by Michael Orland
I have often drawn
block diagrams illustrating the audio chain in the modern P.A.
system, starting with the sound source, to the microphones, mic lead,
multicore, etc, etc, and finishing with the loudspeaker and its enclosure.
strictly speaking, it doesn't end there. The final link in the audio
chain is the brain of the listener. But I'm no Doctor Huffurrrr so I
can't draw brains so good.
Story Number One:
A mate of mine went to see Accadacca at the EntCent time before last
they were out here. He sat in his seat, looked at all the speaker
boxes and thought "Hold onto your hat, boyo, this is going to be LOUD!".
When the band
finally came on, he was almost a little disappointed. Like, it was
loud. It just wasn't LOUD!!!
When he walks out
afterwards, he turns to his mate and says "Whadja reckon!"
And his mate says "I tu k jab ed" And his ears rang for two weeks.
Two: (I'm assured it's
also true) An Arab oil Sheik purchased a top of the line Ferrari
after being assured that nothing could overtake it. He tore off in it
down the open desert road to check out its top speed. The engine
roared, the car started shaking, he felt the G force pulling him back
in his seat, and he thought "Hoo Hoo! Eat my dust, Jackals! I am
indeed Lord and Master of the highway"
Then he looks out
his side window and sees his mate calmly cruising past, smiling and
waving, behind the wheel of his new Rolls Royce. The Sheik was so
pissed off he threw the keys to a minion as a tip and bought his own
Roller the next day. By the way, apparently when you look up the spec
sheet on a Rolls, under the heading"Amount of horsepower capable
of being generated", you'll find just one word: "adequate"
aspires to own one. -Ed}
To be successful
at engineering sound it becomes crucial to understand the brain of
the average listener you are catering to. And there are so many
variants which influence the brain.
Too much noise can
overload the eardrums, distorting the sound and causing pain. This
pain causes you to wince, partially closing the ears as a defence
mechanism. The brain learns to equate distortion and pain. Even low
level harmless distortion can trigger an involuntary wince.
Circular Quay on Sunday arvo, I can stroll past a busking rap dancer
with a ghetto blaster turned up full and sounding like shit, and
think "That's loud" A little further on I can stroll past
four kids from the Con playing a Mozart string quartet and be drawn
closer, not thinking "loud" at all. When a noise level
meter might measure the string quartet at an appreciably higher
level. Lesson: "Loud" is not something you measure."
Loud" is a subjective concept within the brain of the listener.
I would speculate
that my mate, the Accadacca fan, heard a mix that was clean and
virtually distortion-free. A kick drum that was fat without being
flatulent. Cymbals that went ping. A bass guitar that sounded
accurate without mud. Vocals that were in your face without being
confrontational. His brain did not interpret the overall information
as loud, although the resulting Tinitus made him think it must have
been. It's like if you associate speed with loud Vrooms and shaking
bodies, then it becomes something of a shock to see something simply
I must admit, I
actually find it annoying when potential hire customers ring and ask
me how many watts my P.A.s are. Without wishing to sound smug,
there's only one correct answer to what is basically the wrong
We often receive
faxes from overseas acts who might be using our systems, stating
their requirements. And I can't say I've ever seen "Number of
Watts Required". What they do specify is the level of clean,
undistorted dB SPL required at the mix position.
For beginners, the
letters dB stand for decibels, a unit of measurement which on its own
means little. Decibels are used for making comparisons, and are only
useful once a reference is established.
The letters dB
mean more when other letters follow. Like dBu, which is a measurement
of voltage you may have spotted on your mixing desk, limiters, etc.
And dB SPL which is an acoustic measurement of Sound Pressure Level.
1 dB SPL is
normally thought of as the smallest difference between two
measurements that the brain can discern. So 3 dB SPL becomes three
times that difference. When someone talks about 110 dB SPL they mean
110 dB SPL louder than the understood reference, which is always 0 dB
SPL. By definition, 0dBu is 0.775 volts.
Each dBu of
voltage from your desk equates to one dB of power from your amps,
which then translates to one dB SPL from your speakers.
casually snaps at you that they need your system to be twice as loud,
this would, strictly speaking, require a 10dB SPL boost, requiring 10
times the amplifier power. It really does help to have an accurate
understanding of the jargon used by the professionals if you wish to
work and communicate with professionals accurately.
The whole dB thing
may be a little confusing at first, but the more you work with it,
the more you will establish reference points which put figures into
context and thus make them relevant to your working environment.