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Gentlemen, Musical Fidelity is claiming your endorsement for some imho inaccurate and deceptive statements.From the page linked to below:
"The following are not made up or some marketing company’s weird fantasies. They are scientific fact backed up and endorsed by the foremost technical journalists in the world. In alphabetical order; John Atkinson (Editor of Stereophile) Robert Harley (Group Editor for Absolute Sound, ex Technical Editor of Stereophile. He really knows his stuff and has written books about it), Keith Howard (deeply knowledgeable and experienced Technical Journalist in the field of, well, anything technical) and Paul Miller (perhaps the foremost technical reviewer in the world, current Editor of Hi-Fi News)...."
Musical Fidelity then describes how to calculate the amplifier power required to reach a certain sound pressure level at a certain listening distance, but they omit something very crucial: The reverberant field contribution. The calculations they give are based on anechoic theory, and I'm quite sure Mssrs. Atkinson, Harley, Howard and Miller are well aware of reverberant field contribution. I won't bother quoting the lengthy Musical Fidelity page to show that they left the reverberant field out of their calculations - see the link below. If the reverberant field is taken into account, the calculated amplifier power requirement is roughly halved.
Finally, Musical Fidelity does mention the reverberant field under the appropriate heading of "Semi-Science":
"The reverberant field is different in every room with every loudspeaker but it does have an effect. The reverberant field is the sound which we perceive in front of us and is a result of both the system and its room reflections, non linearities and standing waves. This is how and why small amplifiers can appear to fill the room with sound. What you’re actually hearing is the system, its reflections and standing waves in the room and, most strangely of all, its distortion adding to the reverberant field effect making it sound fuller.
"This is why, in some instances, the systems with small amplifiers can seem to have a fuller reverberant field than high powered amplifiers which are not clipping."
The problem here is that clipping does not result in a fuller sounding reverberant field, nor a fuller sound. Audible clipping shows up as high frequency bursts, reproduced by the tweeter. Tweeters beam at high frequencies so the clipping is going to be more of an on-axis phenomenon rather than a reverberant field phenomenon, and increased high frequency energy is not normally described as producing a "fuller" sound. It sure looks to me like Musical Fidelity is using deception to explain away people's experiences of small amplifiers sounding good in big rooms in contradiction of their earlier exaggerated claims about amplifier power requirements.
I presume that the Musical Fidelity's engineering department has zero control over the marketing department, so I don't take this as a reflection on the quality of their amplifiers - only on the credibility of their propaganda.
John Atkinson, Robert Harley, Keith Howard and Paul Miller - how do you guys feel about Musical Fidelity attaching your names in endorsement of their claims?
Duke
Follow Ups:
In my opinion - and I have communicated this to AM - the reverberant field is irrelevant in these power calculations. Why? Because all the evidence (for example, the power envelope data I generated for 'New Media Metrics' in Stereophile in 2004) points to peak amplifier power being drawn on transients that are very much shorter than a typical room's reverberation time (which determines the build-up of the reverberant field as well as its decay). So the anechoic calculation is the relevant one, and it obviates assumptions about listening distance, room RT, speaker directivity etc.
measurements and bafflegab. But then I have been listening to MF products for over a decade -- it is clear to me that's all they've got to sell because their amplifiers are some of the worst I have heard musically. And sure I may prefer SET but when a $30.00 class T amp destroys thousands of dollars worth of MF marketing in a box (even the MF owner agreed) then it is pretty clear that these guys have no clue.But hey every MF owner I have ever met in person has become an "EX" MF owner. When their $3000.00 integrated A300 I heard against a 15+ year old Sugden A48b (not even close to Sugden's Best) in direct comparison it was clear to me that despite the Sugden's limitations it was obviously the one made by people who listen to music rather than sonic "feats."
Yet another reason to "try before you buy." I assume the MF calculations all assume that people listen to their stereos outdoors -- perhaps in the middle of a large cornfield a few miles from the nearest road or airline corridor . . . and in the winter, when there are no insects to make noise.This seems to me to be another instance of "simplifying" a problem to make it manageable -- that yields useless results. The simplification I'm referring to is the elimination of the effect of the reverberant field on the speaker's response. The reason that it's necessary is not only because of the difference between line and point source drivers but also because of the wide variations of reinforcement afforded by people's listening rooms, the result of size, wall composition, furnishing and so on.
One experiment I've yet to do is measure -- as you did -- the falloff in SPL from 1 meter in front of my speaker to my listening position, using pink noise.
The reality is that most people, for a whole variety of reasons, including the sanity of their neighbors and anyone who shares their dwelling, do not expect to achieve SPL peaks of 105 dB, or even 100 dB.
Then, of course, there is the matter of finding a speaker that produces an acceptable level of harmonic distortion -- especially in the bass -- at anywhere near those SPL levels. Only a few subwoofers can do that. So, even if your amp can produce these kinds of SPLs without clipping, you're already experiencing a spectral shift as your speakers' production of harmonics of the bass frequencies goes way up as you exceed 95 db. That's not accuracy.
And, we won't even get into the comparisons of the dynamic range of most program material vs. what's experienced at a symphony concert.
As for me, if I play symphonic music where the softest passages are above the ambient noise threshold in my house, I should be satisfied if I can reproduce the musical peaks in the program at that same volume setting, without regard to what SPL I'm experiencing.
…and I don't mean you, Duke.Since we're concerned about the accuracy of MF's claims, I'd just like to point out another problem claim that no one, including Duke, has commented on.
The final paragraph in the web page response Duke provided a link to, and the final paragraph of the PDF version of the same page, both state:
"Below are a couple of useful charts to help you in your quest for getting the most music possible from your hi-fi system."
THERE ARE NO CHARTS BELOW THE PARAGRAPH IN EITHER VERSION.
Damn, if they can't get it right about what they're putting on their web page, is it any wonder that they can't get something based on science right?
David Aiken
Take a gander at the "The A5CR power amp and a competitor: a real life value comparison" blurb on their web site (see link). They use power measurements to contrast their A5CR with a $19,000 amplifier that "...received an ecstatic review in the October 2004", said comparison shining a favorable light on their unit which can be had with a $16,000 saving.Interestingly it takes about 20 seconds worth of effort to discover that the competing amplifier is the Halcro dm38, an amplifier that the normally reticent John Atkinson practically wet himself effusing praise upon!
In any event the whole premise of the ad, that a few measurement alone could be used to meaningfully contrast the amplifiers, is to any sensible audiophile a text book case of reductio ad absurdum. This is the sort of foolishness that one expects form the likes of a Bose, not from a manufacturer of quality audio products.
No Guru, No Method, No Teacher
> John Atkinson...how do you...feel about Musical Fidelity attaching
> your name in endorsement of their claims?
In discussions I had with Antony Michaelson on the subject of how much
amplifier power is requried, I did point out that his calculations
were based on the anechoic case, and that the in-room situation will
be different, due to the effects of the reverberant field and the
speaker's radiation pattern. A true line-source speaker behaves
differently in-room from a point-source radiator, for example.
John Atkinson
Editor, Stereophile
I hadn't brought up the line source case, but yes that's definitely a factor, as can be radiation pattern shape with a point source speaker (think relative reverberant energy of MBLs vs Avantgardes).A few years ago I made some in-room measurements of a point source speaker (homebrew mini-monitor) vs a line source speaker (SoundLab M-1). I measured at 1 meter and again back at 8 meters, or three doublings of distance. Anechoic theory would predict an 18 dB falloff over that distance for the point source speaker, and a 9 dB falloff for the line source speaker. Actual measurements showed an 11 dB falloff for the point source and a 4 dB(!) falloff for the line source - both far less than anechoic theory would predict.
This has obvious implications for hybrids like the InnerSounds or Martin Logans, which radiate as a line source at mid and high frequencies and a point source at low frequencies.
Duke
I always thought that the reverberation field is determined by the room and by the speaker-room interaction.
Klaus
This is like finding an ad claiming that Alfred E. Newman is the foremost authority on quantum mechanics, and asking Alfred if he objects to being referred to in this way.
What's your worry? Since Alfred E Newman, last time I looked, was in fact the foremost authority on quantum mechanics, why would he object to being referred to that way?
Bravo Zulu.Nice analogy.
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