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Am I Damaging my Speakers?

Discussion in 'Amps and Cabs [BG]' started by Greg R, Apr 15, 2003.


  1. Greg R

    Greg R

    Mar 11, 2003
    Avonmore, ON
    Last night at a gig the sound guy came up to me after the first set and says "Man, I love that cabinet." It's an Ampeg PR-something-or-other with an 18, 2x10's, 2x6's and HF driver. He shook his head at my amp (Peavey Nitrobass) and proceeded to tell me that I am damaging the voice coils because the cabinet isn't getting enough power. Frankly speaking, this sounds absolutely ridiculous. I can't take the amp past 4 and expect to hear the guitarist. My sound is clear, bright and thumpy. I can understand the potential of speaker damage if the signal was extremely over-driven and distorted pushing through the speaks at high volume, but I think the guy just doesn't know what he's talking about. I liken the argument to putting a Suzuki motor (the head) into a HumVee (the cabinet). The motor will eventually blow up but the Hummer will be fine.

    Who's right? Is there something I am missing here?
     
  2. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    You're right, as long as you don't end up pushing the head too hard. Even if you really push the head into distortion (assuming the cab is 4 ohms) it'll only be putting out 600W max and the cab is rated at 600W rms. The only real risk is if a large amount of that power is going into the mid and high drivers because of the extra HF caused by the distortion.

    Alex

    P.S. However, are you not curious to see if that cab could sound even better pushed by a big power amp, just for the hell of it?
     
  3. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    Believe it or not, you can blow speakers if they are underpowered...in fact, that happens more often than speakers that are overpowered (can anyone say headroom?).

    However the watts of your amp seem to match up with the cab so I wouldn't worry about it as long as the ohms are matched as well.
     
  4. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    So long as you weren't clipping, he's full of $#%#.

    You CAN still damage the voice coils even when running the exact same wattage as your cabs are rated for, IF (that's a big IF) you are clipping your amp. That's the same if you are overpowering OR underpowering, it makes no difference. You send a clipped signal to the speakers, and you may damage them.
     
  5. 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
    No, you've got a good handle on that part. The guy was just repeating a common myth.

    An amp, when driven into clipping, will produce more power than its rating indicates. Clipping also compresses the dynamic range, so the average power in the audio can be very intense, with little soft time for the speaker voice coil to cool down. Therefore, it is possible for an amp to burn out a speaker with a slightly higher power rating than the amp has. Many people misunderstand that to mean that you will damage your speakers by underpowering them.
     
  6. Greg R

    Greg R

    Mar 11, 2003
    Avonmore, ON
    I believe my amp puts out 250W or so at 4 ohms. I do occasionally notice the clip light flickering but I would assume that the DDT speaker protection circuit is doing it's job and automatically adjusting the pre signal to trim the clip. At least that's what Peavey says. But the cab is rated at 600W, surely clipping at 250W won't hurt it?
     
  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
    Is that 600 watts continuous power? If so, and the cabinet is 4 ohms and the amp is rated for 250 watts into 4 ohms, then you're in very little danger of damaging your speakers.
     
  8. hmmm... I thought even a 5-watt amplifier could blow a 600 watt speaker when it's clipping, cause then it can put power-peaks (220V) into the speaker... I could be full of ****, though :)
     
  9. 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
    No, even a badly clipping 5-watt amp will barely tickle--let alone damage--a 600-watt speaker. It will not put out "power-peaks" or 220V into the speaker.
     
  10. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    I would have to agree that simply underpowering your speakers does not equal blowing them.

    It's really when you underpower them by using an amp rated way less than the cab, and you crank your amp in an attempt to get more power to your speakers...but the amp doesn't have the power to do that...and so eventually you end up driving your "underpowered" amp into clipping.

    It's the clipping that will cause the speakers to blow. Peavey's DDT does help eliminate the probability that the speakers will blow. The amp, if it detects an overabundance of clipping, will cut the power to the speakers.

    Rather than blowing the speakers, you will simply have no sound until the amp is turned off for about ten minutes to cool down and then you power up again.

    Speaking in generalities, I still feel it's better to "overpower" your speakers than to underpower them and then try to run your amp to the max in an attempt to get more "volume" out of it.

    With a more powerful amp you can run it lighter and reduce the chance of clipping, plus you can run it to the highest the cab will handle and still have the "headroom", so you don't overdrive your amp, cause it to run hot and clip the speakers.

    I am, by no means a technician...I am simply talking practicality.
     
  11. My nitrobass amp says 450w, and I'm using a 4x10 cabinet I got from speakerhole.com. It says it'll handle 800w, but I highly doubt it, as it didn't cost nearly as much as anything else in it's category. I think it was $170 + shipping. I'm very doubtful that it'll handle nearly as much as my amp can give. Am I going to blow these speakers? I'd prefer not to, as it's my only cab for right now. Also, I'm totally not an electronics guy (which is not to say that I won't understand if you explain it in electronics terms), and I feel really stupid saying this, but, What is clipping? Does it have anything to do with that "power management" LED on my amp that turns red for peaks? I admit, I dont' know anything about amps :(
     
  12. Yah, that flashing red light is probably the clipping indicator. It's basically telling you that the levels coming out of the power amp are being cutoff in order to protect your speakers.

    Clipping itself is like audible poweramp distortion. I believe in technical terms the soundwave becomes square instead of round in the extreme cases where speaker blowouts occur.
     
  13. 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
    To understand clipping, it's best to first understand what a power amp does.

    Signal voltage and gain (The simple stuff)
    An amp takes a small signal voltage and multiplies it into a larger and--hopefully--precise replica of the original. That large voltage drives the speaker.

    The amount of multiplication is called gain. Most amps have at least one control for adjusting the amount of gain over a range of zero up to whatever the amp's maximum gain is: 20, 31.5, 40, 50, 80, etc. So in short, the output voltage equals input voltage × gain.

    Basic clipping concepts (More simple stuff)
    Every amp has a maximum output voltage (and it will vary somewhat with the load, too). So let's say a certain amp can put out ±25 volts into an 8-ohm load. As long as input voltage × gain = < ±25 volts, everything's fine. But if the input voltage and/or the gain are high enough, the output voltage should be higher than 25 volts … except the amp can't put out higher than 25 volts. So instead of going up to 25.1, 26, 30 volts or whatever, that part of the waveform just pegs at 25 volts and all that signal that would've gone above 25 volts gets chopped off, or clipped. The more severe the clipping, the more of the signal gets lopped off, and the more distorted the resulting signal is.

    Advanced clipping concepts (It gets worse)
    On top of that, all but a couple amps on the market lose nearly all their damping capabilities during the portion of the waveform that is clipped, so you may get some speaker resonance creeping into the sound, which may make bass frequencies sound kind of floppy.

    And some amps--even from some otherwise prestigious names--have a tendency to "stick" when they clip; that is, the output voltage stays pegged for a short time even after clipping should've ended and the normal waveform should've resumed. That results in the trailing edges of the waveform getting more squared off than they otherwise should.

    And lastly, when an amp clips, the flat-topped portions of the waveform are only as clean as the power supply rails feeding the output section are. Some amps have an awful lot of AC ripple on their supply rails, and this ripple will modulate the audio on the clipped peaks, adding some 100 or 120 Hz component, plus harmonics, to the audio.
     
  14. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    So, in its most basic, practical terms for a working musician (who is not an electrician or technician) that means what exactly? Especially, based on the original posters question?

    For example, I know that Peavey's DDT protection works, even though I don't know how specifically (i.e.- technical details). I know how it works in a practical working environment.

    I also know that (practically speaking) that I should match my amp and cabs with regards to ohms and wattage...and that it's been my experience that it is better to have more than enough power than not enough.
     
  15. 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
    Based on the original poster's question: he doesn't have to worry about damaging his speakers doing what he's doing, and he isn't getting close to clipping.
     
  16. Greg R

    Greg R

    Mar 11, 2003
    Avonmore, ON
    ...but if the amp is doing the job why would I need more power? Like I mentioned in a previous post, I've never gone beyond 4. There is just no need. If we're playing a venue of a size that requires more power, we all just go through the mains anyway and use our personal amps as stage monitors. I would have to lug a pretty hefty amp if I want to match 600W/4ohms. In my experience, (probably limited compared to some of you guys) I have found anything over 2 or 300 watts just isn't necessary if you have an efficient cabinet. I toyed around with rackmount amps, preamps and power conditioners in the past, but I'm happy to have those days behind me. One patchcord, one amp, one cabinet. (Two trips from van to stage)
     
  17. If I'm not mistaken, DDT is a form of compression right? You could do a search in the effects forum and find a wealth of information on how compressors work.

    Basically, once your poweramp output signal reaches a certain level (threshold) the signal is lowered according to a ratio setting. This means signal peaks and high level signals are less likely to be damaging to speakers.
     
  18. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I guess DDT can be called compression, but it's really a limiter. In other words, it does absolutely nothing until you push too hard and exceed the threshold. A traditional compressor will kick in with every single note you play.

    Bob's explaination of clipping is the best I've ever seen - onya mate! Can I just add something. The amp produces more power under clipping, true. The general rule of thumb is it produces 2 times it's rated power. So a 5w amp clipping will produce 10w. Your 250w amp is producing roughly 500 while clipping - so you shouldn't have any problems with a speaker rated at 600w

    But there's something about this thread that isn't sitting right. Greg, you say the amp is only on 4 which suggests the amp isn't working too hard. In a subsequent post you sat that your clip light comes on occasionally. This surprises me a little. Does anyone else find this odd?
     
  19. Every amp I've ever owned (well, both of them) have had clipping indicators come on between 3.5 and 6 on the master volume, so it doesn't strike me as odd, especially if he is pushing a lot of low end.

    I'm pretty sure that compressors don't kick in with every note, that's why there is a threshold setting for compression to start at. Or at least it wouldn't if the threshold was set high enough. You're right about the DDT though, just checked and it is a limiter.
     
  20. Greg R

    Greg R

    Mar 11, 2003
    Avonmore, ON
    Yes Nicoli, I have noticed this too and yes, I am pushing a lot of low end. Playing runs in D or E on the B string of my Spector will make it clip at lower volumes than say my Musician or even P bass. Low end takes a tremendous amount of power to generate compared to highs and mids hence bassists are cursed with heavy amps compared to most of our guitar playing friends.