Decibels and Distance Loss
Decibels confuse people at first, and for a good reason: they don't behave like ordinary numbers. They are a logarithmic scale — a way of describing a very wide range with small, manageable figures — which also means a change that looks tiny on paper can be large in reality.
Which version of the formula you use depends on what you are measuring. Power ratios, like amplifier watts, use ten times the log; voltage and sound-pressure ratios use twenty. The shorthand worth memorising is that +3 dB doubles the power, +6 dB doubles the voltage or the sound pressure, and it takes roughly +10 dB before most people will call a sound "twice as loud." That last figure surprises people, but it reflects how hearing works — our ears compress loudness, so a perceived doubling costs ten times the power, not two.
A decibel on its own means nothing until you say "compared to what," and that reference is baked into the unit's name. 0 dBu refers to 0.775 volts, 0 dBV to 1 volt, and 0 dB SPL to 20 micropascals — about the quietest sound a healthy ear can detect. dBFS is the odd one out: it is referenced to the loudest level a digital system can handle, which is why it only ever reads zero or below.
Distance changes level in a way you can predict. A single point source spreading into open air follows the inverse-square law: every time you double your distance from it, the level falls by about 6 dB. A box rated 100 dB at 1 m — the reference every spec sheet uses — is at 94 dB by 2 m, 88 dB by 4 m, and 80 dB by 10 m. This is simply how sound spreads out into space, and it explains a frustration every engineer knows — the front row is overwhelmed while the back row strains to hear. Pushing the system louder does not close that gap; it only punishes the front. The real answer is to spread the sound out, which is what delay towers and fill speakers are for. Line arrays are the clever exception: they couple into a tall, cylinder-like wavefront that sheds energy more slowly, closer to 3 dB per doubling through their working range.
You don't fix distance with volume — you fix it with placement.