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  • Excursion limits in ported design

    So I am contemplating a ported design using the Dayton RS225-4 and RS28F-4. I have previously built a sealed version of this project with good results when paired with a subwoofer. I want to build a ported version for use without a subwoofer. I have built ported subwoofers before. Since these have been active designs, I always include a high-pass filter slightly below the port frequency to limit excursion and prevent damage. *With a smaller design, I am concerned about excursion below the port frequency (about 30Hz). From the attached frequency response graph, the frequency extension is pretty good with f3=30 and f10=23. I am concerned about the power handling graph. Above the port frequency (40-50Hz) this design is limited to just below 40 watts. In 20-25Hz range, this design is limited to about 6 watts. I can assume most of the music happens above 30Hz, but I know there is still some action in some material at lower frequencies. Only a few watts to get to over excursion makes me nervous. How do people deal with this? I assume all of the people making ported bookshelf speakers arent just blowing them up. I see a lot of small ported speakers on the market with power handling specs of 50, 100, 150 watts. Whats the deal?
    Attached Files

  • #2
    Originally posted by pick View Post
    ... I always include a high-pass filter slightly below the port frequency to limit excursion and prevent damage....
    Note that Eminence provides designs ideas ( Jerry McNutt ) for their drivers ( especially for High Power applications ), they all make recommendations for using a High pass filter to prevent damage.
    "Not a Speaker Designer - Not even on the Internet"
    “Pride is your greatest enemy, humility is your greatest friend.”
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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    • #3
      Pragmatically speaking, what do you listen to, and at what level?
      nothing can stop me now

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      • #4
        Originally posted by Dirk View Post
        Pragmatically speaking, what do you listen to, and at what level?
        These days I listen to a mixture of country, rock, classic rock, and a little pop. No classical or pipe organ kind of stuff. I listen a at pretty high volume with my current system but that's not so much the point of this new project. Moderate listening levels would be OK.*

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        • #5
          20W listening levels will be just plain loud!!
          R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio

          Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51


          95% of Climate Models Agree: The Observations Must be Wrong
          "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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          • #6
            I pick a design SPL like 100 dB and design a port velocity below 26 m/s.* Once I get above my design values the port noise is an early warning.
            John H

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

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            • #7
              Originally posted by pick View Post
              . I can assume most of the music happens above 30Hz
              Most music content is above 50Hz, with very little below 40Hz. For music only there's no need for a lower than 40Hz f3. Move the Fb higher to get a 40Hz f3 and the maximum power above that will improve significantly.

              *
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #8
                Originally posted by billfitzmaurice View Post
                Most music content is above 50Hz, with very little below 40Hz. For music only there's no need for a lower than 40Hz f3. Move the Fb higher to get a 40Hz f3 and the maximum power above that will improve significantly.

                *
                while most of the of the sound we interpret as music is above 50hz, isn't most of the power used to push the drivers in the lower frequencies? So, it'd take more and more power to push the same driver the lower in frequency you attempt. Just askin'
                *

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                • #9
                  The elephant in the room is the accuracy of the simulation itself. Cabinet simulations are using T/S parameters, which are small signal parameters by definition. The simulations do not take account the forces of the mechanical suspension over excursion, so they are not entirely accurate at high output. Rest assured your cone will not fly across the room at 20Hz like many simulations will show, however in a ported cabinet, below the tuning frequency the speaker driver is considered "unloaded" and the excursion will be similar to what you would get if there were no cabinet at all.

                  Scan-Speak claims to have improved the performance of these types of simulations, you may want to compare your results using the Scan Speak Toolbox:
                  http://www.scan-speak.dk/?page_id=496

                  *
                  "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                  exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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                  • #10
                    Originally posted by dcibel View Post
                    ...Cabinet simulations are using T/S parameters, which are small signal parameters by definition....
                    A reality often overlooked.
                    "Not a Speaker Designer - Not even on the Internet"
                    “Pride is your greatest enemy, humility is your greatest friend.”
                    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                    • #11
                      Originally posted by hardcorecap View Post
                      while most of the of the sound we interpret as music is above 50hz, isn't most of the power used to push the drivers in the lower frequencies?
                      Most of the power lies in the 50-80Hz pass band. While the fundamentals of LF instruments go down to perhaps 30Hz it's the 2nd and third harmonics that dominate. For instance, the benchmark electric bass speaker is the Ampeg SVT 8x10. It has an f3 of 58Hz, and that's all it needs, based on the spectrum of the signals it has to deal with.

                      *
                      www.billfitzmaurice.com
                      www.billfitzmaurice.info/forum

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                      • #12
                        Most amps have a built in hi pass filter. You can add a 20hz 2nd order high pass to your Winisd model on the filters tab to see how it affects your design.
                        -Bob

                        The PEDS 2.1 mini system
                        My A7 Project - another small desktop speaker
                        The B3 Hybrid Dipole - thread incomplete and outdated

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                        • #13
                          Originally posted by dcibel View Post
                          Scan-Speak claims to have improved the performance of these types of simulations, you may want to compare your results using the Scan Speak Toolbox:
                          http://www.scan-speak.dk/?page_id=496

                          *
                          Thanks. I'll check out this tool and see how the simulation looks.*

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                          • #14
                            Originally posted by pick View Post

                            Thanks. I'll check out this tool and see how the simulation looks.
                            I don't think that Scan-Speak model takes into consideration the response of the driver when driven beyond Xmax. It seems to be some version of the "semi-inductance" model, which I believe also assumes linear behavior (not totally sure - I really haven't done a lot of research into it yet). Hornresp was recently updated to use that model as an option, and REW can derive the parameters from the driver's measured impedance.
                            Brian Steele
                            www.diysubwoofers.org

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