8. dB Relationships
First, we need to understand that the dB (deciBel, or 1/10th of a Bel) is a relative measurement.
In other words, it doesn’t mean anything without a reference of some sort. If someone says, “did you hear that show last night? It was so loud, it was probably 110 dB.”
Of course, the person is probably referring to 110 dB SPL (sound pressure level), but without the SPL, there is no reference.
There are also electrical references like dBv, dBu, etc., and it’s important to understand what they mean.
The other important concept about dB is that it is on a logarithmic scale (powers of 10). This means that if something is 10 dB more than something else, it is actually 10x the power! Interestingly, for us to perceive something as “twice as loud” as something else (a perception of SPL) we actually need 10x the power to achieve that effect.
A 3dB increase represents twice the power but only sounds “slightly louder”. So it truly boggles the mind to think about huge changes in dB, such as “the reverb tail was 60 dB down after 2.4 seconds”.
This means that 2.4 seconds after the last note ended, the sound level was reduced in acoustic power by 1 million times.
You knew I’d bring this up! One of the main problems we all face is dealing with ground loops and the resulting audio problems, namely hum and/or buzz.
The basic concept is this: if there is more than one “path to ground” with different resistances, then there is a ground loop and the likely result is buzz.
I strongly recommend reading up on this subject in the Yamaha Sound Reinforcement Handbook and also possibly attending a SynAudCon workshop on hum, buzz and grounding.
6. RF Frequency Coordination
Many wireless microphone products have made this task easier the past few years. Some systems auto-coordinate, and some have “wizards” that step an operator through the process.
But I still believe it is important to understand what is happening “under the hood”.
And, frankly, most larger-scale systems at pro events are carefully hand-coordinated using specialized software.
Skilled operators can eek out a few more solid channels by using their superior knowledge and experience versus simply relying on a machine to do it.
Several manufacturers offer courses or workshops on the subject, and most are also more than willing to answer questions on the phone. Take advantage of these resources and you’ll be better off going forward.
5. Inverse Square Law
Like dB relationships, this is an important fundamental concept of acoustics that has powerful ramifications. In basic terms, the law is states: for every doubling of distance from the source (in free space, i.e., no reflections) the acoustic power is reduced by 6 dB (4x).
Mainly, this is important to understand within the context of coverage, the amount and type of loudspeakers needed, and the resulting amount of amplifier power required.