Amp Wattage vs. Cabinet Power Handling

Discussion in 'Amps and Cabs [BG]' started by Morningside, Aug 15, 2018.


  1. Morningside

    Morningside Supporting Member

    Nov 14, 2013
    Seattle
    Okay, so I've read a bunch of threads on here about how to match a head with a cabinet, and there seem to be conflicting opinions about the safe and ideal relationships between listed amp wattage and cabinet power handling.

    I'd always assumed that you should never pair an amp with a cabinet that can't handle the amp's maximum listed power (assuming matching impedance). But in some threads, people seem to be saying the opposite: namely, that you want to be sure the listed wattage for your amp exceeds the power handling of your cabinet.

    Which is right?

    Example

    Let's say you you're working with an Aguilar TH 500, which has a listed wattage of 500 watts into 4 ohms.

    (1) Would it be "safe" to pair this amp with a 4 ohm cabinet that has listed power handling of 600 watts / 800 peak? Would it be ideal, both for the health of the cabinet and tonally? Is this pairing okay at certain volumes / EQ settings but not at others?

    (2) Would it be "safe" to pair this amp with a 4 ohm cabinet that has listed power handling of 300 watts / 400 peak? Would it be ideal? Is this pairing okay at certain volumes / EQ settings but not at others?

    Thanks!
     
  2. seamonkey

    seamonkey

    Aug 6, 2004
    IMHO, with new drivers they don't get all farty and distorted when driven to their extremes. It's hard to tell by ear if you're going to blow them. That's a good thing as you want the most from the cabinet, the bad part is it just doesn't warn you're going to blow them.

    To make it mostly idiot proof, Select a cab that can handle 2x the power rating of the amp head.
    500w into 4ohm then get cabs that are 1000w at 4 ohms. Or use some sense.
     
  3. Morningside

    Morningside Supporting Member

    Nov 14, 2013
    Seattle
    The idea that the cabinet should be able to handle double the power rating of the amp is confusing to me, because people often pair a TH 500 with the SL 212, which is a 4 ohm cabinet with power handling of 500 watts RMS. Is that a dangerous combination for the cabinet?
     
  4. Rick James

    Rick James Inactive

    Feb 24, 2007
    New Jersey
    A 2:1 ratio either way is OK. An amp rated at half the cab rating is probably enough to drive it to full output, which is usually mechanically limited, not electrically limited. An amp rated at twice the cab rating gives as much clean headroom as your ever likely to need.
    Only if you don't know how to use the volume knobs.
     
  5. Morningside

    Morningside Supporting Member

    Nov 14, 2013
    Seattle
    So in other words, a head that's listed at 500 watts into 4 ohms should work fine with a 4 ohm cabinet with a listed power handling of 600 watts, and should also work fine with a cabinet that handles 300 watts--as long as you don't crank the volume and/or the bass to unreasonable levels?
     
    Element Zero likes this.
  6. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Generally speaking, you can run any wattage of amp with any rating of speaker cab. It's all about knowing when you're driving the cab too hard. I almost always run an amp that has a higher wattage rating than that of the cab and I've never blown a speaker in over 40 years.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    From what I see, there are plenty of players that have no idea when they are damaging their speakers until it's way too late.

    Also, be sure that you use the continuous, RMS or thermal rating of the speaker and the RMS rating of the amp, I like to recommend a cabinet that is rated at no more than the RMS rating of the amp, because the mechanical power handling is almost always less at lower frequencies. Beware of program and peak ratings, those numbers are not the same as RMS or continuous average power ratings.
     
    basscapes, Element Zero, Kro and 2 others like this.
  8. seamonkey

    seamonkey

    Aug 6, 2004
    You don't hear your mother's voice in your head? "If every one was jumping off a bridge would you do it?" ;)

    You may like different EQ than these other people, like more low bass where you might not hear driver strain.

    I'm not saying these cab manufacturers do this, but many just add up the power rating of the drivers. Adding up the driver power ratings doesn't always work out. The drivers are rated in free air. When you put then in a cab the heat has to get out, it has to be designed into the cabinet, and it should be tested by the manufacturer to burn-out.

    Closed systems like powered cabs, or combos will almost always have drivers that are rated much higher than the built in amp as a safety measure. Or these days, they will have built in and super accurate limiting built in.
     
  9. chris_b

    chris_b

    Jun 2, 2007
    Why run any risks?

    I always have more watts in the cabs than the maximum rating of the amp, and because I want a clean sound I never run an amp over about half power. With my TH500 I had 600 watts then 700 watts of Bergs, then 1200 watts of Barefaced. I have never blown a speaker.

    I play in a few different bands, so need total reliability no matter what gig or volume I play at. I'm not going to stand there listening for my cabs to start sounding bad, I'll sort those problems in the planning stage.
     
  10. jazzbass_5

    jazzbass_5

    Sep 1, 2007
    NY, Medina
    Just to throw another monkey wrench into this, if the cabinet has a horn/tweeter sometimes the max RMS rating is due to the components on the crossover.
     
    seamonkey likes this.
  11. Kro

    Kro Supporting Member

    May 7, 2003
    New Jersey
    What cab is rated that way? I suppose it's possible, but that's something I don't recall ever coming across.

    Anyways, my personal rule of thumb is to to keep rated amp power at, or under the rating of the cab - assuming ratings are in-kind and accurate.

    While I recognize that tweeters may be more sensitive to certain types of clipping (and sound god-awful in the process - a deterrent in and of itself), IMO the whole "higher rated amp than cab" thing is a carryover from pro-audio where the goal is reproduction with as little distortion is possible. Musical instrument amplification is its own thing - many embrace an amp's unique distortion characteristics as, well, character, so might as well plan on entering that territory from time to time. :)
     
  12. Bassbeater

    Bassbeater Guest

    Sep 9, 2001
    Having surplus wattage on the amp makes sense if you intend to run extension cabs.
    Otherwise you just have to be wise about pushing your gear based on how it sounds and how the gear is rated. @Munjibunga has it right imo.
    Be more concerned with impedence matching than wattage matching.
     
  13. Rick James

    Rick James Inactive

    Feb 24, 2007
    New Jersey
    If that's the case the cab is very poorly designed, probably sounds like poo anyway.
     
    jazzbass_5 and agedhorse like this.
  14. Kro

    Kro Supporting Member

    May 7, 2003
    New Jersey
    But paradoxically, the more cab you have the less watts you need!
     
  15. Bassbeater

    Bassbeater Guest

    Sep 9, 2001
    Precisely why I use a headphone amp to power my 810.
     
    musicman556 and agedhorse like this.
  16. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    I'm hard-pressed to recall any instances where a speaker failure has been traced solely to a mis-match between the amp and enclosure. It's usually due to risky application behavior including excessive EQ'ing, attempting to coax a volume level best served by addt'l cabs, or any scenario where a driver is pushed beyond its operating limits (search "Acme creased cones").

    A builder who shall remain nameless told me 20 years ago "...stupid behavior results in speaker damage". A little blunt and offensive to many, the statement holds truth.

    Riis
     
    Munjibunga likes this.
  17. LXvG

    LXvG

    Jul 7, 2018
    The Netherlands
  18. teemuk

    teemuk

    Mar 1, 2011
    There's the issue that amplifier's output power rating is derived by driving x-ohm load with sinusoidal signal with y% of THD while speaker power handling is derived from driving the speaker with filtered noise with crest factor of x for y period of time. The ratings as is therefore are not directly comparable.
    BTW, I suggest the search function. This has been a very popular topic.
     
    agedhorse likes this.
  19. JohnMCA72

    JohnMCA72

    Feb 4, 2009
    Here's another way to look at the situation: What speaker(s) gets you the sound you want, in terms of tone and volume? Start there, then see how much power it/they are going to require as well as tolerate. Pick an amp that can deliver the necessary power at the speakers' impedance.

    If you start out just trying to match power & power handling, you might never get the sound you want. A perfectly matched amp & speaker(s) that doesn't give you the sound you want is worse than useless.
     
    Bassbeater and Kro like this.
  20. Kro

    Kro Supporting Member

    May 7, 2003
    New Jersey
    This is always my recommendation as well. IMO the cab is the harder nut to crack. Pairing it with an amp is the (relatively) easy part.
     
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