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BMR Curved Line Array

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  • BMR Curved Line Array

    Hello All.

    Despite the technical issues with line arrays, I had to give it a try. Besides, the wife wanted me to nix my old Infinity Quantum 5 monkey coffins beside the new TV.

    My approach was to use the smallest full-range drivers I could find (and afford). 150 bucks-worth of the close-out HiWave BMR12's, some scrap lumber, and leftover cabinet paint, and voila. Some notes:

    - Height was limited, so I know that I am not really operating near-field. Still, I hoped to get some of the advantages of line arrays.

    - I cut the flanges off of the top and bottom of the drivers in order to stack them as close as possible to minimize comb interference. This let me use 16 drivers per side.

    - I assumed that the curved array would reduce the combing, since the path lengths from the drivers would all vary in such a way that nulls between any two drivers would be reenforced by others.

    - I also tapered the width top to bottom to avoid a strong box resonance. I must say that the woodworking was a challenge.

    - The theory is that the base and floor create a sonic mirror image of the array. This would be true if the floor were hard, or the base extended further in front. Esthetics and carpet trumped theory in this case.

    - Since the BMRs are 8-ohm, I wired then as a simple 4-by-4 series-parallel combination for a composite 8 ohms.

    - I added a series and parallel resistor to taper the top four drivers. The top two are 6dB down, the next two are 3dB down. Frankly, I don't know how much this helps the combing.

    - I initially equalized them with a 31-band graphic EQ using a calibrated mic and synRTA. I needed about 6dB boost rising above 2KHz, I assume due to the destructive interference at higher frequencies.

    - I replaced the graphic EQ with a simple parallel RC (8ohm and 10uF) in series with the box. This acts as a passive shelving high pass filter to provide about the same treble boost.

    - Oh, and of course I pair these with a powered sub crossed over at 200Hz. There is a lot of diaphragm area with 16 drivers, but their resonance is at 160Hz, so the low bass is not really there.

    So how do they sound? Pretty good... I guess... I had hoped to be blown away by a huge wide stereo image that filled the room and caused the speakers to disappear. Not so, I assume due to all of the compromises from the ideal. Family and friends really think they sound great and love, LOVE how cool they look. They do sound very good watching music content on TV. Better than the old Q-5s, anyway. Not sure yet.

    Click image for larger version

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  • #2
    Re: BMR Curved Line Array

    they look really nice.

    Comment


    • #3
      Re: BMR Curved Line Array

      I agree with your family and friends, they look cool.
      Nice job.

      Comment


      • #4
        Re: BMR Curved Line Array

        Do you have any measurements on these you can share?
        I have 9 per side ready to do almost the same thing that I haven't started putting together yet. I was going to hang them in the garage and wasn't hoping to make them look as good as you did. I like the flange removal idea and may end up copying that.
        Did you calculate the box volume prior to building and is it ported at all?
        Very nice job on these-

        Comment


        • #5
          Re: BMR Curved Line Array

          Don, it looks like you've empirically arrived at something similar to a CBT array. It also looks like a competent overall design, though you will want to add one or more subwoofers to fill in the low end. There's no way those BMRs will deliver satisfying bass without seriously inconveniencing them with EQ, adding distortion.
          Best Regards,

          Rory Buszka
          Product Manager, Dayton Audio

          The best way to predict the future is to create it.

          Comment


          • #6
            Re: BMR Curved Line Array

            Thanks all for the comments.

            Yes, this is basically a "poor man's CBT array", with giant compromises for size and esthetics. To be a CBT, it would have to be taller, curvier, more aggressive power shading, and set on a hard reflective surface.

            I really just winged it on the cabinet dimensions, since I wasn't worried about bass response. So they are sealed and stuffed, not ported. They are 36" tall, 4-1/4" wide at the top, 6-1/2" wide at the bottom, 2" deep at the top and 5-1/2" deep at the bottom. The curve radius is 10 feet I think. I probably should have made them a bit deeper.

            I have a 12" closed-box sub behind the TV stand. It has the Dayton 2.1 plate amp in it - 50W for the sub and 25W/ch for the arrays. This is fine for TV and casual listening. Since the BMRs are good for 12W each, the arrays can handle nearly 200W per channel. I probably would need a 1000W sub to be able to keep up with them! I don't party like that anymore, though.

            Comment


            • #7
              Re: BMR Curved Line Array

              Very nice job! I can see where the woodworking would be a challenge with all the tapers.
              “I cried because I had no shoes until I met a man who had no feet”

              If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

              Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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