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Hello, and My Second 3-Way

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  • Brian B
    replied
    I'm looking for a fairly simple way to finish these 1.7 cu. ft. MDF towers. They aren't going to be in a prominent place in the house, so nothing fancy is needed. Something somewhat subdued like a satin or textured paint (in a lighter color).
    I was thinking of using a sanding sealer to seal the MDF edges. Any particular primer that works well over that? How about the final coat? Will some type of latex enamel work well?

    Thanks in advance for any suggestions.

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  • Brian B
    replied
    I have both boxes built and fully assembled now, including the crossovers. I wasn't able to get the additional software to work with Open Office (I don't have Windows Office), so I'm limited to WinPCD for now. The crossover is basically unchanged from before (all 2nd order with some padding). The modeled response using the published specs looks like this (using Win PCD):
    Click image for larger version

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    For the time being (and since the boxes buttoned up for the time being), I'll probably leave the crossovers alone and just enjoy listening to them for awhile. Should I find something notably lacking, or acquire better tools, I may revisit the crossover.
    I also need to decide how I'm going to finish these. They are fairly large and will probably stay out of the living room, so I'll probably go with something simpler than veneer. Perhaps some sort of texture paint. I may also need to add some grill cloths to keep the grandkids from poking the neat circles.

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  • Brian B
    replied
    I'll plan to look at those additional tools.

    In the mean time, I've worked more with the crossover and have it sounding pretty good (to my ears). It's all simple 2nd order stuff at this point. WinPCD says it should produce a SPL like this: Click image for larger version

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    And maybe it does. At any rate I'm liking it.

    I have tailored the crossover a few different ways that produce a flatter SPL in PCD, but the octave to octave balance of the one above sounds more pleasant and natural to me than the those others. There obviously could be some things going on that I'm ignorant about (and/or that are outside the model), so for now I'll probably stop the crossover tweaking in order to review the other software tools suggested.

    As an aside, I had enough scrap MDF to put together an Overnight Sensation over the last couple of days. Impressive sound for such a small speaker. But everyone knows that already.
    Last edited by Brian B; 02-04-2018, 06:06 PM.

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  • Millstonemike
    replied
    Two out of three ain't bad ...

    You need the third leg of XO design: Response Modeler.
    Response Modeler will allow you to account for BSC (and diffraction which can cause humps above nominal dB at certain freq.'s) as well as including the lower freq.'s of the box model (and min phase).

    Trace the graph, process with Response Modeler, input the Response Modeler output into WinPCD. If the driver spec's are accurate, the model will be good.

    Bullittstang's comment on BSC is right on.

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  • scottvalentin
    replied
    Those are great drivers in all respects, with some work and some help here you will have a very capable speaker. As Chris and Dynamo allude to, those breakups will need flattening and single order probably won't cut it on the F5, you will want a steeper slope. This also helps the XT25 as well, although at 3k it should work pretty good.

    With FPTrace and PCD you should be able to come up with a pretty good sim that will be able to help you notch out the breakups and get the drivers to work together pretty good. Check out this writeup on how to piece together a sim using traces:
    https://sites.google.com/site/undefi...d-measurements

    If you follow these steps with the manufacturer data sheets, you should get pretty close and will then be able to tweak it to your liking.

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  • dynamo
    replied

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  • Chris Roemer
    replied
    That F5 has 2 pretty bad breakups, one near 1.5kHz (notch) and again near 5k (don't take it that high).

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  • Brian B
    replied
    It's Alive!

    The tweeter will need some padding as expected. The mid is considerably hotter than desired above 1-2K. So the WinPCD 1st pass crossover (based on published graphs) isn't very pleasant sounding (not really a surprise). But it definitely shows promise.


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  • bullittstang
    replied
    Originally posted by Brian B View Post
    ...Never been a big fan of BSC either because of the losses. Of course, the use of a port (with the "gain") helps offset the loss in a BSC circuit
    This statement illustrates you really should read some more about the finer points of designing a competent Speaker/XO design, IF you want the best sounding speaker possible. We would all love to ignore BSC too, but it's PHYSICS, you CAN ignore it, but your design will suffer because of it.

    Decent choice of components - you really should optimize the XO and get the most out of them you possibly can.

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  • Brian B
    replied
    I'll give some consideration to a port, but I generally prefer sealed designs. I know ported designs have been pretty much standard for many years now, but they can sound somewhat tubby or one-note to me at times. I may try it once I get these speakers making noise. Conversely, I don't like the approximate 3dB loss that comes with a sealed design.

    Never been a big fan of BSC either because of the losses. Of course, the use of a port (with the "gain") helps offset the loss in a BSC circuit.

    I beginning to sense how important the overall efficiency is to a lively speaker. It seems like the less sensitive a speaker is, the less dynamic it is, no matter how much power is thrown at it.

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  • Chris Roemer
    replied
    Even in only 1.6cf, adding a (3" x 9" long "Precision") port will drop your F3 by 10Hz (50 down to 40) as well as add a dB or 2 of "lift" near 100Hz, which could be used as part of your BSC.

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  • Brian B
    replied

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  • westrock2000
    replied
    Good start. It took me a while to get the software stuff. I have Dayton Omnimic and DATS combo and it's great. Very simple to use and really adds a whole other dimension to the hobby. I have also tried REW (using the Omnimic mic) and it does work and it's free (plus cost of a USB mic), but I like the Omnimic interface better. But REW does have some cool features, like making a very tight frequency sweep that allowed me to find the exact frequency a panel was vibrating at.

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  • Brian B
    replied

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  • Brian B
    replied
    nd order crossovers all around at approximately 300Hz and 3000Hz.


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