To Overlap Or Not?

The next decision to consider is whether the sub bass loudspeakers are going to be taking care of the specific frequency range of 20 to 60/80 Hz by themselves, or whether the mains are designed and capable of overlapping some or all of the lower frequencies. With the subs flown next to the main and/or side arrays, the need to overlap frequencies may be reduced, although it may be the preference of a mix or system engineer to do this.

There are pros and cons, for sure. If the subs aren’t right next to the mains (physically), the overlapping frequencies will have different arrival times onstage to offstage, so some addition and cancellation issues can arise.

If the choice is to run a preset for the main and side arrays with a high-pass filter at, say 60 Hz, and the subs are low-passed at the same frequency, there will be less overlapping frequency problems. However, if the subs are ground-stacked, the top sections of the arena may be shy of those lowest frequencies, especially if the subs have a lot of bodies in front of them. This often happens at festivals or in arenas without floor seats.

If the choice is to run mains down as low as they’re able (say 40 to 50 Hz, or lower) the benefits can be more consistent low-frequency level throughout the venue that remains linear with the high and mid frequencies, adding cohesiveness to the frequency response of the entire PA. The sub bass loudspeakers could then be used as merely a “bass extension.”

The down side to this approach is a lack of control of the lower frequencies. With the main PA going all the way down to 30 or 40 Hz, a big rumble on stage can occur that can be troublesome for the artists and techs.

Cardioid Sub Arrays?

This brings us to the pros and cons of standard sub arrays versus cardioid pattern sub arrays.

With a cardioid sub configuration (where some of the subs are facing backwards, and polarity reversal and time delay are added to the rear-facing subs), the energy can be “steered” to the front of the sub array (where the paying public is) and significantly reduced behind the subs. This can be especially helpful with an artist who’s sensitive to low frequencies gathering on stage, or there are open mics (such as an orchestra or grand piano) to keep low frequencies away from.

With the help of prediction software that’s available from many loudspeaker manufacturers, the system engineer or audio mixer can “predict” the outcome and design cardioid sub arrays that reduce extreme low-frequency problems on stage as well as back areas where the monitor engineer and band techs may be stationed. Again, this is often determined by the preferences of the artist and their audience, as well as the mix engineer.

With a cardioid sub array (whether flown or ground-stacked), and main/side arrays that are frequency tailored to not overlap with the subs, a very clean-sounding stage can be attained while having all the sub bass and low frequency energy desired out front. Keep in mind that cardioid sub arrays, while very effective at controlling sub energy behind the cluster, may also reduce the sub bass energy on the sides of the stage where people are often sitting, especially in an arena layout.

Diving even deeper, sub bass loudspeaker configurations (altering the location of the rear-firing subs) can be created to control where the “null” ends up on stage. The use of prediction software is great for steering the cancellation points and spreading the sub energy out over the audience area while avoiding walls and other obstacles.

Try aiming the ground or flown cardioid arrays with a slight “out angle” of 15 to 25 degrees. This can create a cancellation of sub bass on stage that can be directed toward certain musicians that may be more sensitive to low frequencies than others, or if they’re positioned straight out, it can make things quite nice for the monitor engineer and backline techs.

Time It, Tune It, Fini

After all of this information is considered and the best overall design is in place to cover the room adequately with full frequency response, power and clarity, time alignment and equalization are the final steps to ensure the best results. Time aligning zones of PA (mains, side arrays, subs and fill speakers) to work together as well as using zone EQ such as high-pass filters on side arrays and fill loudspeakers to reduce unwanted low end build up will be the finishing touches that bring the whole picture together.

The artist/band should also get a feeling of cohesiveness on stage that will make their experience better too, and in the end, they’re the ones signing your paycheck, so making them happy goes a long way.