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SevenSixTwo - InDIYana 2018 Coax Design

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  • KEtheredge87
    replied
    Originally posted by Kevin K. View Post
    I was thinking the same thing Craig said when I saw that this morning but didn't want to rain on the parade Keith. There's always the active option and in this case it's looking like a really good option. Does the contest require passive crossovers?
    Hey Kevin, While I scoured the official contest rules portion of the InDIYana 2018 thread, I didn't see anything explicitly stating no actives. However, post #63 has Ben saying no to Actives. http://techtalk.parts-express.com/fo...97#post1338097

    I'll be interested to see what I can pull together for a passive arrangement here. I had an idea that this coax thing would be a tough nut to crack, but it remains to be seen just how tough. Judging from your response and Javad's, I might have gotten a jawbreaker instead of a nut! Oh well... this is how we learn and enjoy the challenge!

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  • JavadS
    replied
    Originally posted by PWR RYD View Post
    Boy that tweeter response is going to be a bugger to work with.
    It is, and it was, ask me how I know! =) I'm quite happy with how my horn loaded coax is measuring and sounding, but I had to get creative. That was one thing that struck me taking on this project, that how many bad coaxes there are on the market, it's quite clear these pro driver style coaxes are meant to be used with an active crossover as it was trivial to get a great sounding speaker with miniDSP, the response and roll off of both the mid and tweeter leave a lot to be desired compared to the ease of implementation with the typical hifi driver and dome tweeter.

    Javad

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  • JavadS
    replied
    Originally posted by KEtheredge87 View Post
    I took some foam lining out of the vented cabinets to see if my Fb would rise back to 31hz. I got excited when removing the foam from the top of the port and the ceiling in that chamber measured an Fb of 32hz while I held the driver in place by hand. Unfortunately the moment I put the screws back in place for the real seal the Fb dropped right back down to 27.8 Hz. I'm having trouble modeling a vented cabinet with my port geometry in BassBox that ALSO has an Fb of 28Hz. BB insists my Fb should be 31Hz. I am probably making a mountain from a mole hill, but again, it bugs me when I can't get the simulation tools to match reality. Guess I'm putting....
    Keith I feel your frustration, this is why I prefer round ports as it makes it easy for me to make changes, making a round port longer or shorter is quite trivial, and you can see the lengths I went to to make it easy to do in my Strafi build, to this day I can still easily change port tuning from 25-50hz by simply cutting some new tubes and installing them.

    Javad

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  • Kevin K.
    replied
    I was thinking the same thing Craig said when I saw that this morning but didn't want to rain on the parade Keith. There's always the active option and in this case it's looking like a really good option. Does the contest require passive crossovers?

    Leave a comment:


  • jhollander
    replied
    Originally posted by KEtheredge87 View Post
    I did take ~20 degree off axis measurements of the coax as you recommended, but I haven't imported those into PCD yet to see how they look. I assume those 20 deg files do not get combined with nearfield measurements?
    For the off axis files I treat them like the on-axis. The mid gets combined with the near field and the tweeter gets trimmed, then minimum phase extracted on both. Use the same offsets and listening distance as your on axis files when you set up a second sim.

    IMO you are hoping the off axis fixes the dips...

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  • KEtheredge87
    replied
    Originally posted by jhollander View Post
    The little blips might not be anything depending on if your measurements were smoothed. Anything less than 1/48 smoothing might be hiding a spike you will want to see.

    IMO, typical tweeter in a deep guide. It should fill in off axis, but that will be the x-o challenge.
    Thanks John, I used 1/96 smoothing when recording with the OmniMic just to make sure that everything I could possibly see would be brought into PCD. I know that everything gets 1/48 smoothing by default in PCD. I was intrigued when all the individual files came through relatively smooth at 1500 Hz, but the system combined line has that odd blip.

    I did take ~20 degree off axis measurements of the coax as you recommended, but I haven't imported those into PCD yet to see how they look. I assume those 20 deg files do not get combined with nearfield measurements?

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  • jhollander
    replied
    The little blips might not be anything depending on if your measurements were smoothed. Anything less than 1/48 smoothing might be hiding a spike you will want to see.

    IMO, typical tweeter in a deep guide. It should fill in off axis, but that will be the x-o challenge.

    Leave a comment:


  • KEtheredge87
    replied
    Originally posted by wogg View Post
    Looks like you're done.... 40Hz to 20kHz +- 20dB
    Haha, who knew a three way XO would be so easy! I think I'm going to re-create the blended files tonight and see if that little anomaly in the blended PCD response doesn't go away. Unless I figure out some place that I royally screwed up post-processing my raw FRD files, It's time to jump headlong into PCD and get to designing.

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  • KEtheredge87
    replied
    Originally posted by PWR RYD View Post
    Boy that tweeter response is going to be a bugger to work with.
    Hey Craig... yeah, probably going to be a challenge. I'm hoping I can do enough with it to have it sound ok. I'm also hoping i made the blended files correctly. I measured my farfield at 32 inches as opposed to the 20 inches that I figured on after reading Jeff's white paper. Maybe this tweeter response is why no one has left any reviews on the PE page for the FTX0617 coax . Time will tell what I can do!

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  • wogg
    replied
    Looks like you're done.... 40Hz to 20kHz +- 20dB

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  • PWR RYD
    replied
    Boy that tweeter response is going to be a bugger to work with.

    Leave a comment:


  • KEtheredge87
    replied
    Hi Everyone, Quick update this morning. I finally got to take some FRD measurements for all the drivers last night. I fumbled through the blending process for nearfield and farfield measurements and came out with what I think is correct. PCD is doing something interesting though. All of my FRD response files appear to be smooth, yet there's a funny little discontinuity in two places (biggest at 1500Hz, little one at ~5500Hz).

    Wonder what that's about?

    Click image for larger version

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  • augerpro
    replied
    What EC did Bassbox spec? Can you change it? If so, put in 100%, then backwards sim the Fb until it matches the measured Fb in DATS. Calculate the actual end correction. Now you know that for a smallish box, with a certain lining/filling, and slot port with approx. that design, that is the end correction you should use in the future.

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  • KEtheredge87
    replied
    Originally posted by augerpro View Post
    Looks like you're working through the variables well (use measured TS, account for your volumes, etc.). One major factor that doesn't get near enough attention though, is end correction...
    Hey Brandon, you've got that right! This particular slot port doesn't quite match any of the pictures that bass-box includes in it's port suggestions. Part of me wanted to call it "Two flush ends" since I had one legitimate flush end opening on the front baffle, and a barely rounded over internal entrance. The only thing keeping me from that is that the port has 3/4" of material and then the floor of the cabinet on the bottom side of the opening, and 3/4" of material thickness on the top side of the opening, rather than a full length baffle, which is what the picture seems to depict. I've got to be getting some internal reinforcements since the port opens near the floor, rather than floating in the middle of the cabinet like BassBox's picture.

    Unfortunately, I don't get a real chance to fine-tune the end correction value in Bassbox, I'm left to pick from their options. The two flush end choice gave a predicted Fb that was almost identical to my measurement, but I hesitate to use that since it feels inappropriate to the actual cabinet.

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  • augerpro
    replied
    Looks like you're working through the variables well (use measured TS, account for your volumes, etc.). One major factor that doesn't get near enough attention though, is end correction, specifically the fact that it is just assumed by software and the user never considers/questions it. Most software just assumes one, some assign one based on user settings and let you see/change it (unibox), and the best (Soundeasy) don't bother with an end correction at all. They leave it to the user to determine, because if varies so much with different construction methods there is no point in guessing. So you do have to have some experience in working out what you need for EC, but in the process you'll learn a lot more about how different construction methods impact it.

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