02/07/2019
An article by a chap called Chris Panks about how sound works at an open air concert. Very interesting.
Regarding festivals and the sound leakage from open air events, I'm surprised I'm the first one who works in the pro audio industry to comment on the noise problem.
It appears to be the only point of contention
Here goes:
First, 'noise' is like 'weeds'. A sound is noise if you don't want to hear it.
Unlike weeds, noise can be imposed on you by others. The feeling of having your privacy invaded is upsetting. We professionals need to understand that.
Those enjoying the music can't feel how invasive it is to some others.
On the technical side, I can tell you what we have and why.
For the sake of clarity in lay terms we'll use the word 'volume' instead of SPL and dB.
In music and sound, an octave is equivalent to eight white notes on the piano. You can have a go at humming up or down a scale. It isn't a great distance - musically.
Follow me - this is important - The accepted range of perfect human hearing covers 10 octaves. Stay with me because I'm going to explain why the BASS is so loud.
Music frequencies and sound systems cover these ten octaves of pitch range. We call it in the trade '20/20' That is 20Hz to 20kHz.
The thing with human hearing is it is very uneven in its response between low notes, mid notes and high notes. We have evolved to benefit from being able to hear high rustlings and tweetings but low and very low frequencies haven't been so important to our survival.
Our brain interprets middle and fairly high sounds easily but tends to discard low and very low.
The amplifier powering the treble speakers can be - for a round figure - 100Watts of power to give a human, a nice, fairly loud, volume to rock along to.
Here's the catch: because our brain isn't interested in lower frequencies and our ear mechanism hasn't evolved to capture them as much, it takes TWICE the amplifier power, for every octave lower, to give a human, the impression that the volume is the same.
The amplifier handling the middle speakers has to be 200Watts.
The amplifier handling the upper bass needs to be 400W.
800W for the bass and 1600W for the sub-bass.
At the concert, the 1600W sub bass and the 100W treble sound nicely balanced.
Here's the second catch. Volume drops by half for every doubling of distance.
The farther away you get, the less you hear - mainly of the lower powered amps, the treble because their short wavelengths powered by the little 100W amp soon disperse.
The mighty bass notes have long wavelengths and are driven through the air by our monsterr 800W amp.
That's why you can hear the bass, miles away.
And there's nothing we can do about it.
If you turn the bass volume down at the venue - let's say giving half the power (it is NOT that simple but this is LAY TERMS) , say 400W, the treble would have to be down to 50Watts.
"Not bad" you may think.
There's another catch - the turning up and down of volume does NOT half or double with the power. This is where the mysterious Decibel rears it's deranged head.
At the gig, turning the treble down to 50W doesn't just half the volume: it slashes it by a ratio that makes it 'sound' like a measly 5W.
You just can't have a performance that quiet. It'd be silly. The thrill of a popular music concert is largely down to being loud. Like having a roller coaster that is 5 feet from the ground - there's no excitement.
I hope my fellow professionals and enthusiasts will understand my need to keep away from the more accurate physics in an attempt to explain a painfully complex thing to our friends and neighbours.
The bottom line is:
Because of the way humans perceive sound, combined with the physics of the way sound behaves, there is no way to have a decent volume at an open air gig without the bass leaking out for miles around.
Even pointing the bass speaker the other way will have zero effect.
Why?
Because of yet another catch . . . . treble sound waves beam and can be pointed where you want them.
Middle sounds spread out quite a lot.
Bass leaves the speaker and spreads out pretty much in a circle - you can't point bass anywhere.
Treble is a hose.
Bass is a burst swimming pool.
Actually it doesn't just go out in a circle - it's a sphere. Its long wavelengths go around walls, over hills and across dales.
There we are. Asking them to turn it down won't work. If you suffer from the noise of an event, you need to put your thinking and energies into a different solution.
Perhaps ask them to move four times the distance away from your house.
