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Rolls SX21 [24db] crossover question

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  • Rolls SX21 [24db] crossover question

    With all this extra time on my hands going through all my DIY speaker projects and disassembling the ones that are not so good. This DIY build is a mtm: two 6.5" woofers and a 4-1/4" tweeter. I pulled them out and put them on the test-set-up in the living room; I told the wife no one is coming over here anytime soon anyway.

    I did have a passive crossover xo for this pair, but just thought they didn't have much kick and could sound much better. Removed the passive xo board and straight wired them, hoping that I could use a pair of Rolls SX21 active xo.

    First attempt with a power amp and the Rolls: No phase shift at all, there were no signs of a dip by reversing driver connections, the response looked like a straight twisted rope, sounded awful btw.

    Now what, I thought there may be a simple answer and added a 12uf cap at the tweeter, which was a huge improvement in the phase, although the tweeter connection needed to be reversed for the straighter response. [photo] Huge improvement in the sound and the kick.

    The Rolls SX 21 (24db) is a bare bones crossover with a few basic features. I have read reviews that said the polarity is backwards, which is obviously not the case but what are the options to correct phase with caps/coils/resistors. Or maybe I should quit when I'm ahead.

    Are there other options?
    Is a reverse connection a issue, or it just about the final response?

    Many thanks!

  • #2
    I'm guessing the problem is the Z offset of the drivers. The tweeter probably needs a couple inches of digital delay. Your xover doesn't do delay?
    Francis

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    • #3
      I'll also point out that, unless the drivers are flat in the crossover region, you won't end up with LR4 acoustic. Just...some arbitrary response.
      Francis

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      • #4
        fpitas,

        The Rolls has a 50hz - 2500hz control and volume settings for both bass/treble. I believe it may typically be used for quick set-ups for DJ's etc, because the inputs/outputs are 1/4" jacks. Ordered adapter cables down to RCA. But no, no time delay.

        I set up a miniDSP 2x4 a couple of years ago for my main speakers, not this pair but something very similar. Ordered a spare minidsp and that is still in the box, so I may have to use it for this pair.
        [minidsp has delay settings]

        Thanks for the help!





        Comment


        • #5
          Originally posted by HIFY GUY View Post
          fpitas,

          The Rolls has a 50hz - 2500hz control and volume settings for both bass/treble. I believe it may typically be used for quick set-ups for DJ's etc, because the inputs/outputs are 1/4" jacks. Ordered adapter cables down to RCA. But no, no time delay.

          I set up a miniDSP 2x4 a couple of years ago for my main speakers, not this pair but something very similar. Ordered a spare minidsp and that is still in the box, so I may have to use it for this pair.
          [minidsp has delay settings]

          Thanks for the help!




          Sure thing! As far as I'm concerned, digital delay is one of the biggest benefits of active crossovers. Conversely, I don't think a lot of people appreciate the magic that goes on in a properly designed passive crossover, including EQ and correcting for phase.
          Last edited by fpitas; 03-29-2020, 09:31 AM.
          Francis

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          • #6
            Absolutely on the active crossovers and passive crossovers [which very difficult to start from scratch]

            Ok I wouldn't advise this ploy but did improve the sound with 6db "helper" parts added to the the cables on the rear the speaker.
            The biggest improvement was a series coil at the woofer, only .51 [14 gauge-air] but that took out the overbearing mid-range. They are really packing a punch now.
            Secondly, the tweeter, moved from 12uf to 18uf, which added a bit more low in the tweeter's range.
            Third, pulled out a Adcom 7300 5 channel amp, never a popular amp, but I'm not sure why; they do have a little extra punch!

            So now they play much louder and sound like DJ speakers, which was really the goal for the next outdoor BBQ.

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            • #7
              Glad it worked out!
              Francis

              Comment


              • #8
                Forgive me if I'm preaching to the choir here -

                Analog active crossovers are a pretty blunt tool compared to a miniDSP or something similar. Neither account for BSC, the drivers' natural acoustic roll offs, or response irregularities. But you almost always have some parametric EQ capability with DSP boxes, so if you can measure the drivers, you'll get much closer to proper summation and the desired response. Charlie Laub had been working on something called Active Crossover Designer. I played with it a bit when I still had a DCX2496 and it looked to be a worthy design tool.

                http://audio.claub.net/software/ACD/ACD.html
                Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

                Comment


                • #9
                  Originally posted by tom_s View Post
                  Forgive me if I'm preaching to the choir here -

                  Analog active crossovers are a pretty blunt tool compared to a miniDSP or something similar. Neither account for BSC, the drivers' natural acoustic roll offs, or response irregularities. But you almost always have some parametric EQ capability with DSP boxes, so if you can measure the drivers, you'll get much closer to proper summation and the desired response. Charlie Laub had been working on something called Active Crossover Designer. I played with it a bit when I still had a DCX2496 and it looked to be a worthy design tool.

                  http://audio.claub.net/software/ACD/ACD.html
                  Yeah, there's a tendency to think of active crossovers as a magic bullet, but the same old rules apply as with passive crossovers. This whole speaker design thing is too much like work!
                  Francis

                  Comment


                  • #10
                    Originally posted by HIFY GUY View Post
                    fpitas,

                    The Rolls has a 50hz - 2500hz control and volume settings for both bass/treble. I believe it may typically be used for quick set-ups for DJ's etc, because the inputs/outputs are 1/4" jacks. Ordered adapter cables down to RCA. But no, no time delay.

                    I set up a miniDSP 2x4 a couple of years ago for my main speakers, not this pair but something very similar. Ordered a spare minidsp and that is still in the box, so I may have to use it for this pair.
                    [minidsp has delay settings]

                    Thanks for the help!




                    When you measure, look closely at the woofer response from 300hz to 10k. There can be small problems that hide when the tweeter response masks what's going on with the woofer. Same applies to the tweeter measurements. As for delay, I think it can be helpful, but not necessarily needed.

                    Comment


                    • #11
                      fpitas, Tom, rpb thanks.

                      I was coming to the same conclusion about the woofers, but thinking there may be a better tweeter for the project also, which doesn't leave much to work with..lol

                      And kidding myself about pulling them away as-is, less than 24 hours hours completely tore them apart and even cut-off the face/baffle.
                      Also checked what tweeters on the shelf (my buddy gave me several when he moved south).
                      Checked the specs on them and have one or one-pair of the list below.
                      The thinking was the mtm was making thing even more complicated and try a tmm. Also move the xo down to 1,500hz with the shortcomings of the woofer(s).


                      Click image for larger version  Name:	Untitled.png Views:	0 Size:	206.5 KB ID:	1435471
                      Last edited by HIFY GUY; 03-31-2020, 07:54 PM.

                      Comment


                      • #12
                        Knowing that you have some nice tweeters on hand, I think you'll end up with a pretty good sounding speaker. I had a crossover designed by that company in Wisconsin for a Silver Flute 6.5" & Seas tweeter (a buyout based on the 27TDC) almost 20 years ago. I'm not sure if I still have the design sheet, but I think they cross above 2K. They are in my home video/audio editing rig and sound surprisingly good for such modest drivers.
                        Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

                        Comment


                        • #13
                          I have an idea on the null not being present.

                          when i had 6db crossed tweet moved right up against the front baffle, i couldn't hear any difference flipping the phase.

                          once the tweet was slid back closer to the acoustic centers, i could hear the null when flipping the phase.


                          i had the rx321 for years, good unit.
                          and yea, baffle step is needed if your receiver doesnt have loudness and/or bass treble controls.
                          otherwise cd player - eq - active crossover - amplifier/amplifier worked best for non double 15" setups I've had, even then eq helped add high treble to horn compression driver.

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                          • #14
                            Sorry for the slow response.
                            Well as mentioned I did run the boxes thru the table saw and gave this a fresh start with new tmm front baffles and went with the wavecor W11.
                            Glad I did too, they just sounded better right away.
                            Connected them to a minidsp 2x4 and went through the settings; I found that a 200hz differential solved a lot of issues [1400hz/1600hz], at the same time realized the SF does not like to be crossed over too high or too low.

                            I have been curious about the time delay, and which to delay, woofer side or tweeter -- I've been going with whatever has lowest setting.

                            Tom any luck with the Flute 6.5" & Seas tweeter design?
                            Always looking for another project, especially these days.
                            (although my extra SF's are 8ohm)

                            Many thanks!
                            Attached Files

                            Comment


                            • #15
                              If you look at the geometry of your speaker, and mic position, you will notice that the tweeter is probably closer to the mic. Now, picture the situation from 3 meters. The woofers are probably closer.

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