[ondesx]

I believe that sensitivity is a big issue as they have desperately low sensitivity ratings, but also i suspect that in practice the load it presents to amplifiers is a difficult one - despite documentation that states otherwise

1. use a light,thin foam core board or corrugated cardboard sheet : 5 foot by 2 foot mimimum so that bass will be satisfactory.Coating cardboard helps but can be nightmarish

2.use no more than 4 exciters if possible and watch your impedance with paralell/series wiring.
ONE, SINGLE exciter would be best...............until the most expensive and powerful one is purchased and tried, we will not know..................I'm not going there again(see my recent posts).

The Clark Synthesis transducers are ONLY to ''supplement'' stereo speakers. They are primarily ''bass shakers''............................don't forget this fact despite the fact that they state full range audio frequency reproduction

3, use a reasonably high powered amplifier...........I recommend a good solid state one or a push pull beefy valve job.

5.''one panel stereo''..........WTF??..................what ever turns you on.........

6. panel shape is normally ''RECTANGULAR'' and used vertically

7. exciters are used in a VERTICAL array............not horizontal

9. should the panel be firmly attached to the frame?................in our panels, definately ''NO''.
   If you attach the panel edges by clamping them down, you will be entering a different world of DML speakers and require the correct licence and software to pull it off effectively.

Hope this helps.

Well, just some comments on the above points :

- whatever the panel, the electric impedance is resistive (almost) and given by the specified value of each exciter, and changed only with the parallel or series arrangement. We aren't speaking about "mechanical impedance" here of course... This is one of the reasons of the very good linear FR of the panels !

- I understand that a rectangular panel used vertically is preferred,

- One or several exciters remain unclear you say 1 is better, but NO MORE than 4... Some comments welcome.

- the Clark have a large FR and I'll try it as a loudspeaker : why not ? The HF remain probably the main drawback of this exciter

- I think that Class-D amps, less expensive, more efficient and with sometimes high power will be a good choice.

- For the "one panel stereo" please read again the POL's input few pages before...

- The "array" of the exciters is not the question I asked : but the fact they are facing the floor or the ceiling... Because most often it seems that they aren't to be used vertically, at least this is true for the "big" Clark as stated in the user's manual...

- Free panels will introduce distortions and coloration IMHO... But, I need to do some experiments by myself before any conclusion.

[mikadosan]

Hi all,

I see that you have been thinking of splitting the signal to the HF and LF sections. I can give some recommendation on this then. As we all already know, all the materials has their own character and tonal behaviour. Well, why not think this as a possibility then? If you know that some certain material is capable to offer some nice bass exstension but is not that nice on the HF section, split the panel in two different sections. For the bass, use a panel material that you know to work properly and choose a different material and smaller panel for the HF section. Basically there is no need for X-over but it is of course possible to "manipulate" the exciters with x-over as they are pretty much the "normal" transducers anyway...

Of course, the sensitivity of the panels should be close to each other but I can confirm that splitting the panel and using two different kind of materials can really offer you something different. Is it better or worse - you have to test it yourself.

Also, there was some speculation that why the vibrating panel should be straight? This is a good question. We all have been stuck with the flat panels. Why not trying something different. I made one panel of Perspex (it was 2-3mm thick) that was approx 1m tall and some 70cm wide but I bent a "wings" onto it so that the finished panel was some 45cm wide if you look it at front. Very interesting piece of panel it was...   There is a possibility to use different kind of exciter arrangements (all the usual we have already seen but also some extra exciters on the wings, etc...) that can offer some possibilities for the experimenting.

I also have tried a plastic tubes (large ones with thin walls) with height of 1m and diameter of ~20cm. The wall thickness of the tube was 2mm. It´s not very light construction and need some specialties to avoid the tube to rattle against the floor, allow a good bond between the tube and the exciters, etc... I found a solution for all these problems and I can assure you that a tubular "DML" speaker is a weird animal indeed... basically you can get a 360° dispersion for both channels. It sure sound a bit weird for a start then...

Anyway, I would like to encourage you to experiment with different materials, sizes and shapes and also, treat the exciters as a "normal" loudspeaker drivers and do some experiments with the x-overs... I know, it is an endless journey if you give it a possibility and will suck all the money from your bank account but for me personally this is something totally new and interesting and I´m quite confident that this technology really do have some advantages above all the trad. ones then...

Edit: By the way, have you ever tried your already familiar materials as a bended panels? Bending for example a sheet of plywood will indeed change it´s behavior and tonal balance. I´m sure that this might be a situation with almost any panel materials that CAN be bended. Amount of bending will of course affect the sound and tonal balance. Go ahead, give it a go and get ready to be surprised, once again...

If you think that making a two-way loudspeaker with a DML panel is an interesting issue, why not keep it still as a dipole. It would be my next project to investigate something like this. DML panel and dipole woofers, either on the same baffle or separately, I have not made up my mind on this then...

Cheers!!!

-M

[ondesx]

Any picts Mikadosan ?...

[cometarossa]

Hello,
just two questions: Has anyone ever tried panels of metal (steel or aluminum) and a shape as the sphere?
I am especially interested to know if the metal is good for high frequencies.
Thanks!

[doug s.]

7. exciters are used in a VERTICAL array............not horizontal

i think you need to re-think your comment re: using exciters wertically instead of horizontally.  even if you prefer stereo panels instead of two channels on one board, pol makes a good argument why the exciters arranged horizontally across the short width of a tall panel, and off-center, may prowide better results; seems to me it's worth further inwestigation.  go back and re-read his posts...

doug s.

[bobloblob]

Random thought here:  what if you attach 4 (or whatever number) exciters to a rigid bar (preferably light weight) say a foot long, give or take whatever, then attach that bar to the panel?  You would then eliminate the "vibrational mode confusion", since the whole bar would be moving in concert with all the exciters, then transferring that energy to the panel.  This would essentially create one long exciter rather than several small round ones.  The bar could be placed either vertically or horizontally.
It would function differently from a single exciter because of the shape, but is that necessarily a bad thing?

[zobsky]

It wouldn't be prudent to dismiss ideas without first trying them out, for better or worse. I probably will, at some time.

5.''one panel stereo''..........WTF??..................what ever turns you on.........

6. panel shape is normally ''RECTANGULAR'' and used vertically

7. exciters are used in a VERTICAL array............not horizontal

[sedge]

thats right zygadr you have hit the nail on the head,you are dealing with a right load of tight gits 
not me of coarse I bought 40 of the lovely little things
sorry but forgot to say earlier that I have been using single exciters in the centre of the panel for some weeks now as I could not hear any bad sounds .
So Just had a quick test with differant places on the panel ,2/3 up, in the centre, and on the edge 2ins in.
2/3 up had a bit of a peak at 10k before rolling off.
centre has a pritty good overall responce [looks the best to me]
on the edge seemed good in the 1k to 10k but rolled off smoothly below the 1k.
I had shellacked the front of the panel but only an 18 inch die,the panel is cc single layer 4x2, ft I have not compared this to an untreated panel yet ,only my polystyrene panel .I noticed that the panel was bowed in, so thought I would turn it around and stick the exciter on the shellack side , this sounded quite good but I do not know if this is because of the shellack or slight bow ,or both ,sorry this is so rushed as I am about to go to work 

[jeffac]

Well done sedge.

I was wondering who would be the first (to my memory at least) to do the cardinal sin, of god forbid, placing an exciter smack band in the centre of a rectangular panel. Thanks for the report that the earth didn't stop spinning. I've been meaning to test this and it helps in my single exciter per multiple panel thinking.

cheers.. jeffac

[BowerR64]

Here is one idea i thought of but i havnt tried it yet. I think i seen an image in this post somewhere of another production panel or somthing and it made me think of this, maybe it is already designed like this i cant really tell from the single image. I have noticed though that alot of the sound comes from the back and i wonder about the panel ideal loses alot of the sound from the back. Most traditional cabnet speakers take advantage of the back but panels seem to lose it.





ofcorse i wouldnt make it this color 

[ondesx]

Then, you suggest a sort of Horn, isn't ?

[pol_bct]

Hello all!


ZYGADR

>> Bass WILL go low on a large panel, but will not have ''slam''............not ever...... with this type of technology.

indeed ! The way you put the exciters on the panel, this is impossible
they interact destructively on the long path of the board
and contructively ONLY on the short path



>> exciters are used in a VERTICAL array............not horizontal

YES! true for a "classical stereo" config with two panels,
BUT with those two panels, for the reason given just above
the right config would be:  panels used horizontaly with exciters in a vertical array
AND for a single board stereo config
the right config would be:  ONE panel used verticaly with exciters in an horizontal array

And by putting the exciters spaced a few inches,
they generate interferences in the middle of the audio band, something we dont need
they can only be very close together to act as one single  exciter, but with an upper limit of 7kHz
(344/0.05 m)
or as far as possible to reject interferences to the lower part of audio spectrum
or unevenly spaced to spread the interferences, this is my choice of the moment, but YMMV



>> 'one panel stereo''..........WTF??..................what ever turns you on.......

because of the source coherence of this config, all the sound comes from one single panel
moving IN_PHASE from whatever direction you look at it, in the H plane, in the V plane
from left to right, and front to rear
a "classical" two panels stereo set is very far from this kind of coherence

and second argument, if we use this config for a home theater
the source of sound can be the same as the projection area, the screen
Try to explain to a wife that you need TWO big sound panels AND a SCREEN...



>> even at normal impedances, I have found that low powered amplifiers, especially single ended,
 class a, do not like these exciter arrays.

it depends on what you call "normal impedance",
single_ended or low power amps are very susceptible to load mismatch,
with 6 exciters you probably have an impedance around 5 ohms,
this may be already too low

if I had the money I will go for BIG CAR AUDIO amplifiers able to drive 1 or 2 ohms loads



>> use no more than 4 exciters if possible and watch your impedance with paralell/series wiring.

the more exciters, the more destructives interferences they build
I have no problem by using 2x9 exciters (8ohms) , sensitivity +3+9.5dB
but I carefully watch the way they are disposed on the panel
NOT verticaly & NOT on two boards...



>> panel shape is normally ''RECTANGULAR'' and used vertically

We could try a big round structure, this is on top of my ToBeDo_list



>> should the panel be firmly attached to the frame?................in our panels, definately ''NO''.

Agreed, and strongly!


ONDESX

>> I asked : but the fact they are facing the floor or the ceiling...
>> Because most often it seems that they aren't to be used vertically,

I agree, I allready gave a quick try to this, I will comme back on this later
I have tried by supending my single stereo panel about half a meter from ceiling
nice surround sound, but we have to deal with drectivity and board <-> ceiling reflexions



MIKADOSAN

>> I see that you have been thinking of splitting the signal to the HF and LF sections.

This is also one of my zone of investigation, We dont want to reinvent the wheel, do we ?
One of my references is the work of Peter WALKER, we can do something in the same style
a concentric and coherent two ways with serie filter,
why serie filter?  because it may work quite well with those DML exciters
who have fairly clean and constant impedance curves.
by using one single driver for the HF section and 4 on the big bad LF panel
we could get something nice and simple...

http://img42.imageshack.us/img42/6418/nxtpol.jpg


BLOBLOBLOG

>> what if you attach 4 (or whatever number) exciters to a rigid bar (preferably light weight) say a foot long, give or take whatever, then attach that bar to the panel?  You would then eliminate the "vibrational mode confusion", since the whole bar would be moving in concert with all the exciters,


This is exactly what I am doing by placing transducers close & horizontaly on a vertical panel
they radiate alltogether in phase along the long path of the panel
(longest path would be the diagonal) , no need for a supporting structure


SEDGE

>> Just had a quick test with differant places on the panel ,2/3 up, in the centre, and on the edge 2ins in.

How many exciters and how do you spaced them on that center or 2/3 line?
this may be the main reason of the shape of the response rather than the place where you put them



best regards

POL

[mikadosan]

Hi POL,

It seems that we are walking on the same path then...   I mean seriously, you have made almost exactly similar kind of findings that I have. Maybe we should start to work together on the next project then...

There is of course many ways of doing the two-way DML loudspeaker but I have been also interested in concentric way of doing it. There is only very few rational ways of doing this and I have been thinking the following...

Two separated panels, almost exactly like in your sketch. This might be an easy way of doing it if you have a proper chassis that will allow this kind of structure. I´m little bit worried about the sensitivity of the center piece if we use only one exciter. Of course, there is a small possibility to compensate this with a super lightweight center panel (whatever it is...) but if you ask me, I think that it would be important to get the sensitivity of the both panel sections as close to each other as possible...

Other possibility is to make it a bit more traditional way. If we split the panel so that we have 1/3 piece for the HF section and 2/3 piece for the LF section, maybe it would be possible to treat them like a trad. loudspeaker drivers... HF section above the LF section, just like in a normal two-way loudspeakers. This way it would be easy to make a separated chassis for the both units if it is needed.

I think that I will make a prototype of the concentric version of the panel. It is quite easy to do and it will not take longer than few hours to make it to be a working prototype then. I have plenty of different kind of exciters so it is easy to find out which model is best for the HF unit and vice versa...

It would be also interesting project to combine the DML HF/MF unit with a dipole bass unit. I think that I have to construct this one too...

Best regards

-M

[pol_bct]

MIKADOSAN

It's allways nice to meet a guy who thinks about the same as you do...

http://img42.imageshack.us/img42/6418/nxtpol.jpg
It was only a drawing , I have already so much things to test with the large_range version

About the LF/HF split, we have to choose the frq of HiPass/LoPass
Law of 400 000 would suggests 666Hz, but those transducers don't go as low as 20Hz
so this is  probably not the best choice.

Usuable range starts somewhere between 100-200Hz up to 20 000Hz, this give us a median frq of 1.8kHz, one could take 2kHz in order of having about a frequency decade on each side of the Lopass and HiPass filters.

Though measures show a quick drop of frq response under 100Hz, I have noticed that my "feeling of bass" was much lower
I see two possible reasons, ear/brain reconstruction of fundamentals and sympathetic resonance of the panel itself, when excited with 60Hz, if the panel is large enough, he moves at 30Hz...
free lunch !

How about the LH/HF surface ratio? for a two ways, Frqs are in a 1 to 10 scale, so the surfaces should be in the same ratio, let's say 1 m² for bass and 0.1m² in the center zone for HF

the HF zone could be of different material than the bass zone.

The HF/LF ratio of 1 to 4 exciters, could be upgraded to 1 to 9 exciters, because in real world of music 90% of energy is located under 2kHz

POL

[ondesx]

The last improvement of the NXT-like panels is the BMR (Balanced Mode Radiator). Then the diaphragm or the membrane is corrugated in a precise way to control the resonances. Most often only one exciter is used...

The advantage of using only one exciter is the lack of interferences. The resonances are more than enough to limit the behavior of the panel. I think that without the use of finite element simulations it'll be difficult to predict the behavior of a panel and the best place for the exciters given the specs of the membrane... But may be am I wrong...

[bobloblob]

pol-

>This is exactly what I am doing by placing transducers close & horizontaly on a vertical panel
>they radiate alltogether in phase along the long path of the panel
>(longest path would be the diagonal) , no need for a supporting structure

I think I must have been unclear in my post above.  I was not suggesting the rigid bar as a supporting structure, which would be mounted behind the exciters.  I meant using the bar between the exciters and the panel.  If rigid enough, the bar would not absorb and dissipate energy from the exciters, but should transfer the energy (sound waves) from the exciters to the panel with no - or almost no - interference caused by the exciters each radiating independently as in free-mounting each exciter directly to the panel.  If the exciters were placed close together this way, the bar itself would function as a single exciter, increasing the power handling by a multiple of the number of exciters used to power the bar.  Of course, the sound would radiate out in a slightly different manner because of the difference in footprints - small and round versus narrow and long.

One would want a very lightweight and very rigid bar for this, and kept as short as possible with the exciters mounted fairly close together.  I also think placing the bar horizontally on a vertical panel would suit this best.

[sedge]

Pol
At the moment I am only using single exciters per panel.
the reason I placed the exciter in the middle is because everyone says you can’t[hold on wile I have another snort of coke!]
But also because I am not sure If the reason they do not use the centre spot only applies  to multiple exciters ?

I did do a quick try with a large 44inch circular panel and one exciter on the left and one on the right for the two channels ,It sounded ok but was not very convenient for me .
A lot of people have their speakers each side of the hi fi  or a window but I can see it would be great If used as a cinema screen  .
These exciters are so versatile and with just a little effort a good sound can be had by all.
I get very confused with the[ slam ]word ,I think it means different things to different people .
When I have been using a full range panel on my right and a small panel crossing over to a 15inch at say 400 hz on my left ,I have noticed these things .
If I turn off the 15 incher  on the left the sound seems to  lose power and the panel sounds weak in the Lf ,but when they are all playing and I turn off the large panel the Lf sounds muddy and loses attack .It is my impression that the panel is giving the 15 incher the slam it lacks,and makes the 15 incher sound very powerful and dynamic .
I have no idea what frequency ‘s create the impression of slam but the panels do have it in abundance if used in the right way .
The 15 inch unit only goes down to about 40 hz before dropping off fast.
The panel is at a lower level but rolls off at about 25hz.

[Tinnitus]

pol-
Of course, the sound would radiate out in a slightly different manner because of the difference in footprints - small and round versus narrow and long.

Can I propose something?
I realise I may be misunderstanding your concept, and that you may WANT a narrow and long footprint so that you are progagating waves in a deliberately different fashion to the small round footprint approach we're used to, but if that's not your intention:
How about a small plate (just big enough to accomodate your chosen number of exciters without them touching each other) with the same stiff/light/non resonant or 'excitable' properties you propose for your 'bar'.?
This could perform the same duties as your bar, but with a different 'foot' pattern, the foot could be the size of the plate, or a smaller raised area standing slightly proud of the plate to give a small foot.

I must admit though that your 'long thin exciter'  idea sounds like it would definitely be worth trying out.
Sorry if I've totally misunderstood.

[zobsky]

.
I have no idea what frequency ‘s create the impression of slam but the panels do have it in abundance if used in the right way .
The 15 inch unit only goes down to about 40 hz before dropping off fast.
The panel is at a lower level but rolls off at about 25hz.

The slam, punch etc region  ...is ballpark about 60 - 120 Hz

[bobloblob]

Tinnitus-

No, I wasn't deliberately looking for something different in proposing a long bar rather a round plate.  I hadn't really thought of a round plate.  That may work too.  I think both may be worth trying, and both may give different results from each other and from a single exciter.

Zobsky-

I believe "slam" is usually a function more of the mid-bass, as you are pointing out, and also that sometimes cutting off the deep bass gives the perception (false) of an increase in "slam".  Is that your observation too, or am I mis-remembering my own speaker systems of the past?
*****************************************
I am curious about whether anyone has tried "cross-banding" the corrugated cardboard.  That is, gluing two  pieces together with the corrugations of one running perpendicular to the other.  This would increase the stiffness in both directions, coming closer to a Nomex panel, but at a cost of doubling the weight, which may negate the benefits.

Another thing:  if one applies shellac to the two sides to be glued together, the shellac should work by itself as a bond, and the panels would resist warping much better, since each would be pulling in the opposite direction from its mate.  Of course, the panels should be laid flat and some weight applied to them, probably overnight as the alcohol evaporates.  After drying, then the two uncoated faces, now the external ones, could be coated.  I would also use a thicker cut of shellac for this layer, the one between the two sheets - at least a three-pound cut, perhaps even five-pound or greater.