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DIY Flat Panel Speaker Love

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  • rmeinke
    started a topic DIY Flat Panel Speaker Love

    DIY Flat Panel Speaker Love

    Hey fellas,
    How many of you have built a DML panel speaker? Is there any DML panel love out there???

    After reading about the Podium Sound panels and making my way through the expansive AudioCircle thread "NXT.......rubbish??....THINK AGAIN!" (http://www.audiocircle.com/index.php?topic=70541.0) many months ago, I have finally put together some quick test panels to see whether or not these might be an option for the living room were I could set up and tear down the system and carry the light panels away with ease.

    The first panels I put together were small and simple. 1" thick Owens-Corning 2 ft. x 2 ft. Project Panels from Home Depot (http://www.homedepot.com/p/Project-P...-PP1/203553730). The panels are sanded on both sides with a palm sander with 100 grit. Both sides are then treated with a 1:1 mix of PVS white or wood glue and water; this dampens the panel and aids propagation of the sound waves across the panels surface. The exciters are from PE of course, the Dayton Audio DAEX25FHE-4 (http://www.parts-express.com/dayton-...4-ohm--295-224).

    How do they sound? Different. Pleasant. Excellent transients. Percussion and plucked strings are probably the best I've heard. The harmonica sections on Cowboy Junkies "Trinity Sessions" has beautiful dynamic shading that makes for a very realistic presentation. Fast and biting without harshness. Didn't measure the response but think they sound reasonable played full-range. Response likely down to the 100Hz range with a laid back HF response that is quite good and not lacking for my tastes. A 2' x 6' panel is said to get down easily to 50-60Hz. Compared to my Tang Band W4-1879 in OB, they are noticeably more sensitivity; 91+dB range.

    As I said... different sounding. You have to get adjusted to the presentation as the panels are distant sounding after switching from my open baffles. There is a lack of presence and a sensation that the music is emanating from behind the speaker, through the panel, then to the listening space. Once adjusted they are VERY ENJOYABLE and NATURAL sounding. I listened to Muddy Waters "Folk Singer" (on gold disk) and Cowboy Junkies "Trinity Sessions" into the wee hours of the night a few nights ago just enjoying the dynamics and naturalness. Very nice indeed. All from $30 worth of parts and 1 hours time. Amazing honestly. Would be interesting to combine with an open baffle bass panel. Lots of different configurations.

    [edited Jan 4 - The panels have opened after the exciters have fully broken in and the panel treatment has cured (harder panel skin). The small panels are fast, detailed and considerably more clear than the time of the initial post.]

    Curious to hear what others have built and their listening impressions. Anyone enjoying DML panels in their system at the moment?
    Last edited by rmeinke; 07-10-2015, 01:01 AM.

  • geosand
    replied
    So has anyone used a panel product like this before: https://www.homedepot.com/p/Amvic-Mu...-301619814-_-N . Its high density EPS which everyone seems to like (28 PSI compression, which is even higher than XPS foamular 250 @ 25 PSI). Higher compressive density should mean better HF propagation. But whats unique is the sculpted front surface which contains and additional 98 small protruding rectangles! Looks nice. But I wonder if this could be ideal as those smaller rectangles may also have their own resonance points (which is a good thing as the more resonance points the lower any one resonance may be and thus the smoother the FR should be.) Yes it is 2" thick which may not be a plus (or could be who knows) and its only available in 2'x4' sheets. But the size and the front sculpting may be a plus for WAF :-). Any thoughts?

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  • bradley.s
    replied
    Originally posted by ameuba10 View Post

    I was refering to the exciters
    That is an exciter. They call it a BMR (Balanced Mode Radiator.) I think I remember you were interested in PC speakers. Those BMRs are about the size you'd want for computer speakers. They've done the engineering for you. Buy one and see how they did it. Then you'll be able to better make the custom solution you want.

    https://www.tectonicaudiolabs.com/au.../bmr-speakers/

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  • ameuba10
    replied
    I was refering to the exciters

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  • bradley.s
    replied
    A single near field sub is the smart way to go. I won't go the smart way because I'll get caught up trying to figure out how JBL does it. Then I'll look at the monstrosity I built knowing I could have done it cheaper and SMDH ;-)

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  • Kornbread
    replied
    Build the sub into a coffee table and set it beside the couch or just use a butt kicker.

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  • bradley.s
    replied
    One more note about Toole and subwoofers. He said there are two alternatives to multiple subs and the JBL proprietary algorithm. 1) multiple subs and patient manual adjustment. 2) one subwoofer placed in the near field of the listener. Just take a single sub and locate it close to your listening position. He said a guy put a sub in his ceiling directly above his seat and it worked. Nothing special about the ceiling placement other than it was close to the listener's seating position.

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  • bradley.s
    replied
    Oh, btw, I'll need to find a book/info source on DSP equalization so I can flatten the response in the array. Unequalized, the rise around 2kHz is terrible. I hear it and wince. My dog hears it and winces. If I can flatten it and keep the axis response tight like in the image above I'll be able to build the type of system Floyd Toole says will work.

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  • bradley.s
    replied
    My grasp of the CBT sound field is influenced by the graphical representations Don Keele made in his papers. I'm going to verbalize but I might get it wrong. Relative to a point source speaker, a CBT array supplies a more controlled vertical sound field which results in: 1) less volume decrease as you move away from the speaker, 2) reduced combing and lobing at higher frequencies, 3) a more focused polar response, and 4) less ceiling reflection in small rooms. The CBT Keele designed also has wide directivity, however, Floyd Toole said that's just basic good speaker design. It isn't unique to CBTs.

    Keele's straight array is delayed to approximate the physical shape of his curved array. His straight array is delayed at the top not the bottom. However, his physically curved array is not delayed with DSP. It's delayed because the top of the speaker is physically further away from you than the bottom (see attached photo.)

    One of the reasons I tried to do a CBT with DML/MAP is to take advantage of the wide directivity that seems to be inherent in an excited panel. I wanted wide directivity because I was influenced by Floyd Toole's book Sound reproduction: the acoustics and psychoacoustics of loudspeakers and rooms. I'm trying to create the type of sound field Floyd Toole says is preferred through double blind testing. My ear hears what you see in the image I posted above. As I turn the array the high frequencies remain constant but the lower frequencies fall off as I approach 90 degrees. But they don't fall off very much. In my case, I'm ok with that because I planned to make a different speaker to handle lower frequencies.

    Another thing Toole covered in his book was movie dialog for home theater. The center channel is huge for intelligibility. He said they got improved dialog intelligibility by turning down the right and left speakers relative to the center channel. They got the best intelligibility by turning the side channels completely off. However, they lost overall movie sound enjoyment quality. Special effects and soundtrack suffered. DML excited panels seem to have better dialog intelligibility because the reflections aren't as coherent as the direct field. For that reason I want to build a MAP center channel to compliment the MAP arrays. I'm guessing that setup will let me have improved movie dialog intelligibility without turning down the side channels. The nature of the DML will compensate. I'm also going to make the center channel into a CBT, except in the vertical plane. It will also be a full virtual 180 degree CBT instead of a 36 degree arc. According to Keele et al, 180 degrees focuses the center channel source right in the center. However, a 180 degree CBT built with normal speakers creates distracting side wall reflections. I'm guessing the MAPs won't run into that problem because their reflections aren't as coherent so our brains ignore the reflections. I'm just not sure about how to design their geometry yet: long and narrow, wide and tall?

    In the end I'll have two CBT arrays similar to the one I just built located on the ceiling (upside down) at 60 degrees off listening axis. Then I'll place the center channel CBT below the TV screen. I haven't figured out how to do the subwoofers yet. Toole said JBL uses multiple subs and a proprietary DSP algorithm. I still have to hunt that information down and figure out how they did it before I build the subs.

    Toole also said something else in his book. He suggested the future of speakers was active DSP instead of passive crossovers, and that each speaker driver would be driven by an independent amplifier. He said the inexpensive amplifiers of today are ruler flat. Expensive amplifiers are obsolete today. The array I built uses cheap 100 watt Texas Instruments chip amps. They were only $3.50 each. They're powered by an inexpensive Meanwell 300 watt switching power supply, $25. The 300 watt Meanwell power supply will power both right and left channels as well as the center channel and have plenty of power to spare.

    The only semi-expensive part of the system is the DSP. But that's only because I'm creating a pretty complex array of speakers. I'd bet someone could build a basic 3-channel MAP (Right, Left, Center) that would sound as good as the complex system I'm building. In a double blind test a listener probably wouldn't be able to tell the difference between a standard four exciter MAP and a twelve exciter CBT MAP. It might be a case where a microphone could tell the difference but a human brain couldn't. Although, I think you'd still want to use one Mini-DSP to flatten the frequency response of the MAPs. Each MAP would have four exciters with one inexpensive TI chip amp power all four. Then that MAP of four exciters with one amp would be controlled by one of the four outlets on the Mini-DSP. And I'd place the four exciters on the MAP the same way Tectonics places theirs. I'd even use Tectonics' geometry and panel material. The one advantage a CBT array might have is low frequencies. My MAP CBT is five feet tall. I could make it seven feet tall and improve low frequencies. Especially using Keel's ground-plane design like in the image below (placing a CBT on a reflective surface like a hard floor or ceiling.)


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  • Kornbread
    replied
    Just thinking out loud. I though the purpose of delaying the channels was so all sound arrives at the listening position at the same time?

    One exciter, w/spline, foamboard, w/small tabs holding panel in place.

    Click image for larger version

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  • bradley.s
    replied
    I tried to measure speaker directivity. Placed mic six feet from the speaker at 28 inches elevation. I kept the mic in the same location but rotated the speaker for each measurement: on-axis, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. Smoothed to 1/3.

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  • bradley.s
    replied
    I used the mic to make sure each of the five array sections were attenuated by -3dB relative to the previous section. Then redid the impulse response. It's easier to see the five sections now. Though section three is lower than I expected.

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  • bradley.s
    replied
    Interesting. I noticed the initial humps in the response correspond with the delays set in each of the five sections. However, the fifth section is -12db so it barely shows up. In fact, it might be less than -12db. I haven't confirmed the speaker is actually -12db than the first section of the array.

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  • bradley.s
    replied
    Wait, those first images were measuring the back of the speaker. That's probably why it dipped to negative 100 first. These photos are measured from the front of the speaker.

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  • bradley.s
    replied
    This is what I get when I select the Step Response checkbox. First photo with red line is zoomed in to show -500u to 10.0m. Second photo with green is zoomed out to show the whole line.

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