[Russell Dawkins]

Antony Michaelson, designer of Musical Fidelity gear and an unusually straight talker, it seems, said this in regards to the question of power requirements, and with reference to the amplifier the dealer was mentioning to the OP. I can't link to it, because I cant find it online anymore, so will have to paste the entire message. Moderator notify me if this is too long and I'll shorten this to an excerpt and send out the complete text to anyone PMing me for it.

I'm posting this because I have seen precious little written regarding expressing power requirements as a function of our tolerance of clipping. It should be added that this makes sense of the notion that an amplifier's behaviour in recovery from clipping is a key factor in determining its sound quality since, according to this information amps are routinely clipping far more often than is realized.

A letter from Antony Michaelson
 
Dear Fellow Music Lover,
Many customers ask me about the design aims of my products. They are particularly puzzled by how Musical Fidelity can strongly promote the merits of high powered amplifiers such as the 550K or 750K whilst on the other hand producing low powered amplifiers such as the A1. I’d like to try and explain my ideas.
First off, it is not uncommon for companies to produce a wide range of products with vastly different performance potential and technologies. Look at Mercedes. At the bottom of their range they make the Smart car and at the top they have their AMG black range. Similarly with BMW. At the bottom they have a Mini City diesel and at the top their M Series. Look at cameras. Canon, Nikon or Fuji all produce very small budget “happy snappers” at the same time as producing super quality top end products.
There is no philosophical problem with that. People accept that the design ideals of the most expensive products filter down to their entry level range.
Musical Fidelity follows exactly that idea. The philosophy behind all our product designs is the same. Our aim is to give maximum value for money and superb performance at any particular price-point.
Accuracy and realism.
I strongly believe that with an ordinary high quality loudspeaker of about 87dB sensitivity you’ll need about 500 watts to avoid any clipping or limitation. I cannot stress strongly enough that this assumes that you are using the system at a healthy, quite loud, listening level. If you listen quietly or are in a small room or sit close to the loudspeakers, the high power figure is irrelevant. My point is that if you want accuracy and realism the amplifier should never clip or limit.
How can you judge a loudspeaker, CD player, a particular disc or any other component if the amplifier is clipping or limiting? I don’t see how this can be possible.
 
Keith Howard’s research.
Keith Howard is an experienced technical journalist. His research has confirmed that 500 watts power is a good level for a properly neutral system. He also suggests that if you really want no clipping, that you would need even more power. His position certainly appears to agree with ours but there is more to his research. After finding out how much power he thought the system should have, he then set out to find out how much clipping would be subjectively acceptable without much apparent loss of neutrality.
After a lengthy experiment, Keith found that about 3dB of clipping did not cause much upset. This equates to 250 watts.
To summarise the above: if you want to be sure of almost complete accuracy and neutrality you need an amplifier of 500 wpc (or more) but 250 wpc will be acceptable for most people most of the time. A little inaccuracy never did anybody any harm.
Accuracy and impressionism.
A properly designed high powered amplifier such as the 550K or 750K will be highly accurate and faithful to the original recording. It won’t clip, limit or distort driving almost any loudspeaker to the full dynamic range of the recording. This is what I call accurate.
On the other hand as you come down in power the likelihood of the amplifier clipping increases so that, in my opinion, there is a direct correlation between reducing power and decrease in musical accuracy.
Once you are below 100 watts clipping (with my previous points taken into account) is a regular feature. It follows that the dynamic reproduction is no longer neutral, accurate or low distortion. Once you’ve reached this area subjectivity becomes far more relevant. Each amplifier has a unique clipping/limiting characteristic when paired with a particular loudspeaker. Nobody can pretend that the reproduction is accurate, all it has to be is convincing.
This is the true background to the A1.
 
Okay let’s get to the nitty gritty of the A1.
Some people find it almost impossible to grasp that I can put forward the above case for high power but still produce an amplifier like the A1 which has only 30 wpc. It’s like this. Almost as soon as an amplifier drops below 250 wpc, clipping and limiting will become more and more of a feature of the reproduction. In my book that means as the power reduces the inaccuracies increase.
Once you’re down to below 100 watts amplifiers will be clipping regularly. At this point reproduction is inaccurate. Now the amplifier design is rather like an impressionist picture. It cannot be a photographically accurate representation of the recording but somehow has to create the impression of the musical performance. At this level the limitations of the amplifier have to be accepted as a constant and the design has to be created in order to give the most convincing illusion of musical accuracy.
Now to the A1. Yes it doesn’t have much power and yes it’s clipping regularly (but not much more than any other amplifier below 70 or 100 watts) but we have accepted its power limitations and have decided to engineer it to produce a convincing, beautiful, musical experience.
When I listen to the A1, I am completely blown away by it. It has an apparently sweet, subtle, delicate sound which seems to make something of a nonsense of my high powered ideals.
However, as soon as a you switch to an amplifier which has enough power not to be clipping, it is immediately obvious what you have been missing. The point is that whilst listening to the A1, its ability to project and create musical illusion is so strong that I don’t object to its power limitations. In my world, that’s job done.
Let’s get realistic and accurate.
In my opinion the beginning of any properly realistic accurate amplifier is enough power so that it very rarely clips. That power rating is about 250 wpc. Enter the A5.5 and A1008. Both these amplifiers are engineered to produce very accurate high quality sound. They have ample power, very low distortion and produce a sweet sound that appears in contradiction to their high power rating. The thing about high power rating is that if the amplifier is well engineered it won’t sound powerful. Actually quite the reverse a properly designed amplifier will almost never clip or distort. To inexperienced ears it will sound unexciting and undynamic. Actually what these inexperienced listeners can identify is the harmonic enrichment created by clipping. It’s ironic isn’t it? Only when an amplifier is clipping or limiting can they pick up the sound and confuse distortions and non linearities for what they call rhythm incisiveness and richness.
Over the years I have had endless frustrating run-ins with reviewers and hi-fi salesmen about the accuracy of what they’re hearing. When I have taken them a proper, high powered amplifier to use, their immediate reaction was that it was “dull” or “undynamic”. What they were hearing was completely faithful and accurate but what they wanted (or perhaps expected) was the usual clipping and limitation. Very, very, very frustrating.
How to create a super performance system.
If, like me, your quest in hi-fi is musical accuracy and realism then the only way is to have 500+ wpc so that it’s almost impossible to clip or limit the amplifier. Then your loudspeakers can sing the music.
To make a really superb electronic chain, I strongly recommend our A1 CD as the primary signal source. It uses the Philips CD Pro2 and has great technical performance. It has a fabulous, neutral, clean sound. If money is no object the A1008 CD Pro is a bit better.
After the A1 CD Pro should come our A1 fully balanced preamp. This is a super performing, genuinely fully-balanced preamp. Most so-called balanced products are nothing of the sort. What they have is a balanced input and balanced output but the electronics between is single ended. The A1 FBP is fully balanced from beginning to end. Even though it’s in modest casework the circuitry inside is, pretty well, as good as you can get. Not surprisingly so is the sound.
Couple the A1 FBP to a 550K (used in power amp mode) and you have a really extraordinary amplification system. This system will drive any loudspeaker to any reasonable level you might require. It’s really great. I know it’s not the most expensive, or the biggest, or the flashiest but my ears tell me that I’ve hardly ever heard a better electronic system.
If money is very tight (and it’s always tight for me!) but you still want to get an ultimate system and don’t mind sacrificing facilities, I recommend that you use try our X-CanV8 as the preamp to drive either the 550K or 750K. I know it sounds like an extraordinary idea but stay with me for a minute on this one. The X-CanV8 has the same gain as any of our preamps. It has a single ended Class A tube front end with an ultra low output impedance (below 1 Ohm). If you don’t need loads of inputs, a big flashy box or a high price tag then the X-CanV8 used as a preamp (you can easily get an adapter which plugs in the headphone socket) makes a fantastic preamp at a very competitive price.
 

 
If you want even more, then our fully balanced 750K is a revelation. For many years I’ve had a kW750 at home because, in my opinion, I’ve never heard a better amplifier. When I substitute the 750Ks I really can’t decide between the two of them. The 750K’s stereo placement, imaging and (I know this is a ludicrous word but here goes) ability to make the music breathe is really arresting. On the other hand the kW750 power amp seems to exercise an iron grip on the loudspeaker and maybe (or then again maybe not) has a slightly more extended bottom end. The point of the matter is that either of these amplifiers is, in my opinion, as good as I’ve ever heard anywhere.
Musical Fidelity’s aims.
I am proud of Musical Fidelity’s aim of making the best quality performance product at a competitive price. Many hi-fi enthusiasts simply cannot understand that equipment can be modestly priced and yet offer state-of-the-art performance. I don’t think they would ever want to hear what I’ve got to say. If, like me, your religion is music and all you want to do is to get the best possible reproduction then give our stuff a good hard listen and try to forget its modest price. You may well end up feeling the way I do about it.

 
 

[2bigears]

    well,  i have had a kw750 for some time now.  i have brought other amps into the system , and taken them out. the big ass 2 box MF amp has sounded good to me from day one.  i'm glad i bought it.  with the tube pre, it sounds solid and right. power and headroom are good as far as i can tell. 

[Wayner]

I don't think so, Wayner. Look at headphones. They barely need any power. Know why? They're right next to your ears, not because they're efficient or inefficient. So you're partially right. Room size is important to consider, BUT how much power one needs to reach certain SPLs  (at the listening position) depends on how close or far the listening position is. It isn't like the sound from our speakers shoots straight into our ears (from more than a foot or two away), the way it does with headphones. One could have a HUGE listening room, but if they only sit 2-3 meters away, they may not need tons of power. You only need tons of power if you're trying to energize the entire space. Also, power requirements DO depend very much on how dynamic the listening material is. Even if a person sits 2-3 meters from their efficient speakers, if their amp doesn't have enough headroom, and they love listening to classical at high levels, transients will surely be blunted. There's no opinning around this stuff.

It's not important how close or how far away your are, unless you are in a very large music venue. An Amp with about 150WRMS will suffice in almost every event. This discussion has nothing to do with headphones, so lets keep that for another topic.

The best thing you can do to improve a system is to introduce a sub-woofer. It can enhance the listening environment without over powering it with huge dynamics, especially in a smaller listening environment (which most of us listen in).

[Tyson]

Another way to deal with power and clipping is to have efficient speakers.  Considering that 3db worth of volume cost double in terms of power, it's easy to see that a 750 watt amp might be necessary for an 87db efficient speaker (very common rating in hifi).  But you can cut that in half for a 90db efficient speaker - 375 watts gives you the same headroom.  And cut that in half again for a 93db speaker, you only need 187.5 watts.  My speakers are 96db efficient, so I would only need 94 watts. 

As an amp manufacturer, you have no idea what type of speaker your amp will be hooked up to, so best to overbuild it like crazy in order to handle worst case scenarios (like 87db or less efficiency, and very low impedance).  But as a consumer, you know exactly what speaker the amp will be hooked up to.  So you can choose an amp based on your speakers.  I don't need a monster amp for my speakers, so I don't have one.  Some people do.

[Wayner]

A 750 watt amp is common? You are out of your mind.......

[DaveC113]

It also depends on amp type, I have 94.5 dB sensitive speakers and both a 5 wpc SET and a 375 wpc class D amp.

The SET only reveals it's limitations at listening levels that are fairly loud, and even then clipping isn't as big of a deal vs a SS amp because of nature of clipping on a SET amp is not as "hard" as it is with SS amp. So with an SS amp you can't tolerate clipping as much as you can with a SET.

However, at high volumes the D amp is certainly more dynamic and clean sounding, the comparison makes it very obvious where the SET's weak points are...

Which amp is better? Totally depends on what you're listening to and at what volume.

[Freo-1]

The problem with high efficiency speakers isat they tend to deviate from a flat frequency response.  There are very valid reasons that many of the speakers that are considered to be in the upper class of audio reproduction are of lower to mid efficiency levels (84 to 87 db/w). A lot of the high efficiency speakers lack lower bass, and can be a bit ragged. 


I'm not saying they all are like that.  What I am saying is that it's hard to find ones that are neutral across the entire frequency spectrum. 

[RDavidson]

It's not important how close or how far away your are, unless you are in a very large music venue. An Amp with about 150WRMS will suffice in almost every event. This discussion has nothing to do with headphones, so lets keep that for another topic.

The best thing you can do to improve a system is to introduce a sub-woofer. It can enhance the listening environment without over powering it with huge dynamics, especially in a smaller listening environment (which most of us listen in).

Wayner, sorry, but you're wrong. Listening distance makes a HUGE difference in SPL's at the listening position. My example of headphones is ENTIRELY relevant, if not a PERFECT example of how distance from the speakers plays a major role. Just because it doesn't fit your argument doesn't negate facts. Put your speakers right next to your head and see how loud you have to turn the volume up. Now move 3 meters away and see how much more you have to crank the volume knob to reach the same SPLs. Why do you think speaker manufacturers specify their sensitivity ratings (ie how loud a speaker will produce its range of sound) in decibels at X number watts (1 watt per industry standards) over distance (1 meter per industry standards).

Yeah, a subwoofer helps energize the room and can alleviate the need for a large amp to produce bass through the main speakers.

[RDavidson]

You need enough power (amongst other things) to drive the speakers that are housed in your room, to the desired volume you enjoy while playing the music you wish, without clipping.

Since the variables above are so many, it's impossible for anyone to tell you what is the correct answer in your particular and specific case. What's really needed is for you to measure your amp's output to see if you ever clip it under the above conditions. Not practical for most people to do unfortunately. If it were, I suspect more people would realize that they run underpowered amps.

+1 And a lot of people may also find that they don't need / use nearly as much power as they believe. It's a balancing act that is going to be different for everyone's individual needs / habits / preferences.

[DaveC113]

The problem with high efficiency speakers isat they tend to deviate from a flat frequency response.  There are very valid reasons that many of the speakers that are considered to be in the upper class of audio reproduction are of lower to mid efficiency levels (84 to 87 db/w). A lot of the high efficiency speakers lack lower bass, and can be a bit ragged. 


I'm not saying they all are like that.  What I am saying is that it's hard to find ones that are neutral across the entire frequency spectrum.

Yup, this is unfortunately true. My favorite speakers are in fact medium efficiency 3-ways but they cost $30k and up. 

[RDavidson]

The problem with high efficiency speakers isat they tend to deviate from a flat frequency response.  There are very valid reasons that many of the speakers that are considered to be in the upper class of audio reproduction are of lower to mid efficiency levels (84 to 87 db/w). A lot of the high efficiency speakers lack lower bass, and can be a bit ragged. 


I'm not saying they all are like that.  What I am saying is that it's hard to find ones that are neutral across the entire frequency spectrum.

Yup, there's really no free lunch anywhere. That's why I like speakers of all types. All types can do a good job of balancing compromises.........and let's face it, all speakers are a compromise in comparison to live performance.

[Pneumonic]

+1 And a lot of people may also find that they don't need / use nearly as much power as they believe. It's a balancing act that is going to be different for everyone's individual needs / habits / preferences.

A balancing act indeed that is made even more complicated due to the fact that very few people are in position to actually measure their amps performance to see if it is functioning properly (operating linearly) or not under my above noted conditions.

To make matters even worse.  Some of us employ reactive speaker loads (instead of magnetic ones) which very few amp builder's design their amps around.

In my case, 300 w/ch barely turn my speakers on; just south of 1kw and they sing gloriously.

[mcgsxr]

I guess it really does depend.

I am currently running my Totem Sttaf on a NAD 325BEE.  So that's a roughly 88db efficient speaker, with a 50wpc integrated.  I listen at around 6 feet.  According to an app on my iPhone, I peak just under 90 db for 90% of my listening.

So I guess I am routinely using somewhere around 2-3 wpc to drive my tunes in my room.

[Early B.]

It doesn't make sense to buy an amp based on the efficiency of your current set of speakers. Let's be honest -- we're audiophiles and we change out gear faster than we change underwear. Instead, I prefer to buy an amp that can handle anything I throw at it right now or anytime in the future. My amp handles 300 watts at 8 ohms and 6oo watts at 4 ohms. I don't care what the sensitivity of my speakers are (or whatever future speakers I plan to buy) because I'm fully confident that the amp can handle it without breaking a sweat.  More power is better than less power.

[werd]

This is from a post on similar thread in the AVS forums:

You do realize you necroed and quoted a 7 year old thread?   . Nothing wrong it but it was pretty good.

[I.Greyhound Fan]

I need this Pivetta Opera amp, then I will have enough power-

http://www.higherfi.com/audio_amps/1

[clpetersen]

No, it's not that at all. It's all about speaker efficiency. Then it's about the room size and what listening levels you listen to. Almost every one of your statements is wrong, IMO.......

Yes, speaker efficiency is where it starts as I did above, from there it is by desired dynamic range, background ambient, and listening position.

Start with speaker efficiency, say 90 dB. This means 90 dB of sound pressure power from 1 watt of input power measured at 1 meter. I think most reading this know this, but from here you can get everything.

Next you need know how quiet the room is, typically 50 dB, but 40 dB is achievable (this from Xiph.org). Around 25-30 dB you will start to hear the hum from a nearby lightbulb. If you don't hear your lightbulbs, your room is above 30 dB ambient (0 dB in this case is the limit of human hearing).

To hear a sound in a 50dB ambient room, you need 53 dB of sound energy from the speaker (3 dB above ambient to 'register' on you ears)
A 1 meter, this requires -37 dB down from 1 watt (53-90 = -37); this is 200 uW.  If you want 60 dB of range (classical music, without clipping) you will need 20 dB of additional gain above 1  watt (50+60 - 90), so 1 watt becomes 100W (at one meter).  Move 2 meters away, double the distance, and increase by 4X, or 400 watts. Sit three meters away in a larger room, and you will need 900 watts of amplifier power.

If you had a very quiet room, say 40 dB ambient, then the 400 watts requirement becomes 40 watts, and the loud transients won't actually be painfully loud, just really loud.  A 96 dB efficient speaker in a 40 dB room will need just 10 watts at 2 meters to be as (relatively) loud as 900 watts driving a 90 dB speaker in a larger, slightly noisier room.

So it really varies.

Start with speaker efficiency and ambient room noise, everything else follows and is straightforward.   But most people don't need that much dynamic range. From  a survey of popular music, even the widest range acclaimed albums had less than 20 dB of range (16 dB from Dire Straits, Bother in Arms, for example)

[clpetersen]

You do realize you necroed and quoted a 7 year old thread?   . Nothing wrong it but it was pretty good.

Actually the AVS thread is still current, but started a while ago. It seems the necro worked.

BTW, it was my own posting from a week ago in AVS. Perhaps I should have stated that.

I came this forum, looking at the Hypex Ncore class D amps. Looking for some more power (possibly) to occasionally listen to some really loud music from about 2.5 to 3 meters away. Perhaps I should just slide the chair closer. It was instructive to go through the exercise, but I am not looking at 900 watt amplifiers; our house is already heated.

[Freo-1]

Yes, speaker efficiency is where it starts as I did above, from there it is by desired dynamic range, background ambient, and listening position.

Start with speaker efficiency, say 90 dB. This means 90 dB of sound pressure power from 1 watt of input power measured at 1 meter. I think most reading this know this, but from here you can get everything.

Next you need know how quiet the room is, typically 50 dB, but 40 dB is achievable (this from Xiph.org). Around 25-30 dB you will start to hear the hum from a nearby lightbulb. If you don't hear your lightbulbs, your room is above 30 dB ambient (0 dB in this case is the limit of human hearing).

To hear a sound in a 50dB ambient room, you need 53 dB of sound energy from the speaker (3 dB above ambient to 'register' on you ears)
A 1 meter, this requires -37 dB down from 1 watt (53-90 = -37); this is 200 uW.  If you want 60 dB of range (classical music, without clipping) you will need 20 dB of additional gain above 1  watt (50+60 - 90), so 1 watt becomes 100W (at one meter).  Move 2 meters away, double the distance, and increase by 4X, or 400 watts. Sit three meters away in a larger room, and you will need 900 watts of amplifier power.

If you had a very quiet room, say 40 dB ambient, then the 400 watts requirement becomes 40 watts, and the loud transients won't actually be painfully loud, just really loud.  A 96 dB efficient speaker in a 40 dB room will need just 10 watts at 2 meters to be as (relatively) loud as 900 watts driving a 90 dB speaker in a larger, slightly noisier room.

So it really varies.

Start with speaker efficiency and ambient room noise, everything else follows and is straightforward.   But most people don't need that much dynamic range. From  a survey of popular music, even the widest range acclaimed albums had less than 20 dB of range (16 dB from Dire Straits, Bother in Arms, for example)

Classical music in general has a lot more dynamic range than rock/pop (can be up to 40 db).  That is why I own ATC speakers with the super linear driver, so as to take advantage of the ability to replay the wide dynamic range cleanly. 

[Diamond Dog]

The problem with high efficiency speakers isat they tend to deviate from a flat frequency response.  There are very valid reasons that many of the speakers that are considered to be in the upper class of audio reproduction are of lower to mid efficiency levels (84 to 87 db/w). A lot of the high efficiency speakers lack lower bass, and can be a bit ragged. 


I'm not saying they all are like that.  What I am saying is that it's hard to find ones that are neutral across the entire frequency spectrum.

Agree. As to power requirements, my speakers are manufacturer-rated @ 84dB although a couple of reviews have called that number "optimistic". I have run them w/ 150 watts per side and with 600 watts per side and even at sane listening volumes, they are two different listening experiences. Count me in for great big stupid gobs of power.

D.D.