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Drivers max power rating in bassbox pro causes the Xmax to exede it's limit...

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  • Drivers max power rating in bassbox pro causes the Xmax to exede it's limit...

    Ok, this is starting to tick me off , many drivers I am trying in Bassbox pro with Xmax of 4mm or less ...far excede the limit so I reduce the power till it reaches almost the max Xmax of driver and for many of them you have to reduce from 100 watts all the way down to 20 watts before it is at or under the drivers Xmax. Not interested in paying for a driver that can only handle a small percentage of it's rated power because doing so will excede the Xmax.....this I think I am doing or interpeting this wrong, but all the drivers with about 5mm and above don't seem to have that problem

  • #2
    What size are these drivers?
    "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
      4" - 5" - 5-1/4" - 6.5"

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      • #4
        This is totally normal (I use WinISD and I see the same thing). A driver's "RMS power limit" is its "thermal" limit, basically how much power it can dissipate before the voice coil melts into a blob, or when the motor parts (coil, former) get hot enough to come unglued.

        It's up to you (as a designer) to balance box type/size, tuning (if applicable), and bottom-end extension (or high-pass filtering) to get the results you think you want, or need.

        Xmax is more a limit when distortion becomes unacceptable, and (obviously) will typically be quite a bit lower than the v.c.'s thermal limit.

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        • #5
          Behind Excursion:
          http://www.linkwitzlab.com/SpeakerBu...ographs-1c.jpg
          http://www.linkwitzlab.com/SpeakerBu...ographs-2c.jpg
          http://www.linkwitzlab.com/SpeakerBu...ographs-3c.jpg
          http://www.linkwitzlab.com/SpeakerBu...ographs-4c.jpg
          "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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          • #6
            Thank you for the Speaker Builder article, I use to subscribe to it in the 80s miss it, Think I will just set 5mm as the minimum Xmax for selecting any potential driver which then rules out a lot of drivers many of which are highly touted. I only build closed box speakers and do NOT trust this bassbox 6 Pro 100% anyway.

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            • #7
              It will explain the Physics behind what you are observing, and why larger cones have advantages.
              "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."

              Comment


              • #8
                Originally posted by sdep777 View Post
                . Not interested in paying for a driver that can only handle a small percentage of it's rated power because doing so will excede the Xmax.....
                That's actually the case with most drivers, and is the reason why thermal power ratings alone aren't worth much, it's usually the displacement limited power that really matters.

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

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                • #9
                  My latest design can barely handle 10 watts at 50 Hz. It has not been any problem at all for me, 10 watts is plenty loud enough.

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                  • #10
                    Originally posted by sdep777 View Post
                    Ok, this is starting to tick me off , many drivers I am trying in Bassbox pro with Xmax of 4mm or less ...far excede the limit so I reduce the power till it reaches almost the max Xmax of driver and for many of them you have to reduce from 100 watts all the way down to 20 watts before it is at or under the drivers Xmax. Not interested in paying for a driver that can only handle a small percentage of it's rated power because doing so will excede the Xmax.....this I think I am doing or interpeting this wrong, but all the drivers with about 5mm and above don't seem to have that problem
                    Your design application is not everyone's. Some will apply highpass filter(s) and operate at higher output level and the thermal limit will become more important than the excursion limit.
                    "Our Nation’s interests are best served by fostering a peaceful global system comprised
                    of interdependent networks of trade, finance, information, law, people and governance."
                    - from the October 2007 U.S. Naval capstone doctrine
                    A Cooperative Strategy for 21st Century Seapower
                    (a lofty notion since removed in the March 2015 revision)

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                    • #11
                      This is almost always a problem for smaller woofers (<8"). If you find a <8" driver that handles 100W without exceeding xmax what you will probably find that that it is completely anaemic in the bass.

                      It's a basic physics problem - you can't create low frequencies loudly without excursion. A recent design I did with a DA175-8 only takes 15Watts to reach xmax. If i crossed it to a sub it would take rated power all day though. In my case I wanted to run them without a sub so I'm prepared to keep an eye out for excess excursion when I get excited with the volume control. In return I get an F3 of 30Hz.

                      The only advantage I can think of for having a setup where xmax is not exceeded at rated power is to prevent damage due to abuse. If the person manning the volume knob doesn't have any understanding of the speakers xmax then going this route may be a valid design choice. Small sealed boxes are your friend.

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                      • #12
                        Well I have pretty much decided to stop looking at drivers with an Xmax of less than 5mm I want superb transient respose without having to worry if I am pushing to much, I have an Crown 3500 power amp.

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                        • #13
                          There are reasons that you can't just have 10mm xmax or whatever on a small driver and one of them is that it requires having a much longer coil, protruding further either side of the gap. As a result, the inductance of the coil changes more as it moves in and out (its goes up as more of the coil goes into the motor and down as more coil hangs out the front of the motor) and that results in higher intermodulation distortion in the midrange and lower treble. It requires a very good motor design to achieve 6mm or more xmax on a 6.5" or smaller woofer while keeping distortion low. A 6.5" frame also doesn't support much more xmax than that - the spider and surround can only move so far before they provide significantly more resistance and therefore distortion. Consider using multiple drivers to reduce xmax and increase power handling, lower distortion and not impact transient response.

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                          • #14
                            Well, I do model it that way with multiple drivers lately using 8 drivers and the x max gets exceded the same as a single driver based on max power X 8 drivers, so I reduce till I see it no longer excedes the Xmax limit sometimes that goes from 600 watts down to 125 watts ... anyway I feel better if the chosen driver has 5mm or above to keep it out of higher distortion... I belong to the Keep it simple stupid idea .

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                            • #15
                              Originally posted by sdep777 View Post
                              ... I belong to the Keep it simple stupid idea .
                              Personal Philosophy does influence implementation.
                              The reason I queried about driver size, is that it is tied into what you observe in modeling.
                              Model larger drivers and notice how they are more efficient. This is related to Acoustic Impedance.
                              Low frequency sound waves being huge ( 56.5' for 20Hz ), the size of the radiating surface of any EM cone is dwarfed. Compare the circumference of the radiating surface of the 4" - 6.5" cones to the size of sound waves and note they are closer in size to wavelengths in the middle of audible sound range. Even a woofer 18" is smaller than the bass frequencies.
                              There is a market for bass drivers that are designed for small cabinets, however the compromises involved include low efficiency: 82db sensitivity translates into ONLY 0.1% efficiency. 92db = 1%.
                              Larger woofers that offer that efficiency and greater are common.
                              Philosophically another approach is to accept large drivers and large cabs to get efficiency up, so excursion demands are greatly reduced. For example Use of a 7" driver only above 80Hz, and larger drivers for the bottom 2 octaves. Because for every drop in bass frequency by half - excursion demands increase 4X.
                              To produce the same SPL would require 16X excursion to produce the same SPL 2 octaves lower.
                              At the risk of laboring the point; It is a no free lunch deal. Some engineer once said: "Any driver can be made to reproduce low frequencies - but you may not like the results.
                              "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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