As I received an email regarding MF's original Ad and a follow up, I sent a reply asking them the basis for their claims.
No one was more astonished when I actually got a reply from Emma Cleverden. I don't delude myself that this isin any way a unique personal reply but fair play to MF for at least having something ready for the 'outragedMusic Centre' owners emails!
Technical background to our dynamic range/power claims.
This section is slightly technical and may take you a few minutes to read.
We would like to take you through to the basic technical elements that make
up a hi-fi system and explain how they go together.
Loudspeaker sensitivity
Loudspeaker sensitivity is a measure of how much sound a loudspeaker will
give for 1 watt at 1 metre. It is critical to note that the basic measure
of sensitivity is at 1 metre and not at a typical listening distance of
about 10 feet or 3½ metres.
Sound attenuates (reduces) over distance at the rate of 6dB with each
doubling of the distance. At 2 metres distance from the loudspeaker its
perceived sensitivity is reduced by 6dB. At a normal listening distance of
about 10 or 11 feet from the loudspeaker its perceived sensitivity will be
reduced by approximately 10dB.
This is the factual basis for our claims about how much power a system would
need for a decent hi-fi dynamic range. We reiterate that this is not made
up or marketing hype, it is scientific fact.
Loudspeaker sensitivity – is it real?
Regrettably, most loudspeaker sensitivity ratings are not particularly
accurate and are regularly overstated by 2 or 3dB. We have seen several
examples of respected manufacturers’ products specifications overstating
their sensitivity by 5dB or more.
This does not sound like a big deal, but it has tremendous implications for
the power required by the loudspeaker to deliver proper dynamic range.
Amplifier power – confusion reigns.
This is the source of much misunderstanding. Amplifier power is specified
in watts, which are a measure of heating power. They have no apparent
relationship to what we hear, as they are a linear measure. Loudspeakers
(and our ears) perceive things in dB (decibel) steps. These are based on a
logarithmic relationship.
This is the fundamental mismatch between what your ears perceive and how
amplifiers are specified. The solution to the problem is to recalibrate
watts into dB steps. The results are below, in a chart of watts converted
to dB steps. For convenience we have started our chart at 50 watts. These
figures are not made up they are fact.
dBW Watts dBW Watts
17 50 24 251
18 63 25 316
19 79 26 400
20 100 27 500
21 126 28 630
22 156 29 795
23 200 30 1000
As you can see, as soon as you calibrate amplifier power in dB watts, you
get a dramatically different view of what amplifier power really means.
First off, you can see that what looks a large increase in amplifier power,
for example from 50 watts to 100 watts, only gives an increase of 3dB.
Things get really interesting as when you get to higher powers. You start
need vast amounts of power for each dB step. For example, only 1dB
(remember 1dB is the smallest change in sound pressure level that the human
ear can perceive UNDER IDEAL LISTENING CONDITIONS) is the difference between
400 watts and 500 watts. If you really wanted to hear a difference above
400 watts you’d probably need to go to 800 watts (3dB) which should be
audible.
You can see why amplifier manufacturers want to sweep these figures under
the nearest carpet; they make most of their claims look ridiculous as they
predict that most loudspeaker/amplifier combinations will have only limited
dynamic range.
How much dynamic range do I need?
Some years ago John Atkinson (current editor of the Stereophile) made some
measurements of live music using accurate equipment. He recorded 109dB
peaks (brass and percussion) and the quietest was 63dB (solo violin) a
variation of 46dB from the quietest to the loudest moments – a huge dynamic
range.
The question is what sort of dynamic range a really good hi-fi system should
have.
In our opinion, an ability to produce unclipped peaks of 105dB is the
minimum starting point for a really good hi-fi system. You are welcome to
debate different figures, but that is our basic position.
If you listen to small scale chamber music or usually listen at quiet
levels, you will not need the peak capacity we deem necessary. But if you
are trying to recreate the listening experience at reasonable levels, 105dB
peak is not overly generous.
How do you put all this together.
Assuming that you have accepted the scientific facts this is how you
determine what your system can produce.
1. Take your loudspeaker sensitivity (better yet check back to a technical
review to find out what its sensitivity really is). Deduct around 10dB for
the SPL (sound pressure level) attenuation over distance. And then add back
3dB because there are two loudspeakers in the room.
Now you have arrived at the practical, real world, in-room sensitivity of
your loudspeaker system.
2. Decide what peak level you want to achieve. We think 105dB is about
right. Some people think 110dB is more appropriate. It’s up to you.
3. Deduct the result of 1 above from your decision about 2. This is how
much amplifier power you require in dB watts.
4. Use the chart above to translate your dB watts result in to ordinary
watts.
General overview.
None of this is intended as criticism of amplifier or loudspeaker
manufacturers. You could regard it as a criticism of magazines and shops
for not bringing it to your attention. We have been banging on about this
for about ten years and many people have reacted adversely because they
believed it was just marketing hype. This is not marketing hype, this is
scientific fact. Many people do not like the result of a scientific
analysis of their equipment but that does not alter the scientific facts.
People have objected to our position claiming that their system sounds
great. It might. However, you can’t escape the fact that, if they have a
low powered amplifier and relatively insensitive loudspeakers, the system
must be clipping, distorting and limiting regularly, which must dominate the
listening experience. Maybe the listeners like distortion clipping. Well,
each to his own and good luck to them. If you want your hi-fi system to
produce as close an approximation to the real live performance as you can
get, then you must ensure, for a start, that your amplifier is not clipping.
No one was more astonished when I actually got a reply from Emma Cleverden. I don't delude myself that this isin any way a unique personal reply but fair play to MF for at least having something ready for the 'outragedMusic Centre' owners emails!
Technical background to our dynamic range/power claims.
This section is slightly technical and may take you a few minutes to read.
We would like to take you through to the basic technical elements that make
up a hi-fi system and explain how they go together.
Loudspeaker sensitivity
Loudspeaker sensitivity is a measure of how much sound a loudspeaker will
give for 1 watt at 1 metre. It is critical to note that the basic measure
of sensitivity is at 1 metre and not at a typical listening distance of
about 10 feet or 3½ metres.
Sound attenuates (reduces) over distance at the rate of 6dB with each
doubling of the distance. At 2 metres distance from the loudspeaker its
perceived sensitivity is reduced by 6dB. At a normal listening distance of
about 10 or 11 feet from the loudspeaker its perceived sensitivity will be
reduced by approximately 10dB.
This is the factual basis for our claims about how much power a system would
need for a decent hi-fi dynamic range. We reiterate that this is not made
up or marketing hype, it is scientific fact.
Loudspeaker sensitivity – is it real?
Regrettably, most loudspeaker sensitivity ratings are not particularly
accurate and are regularly overstated by 2 or 3dB. We have seen several
examples of respected manufacturers’ products specifications overstating
their sensitivity by 5dB or more.
This does not sound like a big deal, but it has tremendous implications for
the power required by the loudspeaker to deliver proper dynamic range.
Amplifier power – confusion reigns.
This is the source of much misunderstanding. Amplifier power is specified
in watts, which are a measure of heating power. They have no apparent
relationship to what we hear, as they are a linear measure. Loudspeakers
(and our ears) perceive things in dB (decibel) steps. These are based on a
logarithmic relationship.
This is the fundamental mismatch between what your ears perceive and how
amplifiers are specified. The solution to the problem is to recalibrate
watts into dB steps. The results are below, in a chart of watts converted
to dB steps. For convenience we have started our chart at 50 watts. These
figures are not made up they are fact.
dBW Watts dBW Watts
17 50 24 251
18 63 25 316
19 79 26 400
20 100 27 500
21 126 28 630
22 156 29 795
23 200 30 1000
As you can see, as soon as you calibrate amplifier power in dB watts, you
get a dramatically different view of what amplifier power really means.
First off, you can see that what looks a large increase in amplifier power,
for example from 50 watts to 100 watts, only gives an increase of 3dB.
Things get really interesting as when you get to higher powers. You start
need vast amounts of power for each dB step. For example, only 1dB
(remember 1dB is the smallest change in sound pressure level that the human
ear can perceive UNDER IDEAL LISTENING CONDITIONS) is the difference between
400 watts and 500 watts. If you really wanted to hear a difference above
400 watts you’d probably need to go to 800 watts (3dB) which should be
audible.
You can see why amplifier manufacturers want to sweep these figures under
the nearest carpet; they make most of their claims look ridiculous as they
predict that most loudspeaker/amplifier combinations will have only limited
dynamic range.
How much dynamic range do I need?
Some years ago John Atkinson (current editor of the Stereophile) made some
measurements of live music using accurate equipment. He recorded 109dB
peaks (brass and percussion) and the quietest was 63dB (solo violin) a
variation of 46dB from the quietest to the loudest moments – a huge dynamic
range.
The question is what sort of dynamic range a really good hi-fi system should
have.
In our opinion, an ability to produce unclipped peaks of 105dB is the
minimum starting point for a really good hi-fi system. You are welcome to
debate different figures, but that is our basic position.
If you listen to small scale chamber music or usually listen at quiet
levels, you will not need the peak capacity we deem necessary. But if you
are trying to recreate the listening experience at reasonable levels, 105dB
peak is not overly generous.
How do you put all this together.
Assuming that you have accepted the scientific facts this is how you
determine what your system can produce.
1. Take your loudspeaker sensitivity (better yet check back to a technical
review to find out what its sensitivity really is). Deduct around 10dB for
the SPL (sound pressure level) attenuation over distance. And then add back
3dB because there are two loudspeakers in the room.
Now you have arrived at the practical, real world, in-room sensitivity of
your loudspeaker system.
2. Decide what peak level you want to achieve. We think 105dB is about
right. Some people think 110dB is more appropriate. It’s up to you.
3. Deduct the result of 1 above from your decision about 2. This is how
much amplifier power you require in dB watts.
4. Use the chart above to translate your dB watts result in to ordinary
watts.
General overview.
None of this is intended as criticism of amplifier or loudspeaker
manufacturers. You could regard it as a criticism of magazines and shops
for not bringing it to your attention. We have been banging on about this
for about ten years and many people have reacted adversely because they
believed it was just marketing hype. This is not marketing hype, this is
scientific fact. Many people do not like the result of a scientific
analysis of their equipment but that does not alter the scientific facts.
People have objected to our position claiming that their system sounds
great. It might. However, you can’t escape the fact that, if they have a
low powered amplifier and relatively insensitive loudspeakers, the system
must be clipping, distorting and limiting regularly, which must dominate the
listening experience. Maybe the listeners like distortion clipping. Well,
each to his own and good luck to them. If you want your hi-fi system to
produce as close an approximation to the real live performance as you can
get, then you must ensure, for a start, that your amplifier is not clipping.