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Power Rating Question

Discussion in 'Amps and Cabs [BG]' started by Dan1099, Apr 12, 2005.


  1. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    I have an Ampeg 610HLF that is rated at: 600W RMS, 1200W Program.

    What exactly does this mean? What is the program rating? Basically, I'm thinking about buying a QSC RMX1450 or 1850HD, and was wondering...
    I am thinking about running it Bridged Mono into this cab, and being very judicious with my volume settings. I know that even turned down, they are still capable of putting out their maximum power, but if my cab can hand 1200W peak, and I'm not planning on running the volume on this whing anywhere CLOSE to full, I should be okay, right? As long as I didnt blast the damn thing, and I kept an ear out for speaker farting, I shouldn't have a problem, as long as I keep anyone else from dicking around with it, right? Or am I totally off on this?
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    ignore program.

    the rms rating is the "real world" rating of the cabinet.

    you won't be putting program material into the cabinet with a bass guitar.
     
  3. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    I was always under the impression that a power amp for the most part does not operate at it's max rated power. Of course there would be peaks here and there, but I was always told the rated power of the amp is hardly achieved in normal operation, therefore the desire to have more power in order to normally use more of it.

    Eh? :eyebrow:

    -T
     
  4. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    not an engineer (but there are plenty of them on this site - for real not sarcasm), RMS aka continuous is the figure of consequence. Program aka peak from what I've gathered refers to recorded music (refined - doesn't have the peaks) and peak is just that, spikes in output. With an instrument you get raw fluctuations that can reak havic with rigging whereas recorded sound is "tamed" and you can pump a lot more of it without concern for rogue fluctuatons that will be more that the rig can handle. As you can tell, you doulbe RMS to get program or half program to get RMS. I think RMS stands for Root mean squared.

    That's basically it in laye terms. Obviously, I'm not one of the engineers.
     
  5. Passinwind

    Passinwind I Know Nothing Supporting Member

  6. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    So then running one of the aforementioned poweramps bridged into this cabinet would be a no-no, correct?
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    What is the impedance of the cabinet?
     
  8. 4 ohms
     
  9. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Speaker failures can usually be traced to a few causes.

    1) too much power (average power, aka "rms") symptom is typically burnt voice coil.

    2) too much peak power. Symptom usually cone damage, squashed center of cone, torn cone, voice coil loose, dust cap loose, etc.

    3) Speaker moves too far (overexcursion). Symptom usually folded cone near outer edge, torn surround, broken "tinsel lead", etc.

    Any of these can be power related, but overexcursion may not be. Lower than max power below system resonance in a ported box can do it.

    How to avoid it?

    The JBL info is OK, but doesn't really apply to musical instrument usage. They did toss off a couple comments, but not anything you can really use. The 1/2 of IEC power is pretty conservative. You need to remember that they are talking mostly about installs, and they NEVER want the installer to have to crawl up in the roof to replace a speaker.

    A lot depends on style...

    Too much average power:
    It is "possible" to average almost half the amp power without distortion, but it is mighty hard. Your fingers will be busy.

    So probably, for most people, not getting into heavy distortion, not using square wave type octave boxes etc, RMS ratings between 1/3 and 1/2 amp power are unlikely to kill a speaker from straight "rms" over-powering.

    Feedback can do it, even so. And, the more "grunge" the more average power, and the more chance of trouble.
    .
    .
    Overexcursion:
    This is another thing. It does not have to take a lot of power. Usually it takes a ported box and "pushing" the frequency limit. Amp power could be LESS than nominal speaker power rating.
    Can also be from trying to use a 2:10 with a big power amp. Acoustic power is related to how much air moves how far how fast. The more cone area, the more air moves, so the less movement is required. The 2:10 hasn't got a chance of equaling a 4:10 or 8:10 in volume in the low range.
    .
    .
    Too much peak power:
    This type damage tends to be pretty rare. But getting into the 5 and 7 to 1 range is pushing it, an area where you could get into trouble with peak OR average power. The peak power of the amp is twice its "RMS" rating.

    To the original question.....SVT-610HLF with RMX1450

    A 600 watt speaker isn't unusable with a 1400 W amp. If you don't push the low end below the cabinet limit (drop tuning, 6 string bass, etc) and don't get feedback, probably work indefinitely.

    That cab is good to about 50 Hz, with "usable" response to about 40 Hz. The 6 10s are a reasonable amount of cone area, and won't tempt you to boost the low end way up.

    Naturally if you push the frequency limits, you can get into trouble. But for most people, that RMX 1450 would be reasonable. The RMX2450 would NOT be reasonable......

    I'd be inclined to use the LF filter, at least at 30 Hz. The amp has a choice of 30 and 50. The 50 might work too, and you might never even notice.
     
  10. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    Bridged?

    Well, IMO, it wouldn't be the greatest idea in the world to run it bridged and then turn the volume to "DESTROY". Certainly a recipe for dismembered limbs and such. But, I would bridge either one of those amps and turn the volume up enough to get a good clean (meaning not strained) sound with lots of headroom and healthy doses of goodness coming out of the cab. This would be nothing to worry about.

    I guess it's kinda like being the strongest man on Earth. If you picked up everything with all your might and gave a kung-fu death grip on everything you touched, it would suck. But if you excercise your power accordingly, you'd never complain about not being strong enough!

    *I really gotta go home for the day. Work is making me delirious.*

    *edit - With that said, and reading Jerrold's comments above, I also wouldn't put 5,000w into that 6x10. Strong is great. Stupid is not. :D *

    -T
     
  11. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    If you go by the rule of thumb of matching the amp's power point approximately to the loudspeaker's program power, then the RMX 1450 would be the closest matche, as its 4-ohm bridged mono power rating is 1400 watts.

    This rule of thumb assumes that you will avoid clipping the amp. An amp in clipping is actually putting out more power than it is rated for, and even in between clips the average power tends to be very high because of the compressed dynamic range.

    If you feel that you are one to not pay attention, and thus allow the amp to go into severe clipping, you should consider a loudspeaker with higher power handling capabilities.
     
  12. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Good link.

    My post was pretty lame. Later realized I was in the middle of a brain fart at the time and didn't even address the entire question - which was probably a good thing :) Fortuneately there's always someone around to straighten you out on TB.
     
  13. Passinwind

    Passinwind I Know Nothing Supporting Member

    Jerrold's post tops that link in some ways, although my read on the JBL recommendations is quite a bit different than his. The main thing is that we all discuss and learn one way or another though, no?
     
  14. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    Did I ever tell you guys how much I love this place? You ask a question about a QSC into an Ampeg cab, and you get responses from employees at BOTH companies! You can't BEAT that kind of customer service!

    The reason I ask these questions is I'm looking at slowly upgrading my amp set up. I'm starting to runout of headroom with my SVT350, and, since I know the cab can handle more power, it is delegated a lower spot on the replacement timeline, ya know?

    I'm glad to know that through judicious use of power, I can indeed run one of these amps bridged and, as long as I'm careful, not light anything on fire.

    Now all I have to worry about is keeping the unwashed masses away from the knobs on the front of it. :)
     
  15. The RMS value is the max continuous power (sine wave) the cab can handle. A test tone. Basically the average clean waveform power that will not melt down the voice coil. A clipped amp produces more of a square wave, which is more power per the same output voltage (tends to fry the main driver voice coil from heat), and more high freq content (tends to fry the tweeter, which is rated at way less wattage than the main drivers since there's so little high freq content to a clean bass signal).

    Short transients above that don't cause that much heating, so the voice coil can handle much larger peaks without overheating as long as there's enough quiet time around those peaks to dissipate the heat, so the avg power and therefore the voice coil temp stays under the RMS avg rating.

    That's where the "Music or Program" power ratings come from. Don't think there's a uniform definition to music or program power. The idea is you don't usually play continuous sine waves, there's space between notes, some notes are louder than others, so the avg heat in the voice coil (= RMS power) is lower for music than for test tones with the same max level. Rule of thumb its usually claimed to be about 2x the RMS value.

    The peak power rating is higher yet, more often related to speaker suspension damage from overexcursion, what's the highest power level the speaker will survive assuming its a short enough pulse to not melt the voice coil from the heat generated.

    For example, I think my old EVM 15's were rated at 400W RMS, 800W program, and 1600W peak.

    You can drive a Ferrarri on bicycle tires at 25 mph if you don't put your foot in it. Make a mistake and bump the throttle, you'll spin them babies so fast your head will spin, the tires will melt down and explode.

    Same with speakers. You can drive a 50W speaker with a 5000W amp. Unplug the guitar without turning it down to get a 5000W pulse of 60Hz into that speaker and its toast.

    If you play so loud you can't tell the speaker's distorting, you'll blow it sooner rather than later. Even with amp=speaker wattage, the clipping will overdive the tweeters in a 2 way system and blow them. Plus the clipped signal of 100V has higher power output than 100V clean sine wav, so the 200W rms amp CAN put out more than 200W at clipping and exceed the RMS rating of the 200W cab.

    Also if you get much more than 2x the RMS amp power than the speaker can handle continuously, the avg power going to the speaker can exceed the RMS limit without the amp producing audible distortion, so you CAN melt the voice coil down without hearing any distortion. The "amp = no more than 2x the speaker RMS limit" is just a ploy to produce some distortion from the amp early enough so you can hear about where the limit probably is while still allowing you some headroom for peaks that would otherwise clip if you kept the amp RMS = speaker RMS.

    Randy
     
  16. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The commonality between all the posts, and the JBL info is that the amp power is really "sorta" irrelevant.....IF the average power is not over the power handling of the speaker, AND the amp is not allowed to give full power "blasts" that could make the speaker cone jump out of the gap, etc.

    The JBL info can be interpreted several ways, depending on how you describe your usage.

    In some ways, their situation "A" applies, since you probably would notice distortion sufficiently severe for the distortion to boost the power "that" much.
    It is also the best match to the experience of most users here, but is NOT the JBL "music applications" suggestion.

    In some ways "B" applies, if you just look at the "theoretical" considerations, but it does not accord with actual usage experience of many posters right here. It suggests a direct match of power to power handling.

    Case "C", is applicable to guitar, more than bass. It assumes significant to major "distortion" (aka "harmonic enhancement"). Clearly the recommendation does not accord with actual user experience, as many on the board can testify.

    The assumption of "about" double the power is typical. And, yes, it IS based on the idea that you can't get much over 1/3 power, average, with useful musical playing that is not very distorted. I dunno if it is a "ploy"....!

    That gives you headroom for slapping etc, allows for some distortion without putting the speaker in obvious danger, and generally ought to work out best.

    Its it a guarantee? NO.

    You CAN kill a speaker with an amp of far less than the speaker's power rating. I know of examples, some from board members, of speakers being destroyed by amps rated at as little as 30% of the speaker rating.

    In those cases, even 100% distortion could not have gone near, let alone over the power rating And, since the amp was a tube amp, there was no question of DC output or significant subsonic output, because of the transformer. It can be done.

    You might also notice that the JBL folks agree that a very few watts can damage the speaker from over-excursion at low frequencies. That is a good thing to keep in mind when discussing drop tuning, 5 and 6 string basses, etc, especially when discussing power ratings. Power rating is heavily dependent on the cabinet type, tuning, and what frequency range is fed to it.
     
  17. Passinwind

    Passinwind I Know Nothing Supporting Member

    I posted that link hoping that folks would read the part about various rating terms: peak, average, program, et al. I also wanted to show a little love for Prosoundweb, a great resource IMO. Here's another take from JBL, from their website this time. It includes a link to a document on killing speakers with relatively small amounts of power. JBL "How Much Power" FAQ

    In some ways, their situation "A" applies, since you probably would notice distortion sufficiently severe for the distortion to boost the power "that" much.
    It is also the best match to the experience of most users here, but is NOT the JBL "music applications" suggestion.


    I read that section in the first link as "musical applications where the amp is to be run at full distorted power constantly", ie guitar in a rock situation, and maybe Fieldy-type bass playing, for example. IOW, not as a blanket statement for all instrument applications, just as a rule for the specific case. I may have read this interpretation into that paragraph because of all the discussions I've had over the years with the folks at JBL and many other speaker manufacturers, techs, and sound providers. Notice that the new link in this post goes straight to 2X the IEC rating.

    Thanks again to Jerrold and Bob for their participation here. When I was a practicing audio equipment repair tech, it was always nice to have good, caring tech support. It still is.
     
  18. What many people, including some manufacturers ;) don't take into account is that the cab design can have fairly profound effects on the power handling ability of the drivers inside. The actual power handling of a cab is not necessarily the sum of the ratings of the drivers at all frequencies.... :D

    You can melt a voice coil with perfectly clean power waaay less than rated, if you concentrate it at the cabinet tuning frequency, because the air mass damps cone movement almost entirely.... etc....
     
  19. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    YES, YES, and YES again. Very good points

    Per the last point....If the voice coil hangs over the gap quite a ways, because of a large Xmax and thinner top plate, you will get two blackened areas of coil where the coil stuck out past the magnet structure that normally would cool it. Might happen at considerably lower than rated power.....like around 1/2 power.

    If a ported cabinet design was done with a low tuning frequency, there may be an area above that where the speaker motion again is somewhat uncontrolled. There can be Xmax (overexcursion) problems in that range at MUCH lower than nominal power rating.

    If speakers are of different power ratings, and power is not "divvied up" somehow among them according to rating, the effective power rating is actually the input power where the first one gets too much to handle.

    Generally:

    The "thermal power rating" and the "cone movement power rating" are two different things. At low frequencies, small cones (which is MOST single cones) cannot handle the power unless the cabinet properly loads them and controls movement.

    The acoustic power as an unaided direct radiator calls for too much cone movement (volume velocity), far more than the suspension can provide. There must be help from the port/volume system, to load the cone and prevent uncontrolled movement. Hopefully it also provides acoustic output and extends the useful range.

    But, then, below system tuning, a ported cabinet gives almost zero control of movement, unless some frictional assistance is used. Down there, just a few watts can damage a speaker.

    I have seen perf metal screens over the basket holes to help, but that solution has other problems. Small diameter ports also help (an old JBL solution) but they provide hardly any acoustic output assistance around system resonance.

    No free lunch, acoustic volume is all about moving a lot of air, and at low frequencies that generally means more cones, a horn, fancy resonators, etc, etc, etc.