Members drenwick Posted June 20, 2008 Members Share Posted June 20, 2008 Am considering which subwoofer to put on my wishlist and am considering two JBL Models - the MRX518 and the SRX718. $650 and $870 respectively new, but I hope to find one used or b stock. The single sub (we don't need too much oomph for the venues we play) will be run on one side of a QSC PLX2502 (750W @ 4 ohms). Bass and kick run through the sub (no keys). To complete the picture, the other side of the PLX2502 will run our mains (pair of MR925s), a PLX1602 will drive a pair of JRX112s as monitors, all fed from a Mackie CFX12 mixer. So... JBL's literature gives the following info: MRX518 - 400/800/1600W 4 ohms (100 hrs), 500/1000/2000W (2 hrs)Recommended amp - 1000-2000W @ 4 ohmshttp://img3.musiciansfriend.com/dbase/pdf/man/m_600417.pdf SRX718 - 800/1600/3200/W 4 ohms (no mention of hours)Recommended amp - 800-1600 @ 4 ohmshttp://img3.musiciansfriend.com/dbase/pdf/man/m_600443.pdf 1. Help me make sense of why they are recommending more power for the MRX518. What am I missing? 2. When looking at most speaker ratings, which standard (100 hours or 2 hours) am I usually looking at when they don't indicate either? 3. Is my 750W enough for either one of these? Too much for the MRX? (after all - I'm nearly double the cont./RMS rating, yet not even in JBLs recommended range...agedhorse?...) Thanks as always for your time folks! Link to comment Share on other sites More sharing options...
Members srp72ee Posted June 20, 2008 Members Share Posted June 20, 2008 First the SRX718 is an 8 ohm subwoofer...That will change a few things for power. Second, I would recommend the lower (continuous) power rating if you don't have much expierence in setting limiters and controlling your output power. This is a much safer (and cheaper) way to go. There are many who will tell you otherwise about power ratings. I have the SRX series and I only power them to 775 watts RMS. Four weeks ago I was running sound for the Girl Scout Jamboree north of Columbus and I was set up on a football field at a local school. Powering the system to just under the RMS rating still wound up with the Deleware County Sheriff call to respond to a "disturbance". Needless to say they were a bit suprised to find 2500 moms and daughters at the the event. If you are doing small venues, I would go with the SRX because you could always upgrade the amp in the future. The PLX2502 will deliver about 450 watts at 8 ohms for the sub. Link to comment Share on other sites More sharing options...
Members tlbonehead Posted June 20, 2008 Members Share Posted June 20, 2008 Am considering which subwoofer to put on my wishlist and am considering two JBL Models - the MRX518 and the SRX718. $650 and $870 respectively new, but I hope to find one used or b stock. The single sub (we don't need too much oomph for the venues we play) will be run on one side of a QSC PLX2502 (750W @ 4 ohms). Bass and kick run through the sub (no keys).To complete the picture, the other side of the PLX2502 will run our mains (pair of MR925s), a PLX1602 will drive a pair of JRX112s as monitors, all fed from a Mackie CFX12 mixer.So...JBL's literature gives the following info:MRX518 - 400/800/1600W 4 ohms (100 hrs), 500/1000/2000W (2 hrs)Recommended amp - 1000-2000W @ 4 ohmshttp://img3.musiciansfriend.com/dbase/pdf/man/m_600417.pdfSRX718 - 800/1600/3200/W 4 ohms (no mention of hours)Recommended amp - 800-1600 @ 4 ohmshttp://img3.musiciansfriend.com/dbase/pdf/man/m_600443.pdf1. Help me make sense of why they are recommending more power for the MRX518. What am I missing?2. When looking at most speaker ratings, which standard (100 hours or 2 hours) am I usually looking at when they don't indicate either?3. Is my 750W enough for either one of these? Too much for the MRX? (after all - I'm nearly double the cont./RMS rating, yet not even in JBLs recommended range...agedhorse?...)Thanks as always for your time folks!Its silly. Go check the powered PRX version of that cab and see what JBL actually gives it for power. Link to comment Share on other sites More sharing options...
Members drenwick Posted June 20, 2008 Author Members Share Posted June 20, 2008 First the SRX718 is an 8 ohm subwoofer...That will change a few things for power... The PLX2502 will deliver about 450 watts at 8 ohms for the sub. According to their own literature it's a 4 ohm sub. Funny - you're not the first person I've heard that from though. http://img3.musiciansfriend.com/dbase/pdf/man/m_600443.pdf Link to comment Share on other sites More sharing options...
Members drenwick Posted June 20, 2008 Author Members Share Posted June 20, 2008 Its silly. Go check the powered PRX version of that cab and see what JBL actually gives it for power. PRX518 - 500/1000W, 2044e driver (MRX518 is a 2044g - not sure if that makes a diff) Anyway, I get your point... So I'm OVERpowered at 750? Why would they make the recommendation they did? Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 20, 2008 Members Share Posted June 20, 2008 PRX518 - 500/1000W, 2044e driver (MRX518 is a 2044g - not sure if that makes a diff)Anyway, I get your point...So I'm OVERpowered at 750? Why would they make the recommendation they did? Because they are also selling big amps through the Crown brand and there's more profit in the bigger amps. When you blow the speaker, they don't care what you powered it with, they just look to see if it was overpowered thermally or mechanically and you pay the bill. Warranty is for defects in materials in workmanship, not abuse. If you know exactly what you are doing, there are some very small advantages but you are also typically bringing in plenty of PA for the job and have a good idea how much the rtepairs are likely to cost. You will also have more sophisticated liming and high pass filters. The letter after the driver # stands for the impedance. I haven't seen a powered sub fail yet, so I don't know what the "E" impedance is. I'll have to check. The PRX518 is powered by a 500 watt RMS class D amp. That's EXACTLY the same as 1000 watts peak, it's purely a math conversion that exists for the marketing department. There is no use for this peak number. This should give you a good idea how to power your cabinet for best reliability. Also, be sure the 30Hz HPF and limiters are engaged on your amp. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 20, 2008 Members Share Posted June 20, 2008 . There is no use for this peak number. Are you speaking of peak power numbers for speakers or amps (or both) Link to comment Share on other sites More sharing options...
Members drenwick Posted June 20, 2008 Author Members Share Posted June 20, 2008 PRX518 is powered by a 500 watt RMS class D amp. That's EXACTLY the same as 1000 watts peak, it's purely a math conversion that exists for the marketing department. There is no use for this peak number. This should give you a good idea how to power your cabinet for best reliability. Also, be sure the 30Hz HPF and limiters are engaged on your amp. I think what I'm hearing is that the SRX718 at 800W RMS is a better fit for the PLX2502 (which I already own) w/750W - or is that under powered? And on a side note, do I need a crossover w/the limiters and filters available on the amp? Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 20, 2008 Members Share Posted June 20, 2008 Are you speaking of peak power numbers for speakers or amps (or both) Both, it's purely a marketing number based on peak voltage ((V x 1.414)^2)/Rload. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 20, 2008 Members Share Posted June 20, 2008 Either will work quite well at reasonable power levels. There's nothing wrong with an SRX at 750 watts "RMS". That's actually a reasonable power level. Link to comment Share on other sites More sharing options...
Members drenwick Posted June 20, 2008 Author Members Share Posted June 20, 2008 Thank you sir! ...and the need for a X-over? Link to comment Share on other sites More sharing options...
Members srp72ee Posted June 20, 2008 Members Share Posted June 20, 2008 According to their own literature it's a 4 ohm sub. Funny - you're not the first person I've heard that from though.http://img3.musiciansfriend.com/dbase/pdf/man/m_600443.pdf The literature seems to be a bit outdated. Try either of these from the JBL website... http://www.jblpro.com/srx700/PDF/SRX700%20UserGuide.pdf http://www.jblpro.com/srx700/PDF/JBL.SRX718S.pdf Link to comment Share on other sites More sharing options...
Members srp72ee Posted June 20, 2008 Members Share Posted June 20, 2008 I think what I'm hearing is that the SRX718 at 800W RMS is a better fit for the PLX2502 (which I already own) w/750W - or is that under powered?And on a side note, do I need a crossover w/the limiters and filters available on the amp? Yes, the SRX 718 is a better fit. Powering it to the 450 Watts will only make a couple of dB difference. You won't need external limiters (but do use the clip limiters built into the amp). Link to comment Share on other sites More sharing options...
Members Not Serial Posted June 20, 2008 Members Share Posted June 20, 2008 all four of my srx718's are indeed 8 ohm. i run 2 per side of a plx3602. this is plenty loud to match a pair of 722's powered with another 3602. i find the srx718 to be a very detailed sub. Link to comment Share on other sites More sharing options...
Members drenwick Posted June 20, 2008 Author Members Share Posted June 20, 2008 The literature seems to be a bit outdated. Try either of these from the JBL website...http://www.jblpro.com/srx700/PDF/SRX700%20UserGuide.pdfhttp://www.jblpro.com/srx700/PDF/JBL.SRX718S.pdf Thanks! So do you know whether older versions of the SRX718 were 4 ohms or was that a misprint in the PDF manual from Musician's Friend (which was actually a link to JBL as well!!!) Link to comment Share on other sites More sharing options...
Members srp72ee Posted June 20, 2008 Members Share Posted June 20, 2008 Thanks! So do you know whether older versions of the SRX718 were 4 ohms or was that a misprint in the PDF manual from Musician's Friend (which was actually a link to JBL as well!!!) I'm only aware of the 8 ohm versions, I suppose it's possible there was an earlier version. Link to comment Share on other sites More sharing options...
Members coyote-1 Posted June 20, 2008 Members Share Posted June 20, 2008 My last AMS catalog contained an explanation of power ratings. It went like this: RMS power'Program' or 'Music' powerPeak power Program power is @ 2x RMS, and is the minimum power a manufacturer thinks is adequate to power a particular speaker in order to prevent clipping and its associated damage. Peak power is the max the speaker can handle on a momentary basis. So if you have a speaker that handles 200w RMS at 8 ohms, get an amp that puts out 400w at 8 ohms to power it. If the speaker handles 200w 'program' or 'music' power, get a 200w amp. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted June 20, 2008 CMS Author Share Posted June 20, 2008 My last AMS catalog contained an explanation of power ratings. It went like this:RMS power'Program' or 'Music' powerPeak powerProgram power is @ 2x RMS, and is the minimum power a manufacturer thinks is adequate to power a particular speaker in order to prevent clipping and its associated damage. Peak power is the max the speaker can handle on a momentary basis.So if you have a speaker that handles 200w RMS at 8 ohms, get an amp that puts out 400w at 8 ohms to power it. If the speaker handles 200w 'program' or 'music' power, get a 200w amp. Really? Under any conditions and with or without limiters, for any source material? You're attempting to place a general recommendation on a topic that has many variables, and you're leaving out a pile of information that could leave the reader standing before a smoking speaker. Link to comment Share on other sites More sharing options...
Members walkerci Posted June 21, 2008 Members Share Posted June 21, 2008 all four of my srx718's are indeed 8 ohm. i run 2 per side of a plx3602. this is plenty loud to match a pair of 722's powered with another 3602.i find the srx718 to be a very detailed sub. Very true. I A/Bed the MRX518 and SRX718.SRX718 sounded much better to my ears and well worth the extra money. OTOH, I am currently running a pair MRX515 for tops and they are well matched to the SRX718 subs IMO. That said, I really need either another pair of MRX515 or a pair of MRX525 for larger rooms and outdoors. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 21, 2008 Members Share Posted June 21, 2008 A 200 watt RMS amp by definitioin delivers exactly 400 watts peak. Be sure you know exactly what the terms mean otherwise you may end up doing something unintentional. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 21, 2008 Members Share Posted June 21, 2008 Program power is @ 2x RMS, and is the minimum power a manufacturer thinks is adequate to power a particular speaker in order to prevent clipping and its associated damage. No, no, no, no ... it usually represents the maximum power that should be used with a speaker not the minimum. Program power is used to size the amp to the speaker and does not represent the amount of power that should be delivered to the speaker. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 21, 2008 Members Share Posted June 21, 2008 oops! Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 21, 2008 Members Share Posted June 21, 2008 No, no, no, no ... it usually represents the maximum power that should be used with a speaker not the minimum. Program power is used to size the amp to the speaker and does not represent the amount of power that should be delivered to the speaker. See, Don and I agree! Program power is the maximum power that an experienced, qualified user should attempt. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 21, 2008 Members Share Posted June 21, 2008 That's not what I said. I frequently use power amps that are well above the program rating. The program rating is a made up number to suggest power amp size. You can hookup an amp that is way bigger ... that's called headroom. What you can't do is deliver power in excess of the continuous rating ... no matter what the amp size is. Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 22, 2008 Members Share Posted June 22, 2008 Didn't mean to put words into Don's mouth but... It's the delivery that I am talking about. When you program your speaker processing to limit the power the amplifier delivers like both Don and I do, it's effectively the same thing. It's a more sophisticated way of getting to the same place with a better set of tools. The industry has in general taken the program power rating to be twice the continuous, RMS thermal rating of the speaker. Of course it's program and cabinet dependant but in general it's one reasonable way to approach the design for an experienced user. A non-experienced user is likely to make some choices that invalidate the (general) program power profile, so it's not a great choice for these users. Link to comment Share on other sites More sharing options...
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