Tech Feature

This article is adapted from Wireless Systems Guide: Antenna Setup, a Shure educational publication available from shure.com. —ed.

We’re all familiar with transducers, such as speakers and microphones. Yet antennas, which also convert one form of energy to another — in this case, radio-frequency electric current to radiated electromagnetic waves (and vice versa) — are another form of transducer. And with any transducer, following certain guidelines helps ensure maximum performance.

The majority of low frequency sound reproduction is from vented loudspeaker enclosures — that is, loudspeakers that have a port in the enclosure. Nearly all modern professional loudspeaker enclosures are vented to improve their low frequency output, and numerous programs are available to predict the frequency response of vented boxes.

Typically, most professional loudspeakers have been comprised of a low frequency driver and a high frequency driver paired together in the manner common to speakers on sticks. Today though, manufacturers have branched out into many different driver orientations in the search for better performance, better coverage, more output and reduced footprint.

Virtually every production company will come to a point in business where they start doing events in rooms colloquially referred to as “soft seaters.” These are the concert halls, civic centers, theaters, churches, converted movie houses, auditoriums, collegiate centers, etc. that host everything from plays to bands to politicians. Soft seaters can be great venues: a fair number were designed with some acoustic intent and/or treatment, and the better ones are well equipped to support a production company’s infrastructure.

After several months spent discussing various aspects of electricity for professional audio applications, it’s time to turn in new directions. For those sick of the National Electrical Code, take heart, this month we look at the effects the atmosphere has on live sound production. Just as electricity is integral to audio, so too is air, the fluid medium that we live in, breathe in, and rely on to carry sound waves to the audience. In this article we will investigate some of the influences that air has on the sound that travels through it, and also how atmospheric or weather conditions can influence the experience of “combat audio.” First we discuss a little about air as a fluid, and then move on to practical ramifications for gigging.

In last month’s column, we covered the concepts behind common methods of AC power distribution, and a number of power specific terms that have specific definitions in the context of the National Electrical Code (NEC). That article was to lay the groundwork for this month’s discussion of portable power distribution in the language of the code. Readers are encouraged to reference that article, and generally re-familiarize themselves with the definitions within.

Over this past summer in FRONT of HOUSE, we embarked on a three-part series that touched on some aspects of electrical power distribution in the context of portable generators. Those articles covered a broad range of generator topics, from the important distinctions between bonding and grounding to the upcoming code changes for small generators. In light of the positive reception for that series, we undertake a series on portable power distribution (a.k.a., AC distro) downstream of the generators.

A common phrase in pro audio is “I need a P.A. that has enough throw to cover the audience.” Of course, loudspeakers do not lob sound like a baseball, but instead set up sound waves in the air that then travel to the ears of the audience, which then detect the sound as it passes them. Regardless of the questionable terminology, the concepts behind “throw” are an important to the audio industry.

The ability to cover patrons at increasing distances from the sound system opens doors to bid on larger events and ultimately get the show to the ears of more paying customers. Let’s examine the acoustic factors behind throw, the limitations loudspeakers impose on throw and some practical tips for getting the most coverage out of your sound system.

In the July 2013 issue of FRONT of HOUSE, our second article on portable power distribution discussed grounding and bonding specifics of portable generators, including small generators that are “floating neutral” configured. This third article should not be viewed as independent of the other two, and readers are encouraged to read the articles in the June and July issues. In this third article we’ll focus on proposed changes to the 2013 National Electric Code that, if enacted, will have ramifications for generators 15 kW and below.

In part one of this series on generators (FRONT of HOUSE, June 2013, page 50), we investigated some underlying details behind Ohm’s law, and that led to investigating when and why current flows in electrical circuits. We then investigated two key concepts in power distribution: bonding and grounding. We showed that bonding — not grounding — creates the primary low-impedance path for fault current in the circumstance where a ground-fault event occurs. In this second article on portable power distribution, we build on the concepts in part one and investigate generator grounding and bonding in light of the existing 2011 National Electrical Code (NEC).

Generators, and portable power distribution in general, are central to professional audio. Electricity is a powerful means of transferring energy; it is the lifeblood of all pro audio gear. While electricity is ever-present, it is rarely discussed technically in print, in part because of the liability that accompanies its underlying power.

Over the past two years of FRONT of HOUSE, we have covered substantial ground with respect to subwoofers. Whether on the specifics of setting up a basic cardioid array or on how to design your own vented box, we have presented several nuts and bolts articles on the ever-important bottom-end that keeps sound reinforcement exciting.

This installment is very much in keeping with the previous practical articles on subwoofers. I am suppressing my inner egghead tendencies towards discussing topics like “phaser summation in the far-field,” or “radiation impedance,” and instead will look at a number of subwoofer configurations as they were implemented in the field of real gigs. We will briefly overview each configuration and discuss the implementation, and the goals behind the implementation.