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Need help understanding passive crossovers power distribution ratios

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  • #31
    Chris Roemer Thank you for the extensive write-up regarding my setup in question. I landed on the AC drivers because they looked fancy, their specs were what I was after, and the hype in the description sealed the deal. I originally was looking at the Dayton Aluminum Reference 10" drivers, but those required a huge enclosure if I recall correctly. How did you get your data for the tweets? I don't recall seeing it on PE's website. Also I suppose it is a good time to ask, is the graph(s) you posted look good? To me they look like garbage like everything I have been getting. I am not trying to offend you by any means, but I honestly don't know how flat or perfect those plots are supposed to look for a 'good' 3-way. Again take no offense to my ignorance please. I read the entire XO Pro book today that is almost 300 pages and they suggest that everything is supposed to look perfect or you have a junk design. I don't buy into that, but am curious as to what acceptable looks like.

    Cheers,
    Chris
    "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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    • #32

      It depends somewhat on what the initial measurements look like. Using HOLM for measurements, I get pretty smooth measurements for the drivers, and they tend to look like factory measurements. I've seen others post Omnimic measurements, and honestly, I don't know how they build a x-over using them. (Some of them!) I think a 3-way takes more than a sim to get right. The sim can tell you what to expect though. I build most of my x-overs by trial and error, but also get ideas from sims to save a little time. The sim above shows louder bass. That's because of the files Chris used. The bass will drop 6dB when measured.

      This is my latest speaker measurement. The flawed dip on the top end doesn't bother me. Diffraction maybe??? I like this speaker a lot. Needs a sub though.
      The roll-off below 300 is not real. These gated measurements will look bass shy.

      Comment


      • #33
        "Mid/ribbon section runs a (respectable) +/- 1-1/2 to 2dB."

        A pretty "normal" target for a "pretty flat" response is considered to be +/-3dB.
        The reason the bass end (200-800Hz) of MY (13-element) XO is higher than the mid-treble is that I'm showing you the "baffle-step compensation".
        OTOH, the XOverPro XO doesn't really have BSC, the (+7dB) "hump" near 1.2kHz will make them sound "forward", and the tweeter (top 2-3 octaves) really needs to be "flat", if not pitched in the opposite direction.

        You know, asking zillions of ?s after ?s is NOT an efficient way to learn all this stuff. (Speaker Building 201 is a pretty good start, as well as a good reference to have.)

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        • #34
          Originally posted by STIchris722 View Post
          What are the other factors? I’ll be the one to ask.
          Well driver sensitivity of course but also excursion limitations, thermal capacity, the type of enclosure it is mounted in and the type of program material(music) being played. And because a drivers impedance isn't flat it's actually a curve with some pretty big peaks power handling and therefore SPL output will also be frequency dependant.
          Paul O

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          • #35
            Originally posted by Chris Roemer View Post
            A pretty "normal" target for a "pretty flat" response is considered to be +/-3dB.
            The reason the bass end (200-800Hz) of MY (13-element) XO is higher than the mid-treble is that I'm showing you the "baffle-step compensation".
            OTOH, the XOverPro XO doesn't really have BSC, the (+7dB) "hump" near 1.2kHz will make them sound "forward", and the tweeter (top 2-3 octaves) really needs to be "flat", if not pitched in the opposite direction.
            See.. I disagree with that last part, I want to see the response drop off a little bit towards the top end because I find perfectly flat to be fatiquing at higher SPLs. To each their own of course.
            Paul O

            Comment


            • #36
              Originally posted by Paul O View Post

              Well driver sensitivity of course but also excursion limitations, thermal capacity, the type of enclosure it is mounted in and the type of program material(music) being played. And because a drivers impedance isn't flat it's actually a curve with some pretty big peaks power handling and therefore SPL output will also be frequency dependant.
              You should add driver efficiency to the above list. Its the measure of how much acoustic power is generated by the driver's input.

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              • #37
                Originally posted by skatz View Post
                You should add driver efficiency to the above list. Its the measure of how much acoustic power is generated by the driver's input.
                True, from an education standpoint I guess it matters, it underlines the importance of selecting more efficient drivers. As an example a driver with 100dB sensitivity is only 6.3% efficient, that means 93.6% of input power is wasted as heat. If you think that is bad a 90dB driver is only 0.63% efficient, 99.3% of power is wasted. It takes horn loading to get efficiencies above 10%.
                Paul O

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                • #38
                  Originally posted by Chris Roemer View Post
                  Click image for larger version

Name:	ACmtmWWwXT.jpg
Views:	135
Size:	91.2 KB
ID:	1430458 So, here's the XOverPro using a PAIR of AC mids and that XT25 tweeter.


                  Something i FORGOT to mention, is that some woofers don't match the mfr. (T/S) specs much (Dayton is generally good) w/AC being one of the worst reported offenders. I think I've seen guys report that MANY of their woofers have a "Q" MUCH higher than advertised. While not AS significant for a closed box, their data can really lead you astray when designing a vented enclosure. It would be best to see if you can find any data (on the web) about your 10" woofers (or measure them once you get them - BEFORE cutting any MDF !). The mid won't matter much 'cause T/S parms aren't that critical except on the bottom end.

                  (added this the next morn. after locating an old DATS run)
                  Measured a pair of AC-250SW (6 yrs ago) - i THINK these were subs?? (they matched EACH OTHER well, so . . . ?)
                  spec / measured:
                  Qes 0.56 / 1.6 - 3x higher !
                  Qms 2.3 / 3.5 - 1.5x
                  Qts 0.45 / 1.1 - 2.5x (v. bad - for almost ANY use)
                  Fs 35 / 63 - 2x
                  these were # 131008011 & 131008014 (never "run", but broken in by hand)

                  by "spec" they looked good in 2cf w/a 4" x 14" port doing 30Hz, tuned to 33.
                  the measured drivers could only be used in a closed box (also 2cf), and had an F3 in the lower 50s (horrible - esp. if a "sub") PLUS a +2-3dB "hump" @ 80-100Hz. More like a guitar woofer. Others have had bad AC parm matching as well.
                  Actually Aurum Cantus is not bad when you use the same drive levels they do. AC uses a much higher input than T/S parameters call for and is why there is a discrepancy
                  https://www.facebook.com/Mosaic-Audi...7373763888294/

                  Comment


                  • #39
                    Originally posted by Paul O View Post
                    True, from an education standpoint I guess it matters, it underlines the importance of selecting more efficient drivers. As an example a driver with 100dB sensitivity is only 6.3% efficient, that means 93.6% of input power is wasted as heat. If you think that is bad a 90dB driver is only 0.63% efficient, 99.3% of power is wasted. It takes horn loading to get efficiencies above 10%.
                    Exactly. I was always impressed by how inefficient drivers are, even pro drivers (but they are more efficient than home).

                    Comment


                    • #40
                      Originally posted by Chris Roemer View Post
                      "Mid/ribbon section runs a (respectable) +/- 1-1/2 to 2dB."

                      A pretty "normal" target for a "pretty flat" response is considered to be +/-3dB.
                      The reason the bass end (200-800Hz) of MY (13-element) XO is higher than the mid-treble is that I'm showing you the "baffle-step compensation".
                      OTOH, the XOverPro XO doesn't really have BSC, the (+7dB) "hump" near 1.2kHz will make them sound "forward", and the tweeter (top 2-3 octaves) really needs to be "flat", if not pitched in the opposite direction.

                      You know, asking zillions of ?s after ?s is NOT an efficient way to learn all this stuff. (Speaker Building 201 is a pretty good start, as well as a good reference to have.)
                      Chris I appreciate you taking the time to answer my zillion questions. I'll be sure to stop using the forums as a venue for questions and rather read some books instead. I only came here so that people with as much education such as yourself could help with some detailed questions regarding my project at hand. I didn't feel like I was asking elementary questions that could be found in a book's preface. My apologies.
                      "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                      Comment


                      • #41
                        Originally posted by STIchris722 View Post

                        Chris I appreciate you taking the time to answer my zillion questions. I'll be sure to stop using the forums as a venue for questions and rather read some books instead. I only came here so that people with as much education such as yourself could help with some detailed questions regarding my project at hand. I didn't feel like I was asking elementary questions that could be found in a book's preface. My apologies.
                        Keep the questions coming. That's better than books. Most of us like to answer questions. Even Chris. It gives us a chance to show off a little too.

                        Comment


                        • #42
                          Originally posted by rpb View Post

                          Keep the questions coming. That's better than books. Most of us like to answer questions. Even Chris. It gives us a chance to show off a little too.
                          Thank you. I have no objections to reading, but sometimes finding people that know more about the subject than I do helps me learn more effectively. For instance I can google something and read about it in some technical jargon for hours or I could ask my peers that have first hand knowledge. That is just me personally. Understand I am not on here to offend anyone or waste anyone’s time; I can assure you of that. I simply want to learn as much as the next guy, if not more.

                          With that said can someone explain to me what Baffle step is? I am not sure if I phrased this correctly or not. I remember someone (maybe Chris) talking about ‘baffle step correction.’
                          "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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                          • #43
                            You know how you hear about subwoofers being omnidirectional? That's because the low frequencies tend to wrap around the baffle. The wider the baffle, the lower the frequency that wraps around baffle as the baffle can reflect sound. So you're losing about half the bass under a defined frequency, unless you place the speakers on a wall or corner.

                            The three options are either have a naturally db louder woofer and cross at baffle step, lower the frequency above the baffle step, or a combination of the two e.g. 3 db hot woofer and -3 db above the baffle step frequency.

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                            • #44
                              Originally posted by Serpentus View Post
                              You know how you hear about subwoofers being omnidirectional? That's because the low frequencies tend to wrap around the baffle. The wider the baffle, the lower the frequency that wraps around baffle as the baffle can reflect sound. So you're losing about half the bass under a defined frequency, unless you place the speakers on a wall or corner.

                              The three options are either have a naturally db louder woofer and cross at baffle step, lower the frequency above the baffle step, or a combination of the two e.g. 3 db hot woofer and -3 db above the baffle step frequency.
                              I see. Is that why some people talk about the rounding or shaping of the baffle face?

                              Is it safe to assume that baffle step is measured rather than calculated? Or is there a means for calculating it?
                              "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                              Comment


                              • #45
                                Google "Tolvan's Edge" (it's free).

                                You can make up a baffle, place a driver on it, and see how the bass drops off (generally -6dB) at lower freqs.

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