Ultimate Guide To Going Live. Part 4: Amplification

author: Backup Guitar date: 03/11/2004 category: the guide to
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When you're doing a gig, chances are, you're going to have your amplifiers mic'ed up to a P.A. system. However, this doesn't mean you will be able to get away with a flimsy 15 watt solidstate amplifier. I'd suggest that you at least have a 50 watt solidstate amp or a 20 watt tube amplifier. In either terms, an amplifier with one 12" speaker should be the absolute minimum. Gigging with an amplifier that has two 12" speakers is more reliable, because you won't have to crank the amplifier to hear yourself onstage.

Volume Levels

The first issue to deal with is how loud you need your rig to be. The first step you need to take is to be louder than your drummer. This can be determined at band rehearsal. If you're rehearsing or just jamming with your band, everyone should be heard clearly - this includes the singer through the microphone. Your sound in the rehearsal room should be nice and clear, no mud or "fuzzy" areas of the sound. If you notice sounds starting to blend in a bad way, take a few steps to fix it. First, have your drummer play a simple beat at a comfortable volume level. Then, have your bassist start playing at a normal and relaxed volume. Have one guitar (if you have two guitars) enter. Once you identify which instrument the mud is coming from, take corrective measures. Some examples include turning down the gain, correcting the EQ on the amplifier, or taking further steps such as replacing worn out tubes or bad volume or tone pots. Keeping your gear in top shape for a gig is essential. Once you've got your mud cleared up, you need to know how loud you need to be at a gig. Here is a quick introduction to sound pressure levels and their qualities. Remember "volume" is merely the amount of sound that the ear can detect.
  • Volume decreases by 6 dB when you double your distance from the source. This means if you are standing five feet from your amplifier, it will sound noticably quiter when you are standing ten feet away from your amplifier.
  • Volume increases by 3 dB when you double the power to a loudspeaker. If you have your volume control at five on your guitar, it will sound 3 dB louder when you have your volume control at 10
  • Volume is perceived to be doubled when the amount of signal entering a loudspeaker is increased by a factor of ten. This means that a 500 watt amplifier will sound twice as loud as a 50 watt amplifier on full blast. However, this is merely perceived this way, and it is not a true doubling of volume. In fact, it is only an increase of 10 dB. Simply put, an increase of 6dB from an amplifier is heard as a 30% increase, but lowering the volume by 6dB is heard as a 20% decrease in overall volume. An increase of 10dB is heard to be an increase of 100% volume, but a decrease of 10dB is heard to be a decrease of 50%. This is all approximate, and the actual volume varies from ear to ear.

    Applying Sound Pressure Levels

    To apply sound pressure levels to an in-person situation, you need to have a decent understanding of various noises and their approximate dB level. 0dB is considered to be the theoretical point of "no noise", while 130 dB is the average threshold of perceiving pain from loud noise. Think of when two girls meet with exciting news in a school hallway (painfully loud), compared to a library when you can almost hear your heartbeat. Here's a simple list of noises and their volume levels: - Whisper: 15 - 25dB - Quiet Background Noise (rustling papers, coughing): about 35dB - Normal Home Or Office Background: 40 - 60dB - Normal Speaking Voice: 65 - 70dB - Jazz Trio (drums / acoustic bass / grand piano): 95 - 100dB - Loud Orchestra/Big Band: 105dB - Live Rock Music: 120dB+ (this is also approaching the nominal threshold of pain) - Average Ac/dc Concert: 130 - 140dB - Jet Aircraft: 140 - 180dB - Space Shuttle Launch 198+dB (close to the theoretical limit of hearing) Now, when you think about it, a noisy bar where you are likely to play will be about as loud as an orchestra reaching a loud point in music. Fairly headache inducing, plus the echo. Your job, as your band's gear technician (if you hold that position) is to create the ideal level of noise that overpowers the band, but does not cause people to have a migraine. So, the noise you want to aim for is just under 120dB. Simple enough, right? Not so. However, as a playing band, people are likely to pay attention to you. This can be good and bad. During playing, the bar will be quieter than when you aren't, so you can probably hit it off with a 100 - 110 dB level. However, at the end of a song that really hits it off with the crowd, you are going to need to get those amplifiers burning, so you'll at least need 120dB to get the final few bars of a song heard properly. In order to compensate for the situation, have the bar's P.A. manager understand your songs. Give them a sheet with times in the song when you need to have the volume go up and down. The P.A. manager should be able to detect when your band is getting drowned out on his own, but if your sound has certain needs (like you want an acoustic ballad to be softer), then you need to run it through with him quickly, and make sure you have a fully printed off and easy to read sheet for him to hold. Besides that, you want the band to be on good terms with the P.A. manager. He can be your best friend, or your worst enemy. And as a musician, you don't need any more enemies than you may already have.

    Speaker Units

    Consider a speaker unit as one enclosed series of speakers. That means the 412 stack that goes with your amplifier head, or the P.A. units that blast the sound out to the crowd. Ever wonder just how much sound those make? Well, here's an explanation. First, consider this: the term "speaker unit" may differ. Generally, the amount of watts going into the speaker determines the amount of volume. So if you have a 100 watt amplifier head going through a 412 stack, simply look for the proper watt rating. Two 100 watt amplifiers going through seperate speaker units will equal to 200 watts, simply because the different sound pressure levels add onto each other. Sound varies by 3 dB when you double the amount of equally powered speaker enclosures. This means that if you have one 12" speaker running at 100 watts of power, running another amplifier at 100 watts with a 12" speaker will increase the total volume by three decibels. The same rule applies to an amplifier with two 12" speakers. Having another amplifier run at the same watt rating with two 12" speaker increases the total volume by 3 dB. As if you need to get any louder. - 1 enclosure unit running at 10w produces 110dB of noise at a distance of only 1 meter. - 2 enclusure units running at 20w produces 113dB of noise at a distance of 1 meter - 4 enclosure units running at 40w produces 116dB of noise at a distance of one meter - 1 enclosure unit running at 100w produces 120dB of noise at a distance of 1 meter - 2 enclosure units running at 200w produces 123dB of noise at a distance of 1 meter - 4 enclosure units running at 400w produces 126dB of noise at a distance of 1 meter The key to using the data is to remember how sound dissipates over distance. The general rule of thumb is that volume decreases by 6dB - a fairly significant decrease - when you double your distance from the source. So, suppose that you have to project your sound over a distance of 20 meters. Your combined amplification is 400 watts of four amplifier units. For simplicity's sake, P.A. units aren't being considered. Now, 126 dB is being produced at the front - that includes you. So you, as a performer, are in serious pain from the noise. The front frow, two meters away from the power source, are hearing only 120 dB - still plenty loud. Getting four meters away from the source, the crowd hears 114 dB. Eight meters away, the crowd hears 108 dB - this is still a fairly comfortable noise level. Sixteen meters away, the crowd hears 102 dB. Over here, people are likely to be talking to each other, igoring the music. So, really, this seems ideal, right? Well for small gigs where you don't need to blare the volume, it may be okay, but if you think you can get away with this at large gigs, you are simply mistaken. As a musician, you have to be comfortable onstage. And when that much noise is being pumped into your poor little eardrums, you're in trouble. You have to protect your ears very carefully. Steve Vai has said that you should protect your ears with more caution than you should your dick. And I, for one, would take this caution carefully. Ever had to sit in front of 20 trumpets blaring away in a small room? I have. Add to that 15 trombones. Going home, my ears were simply numb and almost ringing. No biggie, right? It's just temporary damage. And I only had to endure about 3 nights of that kind of playing. However, when you're seriously gigging musicians, you have to be more careful. Your ears are the most important part of your skill. This is where P.A. systems come in, which will be dealt with in the next article. Remember, as part of your live gig, to carry plenty of earplugs. Even when you have monitor systems, bring earplugs. Wear them. As long as you can comfortably hear your music, and your voice clearly, protecting your ears is an absolute must. In fact, it is a good courtesy to have a basket of inexpensive earplugs available for fans to wear at the front if they want in on the action of you playing, but don't want to lose your hearing. It's simply good etiquette. You might want to talk it over with the bar owner about earplugs, and that if possible, that they could deduct about 20 dollars of your payoff and buy a bulk package of styrofoam, one-time use earplugs for fans. 20 dollars isn't much divided among four or five individuals, and you rely on your fans for money. Treat them as you would like them to treat you. Always provide proper grounding, and bring volt-meters and ground testing as part of your amplifier setup. Make sure you aren't overloading one circuit, so talk over the electronics of the establishment with the bar owner. Follow all instructions on voltmeters carefully. It could save your life. Keep on reading the Guide to Going Live series, where I will continue on the subject of projecting noise using P.A. Speaker setups. Thank you for reading my article, and I hope anything you've learned will serve you well. I'll be happy to answer any further questions you have. Peace Out, - Backup Guitar
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