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Harm in too much power?

Discussion in 'Amps and Cabs [BG]' started by bassicrunner, Sep 1, 2002.

  1. bassicrunner


    Sep 23, 2001
    Is there any harm in too much power into too small a cabinet? I've got a Bergantino HT-112 and am looking at getting an EA CXL-112.
    I'm thinking a 600 watt bridged amp is the way to go. Is this right? will it be ok to only use one at a time on mono alot? is that enough power? (Sorry, kinda new with this power concept.)

    P.S. - Any suggestions on good heads for this cabinet duo? Thanks in advance!
  2. BryanB

    BryanB Moderator Staff Member Supporting Member

    Surprisingly, you are better off with too much power than not enough. Most speakers can take 2-3 times there RMS rated power during instantaneous peaks. Some can take even more. On the other hand, an under powered amp is more likely to be driven into overdrive. Overdriving an amp can cause it to push out 3-4 times it's normal power. At extreme levels the signal starts to go DC. This will send any speaker to the repair shop. I say, for solid state amps, try to have 2-3 times the rated power of the speaker. Just make sure you don't push the gain past 70% nominal. This _SHOULD_ leave enough headroom to prevent clipping. (Of course some amps can be driven harder because they have better clipping protection.)
  3. i think its good to have plenty of headroom (buy an amp thats got twice as much power as you will actually use) but i also think its important to use speakers that are over-rated. IMHO: if you have an amp rated for 600WRMS, then use a pair of drivers rated for 400WRMS EACH ( 800WRMS total!)

    I had a peavey single rackspace power amp once, i think it was rated for 1000W bridged. I always tried to be very careful to keep all the levels set to "1". In the middle of a show it made interesting blue flames shoot out of my 2-10 cabinet which was loaded with Altecs. Was very colorful, but didnt do much for the sound.... the altecs went in for re-coning the next day
  4. True. Good show.
    No. Twice its rated power at 100% THD. Theoretically.
    Untrue. There's not even a slight fraction of DC in a clipped signal. It is not the clipping that damages speakers. It's too much electrical of mechanical stress that does it.
    Huh? There's nothing you can tell about headroom, judging the setting of the master volume control on a power amp.
    Yes. But clipping will still occur. It won't sound bad, though. That's the purpose of a soft clipping circuit.

    Sorry, needed to set some things straight. All in my humble (but educated) opinion.
  5. punkfunkfreak


    Dec 16, 2001

    oh joris.

  6. BryanB

    BryanB Moderator Staff Member Supporting Member

    Thanks for the info Joris.

    So how does one set up a power amp to insure sufficient headroom?
  7. Joris covered everything I would have said about clipping and stuff. I'd only like to add that tube amps and SS amps overdrive in almost exactly the same way. The sonic differences are mostly due to the prevalent harmonics that each type of device produces.

    I do think that a good rule of thumb for solid state is about 2x the RMS rating of the cabinet. This is safe enough under most conditions, because even when an amp is being driven pretty hard it probably only puts out 1/3 of it's rated power on an average (not to be confused with peaks). Average power to the speaker is probably the thing to be concerned with. The odd peak won't hurt the speaker too much. On the other hand, if you're seeing the clip lights all the time in this situation, you will eventually blow the speaker one way or another as a function of too much power going to the driver(s). I guess the best way to ensure that you have enough headroom is to use common sense! If you have to drive your amp really hard to be heard you need either a more powerful amp or more speakers or both :D
  8. bassicrunner


    Sep 23, 2001
    So for a couple of cabinets with 300-400 watts both, something like an SWR SM-900, Eden WT-800, or on the cheaper side, a Carvin RC-1000? Would all of these be good? Thanks.
  9. awesome


    Aug 14, 2002
    How would you know you're clipping when you haven't got a clip light? Will it sound obvious or should I be carefull?
  10. Let me give you an example. In my early years (;)) I played through a 150 watt solid state amp. I knew 150 watts was tight for the type of music I play, but never thought much about it. It sounded good, so why more power? The strange thing was, my speakers always made these strange waving half inch movements. I thought the amp was just badly constructed (home made, so you never expect it to be perfect). Curious as I am, I put it on a test bench with a dummy load and an oscilloscope (a device that visualizes AC signals). It turned out I had been severely clipping the amp for a few years. It sounded good to me.

    Now I have a 480 watts amp with a clip light, which occasionally lights up, meaning I was underpowered over three times.

    I'm a tech freak. I always recognize an amp clipping. Right? ;)
  11. IMO, if the amp doesn't have any means to see how much power it is providing (a clip light or a peak output power meter) you can't, unless you have very good ears. In that case you would be able to determine when clipping starts, playing your rig at maximum power in a silent room.

    After making the proper adjustments you shouldn't touch any of your knobs again, including EQ and tone controls.

    IOW it's very hard. Clip lights are handy.
  12. Another issue with too much power is over excursion of the cone.

    Speakers have two limits: thermal and displacement. The power rating given to the cabinet is the amount of watts it can absorb before the voice coils melt at the thermal limit. Displacement limited power is the amount of input power that causes the driver to exceeds its mechanical limits. This power level is both frequency and enclosure dependent, and is less than thermal limited wattage.

    Maximum cone excursion for a driver in a vented enclosure is typically 1/2 to 1 octave higher than the tuning frequency. This is the point, above the tuning frequency, where the driver reaches maximum cone movement.

    For example, the Eminence Kappa 15 has an Xmax of only 1.6mm. Enclosed in a vented SBB4 alignment of 109 liters tuned at 36 Hz, this driver can only handle 13 watts at 59 Hz before it exceeds its tiny Xmax. This driver can handle the full 400 watts rated input power above 230 hz.

    The Kappa 15LF in SBB4, with Xmax of 5.5mm will handle 230 watts from 43 Hz and higher. Note the much larger Xmax.

    Note the above excursion is directly related to Xmax. If the driver mechanical limits are substantially larger than Xmax, it will handle more wattage, but with much higher distortion. For example, the JBL 2242H has an Xmax of 8.9mm, but a mechanical limit of 25mm.
  13. Bruce,

    It is my understanding that most, if not all drivers have a mechanical limit (Xdamage) that exceeds Xmax by far. Most speaker designers don't aim at linear, distortionless playback. They want it f**king loud, at all cost (or actually, at low cost).
  14. That's true, and exactly what I mentioned in my last paragraph above. I've not seen it referred to as Xdamage, but that sounds descriptive to me.

    Bad news is, not enough manufacturers publish Xdamage specs. JBL and some of the boutique driver makers do, but most don't.

    The gap height on the two Kappa mentioned above is identical at 9.52mm each. I suspect that Xdamage is identical on both drivers, and only the voice coil is different. The "LF" version has significantly more Xmax, and correspondingly less efficiency (and lower response).

    [ edit ]

    I just heard back from Eminence, and got the "Xmech" specs for the above drivers. This is what Eminence uses to describe maximum cone excursion.

    Kappa 15 - 23.24 mm
    Kappa 15LF - 20.83 mm
    Magnum 15LF - 30.94 mm
    Kilomax Pro 15 - 26.92 mm

    FWIW, I really like the new Magnum 15LF in 150.6 liters at 37 Hz. Perfect for 4-string, and damn near perfect for 5-string. Very good Group Delay numbers too, especially for a vented box. And loud, too. -3dB at 36 Hz.
  15. stop_drop_pop33

    stop_drop_pop33 Guest

    Aug 15, 2002
    under your bed
    better to have it and not need it then to need it and not have it ;)
  16. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    I have Bergie 1/12 that sounds way better and barely flaps at all when run through a channel of my QSC2402, giving it 500 watts....than it did with either my SWR SM400 or my Ampeg SVT3! Headroom is a beautiful thing!
  17. PICK


    Jan 27, 2002
    Sydney, Australia
    I have an Ampeg SVT-2 Pro and the clip light comes on all the time. Is that a bad thing??????
  18. Matthias


    May 30, 2000
    Vienna, Austria
    The peak led refers to the preamp section only, so it does not tell you how hard you drive the poweramp. If you overdrive the preamp to get distortion (e.g. by turning up the drive control) the peak LED will glow steadily.
    If you want to avoid distortion, you have to turn down the gain so that the LED only flashes at the highest peaks.

  19. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    woah! kappa this, kappa that! english pleez...

    i got another question for y'all. my Demeter seems to hate being pushed above 3 on the volume dial and produces some overdrive. is this bad for my speakers? am i od'ing the power amp?

    also, would it be better for me to run my power amp flat out, and juice my Demeter BSC-1 the max 500 watts my Peavey puts out on channel 1?

    am i supposed to control my volume strictly from my preamp's volume?

    if this is the case, then it'll be on like .05 on the dial, cause i honestly dont have to be that loud.

  20. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Jokerjkny...I would try your power amp flat out, and control the volume with your Demeter.....it might help your distortion problem.....worth a try!

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