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What can drive 2 pairs of MRX518's 2 ohm stable

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  • What can drive 2 pairs of MRX518's 2 ohm stable

    Howdy. It was hot, about 90 degrees or so, one of those long days play music during day, then bring it up a little later on, about 4 hours in when bringing it up the 2450 would just stop on the output, all the lights would stay the same, no red lights, just normal lights. I was in the shade under a tent, amplifier had free open room in front and back of amp. Reboot amp. works for short duration, same thing. Take two subs off the chain, seemed to stay up but outside but lacking the 2 extra subs. It was blowing heat out front so I know the fan was running.

    Yes it's at a 2 ohm load and Axis player (think that's his name) (and thank you for all your help in past BTW) told me the 2450's may thermal @ sustained 2 ohm loads......grrr.

    1. No way around this I assume, or is my amp going out? I thought there was a thermal light on these?
    2. The only solution I know if is a different model all together, but really don't have the overhead to be buying another amplifier.
    3. Other solution is 1850HD, they are getting harder to find even used, but I know they are out there, BUT we would have less power for these subs. Within specs of what those subs need I suppose, but again really don't want to put more money into this if I don't have to, in fact I really don't want to at all......


    What would YOU do?

  • #2
    EV's Tour Grade TG-5 offers 1900w at 2~ and their TG-7 3500w at 2~.
    Thanks,

    BillESC
    Back stage since 1973

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    • #3
      Thank you Bill, but I'm not tour grade, I'm redneck grade levels and won't those amps make those MRX 518 coils into melted copper? 600 watts per sub right now is 100 watts over recommended rating.

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      • #4
        I think the 1850hd seems like the way to go. I have run 2 ohms with yamaha p7000s many times. Other considerations.. A $20 fan, Raise your LF cutoff point a bit, Cable gauge to first sub?
        Last edited by witesol; 06-23-2014, 10:41 AM.

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        • #5
          Indeed I used to run the subs off my yamaha cp 2000, but it does not have the juice the RMX does for subs. I am running 40 hz cut (I believe that's the frequency) on the DBX 223 xover, and I have the 50 hz filter switch engaged on the amp. Cables I am using are livewire 12 gauge. Maybe I should go yamaha and go P series and do a tradeup. This 2450 has never had this issue in past and has a quite few hours on it. I did think maybe a fan in back would help get some extra air flow but I'm sure AgedHorse going to tell me won't make any difference. I can always just run one sub at a time per channel once it starts quitting on me, but defeats the point of 4 subs (very handy for outdoor stuff)

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          • #6
            Witesol, what are your thoughts on the yamaha P series on sub duty and overall performance?

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            • #7
              Ive never really had a problem with RMX either so I don't know if the Yamaha would be better. I like the weight and sound of the Yamaha.

              Perhaps Andy can chime in on this. How about putting 8 ohm frames in them?

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              • #8
                Define 8 ohm frames please or what you mean?

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                • #9
                  I've only heard axis player state he he had some thermaling with 2450's in 2 ohm load, so I did hear it first hand from someone...

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                  • #10
                    My 2450's did thermal more than once when less than a year old and clean while driving 2 ohm loads. They did not do it often, but they did do it. I did not have to have it it happen more than a few times before I switched to 1850s. They never did it again.

                    One qualifier is that all 4 ohm loads are not the same. Cabinets do not have an exact impedance. They have an average impedance. It is very possible to have 2 sets of 4 ohm subs where one set NEVER thermals the amp, and the other does. It depends on the actual impedance. If you are drawing max power at a 2 ohm load, and then you suddenly have a situation where the cabinets actual impedance drops to something lower than 2, you will certainly be able to thermal the amp. My JBL SR4733X were the cabs that put the amp into protect.

                    Many people never have an issue with these amps, but QSC basically issued the 1850HD as a de-rated 2450 because the HD could take more abuse and not thermal. If they did not ever have the problem reported, they would not have needed that HD series of amps. The HDs I switched to never went into protect even at full tilt with the same SR4733X cabs. The amps have the same cooling system, but the 1850 is generating less power/heat.

                    EDIT: I am not inferring a defect with either the amp or the cabinets mentioned. I am only saying that certain combinations of gear can exhibit problems where neither piece would exhibit them with other gear.
                    Last edited by Axisplayer; 06-23-2014, 01:12 PM.

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                    • #11
                      Originally posted by Axisplayer View Post

                      One qualifier is that all 4 ohm loads are not the same. Cabinets do not have an exact impedance. They have an average impedance. It is very possible to have 2 sets of 4 ohm subs where one set NEVER thermals the amp, and the other does. It depends on the actual impedance. If you are drawing max power at a 2 ohm load, and then you suddenly have a situation where the cabinets actual impedance drops to something lower than 2, you will certainly be able to thermal the amp. My JBL SR4733X were the cabs that put the amp into protect.
                      .
                      That's the part that is often overlooked. The rated impedance of a cabinet is not the minimum resistance of a cabinet. There is a spec called "DCr". Most are familiar that when you measure "resistance" of a speaker with an Ohmmeter you typically read 6.5 ohms for a speaker rated 8 ohm impedance. You can be fairly certain that at least one frequency the resistance and impedance will be the same.

                      Not a big deal when you are talking 8 ohms but can become critical at 2 ohms. That's why i never design systems right up the the edge of their ratings (based on a "one number rating"). Even if you don't thermal an amp you are probably driving it into current limiting more than necessary which isn't the best thing for sound quality.
                      Don Boomer

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                      • #12
                        Thank you axis. Guess...I will keep working at this, another one outside next week end too. I can always just do 2 subs I guess as a temp work around. Anyone wanna do even tradeup for a 1850 for my 2450? heh.

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                        • #13
                          Turn it down a little. That should be the same as switching to a 1850HD.
                          Mike Pyle ~ Audiopyle Sound
                          www.audiopyle.com
                          Dealer for EV, Yorkville, Turbosound, A&H, QSC, FBT, RCF, Powersoft, R-H, Audix, Ashly, Danley, APB, Shure, K&M, Beyerdynamic, Presonus, Rane, SLS Audio, Denon, Radial Eng, Roadready, Global Truss, Ultimate, Elation, Chauvet, ColorKey, Bizzard, Yamaha, and much more...

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                          • #14
                            Originally posted by Audiopyle Sound View Post
                            Turn it down a little. That should be the same as switching to a 1850HD.
                            Not at all ... in fact it likely would create more heat.
                            Don Boomer

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                            • #15
                              You need the 1850HD. Period.

                              Turning down isn't going to help, nor is it the same. The 1850HD derates the rail voltage and power rating to increase SOA and thermal margins significantly.
                              -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              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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