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Power amp RMS vs. Speaker RMS for subs

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  • Power amp RMS vs. Speaker RMS for subs

    Here's the situation: I have a pair of 8 ohm Peavey SP118 subs rated at 600 watts RMS each and a Behringer EP2500 running at 500 watts a side at 8 ohms. I have noticed at times that the subwoofers make a "popping" sound especially when I'm driving the low end kind of hard. I suspect it's from excursion, but is the excursion happening because the amp output is only 500 watts a side at 8 ohms and my speakers are rated at 600 watts RMS? I have 75 HZ and on down rolled off at the EQ and crossover and the amp limiter is engaged. I was told that you always have at least twice the RMS output on the amp vs. the speaker RMS, and from what I described above..that's not the case. Should I install 4 ohm speakers in the SP118 to increase the amp RMS output to 750 watts? Even then, I still dont have twice the RMS output. What size amp do I need to cleanly run the 600 watt RMS speakers in my SP118 subs?

    Thanks guys,


    Charlie

  • #2
    usually a FARK (or fart) happens when the box loses control of the driver, also called unloading. try a high pass filter. your "roll off at 75hz on down" wont be much help here. also the drivers may already be damaged. 500 watts into a 600watt speaker is fine, more power will not help.
    band status - "its complicated"

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    • #3
      Hey thanks guys for the quick replies. Coaster, you may be right...the speaker that "popped" might already be damaged and just waiting to fail. In the future, how do I best protect my subwoofers from too much excursion? Do I suck out all low frequencies starting from a certain point on the EQ? Do I set the compressor/limiter to kick in at a certain level? The EP2500 has high pass filters and limiting, and both are engaged...or at least I think they are. Funny thing I noticed is when I went to set the dip switches on the EP2500, the left side dip switch chart corresponds exactly to the actual dip switches, the right side is reverse of that. I set the dip switches the same for both sides of the amp. Maybe, the left side high pass and limiting is on, but the right side is not. Hmmm...how can I tell? Any thougts?

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      • #4
        i am unfamiliar with that amp so i cannot help there. exactly what are you using for a crossover? there is likely a 40hz HP filter on that.

        i'm unsure of the tuning of your sp118's but it is likely around that or slightly above. i have an older set of 118SUB and the box tuning is 42hz supposedly. i run the 40hz filters on my crossover and have no issue running 600watts into these; i use a crown sx900.

        if you do find you need a new basket they are not terribly expensive, around $100 or so.

        AFAIK some amps will typically use 12db/octave filters which are likely not steep enough. i think you would be better off with a 24db/octave filter. i am not sure about your amp. maybe andy will chime in.
        band status - "its complicated"

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        • #5
          Amp size is not the problem here .. a proper HP filter is needed. As I remember the box is tuned to about 45 Hz, so set your filter there.

          Actually a 12 dB/oct filter would be the proper "textbook" protection. A speaker's excursion would be 4 times more an octave down and a 12 dB filter is a 4x filter. A 24 db/oct will give more protection though.
          Don Boomer

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          • #6
            with a LR filter alignment, 24dB generally sounds better but with steeper alignments there can be artifacts from the higher filter Q that can be audible. In the old days, higher order filters were built with pretty slow parts and that was a problem too. Digital is a whole new ballgame also.

            Was the OP high passing the sub at 75Hz??? that's awfully high to be useful.
            -------------------------------------------------------------------------------------------------------------------------------------------------------------------
            Former product development engineer: Genz Benz, a KMC Music/Fender Musical Instruments Company, continuing factory level product support and service for Genz Benz

            Currently product development engineer: Mesa Boogie

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            • #7
              Funny thing I noticed is when I went to set the dip switches on the EP2500, the left side dip switch chart corresponds exactly to the actual dip switches, the right side is reverse of that. I set the dip switches the same for both sides of the amp. Maybe, the left side high pass and limiting is on, but the right side is not. Hmmm...how can I tell? Any thougts?
              Say what ? What switches are "on" (to the right) and which switches are "off" (to the left)? I think you want:
              1 on (clip limiter on)
              2 on (low cut filter 30 hz)
              3 off (low cut filter on)
              4 on (low cut filter on)
              5 on (low cut filter on)
              6 off (bridge mode off)
              7 off (bridge mode off)
              8 off (low cut filter on)
              9 on (low cut filter 30 hz)
              10 on (clip limiter on)

              "We Have Met the Enemy and He is Us" - Walt Kelly​

              Comment


              • #8
                Interesting DIP switch arrangement...what happens if you have only one "bridge mode" switch on??
                .....

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                • #9
                  Hey guys, thanks for all the info. This is a cool site. I'm gonna learn some stuff here. As far as equipment, here's what I run:
                  Mixer - Behringer
                  Dual 31 band EQ - Behringer
                  Compressor/Limiter - Behringer
                  Crossover - Behringer
                  Sonic Maximizer - BBE
                  EP1500 for (2) JBL - JRX125 cabinets
                  EP2500 for (2) Peavey SP118 subs

                  I hope this addresses the equipment issue.

                  As far as 12db/octave vs. 24db octave I can select either on the dual 31 EQ but I'm pretty sure my crossover is fixed at 24db/octave. When I select the 12db/octave on my EQ the sound jumps up in volume, but more noise too, so I choose to run it at 24db/octave.

                  The dip switch chart you have shown is missing low cut filter 50hz. Roadranger, I set my switches as you have shown with the exception being that the low cut filter 30hz is ON, and the low cut filter 50hz is OFF. Same dip switch, just moved to 30hz and away from 50hz. I will take a flashlight and look closely again at the dip sawitch settings to make sure I have ON what I need and I have OFF for what I don't.

                  Ultimately, I just want to be able to protect my subwoofers from excursion without having to compromise too much low end. I run midi files and sometimes those files are heavily laden with low end. I know I can edit the files to help with that problem, but having the time to do so...well, that's another issue. That's why it's important to me to have good protection because I can't afford to keep replacing baskets in my subwoofers.

                  Charlie

                  Comment


                  • #10
                    The dip switch chart you have shown is missing low cut filter 50hz. Roadranger, I set my switches as you have shown with the exception being that the low cut filter 30hz is ON, and the low cut filter 50hz is OFF. Same dip switch, just moved to 30hz and away from 50hz.
                    Again, Say what ? I've got the EP2500 manual here and it doesn't match up to what you're saying? You have to have the "low cut filter on/off" switches to the left (off) to enable the low cut filters (yes, back arsewards from what you'd think). Then you select 30 or 50 hz with the "low cut filter 50/30 hz" switches. left (off) for 50 hz and right (on) for 30 hz. Perhaps the confusion is that the on/off state of DIP switches doesn't always correspond to the on/off state of what they control .

                    "We Have Met the Enemy and He is Us" - Walt Kelly​

                    Comment


                    • #11
                      Interesting DIP switch arrangement...what happens if you have only one "bridge mode" switch on??
                      Your car falls in the river half way over .

                      "We Have Met the Enemy and He is Us" - Walt Kelly​

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                      • #12
                        Sonic Maximizer - BBE


                        This is likely part of your problem. Throw this piece of poo in the nearest pond and don't look back. Seriously.
                        Chief fader ape, wire monkey, mic macaque, and speaker chimp.

                        Comment


                        • #13
                          This is likely part of your problem. Throw this piece of poo in the nearest pond and don't look back. Seriously.
                          Hey, send it to me - someone is giving me a couple already and if I can get a whole rack full I can make a blinky light show out of them .

                          "We Have Met the Enemy and He is Us" - Walt Kelly​

                          Comment


                          • #14


                            Ultimately, I just want to be able to protect my subwoofers from excursion without having to compromise too much low end....


                            First ... use the 50Hz filter as the 30 will not give you the protection that you need.

                            Second ... you need to understand that even if you have a filter installed and active, if you boost the lows you can effectively remove the filter.

                            Mark's suggestion is probably your answer ... you don't have enough system to satisfy your needs. There is no way around that. You either have to settle for what you do have or blow up gear as it hits red-line.
                            Don Boomer

                            Comment


                            • #15
                              Seriously, loose the BBE and the rest is OK stuff. The 31 band can be a weapon of mass destruction in the hands of the inexperienced also - I personally would leave it out (or set flat if you can control yourself!) unless you really really really know how to use it.

                              "We Have Met the Enemy and He is Us" - Walt Kelly​

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