We know that our assertion that a 550K Supercharger is necessary for proper hi-fi reproduction seems incredible, so we’d like to explain the science behind it.

How loud should musical peaks be?

Several years ago, John Atkinson, editor of Stereophile, measured, from a normal audience position, the peak level produced by a small symphony orchestra in a concert hall.  He measured peaks of 109dB to 110dB.  One of the top recording engineers in the world, Tony Faulkner, regularly measures 113dB to 116dB peaks from large symphony orchestras.  Rock music is even louder. Please understand that these levels are on musical peaks, and not average continuous levels.

If a hi-fi system is to be realistic, it should be able to achieve realistic peak levels at a normal listening position.

How do I go about getting reasonably realistic peak levels from my hi-fi system?

Theoretically, this is quite easy.  Take a loudspeaker of a given sensitivity, and connect it to an amplifier powerful enough to produce an accurate musical peak level. Unfortunately, reality is far more complex, and expensive, than theory.

Loudspeaker sensitivity and listening position

All loudspeakers’ sensitivities are quoted at XXdB at one metre for 2.83 volts. This sounds straightforward but, of course, nobody listens to their speaker at one metre. The average listening distance from a loudspeaker is around 3.5 to 4 metres.  This is where the fun starts.

Sound pressure level from a loudspeaker reduces by 6dB for each doubling of distance.  This is highly significant.  If a loudspeaker were rated at 87dB sensitivity (in other words, you get 87dB of level for 2.83 volts input) at one metre, then at four metres, you have 12dB less level.  This is huge amount of sound pressure level difference.

Again, many people don’t understand the significance of ‘just a few dB’ in power terms.

Amplifier power and dB Watts

The vast majority of people have no idea of the practical connection between watts and dB watts.  Let us enlighten you. Watts are simply a measure of an amplifier’s heating power. There is no intuitive relationship at all to listening level measured in dB.  Ignorance about the practical connection between watts and dB watts is one of the biggest causes of the problems of the business.

When we explain the basic relationship between watts and dB watts, you might begin to understand why amplifier manufacturers are anxious to sweep it under the carpet.  Essentially, each dB step in sound pressure level requires a 25% increase (approx) in power.  A 3dB increase requires double the power.  This sounds incredible, but it is true.  Perhaps now you might glimpse why amplifier manufacturers are anxious that you don’t look at amplifier power in terms of what the amplifier actually does with music.  Below is a chart which converts watts to dB watts.

    30W                  15dBW
    40W                  16dBW
    50W                  17dBW
    63W                  18dBW
    80W                  19dBW
  100W                  20dBW
  125W                  21dBW
  158W                  22dBW
  200W                  23dBW
  251W                  24dBW
  316W                  25dBW
  400W                  26dBW
  500W                  27dBW
  631W                  28dBW
  795W                  29dBW
1000W                  30dBW

 

How to put together a dynamically accurate system

Once you have converted amplifier power to dB watts, it is pretty straightforward to work out how much power/loudspeaker sensitivity you need to achieve a given peak level.

1. Convert amplifier power in watts to dB watts.
2. Add the amplifier power in dB watts to the loudspeaker sensitivity in dB.
3. Deduct the listening position attenuation (between 7dB -12dB).
4. You now have your system’s peak level ability at your listening position.

 

The results are pretty shocking, aren’t they? They show that the large majority of hi-fi systems are incapable of delivering musically accurate peaks.

Slide Rule

You can also use the enclosed slide rule for this calculation.  The OK/green area starts at 106dB, which is quite a lot less than you would expect to hear in a concert hall.

We think that a top quality hi-fi system should be able to deliver a 110dB peak. An adequate hi-fi system should be able to deliver half that level, a 107dB peak. And to be helpful, I suppose a system that delivers 1dB less than that could still be called hi-fi.  That’s how we got to the green section starting at 106dB.

But my 50W-100W amplifier seems to sound okay

One of the most confusing aspects of all this power/loudspeaker sensitivity stuff is that it doesn’t seem to offer an explanation of how lower-powered amplifiers seem to offer a ‘room-filling sound’.  The apparent paradox arises because of a phenomenon called reverberant field.  This is the sonic field created between the loudspeakers, and it is made up of the sound produced by the hi-fi system plus echoes and other resonances caused by room irregularities, which linger for a few micro-seconds.  Paradoxically, the more distortion an amplifier produces, the richer that reverberant field sounds.  When the reverberant field is enriched with distortions and non-linearities, which then reverberate, this creates the illusion of fuller, richer sound.  Even more paradoxically, a higher-powered amplifier, which is not limiting or clipping, will sound quieter then the inferior amplifier which is distorting regularly.

However, it is beyond dispute that the smaller amplifier will be incapable of ever, under any circumstances, producing a significant dynamic attack.  In our opinion, dynamic attack is vital to the realistic reproduction of music.

The 550K Supercharger

It is for this purpose that we have designed the Supercharger.  It will increase the power of any amplifier from 50-200W to 550W plus. This means that the dynamic range has been increased up to 10dB.  This is a vast increase that will improve the whole sound perspective of the hi-fi system.