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DIY Flat Panel Speaker Love

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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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  • Kornbread
    replied

    Make it look like this.

    Click image for larger version

Name:	impulse resp.JPG
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  • bradley.s
    replied
    Here's the graph under the impulse tab. I don't know what I'm looking at or if I measured this correctly. I placed the mic one meter from the speaker at 28 inches in elevation.

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  • bradley.s
    replied
    A paper somewhat related: Implementation of a Dipole Constant Directivity Circular-Arc Array. Array is physically curved but it's dipole. In contrast, the MAP array I'm trying to learn how to measure is a physically straight delay-curved attempt at a CBT. I assume a physically curved array is better. On the other hand, a physically straight array might gain from near wall placement by angling the axis toward or away from the wall. With a curved array either the bottom or top would need to be moved away from the wall. I don't know, I'm tired and burned out for the day.

    http://faculty.tru.ca/rtaylor/public...ementation.pdf

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  • bradley.s
    replied
    I don't know how to test impulse response. I'll have to learn how to do it.

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  • Kornbread
    replied
    Curious to see what the impulse response looks like. Post that unaltered please.

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  • bradley.s
    replied
    Second photo, no smoothing.

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  • bradley.s
    replied
    Here's the first REW measurement. 20Hz through 20kHz, microphone 36 inches away from speaker on-axis with the mic elevated 28 inches. First image is 1/24 smoothing. Second is no smoothing. But I don't know how to measure speakers so I'll spend the next couple days figuring out how to do it. The CBT array has delays and volume attenuation, however, I have not confirmed the volume attenuation with the mic. I decreased volume with the DSP but haven't confirmed that's what is actually playing through the speaker.

    I have no idea if this is functioning like a CBT or a regular array. That's what I hope to find out after I learn how to take measurements.

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  • bradley.s
    replied
    Originally posted by ameuba10 View Post
    has anyone attempted a small version? Something for desktop use
    https://www.parts-express.com/tecton...4-ohm--297-216

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  • ameuba10
    replied
    has anyone attempted a small version? Something for desktop use

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  • bradley.s
    replied
    One amplifier per actuator. They'll be wired in parallel for each segment of the CBT array. Each segment will be delayed, attenuated by DSP. After it is complete I'll need to figure out how to accurately measure it for polar response with REW. If it works like a real CBT I'll need to figure out how to equalize for frequency response. If that works, I'll see if I can reduce the number of actuators.

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