Picture this: You’ve spent hours carefully setting up a show, only to end up fighting the mix all night because of some annoying thing you forgot to check. Sound familiar?

A year ago I worked on a very dynamic show with quiet talkers punctuated by a loud rock band. I did all of my normal sound system calibration procedures, but forgot one important detail. I never drove the system close to maximum show level.

The show began. Kids started screaming and rushing the stage. I had plenty of headroom on the console, but for some reason my subs started vibrating like crazy. It may have been some sympathetic resonance with a room mode, but I barely had time to think about it at the time. I wish I had followed this checklist!

You already know that proper sub alignment is critical not only for an exciting show, but also to accurately reproduce the performance, protect the equipment and audience health, and keep from pissing off the neighbors.

But, how can you verify that you’ve done it correctly?

Do you have any horror stories? Comment below!

What follows is a seven point verification checklist to give you confidence in your installation. I have included mostly listening tests that anyone can do, but further investigation with your favorite test tools is welcome.

1 – Ensure Rigging Safety

The paramount concern when setting up any live sound environment is safety. Proper rigging not only ensures the stability of your equipment but directly impacts the safety of everyone in the vicinity — from the crew to the audience. It’s vital to start by familiarizing yourself with the product documentation specific to your equipment. Many manufacturers provide guidelines tailored to their products’ design and weight specifications, ensuring optimal and safe setup.

Beyond the manufacturer’s advice, there’s a wealth of general rigging guidelines that can be instrumental. ANSI ES1.18 – 2022, “Event Safety – Rigging,” for instance, offers valuable insights into best practices. Remember, everyone on site is responsible for their actions or the lack thereof. In a field where the margin for error is minimal, it’s incumbent upon all involved to be proactive in reducing risks. By ensuring thorough rigging safety checks, we take a significant step toward guaranteeing a successful, hazard-free event.

2 – Inspect Visually

Are there any lose cables, exposed wires, or anything that looks out of the ordinary? Some systems offer an automated impedance test (eg. L-Acoustics Enclosure Check, d&b System Check) to detected possible circuit continuity issues. A stitch in time saves nine.

A common test here is the console check or continuity check. Solo each output at the most granular level you have available to verify that sound is arriving at its intended destination.

I like to ask other people on the production team, “Did I forget anything?” or “Do you see anything missing?” Something invisible to you might be obvious to someone else. 

3 – Listen for Noise & Distortion

Solo the sub system and listen for any audible noise or distortion. Start with the console muted to listen for ground humm. Check those seating areas closest to any sub since you might not hear it at FOH. Drive the system at show level for realistic results.

Helpful test signals include pink noise, color pulses, and sine tones. There is a risk of hearing and equipment damage by overloading it with low crest factor signals like a sine tone. Take care when introducing these test signals into the system. For a show level test or driving close to system limits it’s likely wise to use a board recording, virtual sound check, or similar high crest factor material.

4 – Balance the Levels

The subs are important, but they are not the star of the show. The subs should act in cooperation with the rest of the sound system and not draw unnecessary attention to themselves. Play a reference track while you slowly raise the sub level from zero until it sounds right. An alignment issue at your listening location may cause you to gain up the sub to compensate. Consider listening at several locations. If there are doubts, spend extra time on the next step.

5 – Check Tonal Balance

A walk up and down the chromatic scale should not produce any large variations in timbre or apparent loudness. You might start with reference tracks, comparing headphone sound to room sound, but then switch to something where you have more control like a warble test or a synthesizer set to produce pure tones at matched volume so you can walk up and down the subwoofer’s operating range to identify holes or peaks in the response.

Other things to listen for:

• Low-end transients lack balance, either being too boomy or lacking punch.
• Low-end is muddy or lacks distinction.
• Fighting the mix, having trouble getting things to sit right.

While this is a subwoofer checklist, consider extending this test through other areas of the sound system, especially the joint custody area between main and sub. Of course, this may expose alignment problems and motivate a revisit of your calibration. This is something you can check with SubAligner in about 30 seconds. 🙂

6 – Achieve Accurate Coverage

Put sound where the people are and not where they are not. Take care that your sub array’s coverage shape matches your audience cover shape while avoid walls and open mics. 

Don’t put FOH in a power valley. This is a big risk with uncoupled subs and a FOH position just off center. Outdoors, this will be fairly obvious as you listen to pink noise and walk across the audience. 

Another helpful test in this area might be a sine tone with a duty cycle (eg 1 second on, 0.5 seconds off). As you move away from the sub array, you may find areas where it’s difficult or impossible to hear the cycle. This can give you clues about critical distance and how well you’re staying off the walls.

7 – Monitor System Health

Without a reliable system to monitor the health of the sub system you may unknowingly fatigue electro-acoustical components by continuously hitting the limiters and driving the system into clipping.

What did I miss? What other verifications steps to take on every show? Comment below.