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Matching power to power-handling...?

Discussion in 'Amps and Cabs [BG]' started by Stewbone, Mar 5, 2003.


  1. The rig:

    -Fender Jazz, stock;
    -Ampeg SVP-BSP;
    -Crest FA901, 850or so watts @ 4 ohms;
    -1x15JBL 2226H, 600watts handling;
    -Flite sealed 410 w/ Eminence Betas, 1000watts handling.

    Cabs are 8 ohms each.

    Q: I'm not usually running full-on wide open, so am I underpowering my speakers? Would I get better sound using spkers closer to tolerance?

    Where are the gearus?...:)

    Rog.
     
  2. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Don't fret. Underpowering speakers only becomes a problem if you send them a clipped signal. You can send 850 clean watts into a 1600 w speakers all day without a drama.
     
  3. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    At the other end of the spectrum you usually can safely couple a 800W head with a 400W cab.
     
  4. Thanks, Pete.




    :bassist:
     
  5. Rockin', JMX. Thanks, guys.

    Rog.



    :bassist: :bassist:
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's true. Believe it or not, very few speakers are blown this way. It's possible to cause a speakers to physically break up but it's not easy. The more common cause of speaker failure is burnt out voice coils, usually due to clipping.

    The odd clipp here and there is OK but continuous, regular clipping is BAD!
     
  7. Learning here... so I got this. Clipping is BAD. Not much else really is. Puts things in a much simpler light. I am enlightened- many thanks for the light!:cool:

    Rog.
     
  8. There's a big misconception about having more power than your cabs are rated for and that's that you can actually put more power into the speakers than they are rated for if it is clean. You can put quick transients of considerably more than rated power into a speaker without any worries, but you can't put more average power in. If you actually put a continuous(average) signal of 800W into a rated at 400W continuous it will damage the speaker no matter how clean it is. The reason you can use more powerful amps is that under dynamic conditions(ie music;)) amps only put out a fraction of their total power on average, even under hard usage. So say if you have an 800W amp and you are playing so that a clip light comes on every once in a while, you're probably only putting an average of 100W into the speaker. There'll be peaks of 800W but there'll also be times when you're putting 10W or less into the cab.

    The big problem with clipping is that an amp will put out more than its rated power when clipped. So under hard clipping an 800W amp could be putting out considerably more than 800W. This is more the crux of the problem than the clipping itself. As they say on the Live Audio Board, it's the heat, not the motion that damages speakers.
    For example, you're not likely to blow a speaker rated for 800W continuous with a 100W amp, no matter how much you clip it, but clipping a 600W amp into the same speaker could get you into trouble.

    Clipping (Solid State) sounds awful, so that's good enough reason to avoid it!
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I knew you'de join in Mark :)

    I'd like to add that even SS clipping is not always audible, especially when playing along with loud giutars and drums as I always am. I've got a clipping paranoia.

    In sound engineering circles, it's generally accepted that and amp will produce 2.5 times it rated wattage under clipping. There's no scientific explaination as to why they adopted this rule of thumb, but it's been adopted anyway. If we assume they're right, your example of a 100w amp cliping should kill speakers rated up to 250 watts.

    And your 850 watt amp under clip will produce upwards of 2,000 dirty watts. Your speakers are rated at 1600w total so they're within the "KILL ZONE". But you'd still have a lot of trouble killing those speakers.
     
  10. "WOOF!"

    A'ight, pretty interesting. Sounds like the kind of critical info one wants to definitely know about. I'll be making an effort to keep a guarding eye on my little red LED.

    Now, preamp clipping: maybe bad,but for different reasons? Obviously not a power problem, right...?

    Rog.
     
  11. You're pretty close, but the numbers aren't quite right.;)
    An amp can theoretically put out an absolute maximum of twice its full clean power. The reason behind this is that a square waves have twice as much energy as sine waves of the same amplitude. This is easily shown by Fourier analysis, I'll leave the details out, but if you add up the area under the curves of a sine wave and a square wave with the same peak value, there's twice as much area under the square wave. I say theoretical maximum because it's pretty much impossible to get an amp to put out true square waves (i.e. the parts of the waveforms below the clip point are still sinusoidal). It's also pretty hard to get an amp to produce a sustained output far beyond its rated power. Most amps will overheat and shut down pretty quickly when you drive them extremely hard.
     
  12. The odd flash of your clip lights is nothing to worry about. If you're clipping the amp hard all the time, you need more power;)

    Preamp clipping isn't really much of an issue. Some preamps sound great when overriven, some don't. There is a school of thought which says that clipping anywhere in the signal chain can damage speakers but I don't buy it, and neither do guys like Bob Lee....
     
  13. Rockin'. I learned something another day in a row! :D
    I can now abuse my bandmates and neighbors with the knowledge that I won't be insulting my voice coils! But seriously, thanks for the sharing of your knowledge with the likes of myself (and whomever else present company may include). More fun to know what's going on when you're doing it!

    Rog.:)
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I consider clipping (specifically Solid state, or worse still Digital) to be similar to smoking. It doesn't kill everybody but it's certainly not healthy for you. The odd clip flash won't hurt your speakers but I still reckon that it contributes to failure down the road.

    This opinion is based purely my observations of sound engineers (my other hobby). The ones who subscribe to my theory never seem to hurt their speakers. The ones that believe " a little bit of clipping isn't a problem" seem to turn up at gigs with different speakers now and then because "the other ones are in getting repaired". I know that Mark has never blown a speaker so maybe my whole theory is co-incidence, but I'm sticking to it anyway.

    I'm also mates with the guys at "The speaker Hospital", not as a customer! They're all musicians and sound engineers who I met around the traps. (I'm trying to convince them to teach me to do re-cones at the moment). They say that 90% of the speakers they recone are burnt voice coils with clipping the likely cause, and the owners of the speakers are often unaware of what clipping is. A majority of the balance are accidental damage such as drink spillage etc. They very rarely get speakers that have been WOOFED to death, and the ones they do get seem to be Car Audio subs murdered by winding up the bass EQ.

    One of these days I'm gonna deliberately kill a speaker on a test bench to see with my own eyes what clipping really does.

    I've got a clipping paranoia :)
     
  15. Pete, it seems to me the second law of thermodynamics says you're right: Everything, given time and whatever variables, breaks down to it's lowest level of order. So I end up with this- Get the most out of it, make it worth having. If I gotta clip to get the rip, I do it! The preamp, anyway...:) I am with you guys about the power issue, glad to be getting the most out of my rig. Many thanks again for the education.

    Rog, the smarter than I was.:)
     
  16. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Fair enough. But speakers seem to break down at the worst possible times, usually during a gig when you need them most.
     
  17. Yeah, I agree! And I'm not promoting abuse, just that you've gotta support your habit! I am, however, interested in being able to support mine- which is the reason for this thread. I apreciate the involvement on your all's part. This forum is an excellent resource!

    Rog.:bassist:
     
  18. frosty

    frosty

    Feb 18, 2003
    Southern USA
    I'd never blown a speaker until recently..even back
    in the 60's when most of us (poor) were grossly underpowered compared to guitarists and we played
    em wide open. I'd picked up a Peavey 1820 and was
    trying all my basses through it with my Ampeg SVT.
    Stupidly, I plugged in an acoustic bass while standing too close and there commenced a terrible
    howl. Speaker was toast after this and a tech told
    me this happens more than you'd think. Of course
    Peavey BlackWidows are basket replaceable and it's
    good as new now but I was so mad at myself I got
    rid of the acoustic.
     
  19. The "stupider" the lesson, the better it sticks. Nobdy'll know that better than Rog!:oops:

    Rog.