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  • #16
    Re: Cheap 'n' simple 2x10 top?

    Originally posted by Brian Steele View Post
    (2) The x-over design: Ideally I should buy the speakers, measure them in the baffle, then design the x-over accordingly. Even better would be if I can use an application to simulate the effect of a passive xover on the drivers. I'll look around to see what's available. And should I go with a 2.5 way design, or just a simple 2 way design?
    Jeff B's PCD will do just what you need. I'd stick with a 2 way for simplicity sake.

    Originally posted by Brian Steele View Post
    (3) The Finish: This speaker is going to be used both indoors and out. Spray-on bedliner isn't readily available locally, and even then might not be the most pleasant-looking finish. I've got about nine(!) square yards of speaker grill cloth available for use, so I'm thinking about removeable grills - a cloth one for use indoors, and a metal one for when I'm using them as part of a portable DJ set.
    What ever looks good to you, it's your speaker, make it truly your own.

    Comment


    • #17
      Re: Cheap 'n' simple 2x10 top?

      Passively assisted?

      The Dayton PA255 is an interesting driver in that the specs suggest that you'd need a pretty large box if you want to use a "maximally flat" alignment.

      The driver's high Qms suggests though that a passively-assisted sealed alignment might be another way to get a bit more bass out of it without having to resort to using a big box.

      For a Qb=1.1 alignment using the PA255, net Vb works out to just about 0.5 cu.ft, with Fc=106 Hz and F3=80 Hz. Some quick calcs suggests that adding 450uF of series capacitance (an ~$6 NP capacitor from PE) could flatten the passband and could drop F3 to 60 Hz.

      60 Hz response and 94.5dB/2.93V/1M in a cabinet that's 0.5 cu.ft in size containing a 10" driver doesn't sound too bad... In fact, it might sound a bit too good to be true....

      Could a passively-assisted vented alignment also work to get a little more low end out of this driver in a small box?
      Brian Steele
      www.diysubwoofers.org

      Comment


      • #18
        Re: Cheap 'n' simple 2x10 top?

        Brian: The initial post :
        Intended use: a pair of tops (>100 Hz)...Build - 44 l (net) sealed box, with the two 10's positioned vertically as close together as possible
        Is probably what I'd do; Don't care for the sound of Qb=1.1 alignments; and wouldn't attempt to go for LF extension to 60Hz
        Just opinions...
        "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."

        Comment


        • #19
          Re: Cheap 'n' simple 2x10 top?

          Originally posted by Sydney View Post
          Brian: The initial post : Is probably what I'd do; Don't care for the sound of Qb=1.1 alignments; and wouldn't attempt to go for LF extension to 60Hz
          Just opinions...
          With the inline capacitor, it will no longer sound like a Qb=1.1 alignment. The response at the low end will be more like a 3rd order system (which it is).

          I've run a few sims through Akabak. Box size reduction and decreasing excursion below Fb seem to be the key advantages of using passive assistance for the PA 255. There's little or no gain in low-frequency performance (in fact, it drops off faster below the 3dB point). I have no idea how to fit the PA255 into a 12L box though, so maybe I'll abandon that idea .

          Here's an idea of what one of the sims looks like. Note that I haven't included the effect of the capacitor's ESR. The result is a nice flat SPL response to just below 100 Hz.


          Def_Driver 'D1'
          dD=21cm dD1=3cm tD1=2.5cm |Cone
          fp=1.3kHz
          fs=46.4Hz Mms=34g Qms=9.64
          Qes=0.48 Re=5ohm Le=1.33mH ExpoLe=0.618

          System 'S1'
          |Generator resistance
          Resistor 'Rg' Node=1=2
          R=1ohm
          |Series Capacitance
          Capacitor 'C1' Node=2=20 C=0.45mF
          |Transducer
          Driver 'Drv1' Def='D1' Node=20=0=30=40
          |Radiation element
          Radiator 'R1' Def='Drv1' Node=30
          x=0 y=0 z=0 HAngle=0 VAngle=0
          |Closed cabinet
          Enclosure 'E1' Node=40
          Vb=12L Qb/Fo=0.1 Lb=20cm
          Brian Steele
          www.diysubwoofers.org

          Comment


          • #20
            Re: Cheap 'n' simple 2x10 top?

            Originally posted by Brian Steele View Post
            Def_Driver 'D1'
            dD=21cm dD1=3cm tD1=2.5cm |Cone
            fp=1.3kHz
            fs=46.4Hz Mms=34g Qms=9.64
            Qes=0.48 Re=5ohm Le=1.33mH ExpoLe=0.618

            System 'S1'
            |Generator resistance
            Resistor 'Rg' Node=1=2
            R=1ohm
            |Series Capacitance
            Capacitor 'C1' Node=2=20 C=0.45mF
            |Transducer
            Driver 'Drv1' Def='D1' Node=20=0=30=40
            |Radiation element
            Radiator 'R1' Def='Drv1' Node=30
            x=0 y=0 z=0 HAngle=0 VAngle=0
            |Closed cabinet
            Enclosure 'E1' Node=40
            Vb=12L Qb/Fo=0.1 Lb=20cm

            Improved a bit (fixed driver dimensions, incorrect Rg)

            Def_Driver 'D1'
            dD=21cm dD1=8.6cm tD1=4.8cm |Cone
            fp=3kHz
            fs=46.4Hz Mms=34g Qms=9.64
            Qes=0.48 Re=5ohm Le=1.33mH ExpoLe=0.618

            System 'S1'
            Resistor 'Rg' Node=1=2 |Lead Resistance
            R=0.25ohm
            Capacitor 'C1' Node=2=20 |Series Capacitance
            C=0.75mF
            Driver 'Drv1' Def='D1' Node=20=0=30=40 |Transducer
            Radiator 'R1' Def='Drv1' Node=30 |Radiation element
            x=0 y=0 z=0 HAngle=0 VAngle=0
            Enclosure 'E1' Node=40 |Closed cabinet
            Vb=12L Qb/Fo=0.1 Lb=20cm



            I'm still fudging my way through AkAbak (Lord, and I though HornResp had a difficult learning curve!), so there are probably a few more tweaks and corrections that have to be done. But the results do look interesting. FWIW, AkAbak predicts that the group delay peaks at 4.75 ms around 70 Hz, and excursion hits Xmax around the same frequency with just over 100W of power.
            Attached Files
            Brian Steele
            www.diysubwoofers.org

            Comment


            • #21
              Re: Cheap 'n' simple 2x10 top?

              Looking at this project again...

              I'm thinking of starting with one of the basic pre-built x-overs and modding it if necessary. Given my choice of drivers, which of these two would you recommend?


              http://www.parts-express.com/pe/show...number=260-142

              http://www.parts-express.com/pe/show...number=260-140

              They're not "pro-audio" xovers like the Eminence ones offered by PE, but they are designed to accommodate either 4 or 8 ohm woofer impedance (the two 10s wired in parallel will result in a 4 ohm impedance). I'm thinking of starting off with one of these, and modifying it if necessary.
              Brian Steele
              www.diysubwoofers.org

              Comment


              • #22
                Re: Cheap 'n' simple 2x10 top?

                Originally posted by Brian Steele View Post
                Intended use: a pair of tops (>100 Hz) to be driven off a car audio amp, open-air venues small (<100 persons) crowd. Looking for high output and 4-ohm load. Doesn't have to be "hi-fi", but should be reasonably clean and clear.
                Don't limit yourself to "4ohm" loads just because the car amp is designed around it. Any higher impedance load is also fine.

                These drivers are great used in multiples if you need some bass extension without any bottom end support from other systems, but will be a source of impractical inefficiency, and, when use in multiples for midrange, a source of unnecessary destructive coupling problems. You mentioned specifically, that you need response from these above 100hz. A single midbass driver solution of better quality, is the better choice in this case, even being 8 ohm. There are several 8 ohm midbass 10-12" drivers, specifically designed for this sort of application. Use anywhere from the same to half the power, half as many drivers, achieve better off axis response capabilities and equal or better maximum SPL capabilities from a very small, easy to handle, portable box. The PA255's are not the driver you are seeking IMO.

                Having thrown out the reasoning for the dual 10's, I wouldn't bother with this smaller horn. Something larger, that will be more apt to carry to a lower x-over should be used if possible. I'd consider something wider horizontally. Small crowd applications often involve a lot of near-field listeners may benefit from this approach.

                1" compression driver (haven't decided yet, but leaning towards one of the Seleniums)
                The 220, easy choice.

                Build - 44 l (net) sealed box, with the two 10's positioned vertically as close together as possible with the BH410 located between them. ~2.5 kHz x-over point, nothing too fancy. Pole-mounted to bring the BH410 up to ear level.
                Pole mount the smaller boxes up higher, with them inverted for better "reach" out over crowd, and easier crossover design (better chance of hitting phase alignment). Putting a PA horn at the front rows ear level is a bad idea unless you want to cause hearing loss for the people in front, and inaudibility for the people in back.

                Sounds good?
                It will sound great when you do it right

                ----------------------------------

                Originally posted by Paul O View Post
                Yes the 202 has a better highend response but less power handling, if you want to utilize all the potential in those 10s then you'll need a CD that can handle upwards of 150w assuming 6-7db of padding,
                I'm not sure where you are coming up with these numbers, after padding, a typical CD will only need to deal with perhaps tens of watts maximum, to keep up with a "single" compact flying PA unit that may be operating at "hundreds" of watts worth of effective "gain" (in fact, these "watts, will only be present at high levels where the system has impedance dips, it's really a voltage based gain, and the CD will be behind a ton of padding to get down to the level of the midbass drivers, especially of flown, and properly designed to pick-up their step loss)

                --------------------------------

                Originally posted by Brian Steele View Post
                Thanks for the feedback. Some rough calcs suggest that my DIY "tops" (if SWMBO gives the go ahead to build them) are likely to see 100W or less from my system, so I think I should be OK with the D202. In any case, I'll be investing in some protection for them, just in case someone decides to be stupid with the volume control. I've seen some circuits online for this that look a lot more involved and useful than a simple inline lamp or polyswitch, and I'm tempted to give them a try.
                I would just go with the 220's regardless... $7 more, 3dB better thermal headroom, flatter response, technically able to reach down to lower x-overs.

                Originally posted by Brian Steele View Post
                One more question - the horn I've chosen seems rather small. Is it really useful down to 2kHz, or am I worrying too much?
                Keep in mind, that the response of a CD in various horns will change a fair bit, the bottom end reach especially... This is where "DIY PA" really turns into a mess- a complete lack of publicly available response data for particular CD's in particular horns. I'd suggest going larger, and hoping for the best in this case.

                Originally posted by Paul O View Post
                Eminence says the lowest recommended crossover freq is 1.2khz so you're plenty safe.
                I wouldn't trust that particular claim without measurement. I suspect that could be a -10dB point, but I really don't know for sure.


                --------------------

                Originally posted by Brian Steele View Post
                Looking at this project again...

                I'm thinking of starting with one of the basic pre-built x-overs and modding it if necessary. Given my choice of drivers, which of these two would you recommend?


                http://www.parts-express.com/pe/show...number=260-142

                http://www.parts-express.com/pe/show...number=260-140
                Neither. Sorry :(

                They're not "pro-audio" xovers like the Eminence ones offered by PE, but they are designed to accommodate either 4 or 8 ohm woofer impedance (the two 10s wired in parallel will result in a 4 ohm impedance). I'm thinking of starting off with one of these, and modifying it if necessary.
                I'll help you design a speaker and crossover, if you are serious about getting it "right" or at least, a lot closer to "right."

                The biggest issue for me, from affar, i won't have any way to figure on the actual response of the CD in a particular horn, so aside from a potential blip around the x-over, I believe it's possible, to get these things very good sounding, especially through the critical midrange from your midbass, which, if flown, should be step loss compensated.

                Regards,
                Eric
                Pro/Fi Cinema Speaker project: "From the Ashes"

                Comment


                • #23
                  Re: Cheap 'n' simple 2x10 top?

                  Originally posted by mdocod View Post
                  I'm not sure where you are coming up with these numbers, after padding, a typical CD will only need to deal with perhaps tens of watts maximum, to keep up with a "single" compact flying PA unit that may be operating at "hundreds" of watts worth of effective "gain" (in fact, these "watts, will only be present at high levels where the system has impedance dips, it's really a voltage based gain, and the CD will be behind a ton of padding to get down to the level of the midbass drivers..
                  Yes technically.. but real world experience suggests that low power(20w-40w) compression drivers are easily blown when the speaker system is subjected to 400-500w of music power, these "lightweight" CDs are common in entry level commercial PA speakers like the JBL JRX and they're notorious for letting out the magic smoke under what is considered normal operation at well under amp clipping levels, so the fix is to replace it with something more robust like a Selenium D210/D220.


                  --------------------------------

                  Originally posted by mdocod View Post
                  Keep in mind, that the response of a CD in various horns will change a fair bit, the bottom end reach especially... This is where "DIY PA" really turns into a mess- a complete lack of publicly available response data for particular CD's in particular horns. I'd suggest going larger, and hoping for the best in this case.
                  I wouldn't argue with that at all.. it's one of the reasons I chose the Dayton H110 for my 12+1 project.

                  --------------------

                  Originally posted by mdocod View Post
                  especially if flown and properly designed to pick-up their step loss
                  Also agree there the mains have to be jacked up overhead, though my suggestion for step loss compensation is not the method commonly used for home audio projects where you "throw away" 6 or more db of sensitivity across the whole spectrum with padding just to achieve flat response with the step loss below 200hz. My suggestion is to use a ported allignment with a high tuning freq so that bass response is boosted and then use EQ or better yet active processing(ie: DSP) to further flatten response where necessary. With PA systems top priority should be given to achieving the highest system sensitivity and therefore power efficiency over everything else.. within reason, super high sensitivity with a stupid peaky response is no good either so you still want to target flat response, but this means active system processing isn't optional it's manditory.
                  Paul O

                  Comment


                  • #24
                    Re: Cheap 'n' simple 2x10 top?

                    Hi Paul O,

                    I like your approach to step loss for Pro Sound. Excellent. Going to keep that in the foreground of thought for awhile till it sticks.

                    Regards,
                    Eric
                    Pro/Fi Cinema Speaker project: "From the Ashes"

                    Comment


                    • #25
                      Re: Cheap 'n' simple 2x10 top?

                      Originally posted by Paul O View Post
                      My suggestion is to use a ported allignment with a high tuning freq so that bass response is boosted and then use EQ or better yet active processing(ie: DSP) to further flatten response where necessary.
                      I like the idea, but that suggestion should also come with a warning statement. If you port it high enough to make a real difference, they will no longer be usable as a 'full range' box, and would ONLY be suitable as tops.

                      Comment


                      • #26
                        Re: Cheap 'n' simple 2x10 top?

                        Originally posted by mdocod View Post
                        Hi Paul O,

                        I like your approach to step loss for Pro Sound. Excellent. Going to keep that in the foreground of thought for awhile till it sticks.

                        Regards,
                        Eric
                        Are we talking about the baffle step here? Because, according to my calculations, that "step" should occur just above 1kHz for a box with a 10" driver (assumed baffle width of around 12")...
                        Brian Steele
                        www.diysubwoofers.org

                        Comment


                        • #27
                          Re: Cheap 'n' simple 2x10 top?

                          Hi Brian,

                          Here's a couple of simulations to get get a feel for the baffle step and diffraction thing, and Paul O's suggestion:

                          Simulation of something like a 2x10 MTM cab, from a listening position 5 meters away back and 2 meters over. Cab flying 1M over the audience "ear" level:
                          Click image for larger version

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                          Simulation of something like an inverted TM configuration with 1x12" driver, same listening position as before:
                          Click image for larger version

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                          This is a better example of baffle diffraction, because it doesn't include the destructive coupling of a pair of drivers... (more on this in a moment)... Notice, how the peak is actually greater than 6dB, this is a culmination of step transition, and edge diffraction coming together to actually produce a peaking response greater than the "6dB" transition. If viewed on axis, this peak would appear even higher and you would also see subsequent dips and peaks in response through the high frequency as wavelengths work constructively and destructively as they reflect and wrap the baffle.


                          Simulation of Paul O's suggestion, based on using the 2x10" drivers you have in mind. 1.5ft^3, 100hz tune, HPF set to 90hz resulting in [email protected]
                          Click image for larger version

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                          Regarding my prior suggestion against the idea of the dual 10" drivers... Notice the response in that first simulation, never even reaches a fully effective step transition of +6dB because from that listening position, the difference in distance to the drivers is already out of sync enough not to couple effectively. By the time 1200hz comes around, it would need to be crossed to a high frequency driver just to prevent this listening position from having a potentially deep null in response. Notice, in the second simulation, the single 12" driver, even being larger diameter (more directional), effectively behaves better off axis because it's not fighting another driver, not getting back down to the 0db mark until more like 2200hz, making this configuration useful for 1500-2000hz crossover options.

                          The MT configuration suffers from a narrow band potential for lulls in the x-over for listeners off axis, the MTM suffers from potentially wider and deeper nulls in more critical frequency ranges for off axis listeners.

                          Regards,
                          Eric
                          Pro/Fi Cinema Speaker project: "From the Ashes"

                          Comment


                          • #28
                            Re: Cheap 'n' simple 2x10 top?

                            The spacing of the 2x10 example looks a bit wider than what I'm expecting it to be with the horn I was planning to use like if the 10s are a bit closer together, let's say 2/3 of that separation in the example? The lobing seems to start above 1kHz - what if I x-over to the horn at around 1.6 kHz instead of higher. Would this reduce the audible impact of that lobing? One other possibility that might be worth considering is rolling off the lower woofer early, say around 500 Hz. Bear in mind this is likely to be a sealed environment, so venting at a higher frequency to make up for the step loss is not an option.
                            Brian Steele
                            www.diysubwoofers.org

                            Comment


                            • #29
                              Re: Cheap 'n' simple 2x10 top?

                              Hi Brian,

                              Spacing can be deceptive when looking at that program, because it is only a simulation of the piston area. The "dotted" area that appears to be the driver, does not include where the frame would be as well, so there is actually less space between those drivers than their appears to be. That simulation assumes a ~14" center to center spacing of approximately 8" pistons... If you get it any tighter than that I would be amazed based on a visual on that horn you have in mind. Furthermore, the effective piston size of a typical 10" is probably a tad bigger than I simulated there, which would actually result in the response looking even slightly worse at that listening position.

                              All this aside, if you are absolutely set on going sealed (I can't imagine why), then you will probably need either a pair of drivers, or a larger driver with similarly "low reaching" characteristics in order to get down to ~100hz. The trade offs of the multiple drivers is something you may just have to live with if you aren't willing to live with the trade off of venting, which, IMO, isn't a tradeoff at all in this case.

                              Regards,
                              Eric
                              Pro/Fi Cinema Speaker project: "From the Ashes"

                              Comment


                              • #30
                                Re: Cheap 'n' simple 2x10 top?

                                Perhaps there is a difference in philosophy of implementation or a difference in the meaning of:
                                Cheap N' Simple
                                Considering the fact that a Pro cab is likely to be set up and used in a wide variety of acoustic settings not a fixed location. These could be outdoors away from external reflections or indoors very close or conversely far enoughaway from reflective boundaries. With this in mind; to implement BSC or fixed compensation might be inappropriate and incur more expense.
                                Most guys I know use EQ; Not to correct for speaker non-linearity but for general tonal adjustments. Many consider acoustic non-linearity to be a design flaw.
                                "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."

                                Comment

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