shape of the node pattern ,adding a roll surround dampens the panel and lowers reflections (nodes).
All of these things have a knock on effect a sort of catch 22 situation,large panels have their problems ,small panels have different problems ,different size panels give different room responses ,moving the panel to another room can totally change the sound.I could go on ,but will leave it there for now as it will only give me a headache.

So far ,for me anyway,the best sounding panel is the free floating poly type panel,with a little help from my TLS to fill in any dips in the room response below 300hz,although I do have the equipment to EQ the panels I must say I have not found it necessary.
The slight mods I do use on the panels,don't have bad knock on effects,if they did I wouldn't use them.

Using multiple panels per channel could help fill in the dips ,especially if you had different exciter positions on the panels, to spread the nodes on the panel and in the room,cancelling the cancellations (which is basically what I am doing with the TLSs).
I've got to the stage now where I just don't want to do any more testing of panels,all I want to do is set up my final system and listen to music,as I'm typing this I'm thinking of other ideas 
Steve

I most certainly agree with you here Sedge.  They are more focused on the academics of the technology and not really sound quality.  The single paper that did have a section on sound quality (I was very excited to first see it) compared it to a set of Apple computer speakers and the DML panel was teenie tiny and make of some thin, bit soft/over damped plastic material.

Yes, there is no single "best" approach... only trade offs and sets of compromises.  Yet what has amazes me is that despite the different shapes, sizes, materials, suspension methods most enjoy them and believe that theirs perform well.  So long as you don't do something strange to botch the whole thing up, the performance is generally quite good and they are enjoyable to listen to.  That is impressive... can't say they same about other speaker technologies!

I do get where you are at with your TLS.  I am still not sold on DML bass.  It is "faster" and tighter and free of boom that you get from a typical boxed speak but still does not surpass even a simple H frame sub using a cheap woofer such as the Eminence Alpha-15A, MCM Audio Select (55-2963) or even the cheap $22 GRS 15PF-8 performs very well in OB and all have a pretty small form-factor considering they are 15" woofers.   (yes, selling OB)   

At some point, I want to formally combine a OB slot loaded woofer with a taller and thinner DML panel.  Should be cheap, simple to build and sound good.  Hmmmm... questioning the large panels now... what to build next!! 

[OB_Newbie]

I also find that the bigger panels move more and requires some more work to not color the sound. Suspending them has worked the best for me. I put two nails in the side abut 5cm from the top so nothing touches the front or back side. I attach a wire to the nails so the panel can move freely in all directions. This is building on the idea of the paper we discussed a while ago with all the theoretical models.

If standing on the floor is a must, the solution I use is putting two nails with rounded heads on the bottom to allow some movement. The round nail heads stands on cedar blocks with moongel underneath.

The difference you see in the LF is huge using these methods  (in particular the suspended) and it really takes out some of the big peaks and dips. If I just have the panels standing on the floor with nothing underneath the frequency response below 100hz has two large peaks and two lare dips.

Hey Odal, interesting on suspension topic.  Do you get double peak/dip with the very light suspension provided by the wire and nail approach? 

I was thinking mine needed more suspension but they are more damped than yours and similar to Sedge's I would say.  I get a somewhat large single peak/dip and (peak around 31Hz, dip around 45(ish)Hz but the peek is not much above the rest of the freq. range so I really don't hear it that much... really only on source material that has heavy content at that particular frequency.  Very narrow peaks/dips tend to be hard to hear anyway no matter where they are int eh audio spectrum.  DML loads the room differently anyway so does not have the boom a typical box speaker would have with a peek which measures the same... another contributing factor that tends to lessen this flaw in DML low frequencies.

Anyway... its been quiet lately on this thread so its good to hear from everyone!

[Odal3]

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.

[sedge]

OB_newbie
I think my used foam pads might smell better too   
Your old athletic socks could also be affecting the the air  and detail in your panels 
But seriously,resting the panel on the floor or even foam will have an effect on the sound ,just touching the panel with your fingers is enough to fill in those dip or even move them around ,if you stand in front of the panel and clasp the edges while playing pink noise you can readily hear the sound close in to the middle area ,using a light and soft foam suspend from a single point allows the panel to shake freely ,is robust and allows you to clamp the panel on to most things with a washing line peg,heck! you could even use a washing line
Time to go to bed.
Steve

[dbishopbliss]

I took measurements of my first panel.  The panel is 24x24x1 inch XPS.  It is untreated and the exciter has very little break-in.  The panel is mounted in a frame made of 1x3.  The frame is 6 feet high and 26" wide with a couple of braces.  The panel is sitting on a sponge on the bottom and held in place with a piece of gaffers tape at the top. The audio interface is a Focusrite Saffire Pro 40 driving a Mauro Penasa's MyRef Rev. C amp. I only measured from 100hz to 18Khz because I have a subwoofer that I plan on using with the speakers.



 

[dbishopbliss]

As a comparison, here is a Fostex FE127E in a Metronome enclosure using the same amp and position in the room.

[Odal3]

I always wanted to hear the metrome - that looks really good!

The DML measurements looks pretty much like a typical DML frequency plot. In my experience it's difficult (impossible ??) to get the super flat output as well designed drivers get. The DML panels tend to drop in the HF (but as you can see in the thread when treated it can be extended much higher). However, the sound presentation of the DML panel and box speakers are very different and some people like it and others prefer the pin-point defined sound. I really like it because it produces a very "unconstrained", "open", "uncolored" type of sound - just like in a concert hall or live performance type of way. Another advantage is that it works much better with the room regardless where you are situated and can work much better in an untreated room.

Try this: play TWO panels in stereo and walk around in the room both sideways and back and forth. Try even to stand behind the speakers. As you will find out the sound changes very little.

But, before moving on you got to treat the panels. When I played the panels raw, I didn't like them either - it sounded like the sound came through a pillow and not very clear. Get some glue on them, and you will hopefully like them better. I actually still like the wood birch panels the best, but I believe I'm almost alone in that corner since most prefer the XPS panels (of course I'm convinced the reason why OB_Newbie et al don't like them is because they didnt' implement it correctly  )

[Odal3]

...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.

Big success - wife like the stained "skinny" and tall version a lot!!!!  Now I'm on the hook to comlete the second one quickly. Need to get some pictures. Just for clarification - I only stained the front side and not the side where the exciter is mounted.

So how do they sound - they sound quite OK. I do have to say that I like the sound of the wider panels better since it has some more impactful bass, but since I will play them with a sub it will be OK. And since the panel doesn't move/vibrate as much I think it improves in other areas. They get down to about 130hz and then they drop ~15db and then stays roughly flat at that level to about 20hz. I'm interested to see how the bass turns out when playing stereo. The stain actually improved the HF. Need to properly mount the exciters before doing more measurements.

BTW: While waiting for the stain to settle, I finally took the time to prepare the 2x2ft pink panter XPS panel that I have had for a while because I think I was the one who "messed" up previously  with my XPS panels so I wanted to give it another shot.

[dbishopbliss]

I always wanted to hear the metrome - that looks really good!

I really like my metronomes.  I have brought them to a couple of audio meets where people who didn't like the Fostex in other enclosures thought they sounded really nice.

But, before moving on you got to treat the panels. When I played the panels raw, I didn't like them either - it sounded like the sound came through a pillow and not very clear. Get some glue on them, and you will hopefully like them better.

Don't worry, I plan on trying lots of things and measuring each change.  This way I can have documentation and empirical evidence of what changed.  I know measurements don't really tell you how something sounds, but at least I will know what changed rather than guessing. Also, I think others will be interested as well.

I have another panel that I have treated with shellac that is drying. I know lots of people use the glue mixture, but I was thinking that shellac is a very hard finish so it should work well.  After thinking I thought of something new I read earlier in this thread that people have used shellac and like it, so I guess no discoveries. 

QUESTION: Should I treat both sides?  The answer is in this thread somewhere but I'm feeling lazy.

So, here are the experiments I plan on running:

• Untreated 24x24x1 XPS
• Shellac'd 24x24x1 XPS
• Untreated 24x22.8x1 XPS (this is the ratio recommend in the white paper reference earlier in the thread)
• Shellac'd 24x22.8x1 XPS
• Untreated 24x14.8x1 XPS (golden ratio)
• Shellac'd 24x14.8x1 XPS

Then, if I'm feeling up to it, I may do the same thing with plywood.

[Nickolay V]

Exactly my thoughts.

I noticed Tectonic uses a tweeter with their DML's, so even the pro's have an issue with high frequencies.

I've really given some thought to make an updated version of my 4 panel DML using high power exciters. Last night I did a quick Photoshop on my previous prototype and took out the feet. My Wife still "hates" the look of it. I guess I'm beating a dead horse.

Jack

I apologize to the community, but I think the theme NXT  not so topical
We studied and tested many NXT speakers (include Tectonic) and finally we came to the following solution: The best of the best sound quality solution  is  vertical line array from  2-2.5" Balanced Mode Radiator Drivers (BMR) with sub-bass section in each L & R  channel.
Like this well known K-Array products (with usual mini drivers)  http://www.k-array.com/en/portable-systems.html
As sub-bass we successfully use subwoofers ( 20-200Hz) with SERVO control
8 or 18 BMR  drivers  section (4ohm resulted) work from 150Hz .

[OB_Newbie]

I apologize to the community, but I think the theme NXT  not so topical
We studied and tested many NXT speakers (include Tectonic) and finally we came to the following solution: The best of the best sound quality solution  is  vertical line array from  2-2.5" Balanced Mode Radiator Drivers (BMR) with sub-bass section in each L & R  channel.
Like this well known K-Array products (with usual mini drivers)  http://www.k-array.com/en/portable-systems.html
As sub-bass we successfully use subwoofers ( 20-200Hz) with SERVO control
8 or 18 BMR  drivers  section (4ohm resulted) work from 150Hz .

Hello Nickolay,
It sounds like you have spend much time building, testing and listening to DML panels.  I'm really curious what panel materials, panel sizes and exciters have been used during your testing?

[OB_Newbie]

OB_newbie
I think my used foam pads might smell better too   
Your old athletic socks could also be affecting the the air  and detail in your panels 
But seriously,resting the panel on the floor or even foam will have an effect on the sound ,just touching the panel with your fingers is enough to fill in those dip or even move them around ,if you stand in front of the panel and clasp the edges while playing pink noise you can readily hear the sound close in to the middle area ,using a light and soft foam suspend from a single point allows the panel to shake freely ,is robust and allows you to clamp the panel on to most things with a washing line peg,heck! you could even use a washing line
Time to go to bed.
Steve

LOL... the socks most certainly are affecting the air; in the room anyway...       

I may try the foam suspension... have to run out to home improvement stores in the area tomorrow when we arrive back home.  If I can find some foam that works well that will be my first option.  On the topic of suspension, has anyone tried using a light fabric around the entire panel; acting to not only lightly suspend but also lightly terminate the edges?  I don't recall if its been used...

[OB_Newbie]

I really like my metronomes.  I have brought them to a couple of audio meets where people who didn't like the Fostex in other enclosures thought they sounded really nice.

Don't worry, I plan on trying lots of things and measuring each change.  This way I can have documentation and empirical evidence of what changed.  I know measurements don't really tell you how something sounds, but at least I will know what changed rather than guessing. Also, I think others will be interested as well.

I have another panel that I have treated with shellac that is drying. I know lots of people use the glue mixture, but I was thinking that shellac is a very hard finish so it should work well.  After thinking I thought of something new I read earlier in this thread that people have used shellac and like it, so I guess no discoveries. 

QUESTION: Should I treat both sides?  The answer is in this thread somewhere but I'm feeling lazy.

So, here are the experiments I plan on running:

• Untreated 24x24x1 XPS
• Shellac'd 24x24x1 XPS
• Untreated 24x22.8x1 XPS (this is the ratio recommend in the white paper reference earlier in the thread)
• Shellac'd 24x22.8x1 XPS
• Untreated 24x14.8x1 XPS (golden ratio)
• Shellac'd 24x14.8x1 XPS

Then, if I'm feeling up to it, I may do the same thing with plywood.

Hey dbishopbliss, most of us could respond with more certainty with the water:PVA treatment but for shellac it a bit of an educated guess.  The water:glue treatment goes on like water and is very thin so in my opinion, 1 coat of Shellac should be more than enough in my opinion.

Have any of the regulars tried shellac on XPS???

[sedge]

OB_newbie
As a mater of fact I do at this very moment have a 10 x 12in shellac coated xps panel in my room ,I made this one a couple of month's ago ,to my ears it sounds too damped and didn't seem to harden to well ,even after a month,I will hook it up again and see if still sounds the same,might even take a pic.
I originally used to coat 3mm cardboard with shellac to try to stop it sounding like cardboard ,it helped to a point but also made it heavier,not what I wanted,looks like it's done the same to the xps.
As for applying a fabric surround ,i think you already know what my answer would be, but maybe you should just try it an see what you think.
The designer of the podium made a curious statement that the panel should ring like a bell !,at the time I thought that was a bit odd,didn't seem to quite ring true to me   but maybe he just meant his panels should have the edges free floating like the Bell ?
By the way looked in your thread on parts express ,looks like you are getting a lot of interest ,well done , I am sure zygadr would have been overjoyed at the spreading of the word 
Steve