Why do speakers have a max watt rating

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  • bleeding ears
    Senior Member
    • Nov 2004
    • 435

    Why do speakers have a max watt rating

    Whilst pondering which amplifier and which output wattage would best suit my speakers, I became a little confused about the whole amp/speaker wattage compatibility issue.

    Eg , if speakers can handle wattages well above the manufacturers specified maximum rating, why do they specify a maximum? Or more correctly, why do they specify a relatively low maximum rating when the speaker can obviously handle much more?

    I can understand that a minimum wattage would be necessary so that the speaker can actually have enough power to run, but a maximum does not make as much sense.

    Also I have noticed that some of the more expensive speakers (particularly bookshelves) seem to have a fairly low maximum wattage compared to other similarly sized speakers of other sometimes cheaper brands.

    Are these manufacturers low ratings because they are just being truthful about their speakers capabilities?, whilst other manufacturers exaggerate their speakers ratings to impress potential buyers?

    What is the truth, and how does a manufacturer determine what their specified maximum watttage should be?

    This might be one for those with an electronics background?

    Any ideas, Im confused LOL

    Pete
  • Kevin P
    Member
    • Aug 2000
    • 10809

    #2
    Usually speaker manufacturers have a recommended power range (min-max), at which the speaker will perform its best. Its absolute maximum power (the point at which the speaker would sustain damage) will likely be much higher.

    In general, it's better to use a more powerful amp than a less powerful one for a given set of speakers. This is because clipping (due to too little power) is far more likely to damage speakers than too much CLEAN power. If you exceed the maximum wattage rating of speakers with clean power, you may experience distortion or degradation in sound quality as the drivers or enclosure gets maxed out, but you're not as likely to damage the speaker as if you use too little power and clip the amp.

    Comment

    • bleeding ears
      Senior Member
      • Nov 2004
      • 435

      #3
      Thanks for your explanation Kevin, It now makes more sense but knowing when enough watts is enough might be the hard part.

      Considering that many (that can afford it) seem to go for amps with higher outputs than their speakers max rating, this appears to be the way to go.

      Is this going to always be the case?

      When is enough, enough?

      Eg is 300 watts per channel too much for speakers rated at 250 watt?

      Pete



      Pete

      Comment

      • Clive
        Former Moderator
        • Jan 2002
        • 919

        #4
        No, but you may want to look at the *RMS power ratings for a more secure guide. I find that some manufacturers esp. the cheapy ones, tend to overstate the power ratings. Maximum power may not produce "Clean" sound and could cause more damage to the speaker not to mention your BleedingEars (No real pon intended)

        Yes, better built speakers does show a lower maximum power rating which is where the manuf. believes should be a comfortable level (with slightly higher distortions) to play without damage.

        Taken from "The Starting Block"
        *RMS: Root Mean Square or the square root of the arithmetic mean (average) of the square's set of values. A reasonably accurate method of describing an amplifier's power output.
        CLIVE




        HEY!! Why buy movie tickets when you can own a Theater?

        Comment

        • whoaru99
          Senior Member
          • Jul 2004
          • 638

          #5
          Originally posted by bleeding ears
          Thanks for your explanation Kevin, It now makes more sense but knowing when enough watts is enough might be the hard part.

          Considering that many (that can afford it) seem to go for amps with higher outputs than their speakers max rating, this appears to be the way to go.

          Is this going to always be the case?

          When is enough, enough?

          Eg is 300 watts per channel too much for speakers rated at 250 watt?

          Pete



          Pete

          Having too many watts is really not much of an issue. You just keep the volume at a comfortable level and then there is plenty on reserve for peaks.

          When the sound starts to become flat or harsh sounding or strange noises not present in the music are heard from the speakers it's time to turn it down a notch or two.

          Other than using common sense, there is little to worry about having too many watts.

          I've used a 500wpc amplifier with speakers rated at 210wpc and they survived just fine. It all goes back to using the power wisely and being able to identify when things have reached their limit and then (the key part) backing down a bit.
          There are some things which are impossible to know, but it is impossible to know which things these are. :scratchhead:

          ----JAFFE'S PRECEPT

          Comment

          • Karma
            Senior Member
            • Nov 2005
            • 801

            #6
            HI Clive,
            You gave a good explanation. Power ratings are difficult for everybody, not just beginners. For example, my B&W 805S monitors are rated at 125W. I was buying a new Krell KAV3250 power amp with a rated output of 250W per channel. I usually use power amps that are rated over the speaker power ratings. But this difference (6 dB) was enough so that I was concerned for the health of my speakers with that much power available.

            I was contemplating reducing the speaker protection fuse current rating by about 2/3 of the factory value. I called Krell and they said I did not have a problem. Not staisfied, I talked to my very knowledgable Krell and B&W dealer and he told me to not worry about it. So, I quit worring about it and, so far, I've had no problems. But, it only takes one high power incident to send the speaker to the hi fi hospital.

            It's no wonder that folks get confused about these ratings.

            Sparky

            Comment

            • aud19
              Twin Moderator Emeritus
              • Aug 2003
              • 16706

              #7
              Chances are if you had a 300w amp connected to 150W rated speakers, it will be uncofortably loud long before you get anywhere close to using the amp's full 300w cpabilities. In general I'd bet you use something like 25% of an amps power (if that) even at fairly loud volumes in anything but peak sections of material
              Jason

              Comment

              • Karma
                Senior Member
                • Nov 2005
                • 801

                #8
                HI Aud,
                That's true for normal operation but unpredictable things can happen. For example, a ground can come loose or I could play War of the Worlds at a respectively high volume then be blown out of the water by the lightning scene. Sh*t happens.

                Sparky

                Comment

                • dyazdani
                  Moderator Emeritus
                  • Oct 2005
                  • 7032

                  #9
                  Originally posted by aud19
                  Chances are if you had a 300w amp connected to 150W rated speakers, it will be uncofortably loud long before you get anywhere close to using the amp's full 300w cpabilities. In general I'd bet you use something like 25% of an amps power (if that) even at fairly loud volumes in anything but peak sections of material
                  Exactly. Another thing to figure in is the distortion vs. power output curve. Tha amount of distortion varies with power output, with a sharp increase around the point of maximum power. You want to buy an amp big enough for your needs so that you don't run near this point.

                  I'm not saying that you need a copy of this curve before you can buy an amp, but just to keep it in mind if you're trying to buy the smallest amp you can (i.e. saving a few bucks).
                  Danish

                  Comment

                  • JazzGuyy
                    Member
                    • Nov 2003
                    • 31

                    #10
                    In theory at least the maximum power rating for speakers is supposed to represent how much continuous power the speakers can take, not just peak power. Now continuous is not hours on end but is so many milliseconds or seconds (I unfortunately don't remember exactly what the value is but it is supposed to contrast with momentary peaks lasting very small fractions of a second -- I suspect a Google search can get you the exact info).

                    Interestingly, I think you are far more likely to have problems with high power situations lasting for extended periods of time with movies than with music. Some explosions and like sound effects go on for extended times in movies. Music peaks tend to be more short-lived. Of course, simply turning up the volume all the way and listening to metal probably means all peaks all the time and you could expect almost any speaker with a high powered amp feeding it to blow.

                    Comment

                    • bleeding ears
                      Senior Member
                      • Nov 2004
                      • 435

                      #11
                      Ok guys, so too many watts at very high volumes could do damage.(overpowering)?

                      Also too low a wattage at very high volumes could do damage. (underpowering)?

                      Ok, so having power in reserve is great, but also keeping the volume at a safe level is the secret it seems. So but how loud is too loud, 90db, 100db?



                      I know if smoke starts coming from the speaker I have gone too far, but I would prefer to pickup the hints before I need to call the Fire Dept. LOL


                      Is it when things start to sound annoying in the highs?

                      Or is it when the bass is so strong that you think the drivers are going to jump out of the box?

                      I think I know the answer Both right!

                      Eg see the explosion in Teminator 3 (scene 12 or 13) where Arnie cuts open his chest and throws the power cell out the window of the car into the desert, it explodes like an atom bomb! WOW! check it out awesome.
                      You can almost feel the debris hitting you in the face.

                      PS I take no responsibility for blown speakers or subwoofers if turned up too loud, LOL.

                      My old Kenwood receiver (claimed 5 x 110 watts) shut down on this scene once, but it was at house demolition volume levels. LOL

                      Thanks again guys, looks like I will just have to use some commonsense (staying off the booze will help) and keep the volume to sensible levels with a quality well but not excessively powered amp.

                      I think a Rotel 250 watt class d amp should do the trick. LOL

                      I just have to wait until they make one at a price competitive with analogue amps.

                      PS My wife and kids (and neighbours) will also appreciate me keeping the volume to sensible levels

                      Pete :T

                      Comment

                      • purplepeople
                        Senior Member
                        • Aug 2004
                        • 242

                        #12
                        I tend to use the sensitivity rating of a speaker for this type of calculation.

                        Take my cheap little Tannoy studio monitors with a fairly common sensitivity of 87dB/W @ 1m. These speakers require 128W to deliver 108dB @ 1m. They have a two power ratings, 50W continuous (RMS) and 100W program (peak), which is only a 3dB difference for the amplifier. Since the max power rating for the speaker is 100W, then you are looking at around 107dB before distortion makes things awful.

                        For these speakers a 250W amp has enough headroom to blow down both my apartment and the neighbour's. I just so happen to be driving them with an antique Marantz receiver at 33W RMS... or about 102dB SPL at max volume. I don't know what the headroom of the amplifiers are but it doesn't matter anyway since I've never had the volume up beyond around 75% (and only once just to make a point).

                        One more thing... the most likely reason your Kenwood shut down is because it ran out of stored energy in the power supply. Most of these new receivers cannot deliver 100W RMS through all channels. Look at the power draw on the back near the cord. At 100% efficiency, a 5 x 100W amp should draw 500W. Even with a 90% SMPS and 90% Class D ICs, the receiver should draw at least 600W. Most do not. A basic test when I go shopping.... just look at the back.

                        ensen.
                        Those who claim to be making history are often the same ones repeating it...

                        Comment

                        • whoaru99
                          Senior Member
                          • Jul 2004
                          • 638

                          #13
                          Originally posted by purplepeople
                          Look at the power draw on the back near the cord. At 100% efficiency, a 5 x 100W amp should draw 500W. Even with a 90% SMPS and 90% Class D ICs, the receiver should draw at least 600W. Most do not. A basic test when I go shopping.... just look at the back.

                          ensen.
                          While in theory this would be nice to be able to do, we really don't know the test conditions for which the back panel power consumption is given so comparisons between manufacturers (or maybe even different models) may or may not be valid. Here's one example.

                          In the service manual for one of my amps is given all the technical specifications. This amplifier was marketed in several different geographical areas of the world with subtle differences for each market such as the input voltage, power cord, etc., but as far as I can tell, the vast majority of the amp circuits are the same including output devices, power supply capacitors, and rail voltages.

                          In the service manual, the power output rating is given as 250wpc @ 8 ohms for all markets, however the back panel rating varies considerably as in very nearly 3:1.

                          For this amp, rated the same power output in all markets, input current consumption (back panel number) varies from 600 watts, to 850 watts, to 1100 watts, to 1700 watts. Interesting, yes?

                          So what does it mean? Not really sure except that back panel ratings are not necessarily reliable indicator in the comparison of the receiver/amp power.
                          There are some things which are impossible to know, but it is impossible to know which things these are. :scratchhead:

                          ----JAFFE'S PRECEPT

                          Comment

                          • Sim reality
                            Senior Member
                            • Aug 2005
                            • 173

                            #14
                            I have not done this personally but usually you will burn out a tweeter far sooner they you will break a woofer.

                            The reason I say this is that gauge of windings on the tweeter are a lot smaller relative to the windings on the woofer and don't have as much mass (metal or magnet) to dissapate heat and therefore build up heat a lot faster (there isn't as much mass to use as a heat sink in a tweeter in general). This means the most common way for a tweeter to fail (asside from someone physically damaging the dome) is to burn out.

                            Woofers on the other hand have more mass to use as a heat sink so it's method of failure will most likely be more physical (like the spider or surround becoming unglued). But on well build speakers this is very rare (I have heard it on cheap subwoofers and you can't really tell until something breaks... Probably because it was so loud it hurts, so I wasn't paying attention).

                            Most likely you will only encounter clipping over overdriving because the costs involved (you wouldn't buy a $10 000 amp to drive $1000 speakers) and the space you are trying to fill (unless you were really cheap and trying to fill a hall full of sound).

                            Comment

                            • purplepeople
                              Senior Member
                              • Aug 2004
                              • 242

                              #15
                              Originally posted by whoaru99
                              ...back panel ratings are not necessarily reliable indicator in the comparison of the receiver/amp power.
                              No... for comparing between units, but for determining if the ratings are even close to truthful. I've seen enough equipment that actual used less power than the claimed output, the equivalent of a perpetual motion machine.

                              ensen.
                              Those who claim to be making history are often the same ones repeating it...

                              Comment

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