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  • #16
    Tom was asking to see the electrical (impedance) phase plot. On that you don't want to have wild phase swings. Rule of thumb is keeping the electrical phase between + and - 30 degrees, but I've broken that rule a bit ;)
    I can't seem to keep it between +/- 60 degrees most of the time. I think I'm missing/not understanding a key concept to control it better. If anyone has any rules of thumb, I would appreciate any guidance.

    Keith - there's a button in the System Impedance graph to show impedance phase.
    Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

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    • #17
      Originally posted by PWR RYD View Post
      Those are going to look bada$$. Glad you decided to move forward with that tweeter. I think you will find its FR is even smoother when measured on the actual baffle. I always use 1/24th octave smoothing with my OmniMic.

      Tom was asking to see the electrical (impedance) phase plot. On that you don't want to have wild phase swings. Rule of thumb is keeping the electrical phase between + and - 30 degrees, but I've broken that rule a bit ;) ...

      ...And to expand a bit on what John was saying about lifting the FR above 15kHz... you could try placing a small value cap in series with your 5.1 ohm padding resistor. Try 1 uF and go up and down to see the effects.
      Thanks PWR RYD, The explanation definitely helped. Now to re-answer Tom's question. The electrical phase (yellow line) looks like a curvy line to me! Based on the +/- 30 deg rule of thumb, I think I'm bending the rules a bit at ~120Hz. I don't quite understand the implications of this though... harder on my amplifier?

      Click image for larger version

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      I'll mess around with the additional series cap on the 15kHz response to see where I land. I'm currently deciding how I want to power this speaker for OmniMic measurements. I have separate wires for the woofer and tweeter, but constantly reaching behind the Marantz AVR in the living room to change wires sounds like a hassle.

      Also, I hear I should put a series capacitor on my tweeter to protect it from low frequencies during impulse measurements? I have some 100 uF Ruby Tube capacitors that PE sent me by mistake one time (https://www.parts-express.com/ruby-t...citor--020-656), so that will probably work in conjunction with the "bass removed" tracks on the OmniMic test CD. Just gotta line the + and - up on that cap. Pretty sure it is polarized.
      Voxel Down Firing with Dayton SA70
      Translam Subwoofers - The Jedi Mind Tricks
      The Super Bees - Garage 2 way

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      • #18
        This is a really cool design. So long as you use the bass removed sweep in Omnimic you shouldn't need a cap. If you use the ruby caps you need two of them in series back to back, negative to negative, to make them non-polarized, which also halves the value.
        Projects:

        transcenD: http://techtalk.parts-express.com/fo...5035-transcend
        Summits: http://techtalk.parts-express.com/sh...75-The-Summits
        References: http://techtalk.parts-express.com/sh...-My-References
        Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

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        • #19
          Awesome looking concept Keith.

          Man, you got awful good at this crossovering thing really quick... Took me years of brain pain to get to where you are... heck, If I'm even that far yet!

          Looks great, and I love the Mopar nod. My first car was a 1974 Plymouth Duster with a 198 cu. in. Slant 6 engine. Not fast, but I poured myself into fixing it up on a shoestring budget and I truly loved that car... still do. If I ever hit the lottery, I'd love to Resto-Mod one of those with a nice Hemi and modern suspension... maybe even air conditioning!

          TomZ
          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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          • #20
            Originally posted by dynamo View Post
            This is a really cool design. So long as you use the bass removed sweep in Omnimic you shouldn't need a cap. If you use the ruby caps you need two of them in series back to back, negative to negative, to make them non-polarized, which also halves the value.
            Thanks Dynamo! Glad you like it so far. I find that looking good is almost as important as sounding good, since there will be some times where they aren't playing

            On the tweeter measurements, I'll have to be careful and use the right Omnimic tracks. Turns out the radioshack here in my town closed recently, so I'd be waiting a few days to get any other capacitors if needed. To be fair, I've never visited any of the electrical supply companies in town before, I just assume they aren't carrying large stocks of audio grade capacitors!
            Voxel Down Firing with Dayton SA70
            Translam Subwoofers - The Jedi Mind Tricks
            The Super Bees - Garage 2 way

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            • #21
              Originally posted by tomzarbo View Post
              Awesome looking concept Keith.

              Man, you got awful good at this crossovering thing really quick... Took me years of brain pain to get to where you are... heck, If I'm even that far yet!

              Looks great, and I love the Mopar nod. My first car was a 1974 Plymouth Duster with a 198 cu. in. Slant 6 engine. Not fast, but I poured myself into fixing it up on a shoestring budget and I truly loved that car... still do. If I ever hit the lottery, I'd love to Resto-Mod one of those with a nice Hemi and modern suspension... maybe even air conditioning!

              TomZ
              Thanks Tom! Did the Duster at least have 455 Air Conditioning? I only got this far, this quickly, thanks to the awesome people on this forum like yourself, Johnny Richards, PWR RYD, and Altoid. Watching those videos on how to use Mr. Bagby's PCD program was an immense help! I still don't have a total grasp on the finer points (see electrical phase vs. acoustic phase goof-up in the above posts ) but I'm getting there bit by bit. I think I saw you had a request for a video on how to do Omnimic work in the other forum category a year back or so... If I ever start to feel like I know what I'm doing, I might take a crack at it. Gotta give back to the community somehow!
              Voxel Down Firing with Dayton SA70
              Translam Subwoofers - The Jedi Mind Tricks
              The Super Bees - Garage 2 way

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              • #22
                No reason to add a cap on the tweeter when measuring, you will shift the phase when summing with the woofer to find the offsets. If you use the base removed track be sure to use it on the the woofer. You can change to full spectrum for the near field measurement. I usually just give the tweeter full spectrum, track 2... The volume is pretty low so I have yet to burn one up. I'm a bit more careful with ribbons.
                John H

                SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                • #23
                  Thanks John! I appreciate the practical advice. To make sure I follow you 100%, did you mean:

                  1) No capacitor and reasonable volumes on the tweeters - Full spectrum impulse content on both near field and far field measurements for the tweeter.
                  2) No capacitor and reasonable volumes on the tweeters - Full spectrum impulse on near field only, Bass removed on far field.

                  Note - Mr. Bagby's paper recommended 85 dB for gated impulse measurements, so that's my target for "reasonable volumes"
                  Voxel Down Firing with Dayton SA70
                  Translam Subwoofers - The Jedi Mind Tricks
                  The Super Bees - Garage 2 way

                  Comment


                  • #24
                    On the Impedance phase plot - I know is a swing one direction presents more of an inductive load to your amp, the opposite swing is capacitive. Not sure which way is which. Also not sure if how much of an issue it is for most decent amplifiers. I have seen many well thought of designs with Impedance Phase that isn't quite as nice as what you have right now.
                    Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

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                    • #25
                      Originally posted by KEtheredge87 View Post


                      Hey Kevin, I agree the 'Cuda is fantastic. Maybe some day I'll own one (If I ever quit spending money on speakers...hah!) The port I'm using is actually a couple of modified Goldwood 1.5" x 4" ports that I had left over from the Voxel project I did last winter. Since these boxes were premade, there really wasnt an easy option for flush trimming any PVC ports unless I stuck them forward firing, and I used all my real estate on the front for drivers. If you look at those ports, they are actually a bit tapered. Might be hard to tell by internet photos alone, but the vernier calipers don't lie. I measured the ports with calipers and modeled them in Fusion 360 as well, then made a combined version to determine what my minimum ID would be after cutting two ports down equally and butting them together. I made some drawings of each to help detail the idea a bit more. That's where my oddly specific 1.728" ID came from.

                      As for BassBox, I'm using "typical" as the damping setting, and 1.728 inch as my vent diameter (Dv) and 4.75 inch as my length (Lv). I have the vent cross section set to "round", so I wonder if the port having a slight taper may be messing with the calculation. Additionally, I never did fully grasp port length when including flares. Was this supposed to subtract from your assumed port length? or add to it? May need to study the bassbox help files to understand the assumptions better.

                      As always, thanks for following along!
                      The Goldwood port measures close to your 1.728" ID at the opening but tapers down to 1.575" at the other end. This is one of my favorite ports that PE carries and anytime a driver allows it, I try to use it. With the taper, I've found this port measures closer to 1.5" PVC (1.61" ID). Flares increase the length requirement but as you know help with chuffing if you have a higher vent velocity. Good luck!
                      My "No-Name" CC Speaker
                      Kerry's "Silverbacks"
                      Ben's Synchaeta's for Mom
                      The Archers
                      Rick's "db" Desktop CBT Arrays
                      The Gandalf's

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                      • #26
                        Mopar! Love it! (Yet another reason I like you guys!)I still recall sitting in the back of my Uncle's '72 olive-green/black-top 440 'Cuda, and not being able to lean my 3 year old body forward when he hit the gas.
                        I still drive my Magnum....

                        As to the 1 uF cap, that should be placed in parallel with the series resistor to lift the top-octave a smidge, not in series. In series will rolloff the bottom end way too early compared to what you have currently.

                        The impedance phase represents inductive in the positive swing, and capacitive in the negative swing. The swings regarding bass tuning and driver self resonance at Fc, Fb, or Fs really can't be helped, so I generally disregard the impedance phase in that region. If you have a low impedance magnitude (minima) in the same region as a very capacitive swing, then your amps might not like you so much since they have to work harder. The +/-30 deg is a good ROT. I've gone outside on the inductive side and not worried about it, as these tend to be very minimal at best. It's rare for me to actually exceed +30. On the other hand, I try hard to keep the capacitive swing above -40deg if at all possible, with good impedance magnitude. There is the rare case where this does happen, and there isn't much you can do to fix it- my MAX project was one of those particular cases. It was high in acoustic order, high in parts count for taming issues, and just plain difficult.

                        There are a couple ROT to keep Z-phase at a minimum. Move the series resistor out front on the tweeter- which you have already done. This does help quite a bit. Also- keeping the impedance rise (hill) at the xover point (or in other large magnitudes) lower in magnitude across the range. Since the Z-phase is the derivative (calculus, same for FR and acoustic-phase too) or 'rate of change' of the impedance curve; the more diverse the curve, the more the rate (phase) will change in magnitude.

                        The only way to ensure flat impedance phase with these peaks is to comp the impedance rise with an LCR across the speakers' input, and that then places higher demands on the parts directly across the amplifier's outputs. I have compensated for these a few times (I believe 3 cases) when the peak was horrendous, but it was normally a very limited bandwidth, higher power rated resistor, and centered around the frequencies of issue very tightly. It's not always a good idea to go this route.

                        Later,
                        Wolf
                        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                        "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                        "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                        "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

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                        • #27
                          Originally posted by Kevin K. View Post

                          The Goldwood port measures close to your 1.728" ID at the opening but tapers down to 1.575" at the other end. This is one of my favorite ports that PE carries and anytime a driver allows it, I try to use it. With the taper, I've found this port measures closer to 1.5" PVC (1.61" ID). Flares increase the length requirement but as you know help with chuffing if you have a higher vent velocity. Good luck!
                          Good info, bud! Makes me wonder how we ought to treat slightly tapered ports in BassBox? We clearly have to pick one port diameter to use, so I wonder if the bigger ID or the smaller ID makes the most sense. Double that conundrum if (as I am doing) you're butting two tapered ports up against each other. Sounds like a fluid mechanics problem for sure.

                          With the flare increasing the length requirement, I probably should NOT do anything different since bass box has a button to select double flares. I trust they're already taking things into account, and my entered port length should still be total overall distance, not some odd length of the tubes without the flared sections.
                          Voxel Down Firing with Dayton SA70
                          Translam Subwoofers - The Jedi Mind Tricks
                          The Super Bees - Garage 2 way

                          Comment


                          • #28
                            Ben, Lots of great information in your post above. Thanks for sharing your knowledge with me. I've read it twice now, and I'll be reading it again as I get back into XO tweaks with real frequency response data. Gotta let that information gel in the brain for a bit. Everything's interconnected!
                            Voxel Down Firing with Dayton SA70
                            Translam Subwoofers - The Jedi Mind Tricks
                            The Super Bees - Garage 2 way

                            Comment


                            • #29
                              Originally posted by KEtheredge87 View Post
                              Good info, bud! Makes me wonder how we ought to treat slightly tapered ports in BassBox? We clearly have to pick one port diameter to use, so I wonder if the bigger ID or the smaller ID makes the most sense. Double that conundrum if (as I am doing) you're butting two tapered ports up against each other. Sounds like a fluid mechanics problem for sure.

                              With the flare increasing the length requirement, I probably should NOT do anything different since bass box has a button to select double flares. I trust they're already taking things into account, and my entered port length should still be total overall distance, not some odd length of the tubes without the flared sections.
                              If you were not cutting the Goldwood port, (1.725 (big end) +1.575 (small end))/2=1.625 average ID. Since you are cutting and splicing two of them, best bet is the DAT's measurements to dial it in and a "WAG" on the ID to start off with until you can take the measurements. Yea, if you are selecting "flared port", one end or both, BassBox is already taken that into consideration for it's "total" length calculation, end to end including flares.

                              What you have now is a "known" FB based on the first length you tried. Should be easy enough to manipulate in BB now to come up with the adjustment you need. Leave the ID of the port alone. Go back to the FB and increase it by the amount you are off, 11Hz (target 56Hz - actual 45Hz). Take the difference between the two lengths and subtract that from your ports. Just guessing, it'll be around 2" total you need to cut off. If you are nervous about my method for correcting the length, take half of it on the first try and measure again to see how it works out. Good luck!
                              My "No-Name" CC Speaker
                              Kerry's "Silverbacks"
                              Ben's Synchaeta's for Mom
                              The Archers
                              Rick's "db" Desktop CBT Arrays
                              The Gandalf's

                              Comment


                              • #30
                                Originally posted by KEtheredge87 View Post
                                Thanks John! I appreciate the practical advice. To make sure I follow you 100%, did you mean:

                                1) No capacitor and reasonable volumes on the tweeters - Full spectrum impulse content on both near field and far field measurements for the tweeter.
                                2) No capacitor and reasonable volumes on the tweeters - Full spectrum impulse on near field only, Bass removed on far field.

                                Note - Mr. Bagby's paper recommended 85 dB for gated impulse measurements, so that's my target for "reasonable volumes"

                                1) no cap and 85 db volumes on the tweeter with track 2. There is no near field measurement on the tweeter. Assuming your are extracting minimum phase you can trim the tail in the blender.
                                2) N/A no near field on the tweeter.

                                Whichever you choose use the same track, same volume, same mic position, same gating, same smoothing (I like 1/48). Measure 1) tweeter, 2) woofer, 3) woofer plus tweeter in parallel. 4) Move mic and measure woofer within 1 cm of cone center, ungated (you will need track 2 for the full spectrum), turn volume down so mic does not clip. Some people like measuring the port I skip it because I'm lazy.

                                I usually measure the impedance and save the ZMA files at this time.
                                John H

                                SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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