DIY Flat Panel Speaker Love

[klane]

Re: DIY Flat Panel Speaker Love

Thanks for your reply. I have experimented with a polyethylene honeycomb material. The polyethylene was not as efficient as a XPS foam. I assume the reason for the less efficiency is XPS is more rigid. Would you agree the softer material would absorb some of the vibrations and thus be less efficient?

I want to use a DML type speaker for an outdoor speaker because of the advantages a DML has over a piston type speaker.

I would like to talk more but I do not know how to PM. Can you share with me how to PM?

[rmeinke]

Re: DIY Flat Panel Speaker Love

Less rigid and I'd venture a guess that the polyethylene honeycomb material is also overly damped. Heavier and more flexible so I also assume high frequencies are muted, low freq. are lacking in definition?? Slow and muddy I assume!?

It is amazing what a difference even small changes in material can make with the fidelity of the panel!!

[dlneubec]

Re: DIY Flat Panel Speaker Love

Hi Rich. Cool thread. This looks like an interesting and fun speaker approach to explore. I'm interested in experimenting with it.

What I see lacking so far is much fundamental study trying to establish what happens when just one variable is changed. This is typical for us DIYer's because of our desire to get to the best results, asap. For example, one could take one model exciter, measure it under the exact same conditions, same position, on the same size panels, same material and just vary thicknesses. That way we might better understand the role of thickness. The same thing could be done from one material to another, once exciter to another, one panel shape to another, one exciter position to another, one panel surface treatment to another, one panel edge termination to another, and so on.

At this point there seems to be lot of experimenting and suggested conclusions, which is fun and exciting, but probably more guesswork than educational.

Also, I think it would be good to use an gated MLS type measurement so you can first understand what is happening with the panel without including the influence of the room. Once the panel response is better understood, then you can include the room.

Some other fundamental questions that have occurred to me while reading this are:

What specs in the exciter determines their performance on a given panel and/or frequency range?
What is the role of exciter Fs in terms of frequency response?
It appears that panel size has something to do with panel response, but how. For example it it simply area based, in which case a 1'x4' panel would perform the same as a 2'x2'. Or is it max dimension in one direction? For example does a 2'x4' panel perform the same with low frequencies as a 2.83x2.83' panel (same sq')?
What happens to a panels performance if it is stressed, ie. if one were to bend it slightly?
What about multiple panels of either various sizes or various materials, or both to better cover full range?
Could a bass shaker possibly be used with the proper type panel to cover the last couple octaves?
What are the effects of rigid mounting of the exciter, as the Podium speakers do?
What are the effects of different types of mounting systems, spline from behind, hung from a frame, rigidly mounted in a frame, mounted in a frame, but isolated from it, etc.?

One approach I would want to look at closely is what happens with tapered panels rather than rectangular. For example might a 30" base with an 18" top and 4' tall work better overall than a 2'x4' panel of the same area, as the 30" width might be better for lows and the 18" better for highs? Personally, I would stay away from EQ until you better understand most of these factors and are more certain the the only answer to better the sound is EQ, not just a different configuration.

Obviously you are getting pretty satisfying results without a fundamental understanding of what is going on. How good could it be with a much more thorough knowledge?

My final suggestion would be to avoid using somewhat meaningless and certainly controversial terms like speed, fast, etc., especially on a technical forum as opposed to an audiophile forum. You might get more buy in from the locals.

[dlneubec]

Re: DIY Flat Panel Speaker Love

I forgot to ask. I saw this at Menars's the other day and thought of this thread. Has anyone tried HDPE panels? http://www.menards.com/main/p-2246284.htm They have it available in 1/8", 1/4" and /3/8" thicknesses.

[Pete Schumacher]

Re: DIY Flat Panel Speaker Love

I forgot to ask. I saw this at Menars's the other day and thought of this thread. Has anyone tried HDPE panels? http://www.menards.com/main/p-2246284.htm They have it available in 1/8", 1/4" and /3/8" thicknesses.

Might be neat to bend that material into enclosure panels.

This might be useful data.

http://www.olympus-ims.com/en/ndt-tutorials/thickness-gage/appendices-velocities/

The speed of sound in the material would allow you to take into account the wave propagation across the panel. Maybe that device could be used to drive one end of a cone of material made from that stuff, like a Walsh driver?

[dlneubec]

Re: DIY Flat Panel Speaker Love

Might be neat to bend that material into enclosure panels.

Had the same thought when I saw it, Pete.

[rmeinke]

Re: DIY Flat Panel Speaker Love

Hi Rich. Cool thread. This looks like an interesting and fun speaker approach to explore. I'm interested in experimenting with it.

What I see lacking so far is much fundamental study trying to establish what happens when just one variable is changed. This is typical for us DIYer's because of our desire to get to the best results, asap. For example, one could take one model exciter, measure it under the exact same conditions, same position, on the same size panels, same material and just vary thicknesses. That way we might better understand the role of thickness. The same thing could be done from one material to another, once exciter to another, one panel shape to another, one exciter position to another, one panel surface treatment to another, one panel edge termination to another, and so on.

There has been a load of experimentation done over at AudioCircle in the Open Baffle section, thread "NXT.......rubbish??....THINK AGAIN!"... where the NXT/DML body of knowledge and experience exists. It started in 2009 and has over 113 pages to date. What I have done with these panels is to implement what has been established as providing reliable results. But there is much, much more work to do.

The NXT Designer modeling software would be able to predict fairly accurately most of what you mentioned above. Its been stated that DML is very deterministic. While I can't say with 100% certainty, I do believe all or most of the math to predict DML behavior is available in either white papers, thesis, patent documentation, etc. that I've perused over the last few months and if you were or anyone else has the ambition we could probably roll our own modeling software to take some of the guess work out. But my opinion, not unlike any other speaker building endeavor, what the panel actually sounds like is another situation entirely.

At this point there seems to be lot of experimenting and suggested conclusions, which is fun and exciting, but probably more guesswork than educational.

Also, I think it would be good to use an gated MLS type measurement so you can first understand what is happening with the panel without including the influence of the room. Once the panel response is better understood, then you can include the room.

I just picked up a copy OmniMic v1 and looking forward to measuring. I'm very curious about distortion and CSD measurements for these panels. I have never used any serious measurement systems so I need to spend some time familiarizing myself with it before I can really contribute something of quality there.

Some other fundamental questions that have occurred to me while reading this are:

1. What specs in the exciter determines their performance on a given panel and/or frequency range?
2. What is the role of exciter Fs in terms of frequency response?
3. It appears that panel size has something to do with panel response, but how. For example it it simply area based, in which case a 1'x4' panel would perform the same as a 2'x2'. Or is it max dimension in one direction? For example does a 2'x4' panel perform the same with low frequencies as a 2.83x2.83' panel (same sq')?
4. What happens to a panels performance if it is stressed, ie. if one were to bend it slightly?
5. What about multiple panels of either various sizes or various materials, or both to better cover full range?
6. Could a bass shaker possibly be used with the proper type panel to cover the last couple octaves?
7. What are the effects of rigid mounting of the exciter, as the Podium speakers do?
8. What are the effects of different types of mounting systems, spline from behind, hung from a frame, rigidly mounted in a frame, mounted in a frame, but isolated from it, etc.?

I numbered the questions above for easier answering.
1. I would have to go back through and try to find some of the posts on modeling with the NXT designer but I remember BL and the voice coil/mounting size of the exciter as being 2 critical parameters to the modeling but have to think that moving mass, Qts and compliance would factor in as well.
2. Very little, panel material properties and size play a dominant role in terms of freq. resp. The size of the exciter base/mounting as mentioned plays a part, based on modeling it affects the HF response. Measured response yes but more so (my experience and others) from a sound quality perspective. The Visaton exciters I tried did not sound good on XPS compared to other exciters I've tried. Others have had the same expirience. Other exciters witih larger mounting surfaces have not faired as well in regard to sound quality yet measured well.
3. This could be determined by the NXT Designer. Panel material, mounting/suspension, size, nbr of exciters/placement all are part of the modeling. On shape, approaching square allows for the most even distribution of modes on the panel. The golden ration was used in the patent and other white papers. This link has some really good information will provide good insight into this topic : http://publications.lib.chalmers.se/...ext/154618.pdf
4. This would increase the rigidity of the panel, altering the panels properties. Doubt the NXT Designer would be able to model that straight away but if you can determine parameters of the material that is stressed Designer would be of value.
5. I had thought about that when I first started reading the NXT thread an AC and others have suggested it but as I thought about it more I started to question the complexity it brought and its usefulness in general. But of course it is an option but I would consider simple EQ before I would attempt the complexity that a multi-panel, multi-exciter and network needed to make it work. Especially when something like an XPS panel comes as close as it does to delivery near full-range in a single panel/single exciter solution (which I believe is important). I am still planning to go to a panel array. Personally, I really like the sound quality of a small panel. Larger panels can produce audible resonances on very dynamic passages that go from quiet to very loud quickly and with significant bass energy... my panels are near free standing so with suspension/better termination I do imagine that this could be dealt with. Love the sound quality of small panels and whether or not they can produce bass via EQ we shall see.
6. Someone attempted to combine a bass shaker (which they did say gave the best drum performance they had ever listened to via recorded music) with a conventional exciter on a large single panel but gave up on the approach. It was been stated that it often ends in roundabouts and switchbacks.... I read into this as typical trade offs and hard core physics. Statements such as these have formed my opinions and approach to DML. There is an uncountable number of things that we could try and many people have taken many different runs at these over the years but most leave with a simpler and more practical approach to DML.
7. I thought for sure that rigid spline mounting was the way to go. It only makes sense to me that the push from the rigid exciter is the only impulse that should be applied to the panel; I still don't understand how DML can sound as good as it does with simply attaching a puck to a panel. I would still like to explore that via listening and measurement at some point. Many of the DIYer abandoned this as it often lead to stress on the exciter and mis-aligned voice coils. One side effect that I hadn't really considered is that the frame (like in the case of the Podium panels) becomes part of the music chain. Exciters are more powerful than I had imagined and I'm not sure sure a vibrating frame is all that good for sound quality either. So more research needed here.
8. Similar to 7, but the suspension I am finding has a large impact on the smoothness of the freq. response. Read the link above. That one gave good insight into mounting if even pretty limited. What I read is seen in my simple RTA measurements.

One approach I would want to look at closely is what happens with tapered panels rather than rectangular. For example might a 30" base with an 18" top and 4' tall work better overall than a 2'x4' panel of the same area, as the 30" width might be better for lows and the 18" better for highs? Personally, I would stay away from EQ until you better understand most of these factors and are more certain the the only answer to better the sound is EQ, not just a different configuration.

I had thought about that as well in an attempt to possibly produce more HF response at the top of the panel and more bass potential at the bottom of the panel. But based on the papers read I doesn't work that way. It appears to me that the best panel is the panel that will produce the most nodes. Golden ratio.

I'd rather not use EQ either but I'm not religious about it nor opposed to EQ if the result of the panel is a smoother and better sounding panel.

Obviously you are getting pretty satisfying results without a fundamental understanding of what is going on. How good could it be with a much more thorough knowledge?

My final suggestion would be to avoid using somewhat meaningless and certainly controversial terms like speed, fast, etc., especially on a technical forum as opposed to an audiophile forum. You might get more buy in from the locals.

Well that is a friendly statement. I'd like to think that I and others like me have taken advantage of years of real experimentation that took great effort by some dedicated folks.

As for explaining what something sounds like, what vocabulary do we use?

[dlneubec]

Re: DIY Flat Panel Speaker Love

I read a bit of the last half dozen pages from the AudioCircle thread so far, but that's all. One link was posted on the last page, which seems to question the NXT theory their software is based upon: http://www.tnw.tudelft.nl/fileadmin/...jen_200104.pdf

I skimmed through much of this, though a lot of the math and physics went over my head. They are questioning NXT's theory at one point, so it leaves me wondering just how well their software does as a predictor of panel behavior. The tests they did on NXT small panels did not show them to be very good drivers. Is their software even available?

I saw that other paper you linked in the AudioCircle thread, but have yet to take a look at it.

[rmeinke]

Re: DIY Flat Panel Speaker Love

I forgot to ask. I saw this at Menars's the other day and thought of this thread. Has anyone tried HDPE panels? http://www.menards.com/main/p-2246284.htm They have it available in 1/8", 1/4" and /3/8" thicknesses.

Yeah, high density EPS is good stuff and want to get my hands on some for experimentation. The guy who started the thread over at AC just started to use HD EPS with the new Dayton Thrusters and had reported good results but he really didn't expound on it much. He, unfortunately, passed recently so will not have a full assessment.

[rmeinke]

Re: DIY Flat Panel Speaker Love

I read a bit of the last half dozen pages from the AudioCircle thread so far, but that's all. One link was posted on the last page, which seems to question the NXT theory their software is based upon: http://www.tnw.tudelft.nl/fileadmin/...jen_200104.pdf

I skimmed through much of this, though a lot of the math and physics went over my head. They are questioning NXT's theory at one point, so it leaves me wondering just how well their software does as a predictor of panel behavior. The tests they did on NXT small panels did not show them to be very good drivers. Is their software even available?

I saw that other paper you linked in the AudioCircle thread, but have yet to take a look at it.

This paper's focus is on the use of DML technology for use in a WFS arrays. Not so much on DML technology specifically. The DML panels they used in their research were more specific to the application... no focus on DML sound quality. The panels were uber small 12 cm x 12 cm and made of foamboard so pretty low fidelity. But with each paper you get a little more insight and if your lucky, lean a little more.

[rmeinke]

Re: DIY Flat Panel Speaker Love

Might be neat to bend that material into enclosure panels.

This might be useful data.

http://www.olympus-ims.com/en/ndt-tutorials/thickness-gage/appendices-velocities/

The speed of sound in the material would allow you to take into account the wave propagation across the panel. Maybe that device could be used to drive one end of a cone of material made from that stuff, like a Walsh driver?

Hello Pete,
Have you ever listened to a Walsh driver? Curious how they sound. I remember the Walsh back in the early 80's... thought they were really exotic and always wanted to listen to a set.

They are interesting and I would like to try to DIY a set with a set of exciters but wonder what type of output you can expect from such a small cone?!?

[rmeinke]

Re: DIY Flat Panel Speaker Love

They are questioning NXT's theory at one point, so it leaves me wondering just how well their software does as a predictor of panel behavior. The tests they did on NXT small panels did not show them to be very good drivers. Is their software even available?

I saw that other paper you linked in the AudioCircle thread, but have yet to take a look at it.

Hey Dan,
I forgot to response to the modeled vs. measured response. From what I have seen (which is not a large number by any means), the measured response is very close to measured. Modeled shows larger peaks than actual measurements but that might be the resolution/smoothing of the actual measurements.

I think I did response to the DML implementation that they used for the research. It was a 4.75 inch x 4.75 inch on foamboard which is not a very good material... most certainly a low-fi implementation but given the fact that it was research for use of DML in a WFS array where many panels where needed fidelity was not a priority. Completely different use case.

btw - Where in the paper did the authors question NXT's theories? I didn't find it but curious on what specific DML area... I would be interested in that.

Rich

[rmeinke]

Re: DIY Flat Panel Speaker Love

Duplicate post... arg...

[dlneubec]

Re: DIY Flat Panel Speaker Love

btw - Where in the paper did the authors question NXT's theories? I didn't find it but curious on what specific DML area... I would be interested in that.

Rich

It is in the section where they are discussing radiation models (around pg 13-16 or so). They discuss the first model, which call the rectangular array of elementary sources and say this is the NXT model, concluding the following:

This model has been proposed by NXT, and included in their DML design software ([1]). Although we have decided to present it here, we do not think this model is a good model. There are several reasons to doubt the correctness of the model:
• The choice to observe the normal velocity Vn on a control surface S instead of on the vibrating surface itself can be justified (and is not mathematically wrong). However, the validity of the assumption that the velocity distribution can be represented by an array of elementary sources has not been proven satisfactorily.
• The validity of the choice of the spacing dw = dh = π/k is not given by [1]. It would be more appropriate to use π/kb as a measure of the spacing dw and dh.
• Setting Vn constant over the entire panel is quite dubious.
• The calculated number of sources has to be set to an integer value in order to be able to actually perform the summation of (2.34). Hence, the predicted acoustic response is equal over a frequency range.
• The model breaks down for small panels: the number of elementary sources is dependent on the physical size of the panel. For small panels, the number of predicted sources can be smaller than one, which leads to erroneous predictions. For instance: the AM1-3 panel has a size of 12 by 20 cm, hence for frequencies underneath 1450 Hz a single sources is predicted for the small side.
• Given the previous points, the model is most appropriate for large panels observed from a great distance, although these conditions are seldom fulfilled in practice. The model of elementary sources seems to have very limited applicability. It is included here for reasons of completeness.[/COLOR]

Then they talk about the second model, which the call the Velocity model and conclude:

This radiation model seems to be more applicable than the model given in the previous section. This model does not involve dubious assumptions and simplifications. Remember that the pressure calculated by this model can only be a far-field pressure. Otherwise, this model is universally applicable to calculate the acoustic pressure P(r,φ,θ, k) induced by a vibrating panel.

[dlneubec]

Re: DIY Flat Panel Speaker Love

Rich,
I see on the AudioCircle thread you have tried a 1/8" plywood panel. I've very curious to know what happens to both the sound and the measured results when going from flat and then to stressed by slightly bending it. I suppose you would have to pull the sides toward on another and hold them in that position with some sort of cable or something from side to side. You might need several of them along the length. The places where these cables connected would seemingly constrain the movement of the panel edge to some degree, which could be good or bad.