Theory and Practice

I don't mean to brag, but the world of hum has been an absent partner for all my recent gigs. While I tackled hum back in the "good ol' days" at my local soundco, I now look back on how I was inflicting hum and noise problems onto myself. This diatribe is meant to bust the demons of hum out of your system, but also outlines how to take preventive measures and minimize its occurrence.

These days, when confronted by a digital speaker processor or digital crossover, you have multiple choices in the high pass, low pass and crossover filter selections. For those not up on filter lingo, words like Butterworth, Chebychev, Bessel, Elliptical and Linkwitz-Riley sound more like European law firms than filter types. So for those of not possessing an electrical engineering degree with a minor in control systems, this article is to introduce basic "pass" filters and help you make some choices in setting up a drive processor.

As we head into the outdoor gig season, there's always a lot of concern about the subject of scrounging for power for the show. Now, the big shows can demand genny trailers and venue/city electricians for hookups, but many of the smaller performances are left to people who think any electrical access is enough to get the job done. In the past, I have written about power distribution and load balancing; but let's think about not having enough power and what to do about it.

Making mistakes while mixing is the human component of live sound production, and we all are guilty. However, with a little more attention to details, these minor blunders can be averted. This installment of Theory and Practice will recap common mixing mistakes as a reminder to avoid them in the future.

Now, we are not talking about gain structure issues, but having good gain structure habits being taken for granted. This means that zero dBu is more than a good suggestion for average signal levels. Keep it in the green and out of the reds.

Poor positioning of loudspeakers has been a pet peeve of mine for quite awhile. For outdoor situations and large, wide rooms, I can go with the flow of whatever install or system is provided. But there are many occasions, especially in narrow or "tight" rooms, where I come away shaking my head about speaker positioning.

Flat Front vs. Cocked

When the performance area is a narrow room, or a partially segregated performance area where the loudness is to be confined, the typical speaker stacks on the side of the stage should be slightly tilted or "cocked" inward. Of course, this may be a bit fruitless if you have been provided music store-grade top boxes with 90- by 40-degree horns. In that case, just cock them 15 degrees and prepare for wall splatter reverberation.

Frequency crossover networks have been around since the early days of movie theaters. Today we have active crossover networks besides the legacy passive networks for splitting out bands of audio signal to frequency-specific drivers (speakers). This installment of Theory and Practice will go backwards in history by first discussing crossovers, and working through the basics of passive crossover networks for a two-way speaker system.