How much amplifier power do you realy need?

[Confused]

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 a Devialet event at Oxford Audio, when Devialet's Chief designer 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 my little Devialet providing the thundering bass power.  

[Ralf11]

if the amp don't clip, you must acquit 

[psjug]

I don't know...  I looked on a scope playing that track into 8-ohm, 87dB speakers.  I turned it up about as loud as I could stand it and peaks were only about 25V.  I think 100 watts is good enough for me.  I do wish I had clipping indicator though.

[sandyk]

3 hours ago, psjug said:

I turned it up about as loud as I could stand it

 

How many people normally play music at a level as high as you can stand ?

 That's a recipe for premature deafness .

 I also have speakers that are the same sensitivity as yours. At typical domestic listening levels with TV Audio from Movies etc. the power output level rarely exceeds 1W !!!

 

 

[psjug]

43 minutes ago, sandyk said:

 

How many people normally play music at a level as high as you can stand ?

 That's a recipe for premature deafness .

 I also have speakers that are the same sensitivity as yours. At typical domestic listening levels with TV Audio from Movies etc. the power output level rarely exceeds 1W !!!

 

 

Don't know if you bothered to watch the video in the OP, but if you had then you would know that I was making the case that many hundreds of watts are not required, at least in my case.  Of course average power at normal listening is very low, and also does not say much about what peak power you need.  Care to offer anything on that?

[sandyk]

31 minutes ago, psjug said:

Don't know if you bothered to watch the video in the OP, but if you had then you would know that I was making the case that many hundreds of watts are not required, at least in my case

Perhaps I didn't make it clear enough, but I was actually supporting you.

 I have previously had DIY amplifiers of 100W/Channel and 240W/Channel, but in my domestic situation I have never gone close to pushing my DIY Class A 15W/ Channel to anywhere near it's limits. Although capable of pure 15W in Class A it can also go to >30W into 4 ohms in Class AB.

[psjug]

25 minutes ago, sandyk said:

Perhaps I didn't make it clear enough, but I was actually supporting you.

 I have previously had DIY amplifiers of 100W/Channel and 240W/Channel, but in my domestic situation I have never gone close to pushing my DIY Class A 15W/ Channel to anywhere near it's limits. Although capable of pure 15W in Class A it can also go to >30W into 4 ohms in Class AB.

In that case, thank you very much for your support!  Ha ha.

 

I am still trying to wrap my head around the peak power numbers shown in the video, since it seemed that they were not playing at very high volume.  I guess the room is pretty large, though.

[botrytis]

My Pioneer M-22 Class A 30 WPC amp is plenty for me with all the speakers I own, including my Wharfedale Linton Heritage.

[STC]

Ideally, it should be 4 times of the continuous power of the speaker. Although, amps could go 3 or 4 times of the RMS, it is always recommended to get a power amp at least twice the maximum power handling of the speakers. 

 

https://www.crownaudio.com/how-much-amplifier-power

[fas42]

3 hours ago, sandyk said:

 

How many people normally play music at a level as high as you can stand ?

 That's a recipe for premature deafness .

 I also have speakers that are the same sensitivity as yours. At typical domestic listening levels with TV Audio from Movies etc. the power output level rarely exceeds 1W !!!

 

 

 

What an amplifier needs to be able do is "effortlessly" - that is, with no obvious subjective distortion - produce the peak levels that the track has encoded; in previous decades this was beyond the scope of nearly all power amplifiers, I gave up trying to find a unit, any unit, on the showroom floor that was engineered well enough to do this.

 

These days things are much better - one can find examples without too much difficulty; progress has been made. Which means that one can use the full rated power, or more accurately, the full voltage swing to deliver clean sound, at a high gain setting.

 

Which is not the same thing as playing a modern, highly compressed pop track at elevated gains. This outputs average intensities of sound which very quickly reaches dangerous levels of exposure - the ears start ringing, to warn you to back off ...

 

[Melvin]

7 minutes ago, STC said:

Ideally, it should be 4 times of the continuous power of the speaker. Although, amps could go 3 or 4 times of the RMS, it is always recommended to get a power amp at least twice the maximum power handling of the speakers. 

 

https://www.crownaudio.com/how-much-amplifier-power

 

Except in the SET/high-effeciency loudspeaker world. Always exceptions.

[STC]

14 minutes ago, Melvin said:

 

Except in the SET/high-effeciency loudspeaker world. Always exceptions.

 

It doesn’t work that way. It depends on the desired loudness level at LP and speakers efficiency/sensitivity. 

 

Even in a typical room playing where the peaks could hit 100dB, the minimum recommendation is from 15W. 

 

Technical data

Size	230 x 150 x 130 (HxWxD)
Efficiency	100 dB/1W/1m
Long term power handling	100 W continuous; 1000 W peak (10 ms)
Recommended amp power	from 15 W sinus/4 Ohm
Weight	620 kg per System
Room size	from 40 m²

[GregWormald]

All specs should ideally be measured. Relying on a manufacturer's PR machine is not necessarily wise.

 

IIRC:

Take the efficiency of the speaker (generally xxdB/watt @ 1 metre). [eg. 88dB]

 

Work out the power required at your listening position. Sound pressure attenuates as the SQUARE of the distance.) [Listen at 3 metres=9 watts for 88dB]

 

Work out how loud you want the LOUDEST transients to be. [orchestra=115dB, so say 106 dB in your room]

 

Each 3 dB over the attenuated level at your listening position requires a doubling of the power.

 

Therefore: 106-88=18dB, 18÷3=6. THATS 6 DOUBLINGS of 9 watts--9-18-36-72-144-288-576. 576 watts needed or 288/channel (for 2 channel stereo).

 

[psjug]

15 hours ago, GregWormald said:

All specs should ideally be measured. Relying on a manufacturer's PR machine is not necessarily wise.

 

IIRC:

Take the efficiency of the speaker (generally xxdB/watt @ 1 metre). [eg. 88dB]

 

Work out the power required at your listening position. Sound pressure attenuates as the SQUARE of the distance.) [Listen at 3 metres=9 watts for 88dB]

 

Work out how loud you want the LOUDEST transients to be. [orchestra=115dB, so say 106 dB in your room]

 

Each 3 dB over the attenuated level at your listening position requires a doubling of the power.

 

Therefore: 106-88=18dB, 18÷3=6. THATS 6 DOUBLINGS of 9 watts--9-18-36-72-144-288-576. 576 watts needed or 288/channel (for 2 channel stereo).

 

This seems to make sense, but the attenuation factor does not consider room reflections so results in an overestimate of required power.  I really don't know the peak SPL I would want in short bursts.  Is 103dB more appropriate?  Or should I allow for more than 106dB for the occasional short duration peaks in very dynamic music?  Obviously this makes a huge difference in your calculation.  I think it is really hard to know unless you try the equipment in your room, and that's where a clipping indicator would be helpful.

[Ralf11]

Go for All the Gusto You Can Get

[Kal Rubinson]

7 minutes ago, Ralf11 said:

Go for All the Gusto You Can Get

What's the unit of measurement for gusto?

[mansr]

1 hour ago, Kal Rubinson said:

What's the unit of measurement for gusto?

Beaufort scale?

[Ralf11]

in the US, the unit of measurement is the "Schlitz"

 

I believe that European countries, with help form the better breweries in the PNW, NYC, Boss-town area, and even Denvar, have blocked any "progress" towards a SI unit.

[fas42]

The topic of how much amplifier power is needed is as good as an example as any of how conventional methods of testing are completely inadequate, with regard to being able to relate to the subjective experience. What provides highly listenable SQ are electronics which are operating in a "zone of comfort" at all times, irrespective of whether a peak level is currently being played.

 

Which is not the reality for many power amplifiers - when asked to deliver sound levels which are getting closer to the specified maximums, the circuits are very close to, or actually enter unstable, non-desirable operational conditions; one may still get distortion numbers out at these times which seem reasonable, but which hide circuit behaviour which is a long way from being how the designer conceived it working.

 

Part of it is inadequate power supply design, part of it is being reliant on feedback "fixing everything" - simplistic analysis of what's going on stops understanding of how the whole behaves, and one ends up with unsatisfactory SQ ... some time ago I did quite involved simulations, testing Spice models of amplifiers much, much closer to real world situations - and it was easy to get examples of the circuitry misbehaving; the amplifier was no longer amplifying, it was trying to recover after entering a non-stable operating status.

 

Which is why the real world workaround of buying an amplifier far more powerful than is theoretically needed "works" ... this amplifier is never provoked into unstable internal behaviour, the circuitry always behaves itself because the demands upon it never propel it into 'uncharted territory'.

[sandyk]

8 minutes ago, fas42 said:

the amplifier was no longer amplifying, it was trying to recover after entering a non-stable operating status.

 

 On a couple of occasions Silicon Chip magazine had to publish modifications to their designs where a few constructors pushed the amplifiers way past their limits, and this happened causing damage to the amplifier.

[audiobomber]

IMO this is a simplistic and deceptive video. Watts per channel is next to useless as a measure of an amp's ability to drive a loudspeaker. Current is what really matters, not voltage. I will forever recall hearing a 40W amp blow away a 200W amp in a store demo decades ago. A real eye-opener.

 

In the video they strapped the amp channels. Monoblocking is for sound reinforcement, not for home stereo; lots of voltage, but compromised current capability, thus inferior SQ. If they had vertically biamped instead, the sound would have improved by leaps and bounds, and the amps would still not have run out of steam. 

 

How about the infamous Apogee Scintilla, which only a handful of amps could handle? One of the most famous pairings was the 25wpc Classe. Most high-powered amps totally crapped out with this 1-ohm load.

 

I have two stereo amps from the same manufacturer rated at 50Wpc into 8 ohms. My speakers are 89dB/w/m, and 4 ohms. Driving the speakers with one stereo amp sounds fine, even at the highest levels I care to listen. Adding the second amp in vertical biamp mode increases sound quality markedly, with improved bass control, soundstage, instrument separation and detail. Watts per channel does not explain the difference in these two setups.

[Ralf11]

Current is what really matters, for the example you chose and some other panel design types (my Maggies for example).

 

Of course, for a conehead speaker you have to have enough current delivery (at all freqs.) to move the motor.  Today, it is usually not too hard to do that.

 

For horns, a small amp will do.

 

- Those are the 3 tiers I would identify.

[audiobomber]

20 minutes ago, Ralf11 said:

Current is what really matters, for the example you chose and some other panel design types (my Maggies for example).

Current matters for cone speakers. My speakers use conventional drivers in MTM configuration, 4-ohms nominal. As described above, doubling the current capability with biamping makes a significant improvement. 

 

My friend has a pair of Nautilus 802's (91dB, 8-ohms),  and two Bryston 3B-ST amps. The store set up his system with the Brystons monoblocked. I reconfigured for vertical biamp and the difference was stunning.

 

Current capability is the reason that even high-power spec'ed domestic type receivers sound wimpy.

[sandyk]

4 hours ago, audiobomber said:

Current capability is the reason that even high-power spec'ed domestic type receivers sound wimpy.

 

 Are you talking about sustained current capability here ? That is mainly a function of the power supply area.

[mansr]

There is a simple relationship between current, resistance, and power. With reactive loads, it gets a little more complex, but not terribly so.