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considering a line array build, using TC7FD00-04 2-1/2 speakers

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  • considering a line array build, using TC7FD00-04 2-1/2 speakers

    I just happen to have a large number of these speakers (bought from parts express), which I've used in various projects. Despite their being tagged as "woofers", I've always been pretty impressed how far into the high end they go. In fact the "on axis" response goes clear out to 20Khz. Well I've I've been thinking of making a line array out of these. For background, I'm a musician and typically play guitar (electric and acoustic) and sing, in small clubs, using various samplers, drum machines, and sometimes home brewed tracks . I've built my own pair of floor speakers using traditional bass-reflex design, with 2 way crossovers to horn tweeters. they can be stacked as needed, or spaced apart "left and right" when there's an elevated stage available. I'll stack them in a long narrow room. But long narrow rooms are always a challenge, and I can't help notice how many musicians are starting to add line arrays to their setup. I can immediately see the advantages, especially in a club where there are often people sitting 20 feet or more away at a bar, and the musicians have to work from the floor off in some corner. in addition to some people sitting closer at tables, these line arrays nicely push some of the audio at all possible head heights, and offer significantly more clarity (you can understand the words being sung!) at a distance where you'd normally expect to hear only muddled tones, or alternately the harsh gritty tones from cheap horns on low budget PA speakers, that probably have more piercing 2kHz than anything.

    So anyway, I'd like to experiment adding my own home brewed line array, and since I already have a LOT (literally over 3 dozen) of those small peerless / VIFA speakers, I thought I'd give it a try. Now I'm willing to accept that my first attempt here will be less than ideal, and that I'll likely end up modifying it down the road. In fact, based on what my ears tell me about these little speakers, i wasn't even going to include tweeters the first time, or if I do it will probably be just one on top. But there are a few confusing principals I'd like some advice on, from those who've tried their hand at these arrays.

    1) I see that some companies like BOSE seem to angle each speaker slightly left or right in an alternating pattern. Sounds like a great idea, since the best high frequency from full range speakers seems to be when listening head on. But how much of an angle is sensible? And should I just alternate just left and right, or should I do something like a center / left / center /right, etc., in a repeating pattern?

    2) I see some builders wire their speakers so that the center drivers get the most power. If the main problem I'm trying to solve is reaching those further back, shouldn't I be sending more power to the top speakers?

    3) I've read a lot about the "comb" effect, which basically cases dead spots in the sound field when the speaker spacing is wrong. Is there a simple rule of thumb (without 4 pages of math) that would tell me, perhaps based on room size, what the ideal spacing for my 2-1/2" speakers should be?

    4).equipment weight vs good sound always seems to be a trade off. But these are small speakers. Need I make an array like this out of heavy particle board? Could I get away with simple plywood reinforced at the corners? And if so, how thin can I get away with for the plywood? I'd much prefer to avoid anything beyond 1/2" unless there is a clear advantage.

  • #2
    Jim's white paper should help http://www.audioroundtable.com/misc/nflawp.pdf

    Don has some good reading on shading but I can't find the link http://www.xlrtechs.com/dbkeele.com/CBT.php

    The TC7s have been used without a tweeter in several designs.
    John H

    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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    • #3
      Originally posted by RandyC View Post
      I see that some companies like BOSE seem to angle each speaker slightly left or right in an alternating pattern.
      That's done to try to overcome the fact that a 2.5 inch driver doesn't have good dispersion above 8kHz or so. A far better result is had with midbasses capable of reaching a sensible crossover point to subs, say 100-125Hz, and tweeters for the highs. It's also much more expensive, which IMO is why Bose doesn't do it that way.

      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        Originally posted by billfitzmaurice View Post
        That's done to try to overcome the fact that a 2.5 inch driver doesn't have good dispersion above 8kHz or so. A far better result is had with midbasses capable of reaching a sensible crossover point to subs, say 100-125Hz, and tweeters for the highs. It's also much more expensive, which IMO is why Bose doesn't do it that way.

        I figure, especially as I'm hoping to just get by with one of these, I think I'm going to have to try to do that angling. I'm just trying to make a good guestimate as to how much of an angle makes sense. I've already got separate floor speakers to help with the bass and lower mids, and I yet may add some tweeters. But since I'm just building one, I can deal with the extra trouble of angling the speakers. Just trying to figure out a sensible angle.

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        • #5
          You likely will need to equalize (increase in this case) the upper two octaves (5K-10K and 10K-20K Hz) to better cover the treble area. Because of comp lining and physical spacing of the drivers, the frequency response will exhibit roll off as frequency increases. Usually an equalizer is useful as most electronics these days do not have treble adjustment. An equalizer can also mitigate some low frequency roll off. But as this is a pro audio app, you will not really need flat to 20K Hz kind of response.

          I'm not much on angular directing the drivers like the BOSE drivers. For best results locate those drivers about 3 inches center to center apart. More drivers per side would improve performance as I cover in my white paper.

          Good luck! I love line arrays.

          Jim

          Comment


          • #6
            Originally posted by Jim Griffin View Post
            You likely will need to equalize (increase in this case) the upper two octaves (5K-10K and 10K-20K Hz) to better cover the treble area. Because of comp lining and physical spacing of the drivers, the frequency response will exhibit roll off as frequency increases. Usually an equalizer is useful as most electronics these days do not have treble adjustment. An equalizer can also mitigate some low frequency roll off. But as this is a pro audio app, you will not really need flat to 20K Hz kind of response.

            I'm not much on angular directing the drivers like the BOSE drivers. For best results locate those drivers about 3 inches center to center apart. More drivers per side would improve performance as I cover in my white paper.

            Good luck! I love line arrays.

            Jim


            Thanks Jim. Yes that excellent white paper was the first thing I read! ;-) Here I was mainly trying to get a little insight on some of these variations I mentioned. But I must say i was a little taken aback when I read in your paper about the far field (probably my biggest concern) comb effect. When I realized that even my little 2-1/2" speakers would pretty much have to overlap to avoid the cancellations at 8Khz, it dawned on me that there is no ideal way to do this. But now I'm thinking (hoping at this point) that since these speakers have their best high end output when listening head on, just MAYBE facing the speakers slightly at different angles might mitigate the cancellation problem. Then again, it could make it worse. I'll say this... its a good think I HEARD some musicians using various line arrays BEFORE I read your paper, or I might have concluded there was no way to really make them sound good. But sometimes when I over analyze things like this, I do have a tendency to throw out the baby with the bath water! LOL!

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            • #7
              Originally posted by RandyC View Post
              When I realized that even my little 2-1/2" speakers would pretty much have to overlap to avoid the cancellations at 8Khz
              That's not an issue with a vertical array. You'll get some lobing close in, but that resolves at distance. This shows how:
              http://www.acoustics.salford.ac.uk/f.../diffract4.htm
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

              Comment


              • #8
                Originally posted by billfitzmaurice View Post
                That's not an issue with a vertical array. You'll get some lobing close in, but that resolves at distance. This shows how:
                http://www.acoustics.salford.ac.uk/f.../diffract4.htm

                INTERESTING! Seems to make a good case that the near interference patterns actually help distribute the sound horizontally. So maybe I don't need the extra construction headache of angling my speakers left and right. Though as one person has noted, for better horizontal dispersion of the higher frequencies with small speakers, it might be a good idea. especially if BOSE went this route. Hmmm... dilemmas dilemmas !

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                • #9
                  Originally posted by RandyC View Post


                  Iit might be a good idea. especially if BOSE went this route. Hmmm... dilemmas dilemmas !
                  I would not consider anything that Bose does as an impetus to do likewise! The opposite perhaps? You will find very little admiration for what Bose does by people who have some knowledge and understanding of proper speaker system design.
                  “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

                  Comment


                  • #10
                    I think this is a great practical project. Figure the box length you can fit in your vehicle, if this will be stand mounted, power handling required & number of drivers, and build a simple narrow tower out of 1/2 inch baltic birch. You will end up with something that sounds better than 90% of the high tops out there.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                    Comment


                    • #11
                      When line arrays are deployed in sound reinforcement, they typically curved with delay at the center of the stack. This could be emulated at home, with the top and bottom of your array closest to the listening position, and the center recessed (further away). Line arrays work best when the wavefront is coincident, the opposite of a point source. Sent from my Nexus 6 using Tapatalk

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                      • #12
                        Originally posted by RandyC View Post
                        INTERESTING! Seems to make a good case that the near interference patterns actually help distribute the sound horizontally. So maybe I don't need the extra construction headache of angling my speakers left and right.
                        You're looking at two different concerns. The wave front integration resolves lobing on the vertical axis. It has no effect on dispersion on the horizontal axis. At high frequencies that's determined by the width of the radiating plane, as show by this applet:
                        http://www.acoustics.salford.ac.uk/f...tionslider.swf
                        Angling the drivers left/right will widen dispersion at high frequencies, but it also creates other issues, so in a nutshell it's the wrong way to fix the problem. The right way is to make the line a 2 way system.
                        it might be a good idea. especially if BOSE went this route.
                        Bose does whatever gives the highest profit margins, not the best results. From a business model standpoint they're worth emulating, but not from an engineering standpoint.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #13
                          Originally posted by billfitzmaurice View Post
                          Bose does whatever gives the highest profit margins, not the best results. From a business model standpoint they're worth emulating, but not from an engineering standpoint.
                          Totally agree with this! They are bad in speaker system design, but they are Master-Marketers. In the end a bad design heavily promoted will always win compared to a great, but unpromoted design.
                          “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

                          Comment


                          • #14
                            Originally posted by thekorvers View Post

                            I would not consider anything that Bose does as an impetus to do likewise! The opposite perhaps? You will find very little admiration for what Bose does by people who have some knowledge and understanding of proper speaker system design.

                            I appreciate your input of course. But let's consider... *I* got interested in line arrays, AS a musician, AFTER having personally HEARD the BEST club sound in a noisy and combo sound I have EVER heard (and I've been around a while), from an array, used by small band combos. THEN, taking a close look during the band's break, I saw that it was a BOSE system. AND... this has happened on a couple of occasions with different bands... not the exact same BOSE system, but a BOSE system line-array system still. So after having heard great sound from BOSE, and now trying to learn what i can to see what design features I could learn to come close to that sound, you're saying I should NOT, and in fact I should do the opposite of whatever I learn. Again, I appreciate all input. But I hope you can see that in this case what you're saying makes no sense to me. ,

                            Comment


                            • #15
                              Originally posted by RandyC View Post
                              I...1) I see that some companies like BOSE seem to angle each speaker slightly left or right in an alternating pattern...
                              2) I see some builders wire their speakers so that the center drivers get the most power. If the main problem I'm trying to solve is reaching those further back, shouldn't I be sending more power to the top speakers?

                              3) I've read a lot about the "comb" effect, which basically cases dead spots in the sound field when the speaker spacing is wrong. Is there a simple rule of thumb (without 4 pages of math) that would tell me, perhaps based on room size, what the ideal spacing for my 2-1/2" speakers should be?

                              4).equipment weight vs good sound always seems to be a trade off. But these are small speakers. Need I make an array like this out of heavy particle board? Could I get away with simple plywood reinforced at the corners? And if so, how thin can I get away with for the plywood? I'd much prefer to avoid anything beyond 1/2" unless there is a clear advantage.
                              Lot of Questions Randy
                              1: I've worked with the Bose arrays and they are not awful - for your purposes I would not worry about staggering the drivers.
                              2: You are sort of describing a procedure called shading; IMO theses should be designed to allow for shading.
                              The math is not 4 pages, but does require understanding the relationship of wavelength vs frequency
                              3: The drivers should ideally be touching. Realistically as close as possible.
                              4: I think you could get away with thin plywood especially if it were reinforced.

                              The Bose array locked smaller segments together to make a long array.
                              .
                              .
                              "Not a Speaker Designer - Not even on the Internet"
                              “Pride is your greatest enemy, humility is your greatest friend.”
                              "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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