[CXW1219]

 
I have just put my first Paper-Cardboard Honeycomb-Paper composite panel under vacuum....

...now have to WAIT 24 HOURS before seeing the product of my labour 

[Odal3]

Since my daughter has gotten into Karaoke( ) I now have a reasonable mic to do measurements with and have been VERY impressed with the linearity one can achieve.

Sounds like you are having fun exploring the great sound one can achieve with panels    .  Note that a microphone designed for vocals or instruments may not be the best to use for measuring speaker response. They all have different frequency profiles depending on the sound that wants to be achieved. Take a look at for example this: http://blog.shure.com/how-to-read-a-microphone-frequency-response-chart/

A better option would be something like the umik microphone or similar. You can buy them from many places but I bought mine from crossspectrum since they test it first and provide calibration files.

http://cross-spectrum.com/measurement/calibrated_umik.html

I also saw that you are using the thruster exciters. While good I also find they fall off a bit on the HF side.

Don't forget to play around with how you mount, lean or hang the panels. They will all change the sound in different ways. My preference is free hanging, but some have posted they like the other methods better. Not saying one method is better than the others - just that its worth checking out what works the best for you.

Good luck with your panels and enjoy!

[Bendingwave]

Another way to increase high frequency is to use a wave guide....If you look at the Sony APM Speakers they use a wave guide on there exciter used as a tweeter....The same goes for Bertagni speakers as they use a simple concave circle crator as there wave guide of there high frequency exciter.

What I believe the wave guide does is it focuses the high frequencies forward so it sounds more pronounced instead of the high frequencies being dispersed through out the sides of the panels.

[CXW1219]

OK my DML panel version 0.2 is out of the vacuum bag:

Aesthetically just a matt black A1 paper panel, but the slight texture of the honeycomb underneath is visible.
From a mechanical POV the panel feels about twice the weight of the foamboard, but with vastly increased rigidity - esp in horizonatal axis.
Initial tap test implies a slightly higher resonance than foamboard - which bodes well for higher frequency performance.
The paper skins have adhered well to the honeycomb so I am expecting reasonably good excitation performance.

Sadly I have to go to work now - so shall do some proper measurements in the morning. This is probably no bad thing, since I think the PVA glue will benefit from some more time air-curing out-of-the-bag.

Initial impressions are favourable, but I am expecting this to be a first step on a longer journey....

Wave Guides: I agree that they have a role - but I think my first steps are to find the right panel construction technique, then move onto multiple exciters & their associated complications.

[CXW1219]

Not slept in over 24 hours... but HAD to try the new panel...
Here is some data....

Listening DEFINITELY  a significant audible difference.

Have Amazon'd a USB measurement mic....proper data tomorrow...

[crackie]

Hello all........what a fascinating thread.

Its interesting to see just how far it is possible to get using empirical development. I was first involved with NXT in 1997 and 1998 when I attended their training courses in Huntingdon. In 1999 I moved to Huntingdon and worked for an injection moulding company who carried out most of NXT's & Mission's prototyping work; Mission / NXT were owned by the same people at the time. The moulding company also supplied various components to Amina technologies and in 2012 I began work in their design department.

The best impirical experimenters on this thread have reached similar conclusions to some extremely sophisticated FEA modelling. When understanding DML behaviour its best not to compare it with conventional moving coil speakers at all. Moving coil drivers are pistonic or at least they aspire to be whereas DMLs are incoherent devices with multiple areas of the panel being in or out of phase with each other at any given time. DMLs oftem struggle at high volumes or when there is a lot of LF in the programme material. This is because the nodal behaviour of the panel, at the exciter drive point, is often very different / contradictory to the input signal being fed to that exciter. Hope that makes sense.......

Panel suspension / termination is important too.........less is more. Good old fashion elastic bands are a simple and very effective solution.

If you keep volumes levels sensible and/ or keep extreme LF away from the panel then they can be superb, just like any well designed cabinetless speaker ( electrostics, ribbons, Linkwitz dipoles etc etc )

[CXW1219]

Interesting read...
https://urresearch.rochester.edu/fileDownloadForInstitutionalItem.action?itemId=32717&itemFileId=182509

" Specifcally, through a program of modeling and experiments we
demonstrated that isolated panel modes produce ringing at discrete frequencies in the
impulse response, which adds a reverberant, ?hollow? quality to the reproduced audio.
This also leads to the appearance of distinct peaks and dips in the spatial acoustic
radiation patterns, which previously had been dubiously described as difuse radi-
ation and portrayed as an advantageous property of such loudspeakers. Rather, this
behavior of previous flat-panel loudspeaker designs is inferior to conventional pistonic
loudspeakers, especially at low frequencies, and leads to objectionable audio artifacts.
In our efforts to address these issues we found that by exciting the vibrations of a
flat-panel loudspeaker with an array of drivers whose locations and force amplitudes
have been carefully predetermined the vibrations of isolated panel modes can be ef-
fectively canceled out"

Quite fancy a PDF of this one too:
http://www.aes.org/e-lib/browse.cfm?elib=19202

[Odal3]

Crackie - thanks for sharing. Please tell more

[Bendingwave]

Crackie welcome to the this thread........What I want to know is what is the definition of the word pistonic?.... Dont all drivers have moving coils and or move/vibrate in and out in a pistonic fashion to varying degrees? IF not, when EXACTLY does a driver become pistonic, what excursion levels of Xmax is required for a driver to be labeled as pistonic?

A sub driver aspires to be highly pistonic because it needs that excursion to produce a good amount of bass, while a mid range driver and or tweeter does not aspire nor requires to have a high degree of pistonic/excursion movement, since they are only reproducing the high frequencies.

[pol_bct]

What caracterize a pistonic driver is that the moving surface is less than a quarter wave so it moves in-phase all along his range of  frequency and  it has a peripheral suspension  (external spider) which gives him a so-called aperiodic behaviour, this is pure theory, in the real world, pistonic loudspeakers have a frequency range which is quite short (3 octaves) and turn to modal as the frequency rises. A DML does exactly the contrary, modal everywhere (6 or 7 octaves) but poor pistonic in low frequencies because of the lack of excursion and modes.

POL

[Bendingwave]

What caracterize a pistonic driver is that the moving surface is less than a quarter wave so it moves in-phase all along his range of  frequency and  it has a peripheral suspension  (external spider) which gives him a so-called aperiodic behaviour, this is pure theory, in the real world, pistonic loudspeakers have a frequency range which is quite short (3 octaves) and turn to modal as the frequency rises. A DML does exactly the contrary, modal everywhere (6 or 7 octaves) but poor pistonic in low frequencies because of the lack of excursion and modes.

POL

That sounds exactly like how a tweeter and some mid range drivers produce there frequencies, where modal everywhere but poor pistonic in low frequencies because of lack of excursion and modes.

Also pol is that from your own words or did you copy it from some sort of article? If it was from a article could you please post the full article so I can read up on it, thanks.

[Bendingwave]

I did some low frequency test on my panels to see how low they can go before they become inaudible.....My center channel panel uses the tectonic 19mm exciter and can reach down to 50hz before it starts dropping like a rock and almost inaudible at 45hz.

My Sub panel uses the bigger and higher excursion Dayton DAEX30HESF-4 30mm exciter and can reach down to 30hz before it becomes almost inaudible at 25hz.

Why does the Dayton exciter able to reach lower then the tectonic? Is it because of there size difference or because the Dayton exciter has more excursion? or both?

When it comes to the high frequencies though the smaller tectonic 19mm exciter has better high frequency then the bigger Dayton 30mm exciter.

It seems like the more pistonic/excursion a exciter has the better bass output and lower extension but with lesser high frequency while the exciter with less pistonic/excursions have less bass out put and extension but better high frequencies.

Maybe with all full range drivers there is a balance between the amount of pistonic/excursion to not off set either ends of the spectrum in a full range driver or exciter?

I believe even the full range BMR exciters have a certain limit to excursion/Xmax before it starts to effect and hamper the high frequencies.

Not sure if what I said made any sense but I am not really into the technical aspects, just as long as I am satisfied and happy with my panel designs and it sounds good to me, then thats all that really matters. 

[CXW1219]

They are evolving...
V0.9 = foam board    (with minor tweaks now have "flat" frequency response and easily driven by 30wpc @8ohms (volume good at 3/10), but delicate so lacking durability)
V1.0 = Paper vaccum formed onto cardboard honeycomb with pva glue (Still reasonable acoustically but funny resonances due to odd paper edge behaviour due to inaccuracies in my fabrication process - my bad: too much glue)
V1.1 = Paper vaccum formed onto cardboard honeycomb with less pva glue    (Made but untested fully - fell apart - too little glue)
V2.0 = Silk fabric vaccum formed onto cardboard honeycomb with less pva glue    (Provisional testing better than expected - but much less efficient than paper volume at '11' - possibly due to lack of rigidity)

Future work:

I have just been to a marina and bought a load of epoxy resin...

So.... next steps include:
A. Paper epoxied to honeycomb - cheap and cheerful and will teach me how to use this stuff
B. Fabric embedded in epoxy, no honeycomb sandwich composite: Low mass, but will it be rigid enough?
C. Silk epoxied to honeycomb - bit more expensive but will getting into 'fancy' territory both for performance and aesthetics

D. 'Oddball': Stretched fabric in frame vibrating freely in space with no honeycomb

Any thoughts, comments before I procede? Usual disclaimer - I have read multiple fora but I do not wish to retread other people's mistakes...feel free to chip in if this stuff has tried & failed before...

Ta!
Ben

PS: It is hilarious the way my 'study' is now gradually accumulating panel material...how long before I start looking like I live in a builders yard?

[coinmaster]

Ive been obsessed with these DML panels for the past 2-3 years as you can get sound quality that equals speakers costing 1-2k but at a fraction of the cost.

Wait, DML panels can only sound like panels costing 1-2k? That's pretty disappointing  , from the way people talk about them I would of thought they sounded much better.
For $1000 I could make a speaker using traditional technology that sounds like a $10,000 speaker or more, I haven't heard a 1-2k speaker that sounded anywhere near as good as my HD800 headphones.
I'm guessing DML isn't for me?

[Bendingwave]

Wait, DML panels can only sound like panels costing 1-2k? That's pretty disappointing  , from the way people talk about them I would of thought they sounded much better.
For $1000 I could make a speaker using traditional technology that sounds like a $10,000 speaker or more, I haven't heard a 1-2k speaker that sounded anywhere near as good as my HD800 headphones.
I'm guessing DML isn't for me?

I never said they can ONLY sound like speakers costing in the 1-2k range  ....I can only speak for myself as EVERYONES DESIGNS and the sound of there panels are different. The speakers I was comparing them to are Magnapen speakers because Ive heard maggies before and these panels sound very similar to the maggies more so then the conventional cone speakers but at only a fraction or less of the cost as you can build a pair of my DML panel designs for under $150.00 a pair.

Dont guess, experience it for yourself....either you will like the sound or you wont but the would also depend on your DESIGN.

Whats odd is your FIRST post on this forum, instead of actually contributing something useful to this thread, is too nit pick and argue with me about something so insignificant? things that make you go hmmmmm 

[Bendingwave]

This is when one takes bending wave technology very seriously with vast amounts of resources and technology to back them up.

https://www.youtube.com/watch?v=YOy4XmVICRw&t=127s

https://www.youtube.com/watch?v=XgoMMihVVu4

https://www.youtube.com/watch?v=n2Lq19U7t8E

https://www.youtube.com/watch?v=QGFFKe-7SYA

Coin master I guess you didnt see this post of what Bending wave technology can do when someone takes it very seriously to the extreme with vast amounts of resources and technology to back it up.....Those speakers probably cost over 50K

[coinmaster]

Whats odd is your FIRST post on this forum, instead of actually contributing something useful to this thread, is too nit pick and argue with me about something so insignificant?

In what way was I being nit-picky or argumentative? I asked a question to get a quantitative understanding of BML sound.
Also not sure what is so insignificant about trying to avoid countless hours of unneccesary R&D.

This is the only active forum still discussing this topic and I spent an entire day reading through old forum threads on the subject.

I've seen very little objective observations on the sonic quality of DMLs in all the years worth of posts that I've read. Other than Ziggys enthusiasm it's mostly been discussion on theory.

I wanted to hear your response to what I said to decide whether or not I should devote time or effort into this endeavor.

[FullRangeMan]

When Zigadr was live I used to post in this thread til I realize there was no Gatorfoam in my country.
What panel and exciters you guys are using today?
Thanks

[coinmaster]

Yeah I'd like to hear an updated consolidation of how-to information if there is one.
The thing I hate about long threads like this is they are filled with so much information scattered throughout the entire thing.
Has anyone made something like a checklist of consensus?

Off the top of my head I can think of a few questions such as:

Are lower powered modules more detailed, lower distortion?

Can many smaller panels be used to form a giant panel with the same effect? Or perhaps to a better effect? I assume based on the ability to remain small, which is conventionally good for tweeters, while still being able to consolidate into a larger entity for lower frequencies.

Is there a consensus on the best sounding brand/model?

What panel material is best overall?

In 2009 Ziggy stated that taking the exciters out of their shell was the way to go, are we still doing that?

I'm sure I have lots more questions but those are the most pressing ones.

If someone has a guide somewhere that would be great too.

[Bendingwave]

In what way was I being nit-picky or argumentative? This is the only active forum still discussing this topic and I spent an entire day reading through old forum threads on the subject.

I've seen very little objective observations on the sonic quality of DMLs in all the years worth of posts that I've read. Other than Ziggys enthusiasm it's mostly been discussion on theory.

I wanted to hear your response to what I said to decide whether or not I should devote time or effort into this endeavor.

I never said they can "ONLY" get sound as good as speakers costing 1-2k.....I said you can get sound quality that sounds as good as speakers costing 1-2k, but I have never put a set limit of how much sound quality one can get out of there own panel designs and even at that I was only speaking of my OWN design in this moment and time with the set resources and technical knowledge I currently have at my disposal and NOT anyone elses.

On this forum as well as others there have been many objective observations of each individuals panel designs sonic qualities...A fellow on the DIY forum (I forget his name) gave a great explanation to the general qualities of the DML's sonic qualities.

For example do the speakers in the videos I posted sound better then my panels? I can honestly say they do even though I have only heard them through youtube but I can tell by there accuracy and clarity especially in the high frequency response that they sound better then my panels but of course they should with millions of dollars, resources and technology backing them up.

I did give you my response and I said dont guess , experience it for yourself either by doing it yourself or doing research on it or both because it all boils down to PERSONAL PREFERENCE and of course different DESIGNS.

The most basic design is Rich M. design posted on Part Express speaker building gallery which is the basic start up design into DML technology......the farthest most advanced end of the spectrum (IN MY OPINION) so far is those Globel bending wave speakers I posted in the videos above.

Skys the limit as there are endless possibilities of designs of DML technology depending on each individuals resources and technical know how.