Live sound applies to both the musician and the DJ. The first thing you need to learn about sound is sound itself. What is sound? Sound is nothing more than waves of changing air pressure that cause your eardrums to move. Sound starts with a physical resonant source this could be your vocal cords, a speaker or anything else that makes sound. This vibration causes air to move. And when this moving air hits your eardrum, your eardrum will resonate in proportion with the source.
This is the essence of sound. It takes all three ingredients; a source, a medium to pass it through and something to receive it. OK now let's talk about dispersion. Dispersion is the direction that sound will go, after it has left the source. You'll usually hear the term dispersion in reference to live PA speakers. You know, 90X60, 60X40 and so on. Once sound leaves a piezoelectric or compression driver it needs to be controlled. A horn attached to a driver will do just that. At the base of the horn, is the throat. The throat is a narrow channel that the sound squeezes through. Once the sound leaves the throat, it wants to explosively spread out in all directions. Now it's up to the horn flare to control the angles of dispersion. Some horn designs are better than others though. If you have a 90X60 horn, you would expect that all the frequencies would be dispersed in this pattern. This is not always the case.
The best horn designs that we deal with are waveguides and constant directive or CD horns. These are both designed to disperse all audible frequencies in the specified angles. Waveguides look like round dishes and naturally, they give a cone shaped dispersion. CD horns are what you see in most PA cabinets today. They offer a more horizontal dispersion. Which bring us to phase. Most of you know that when you're wiring a system, it's important to connect positives to positives and negatives to negatives. But what really happens if you don't follow this rule? One speaker will push while the other pulls. The result: phase cancellation! You'll find that some consoles have phase reverse switches on each channel. This is so you can solve phase problems without rewiring.
Think about micing a snare drum on the top and bottom. Even though your cables are wired correctly, since the mics are pointing directly at each other, they're out of phase right from the get go. Flip the phase reverse on the console and your problems solved. A more advanced application. Let's say you have a 60 cycle hum in the system. Take a signal generator set at 60Hz, plug it into a channel, and flip it out of phase so it cancels out the interference. Most of us can tell when sound gets about twice as loud. This a good starting place, but it needs to be more precise. So if you were to break it down into tenths you would have a decibel. The literal translation of "decibel" is tenth of a doubling in volume. Where deci means "tenth of" and bel means "twice as loud". In other words, a10dB increase in sound will seem twice as loud.
Herbert E. Kelly Owner of Crossbones Recording located in Fort Collins,CO and Music and DJ Instructional Media which is a site that offers online music and DJ courses combined with two very unique beat machines and awesome home recording course. So if you or someone you know is looking for online instruction without the cost of time consuming lessons. Please visit my site at http://www.musicanddjinstructionalmedia.com/ I'm always adding new products to this site so visit often it's just a click away.
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