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How Loud is Loud?

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.

Of course, 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.

Story Number 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"

{Clearly Orland 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.

Walking around 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 glide past.

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 question. "adequate".

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.

When someone 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.


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