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How much amplifier power do I REALLY need?

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  • How much amplifier power do I REALLY need?

    Originally posted by Batears View Post
    Why poor Alan? I happen to be driving a pair of large, efficient speakers that only draw .085 W/ch at a serious listening level.

    There was a recent survey on another audio site on just how much amplifier power was necessary with ones speakers. A test was offered that required a test tone and a multimeter plus some simple arithmetic.

    78% of those that responded required an amplifier of 25W/ch or less and out of those, 43% needed no more than 5W/ch.

    I guess the survey method was correct, forums being forums, it never once got shot down!
    1. It hapened to me that I asked very exerienced manufacturer of top hi-fi ampifiers about the real wattage of energy supplied to loudspeakers at most realistic levels. Most of amateur audio lovers go to some conclusions observing (if they have) analogue or lcds styled on analogue meters, which are slow and indicate average amount of top energy delivered in very long time as for musical signal variation. The matters look completely different if you could see the same measurement done by superfast digital system. How do you think what are the top catched readouts? Two, three times higher? Nope, sometimes much much more.

    2. I also happened to have got a friend who is also amazed (even more his wife) with his 15" co-axial very efficient famous British loudspakers. In the beatifully edited ad printed user manual attached we read:

    "Consult the product specification section within this manual as this clearly shows the acceptable power range for amplifier matching to your speakers. The high peak power handling of ****** loudspeakers permits responsible use with more powerful amplifiers - Please read the Warranty conditions (page 44). As with all loudspeaker systems, the power handling is a function of voice coil thermal capacity. Care should be taken to avoid overdriving any amplifier, as this will cause output overload resulting in ‘clipping’ or distortion within the output signal. This can cause damage to the speakers if done for any extended period. Generally an amplifier of higher power that is running hard, but free of distortion, will pose less risk of damage to the loudspeaker than a lower power amplifier continually clipping. Remember also that a high powered amplifier running at less than 90% of output power generally sounds a great deal better than a lower powered example struggling to achieve 100%. An amplifier with insufficient drive capability will not allow the full performance of the loudspeakers to be realised. Some users may have a preference for low power valve (tube) amplifiers which are below the recommended minimum amplifier power. While this does not cause potential or damage, consideration should be given to musical preferences, maximum listening levels and room size".

    Also in technical specifications:

    "Performance

    Recommended Amplifier Power 20 to 350watt per channel

    Continuous power handling 175 watt RMS

    Peak power handling 700 watt

    Sensitivity 99 dB (2.83volt @ 1 m)

    Nominal Impedance 8 ohm

    Minimum Impedance
    5 ohm


    Frequency Response 18 Hz - 27kHz (-6 dB)

    Dispersion 90 degrees conical"

    It would mean, that in case of your 15" and 15 ohm model, the minimal recommended power for amp should be 40 Watts!


    3. Try please find modern digital recording from last decade of e. g. double-bass jazz player performing solo dynamic passages up to the lowest note possible. I made comparison with weak tube amp and very beefy solid state. Since then no one will convince me the surplus power is not essential while listening more seriously to music from these big elegant cabinets.

    ATB

  • #2
    Video of M40.1 playing dynamic music and small-scale classical music. A look at the amplifier power meters.

    Video to follow in next 48 hours.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #3
      Half the power?

      How much less power does the SHL5+ need than M40.1? Can we assume that it needs about half of the power of the M40.1?

      Also, I must admit that I feel convinced by the logical arguments and musical clips posted in the previous thread. 15W is too little for the SHL5+. But can I keep the 15W tube amp to power my P3ESRs provided that they need less power than SHL5+, they are placed in a small 12m2 room and I don't listen very loud?

      Comment


      • #4
        "Need power"?

        Originally posted by Milosz View Post
        How much less power does the SHL5+ need than M40.1? Can we assume that it needs about half of the power of the M40.1?

        Also, I must admit that I feel convinced by the logical arguments and musical clips posted in the previous thread. 15W is too little for the SHL5+. But can I keep the 15W tube amp to power my P3ESRs provided that they need less power than SHL5+, they are placed in a small 12m2 room and I don't listen very loud?
        Ah ha. We have actually covered this subject in great detail before here.

        Let's look again at the issue of speakers and power.

        Taking your statement ...

        How much less power does the SHL5+ need than M40.1? Can we assume that it needs about half of the power of the M40.1?
        There are two issues with this quote which we absolutely have to nail. It says to me that there is still backwards thinking - the effect coming before the cause.

        So my question to you: when you say "How much less power does the SHL5+ need than M40.1?" what thinking is behind that question? Why should there be any difference? Why couldn't the situation be reversed so that, for example, the M40.1 needs less power. Are you looking at the physical size of the cabinets and deducing that power is somehow related to box size? Or is it number of bass/mid drivers? Or stated power handling capacity in the sales catalogue? Or the fact that M40.1s are used as studio monitors? Or what .....

        The key word here upon which this discussion revolves is "need". Why does a speaker - any speaker need power? What creates that need?
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #5
          Contradictory statements about power?

          We have discussed here in great detail before whether the speaker or the amplifier is really the first in the chain, if the amplifier pushes the power into the speaker or it's the speaker that draws the power out of the amplifer. We agreed that the latter is true, i.e. the speaker is in fact the first, active element governing the amplifier, deciding how much power it "needs" and taking as much as needed, within the limits of the amplifier's power repository.

          Having the above in mind, my amateur thinking is that the physical dimensions of the bass/mid driver or drivers are the main factor that we have to take into consideration to establish how much power the speaker "needs" since the amp has to be strong enough to move the heavy speaker's cones. I have to look at the manufacturer's catalogue anyway, to see effectiveness and impedance rating of the speaker because I cannot tell them by the looks. Finally, I look at the power rating stated by the manufacturer and having in mind that it's estimate only, as the manufacturer cannot know how loud I am listening, what music I like, how big is my room and how far from the speakers I am and therefore can guess only.

          Harbeth states that the SHL5+ works with amplifiers ideally from 25W/channel and its power handling is 150W "programme" (I do not know what the latter means, continuous?) and the M40.1 works with amplifiers ideally from 50W/channel and its power handling is 200W "programme". That is why I stated in the previous post that the SHL5+ is likely to need about half of the power of the M40.1. I might as well be wrong.

          P3ESR has a small mid/bass driver, but it's sealed cabinet and has 83.5dB sensitivity only. It is stated by Harbeth to work with amplifiers from 15W/channel and its power handling is 50W "programme". Nevertheless, there are many people who are of the opinion that it's actually the most difficult Harbeth to drive and actually "needs" as much power as M40.1. Those people say that the SHL5+ is actually "easier" to drive than the P3ESR. I must admit that I'm confused by all these contradictory statements.

          Comment


          • #6
            Back to the microphones

            OK we're jumping ahead. I think we should really take this step by step. Clearly the thousands of words written here alone have not cleared up the confusion.

            My question was about the word "need", as in 'how much power does speaker XYZ need?"

            A) So can I ask this: do we agree that somehow or other, that the music waveform cut into an LP groove, recorded as bits in a digital stream or received over the radio represents the sound pressing on the recording microphone's diaphragm instant by instant?

            B) Would it then follow that in a completely silent and empty studio in the dead of night, that there are no sound waves, nothing pressing on the microphone's diaphragm and as a consequence, no signal at all coming out of the microphone's cable?

            C) Physically, what is that signal from the microphone - what type of energy is it - or from the phono cartridge or at the output of a CD player or streamer or radio tuner? What technical equipment could we use to assess the energy in that ex-microphone/phono/CD/streamer/tuner music signal and in what physical units (kg, Nm, Wb or whatever) would we report that measurement information to others?

            It's absolutely vital that we grasp this.
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

            Comment


            • #7
              Simple explanation

              Your early simple explanation was the best in my view. To re-phrase:

              The user of a hifi system 'demands' a voltage at the speaker when he/she rotates the volume control on their amplifier.

              The speaker effectively says "OK, if you want that voltage across my impedance (drivers and crossover), you must supply this current = (from Ohms law) voltage / impedance). If you can't produce this current then I cannot give you the voltage you requested!"

              The user then says "But my amplifier can provide a maximum of N watts" to which the speaker replies "OK but that will generate a maximum current of only the square root of (N / impedance) amps so the maximum voltage that your amplifier can support with me is the square root of (N x Impedance)."

              Comment


              • #8
                The output of the microphone

                Originally posted by davidlovel View Post
                Your early simple explanation was the best in my view. To re-phrase:

                The user of a hifi system 'demands' a voltage at the speaker when he/she rotates the volume control on their amplifier.

                The speaker effectively says "OK, if you want that voltage across my impedance (drivers and crossover), you must supply this current = (from Ohms law) voltage / impedance). If you can't produce this current then I cannot give you the voltage you requested!"

                The user then says "But my amplifier can provide a maximum of N watts" to which the speaker replies "OK but that will generate a maximum current of only the square root of (N / impedance) amps so the maximum voltage that your amplifier can support with me is the square root of (N x Impedance)."
                That's the ultimate description of the entire amplifier/speaker power game. But it presumes a lot of the non-technical reader, and as we have failed so many times before with what we thought was a simple, basic technical explanation, I'll wager that we'll fail yet again.

                Let me answer my own question, posed in #6 above. If you understand the explanation immediately above this line then you can skip this. If you don't then I suggest investing the time in reading on!

                So to requote myself ...

                Originally posted by A.S. View Post
                OK we're jumping ahead. I think we should really take this step by step. Clearly the thousands of words written here alone have not cleared up the confusion.

                My question was about the word "need", as in 'how much power does speaker XYZ need?"

                A) So can I ask this: do we agree that somehow or other, that the music waveform cut into an LP groove, recorded as bits in a digital stream or received over the radio represents the sound pressing on the recording microphone's diaphragm instant by instant?

                B) Would it then follow that in a completely silent and empty studio in the dead of night, that there are no sound waves, nothing pressing on the microphone's diaphragm and as a consequence, no signal at all coming out of the microphone's cable?

                C) Physically, what is that signal from the microphone - what type of energy is it - or from the phono cartridge or at the output of a CD player or streamer or radio tuner? What technical equipment could we use to assess the energy in that ex-microphone/phono/CD/streamer/tuner music signal and in what physical units (kg, Nm, Wb or whatever) would we report that measurement information to others?
                A) Surely we must agree that the music is encoded onto some varying physical thing that instant by instant captures all and every nuance of the music. If we don't agree this, we have to admit that the recording and reproduction of sound is an impossibility.

                B) Cause and effect. If there are no sound waves in the proximity of the microphone i.e. silence, it must follow that the output of the microphone is equally silence.

                C) There is no theoretical reason why the physical output of the microphone could not be 'encoded' into a stream of, say, daffodil bulbs or peanuts, or grains of salt or ... a magnetic field. In fact, the output of the microphone is that of a varying voltage.

                That is: instant by instant, the voltage that comes out of the microphone plug is a voltage that describes exactly the musical sound waves that passed the microphone's diaphragm at that percise instant.

                If there are no sound waves (silence) around the mic, there is no voltage output from the mic. If the sound waves have high energy (a jet aircraft at 10m) the output voltage will be high. For normal music, the voltage will be within a normal range, rising in voltage as the mustic becomes louder, and falling in voltage as the music becomes quieter. So, we can expect that the voltage from a good quality high fidelity microphone will be perfectly proportional to the sound pressure at the diaphragm, instant by instant.

                OK with this?
                Alan A. Shaw
                Designer, owner
                Harbeth Audio UK

                Comment


                • #9
                  Video of M40.1 and huge amplifier playing loud

                  Let's park the idea of a wiggling voltage perfectly representing the sound waves around the microphone for a moment. Let's look in the real world at how much power we might need to drive a loudspeaker replaying music.

                  Voltage and power are not the same thing. They are definitely not alternative words for each other. They are wholly different phenomena, but curiously, they are inextricably linked together. They don't 'know' about each other but they behave as inseparable twins. Change one, and that change magically impacts on the other and vice versa.

                  Trevor and I were invited to Hilversum, Holland a few weeks ago. The demo room was set-up with M40.1s and some mighty amplification, far beyond the power potential (rating) and price of any amplification I've ever been lucky enough to use. So, we asked to play some music which the staff knew from experience appealed to their customers, and sounded fun and involving on the M40.1s playing loud. And this is what we found when we filmed the experience and observed the power meters. The sound was completely smooth and sweet - there was nothing that gave away the true loudness of power involved, other than the power meters. I fully appreciate why Sony Corp. purchased two pairs of M40.1 recently for music mastering.

                  Be prepared for a surprise. We used the inbuilt microphone in the camera, so the sound quality you'll hear is limited by that.


                  Loading the player ...


                  Hopefully this will make a few memorable points for further consideration. Remember! We, the listener are in command of the volume control, and it is the combination of the music waveform plus the speaker connected to the amp that defines how much power is DRAWN from the amp. For the same volume setting if the speakers are not actually plugged in, there is NO power being drawn (obviously).
                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK

                  Comment


                  • #10
                    A shocking difference in power drawn

                    I am absolutely shocked, not only by the amount of power being continously drawn by the M40.1 but by the enormous difference of power demand between different types of music. Of course I did know that type of music is one of the factors that have to be taken into account when deciding how much power one needs. But the difference between electronic music and string quartet was up to 100 times (sic!) on the same loudness. Electronic music was demanding 500-750W while string quartet demanded 5-28W. Scale of the difference is shocking for me.

                    On the other hand, I have to emphasize that I never listen to that type of electronic music presented that loud. I've got neighbours and listening on that level of loudness in an acoustically untreated room would be a sonic disaster anyway. I think this is true for many music lovers around the world and has to be taken into account as well. We do not live in a perfect world where everyone has a listening studio at home.

                    Therefore, I think that an amplifier powered between 100-200W should be enough to power my SHL5+ in my 30m2. Tell me please if I'm wrong.

                    Comment


                    • #11
                      Sensible power minima

                      Originally posted by Milosz View Post
                      I am absolutely shocked, not only by the amount of power being continously drawn by the M40.1 but by the enormous difference of power demand between different types of music. Of course I did know that type of music is one of the factors that have to be taken into account when deciding how much power one needs. But the difference between electronic music and string quartet was up to 100 times (sic!) on the same loudness. Electronic music was demanding 500-750W while string quartet demanded 5-28W. Scale of the difference is shocking for me.

                      Therefore, I think that an amplifier powered between 100-200W should be enough to power my SHL5+ in my 30m2. Tell me please if I'm wrong.
                      I think an important factor is related to the overall Harbeth sound, a characteristic across the entire Harbeth range. Just as we found at the Bristol show in February, the sound is so sweet and natural that there is no hesitation in playing loud, really loud, if the music, your mood and your neighbour's tolerance are in harmony.

                      That's quite unusual: most so-called quality speakers (especially studio monitors) sound so unbelievably harsh and hard (or out of control in the bass, or both) that when played loud the practical maximum replay level is not in fact the power limitation of the amplifier, it's the listener's ability to bear the harshness of sound; minutes only perhaps. Since listening fatigue is, as far as I am concerned, an absolute no-no, that's not an issue with Harbeths, so for our speakers the practical limit on loudness is not listener forbearance but sheer amplifier power - available watts - up to the limit of the drive unit excursion. More on that later.

                      Yes, I'd agree with you completely. For the normal listener in a normal room listening to music with normal dynamics at a normal distance with normal neighbour issues and having some power in reserve, I'd say 100W is the right sort of practical power reserve. Which, coincidentally, is the power output of the QUAD 405, a great power amp. Even the 405's 100+100W power potential could be all drawn by normal speakers playing pop/rock excitingly loud. As we've seen, 100W is closer to 28W than 700W!

                      I think that I've amply and comprehensively demonstrated that flea powered amps are a very poor choice, regardless of the sweet talk of the marketing romance. Consider the entire human muscle power of an orchestra playing - perhaps 50 lungs and 200 arms - converting the chemical energy stored in muscle tissue into motion, and via their instruments into sound. What sort of bizarre logic is there behind thinking that a 7W micro-powered amplifier could regenerate those sound waves at home with anything like the true dynamic range of the recording?

                      To put it into context, 7W is about the same amount of power as a night light placed into a child's bedroom. Nothing.
                      Alan A. Shaw
                      Designer, owner
                      Harbeth Audio UK

                      Comment


                      • #12
                        Synthetic "noise" of purely academic interest

                        For me, the video keeps quitting at about the 9 minute mark.
                        Is there something beyond more of that dreadful noise in the remaining 3 minutes?

                        While the video demonstrates that, with certain "program material," power demands on an amplifier can be made to be remarkably high, it doesn't really give me a clue as to how much power might be required to reproduce without clipping the peak amplitudes for my typical listening selections.

                        Is there any way you could repeat the demonstration using, say, some Bach organ music or a Liszt piano piece or a Beethoven symphony?

                        Comment


                        • #13
                          Total surprise?

                          I must have had not less surprised expression of my face than Alan had on video above attached when I was presented with similar demonstration first time .

                          It is a pity that full scale symphonic music (big kettle, organ, double basses passages) with sudden "outbursts", recorded in modern high-dynamic technique, hasn't been (or could not be) analyzed. It is even more demanding as for its dynamics - maybe less current surge as in case of those electronic gigs where low frequency region (35-70 Hz ) is very elevated, but can tell more about quality of auditoned amplfier (e.g its real slew rate, timbre of acoustic instruments ....). That is why I love so much my solid state fast monoblocks!

                          ATB

                          P.S. Also presented 40.1 monitors and what they can do in symphonic music! Fabulous real big monitors, period.

                          Comment


                          • #14
                            Real life implications of power requirements

                            This is remarkable indeed, and even though Alan has always said that one needs a lot of amplifier power, I think this was even more than he bargained for. Together with the clipped track that he posted earlier, it also explains why with my move to a rather bigger house, my trusted old Quad 303's 2x45 watts did not sound so good anymore playing larger scale and more dynamic music (even though recapping helped a bit), and all the more so with less sensititive speakers than before.

                            It also explains the American tradition of brutish amplifiers and sometimes more sensitive speakers: by and large their houses are far bigger than in Europe, and particularly in the UK. However, in Europe too our houses and listening rooms have increased in size significantly, with the doubling of per capita incomes during last few decades. In addition, digital sources now provide the wider dynamics and usuable low frequency signals that require huge amplifier power compared to what was needed in the age of vinyl.

                            This has two immediate consequences. The first is that speakers must be able to cope without self destructing. The 40.1's coped nicely, but that is unlikely to be true for the smaller models. The second implies a search for affordable watts. In home audio, about 100 watt per channel seems to be a practical limit in the market. If you want more, you either have to pay through the nose for esoteric north American monoblocs etc, or you have to go the pro audio amplifier route. There is not much in between.

                            One practical way out of both issues is to use a beefy powered subwoofer and a high pass filter. This protects the main speakers, and frees the main amplifier from having to power the demanding lowest frequencies. Interestingly, precisely pro audio amplifiers mostly have built in adjustable high pass filters.

                            Comment


                            • #15
                              Unsatisfied demand for power?

                              The video is very instructive.

                              So for that given electronic track played at that volume (unclipped) the speaker demands that power and so from that I see any amp that could not provide that power but playing at that same volume would simply be clipped.

                              Alan, could you make an estimate as to the volume in the room for that electronic track?
                              Getting to know my C7ES3

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