Working from home? Switch to the DIGITAL edition of FRONT of HOUSE. CLICK HERE to signup now!
Generic selectors
Exact matches only
Search in title
Search in content
Search in posts
Search in pages

Subwoofers in the H.O.W.

John McJunkin • December 2020Sound Sanctuary • December 10, 2020

Socially distanced attendees at The Shepherd’s Church in Midlothian, TX get a rich range of sound with a new QSC system that includes eight KLA12 active line array cabinets and four KS118 active subwoofers.

When I was a kid, I was fascinated with the hi-fi loudspeakers my dad built during college, and I wanted to learn more about speaker design so I could build my own. He taught me about tweeters, woofers, midrange speakers, crossovers and all, and — somewhere along the way (probably when I was in high school or college) — the term “subwoofer” crept into my vernacular. Initially, my thought was, “if woofers handle the bottom-end of the frequency range, why would I need or want a subwoofer?” Turns out that as materials and technology advanced, it became plausible for even the consumer domains of home and car audio to represent the deep bass down below 60 Hz the same way it was done in the professional world. Similarly, subwoofers even made an appearance in the domain of “pro-sumer” audio. It seems that hip hop music with its deep Roland TR-808 bass started to become popular about the same time that car audio started offering the subwoofers necessary to reproduce it. I shan’t venture a guess at which was cause and which was effect, but I will note that when my car audio’s bass is overwhelmed by the subs in the car next to mine at the intersection, I don’t like it!

Deep bass has also landed in church, too. As audio production values have increased and inflation-adjusted costs have decreased across the domain of pro audio, presenting the entire audio spectrum from top all the way down to the bottom has become de rigueur, and house of worship audio is no exception. Churchgoers have come to expect that the audio portion of what’s presented during services will be as rich and full as what’s experienced at a rock or pop music concert. And as hip hop, rap and EDM music genres continue to cross over into the faith-oriented domain, the capacity to present the same kind of bass becomes a necessity in the modern house of worship. Obviously, there are exceptions to the rule: subs are not going to be important if worship is completely restricted to acoustic guitars and vocals. Yet, on the other hand, if you want to amplify that 16 Hz note emanating from the 32-foot organ pipe, you’ll need a sub or two. I would respectfully submit that for modern worship, the capacity to reproduce sub bass is important, if not critical, and the expenditures of time and capital necessary to make it happen are well worthwhile.

‡‡         Some Background

One of the great benefits of introducing subwoofers is that we eliminate some of the heavy lifting that we’re forcing the rest of the system to do. Even if our system is not capable of reproducing deep bass, we can rest assured that engineers, particularly young and inexperienced engineers, will still try to force it to do so. The likely outcome is an increase in distortion and the possibility of damage to various components. The introduction of subs in order to create deep bass capacity reduces the likelihood for such calamities. For a long time, we’ve known that a 3-way system generally produces better results than a 2-way system, and a 4-way system can be superior to a 3-way, and so on. The deployment of that additional band brings us all of the same benefits we get by dividing the spectrum up further in general.

While it’s preferable to design and deploy a complete system at one time, it is plausible to simply add subwoofers to an existing system. That said, being deliberate and scientific about that process is recommended. I’d strongly suggest formally measuring the capabilities of the existing system before adding subs. Not only will careful measurements show you how much sub-bass energy you’ll need to match the existing system, but also the crossover frequency below which you’ll need to add SPL — in both quantity and quality. Once the additional drivers and amps are deployed, additional measurement is also necessary to integrate the subs into the spectrum in the proper way — with a smooth, seamless transition from the lows to the sub-lows, and with care to establish as flat a response as possible over the entire spectrum.

This notion of presenting a smooth, flat frequency response brings up a practice we know as “bass management.” In some cases, we choose to give the sub lows their own signal path so the FOH engineer can grab a fader and adjust to taste, contingent upon the program content. In other cases, we may just send a full-spectrum signal to our drive racks and let the purpose-adjusted system take care of delivering the appropriate amount of low-end based on how we’ve configured it. Both options are valid, based on circumstances. It’s best to leave the bass management up to technology if the FOH mix is usually handled by volunteers. But if seasoned professionals are at the controls, it’s nice to have a fader controlling the sub levels.

‡‡         The Details

So how do we go about adding subs to an existing system? Here’s where the careful measurements come into play. The only way to determine how many additional cabinets we’ll need is to establish how much SPL our existing system produces. In fact, we’ll want to measure how much SPL the thing produces above the crossover frequency of our new subs. If the current “full-range” system is adding SPL below that crossover frequency, our measurement will not tell us how much additional low-end is needed; it will tell us how much low-end we need if the current system is still providing some bass. Cut the lows completely out below the crossover frequency so we can sort out what the rest of the system is doing without the bass that will be provided by the new subs. Only then will we have a handle on the actual requirement. We’ll largely have to rely on the published SPL figures for the new subs, and I recommend planning on bringing in enough boxes to deliver more sub-bass than necessary — we can turn it down if we have to.

Volumes could be written about the tricky nature of measuring soundwaves that are dozens of feet in length. That is beyond the scope of this article; however, you’ll want to sort out what the bass is doing out in the middle of the sanctuary where most of the congregants sit. Obviously, the FOH mixer must hear a good representation of what’s happening in the deep low-end as well. Another question to be addressed is whether traditional (omnidirectional) subs will be installed, or a modern, multi-cabinet system will be deployed to accomplish directionality. A more sophisticated directional subwoofer system is vastly more likely if a completely new system is going in versus the addition of subs to an existing system. Yet another consideration is whether the subs will be flown or sit on the floor, the latter situation requiring some consideration of what happens to SPL with the speaker located in half space, quarter space or even eighth space. Also bear in mind that the lowest frequencies in the audio spectrum require the most power to reproduce, and the solution of “just buying some subs and plugging them in” may be thwarted by insufficient power — and you may be limited by the existing AC power service to your building.

‡‡         Turn It Up!

Extending the lows into the deep bass spectrum can be a wonderful upgrade and may substantially enrich the quality of your worship experience. Take time to investigate the options, measure carefully, and deploy a system that will bring that sweet low bass that everybody loves to hear.

John McJunkin is the chief engineer and staff producer in the studio at Grand Canyon University.

The Latest News and Gear in Your Inbox - Sign Up Today!