Subwoofers: Configuration Options Matter for Your Worship Space

Subwoofers: Configuration Options Matter for Your Worship Space

A small- to mid-sized church may need to implement anywhere between two to four subs, and a mid-sized to larger church may require between four to eight subwoofers.

Among the major components of a live sound system are subwoofers. Let's take a closer look and explore.

Subwoofers, while entirely optional, add low-end "punch" to a sound system that a full range system is not capable of delivering on their own. If you're considering adding subwoofers to your current full-range sound system at your worship facility, the following information will give you a pretty good idea of how subwoofers work and what to expect from them.

Depending on where the low frequency crossover points are set, the subwoofer can typically handle frequencies up to and including the 80 to 100 Hz range.

There are various types of subwoofers and placement options to consider, and we'll review what some of them are.

Most full-range loudspeaker systems are comprised of a combination of a tweeter, mid-range driver and bass driver. The tweeter typically delivers high frequencies in the range of 2,000 to 20,000 Hz, while the mid-range driver often does so for frequencies in the 250 to 2,000 Hz range. Lastly, the low frequency driver often is tasked with frequencies ranging in the 60 to 250 Hz range.

To add lower or "sub-bass" frequencies, in the 20 to 60 Hz range to your sound system, you will need a subwoofer.

Depending on where the low frequency crossover points are set, the subwoofer can typically handle frequencies up to and including the 80 to 100 Hz range. Subwoofers, commonly referred to as "subs," can be seamlessly added to any stereo or mono full-range sound system by using an active crossover, which receives audio from the mixing console. The crossover gathers the audio signal, segregates that signal to each speaker component (high frequency tweeter, mid-range driver, and low frequency driver), and that speaker enclosure then delivers the full range sound.

Most sound engineers might prefer to add sound to the subwoofer by using an aux, or separate mix bus, from the mixing console. This method is useful to reduce the number of sources feeding the subwoofers to include only the instruments that produce sub-bass frequencies. Those instruments include the bass guitar, bass (or "kick") drum, keyboard synthesizers, and drum machines. This "aux-fed" method offers greater low end punch and clarity.

Subwoofers come in two varieties: passive and active. A passive subwoofer is just a woofer or woofers in an enclosure that must be driven by an external amplifier, providing the necessary power to be heard.  An active subwoofer will have an amplifier and crossover built into the enclosure. The size and seating capacity of your worship facility will determine the type and the amount of subwoofers needed to accompany the full-range sound system.

Subwoofers are typically loaded with 12-, 15-, 18-, and 21-inch woofers, sometimes referred to as drivers. The subwoofer enclosure may be double loaded, for example, with double 18-inch drivers.

The quality and efficiency of the subwoofer will also determine how many your worship facility will need. A small- to mid-sized church may need to implement anywhere between two to four subs, and a mid-sized to larger church may require between four to eight subwoofers.

If your worship space wasn't built with subwoofer placement in mind, and the decision is made to retrofit subwoofers, there are a few placement options to consider. The most common placement location for subwoofers is around, and preferably under, the downstage perimeter.

No matter where the subwoofers are placed on the floor, they may need to be "time aligned" with relation to the full-range main speaker arrays already installed in your space. Advantages of a properly time aligned sound system include more even coverage throughout the venue, and an increase of sound pressure levels (SPLs) in the sub-bass frequency range. The most widely used method of time aligning subs to the main speaker is to delay speaker system back to the kick drum. If the drum set is not in an enclosure, and it sits approximately five to 10 feet behind the main speaker array, think of the kick drum as another speaker. The undesired effect is that the audience hears the kick drum at a different time than they hear it from the subwoofers in the sound system.

Time alignment is necessary whether the subwoofers are ground supported or "flown." If the decision is to "fly" the subwoofers, there are a few configuration options to take into account. One option is to integrate them into a full range vertical array of speakers, or completely stack subwoofers in their own "flown" vertical array. The term "flying' and "flown" refers to hanging the subwoofer stack using hardware (typically chains and motors onto the structural steel of the building), as opposed to ground supporting them.

With the options of either flying or ground supporting subwoofers, achieving directionality (as much as possible) has been proven to increase in the vertical dimension, resulting in a radiation pattern that is wider than it is tall.

I should mention that sub-bass frequencies are omnidirectional, which is not always a positive result for stage performers and monitor mixers - if your church has a separate monitor mix position.

In a worship space, where there is a wall behind the vertical array, the wave of sub-bass energy will hit the back wall and cause a cancellation effect. In other words, the reflected wave from the back wall will arrive at a different time with respect to the direct wave causing a phase difference between them. That phase cancellation can be minimized by using a cardioid configuration for the subs, which will radiate very little sound pressure backwards, thereby gaining clarity on stage and in the house, reducing the amount of low frequencies on stage and in the audience. Placing subwoofers in a cardioid pattern requires reversing the orientation (180 degrees in reverse) of all other subwoofers. If they are ground supported and you have two or three subwoofers, one would actually face the stage and upstage (rear) wall.

Another cardioid configuration is to place one subwoofer directly in front of the other. Again, time alignment is very important because the subwoofers would need to be delayed in relation to distance between each other, so that sound from both subwoofers arrives at the same time. Some loudspeaker manufacturers build subwoofers specifically to be used as a cardioid subwoofer.

To recap, when considering adding subwoofers to the sound system keep in mind placement, proximity to stage, how many subwoofers fit the size of your worship venue, and time alignment. If each element is given proper consideration and attention, you'll be well on your way to enjoying the low end weight and punch you're looking for.

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