The EM Poll

Tech Basics Without Tears

Mar 14, 2008 5:29 PM, By Jon Chappell With Steve Oppenheimer

           

A PAIN-FREE EXPLANATION OF FIVE CONCEPTS ALL MUSICIANS SHOULD UNDERSTAND

Technology can be fun when it involves drooling over new gear features, ogling bold new designs, and wallowing in the benefits of an enhanced feature set. But technology stops being fun and becomes more like taking a math test when it involves, well, math.

On the other hand, a little technology savvy can increase your understanding of your gear and can often get you out of a jam. Knowing a few basic principles can help you solve an assortment of annoying problems that commonly plague gigging bands.

To get you started, we'll discuss five basic yet important electrical and audio concepts that musicians regularly encounter. We'll tackle some of the more technical aspects of these subjects using simple, everyday language, keeping the math and jargon to a minimum, in order to make these seemingly daunting concepts clearly understandable to the technically challenged musician. Of necessity, we are going to offer abbreviated and sometimes quick-and-dirty explanations. Be forewarned that in almost every instance there are plenty of exceptions, “yeah buts,” and so on. If you want greater precision and detail than we can offer here, we recommend starting with Scott Wilkinson's book Anatomy of a Home Studio, published by ArtistPro (www.artistpro.com).

Once you've mastered the principles presented in this article, you'll be able to do a number of cool things to impress your friends and bandmates:

• Safely choose or wire an extension speaker cabinet.
• Understand the function of a crossover in a biamped or triamped system.
• Know in what situations a balanced audio line will deliver better results than an unbalanced line.
• Optimally combine the signal of two mics aimed at the same source.
• Grasp how sound-pressure level, decibels, and frequency influence perceived loudness.

Are you relaxed and ready to learn? Good, then let's get technical!

Speaker Specs

P.A. systems are often modular affairs, with separate speaker cabinets and power amplifiers. This provides more versatility, as you can often mix and match speaker systems to suit the job. But before you start using your Crown power amp with your guitar player's Celestion cabinets, you have to know that you can safely match up those particular components. If you get it wrong, you could permanently damage your amplifier, speakers, or both. (Of course, a speaker system designed for guitar amps might not be the best choice for a P.A., but that's a separate question.)

The most important factors in matching an amp with a speaker or speaker cabinet are their power and impedance ratings. These specs are related, so we'll discuss them together. We are not going to get into much detail because that would require a separate article; we're just going to give you enough to assemble a properly matched system.

Keep in mind that a given power amplifier is designed to deliver a specific amount of AC power, and that a given speaker system is designed to handle a specified amount of AC power. If your amp delivers too much or too little juice to the speaker, the amplifier, the speaker, or both can be damaged. The amplifier and speaker are a team, and they need to be properly matched. We're going to discuss how to make a good match

Don't Impede Me!

You undoubtedly have heard other musicians talk about high- and low-impedance inputs on mixers, power amps, speakers, and guitar amps. Indeed, impedance is an important factor in matching parts of the signal chain, and it pays to understand at least a little bit about it.

For practical purposes, an electrical current always meets some opposition when flowing through a circuit, even if that circuit is merely a straight copper wire. Therefore, a speaker's electronics always present a certain amount of opposition to the AC electrical flow coming from the power amplifier. The opposition to alternating current is called impedance because it impedes, or hinders, the flow of electrons. Impedance is represented by the letter Z in equations, and it's measured in ohms, which is symbolized by the Greek letter omega (ž). (Impedance is closely related to resistance, but the two are not identical. The quick-and-dirty explanation is that resistance is the opposition to direct current, rather than AC. Also, impedance is frequency-dependent, while resistance isn't.)

Every speaker system has an impedance rating that indicates how much opposition its circuitry presents to the signal coming from the power amplifier. Common impedance ratings for speakers are 2, 4, 8, and 16ž.

If the speaker impedance is high, it won't let much current flow, so it doesn't demand much from the voltage source (the power amp). In such a case, the speaker is said to present a small load to the power amplifier. On the other hand, if the impedance is low, a lot of current can flow, and that puts a high demand on the power amp — that is, it presents a large load.

Remember: high impedance, small load; low impedance, large load. Got it? Good, let's talk about power.