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Flex Your PCD Mettle:

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  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    Thanks, but the summation vs. angle is all looking correct to me, and manageable with a crossover. What I don't understand, is how it makes sense that I see these two graphs when I take the tweeter z-offset from zero to -.12m, while moving the woofer offset accordingly to keep the relative offset the same (it seems to be pretty much exactly +10cm woofer from straight off the midpoint between drivers). I'm not sure if I'm just being dense about phase, or there is a problem with my frd generation? (please ignore the two measurement glitches - I just didn't bother repeating the last round when those showed up).

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  • Pete Schumacher
    replied
    Re: Flex Your PCD Mettle:

    Originally posted by dtruck View Post
    I have another PCD question: Can anyone explain to me the changes in driver phase that result from changing the offset? For example, if I put a tweeter at -9cm and woofer at 0cm, the woofer phase will be as imported but the tweeter phase goes crazy. If I put the woofer at +9cm and the tweeter at zero, the woofer phase is the one that changes. Logically, it seems like the "real" numbers are both negative, one more than the other, in which case both change. This makes no difference to the summed response, but it does make a big difference to the total phase.

    I guess the question is: is there a way to go about this that's most likely to result in a realistic simulation of total phase? My almost complete lack of understanding of what minimum phase means may have something do with this....
    Originally posted by dtruck View Post
    Anybody have an opinion on whether this is too optimistic for a DE250?
    [ATTACH=CONFIG]27225[/ATTACH] [ATTACH=CONFIG]27226[/ATTACH]
    Minimum phase is derived directly from the driver response. When you use minimum phase files, PCD will allow full simulation, including driver offsets and off-axis response given flush mounted drivers. The relative phase will be calculated for an offset driver if accurately positioned (x, y, z) in PCD. With large offsets, like 9cm, there will likely be summation issues to overcome, especially for higher crossover points. You may find that mounting the woofer to the back of the baffle could help, or inverting tweeter polarity, so that the relative phase at the crossover point lines up between drivers.

    1500Hz for the DE250, which is about what you have there, seems about par for the course.

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  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    Anybody have an opinion on whether this is too optimistic for a DE250?
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  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    I have another PCD question: Can anyone explain to me the changes in driver phase that result from changing the offset? For example, if I put a tweeter at -9cm and woofer at 0cm, the woofer phase will be as imported but the tweeter phase goes crazy. If I put the woofer at +9cm and the tweeter at zero, the woofer phase is the one that changes. Logically, it seems like the "real" numbers are both negative, one more than the other, in which case both change. This makes no difference to the summed response, but it does make a big difference to the total phase.

    I guess the question is: is there a way to go about this that's most likely to result in a realistic simulation of total phase? My almost complete lack of understanding of what minimum phase means may have something do with this....

    Leave a comment:


  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    The z offset is the difference in straight line distance from the acoustic centers to the mic position. The "zero plane" or baffle is not considered. When you set the tweeter offset to "0", you're then establishing the woofer relative to that position.
    Excellent, that clears that up. Thanks.

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  • Pete Schumacher
    replied
    Re: Flex Your PCD Mettle:

    Originally posted by dtruck View Post
    Yeah, I suppose just building something is the best way to find out what's what. I would still like to know what the math is based on, though. Is z-offset as entered in PCD intended to be the difference in straight line distance from measurement position to each acoustic center? Or, is it relative to a hypothetical zero plane that is perpendicular to the drivers? Thanks.
    The z offset is the difference in straight line distance from the acoustic centers to the mic position. The "zero plane" or baffle is not considered. When you set the tweeter offset to "0", you're then establishing the woofer relative to that position.

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  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    Yeah, I suppose just building something is the best way to find out what's what. I would still like to know what the math is based on, though. Is z-offset as entered in PCD intended to be the difference in straight line distance from measurement position to each acoustic center? Or, is it relative to a hypothetical zero plane that is perpendicular to the drivers? Thanks.

    Leave a comment:


  • Pete Schumacher
    replied
    Re: Flex Your PCD Mettle:

    It's not unusual for the woofer to be forward of the tweeter acoustic center, even if the magnet isn't, especially with horn loaded CDs.

    The way you derived the relative offsets should be accurate. I'd trust it and start developing your crossover based on that. You'll know if you got it right when you take the system response.

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  • dtruck
    replied
    Re: Flex Your PCD Mettle:

    Paging Pete? I'm getting very confused in PCD here. I can measure from one location, generate frds with min phase, import everything, put in the geometry, overlay the summed measurement, find a z-offset that matches, and go on from there. The only thing is, the offset doesn't seem to make any sense. I am using a woofer that is a little deeper than most, with the magnet center a few centimeters back from the compression driver. In PCD 7, I got a z-offset of +11.5cm for the woofer if I leave the CD at 0. That's on the CD axis. That seems a bit odd, right? According the update notes, that means the acoustic center of the woofer is closer to the mic?

    I figured a good sanity check would be to re-do everything way down on the woofer axis. When I did that, I got +8cm for the woofer. Since I'm on the woofer axis now, the woofer is close to the mic, and the CD is farther from it, so shouldn't I have gotten a higher offset? Or, is the offset number supposed to be straight back from the zero plane? If that's the case, I should have gotten the same offset at both locations, right? If so, maybe it was measurement error, but I'm hoping you can tell me what I should be seeing so I don't start chasing my tail here. Thanks!

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  • qfish
    replied
    Re: Flex Your PCD Mettle:

    Hi all!
    It was kind of hysterical purchase :D
    Anybody tried this www.sicaspeakers.com/sshfd1.html ?

    Leave a comment:


  • isaeagle4031
    replied
    Re: Flex Your PCD Mettle:

    That's probably what I will end up doing. Too many projects going on right now. I may part these out and scrap the cabinets. They need quite a bit of work to restore and the value just isn't there.

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  • donprice
    replied
    Re: Flex Your PCD Mettle:

    Originally posted by isaeagle4031 View Post
    So I will look into the dayton units and a couple of eminence as well.
    You might want to ditch the whole system (for some real $) and start over if you aren't into the vintage Atlec stuff. I bet you can fund some nice builds of what you really want. Real nice:D

    Leave a comment:


  • isaeagle4031
    replied
    Re: Flex Your PCD Mettle:

    The cost to recone my model 14's is $95/ea! Seems silly to me then to spend that much on them when I can replace them with much better units for less money. Even redesigning the crossovers (upgrading as well) doesn't seem to justify the expense. So I will look into the dayton units and a couple of eminence as well.

    Leave a comment:


  • davepellegrene
    replied
    Re: Flex Your PCD Mettle:

    The directivity is going to be directly tied to the diaphragm shape. With planars like this AMT, or long ribbons, the vertical directivity is going to be narrower, and the horizontal, wide. This is the type of guide you really need to use with such diaphragm shapes.

    I'd make a rectangular form, and press your guide using a rectangular plunge instead of the circular dowel you use for domes.

    I contemplated using a quarter of an 8" piece of PVC tube, to make the horizontal sides of a guide for large planar devices. The Beyma is pretty much a straight sided guide, with flared ends to meet flush with the baffle. But I wonder how a circular profile might aid/detract from the overall response.
    I tried a 4" piece of PVC cut into 1/3 pieces laid flat with 45degree corners and it did not do all that well. It looks as though your guide has the exact opposite profile a standard guide has.
    The planner I have is 1" square and I do have a tip made square to match the size an shape. I'll have to try a square or rectangle shape at the baffle but I have a feeling the horizontal shape of your guide may be the key to a good boost down low without creating cancellation from a steep throat.
    Dave

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  • teddytusen
    replied
    Re: Flex Your PCD Mettle:

    The WG on the Arcus (white stand mount above) is simply the stock WG painted white.

    Those are massive speakers you have there. My friend here in town is upgrading his HT, and I know he'd love to see your set up. His will be in-wall, but I think he's leaning toward a 15" woofer and CSS Planar 1, which we now have on order. I can' t wait to begin testing that new CSS Planar 1. The Planar 2 looked incredible from the data Dave Thomas took a while back, and I understand the Planar 1 is designed for 500Hz operation.
    They are massive, no doubt. 208 liters is too large for most livingrooms, and that is why I went for the Econowave`s there. Not shure, but I might go for Econo as surrounds in my HT. The TPL-150H is a bit to expensive for all channels. I am currently building a center with the TPL-150H and one 15P80Nd.

    The Planar 1 (and 2) was new to me. Interesting.

    Leave a comment:

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