[Odal3]

OZZIOZZI
The best method is to buy a few exciters and just try them on a couple of different materials and see what you think. It's rather cheap to experiment unless you use expensive panel materials.

As can be seen from this thread, there are many ways to get good sound with DML. I agree with Pol's statement that larger  area definitely give you better low end. However, I tried some larger panels but they were visually too large for my room so I have been using smaller panels with a sub instead. I have been more than happy with the result.
There have been a few others that have also posted good results as well. I wouldn't go too small though since you would then have to cross them too high and miss out on the excellent DML bass. 150 -200 is IMO too high unless you have something like stereo OB subs standing just next to the panels. I good compromise for me has been 2 x4 ft panels. I can't remember the exact cross over point I have at the moment but I think it's around 50hz.  I currently also have an even smaller pair for the family room only used for TV and movies. To meet WAF they are only 2 x 2 ft coupled with a single HT style sub. It works OK for movies but I do miss better bass when playing music.

Best of luck and have fun!

[Odal3]

Hello,
Yes, it's quite a long time since my last post, and no, I moved to Madagascar, so I sold my one piece stereo panel, and I have rebuild a tryptic... 5m² LOL, (yes! I'm single, in a wood cabin , in the wild)

That looks like an amazing set-up. I never tried a corner like that before. How do you like it vs having it in the middle of a wall or more out in the room?

[OZZIOZZI]

Odal3 said There have been a few others that have also posted good results as well. I wouldn't go too small though since you would then have to cross them too high and miss out on the excellent DML bass. 150 -200 is IMO too high unless you have something like stereo OB subs standing just next to the panels

I was planning stereo OB subs anyway and I have some 12" woofers suitable for OB (Qts 0.71) that will run 31Hz -> 120Hz, two octaves is pretty good range for a woofer without running into directional or H-frame resonance issues. I was thinking H- frames for compact bass. This would match with a panel of around 16" wide x 20" high ( could stretch higher ).  How do those dimensions sound ?  That is compact enough for me.

Pol_bct  What SPLs are you running? I *think* oyou are saying that smaller panels will not play loud or Low enough. I have an all- in- one stereo NXT panel sold by Logitech driven by its own 3W/ ch internal amp. That is loud enough for most purposes and I find myself turning it down at times. It is extremely clear and extends to high frequencies. Of course the bass is limited, but it does nice mid- bass. It is about 6" x 14". I have a pair of thrift-shop TDK NXT panels that are about 8 x 10". They are designed to be used with a sub running up to about 150hz. They sound OK supported by a single sub. I was just hoping to get slightly higher SPLs to give me a bit of overhead for just the impulse you have mentioned, drum rim shots, cymbals etc. BTW what do you do to reduce the background jungle noises? I guess they are no worse than a wife and kids or suburban lawn mowing etc BTW I had considered the 2" BMR speakers in a line array, but I will try my panels first.
OZZIOZZI

[pol_bct]

That looks like an amazing set-up. I never tried a corner like that before. How do you like it vs having it in the middle of a wall or more out in the room?

Simply that this puts out the sound in a PI steradian, this explain partly the bigger bass slam I get, no more need for a sub...

I listen to them with an old NAD C340 but never goes above 20W, it's already very loud, with 12 exciters all together

POL

[sedge]

Fidel costar
On page 90 there is a reply 1791 from WIRES which is very informative ,it is the link to Google/patents/us6904154,if you also follow some of the links at the bottom of this patent you can find some very interesting old patents some going back to the 30s.
Hope this is of some help.
Wires
A little late but Thank you for posting this ,some great information .

Steve

[j gale]

sedge, It's been awhile since you posted. Any new developments?

[sedge]

J Gale
I have been a little distracted with births deaths and weddings,so no new developments ,hopefully 2017 will be more normal .
Steve

[sedge]

J Gale
I have though, read a lot of the old patents from WIRES post,one of them us3236958 A is very similar to my ply panel,this was patented in the early 60s (it seems I have re-invented the wheel again)could have saved my self a lot of trouble if I had read this in the 70s or even heard them,sound boards have been around since the late 20s at least,seems no one took them seriously(no change there then).
Another thing that I thought was interesting ,was shelley katz and his, layered sound , using a separate drive unit to produce longitudinal sound waves to blend in with the transverse waves produced by dml panels,this I think is essential for hard rigid panels ,shelley states that it is impossible to propagate longitudinal waves with a resonating panel loudspeaker,sticking my neck out ,I would say that the panel radiates directly longitudinal waves from the area of the exciter but not as efficiently as the transverse waves on the panel,you do get beaming from the exciter area.
As for the less rigid panels ,as most of mine are,they radiate more from the central area and less from the panel area ,the less rigid and thinner you go,this is my way of blending the sound without using a separate driver.
The ear does very strange things,I know my ply panels put out plenty of hf up to and above 20k but they tend to sound a bit lifeless, very good but something is missing,I thought this when I heard the podiums first launched ,as well as other DML s I had heard,at first they sound really good but then after a little while you start to think mmmmm something is missing.
For pro use say an acoustic guitar for instance on stage does not necessarily need depth and space and imaging but an accurate reproduction of the guitar.
But our home audio is a different matter we need to hear and feel ,almost ,the depth and the ambience ,this is where I feel rigid dml alone has a problem,they radiate from a very large area on the big panels,we think the sound is very good but our ears are very annoyingly saying that something isn't right,our ears are very sensitive and our brain is trying to sort it all out,wether this harks back to when we used our ears to protect us from danger or to find our prey .
That's enough of that,anyway,getting back to thinner lighter panels ,the art of finding or designing a panel that combines dml and direct radiated by blending the efficiency of the two was my goal,but adding a second driver could be the easy option as you wouldn't lose the low end output,I'm talking single exciters per panel here.
Hopefully this is something for everybody to think hard about as it is very important.
Hope this has been helpful after my long break.
Steve

[OZZIOZZI]

Recently I acquired a TDK/NXT system consisting of a powered sub (including L + R amps) and two satellite speakers which were NXT flat panels. The right one had a slight buzz that was set off by certain midrange frequencies although its low and high frequencies were excellent. I couldn't resist opening up this speaker as I figured I could not listen to it in that condition. I thought you all might be interested in its construction.
1. Perforated metal front and back.
2. Aluminium honeycomb panel covered both sides by thinsolid cardboard or thick paper that seemed rigid when tapped with a fingernail. Thickness around 4 mm .
5. Panel suspension all around was black rubber foam about 2-3 mm thick, like weather seal for doors. Very thin foam strip at top, bottom and both sides between back of panel and frame.
6. Exciter rigidly mounted to rear of frame. At approx Monacor NXT position 1.

After replacing the foam I re-assembled the speaker, plugged it into system and played some more music. It matchedthe left speaker and sounded pretty good. Panels were about 20 X 25 cm (8 X 10"). I judged XO point to sub at around 100-150 Hz. They produced a very clear centre phantom image and stereo spread.

Regards
OZZIOZZI

Hope this inf helps with panel building.

[sedge]

Ozzi
Smaller panels do have a much better central image and space,but the down side is they loose the large scale performance of of the larger panels ,still not shure which I will finally end up using ,maybe just keep rotating them if and when I feel like it,it's that easy.
Some pics of the inside of the TDK panel would be good if you can,if you go into my gallery under  pics you will see a 2mm approx 12x9 inch Poly panel with the exciter mounted on to a wood stand,it can be they easy .
There are a few others in the gallery that might be of interest.
I find a 10 watt exciter more than enough to drive small panels,but don't be tempted to use a lower wattage,with proper treatment to the panel I have had no problem filling the room with sound,as long as you have a sturdy driver to fill in the low end to complement the sound,I have tried lower quality subs and it didn't work,I would also suggest trying to get a low end driver that could help fill in the lower midrange to help drive the room better ,otherwise they could sound a little thin,form how you describe the TDK panel I would expect a thin ish or even a not so thin poly panel to be a lot louder for the same watts.
By the way ,the 12x9 inch panels were from the poly base of a pizza ,yum yum,I have quite a collection now it's free if you don't mind eating a lot of pizzas .
All the best
Steve

[OZZIOZZI]

Hi Sedge, up until now I have been mainly listening to these small panels in the near field so it is a bit more difficult to experience the full effect of DML panels. I have listened to larger panels, maybe 24X36", driven by Dayton 25W exciter from a greater distance and away from walls and they work well to give a feeling of depth, width and feeling that you are IN the space where the recording was made. Of course this works best where the original recording was done in true stereo ie: with  two mics or a well engineered multi-mic setup. I have found that live or concert recordings sound good on panels.

A lot of modern recordings, especially pop, are really panned, close-miked mono recordings with all sorts of added reverb, compression etc. I don't think DML panels perform at their best with that type of recording. For that reason I believe I need two types of speaker systems easily switched depending on the type of music.
Here is apic of the panels I am playing with. Sorry I don't want to pull them apart again, it took a bit of fiddling to get the repaired panel to sound the same as the other good one.



Cheers Sorry about the upside-down image, taken with iPad.
Ozziozzi

[sedge]

OZZI
The TDK panels you describe are obviously a heavily damped and enclosed panel ,a diy panel would easily out perform them ,you will have to do a lot of experimenting to achieve the sound you prefer.
I believe that a lot of the problem of modern studio recordings sounding bad on poly panels is down to the panel not being able to drive the room in the 100hz to 300hz or higher depending on the panel,this is caused by the  room and panel cancellations,even if the near field plot looks great ,if you can ,running the low end driver up into this area will sort out this problem,obviously it helps if you have some way to measure the panels response at a distance into the room.
Rigid panels don't seem to suffer so much from this problem ,but it still has to be monitored just in case .
Steve

[Fidel Costar]

I intend to build DML/NXT panels, but for mid-treble duties only (say from 300 hz upwards). And I have the intuition that I should use some kind of wood (spruce, birch, bamboo?). What do you think? What wood, what shape, what thickness, what exciter? I would appreciate to read more stories from people using wood panels DML/NXT.

[OZZIOZZI]

Sedge said The TDK panels you describe are obviously a heavily damped and enclosed panel ,a diy panel would easily out perform them ,you will have to do a lot of experimenting to achieve the sound you prefer.

The TDK and TEAC panels are most likely designed with optimum size/frequency/damping/mounting and exciter placement using proprietary information from NXT (or whatever they are called now) and their DML design software using exact parameters provided by the manufacturers of the panel material. The fact that both brands need a subwoofer tells me that most customers would not accept a very large panels to get a full audio spectrum. The commercial examples of single panel designs such as Podium are large and the multi-thousand Euro Goebel DMLs resort to multiple cone drivers to fill in the bottom octave or two. Hobbyists can build panels as large as they like and experiment as much as they like to achieve their desired goal.

I think Fidel Costar is on the same wavelength as myself.   I intend using the smaller panels I have for mid-tweeters where they are incredibly sweet sounding and produce that ambience that is difficult to achieve with cone type speakers. I might try very thin plywood laminated on both sides with some tissue or fibreglass and very thin epoxy as bass panels, but I am not too optimistic about the result unless I make them fairly large.

FIDEL, Look back over this thread to a post that includes the NXT patent application. In that they describe panel construction much better than I can and specify core materials and surface treatments/ materials.
I personally think very thin plywood is preferable to the same thickness wood. Look at the Goebel lodspeaker and you can see that they use end-grain balsa wood for its lightness and stiffness front to back of panel. Then they coat it with probably very thin chopped strand mat fibreglas and epoxy resin. The slits they use around the panel edges are also  described in the NXT patent, although briefly.

Btw I would like to hear more about those picture-frame panels and how the panels are mounted to the frames.

Cheers

Ozzi

[sedge]

Fidel
First, I think you need to sort out what size panel you think you can handle in your room,this will give an idea of the best type of panel material for the job.there is a few to choose from.

Ozzi
I have to say I prefer free floating panels,I have tried and still do try to clamp or damp panels to increase it's frequency response as your TDK panels do but the sound has always suffered .
Personally I would start off with a simple free floating panel hanging in the air ,not resting on or touching anything,this is the simplest form of panel and easy to make,from there you can add damping clamping coatings to see if this improves the sound for you,it is a bit of an art I'm afraid.
Have fun
Steve

[OZZIOZZI]

Steve said "it is a bit of an art I'm afraid."
The "art" is only because the design software and panel parameters are closely guarded information unless you pay thousands of dollars for a manufacturing licence and design software.

OTOH, much basic information about materials selection, panel dimensions, length to width ratios, exciter positioning and panel mounting is readily available from the NXT and other patents and manufacturers' data sheets. Carving a violin body is an art. What I can't comprehend is why so many posts on this thread choose to ignore the basic designs that have been published in patents and manufacturer's literature.

As I understand it, what is needed is an extremely lightweight, but rigid panel that has inherent damping in it's construction, driven at a specified spot on the panel by an exciter with sufficient power handling not to burn out at desired listening SPLs. One example would be a thin End-grain balsa wood panel covered on both faces by a laminate of rigid epoxy or plastic resin and embedded material such as thin kraft paper or several layers of tissue paper--Japanese lampshade paper sounds like a nice material to work with. All readily available.

Then mount the panel in a surround by a very low compliance material such as soft plastic or rubber weather stripping, or hang it by strings from the ceiling. It looks as though Nxt recommend mounting only from the front face.  The only parameter to be considered is how low or high you want it to play. Think small panel low mid-treble, very large panel for bass. There is no reason why you cannot have different size panels for each part of the spectrum--according to NXT at least. Then see what your wife or partner thinks of your fullrange panel hanging from the lounge room ceiling NXT's home cinema screen sounds like a good way to hide the panel in plain sight. White paint seems to have no effect on panel performance.

THE ONE critical point that still concerns me is whether to rigidly mount the exciter to a rear spine. The exciters I have are fitted with four mounting lugs for this purpose. If the mounting surface was aluminium it would also serve as a heat sink for the exciter, without affecting the magnetic field.

I am planning something like the pics below with NXT panel(s) up top for 100-16kHz and 10" cone drivers 30-100 for OB dipole bass, total width about 14" height about 36". I may make them slightly deeper so that the bass drivers are effectively in H-frames. I like the front and back grilles so that the "guts" are hidden and also protected from dust, insects and prying fingers of young grandchildren 





Cheers
Ozziozzi

[Fidel Costar]

Sedge and Ozzi,

Thank you for the information. I'll try to read (and understand... ) the NXT patent application.

Concerning panel size: anything up to one square meter is OK for me (one meter is more or less 40 inches), but I doubt I need something this big for mid-treble.

[OZZIOZZI]

The NXT patent is not that complicated if you skip the math equations--unless you understand them . I found it was best to print out the diagrams and then refer to the description of them. Once you tune in to the legalese language it is fairly basic. They even give a range of parameters for panel materials, which is handy if you have a supplier of that sort of thing. Two leads I am following up are plane, .boat and caravan builders (called travel trailers in the USA I believe) who use composite panel materials to save weight in decks or interior fitouts. Getting them in small quantities probably involves looking for off-cuts or panels rejected for cosmetic flaws. One source that just occurred to me was wreckers of planes, boats and caravans.

Cheers

Ozziozzi
PS I read that EXACT square panels are not a good idea, the ratio should be not quite square. NXT also mention the A series of paper or card sizes as suitable. A4 measures 210 × 297 millimeters or 8.27 × 11.69 inches. A3 is 4x the area of A4. I suspect you would be happy with an A2 size sheet which would be about 840 mm x 1188mm which is about 0.997square metre. That is about the size of a large movie poster which suggests a good way to disguise it!!!! Hope this helps.

[sedge]

Ozzi
Ziggy started THIS thread in 2009 (although he did delete himself at sometime time  a little confusing) because he found he could build far better sounding panels than the NXT panels he had heard.
As far as he was concerned the sound was everything (he was very vocal on this),the NXT patents on the other hand are great ideas to increase the performance and bandwidth , not necessarily to improve the quality of sound (imo) .
Panel material and what you do with it has a lot to do with how they sound ( carving a violin body is an art ,as you say) I can make a small panel that plays very loud and very low hz , but as yet I can't say I have mad it sound better,only in some ways so.
Not all panels described on this thread are about ultimate sound quality ( ziggy would not be a very happy bunny) but everyone has their own idea of what they want , and what they can fit in the house, so they make compromises ,or just don't understand the problems.
I can't wait till a manufacturer builds an NXT panel that I would love to listen to at home,and wouldn't cost the earth,with the perfect panel for sound quality,but I bet I could still do better myself and a lot cheaper.
Hope this helps you comprehend this thread a little better ,with it's good and it's bad info.
But I do understand that there is a lot to read,and sort out .
Steve

[OZZIOZZI]

Re Sedges comment about aims.  The only aim I can guess with certainty is that they wish to remain in business. There are enough commercial speaker manufacturers willing to licence their design and softwRe that they are onto something significant. There is a tendency among DIYers to dismiss speaker companies as somehow sinister with base motives such as making a profit.   I cannot see the difference between "performance and bandwidth" and "quality of sound". My reading of NXT articles is that they are trying to achieve a neutral sound to the panel. I have always thought that the quality to be sought in a panel is that you cannot hear the panel, only what it is playing. Reviewers of commercial NXT type panels remark that the speakers "just disappear" and the sounds seem to emanate either behind the panels or that the listener seems to be IN the space where the recording was made. If you hear a "sound" other than the music/speech then I think there is something wrong with the panel. The self-noise that some describe would be like listening to a concert in the shower or behind a waterfall.

It seems to me that some people are comparing panel sounds vs materials when they should be looking for a panel that just"disappears" that is, it has NO sound of its own. The one design I have seen here that makes an impression on me is the one disguised as a picture on the wall. (Poster?) although we haven't heard much about that lately. Perhaps going commercial has made him reluctant to post further information about a successful design or maybe he is just too busy making panels so good that people are willing to buy them .

Pardon my skeptical mood today. I think it is time for me to retire from this discussion. There appears to be an element similar to the debate about the  "sound" of loudspeaker cables or interconnects that I find a waste of bandwidth.

 

Ozziozz