Members nchangin Posted June 23, 2014 Members Share Posted June 23, 2014 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? Link to comment Share on other sites More sharing options...
Members Bill.ESC Posted June 23, 2014 Members Share Posted June 23, 2014 EV's Tour Grade TG-5 offers 1900w at 2~ and their TG-7 3500w at 2~. Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members witesol Posted June 23, 2014 Members Share Posted June 23, 2014 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? Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 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) Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 Witesol, what are your thoughts on the yamaha P series on sub duty and overall performance? Link to comment Share on other sites More sharing options...
Members witesol Posted June 23, 2014 Members Share Posted June 23, 2014 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? Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 Define 8 ohm frames please or what you mean? Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 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... Link to comment Share on other sites More sharing options...
Members Axisplayer Posted June 23, 2014 Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 23, 2014 Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members nchangin Posted June 23, 2014 Author Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members Audiopyle Sound Posted June 23, 2014 Members Share Posted June 23, 2014 Turn it down a little. That should be the same as switching to a 1850HD. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 23, 2014 Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 23, 2014 Members Share Posted June 23, 2014 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. Link to comment Share on other sites More sharing options...
Members wesg Posted June 24, 2014 Members Share Posted June 24, 2014 Why would turning down the 2450 create more heat? That seems counter-intuitive....not being smart here, looking to learn! "2-tier Class H" - this is basically a pair of linear amplifiers in series, right? Wouldn't turning it down prevent the output from swinging all the way rail-to-rail and generate less heat? Wes Link to comment Share on other sites More sharing options...
Members WynnD Posted June 24, 2014 Members Share Posted June 24, 2014 I'm also confused about how turning down generates more heat. And I understood that the 1850HD was just a derated 2450. There might be more to derating than I know. I never run loads that low and have never had an power amp thermal. (I have had a powered speaker thermal once.) I also generally don't push my equipment. Link to comment Share on other sites More sharing options...
Members Bugzie Posted June 24, 2014 Members Share Posted June 24, 2014 An old PLX 1802 works well on a pair of MRX 518's when run 2 channel. A 2 ohm load is tough on most of the amps available. The RMX 1850 was always advertised as 2 ohm stable where the 2450's didn't make that claim. The heat thing also has piqued my interest. Would you explain please Andy? Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 24, 2014 Members Share Posted June 24, 2014 Turning a 2450 down to match an 1850's power will still dissipate greater power because the dissipation is a function of rail voltage which is higher on the 2450. Class H doesn't matter since both amps are class H. Look up the dissipation curves for class h amps and plot for 2 different sets of rail voltages and you will see what I mean. Since the hi-low rail ratio is about the same between amps, the heat ratios track as well. Class d does not suffer the same way, as it's non-linear and does not scale proportionally. Link to comment Share on other sites More sharing options...
Members Tomm Williams Posted June 24, 2014 Members Share Posted June 24, 2014 Or buy another 2450 and run 4ohm loads instead of 2. Running subs at 2ohms seems like an invitation for issues. Link to comment Share on other sites More sharing options...
Members nchangin Posted June 24, 2014 Author Members Share Posted June 24, 2014 Or buy another 2450 and run 4ohm loads instead of 2. Running subs at 2ohms seems like an invitation for issues. I respect your opinion, BUT why put it in the manual if it can't meet the exepctations of the customer? Link to comment Share on other sites More sharing options...
Members Unalaska Posted June 24, 2014 Members Share Posted June 24, 2014 If you're running 2ohm on both channels I'd recommend the 1850hd for sure. How about 2 smaller lighter amps with 1 box per channel? I have only 1 pair of mrx518s. Most often they are powered off 1 channel of a yamaha P5000 with the other channel powering tops (ev sx300 or jbl 4725). I didn't know how this was going to work long term but the amp has been rock solid through 100+ gigs! same with the amp too, and this is using the crossover built into the amp. Another amp rack I use has yamaha P7000s and with 2 dual 15/2" over dual 18 per side the mid channels are at 2 ohms. Also rock solid. I used to have one amp at 2 ohms stereo driving mids and I could get it to shut off by sweeping the mids with the channel strip eq at +9 or so. It would just turn off, I'd have to turn it back on again. But with one channel driving 2 ohms and the other at 4 it has never had any issues. The point is... Run top boxes off the second channel of the 2450 and get a another 2450 and do the same. Or sell it and buy 2 lighter amps (p5000 or p7000) Link to comment Share on other sites More sharing options...
Members nchangin Posted June 24, 2014 Author Members Share Posted June 24, 2014 Unalaska: Thank you for the post, I see what you mean, love the yamaha stuff I already own. Unfortunately I am running Stereo (those damn DJ's!!). I don't want to do it, but probably for this weekend I will put the yamaha cp 2000 on sub duty, it has never went down running 2 ohm loads, BUT to the ear it just doesn't seem to sound as good as the 2450 (probably just me), so not all is lost, there is a solution, your post has helped to turn me to that solution. Link to comment Share on other sites More sharing options...
Members wesg Posted June 24, 2014 Members Share Posted June 24, 2014 Stereo subs? Link to comment Share on other sites More sharing options...
Members nchangin Posted June 24, 2014 Author Members Share Posted June 24, 2014 Stereo subs? No but the tops are. Link to comment Share on other sites More sharing options...
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