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RS100-4 x2 + RS75T-8 + OT19NC00-04 Center Channel

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  • #16
    Fifty-seven (57) measurements later, at two (2) different resolutions each I can say that I have characterized the frequency response of the individual drivers in room.
    All measurements are without gating and show full diffraction and room boundary effects.
    I thought that I might try VituixCad for the crossover on this one in addition to my usual PCD endeavors, hence all the measurements.

    First the OT19NCOO-04:
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    • #17
      Measurements took about six (6) hours and had me questioning just how flawed the off-axis frequency measurements approximated by PCD could be.
      However, it was very interesting to see the boundary and diffraction effects in practice. Apart from a very prominent 200Hz room mode, the predicted ripples just weren't there.

      Now the RS75T-8

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      • #18
        Finally the two (2) RS100-4 wired in series, measured at their center point.

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        • #19
          I love those RS100s. I have the paper versions and they sound wonderful. Excellent choice for center channel. I am using mine from 250 hz to 4khz.

          Comment


          • #20
            Hi Greg,

            I was wondering if you completed this project and are satisfied with the result. I am looking for some very small DIY L/R and surrounds with a matching center and the RS100 driver with some tweeter might be a good option. When looking for a center design with an RS100 I stumbled upon this build. I would love to hear the outcome!

            And just being curious, in the opening post on the far right I see a small 2-way speaker too, which drivers are used in that build?

            Bob

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            • #21
              Hi Bob,

              the two-ways are these:
              https://techtalk.parts-express.com/forum/tech-talk-forum/1381604-rs125p-8-xt25sc40-04-mini-monitor

              I used a bought-out assembly as the waveguide for the XT25SC40-04, which I believe contributed to the directivity matching through the crossover region, but makes replication difficult.

              For the center channel, I have only just begun crossover prototyping. I’ve spent a good bit of time experimenting with my AV receiver’s GEQ and digital crossover functionality in an attempt to EQ out the room mode at 200 Hz. I also have some beefy inductors on order that are necessary to keep the project moving forward.

              I’m glad the project looks interesting to you. I will keep posting updates as I progress.

              Cheers!

              Comment


              • a4eaudio
                a4eaudio commented
                Editing a comment
                That link isn't working ("404 - File or directory not found" error), but the build is there just by doing a quick Google search. My guess is something is wrong with the cut-and-paste of the link.

              • buggers
                buggers commented
                Editing a comment
                https://techtalk.parts-express.com/f...ini-monitor%20

              • gregrueff
                gregrueff commented
                Editing a comment
                Hey, thanks for hunting down my link!
                I am user error.

            • #22
              On axis frequency response with reverse null(s):
              The on axis measurement is not gated and shows full room effects, including boundary modes. My HD receiver's GEQ has been used to smooth some of them out, but this is an in-room curve.
              The reverse null(s) were taken as gated measurements.
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              System harmonic distortion at 12" on axis:
              The 3rd order peak at 2.5 kHz is from the RS75T-8 and was present in my infinite baffle testing of the driver.
              I call it a "win" that system 3rd order distortion basically stays below 50 dB down through the pass band, up to and including down to 100 Hz where the center is crossed for all intents and purposes.
              Excursion related distortion from the RS100-4(s) was lowered by pairing them up and placing them in a vented alignment that has the port pick up the low end output, limiting the driver excursion right before roll-off.
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              • #23
                Not bad for eight (8) components:

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                • #24
                  Having worked with the XT25sc50 and 90 before I would highly recommend placing a 30 Ohm resistor across it. This will get rid of that bump down there about -18 DB where the fs spikes and you may no longer have any nasality qualities. You'll notice it in some recordings just in case you haven't heard it yet. I know you are crossing about 2.8k and second order, and I did as well.

                  Yes, though, great for 8 parts as is.
                  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

                  *InDIYana event website*

                  Photobucket pages:
                  https://app.photobucket.com/u/wolf_teeth_speaker

                  My blog/writeups/thoughts here at PE:
                  http://techtalk.parts-express.com/blog.php?u=4102

                  Comment


                  • #25
                    These look and measure very nice!
                    Craig

                    I drive way too fast to worry about cholesterol.

                    Comment


                    • #26
                      Originally posted by Wolf View Post
                      Having worked with the XT25sc50 and 90 before I would highly recommend placing a 30 Ohm resistor across it. This will get rid of that bump down there about -18 DB where the fs spikes and you may no longer have any nasality qualities. You'll notice it in some recordings just in case you haven't heard it yet. I know you are crossing about 2.8k and second order, and I did as well.

                      Wolf
                      Ha, I knew we'd be talking about this!
                      I appreciate your input of course and foresaw the debate, so I actually tried the tweeter by itself with and without a full blown LCR trap. I personally could not hear a difference.
                      I am crossing it LR2 closer to 4 kHz though, and in its current state the resonance bump is -17dB down.

                      If I were to cross it at 2.8 kHz and throw a 30 ohm resister across the tweeter the peak is about -14 dB down.
                      Keeping it in its current state and throwing in the resistor actually doesn't drop the peak appreciably, but does electrically damp and attenuate the resonant peak by about 4 ohms.

                      I will continue to keep my ears open for any honking, but I'm not sure I am discerning enough. I decided to drop the LCR trap because I couldn't justify it to myself. I had no problem using the parts if I needed to though.
                      Similarly I had a cap on the shunt leg of the midrange lowpass but dropped it because the value was so low (1.5 uF) and it only marginally made the phase tracking better. It just didn't make sense to keep the part for such a marginal benefit (to me at least).

                      We have debated this before when I used the XT25SC40 for the first time and learned what a true undamped resonance peak looks like, lol, and I heeded your advice there with the full blown LCR trap. But in that instance I was crossing LR2 at 2 kHz where the bump wasn't too far down.

                      But I respectfully think you just have better ears than me.

                      Cheers,

                      Comment


                      • #27
                        Play some James Taylor, you'll know....

                        Fair enough, if you're happy.
                        I misread the graph, you are about 4k.
                        Keep up the good work,
                        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

                        *InDIYana event website*

                        Photobucket pages:
                        https://app.photobucket.com/u/wolf_teeth_speaker

                        My blog/writeups/thoughts here at PE:
                        http://techtalk.parts-express.com/blog.php?u=4102

                        Comment


                        • #28
                          Just for the sake of amateur hour, are you talking about the purple response line that appears at 2.5khz?

                          I have been looking for a center channel that would work well with my Anarchy MTM mains so I am really interested to see how this one turns out.

                          Comment


                          • #29
                            Originally posted by davidroberts View Post
                            Just for the sake of amateur hour, are you talking about the purple response line that appears at 2.5khz?
                            Hi David,

                            We're discussing the response of the OT19 tweeter.

                            It, like the other ring radiators does not use ferrofluid and as a result has a fairly large impedance spike at Fs.
                            Some view this lack of ferrofluid as a positive, but what is not up for debate is that it can make crossover work difficult.

                            Usually the high-pass roll-off gets a bump in the frequency response right where the resonance is, especially as you cross lower and lower, closer to Fs.
                            One way to get rid of this is to put an LCR trap across the tweeter which neutralizes the impedance bump and basically flattens it. You can also use an L-pad to damp it, or as Wolf has stated you can put a large resistor across the tweeter to damp it as well.

                            So we are debating whether the impedance bump that manifests as a frequency anomaly right above 1 kHz is far enough below the fundamental signal to be impactful (or audible).
                            For the record, I have kept the impedance bump undamped since I am crossing fairly high (above Fs and by crossover standards) and it is already -17 dB down.
                            Some have demonstrated that they can identify (hear) frequency anomalies as low as -30 dB down or even lower.

                            Cheers!

                            Comment


                            • #30
                              Originally posted by gregrueff View Post

                              Hi David,

                              We're discussing the response of the OT19 tweeter.

                              It, like the other ring radiators does not use ferrofluid and as a result has a fairly large impedance spike at Fs.
                              Some view this lack of ferrofluid as a positive, but what is not up for debate is that it can make crossover work difficult.

                              Usually the high-pass roll-off gets a bump in the frequency response right where the resonance is, especially as you cross lower and lower, closer to Fs.
                              One way to get rid of this is to put an LCR trap across the tweeter which neutralizes the impedance bump and basically flattens it. You can also use an L-pad to damp it, or as Wolf has stated you can put a large resistor across the tweeter to damp it as well.

                              So we are debating whether the impedance bump that manifests as a frequency anomaly right above 1 kHz is far enough below the fundamental signal to be impactful (or audible).
                              For the record, I have kept the impedance bump undamped since I am crossing fairly high (above Fs and by crossover standards) and it is already -17 dB down.
                              Some have demonstrated that they can identify (hear) frequency anomalies as low as -30 dB down or even lower.

                              Cheers!
                              Roger that. So you are looking the impedance and not necessarily the predicted frequency response.

                              It has been quite some time ago but I worked with Dennis Murphy on some cover designs for the RS series speakers that included a WMTW design. He was gracious enough to share his measurements with several other designers. His used the least shallow slopes and that what preferred by many builders.

                              Comment

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