Members pktaskes Posted December 4, 2006 Members Share Posted December 4, 2006 This is a continuation of another thread I had: http://acapella.harmony-central.com/forums/showthread.php?s=&threadid=1449780 Anyway, I hooked up the JBL MP225S (2x15's) to my QSC running 1400 W bridged. Ran the monitor line out to the QSC and killed the top end on the monitor EQ (poor mans crossover till my new one comes). The Yammy's (powered mixer) internal power amps went to the top cabs. Anyway, I had the mixer delivering a bit over 0dB and the QSC running full out (ie - zero attenuation). Clip light on amp was just barely lighting so I backed off the signal a bit. No clipping at all now. Amp had 50hz filter and clip limiter engaged. Sub was pumping some decent bass out...not as snappy as better drivers would have delivered of course but no distortion/flapping of any sort that I could hear. Source was bass heavy classic rock ala CD. Ran for about a 20 minutes. My question: This amp bridged at 4 ohms (1400w) out-matches my sub(500/2000 peak). People who know this box know that these aren't the greatest 15" speakers around BUT - if what I described above sounds clear and clean and there is no discernable/visible clipping or distortion, do I still have to worry about blowing the drivers with this amp? Does damage happen slowly wihtout warning and then BOOM? I'll add that when I reduced the monitor signal to under 0 dB or backed of the amp, I lost all that good sounding thump. Maybe run another test at lower levels and switch the filter to 30hz? Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by pktaskes do I still have to worry about blowing the drivers with this amp? Does damage happen slowly wihtout warning and then BOOM? Most certainly on both accounts. Often damage occurs without beingable to hear it... and the top cabinets can also mask the sounds being made as the sub driver enters it's death spiral. Link to comment Share on other sites More sharing options...
Members pktaskes Posted December 4, 2006 Author Members Share Posted December 4, 2006 What does a death spiral sound like? Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 4, 2006 Members Share Posted December 4, 2006 muddy distorted sounding, with possible extraneous noises, possible mechanical noises, buzzing rattling noises etc. Link to comment Share on other sites More sharing options...
Members smaynor Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by pktaskes What does a death spiral sound like? It sounds like $100 bills flying out of your wallet at an alarming rate. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by smaynor It sounds like $100 bills flying out of your wallet at an alarming rate. Link to comment Share on other sites More sharing options...
Members Ear Abuser Posted December 4, 2006 Members Share Posted December 4, 2006 There really a couple ways to kill woofers- mechanically or thermallyYou can push them so hard that they mechanically fall apart (torn cone, spider or surround). Sometimes you can push them so hard that you drive the voice coil into the back plate which makes a very ugly "Brap" sound. The cone falling apart can be indicated by buzzing or a general distorted sound. Some cabinet designs like bandpass or folded horn enclosures naturally filter out the high frequencies that let you know something is going wrong. As Agedhorse says, If the topend is clean, it can cover up the fact the subs are starting to fart. There usually isn't much audible warming when you kill a speaker thermally. Sometimes the heat loosen the voicecoil from the aluminun former and it will start to sound wierd, but by that time it's shot anyway. Something to keep in mind-An electric stove burner is about 1250 watts- think about how hot they get. That's what you are asking your speakers to withstand. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by Ear Abuser Something to keep in mind-An electric stove burner is about 1250 watts- think about how hot they get. That's what you are asking your speakers to withstand. Bingo, good analogy. Link to comment Share on other sites More sharing options...
Members The Real MC Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by agedhorse muddy distorted sounding, with possible extraneous noises, possible mechanical noises, buzzing rattling noises etc. You forgot smoke Link to comment Share on other sites More sharing options...
Members Gregidon Posted December 4, 2006 Members Share Posted December 4, 2006 Originally posted by Ear Abuser Something to keep in mind-An electric stove burner is about 1250 watts- think about how hot they get. That's what you are asking your speakers to withstand. What's a really good analogy! Wow, I never really thought about it like that. Link to comment Share on other sites More sharing options...
Members tlbonehead Posted December 5, 2006 Members Share Posted December 5, 2006 Is this the person who posted a week or so ago and everyone told him NOT to run that amp bridged into that cab? Man, I hope it isn't the same person. Link to comment Share on other sites More sharing options...
Members OverDriven Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by Ear Abuser Something to keep in mind-An electric stove burner is about 1250 watts- think about how hot they get. That's what you are asking your speakers to withstand. I don't think this analogy holds any water. The energy is being transformed and disapated into kinetic and then sound energy. On a stove, only heat and a low level of light are produced. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by OverDriven I don't think this analogy holds any water. The energy is being transformed and disapated into kinetic and then sound energy. On a stove, only heat and a low level of light are produced. Correct, but for an efficient speaker, roughly 10% of the energy is mechanical and the remaining 90% is thermal energy that must be dissipated as heat. So (1200 x .9) = 1080 watts of heat. Close enough to make Ear Abuser's analogy pretty insightful IMO. Link to comment Share on other sites More sharing options...
Members tlbonehead Posted December 5, 2006 Members Share Posted December 5, 2006 Plus, what some people don't realize is that power ratings usually relate to how much heat the VC can handle and dissapate, and not so much the actual mechanical limits. 1400 watts is just silly for a pair of MOR Eminence woofers. Link to comment Share on other sites More sharing options...
Members kobe Posted December 5, 2006 Members Share Posted December 5, 2006 i've been using 2x JBL Mpro 255 2x15" subs for a few years now in one of my small rigs, they've always been powered by a Peavey GPS2600 in stereo putting out about 900watt into 4 ohms, the subs see from about 50 - 150hz. i've had no problems with this set up although the 450 watts per driver is slightly excessive. but the subs generally only need to reproduce kick and bass guitar in venues holding about 100 people. John Link to comment Share on other sites More sharing options...
Members Mopo4 Posted December 5, 2006 Members Share Posted December 5, 2006 wow!regards, Mopo4 Link to comment Share on other sites More sharing options...
Members pktaskes Posted December 5, 2006 Author Members Share Posted December 5, 2006 Originally posted by tlbonehead Is this the person who posted a week or so ago and everyone told him NOT to run that amp bridged into that cab? Man, I hope it isn't the same person. Yes! I'm hooking this up to a live band this weekend and I'll see how it goes. With a CD, the bass response left a lot to be desired unless I pushed things. I'll be more careful for sure but, if the speakers blow, I'm not going to cry over a box I spent $200 for used. Next post: "Good 15 inch speakers for subs?" Link to comment Share on other sites More sharing options...
Members pktaskes Posted December 5, 2006 Author Members Share Posted December 5, 2006 Originally posted by kobe i've been using 2x JBL Mpro 255 2x15" subs for a few years now in one of my small rigs, they've always been powered by a Peavey GPS2600 in stereo putting out about 900watt into 4 ohms, the subs see from about 50 - 150hz. i've had no problems with this set up although the 450 watts per driver is slightly excessive. but the subs generally only need to reproduce kick and bass guitar in venues holding about 100 people. Pretty much us. There are bigger places we play although that doesn Link to comment Share on other sites More sharing options...
Members pktaskes Posted December 5, 2006 Author Members Share Posted December 5, 2006 Originally posted by tlbonehead Plus, what some people don't realize is that power ratings usually relate to how much heat the VC can handle and dissapate, and not so much the actual mechanical limits. 1400 watts is just silly for a pair of MOR Eminence woofers. If this is the case, why don't we see more cast aluminum heat sinks on the back of drivers? I've seen them on some but not many. I'm grabbing a thermocouple from work today and running a little test. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 5, 2006 Members Share Posted December 5, 2006 Depending on the driver's application and bandwith that is being considered, the limits can be either thermal or mechanical. For example, if you are looking at a sub, it's mostly mechanical but that changes if you increase the crossover frequency. For a mid driver, it's generally more thermal limitations, as the cooling effeict of cone motion are more limited. The "heatsinks" are IME of very limited value because of the thermal resistance between the voice coil itself and the surrounding structure. They do make for good marketing though. Link to comment Share on other sites More sharing options...
Members OverDriven Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by agedhorse Correct, but for an efficient speaker, roughly 10% of the energy is mechanical and the remaining 90% is thermal energy that must be dissipated as heat. So (1200 x .9) = 1080 watts of heat. Close enough to make Ear Abuser's analogy pretty insightful IMO. Wow I had no idea that only 10% was mechanical energy. Seems like quite a waste. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by OverDriven Wow I had no idea that only 10% was mechanical energy. Seems like quite a waste. 10% is for an efficient driver too!!! This is a big stumbling block in transducer design. Link to comment Share on other sites More sharing options...
Members Ear Abuser Posted December 5, 2006 Members Share Posted December 5, 2006 Most speakers make better toasters than transducersBut Incandescent lighting is only about 1% efficient, so speakers kick butt in comparison. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by Ear Abuser But Incandescent lighting is only about 1% efficient, so speakers kick butt in comparison. Which is why there's so much potential for energy conservation looking forward. Link to comment Share on other sites More sharing options...
Members moody Posted December 5, 2006 Members Share Posted December 5, 2006 Originally posted by pktaskes Yes!I'm hooking this up to a live band this weekend and I'll see how it goes. With a CD, the bass response left a lot to be desired unless I pushed things. I'll be more careful for sure but, if the speakers blow, I'm not going to cry over a box I spent $200 for used. Next post: "Good 15 inch speakers for subs?" My pair of subs cost only barely over $200 used - I'd cry if they got stuffed through mis-use. Why cause a problem when you don't need to. By the way.... A blown speaker can blow a good amp (depending on the situation and the protection circuitry in the amp of course). So you could be up for more than $200. Link to comment Share on other sites More sharing options...
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