Here's a decent guideline that I've used when calculating power needed/used. See the information below... Pay attention to the fact that most speakers rate their db-output at 1-meter and your listening position may be 3X that. You have to consider the drop in db from that measured position as well as how much amplifier head-room you need for your personal listening experiences. I also use a db-meter at my listening position and add 7db to the reading to get a good idea as to how much power I'm really using. For example, my speakers are 9-ft from the listening position. At 94db at 1-meter (assuming my speakers' rating is correct) I lose ~10db at the listening position. Adding 3db then since there are 2-speakers in the room I end up with -7db at the listening position. So, starting at ~ 87db (94db - 7db) at the listening position, at 1-watt of power, I need 16-watts of power for 99db sound at the listening position. I have a 10WPC solid-state amp and an 18WPC SET amp and most of my listening is in the 87db - 93db range at my listening position. So I have ~ 3db head-room with the 10WPC amp and about 6db head-room with the 18WPC amp. My 10-watt amp has only 1 output device/channel and is the most detailed and articulate solid-state amp I've ever heard on my system. The more output devices, the greater chance the subtle differences between them may cause subtle but audible differences in the music. High-end/high-quality mfg.'s (with correspondingly high $$$ cost) painstakingly match their output components to reduce this, however it's not perfect. This is one reason I've chosen efficient speakers and lower-powered amplifiers.
I hope this information is helpful to you.
Good Luck in making whatever corrections you need to !
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.
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 like 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 needing 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
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.
