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Feb. 2018
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'How loud?' versus how far you turn the volume control

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  • This is really quite disturbing. It is surely nonsensical for folks to have strong subjective opinions about this or that amplifier when the absolute basics of how the amplifier works are completely misunderstood. And who is to blame? Certainly not the consumer. I am really concerned about this. Unless the basics of 'power' are appreciated then the consumer is setting himself up to be a victim of marketing.

    OK, let's approach this from another direction: back to the car analogy - not perfect, but good enough.

    Imagine the comment from a motorist was ....

    "I'm concerned I might drive too fast and the car goes out of control and crashes..."

    and/or

    "I'm concerned that my fuel economy is so bad..."

    What is the solution to both?
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • Originally posted by Anyfi View Post

      It's not the position I'm concerned about. It's power. The worry that too much power is constantly sucked (as Alan explained) from the amp because the voltage has been attenuated, leading to heat that is bad news for speakers.
      Ah, see what you are saying.

      If I understand it correctly an attenuated signal will require extra (something???) from the amp to reach the same volume at the loudspeaker, what I am suddenly confused by is that the amp needs to provide more GAIN to get that voltage increase however I don't think that affects the actual Watts being delivered to the loudspeaker (that is surely the same for a given loudness). So I think there is a two step process: the amplifier ups the gain (ie the turn of the volume) which results in the same Watt delivery for a given volume at the transducer. So in that case the amplifier or loudspeaker is not being taxed any more or less (heat) at a given output volume???

      All assumptions, trying to understand, I am not an engineer, plainly.
      Getting to know my C7ES3

      Comment


      • Think of it this way ......

        The flow of energy through the air between the speakers and the ear is what we call 'sound'. The 'quantity' of air that flows must be connected to the amount of energy neded to push those waves into the air, which incidentally is surprisingly massive: a 1m x 1m x 1m cube of ordinary air weighs a suprising1.2kg. Amazing isn't it.

        Air might be invisible to our eyes but it has a very appreciiable mass to it. And the speaker cones have to persuade that mass to jump around.

        So, to generate a satisfying sound level at our ears, the speaker is going to have to push sound waves through the 1.2kgm3 of air in the room to reach our ears. The louder we want that sound to be, the more flow of air there has to be and hence, logically, the more energy must be needed to generate the appropriate flow to make a given desired sound pressure at our ears. When there is no sound flow - the hifi is turned off - the air in the room just hangs there limp but still weighing 1.2k per cubic metre, but turn on the system and genuine and real power needs to be applied to the speaker cones to give them enough energy to start pushing agains that mass of air to start the generation of sound waves. Of course, in a vacuum, there is no 1.2kg of air to press against - there is zero atmosphere, and hence there is no carrier medium for sound*.

        So you can forget all about the goings-on inside the amp, attenuators, gain and so on. The issue is that somehow or other, the amp has to have enough power available to motivate the speaker cones to generate the sound waves flow from the speakers.

        It's the same with the car. What comes first: the speed or the use of energy by converting fuel to motion? Of course it's the use of energy according to how hard you press the throttle which, a period of time later causes acceleration of the wheels and hence velocity of the car. In the speaker, assuming that the energy causes the cone to wobble about practially instantaneously, the time delay from cause (cone motion) to perceived change in sound at the ear is the time it takes for the sound waves to flow through the air medium in your room, which is an absolutely predictable 2.9mS per mtr i.e. 344mtrs pe second.

        There is cause and effect in sound generation. The music waveform in the CD or whatever describes the forwards-backwards position of the speaker cones instant by instant which, in a perfect world, would be exactly the same position that the microphone capsule was. The sole purpose of the amplifier is to provide enough energy for the speaker cones to overcome the dead mass of the air in the room to generate an adequate sound pressure at the ear. That is all it has to do, and clearly, if the amp does not have enough power available, it is absolutely the case that it will be overwhelmed by the mass of air in the room and will not be capable of generating loud (lifelike) sound.

        *One of my favourite scened in 2001:A space odyssey is when Dave lets himself into the airlock from the vacuum of space. It is not until there is enough air present in the chamber that we can hear the rush of air, although the motion of air is visible from the moment he enters.
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • Originally posted by A.S. View Post

          Imagine the comment from a motorist was ....

          "I'm concerned I might drive too fast and the car goes out of control and crashes..."

          and/or

          "I'm concerned that my fuel economy is so bad..."

          What is the solution to both?
          A reasonable and skilled driver, a regularly maintained, well constructed and conscientious assembled car, road maps, indicators (rev counter, fuel indicator etc.) to solve the first problem.

          A modern highly efficient engine, adjusted to the weight/ payload can increase fuel economy.

          By the way: given a simple acoustic live recording with a single pair of microphones. If we measure the averaged spl at the microphone, shouldn't the listening level be the same? Do we need specs not only for the equipment but for the recordings? Isn't there an optimum spl for each recording? The acoustic payload?

          Comment


          • Originally posted by Goergenchr View Post

            A reasonable and skilled driver, a regularly maintained, well constructed and conscientious assembled car, road maps, indicators (rev counter, fuel indicator etc.) to solve the first problem.

            A modern highly efficient engine, adjusted to the weight/ payload can increase fuel economy.

            By the way: given a simple acoustic live recording with a single pair of microphones. If we measure the averaged spl at the microphone, shouldn't the listening level be the same? Do we need specs not only for the equipment but for the recordings? Isn't there an optimum spl for each recording? The acoustic payload?
            I would say, in the simplest possible answer, that both relate to the use of the throttle peddle. Too much pressure on the throttle for the conditions and power available and you have a runaway situation, and similarly, too much inappropriate pressure on the throttle peddle for the conditions and you waste fuel.

            The optimum pressure on the throttle, and in the same way the optinmum setting of the volume control both mandate a sensible driver. It doesn't matter if the power available is 500cc or 5ltrs, or 100W or 5000W, what governs the delivery of power to the point of use (the road, or the ears) is the maturity of the users hand or foot. The car doesn't draw more power that it should, it just dumbly converts the amount of fuel squirted into the cylinders into motion. The speakers don't draw more power than they need from the amplifier, they just dumbly convert the energy delivered to their terminals into motion.

            Is it now obvious that a flea powered amp is fighting a losing battle to move cubic metres of air each at 1.2kg to deliver a loud spoun or that a 500cc engine up a mountain road is equally doomed?

            Cause and effect: you want a fast car you need power reseves. You want a loud sound, you need power reserves. Conversely, for 'pottering around' 500cc is adequate as is one or two watts of amp power.
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

            Comment


            • Originally posted by A.S. View Post
              Think of it this way ......

              The flow of energy through the air between the speakers and the ear is what we call 'sound'. The 'quantity' of air that flows must be connected to the amount of energy neded to push those waves into the air, which incidentally is surprisingly massive: a 1m x 1m x 1m cube of ordinary air weighs a suprising1.2kg. Amazing isn't it.

              Air might be invisible to our eyes but it has a very appreciiable mass to it. And the speaker cones have to persuade that mass to jump around.

              So, to generate a satisfying sound level at our ears, the speaker is going to have to push sound waves through the 1.2kgm3 of air in the room to reach our ears. The louder we want that sound to be, the more flow of air there has to be and hence, logically, the more energy must be needed to generate the appropriate flow to make a given desired sound pressure at our ears. When there is no sound flow - the hifi is turned off - the air in the room just hangs there limp but still weighing 1.2k per cubic metre, but turn on the system and genuine and real power needs to be applied to the speaker cones to give them enough energy to start pushing agains that mass of air to start the generation of sound waves. Of course, in a vacuum, there is no 1.2kg of air to press against - there is zero atmosphere, and hence there is no carrier medium for sound*.

              So you can forget all about the goings-on inside the amp, attenuators, gain and so on. The issue is that somehow or other, the amp has to have enough power available to motivate the speaker cones to generate the sound waves flow from the speakers.

              It's the same with the car. What comes first: the speed or the use of energy by converting fuel to motion? Of course it's the use of energy according to how hard you press the throttle which, a period of time later causes acceleration of the wheels and hence velocity of the car. In the speaker, assuming that the energy causes the cone to wobble about practially instantaneously, the time delay from cause (cone motion) to perceived change in sound at the ear is the time it takes for the sound waves to flow through the air medium in your room, which is an absolutely predictable 2.9mS per mtr i.e. 344mtrs pe second.

              There is cause and effect in sound generation. The music waveform in the CD or whatever describes the forwards-backwards position of the speaker cones instant by instant which, in a perfect world, would be exactly the same position that the microphone capsule was. The sole purpose of the amplifier is to provide enough energy for the speaker cones to overcome the dead mass of the air in the room to generate an adequate sound pressure at the ear. That is all it has to do, and clearly, if the amp does not have enough power available, it is absolutely the case that it will be overwhelmed by the mass of air in the room and will not be capable of generating loud (lifelike) sound.

              *One of my favourite scened in 2001:A space odyssey is when Dave lets himself into the airlock from the vacuum of space. It is not until there is enough air present in the chamber that we can hear the rush of air, although the motion of air is visible from the moment he enters.
              Thanks for taking time to explain. I see what you mean now. Loudness is proportional to how much air the cones have to move, and that depends on how much power the amp can offer. So at any given loudness, the power required is the same, regardless where the volume pot is positioned. Correct so far?

              So the only danger appears to be making an amp play louder (move more air) than its power allows. (I now recall your analogy about making a car move faster than it's designed to.) At sensible levels, a properly designed amp is unlikely to be overdriven, and cause mechanical or thermal failure in speakers.



              Comment


              • Originally posted by acroyear View Post

                Ah, see what you are saying.

                If I understand it correctly an attenuated signal will require extra (something???) from the amp to reach the same volume at the loudspeaker, what I am suddenly confused by is that the amp needs to provide more GAIN to get that voltage increase however I don't think that affects the actual Watts being delivered to the loudspeaker (that is surely the same for a given loudness). So I think there is a two step process: the amplifier ups the gain (ie the turn of the volume) which results in the same Watt delivery for a given volume at the transducer. So in that case the amplifier or loudspeaker is not being taxed any more or less (heat) at a given output volume???

                All assumptions, trying to understand, I am not an engineer, plainly.
                Yes, that was what bothered me. I'm not an engineer either, and it seems I misunderstood how amps work (after all these years!).

                Comment


                • Originally posted by Anyfi View Post

                  Yes, that was what bothered me. I'm not an engineer either, and it seems I misunderstood how amps work (after all these years!).
                  Yes, seems in any case no matter what level the signal is at the input, the power output to the speaker is the same for a given volume level, the voltage gain in the preamp step (if it is an active stage) is what increases the level prior to the power stage (the gain in most hifi power amps sections is set to one level, a few like parasound power amps do have variable gain) if I understand (and to repeat myself)

                  If I'm not mistaken the amp designer still has to have sufficient input sensitivity in order to keep the noise floor down, just that many modern amps the sensitivity is too high at the line input.

                  One of my systems uses a dj mixer and a pro power amp, that allows input level adjustment and power amp gain adjustment as well as the actual volume control, it allows me to set the levels so that a close to fully open volume control is around the maximum volume I want to drive the speakers, in keeping the power amp gain as low as needed it actually keeps the noise floor down, best of all worlds.

                  Getting to know my C7ES3

                  Comment


                  • Originally posted by acroyear View Post

                    One of my systems uses a dj mixer and a pro power amp, that allows input level adjustment and power amp gain adjustment as well as the actual volume control, it allows me to set the levels so that a close to fully open volume control is around the maximum volume I want to drive the speakers, in keeping the power amp gain as low as needed it actually keeps the noise floor down, best of all worlds.
                    That's quite a set up. So you reduce input level and gain, and use a fully open volume control? Lower input levels gives us lower noise, if I understand you correctly? I might give that a try.

                    Comment


                    • Originally posted by Anyfi View Post

                      That's quite a set up. So you reduce input level and gain, and use a fully open volume control? Lower input levels gives us lower noise, if I understand you correctly? I might give that a try.
                      At the mixer the input is variable to allow different sources eg cd/vinyl to have same average levels as you switch between them (important in a dj setting, though I use it simply as a preamp) the idea is to have the highest input signal that is not clipped (peaks need to sit below the red leds flashing, so about +6dB on the meter) as this keeps the noise floor down relative to the music. Then you have a master out knob which I keep about 85% open (I think fully open would be ok, again this keeps noise down). Note this is still all before the actual regular volume control.

                      Then what I do is turn the power amp pots right down then turn the mixer volume control (a slider up/down) up to about 90% open (equivalent to the pot on a typical integrated amp/pre amp) and then on the power amp pots open them (on indents) until I reach the maximum volume I want to play at, the lower you open the power pots the lower the noise floor. In practice for domestic medium sensitivity speakers (86dB sens) they are sat at about 10-11 o clock, this gives a good range or usage on the volume control so even half open the volume is only background levels. In my case the mixer (its an inexpensive model)does have quite high floor noise however it only becomes intrusive if the power pots are past 1 o'clock but in PA set up as designed for that would be moot as the loudspeakers would be playing extremely loud.

                      Domestic integrated amps with the problem of poor volume control I think in part because the gain stages are unadjustable at the power amp. Parasound domestic poweramps for eg have a gain knob at the rear that when lowered to say half would reduce noise floor (if it were even audible) an allow more usable range on the preamp.

                      I think with domestic amps the issue isn't the loud cd signal (that keeps noise down) we are simply forced into trying to attenuate it to make up for the problems upstream.

                      In practice I use this set up because its just what I had handy BUT it does give plenty power (400W), excellent volume control ability and the power amps has some dsp to remove subsonics on vinyl which I feel are a massively overlooked problem in domestic audio, oh and a bit of EQ to make bad recordings sound much more pleasing!

                      edit: In practice, limiting the gain pots actually limits the potential power (it is dependant on signal input voltage and pot position), so even though the amp can deliver about 400W into 6Ohms in reality I might be running it more like a 150W unit. The only thing I wonder is if by keeping the pots low if I'm compromising anything by in a sense throttling the power, however the power amp front indicator lights show that even at the loudest I play the compact 7 the leds light at -20dB so way below clipping in any case.

                      I think I have my settings correct but I would be entirely willing for an audio engineer to tell me if anything is awry.
                      Getting to know my C7ES3

                      Comment


                      • Originally posted by acroyear View Post

                        At the mixer the input is variable to allow different sources eg cd/vinyl to have same average levels as you switch between them (important in a dj setting, though I use it simply as a preamp) the idea is to have the highest input signal that is not clipped (peaks need to sit below the red leds flashing, so about +6dB on the meter) as this keeps the noise floor down relative to the music. Then you have a master out knob which I keep about 85% open (I think fully open would be ok, again this keeps noise down). Note this is still all before the actual regular volume control.

                        Then what I do is turn the power amp pots right down then turn the mixer volume control (a slider up/down) up to about 90% open (equivalent to the pot on a typical integrated amp/pre amp) and then on the power amp pots open them (on indents) until I reach the maximum volume I want to play at, the lower you open the power pots the lower the noise floor. In practice for domestic medium sensitivity speakers (86dB sens) they are sat at about 10-11 o clock, this gives a good range or usage on the volume control so even half open the volume is only background levels. In my case the mixer (its an inexpensive model)does have quite high floor noise however it only becomes intrusive if the power pots are past 1 o'clock but in PA set up as designed for that would be moot as the loudspeakers would be playing extremely loud.

                        Domestic integrated amps with the problem of poor volume control I think in part because the gain stages are unadjustable at the power amp. Parasound domestic poweramps for eg have a gain knob at the rear that when lowered to say half would reduce noise floor (if it were even audible) an allow more usable range on the preamp.

                        I think with domestic amps the issue isn't the loud cd signal (that keeps noise down) we are simply forced into trying to attenuate it to make up for the problems upstream.

                        In practice I use this set up because its just what I had handy BUT it does give plenty power (400W), excellent volume control ability and the power amps has some dsp to remove subsonics on vinyl which I feel are a massively overlooked problem in domestic audio, oh and a bit of EQ to make bad recordings sound much more pleasing!

                        edit: In practice, limiting the gain pots actually limits the potential power (it is dependant on signal input voltage and pot position), so even though the amp can deliver about 400W into 6Ohms in reality I might be running it more like a 150W unit. The only thing I wonder is if by keeping the pots low if I'm compromising anything by in a sense throttling the power, however the power amp front indicator lights show that even at the loudest I play the compact 7 the leds light at -20dB so way below clipping in any case.

                        I think I have my settings correct but I would be entirely willing for an audio engineer to tell me if anything is awry.
                        Thanks for the in depth desc. Iíve been curious about mixers. And you might have just tipped me over to get one.

                        Comment


                        • Originally posted by Anyfi View Post

                          Thanks for the in depth desc. Iíve been curious about mixers. And you might have just tipped me over to get one.
                          I use a cheap ($250-300 originally) mixer as it was what I used to connect a source to a big power amp (via xlrs) to drive a pair of cerwin vega a few years ago. I now use for either the p3 or c7 depending on what is where at the time. The cerwin vega would take all the power of the amp, naturally I'm far more careful with the Harbeths, it may seem like insanity to some to run the 3 with a PA amp but as long as you are careful it is not a problem. The only downside to the mixer is that it does have more noise than say my other more standard hifi amp but I'm sure better models have a lower noise floor. For me the beauty of the mixer is just being able to set the gain structure yourself and have some EQ. Eventually I might get some more traditional electronics but to be honest it sounds ok to my ears. Actually a mixer can also be connected to a standard power amp via rcas just via the monitor out jacks. They are very versatile.
                          Getting to know my C7ES3

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