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  • #46
    Originally posted by dcibel View Post
    How do you like it?
    ​It actually sounds pretty decent using the test baffle, though I don't know if I have a preference for this version or the piezo-equipped version of the Blastoramas. I have a recording of the new version (using the test baffle at link below (listen with headphone. There's a bit of "room boom" below 200 Hz and there are a few glitches in the recording due to the brain-dead Atom-based laptop losing sync, but this should give you a good idea of how they sound in-room. BTW, this recording was done with the UMM6 mic, and the music was hitting 100dB peaks at the recording position.

    http://www.diysubwoofers.org/project...-Bodyguard.wav

    Brian Steele
    www.diysubwoofers.org

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    • #47
      Ok, the blue looks pretty decent (just testing the fit here). SWMBO prefers the orange though, and the DayGlo Orange of the previous baffles did make them a lot easier to see (and therefore a lot less likely to get knocked over at the next night-time outdoors party).
      Brian Steele
      www.diysubwoofers.org

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      • #48
        Originally posted by Brian Steele View Post
        Ok, the blue looks pretty decent (just testing the fit here). SWMBO prefers the orange though, and the DayGlo Orange of the previous baffles did make them a lot easier to see (and therefore a lot less likely to get knocked over at the next night-time outdoors party).
        Well who ya gonna listen to, your SWMBO, or some guy you only know via TT?

        That blue does look nice, but I understand the arguments for orange.

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        • #49
          Originally posted by Brian Steele View Post
          I'm going to try the following simple xover with the PDS222 / Beta 8A combo - 1uF + 10 ohms on the tweeter and 0.60mH + 15uF + 3.3 Ohms on the woofer. WinPCD predicts a 4th order acoustic LR x-over @ 3kHz for this combo, and a fairly smooth passband. Unfortunately no screen captures - the PE Tech Forum is apparently not allowing me to add any pictures at this time.

          ​I used the Blastorama V2s at the "hash" this weekend and I found that the output was a bit.. "dull". I fixed it with a bit of EQ at the high end and I'm thinking I'll just build this into the design. I'm curious though as to why it would sound better with the high frequencies (3k and up) boosted by a few dB. The crossover tweak basically involves replacing the 1uF cap with 1.2uF, and the 10 ohm resistor with a 4 ohm one. This shelves the response from 7kHz and up by about 2~3dB, peaking at about 5dB @ 18kHz, which is a close match to what I did via EQ. I'm wondering why this would sound "better" though.

          I'm still looking out for a cheap but consistent new-magnet screw on CD. The Pyles are cheap, but they're inconsistent, so this really isn't a design I can post up design notes about. Anyone who tries to replicate it will likely end up with something sounding very different above 3kHz...
          Attached Files
          Last edited by Brian Steele; 09-04-2016, 11:50 PM.
          Brian Steele
          www.diysubwoofers.org

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          • #50
            Originally posted by Brian Steele View Post

            ​I used the Blastorama V2s at the "hash" this weekend and I found that the output was a bit.. "dull". I fixed it with a bit of EQ at the high end and I'm thinking I'll just build this into the design. I'm curious though as to why it would sound better with the high frequencies (3k and up) boosted by a few dB.
            I'm not sure what the environment was but I do wonder when otherwise flat speakers are used in a crowded venue, if the crowd (their clothing, hair, etc.) can absorb some HF?

            Personally, I'd keep them flat and use EQ when needed.

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            • #51
              Originally posted by philthien View Post
              ... if the crowd (their clothing, hair, etc.) can absorb some HF?...
              Yup
              http://www.leoberanek.com/pages/sabineandeyringeq.pdf
              http://www.iiste.org/Journals/index....File/4359/4422
              Indeed a band can have a soundcheck early in the day and find the system has to be tweaked later when audience (bags of mostly water) arrives ( and a change in temp and humidity )
              "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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              • #52
                Originally posted by Sydney View Post
                Yup
                http://www.leoberanek.com/pages/sabineandeyringeq.pdf
                http://www.iiste.org/Journals/index....File/4359/4422
                Indeed a band can have a soundcheck early in the day and find the system has to be tweaked later when audience (bags of mostly water) arrives ( and a change in temp and humidity )
                ​Thanks. Unfortunately this happened when I was first setting up the speakers. There was little or no crowd in front of the speakers at the time.

                ​I guess I'll have to connect them up to the car again and actually measure the FR rather than playing it by ear. Maybe the high impedance of the Blastoramas at high frequencies isn't the best match for the car's Class D amps (though the FR of those particular amps are supposed to be pretty impervious to output impedance).

                Brian Steele
                www.diysubwoofers.org

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                • #53
                  Here's a comparison of the Blastorama's FR against that of one of my Mission 751s. The slight "lift" in the upper FR of the Mission can be clearly seen. The Blastoramas do sound a bit dull in comparison, as one would expect from the FR graph. If I adjust the Blastorama's FR to include a similar lift in the upper FR, a positive side effect is that the midrange frequencies are also raised slightly and the dip around 5kHz disappears. I'm definitely tempted to try it now.
                  Click image for larger version

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                  Brian Steele
                  www.diysubwoofers.org

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                  • #54
                    I'm putting together a parts list for the x-over mods, and I want to throw another idea into the mix.

                    ​It's well-known that the interaction between the output filters of class D amps and the speaker's impedance curve at high frequencies can introduce some response aberrations. Has anyone tried to negate this by using an impedance compensation circuit in parallel with the speaker to flatten the overall impedance curve above about 1kHz or so? It looks like I might be able to accomplish this with the Blastoramas by adding a simple LCR filter in parallel with the speaker (5.6uF,2.2mH,12 ohms). The only "gotcha" seems to be that I might have to use a high power resistor for the circuit. See simulated impedance curves attached.
                    Attached Files
                    Brian Steele
                    www.diysubwoofers.org

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                    • #55
                      So, I've decided to upgrade the x-over as planned. The LP filter on the bass speaker now has a shallower cutoff, which should result in a flatter responst between 2kHz and 3kHz and the filter on the tweeter has been adjusted to move the overall sensitivity at higher frequencies up a bit, and lower the impedance at high frequencies (if it's too high, this can cause response aberrations when the speaker is used with cheaper class D amps). Seeing that I was already ordering x-over parts, I've also ordered parts for the "high-frequency impedance compensation" circuit I spoke about in my previous message. I'll do some tests with it in place to see it has an audible impact when I'm pushing these speakers with my iNuke 3000DSP.

                      ​First here's the FR sim of the modified x-over, from 500 Hz. Note that the vertical scale is at 3dB intervals.
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                      ..and here's what the modified x-over looks like:

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                      Note that I've switched to using XSim for the x-over simulation at this point, as not only can it model the impact of the impedance compensation circuit I was considering, but now that I know it can model z-axis offsets as well. There is also another unique features in XSim that really come in handy for designing speakers for pro audio use - it allows you to examine the power dissipation across the speaker and for various components in the circuit. For example, I've included a graph below that shows the sim'd power dissipation across the tweeter (S1), the midbass driver (S2) and the resistor in the impedance compensation circuit (R3), when driven by the equivalent of 75W into 8 ohms.

                      Click image for larger version

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                      Based on this graph, I think that the tweeter is going to be very safe at the 75W I'm likely to be using this speaker at most of the time. I'm not so sure about that resistor though, considering I've ordered a 10W version to do the job! It's hardly likely that the speaker is going to see 75W at such high frequencies though, so I'm not TOO worried. What's interesting too is where most of the power appears to be dissipated - between 200 Hz to 500 Hz in the midbass driver. I suspect that in real life it's likely to be less, as most of the "power" in a musical signal is usually at bass frequencies.
                      Brian Steele
                      www.diysubwoofers.org

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                      • #56
                        Originally posted by Brian Steele View Post
                        I'm going to try the following simple xover with the PDS222 / Beta 8A combo - 1uF + 10 ohms on the tweeter and 0.60mH + 15uF + 3.3 Ohms on the woofer. WinPCD predicts a 4th order acoustic LR x-over @ 3kHz for this combo ...
                        How does WinPCD predict the 4th order acoustic xo?

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                        • #57
                          Originally posted by Millstonemike View Post

                          How does WinPCD predict the 4th order acoustic xo?
                          ​WinPCD provides a feature that allows you to overlay a filter's output on the FR graph which you can then use as a guide to fine tune the x-over elements.to achieve a similar response curve.
                          Brian Steele
                          www.diysubwoofers.org

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                          • #58
                            Originally posted by Brian Steele View Post

                            ​WinPCD provides a feature that allows you to overlay a filter's output on the FR graph which you can then use as a guide to fine tune the x-over elements.to achieve a similar response curve.
                            I understand, thanks.

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                            • #59
                              So goddamit, a freak wind took one of my Blastoramas on its 4 foot stand and toppled it over. The Blastorama went crashing backwards into the concrete pavement below. The box survived intact (held together only by wood glue!) and the drivers and x-over appear Ok, but the terminal cup was destroyed - the box hit the ground so hard that the Speakon connector was punched through the terminal cup and into the enclosure, and the terminal cup was warped beyond repair. So I've purchased two new terminal cups of the same size (because of course I couldn't have mismatched terminal cups), and these new ones have two holes for SpeakOn connectors. What's the established practice for wiring these connectors together? Both of them are two-way (1-1 and 2-2 wires) Should I connect them 1->2 and 2->1, or 1->1 and 2->2? I'm tempted to use the former, as that way I can use a two-pair cable to feed both A and Bchannels to one Blastorama, then connect the next Blastorama to the B channel by attaching it to the first Blastorama with a single-pair cable.
                              Brian Steele
                              www.diysubwoofers.org

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