How LOUD is LOUD ?
To fill a space with water, you'll need more water for a large hall then for a small room. It turns out that this principle is not much different when filling a space with sound. To reach the person in the middle of the space, you'll have to shout more in a stadion then in your kitchen back home. However, if you turn up the playback level, your whispering will not become shouting. And vice versa, turning the shouting down in playback level doesn't turn it in whispering. Making murmuring louder, doesn't make it more intelligible, it is just LOUD murmuring. However loud whispering isn't whispering any more either. For your personal voice, you (should) know how much energy you spend to know that you are still whispering. For alien sounds this information is missing. Yet you need to know how loud your loud is.
This is where the K-System comes in very handy. It will enable you to adjust your playback levels such that your loud will be loud, yet not too loud. Bob Katz made a fine proposal to define the Reference Level for audio playback. In a small room you'll hear the same sound impression as when playing that same recording in a larger space. The energy needed to get the similar impression will vary of course. However, your ears will hear about the same.
How is it done?
If you think of photography, things become clear in a flash. When isolating an object into a picture, it is difficult to tell afterwards how large the original object was.
By including a human into the same frame, it will immediately show how large or how small the original object actually is.
So what we need is a human reference to include in an acoustical
Thanks to Bob Katz we do have such reference in the form of the K-System reference.
Adjusting your playback system to the human K-system reference is very easy (Bob is always 83dB tall :-)
You' ll need a sample of the reference signal on CD and a noise level meter in your hand.
Set to slow C weighting, and adjust your playback level so that your noise meter indicates 83dB Spl per channel or 86dB Spl when played on the two channels simultaneously.
That is all there is.
All CD productions mastered by Klankschap contain a hidden track with the appropriate K-System reference signal. That makes it very easy for the end user to adjust the playback level for that CD. Just start the playback of the first rack and rewind into the negative time. You'll hear a pink noise signal over your speakers. It has to sound at 83dB Spl per channel in slow C weighting. The sound pressure meter that you need is nothing fancy and worth the investment.
There are three flavours of K-System. K-20, K-14, K-12. For your side of the story, nothing changes. You still align the reference signal to the 83dB Spl. What you will notice is that the recording of the first, will provide you with more headroom then the latter. Or in popular terms, the difference between soft and loud will be large in the first case then the last. There is more space for the peaks in the music. The acoustic image becomes more open.
The K-System was designed to set the playback level for loudspeakers, not for headphones. It is possible however to use the system to set the levels for headphones aswell. To do this, first set the levels or the loudspeakers in your room. Then match the level of your headphone to that level by listening with one ear to the room and one ear through the headphone. Once you hear the signal in the center, you have an approximation of the k-reference. Write down the positions of the level dials for future use.