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+--- Thread: How much amplifier power do you really need? (/Thread-How-much-amplifier-power-do-you-really-need)
How much amplifier power do you really need? - Confused - 07-Jul-2019
I found the video per the link below pretty much by accident when searching for something rather different. I have to be honest, I found this to be utterly gobsmacking, I had always suspected that amps needed a little more power than simple maths based on required dB(A) and speaker efficiency would suggest, but nothing like this. The video of the amp's display is a little blurry, but's lets just say that I has mentally parked the decimal point in the display a factor of 10 backwards until it dawned on me what was really going on.
I would say it is well worth 10 minutes of your time to watch.
https://www.youtube.com/watch?v=bRMR9JZ1m0s&app=desktop
So what exactly are the amplifiers measuring? As mentioned in the video it is the peak / tranient power that is captured, so not a continuous average. The amps are CH Precision A1's. This from the CH Precision manual:
Power monitoring. Each power amplifier board is equipped with a DSP that monitors the instantaneous output voltage and current of each M1 channel. Both values are sampled at around 100 kHz, ensuring peak values are properly detected. This circuitry has several purposes: give the user a feedback of the peak power fed to the loudspeakers, and detect malfunctions such as short-circuits or amplifier damage.
As many will know, Harbeth's are not the most efficient speakers you can buy, in fact rather the opposite, the 40.1's are rated at a lowly 85dB/w/1m.
This is another video showing the CH Precision power meters. It is not clear what speakers are used here, but the peak levels are clearly lower than are seen on the Harbeth's. (but still hit the odd spectacular peak)
https://www.youtube.com/watch?v=UP8i8F62OlM
I have to say that when I first viewed the Harbeth clip I was staggered by what I was seeing, this was not what I expected at all. Thinking about it though, it does make sense of some of my past experiences. For example, I first listened to the KEF Blades with a Devialet Expert D240. This appeared to drive the Blades with ease, which is what you might expect. Later, I heard the Blades with a D170. It was terrible. This was not some subtle step back in performance, but a case of the amp not really working with the speaker, dynamics vanished, the bass was a mess. Not good to listen to at all. I remember being puzzled by this at the time. The Blades are rated with a sensitivity of 91dB/w/1m. So for normal listening levels surely you only need 10 or 20 Watts or something? Why should the drop from 240 to 170 make any difference? Based on simple maths re dB(A) levels and power, it did not make sense. However, looking at those figures that the CH Precision amps are displaying, it would seam possible that the D240 was coping with the Blades, but the D170 struggling, with audible consequences.
It also reminds me of the day at Oxford Audio, when Mathieu Pernot stated that his perfect amplifier design would have "infinite power". This seamed slightly absurd to me at the time and I was talking to him about this later in the day. I was making a real world point about the rated power capability of typical speakers. In response Mathieu pointed out that there is no agreed method or protocol for measuring manufacturer quoted speaker power ratings, no agreed standard if you like, so manufacturers tend to give figures that are more like "recommended amplifier power ratings. He then went on to explain that a speaker "rated" for say 50w to 400w, could easily take instantaneous peaks of power way over the 400w "maximum" with ease. OK, try putting that kind of wattage through continuously and heat will generate, voice coils will melt or seize, but very high transient peak power levels are not an issue. For me, knowing (based on maths) that a typical speaker could run at well over 100dB(a) with less than 20W, Mathieu's explanation seamed a little theoretical. Now I have seen the above video, it makes perfect sense. I have always though that higher power amplifiers provide a certain sense of "ease" to the presentation, but I could not really rationalise the science behind what was just a subjective view.
Now I have seen the above video, many things make a lot more sense.
For those interested, this is a link to the track used in the Harbeth video:
https://www.youtube.com/watch?v=XhuJxdaU87I
Playing this at home, I would have to say that it does include some rather extreme bass content, which combined with the Harbeth's low efficiency does perhaps go some way towards explaining the rather high power figures on that CI amp. I can also see that my habit of using one or two electronic tracks when auditioning kit might have some merit, I can't see any other music genres providing quite the speaker / amplifier challenge of something like the Pan Sonic track linked above. (plus, I quite like electronic music)
Although even with miserable YouTube 128kbs streaming, it does sound pretty awesome with a Devialet providing the thundering bass power.
(I'd imagine it would be a good one for the Phantom bass freaks too, give it a go!)
RE: How much amplifier power do you really need? - Jean-Marie - 07-Jul-2019
You have a perfect illustration with the phantoms gold, which deploy a peak power of 4500W for 108 dB SPL.
Of course that peak power is for low bass and required even more because of SAM.
Jean-Marie
RE: How much amplifier power do you really need? - thumb5 - 07-Jul-2019
Interesting post, @Confused. It agrees nicely with what Roger Sanders says in his white paper (which I know I've linked to before). To pick some salient points:
Quote:You will find that conventional, direct-radiator (not horn-loaded), magnetic speaker systems of around 90 dB sensitivity, require around 500 watts/channel to avoid clipping. More power is needed in larger rooms or if you like to play your music more loudly than most.
The key point I'm trying to make is that audiophiles usually are using underpowered amplifiers and are therefore listening to clipping amplifiers most of the time. When an amplifier is clipping, it is behaving (and sounding) grossly differently than its measured performance would suggest. This is because we always measure amplifiers when they are operating within their design parameters -- never when clipping. A clipping amp has horrible performance, so attempting to measure it is a waste of time.
In other words, we usually listen to an amplifier when it is clipping and we measure it when it is not. This is why amplifiers sound so different than their measurements would imply. It is not that measurements are wrong, it is simply that we are listening and measuring different conditions.
Quote:It should now be obvious why objective measurements don't seem to give much insight into the performance of amplifiers. It is not that objective measurements aren't accurate (they are superb), but simply that we don't usually operate amplifiers within their design parameters. So we aren't listening to them at the power levels where they operate properly and where their measurements are meaningful.
Quote:To have a truly high-fidelity music system therefore requires very powerful amplifiers. Amplifier power is the single most important factor in choosing an amp. Without adequate power, all amplifiers sound badly. You can pick a clipping amplifier based on it not sounding as badly as another amplifier (tubes usually preferred over transistors), but if you really want clean, dynamic, effortless, and smooth sound, you simply must use adequate amplifier power.
RE: How much amplifier power do you really need? - RebelMan - 07-Jul-2019
Hold the press @Confused the math still holds.
There are several glaring errors with the first demonstration. First, nothing is said about the the SPLs they are producing, perhaps because they didn't measure them. Second, the amplifers are operating in "bridged mode". When an amplifier is operating in bridge mode the load it sees doubles. The Harbeth M40.1's dip below 6 ohms which at first glance would seem like a fairly easy load on the amplifier but that's not the case as the amplifier actually sees 3 ohm dips. Third, the "marketing geniuses" (sarcasm) in the video do not understand or do not clarify what the meters are actually telling. The amplifier may have displayed a 700W peak reading but the marketing geniuses are taking that information out of context, it needs to be qualified. Remember that music is dynamic and at any given time there is a relationship between the power a load needs and the power the load receives. At what load was the 700W produced? Was it at 30 ohms or was it at 3? I venture to say the latter.
The takeaway here isn't about needing more power but rather needing linear power.
THE MATH
How would a Devialet handle the same set of conditions? Working the problem backwards it would see a max load of 350W at 6 ohms, more than most of the units in the line could handle. But is listening to 350W at 6 ohms realistic? Again, they didn't state the listening parameters, so we will. If we assume the listener it positioned 4m away and the amplifier needed to supply 350W into a 6ohm load the SPLs would register a staggering 101.4dB! Keep in mind I am using the Harbeth M40.1's sensitivity level of 85dB in my calculations. The answer is NO, 350W at 6 ohms is not realistic at all. If we limited the power to the max output of say the Devialet 140 what then? The SPLs could reach as high as 97.5dB which is still very high, aka LOUD and also unrealistic as these are reference level volumes and no one in there right mind is going to comfortably listen to their music at these levels.
Taking power into consideration only, the thing to look for is a stable amplifier with linear output. As the load increases so too should the power supplied. The Devialet 170 is measured to deliver very linear power according to HiFi News measurements. The Devialet D-Premier for which the Devialet 240 was patterned after is not, also according to HiFi News measurements. I suspect the beefier power supply that went into the Expert series rectified that for the 240 but it's the same power supply that fuels the 170. It puzzles me why you found the 170 so lacking as compared to the 240 when driving the Kef Blades. I suspect the conditions between listening sessions differed significantly.
By the way, I also reviewed the second video and while I found the outcome more realistic there is still to little known about the setting to draw anything really meaningful from it.
The marketing geniuses are once again WRONG. Most systems do not need lots of power. They need GOOD, CLEAN and LINEAR power and proper testing proves this time and again.
RE: How much amplifier power do you really need? - RebelMan - 07-Jul-2019
(07-Jul-2019, 11:27)thumb5 Wrote: Interesting post, @Confused. It agrees nicely with what Roger Sanders says in his white paper (which I know I've linked to before).
It appears Roger is making some pretty big assumptions.
Once again he, like other marketing geniuses, are taking things out of context. At what point is 500W needed? He doesn’t specifically say. He is also pro solid-state so it stands to reason he would be biased in his remarks. Although I am too, he is making a bigger case against SET amplifiers not other quality solid-state amplifiers making his point less considerable in general. I suppose if I needed a little more confidence in my system I would lean on this white paper too.
RE: How much amplifier power do you really need? - Confused - 07-Jul-2019
(07-Jul-2019, 13:56)RebelMan Wrote: It puzzles me why you found the 170 so lacking as compared to the 240 when driving the Kef Blades. I suspect the conditions between listening sessions differed significantly.
The amps were swapped in front of me, with everything else left unchanged, the same music was used too. The D170 went first, and had been powered up and running for some time, so arguably it had an advantage over the "swapped in" D240.
RE: How much amplifier power do you really need? - thumb5 - 07-Jul-2019
@RebelMan: To be frank, a lot of what you wrote above doesn't make much sense to me. For example:
* What is the distinction you're drawing between "clean" and/or "linear" power and any other kind? Power is a well-defined, single, measurable quantity so in itself it can't be clean, dirty, linear or non-linear. Maybe you are talking about distortion instead.
* Why does it matter "at what load" the power was measured? Power is power.
Your argument based on the loudness of an 85 dB/W (at 1m?) speaker driven by a continous 350 W (RMS) would be valid. But that is not the point: the video is talking about instantaneous power needed to drive the speakers with a faithful signal at music peaks. @Confused helpfully made that clear by quoting the description of the power meters from CH Precision's documentation.
What this discussion revolves around is the crest factor of the music being reproduced. For some uncompressed music this can be over 20 dB, meaning that to reproduce the full dynamic range of the music the amplifier needs to have more than 100 times as much power available (for peaks) than the average (RMS) value for a given volume. This is a good article that goes through the maths.
RE: How much amplifier power do you really need? - thumb5 - 07-Jul-2019
(07-Jul-2019, 14:41)RebelMan Wrote:(07-Jul-2019, 11:27)thumb5 Wrote: Interesting post, @Confused. It agrees nicely with what Roger Sanders says in his white paper (which I know I've linked to before).
It appears Roger is making some pretty big assumptions.
Which assumptions in particular do you think invalidate his analysis?
(07-Jul-2019, 14:41)RebelMan Wrote: Once again he, like other marketing geniuses, are taking things out of context. At what point is 500W needed? He doesn’t specifically say. He is also pro solid-state so it stands to reason he would be biased in his remarks. Although I am too, he is making a bigger case against SET amplifiers not other quality solid-state amplifiers making his point less considerable in general.
As I read it, his analysis about power requirement is based on straightforward, easily-verified measurements and does not depend on whether the amplifier is solid state or valve. Calling Sanders a "marketing genius" is clearly intended to be derogatory, and does your argument no favours.
(07-Jul-2019, 14:41)RebelMan Wrote: I suppose if I needed a little more confidence in my system I would lean on this white paper too.
What exactly are you referring to?
RE: How much amplifier power do you really need? - Confused - 07-Jul-2019
(07-Jul-2019, 13:56)RebelMan Wrote: They need GOOD, CLEAN and LINEAR power and proper testing proves this time and again.
Interesting, can you provide a link to some good examples of such testing. It is good to add proper test data to the discussion.
RE: How much amplifier power do you really need? - Jim_Anderson - 07-Jul-2019
Each step in my audio quest from 170 --> 200 --> 220 --> 440 --> 250 was a definite upgrade in what I perceived as better audio
I am currently playing with the 250 teamed up with a 220 (both Pro Ci) as a dual mono system (until I can get a second 250). I've not shy'd away from turning the system up sometimes to say 95db, and through the upgrades have truly enjoyed what I was getting in that configuration.
I believe I will see the Harbeth's truly shine with the D1000 and look forward to that day.
Jim