DIY Flat Panel Speaker Love

[Kornbread]

Somewhere in this thread or the diy thread, there is discussion about cutting grooves into the foamboard that basically serves to sever vibration propagation. For example, out of one large sheet of blueboard, or whatever panel is chosen, a basic 'two-way' could be formed. While my experiments have come to a complete standstill due to very little free time and the aggravation caused by dealing with their unreliability, I have often though about creating a multi-panel in this fashion using 'bass shakers' for the bass, and exciters more suited for the mid and treble ranges. My thoughts are that over-excursion combined with tin leads on the daex32 were the cause of the failures. Like an ordinary driver, the motor must be able to control the panel but once the vibrating panel overcomes the exciters ability to control the panel, it basically beats the exciter to death. This was the thought process leading to a more conventional two-way design using bass shakers for the bottom end.

[Unbiasedsound]

New to the board and this thread. Some questions that hopefully haven't been asked too many times before.

On panel material: Has anyone tried Polyisocyanurate foam board. Its denser and thus a bit heavier than say foamular 150 and maybe a bit more dense than foamular 250. https://www.homedepot.com/p/R-Matte-...stomer_reviews

On reducing board resonances, in the original Tech Ingrdients video, during the part on reducing resonances, just before he mentions using weights placed at the 2/5,3/5 locations of the sub-divided rectangles, he quickly mentions you could also just cut holes at those locations. Has anyone tried this or determined how big/small those holes would be? Seems like it might work better than adding weights/mass at the resonant points?

Go for it and see for yourself.

[bradley.s]

If I were to do a line array type of DML or I should say BMR type of speaker I would use multiple separate panels with one exciter on each panel instead of multiple exciters on a single panel.https://www.youtube.com/watch?v=L5zJ4C9mYLk

If the CBT array works you could do 24 individual exciters. I'm trying to see if you can cut the exciters in half and still get a CBT. If that works the next step would be to see how few exciters you could use to produce a CBT. Maybe you could get away with as few as 3,2,1,1,1 with a five foot CBT.

[Unbiasedsound]

Personally though I wouldn't do a line array with DML/BMR panels as it defeats the purpose of using larger panels plus its not needed since the panels throw a huge soundstage horizontally as well as vertically.

[bradley.s]

These guys call it a MAP (Multiactuator panel.) But as of this paper they didn't try it in the form of a CBT. Maybe they did in a later paper.

https://www.researchgate.net/publication/290031625_Multiactuator_Panels_for_Wave_Field_Synthesis_Evolution_and_Present_Developments

[bradley.s]

This paragraph makes me think MAPs are good candidates for Floyd Toole's speaker placement in conjunction Keel's CBT flat array. This paper was written in 2010. Today, we have inexpensive multichannel DSP as well as very inexpensive digital amplifiers that can make something like this accessible to DIYers.

"Multiactuator panels can be used alternatively to
dynamic loudspeaker arrays for wave field synthesis with
added benefits. Due to their low visual profile, they can be
integrated into the listening environment as part of the
room decoration. Furthermore the radiation of multi-
actuator panels is evenly distributed across the listening
area and over a wider frequency band. This characteristic
helps in merging the individual secondary sources of
wave field synthesis correctly for a large listening area. In
addition when multiactuator panels are used in non-
anechoic wave field synthesis setups, room reflections are
less correlated to the direct sound than those radiated
from pistonlike loudspeakers, and thus constructive and
destructive interference of sound is minimized. As a
consequence the localization precision is not degraded by
room acoustics as with dynamic loudspeaker arrays. The
proper sound localization and the minimum degradation
provided by multiactuator panels are important for wave
field synthesis installations"

[Unbiasedsound]

Since that paper was written 10 years ago with no new info it could also mean it was a failed DML design attempt. There are a lot of these type of thesis papers of DML tech that lead nowhere. I pull my ideas from others successful designs like the Podiums, BERTAGNIS, Yamaha NS-20/30 ear speakers, sony apm's etc....I even use other successful techniques like XRK's foam core enclosure with some modifications and techniques from the Karlsonator on my frames oooppps giving away another secret technique. LOL

Like I said before the most coherent in sound is when only 1 exciter is used per panel because when more then one exciter is used the sound waves over lap each other and there is no way to completely stop them from overlapping. The only way to do this is to use large separate panels with only 1 exciter per panel basically like STACKING separate panels together.

Bertagni's and my modified Bertagni panels are two ways but there are techniques use to minimize and control the vibrations from overlapping each other to a degree but there is no way to completely stop them unless using separate panels. My modified Bertagni 2-way panels sound really good but they do not sound as coherent/accurate as my panels utilizing only a single exciter.

Also I am not saying the CBT array using DML tech cant be done, its just that no one has SUCCESSFULLY done it yet. Maybe you might be the one to prove me wrong. I don't mind because my design everytime I hear them play puts a huge smile on my face. LOL

My main goal for DML panels is hi fidelity sound quality and everything else is secondary.....I am not here to make novelty panels that can be used for room decorations and or surround sound/back ground music.

[bradley.s]

Single exciter panels are good but they will always generate sound fields that look like image (a). You wind up with hi-fi sound at a limited position. In order to create an array of single exciter panels to perform like (b) you have to shrink the panels down, which degrades low frequencies. MAPs allowed them to create an array with better low frequency response. They attempted to deal with crosstalk in the MAPs through internal dampening.

We know MAPs work as suitable wave field synthesis arrays based on citation [25], W. van Rooijen, ‘‘Distributed Mode Loudspeakes for Wave Field Synthesis,’’ Master’s thesis, Faculty of Applied Science, Technical University Delft, Delft, The Netherlands (2001). The 2010 paper was concerned with improving MAP performance.

There's nothing wrong at all with creating a traditional stereo sound field with single exciter panels. MAPs with inexpensive DSP is just the DIYer's next level up.

[Unbiasedsound]

I said what I had to say in my above post but if you feel there is something in that MAP design worth trying then go for it and let us know your results.

[Kornbread]

Personal ramblings ...

" ... various edge-supporting techniques [36], [37]. Both free and simply supported edge options do not present a viable technology for a multiactuator panel frame. The free condition is a free radiating panel with dipole radiation characteristics. However, when observing the typical polar response of a free distributed-mode loudspeaker, a reduction of pressure in the plane of the panel is noticed because of the cancellation effect of acoustic radiation at or near the edges. For that reason the panel is usually placed in a baffle, where radiation caused by the rear part of the panel becomes contained (Pueo, Escolano, Lopez, & Horchens, 2010).

Zero of my experiments used any kind of baffle and according to this paper they acted as a normal dipole. I agree, sound output 90* to the side was minimal, but isn't less interaction with room boundaries what we desire in a normal listening room? It comes at a cost.

Their study also used a small rear chamber to absorb the rear wave. In hindsight, I do have several diy sound absorbing panels that would have been ideal for this purpose, hm .....

"In the technical literature the response of flat panel loudspeakers has been investigated using various edge-supporting techniques [36], [37]. Both free and simply supported edge options do not present a viable technology for a multi-actuator panel frame. The free condition is a free radiating panel with dipole radiation characteristics [and] alternatively, elastic boundaries are a compromise between supported and free edges and can form a viable technology for a multi-actuator panel frame".

Agreed. The manner in which the panel is supported makes a large overall difference. My panels were blue foam board supported by a wooden frame compromise of 1x2, with the foam panel being lightly sandwiched into place around its entire perimeter with light weather stripping foam. As the panel area next to the frame was cut away, effectively releasing the panel from the frame, the sound 'opened up' and output increased, especially the bass. Eventually, only a few small 'tabs' held the panel in place. Oddly enough, the next panel of treated cardboard sounded best hung from the ceiling, but that experiment was cut short.

Something along this same area of thought is that there is no mention of stabilizing the exciter (actuator). In personal experiments, there was another large measurable increase in sound output, especially noticeable with music containing bass, when the back of the exciter was glued to a 'spine' effectively anchoring the exciter to the wood frame supporting the panel. The exciters like a solid footing.

Personally, I feel this is viable technology, especially where space and weight are of concern; car interiors and airplane cockpits first come to mind, and that there is potential, but the complexity of 'getting it right' for the average diy'r is daunting.

bradley.s and whoever else comes along; continue the experiment, but please measure and report the results for others to grow from.

Reference

Pueo, B., Escolano, J., Lopez, J. J., & Horchens, L. (2010). Multiactuator Panels for Wave Field Synthesis: Evolution and Present Developments.  Journal of the Audio Engineering Society,1045-1063. Retrieved from https://www.researchgate.net/publica...t_Developments.

[Unbiasedsound]

The problem is I don't have the money or the time to try experiments like MAP that I feel leads to nowhere. I will let someone else do the dirty work and if and when it does work I will try it. Until then I rather concentrate on techniques that have proven to be successful.

Since around 4 years ago when I first started with these panels I have spent over 2k on experiments. Today I have gotten to a point where I am satisfied and happy with the sound quality of my panels. If back then I knew what I know now my expenses would have been less then $300.00. LOL

What I don't understand is that I don't see many (if any at all) people trying to mimic successful DML designs like the Podiums, Bertagni's,yamaha's etc etc. A lot of techniques I am giving out actually comes from these successful designs. For example one technique I mentioned is to put a piece of damping material right on the back of the exciter or on the spline, this technique comes from Shell katz and his Podiums.

What I want to know about maps design is where are the reviews of MAPs panels sound quality? Who here has ever heard that particular MAP dml design? If it was so great why wasn't it marketed? Does one even know if that MAP design was a successful or failed attempt at producing a good sounding panel? Its been almost 10 years since they did the MAP experiment, WHERE ARE THEY NOW and what have they produced? With so little or limited info on this design I personally wouldn't even take chance on it.



Oh my bad just rambling. LOL

[Unbiasedsound]

Double post because my first post above got erased.

[Kornbread]

The problem is I don't have the money or the time to try experiments like MAP that I feel leads to nowhere. I will let someone else do the dirty work and if and when it does work I will try it. Until then I rather concentrate on techniques that have proven to be successful.

Since around 4 years ago when I first started with these panels I have spent over 2k on experiments. Today I have gotten to a point where I am satisfied and happy with the sound quality of my panels. If back then I knew what I know now my expenses would have been less then $300.00. LOL

What I don't understand is that I don't see many (if any at all) people trying to mimic successful DML designs like the Podiums, Bertagni's,yamaha's etc etc. A lot of techniques I am giving out actually comes from these successful designs. For example one technique I mentioned is to put a piece of damping material right on the back of the exciter or on the spline, this technique comes from Shell katz and his Podiums.

What I want to know about maps design is where are the reviews of MAPs panels sound quality? Who here has ever heard that particular MAP dml design? If it was so great why wasn't it marketed? Does one even know if that MAP design was a successful or failed attempt at producing a good sounding panel? Its been almost 10 years since they did the MAP experiment, WHERE ARE THEY NOW and what have they produced? With so little or limited info on this design I personally wouldn't even take chance on it.

Bertagni used the technique (in the 60's) of stabilizing the exciter in place with a spline because he new that the magnet needed to be held in place so the voice coil would only push the panel material its just plain (Dr.Jose Bertagni was a physics professor) physics. With heavy bass tracks the exciter uses more pistonic motion there fore it needs something to push off of like a spline. Anyone play the push hands game? Well if one person is leaning against a wall and the other person isn't the person leaning on the wall will always win because the wall acts as a brace/spline so he can stabilize him self to push off of. Also like I mentioned before that without a spline to hold and stabilize the exciter in place the magnet will move and that rattling sound you are hearing is coming from the magnet moving especially at higher bass excursions.

Oh my bad just rambling. LOL

The research paper referenced is "a technical review of the development of a special type of planar loudspeaker array for wave field synthesis, known as multiactuator panel". It is not add hype for some new speaker manufacturer. It is a fact based research paper that simply lays groundwork for others to build upon if they choose to do so. I for one am glad it, and similar research, has been freely shared and encourage others to continue the vibrating panel experiment.

Great things have arisen from failure.


On to sound quality. I am one of those that believes there are some things we cannot measure but can hear, but I also feel 95ish'% of what we can hear can be measured. Most people on this forum want to see measurements, not hear someone gush over how there latest creation is so much more betterer than anything else everer. That tells us very little about how a product actually sounds.

Repeatable, accurate, and real measurements please. Everyone has a laptop, calibrated mics are not that expensive and there's some very accurate low-cost/free software (REW is one of many) floating around the net.

[bradley.s]

Tectonic sells MAPs. These have eight exciters per panel. https://www.tectonicaudiolabs.com/pr...id=product-805

Billionsound also uses MAPs for their subwoofers. http://www.billionsound.com/products...uctId=380.html

Keele said some things that make me think separated MAPs might work. He also found a straight array can behave like a curved array starting on page 23 of this paper. https://www.xlrtechs.com/dbkeele.com...0Paper%205.pdf

Something I'm interested to find out is what happens when a MAP CBT straight array radiates to both the front and the rear. Earl Geddes said you need a minimum of 10ms delay on rear and side reflections. So far, every CBT I've seen is enclosed and radiates to the front.

The one thing most hi-fi audio DIYers are dealing with is small rooms. Thankfully, Floyd Toole, Earl Geddes, and Don Keele have provided some evidence based strategies to deal with small rooms. The authors of the 2010 paper provided evidence based strategies for multiactuator panels. Somewhere in all that research a good small room MAP design exists.

[bradley.s]

Zero of my experiments used any kind of baffle and according to this paper they acted as a normal dipole. I agree, sound output 90* to the side was minimal, but isn't less interaction with room boundaries what we desire in a normal listening room? It comes at a cost.

Yes. But you're designing for small rooms like most of us. They were concerned with large rooms with a few side references to small rooms. Large rooms don't have reflection problems. So, I'd tend to think dipole is a better design for small rooms. At the same time, I'll keep Geddes' room reflection in mind as well as Toole's. I'll put the speakers in the center of the room and five feet or more away from the rear wall. Then I'll move them out to Toole's 60 degree off-axis listening positions.

Personally, I want speaker plane cancellation in the hopes it will reduce sidewall reflections.