A Simple Guide to Audio

SECTION 1: The Difference Between A DJ Audio System And A BAND Audio System.
DJ sound systems are different from BAND sound systems in one basic way. A BAND sound system is for "live" audio amplification while a DJ and Dance Club sound system is for "Pre-Recorded" audio amplification. The dominant input device for a BAND sound system is multiple microphones. The dominant input device for a DJ and Dance Club sound system is a CD player or turntable. Since most vocal ranges fall into the "Midrange" category, this is by far the most important area for a BAND sound system. Ironically, the exact opposite is true for playing pre-recorded music from a CD. If you ever look at the equalizer in a DJ system or Dance Club, you will notice that it look like a big V. The extreme lows and highs are raised while the mids are dropped. This is not usually true for equalizers in a BAND sound system since bands want to emphasize the vocals in the midrange area and constantly have to battle feedback caused by the microphones.
SECTION 2: The Components Of A Basic DJ System.
All sound systems need to have an INPUT device. This is the device that creates the sound. There are many steps above this, but this is where we start. The devices that fall into this category are Microphones, CD Players, MP3 Players, Turntables and tape decks. These devices create sound, but not at a level that will drive a speaker so we can hear it. The next link in our chain is a mixer to manipulate the input devices. A very basic mixer might just have 2 volume controls, but the most common mixers have a lot more than that. Since most DJ's want to raise the extreme low's and high's of the dance music, but not for their mic, it is important to have separate EQ for the DJ mic. Ideally you would have separate EQ for each input. The most common form of EQ for each input is a simple bass and treble knob. Most popular mixers also have a dual 7 to 10 band EQ for the output as well. The output of your mixer connects to the input of the amplifier. Most amplifiers have two channels and a volume control for each channel. The output of the 2 amplifier channels connect to your full range speakers. This is a basic DJ or Dance Club sound system.
SECTION 3: A Better Equalizer.
Some people would say that the next step to perfecting your sound system is an electronic crossover, but I disagree. Although I strongly believe electronic crossovers add tremendously to the clarity of your sound system, I think the next step for any DJ would be a better equalizer. In my opinion, if you have no equalizer or even a dual 10 band EQ built in your mixer, the next important step is to get a good dual 15 band EQ that connects to the output of your mixer. You need the flexibility and control that a good dual 15 band EQ offers if you want to make any sound system sound it's best.
SECTION 4: Now Add A 2 Way Electronic Crossover.
Here's what we have so far: a dual CD player and a mic connected to a 19" rack mount mixer with a dual 7 band EQ. The output of the mixer is connected to the input of a new dual 15 band EQ. The output of that EQ is connected to an amplifier with 2 full range speakers connected. After you have a good dual 15 band EQ, then it's time to add an electronic crossover, but keep in mind, this means you have to add another amplifier and more speakers as well. When you add a 2 way electronic crossover, it is usually done to add sub woofers to your system. The output of your dual 15 band EQ connects to the input of this new electronic crossover and the HIGH outputs of this electronic crossover connect to the inputs of the amplifier for your full range speakers. The electronic crossover has another set of outputs for a sub woofer amplifier. You would connect the SUB-WOOFER outputs on the electronic crossover to the inputs of a second amplifier that had one or two SUB-WOOFER speakers connected to it. You can usually adjust the point at which the frequencies split between the full range amplifier and the sub woofer amplifier. Technically you now have a TWO WAY sound system now made up of sub woofers and full range speakers. The signals for each speaker are split before amplification. You still have a PASSIVE (coil & capacitor) crossover in your full range cabinets, but you now have an ACTIVE crossover separating the very low frequencies from ever reaching your full range speakers. 
Crossing over these signals BEFORE the amplifier, in an electronic crossover is much cleaner and safer than using "PASSIVE" (Coil & Capacitor) crossovers inside the speaker cabinet.
Here's why: If you have a 500 watt per channel amp, then your PASSIVE (coil & capacitor) crossover has to do it's job of separating the signal at a very high volume or power level.  This is a job that creates heat. The higher the power of your amp, the hotter your PASSIVE crossover gets. When a coil & capacitor get hot, they let some signals slip through that they shouldn't and this is how you blow horn and tweeter drivers. 
SECTION 5: A 3 Way Electronic Crossover Is Even Better.
The next step would be to replace the 2 WAY Electronic Crossover with a  3 WAY Electronic Crossover. The IDEAL DJ or Night Club sound system would have a 3 way Electronic Crossover and a separate amplifier for each set of speakers. This 3 way crossover has a Sub Woofer output that connects to the input of an amplifier that has one or two SUB-WOOFER speakers connected to it. These Sub Woofer speaker cabinets will typically have 18" woofers in them. The 3 way crossover has a MID RANGE output that connects to the inputs of a second amplifier that powers the MID RANGE speakers. These MID RANGE speaker cabinets will typically have 15" or 12" woofers in them. The 3 way crossover has a HIGH RANGE output that connects to the inputs of a third amplifier that powers the HORNS. These HORN speaker cabinets will typically have compression drivers with titanium diaphragms in them. This "3 Way" system is ideal because you have protected your speaker components the very best way possible to keep dirty signals from getting past over-heated PASSIVE (coil & capacitor) crossovers that lead to burnt drivers. This keeps you from burning out your horn drivers as easily and it makes you system produce CLEARER sound. The sound will be clearer because you have eliminated all coil & capacitor crossovers that can get hot and send distorted signals to your speakers. 
SECTION 6: Loud Versus Pleasing To Your Ears.
This is the biggest mistake I have ever seen DJ's make. They think that having the "Loudest" system is what it's all about. WRONG!!!  There is a HUGE difference between "Loud" and "Pleasing to your ears". How many times have you walked into a club or hotel ballroom to discover that the loud music you heard hundreds of feet away, (the music that actually drew you in the room) sounded horrible, or even intolerable once you were in the room? It happens all the time! Why? Because so many DJ's (and bands too) think loud is all that matters. I can take the IDEAL sound system we designed above and have music that you are not fond of playing at 128db and you will find it pleasing to your ears. I can take the same sound system and play your favorite song at the same 128db, but after I use the EQ to adjust the wrong frequencies up and down, you will want to run out of the room! 
Here's how and why: Distortion pains our brain. Certain frequencies pain our brain. The type of music is irrelevant. It's how it is heard that matters. 
RULE#1. Never play your music so loud that it sounds distorted. This means that you will have to walk out in front of your speakers MANY times during the night to hear for your self. 
RULE#2. Not all songs are equalized in the same manner or to the same standard.  This is even more of a problem now that most of the music played by DJ's and Night Clubs is coming from computers or MP3 players. When music is compressed for mp3 players, you lose the extreme highs and extreme lows and there is NO GETTING THEM BACK! You can use every sound processor or sonic maximizer out there and they may make your compressed music sound better, but it will NEVER sound as good as it did before it was compressed. Period.  Did you know that a top of the line cassette deck can play music with a broader frequency range than compressed music on an mp3 player? It's true. I didn't believe it at first, but I tried it and heard the difference. 
If you have to use a computer or mp3 player and want to improve the sound of your system, start with the original music CD and import it using the highest quality compression rate available. For example, iTunes offers 256kbps as their highest quality rate. Most people can hear the difference between music played on a good DJ sound system that is 256k and others that are 128k. Anybody playing music on a DJ or Club system that was compressed at anything below 128k should be arrested for irritating our ears and brains! 
Remember, The original CD is still compressed music, but it is usually the best we have access to.
SECTION 7: Multiple Amplifiers.
As is most of what I have written above, this is MY PERSONAL OPINION based on 34 years in the audio business. I believe that if you are a DJ and you have four speakers that need 250 watts each, you should have TWO AMPLIFIERS instead of one big one. Here's why: If you are a DJ that travels around and sets up your gear a few hours before the show, you don't have time to buy or borrow another amplifier if yours dies. If you are a night club, you can't afford to not have sound one night if your only amplifier dies. So, the answer is to always have a Plan B. Multiple amplifiers. Amplifiers are cheap now and racks have wheels, so do yourself a favor and boost your confidence by knowing you always have a back up. It's a lot better than refunding money because you couldn't perform! 
SECTION 8: Speaker Cables.
First of all, you should read our SIMPLE GUIDE TO SPEAKERS on our web site. It gives quite a bit of information about speaker cables and plugs. Here's the important stuff:

1. Speaker cables do not have to be shielded. NOT Shielded means the two wires do not need to have what looks like aluminum foil wrapped around them. Audio patch cables that are used for connecting any and all audio equipment except for speakers, must have a shield around the two or three wires to prevent radio signals and power line signals from interfering with the pure audio signal.2. Size Matters! The more power you are running to your speakers, the heavier gauge wire you need and the better the connector needs to be on each end of that cable. You can never go wrong using 12 gauge cables. You are never using the best connector when you are using common 1/4" plugs. A DUAL BANANA plug provides the BEST connection for flow of power of all connectors readily available for Clubs and DJ's.