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Discussion: wattage control to your speakers......

Discussion in 'Amps and Cabs [BG]' started by keyboardguy, Apr 28, 2009.

  1. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    Hi all;
    I've been mulling over this and hope you 'smart folks' can explain this.
    I know volume controls on amps and basses don't work exactly like this, but bear with me.

    What volume control determines the actual wattage getting your speakers?

    Let's say that you have an amp that can deliver, say, 100 watts to your cabinet.
    The amp's volume (master) will send 50 watts output when it's set at 50%, 35 watts when set at 35%, etc. and so on.

    Now, your bass guitar's volume control will be similar; 70%volume output when knob is set 70% open, 25% volume when 25% open etc.

    Now some scenarios:
    amp 100%, bass volume 100%= 100 watts to the cab.
    amp 100%, bass vol 50%" will it be 50 watts to the cab?
    OR amp 50%, bass volume 100% will it still be 50 watts to cab?


    amp 80% bass 100% open; 80 watts to speaker? OR
    amp 100% and bass 80%; STILL 80 amps to speaker?

    A different one:
    an amp that delivers 750 watts.
    If I put the amp at 100% and set the bass at 10%, would only 75 watts get to the cab?

    Sorry for the long post but this has been bugging me for years.
    If you left your amp on full volume, could/should you control the wattage output JUST with you bass guitar volume?

    Thanks folks.

  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    No level or volume control will limit the output capability of your amp. You can have all of them set to say 10% and still get the full output from your amp with a hot enough signal.

  3. cadduc


    Mar 4, 2006
    back around 1970 the following was said to me when i blew up four ev sro-12's with my ampeg svt both the ev tech support and ampeg tech support gave this advice

    with a 300 Watt amp that delivers 700 Watts peak, you will get transients that are full power, even if the amp is just barely turned up, you wont hear the transient, but the voice coil will pop when there is not enuf headroom

    so as i understand it, it may not seem to be really loud, but the speakers will be working really hard
  4. seamonkey


    Aug 6, 2004
    Audio gear uses Audio taper pots. It's not linear, at "5" you don't get half the output. Ears are most sensitive to changes on the quiet end sound. So it's a good thing there's a lot of adjustment on the lower levels. If it were linear power adjustment you'd hear a big jump in volume for a small change in the knob.

    You'd need a calibrated limiter to really limit what power goes out of an amp. Most modern amps have built in limiters, but most don't let you adjust them down. If you have much more amp power than your speakers can handle, you have to use your ears to hear the stress you're putting on your speakers. Even if you use a distortion effect you can usually hear stress - it's not a good distortion. (unless you like that old torn speaker sound blues players use)

    Most modern amps also have rumble filters to prevent subsonics from passing through and causing cone movement you can't hear. (Not all do)
  5. Just to muddy up the waters more.....the power output rating of the amp is at a specified amount of THD (Total Harmonic Distortion) a "clean signal power rating". The amp is still capable of putting out much more power.
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    None of them. The only way to control power output is via a limiter. They're SOP on good PA systems.
  7. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    Great info folks.

    If I'm understanding correctly, When I have My Carvin B1500 ((1250 watts @ 4ohms) hooked up to my Dr. Bass cab (rated @ 600 watts), I could theoretically blow the speaker EVEN if I'm turned way down on the amp? (I play it with the volume at "2" of "10".
    I would think one could judge the apparent loudness and listen for distortion......

    You guys are scaring me :eek:

  8. rpsands


    Jul 6, 2007
    Phoenix, AZ
    You could but it's pretty unlikely if your bass signal isn't crazy hot. The danger lies in when you get carried away with dynamics and pluck the heck out of a string..or slam your hand down on the pickups, or drop your bass, or whatever.

    If you play with the vol on 2, you're probably safe. I wouldn't be afraid to turn up quite a bit more (personally).
  9. dog1


    Dec 30, 2008
    I agree that you are probably safe, but who really knows. I am curious though. Why are you pumping so many watts into a cab designed to take half what you are sending it?
  10. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005

    Oh, I rotate my equipment now and then for grins. :)

    I have an Avatar B410 neo that takes 1,000 watts. Next week I'll probably hookup my Peavey Deltabass (160 watts) and have an underpowered setup :D

  11. Sandu


    Oct 23, 2007
    Bucharest, Romania
    So basically, regardless of the power rating of the amp, the danger lies within the first part of the signal chain (bass, pickups, technique)? Then, theoretically, I'd be in the clear if I were to use a high pass filter to cut out the rumble and multiband compression + limiter in the preamp stage to subdue the hi freq transients and boomy notes.
  12. I had a SWR GT Studio Preamp which was basically a SM-400 and it was capable of going down to 10hz and It did you could see the speakers fluctuating and over traveling if you would even thump the strings,I found some 30hz 12db inline High Pass RCA's that I was going to buy but I sold the preamp.
    I hated to see those speakers moving so much and it was more muddy with all of those inaudable low tones.
    I was also looking at using my PA amp which is a Mackie 1400I that has a built in adjustable high pass crossover,I did try it out and thats how I fiqured out the problem and discovered how much cleaner the lower notes were when I would set the crossover between 35hz and 40hz.
  13. MooseLumps

    MooseLumps Supporting Member

    Nov 4, 2007
    That would certainly help. personally I like using speakers that can take the wattage. Right now I'm running two Carvin lsx1503's which are 8 ohm 800 watt cabs. I'm feeding them with a SWR SM400x, a 500watt amp (@ 4 ohms). I feel that if I double the power with an extreme transient, I'm still only feeding my 1600 watt speakers 1000 watts. This is not how I planned the setup, it just sort of happened this way. I would not be afraid to double my program wattage into the stack.

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