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How to know how much wattage your speakers are getting?

Discussion in 'Amps and Cabs [BG]' started by ChrisB2, Oct 5, 2008.


  1. ChrisB2

    ChrisB2 Bass... in your fass

    Feb 27, 2008
    TalkBass > Off Topic
    I run a pre/poweramp setup, and am not sure when the poweramp would be outputting its maximum power.

    On a recent outdoor gig I ran my poweramp maxed (no attenuantion). While sound checking I had to keep turning everything up to get loud enough, and ended up with the EQ and master on the pre almost maxed. However If I turned on the pre's additional graphic EQ, the volume would increase dramatically. I suppose if I were to put my multi-effect pedal in the chain I could push even more signal into the poweramp.

    That made me curious-- in a pre/power rig, at what point is the poweramp sending its maximum power to the speakers? Is there a point where the pre-amp processing, EQing, effects pedals, etc., do not continue to increase the overall volume? Or, can it be assumed that if there is unused volume, the poweramp is not maxed? Can a poweramp be made to exceed its maximum output if enough preamp signal is sent to it?

    Just wonderin'...... any thoughts?
     
  2. Mcrelly

    Mcrelly

    Jun 16, 2003
    Minnesota, USA
    what are the specs of you amp??

    what is the make and model of your amp??
     
  3. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Wattage is dependent on the level of the signal you send through the amp (i.e. if you play a rest, no wattage at all is being generated, quiet note = a little wattage, loud note = higher wattage) and the load connected to the amp. Speaker cabs are rated with their nominal load, but the actual load changes value at different frequencies.

    So no, there is no "real" way to know how much wattage you are using. Best you can do is listen for any strain on the speakers (farting, fizzing, etc.) and turn down if you hear anything like that.
     
  4. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Forgot to answer the more specific questions. :) Sending a higher level signal into the power amp can make it put out a higher amount of wattage than it's rated for. There are two main limitations: (1) the amp may not be able to sustain that for long without overheating and burning up or shutting down, so I wouldn't rely on it as a normal course of action; and (2) every part of the chain -pedals, preamp, power amp, speakers- has a point where it will distort if the signal level gets too high. How high can you go? 'Til it distorts. How do you know where that is? Turn it up until you hear distortion. How do you solve the distortion problem? Turn it down.

    Incidentally that was intended to be humorous, not condescending. :) Factual though.
     
  5. Loudthud

    Loudthud

    Dec 25, 2007
    Dallas Texas
    With the power amp's volume control at max (no attenuation) your preamp should be able to provide enough signal to it to drive the power amp to clipping. If the preamp has an input gain control, it might be possible to reduce the gain to a point where this is not true. Could you hear any audible distortion?
     
  6. will33

    will33

    May 22, 2006
    austin,tx
    SOP in PA situations is to crank the power amps and control volume with the input to the power amp. That's where you get your headroom but there are many variables that have already been mentioned in above posts. Resistance varies with frequency in any speaker, various amounts of gain in whatever is hooked up in front of the amp, consistent power vs. transients/spikes etc. If everything in front of the power amp is cranked up to but not beyond the point of clipping and you hit a hard note, you might be feeding full power depending on the freqencies and harmonics of the note you're feeding it but the best advise here is to listen for signs of stress, distortion, farting, harshness, etc. and consider that the point where you need to back off. Also in most bass cabs, the driver(s) will reach their excursion limits long before they hit wattage limits. The wattage rating of your speakers means that's how much heat the voice coil(s) can take before they burn up. That's often much more than the wattage they can take before the demand to flap back and forth producing lower frequencies exceeds the mechanical limits of the driver(s). Basically your 500 watt speaker (how much juice/heat it can take) might crap out at 200 watts because it physically move back and forth any farther (mechanical limits).
     
  7. Hi.

    Without test equipment, it's really only Your ears that can tell the level. You most probably won't be able to tell what combination of amp stage gains give the absolute maximum power at any given frequency though.

    You can measure the output of Your bass and the the gain of the amp stages and determine what RMS voltage should be below the 1% or so distortion level (or whatever You choose). Then with a signal generator feed pink or white noise to the chain and measure the output of the power amp. The problem will be to reproduce the load. A resistive load will give You repeatable results, but only a reactive load will give the real world results.

    The bottom line is that Your pre(s) have to produce hot enough signal to be able to use the full potential of the power amp. That can be measured as well.

    Regards
    Sam
     
  8. ChrisB2

    ChrisB2 Bass... in your fass

    Feb 27, 2008
    TalkBass > Off Topic
    Wow, lot of informative replies, thanks everyone.

    I'm running an Ampeg SVP-Pro into a Crest CC2800, and one side of the Crest into an 8 ohm Avatar 2x12 (500 watts).

    One side of the Crest puts out a max of 595 watts to an 8 ohm load. With the one side of the poweramp unattenuated, and the SVP almost maxed, I heard no distortion whatsoever in the Avatar cab. Only a great sounding tone.
     
  9. Thor

    Thor Gold Supporting Member In Memoriam

    I don't know the Crest model, sounds like a stereo (you said
    one side into your 8 ohm).

    Can't you bridge both sides of the amp into the cab thus doubling your signal into the cab? Check the owners manual.
     
  10. ChrisB2

    ChrisB2 Bass... in your fass

    Feb 27, 2008
    TalkBass > Off Topic
    Good idea, yes but that could potentially send somewhere around 1800-1900 watts into the Avatar 500w cab. The manual doesn't specify the wattage at 8 ohm in bridged mono mode but at 4 ohms it's 2800.

    Bridged, 4 ohms = 2800w
    2 ch x 2 ohms = 1400w per channel
    2 ch x 4 ohms = 965w per channel
    2 ch x 8 ohms = 595w per channel
    1 ch x 2 ohms = 1850w
    1 ch x 4 ohms = 1150w
    1 ch x 8 ohms = 665w

    Since the bridged mono output at 4 ohms is double that of 2x2ohms, I "guess" the bridged mono 8 ohms wattage would be 2x4ohms, or 1930?

    Also, looks like I can potentially send 665w to the cab now. Thought it was 595. That is one reason I was curious about "when" the poweramp maxes it signal; the way it's rigged can potentially send more to the cab than it's rated for... But I still haven't heard any complaints from the cab.......

    Thinking more about your idea... it would only "potentially" send 1900 watts into the cab, but would also give me more headroom.....? would that be safe?
     
  11. Thor

    Thor Gold Supporting Member In Memoriam

    I'd try it.

    Those are peak outputs. And who is to say if those figures
    are realistic. I wouldn't know. If the cab begins to distort,
    you know you have maxed it.

    Speaker cable with banana plug is cheap. Give it a shot.
     
  12. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    I wouldn't bridge your amp into your cab - you have more than enough power on one channel to push both woofers past Xmax and beyond that more power just equals more compression and distortion and little extra low frequency output - and increased risk of damage.

    Alex
     
  13. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    When the power amp's clip light starts to flicker little bit.

    If you can't get the clip light to come on, then your preamps etc aren't boosting the signal enough for the power amp to do it's job properly. It's kinda like driving a really fast car, but putting a brick under the gas pedal so you can't floor it.
     
  14. ChrisB2

    ChrisB2 Bass... in your fass

    Feb 27, 2008
    TalkBass > Off Topic
    That sounds right to me, but reading the poweramp manual has me confused. In one place it says:

    "The input overload point is high enough to accept the maximum output level of virtually any signal source."

    Then in the paragraph on the built-in Automatic Clip Limiting circuit, it says:

    "Situations that may activate the clip limiter include uncontrolled feedback, oscillation, or an improper equipment setting or malfunction upstream from the amplifier. Normal program transients will not trigger the clip limiter ..."

    This sounds to me like the amp can handle any preamp input, and will not reach clipping due to any such signal....

    :confused:
     
  15. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Any power amp can be made to clip, and when it does, the limiter on yours will help reduce the clipping. That's how I read it, and that's what my experience tells me.

    What sort of pre are you using?
     
  16. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    A current transformer on the cable hooked into a power meter.
     
  17. Humblerumble

    Humblerumble

    Feb 22, 2004
    VA.
  18. could it be that you have attentuated the signal through the eq? you say something about additional graphic equaliser, dont quite know what you mean by that but it could be that the eq is draining some signal and you need to turn it up. after all, an equaliser is a volume control that acts on certain frequencies.
    id play with it at lower volumes on the pre amp, get it as loud as possible then turn up to where you want with the pre amp volume control. dont want to suddenly flick a switch and blow your speakers, which you could easily do by exceeding x max.
    could also be that your bass is sending a weak signal. amps have specific gain levels, and the volume knobs just drain off some signal. they don't boost infinitely.
     
  19. ChrisB2

    ChrisB2 Bass... in your fass

    Feb 27, 2008
    TalkBass > Off Topic
    Ampeg SVP-Pro
     
  20. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    On most power amps, to over-simplify a bit, there's an input circuit, followed by the gain knobs, followed by an output circuit. Clipping can occur in either the input circuit or the output circuit. For instance:

    If the gain knobs are set too low, an extremely strong signal can cause the input circuit to clip, without driving the output circuit to clipping. In contrast, if the gain knobs are set all the way up, then any signal will cause the output circuit to clip before the input circuit clips.

    The clip limiter probably acts only on the output circuit. It automatically reduces the gain of the power amp if necessary to minimize clipping. Typically the clipping LED would turn on at this point too. On some power amps the clip limiter can be enabled or disabled by a little switch.

    What the manual is telling you is that the input circuit can handle pretty much anything that a normal preamp can throw at it, and that the output circuit has a clipping limiter.

    In some amps, the clip limiter is designed so that it ignores very brief transients, and only acts on sustained overload conditions. Ideally, the design should be as musically forgiving as possible, so there are a number of tradeoffs in the details of how it actually works.
     

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