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2 way with RS225-4 in large box???

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  • 2 way with RS225-4 in large box???

    Shifting to a new thread from here

    The RS225-4 seems to have a pretty unique graph from the rest of the RS225 family including the RS225Ps. There doesn't seem to be any cone breakup! See the published graph here. This is very similar to some large full range drivers.

    So, the question is, can this driver be used in a two way? If so then

    1. Which tweeter to use? Obvious would be the RS28A, but it looks like it will be out of stock for a long time. I have a pair of RS28F, would this mate well with the RS225-4 Aluminium? I might be able to obtain a pair of RS28A, but looking for alternatives. Would any of the SB26 do - SB26STAC or SB26STCN, any others?

    2. What crossover point? Assuming that it really doesn't have a horrid come breakup, then it can be crossed high. Beaming starts above 13740/6.5 = 2113hz, so a 2k is possible? From mid surround to mid surround, it is 6.5". 13740 is speed of sound in inches. CTC plament based on the tweeter diameter suggests 1800Hz, especially if it is huge 4" tweeter. Smaller diameter tweeter faceplate might get us to 2Khz

    3. How do i verify the FR graph of the RS225-4? I have the driver, but haven't built the box. I am going to build the box, but whant can i do now so that the box isn't a complete wasted effort?

    4. The box in question is a 60Lt tuned to 30Hz for 29Hz F3 on a 12" x 40" baffle, with the tweeter at 36" and Woofer centered at 29" above the floor (Assuming 4" tweeter face plate diameter). What about floor bounce and nulls?

    Feasible / measurable / not worth it? Any published desgind with RS225-4? All i could find were lots and lots of projects with the RS225-8.

  • #2
    Re: 2 way with RS225-4 in large box???

    You don't have measuring equipment ?? Come on man... I used those as a woofer on my RSR's but didn't need to measure the top end. I can't imagine it not having the typical aluminum cone break up.
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    • #3
      Re: 2 way with RS225-4 in large box???

      Originally posted by 6thplanet View Post
      You don't have measuring equipment ?? Come on man... I used those as a woofer on my RSR's but didn't need to measure the top end. I can't imagine it not having the typical aluminum cone break up.
      That's what i intend to find out what sort of a top end break up they have.

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      • #4
        Re: 2 way with RS225-4 in large box???

        I would agree that it is very hard to believe the 4-ohm version would be much different than the 8-ohm.

        For reference only - RS225s-8 (it is the shielded version) but at 41 inches on a 10x19 baffle at 1/48 octave, it measures pretty close to PE's specs. That being said, I would assume the only big difference in these would be sensitivity.

        Click image for larger version

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        Paul

        The "SB's" build page
        http://techtalk.parts-express.com/sh...-4-(pic-heavy)

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        • #5
          Re: 2 way with RS225-4 in large box???

          I'd cross it 4th order, and as low as the tweeter will allow. Going 4th order might push your x-over cost up rather high. I own some Morels that will cross under 1.5k. It really may depend on how loud you want to be able to play these speakers.

          Just had an inspiration while looking out my window. Cut a 2' x 3' baffle, and lay it on top of a trash can. Hold the mic by hand if needed, and get a rough idea of the response.

          You could make a "test box" for quick measurements like this. Just something crude with a screwed on baffle to allow different drivers to be tested. I use old speaker boxes. The size hardly matters since you are not measuring bass so much as the midrange.

          I recently did a 4th order x-over on a small speaker using 8 ohm drivers. I think the x-over parts cost about $100 per speaker. (Ballpark estimate) The part count was a bit high at 16 parts. Too much to fit in the box. I might make a larger version

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          • #6
            Re: 2 way with RS225-4 in large box???

            Don't know how useful this is but my 2-way RS Duets used the RS225-8 with the RS28F and performed quite nicely. The crossover is a notched Cauer-eliiptic, with quasi-8th order slopes and a corner frequency of 1400 Hz.
            Paul
            Click image for larger version

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            • #7
              Re: 2 way with RS225-4 in large box???

              A quick and dirty measurement. The driver is on the floor, sitting inside the cardoard cutour and surrounded by pillows. Nearfield measurement, mic about 9 inches from the phase plug.

              It looks like the RS225P-8 has a 10db breakup at around 3.5k, whereas for the RS225-4 there is 8db roll off from 2k to 3k.

              Click image for larger version

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              • #8
                Re: 2 way with RS225-4 in large box???

                Another fresh set of measurement this time only for RS225-4 - same cardboard box cutout which is there inside the Box and 9" from phase plug.

                Click image for larger version

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                PS, I am not too experienced about this nor do i know what to expect hence the questions. Does this response looks good enough to warrant a box build? The box can be used for 2 way RS225-4 / two way RS225P-8 / # way with either driver - I need to change baffle and port tuning, but both RS225-4 and RS225P-8 model well in 60 Lts. So not a complete throwaway!!!

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                • #9
                  Re: 2 way with RS225-4 in large box???

                  Originally posted by Paul K. View Post
                  Don't know how useful this is but my 2-way RS Duets used the RS225-8 with the RS28F and performed quite nicely. The crossover is a notched Cauer-eliiptic, with quasi-8th order slopes and a corner frequency of 1400 Hz.
                  Paul
                  [ATTACH=CONFIG]57215[/ATTACH]
                  Thanks Paul. This was another question. How would the RS28F sound with the aluminum drivers? As the RS28F is what I have on hand.

                  Regards
                  Ani

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                  • #10
                    Re: 2 way with RS225-4 in large box???

                    Originally posted by ani_101 View Post

                    It looks like the RS225P-8 has a 10db breakup at around 3.5k, whereas for the RS225-4 there is 8db roll off from 2k to 3k.
                    Regardless whether peak or dip, both are examples of resonance, linear distortions some of which can be partially corrected with a resonance trap in shunt across the voicecoil, but the worst of it cannot be adequately smoothed out and needs to be placed well down in the stop band of the low pass. Another problem is distributed phase within the breakup resonance, usally visable as change in directivity. A rigid aluminum cone, if well terminated at the surround, can be rather clean of resonance in the usable passband. With that rigidity it begins beaming like a flashlight above that usable passband, but at higher frequency the directivity may widen in the region of the breakup resonance where phase becomes more distributed, illustrated where the off axis response swings back toward the on axis response. Response will sum a little differently with the tweeter where radiation off the woofer cone is exhibiting less coherent distributed phase (consider a panel exciter as an extreme example of distributed phase over much wider bandwidth).
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                    • #11
                      Re: 2 way with RS225-4 in large box???

                      Originally posted by JRT View Post
                      Regardless whether peak or dip, both are examples of resonance
                      Pretty much what I was going to say. That notch at 3k IS a "breakup" . . . just manifesting as a null instead of a peak. Crossover should be well below it, and it should NOT be treated as part of the "crossover curve".

                      The "P" (in RS225P) is for "pointless" . . . when crossed below 700Hz (in a 3-way) there is simply no difference in "sound" between the cone materials, and neither of them should be considered crossed above 1500-1600Hz (which is really pushing both on the high end, as both are well into beaming at that point anyway, and you might hear a difference because of the different breakups). Used below 700Hz, though, you can spend five times the money and not get anything even slightly better . . .
                      "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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                      • #12
                        Re: 2 way with RS225-4 in large box???

                        Originally posted by ani_101 View Post
                        How would the RS28F sound with the aluminum drivers?
                        It would sound like a RS28F. The cone of the woofer has no effect on the sound of the tweeter.
                        "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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                        • #13
                          Re: 2 way with RS225-4 in large box???

                          ok, got it - the notch is also a resonance / breakup artifact. So which reasonalby priced tweeters come close to be crossed at 1500 - 1600 Hz? any alternatives to the RS28 A/F?

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                          • #14
                            Re: 2 way with RS225-4 in large box???

                            Originally posted by ani_101 View Post
                            ok, got it - the notch is also a resonance / breakup artifact. So which reasonalby priced tweeters come close to be crossed at 1500 - 1600 Hz? any alternatives to the RS28 A/F?
                            Probably not any that would out perform an RS28 at anywhere near the RS28's price point.

                            As mundane as these two drivers are it's a tough combo to beat witout a considerably larger budget.
                            Thanks,
                            Aaron

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                            • #15
                              Re: 2 way with RS225-4 in large box???

                              What Aaron said . . .
                              "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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