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Inspired by the Bose L1 PAS, I tried for better results with a DIY for my gigs

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  • #16
    Originally posted by RandyC View Post
    ... So should I build it assuming a totally sealed "acoustic suspension"?
    Yes - a sealed column
    I understand that method has low efficiency, but has the flattest response....l
    Estimate a little under 94db @ 1 M

    "Not a Speaker Designer - Not even on the Internet"
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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    • #17
      Originally posted by Bwarchitect View Post
      Re: Inspired by the Bose L1 PAS, I tried for better results with a DIY for my gigs

      PSEUDO-BOSE LINE ARRAY PA

      I'm considering building two line array modules of (12) speakers each, using
      Dayton Audio CE65W 2-1/2" drivers, hoping to achieve response of 150-16,000 Hz
      and planning to use them with a separate powered sub to handle below 150. Dayton claims response
      of 105-16,000, with a sealed F3 of 98hz.

      Two questions: 1) If I make the enclosures smaller for easier handling, (to about .03 vs. .05 recommended) would I reduce the
      low end too much to get my desired 150 hz floor? 2) I'm thinking of angling the face plates
      as shown for maximum lateral dispersion- Bose does this, but other commercial line arrays don't.
      Is it worth the trouble?
      Here's an illustration of my concept:
      [ATTACH=CONFIG]58607[/ATTACH]
      Generally smaller volume must cause some loss of low end, but honestly to me I can't imagine using a system like this without planning on also using separate floor speaker with full bass range. But just so you know, I'm planning something similar, so if you've gotten further along and have discovered any "gotchas", please let me know.

      I've also seen some builders adding wooden blocks at various places along the back, lining the inside with carpet runner, and stuffing the cavity with foam and pillow stuffing... and to battle resonances and standing waves.

      I am curious if you have any idea what the actual angles are that bose uses. While I've heard a lot of arguments for and against doing this, the bottom line is BOSE does it and it works well, better in my opinion then some line arrays that don'e. You can't argue too much with success.

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      • #18
        Don't want to keep being a pest, but I have another question. While researching different people's line array builds, I've come across a few where the builder went to great pains to add blocks of wood to serve as baffles, to break up and block standing waves, and also wen to great lengths to put carpeting on the inner walls, and and tightly pack the inside with foam and pillow stuffing. All this, I imagine, to prevent resonances, or that awful sound of a "speaker in a pipe". Am I correct that the original poster here did just left the inside completely open, hollow, and unpacked, and had no regrets?

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        • #19
          Originally posted by Sydney View Post
          Yes - a sealed column

          Estimate a little under 94db @ 1 M
          Thanks. Amid a lot of discourse, I very much appreciate those who actually add useful information. I've raised my questions on many forums, and too often the responses are all about comparing brands instead of technical building guidance. Do you have any thoughts on my last post? Specifically, would you build any kind of baffels inside the column to help break up standing waves? And also, should I be damping by stuffing the inside of the column with foam and such? This is especially important to me because I'm planning a thinner column (maybe 4" square at most), and only about 4 feet long, to supplement an already adequate pair of floor speakers with plenty of bass and low mids. It will be suspended about 2-1/2 feet up. But a thinner column could easily resonate and sound like a wah-wah- pedal stuck on a middle position if I don't plan for it.

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          • #20
            Originally posted by RandyC View Post
            ... Do you have any thoughts on my last post? Specifically, would you build any kind of baffels inside the column to help break up standing waves? ...
            Yes I would strive to make it less like a pipe, The baffles could even be continuous, completely isolating each driver in it's own cell., and also connecting front to back.
            The material wouldn't have to be thick.

            "Not a Speaker Designer - Not even on the Internet"
            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

            Comment


            • #21
              Originally posted by Sydney View Post
              Yes I would strive to make it less like a pipe, The baffles could even be continuous, completely isolating each driver in it's own cell., and also connecting front to back.
              The material wouldn't have to be thick.

              Can i pick your brain one more time? There's good news but also some trouble, and I'd appreciate you opinion (and other opinions) on my proposed solution. thanks in advance!

              My array ended up with 15 of those 2-1/2" VIFA speakers, and I included 4 multi-point terminal mounting strips inside, to make experimenting with different combinations of power weighting among the speakers easy. To start I just paralleled 3 groups of 5 (4 ohms each) in series, for a total "demonic" impedance of 6.66 ohms.

              Before any measurements, I tried a simple ear test, in its expected environment. That is, the array sits 2 feet up, on top of my bass box, which is a ported bass reflex speaker. Well the ear tests were great!! I did have to turn up the high treble end on my mixer about 4 dB since no tweeters are in the design. But the sound with acoustic guitar and singing were awesome. Using a wireless link I was able to move all around a 20 foot room and I feel i've achieved the first goal: Clear articulate sound over at least a 120 degree range. FYI, 14 of the speakers are alternately shaded left and right, by 15 degrees, and the 15th speaker on top points straight out.

              So now on to the actual measurement testing of the array by itself (no bass box), and all EQ set flat. As this was intended as a midrange and upper mid array, I wasn't too disappointed to see response drop off pretty quickly below 200 hz. I was also happy to see reasonably robust response out to about 15K. But I was disappointed to see some obvious mystery resonance peaks at 1K, 1.5K, and another at about 8.5K. So after plugging these into a calculator I got wavelengths of 13" , 9", and 4". Then i remembered... I have 4 structural braces across the inside extending from flush with the back (to receive screws), and extending about an inch short of going all the way to the front baffle. Well this makes perfect sense! 3 of the support braces are 13" apart, the middle one is 9, and inner width (and depth) of the array box itself is about 4".

              This may seem discouraging, but actually is very satisfying to be able to mentally map each "bump" on a response curve to an actual structure! Especially since by ear (and with real guitar and vocals), the array is already a success.

              So the next thing I need to do is some experimenting to combat those resonances. Obviously putting dense soft craft foam on all inner surfaces, and tightly stuffing the box with teddy bear pillow foam was not enough. So what I'm thinking of doing now, is I'm going to cut some light wood into 3-1/2 " strips, maybe 10 inches long, and mount them internally at angles. spanning from one inner side wall across one side to the other. My plan here is make an apparently simple resonance situation into a very complex situation, with multiple broad angles everywhere. The hope will be to cause nearly infinite resonance points, so that they all become irrelevant. I suppose I'll have to cover these inner baffles with more of that soft craft foam, and then push back all the pillow stuffing. But maybe something even denser like pieces of an old blanket? I do understand that I could also opt for a multiple resonant LC+R circuits to force the response flat. But I think it makes sense to do everything mechanically possible first. Good build before EQ, right?

              Anyway, thanks in advance to your time.

              Comment


              • #22
                Originally posted by RandyC View Post
                .. obvious mystery resonance peaks at 1K, 1.5K, and another at about 8.5K. So after plugging these into a calculator I got wavelengths of 13" , 9", and 4". Then i remembered... I have 4 structural braces across the inside extending from flush with the back (to receive screws), ...
                So I presume that these peaks were present on and off-axis?
                How big were the peaks?

                "Not a Speaker Designer - Not even on the Internet"
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                Comment


                • #23
                  Originally posted by Sydney View Post
                  So I presume that these peaks were present on and off-axis?
                  How big were the peaks?
                  Click image for larger version

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                  Honestly the on/off axis part is a little hard for me to guage. The speakers point left and right after all. But I try to be on one axis or another during test. The lower peaks weren't terrible... about 3dB. Ther 8.5K one was a bit more severe, around 6db, and I forgot to mention that one was preceded by an equal dip at around 5Khz.. Honestly I may be making too big a deal about this, because once I shrink down the vertical scale so its closer to what is supplied with the actual speaker, its really not that bad. (Ignore the green line as that's supposed to be THD,). But it just seemed too much coincidence when i expanded the scale that the peak wavelengths corresponded so exactly to the distances between walls and barriers. I'm still very curios if adding angular baffels will help, since that eliminates the chance of any one distance prevailing. Then again, I've NEVER seen anyone advocate angular baffels inside a speaker enclosure.

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                  • #24
                    Originally posted by RandyC View Post
                    .... Honestly I may be making too big a deal about this, ...
                    Maybe - your call
                    Seriously - If you are familiar with this
                    https://www.trueaudio.com/array/MCLA...ct_details.htm
                    Notice how much EQ is integral to get a desired response.. This is not unexpected with an "unshaded" array or other clustering of small speakers to flatten response.
                    So in your case - If a simple pull down of a couple of db fixed these...
                    I wondered how the sound was outside ( were these peaks present ).
                    Also does a singular driver ( placed upon a large test board ) have these peaks.
                    One test trick I used before is to drape/wrap a moving blanket around the other sides of the cab to notice any change in sound.
                    Not ruling out internal resonance here but rather making sure it is indeed an issue.
                    "Not a Speaker Designer - Not even on the Internet"
                    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                    Comment


                    • #25
                      Originally posted by Sydney View Post
                      Maybe - your call
                      Seriously - If you are familiar with this
                      https://www.trueaudio.com/array/MCLA...ct_details.htm
                      Notice how much EQ is integral to get a desired response.. This is not unexpected with an "unshaded" array or other clustering of small speakers to flatten response.
                      So in your case - If a simple pull down of a couple of db fixed these...
                      I wondered how the sound was outside ( were these peaks present ).
                      Also does a singular driver ( placed upon a large test board ) have these peaks.
                      One test trick I used before is to drape/wrap a moving blanket around the other sides of the cab to notice any change in sound.
                      Not ruling out internal resonance here but rather making sure it is indeed an issue.

                      SIGH--- I'm sad to say that you may be right about outside influence. This is an awfully hot room, with many large sources of unwanted reflection and interference. Listening to all the things in the room getting excited by different points along the frequency sweep is almost comical. But doing the test outside has proven futile, as the ambient noise is horrendous. I'll have to try your blanket technique after I finish with my addition of the angled baffles. I've also packed it more tightly this time with poly fill. EQ I expect, but I think I'll need to build some precise LCR circuits to really address all those little peaks. Oh well... it sounds pretty good, and i've been warned several times this wouldn't be easy.

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                      • #26
                        I thought maybe you lived near somewhere quiet...
                        IF you do determine it is NOT resolvable with EQ and actually due to internal resonances...There are numerous things people have tried, including ( but not limited to ) used denim, floor carpet backers.
                        I have used DIY grout on panel interiors as well.

                        All in all though - it would appear that it is working well.
                        "Not a Speaker Designer - Not even on the Internet"
                        "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                        Comment


                        • #27
                          Originally posted by Sydney View Post
                          I thought maybe you lived near somewhere quiet...
                          IF you do determine it is NOT resolvable with EQ and actually due to internal resonances...There are numerous things people have tried, including ( but not limited to ) used denim, floor carpet backers.
                          I have used DIY grout on panel interiors as well.

                          All in all though - it would appear that it is working well.

                          Thanks for all your help man.And by the way... I think I may be on to something with my "angled baffles"!!! Hey it wouldn't be the first time a total dummy discovered something new that worked! :-) Outside of a small increase in the density of POLY fill, those baffles were the only change I made, and under the same conditions not only does the curve look flatter, but I was not hearing all the apparent little "ups and downs" during the frequency sweep! Of course this is still without the bass box.
                          Attached Files

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                          • #28
                            That's great
                            "Not a Speaker Designer - Not even on the Internet"
                            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                            Comment


                            • #29
                              By the way, I documented my completed array on my own web site here. Thanks again everyone for all the help.

                              http://elfintechnologies.com/LineArray.html

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