As I sat down to write my April article, I was reminded that the month’s theme was “Spring Cleaning.” Naturally, I started with an article about cleaning up audio systems, organizing wiring, and performing routine maintenance. But after letting it sit for a few days, it felt a little too generic, as if it wasn’t addressing the real issues I wanted to tackle.
So, I pivoted. Let’s talk about spring cleaning your audio by working to remove—or at least lessen—comb filtering in your classrooms. Comb filtering is subtle, but its impact on speech intelligibility and listening comfort is very real. The good news? With just a few thoughtful changes, you can dramatically improve how your classrooms sound.
What Is Comb Filtering?
If you’re unfamiliar with the term, comb filtering happens when the same sound reaches a listener at slightly different times—either from multiple speakers or reflections off walls, ceilings, or floors. These minor timing differences cause interference, resulting in a series of frequency peaks and dips that give the audio a hollow, tinny, or “phase” quality.
Comb filtering gets its name from how the frequency response looks when visualized on a graph: a repeating pattern of notches and peaks that resembles the teeth of a comb. These notches occur when sound waves cancel each other out (destructive interference), and the peaks occur when they reinforce each other (constructive interference).
This can lead to students struggling to understand what’s being said clearly in a classroom, especially in the back of the room or off to the side.
Time to Tidy Up: Spring Cleaning Your Sound
As an AV and audio nerd, I could discuss speaker types, placement strategies, DSP delay alignment, and more. But in the spirit of spring cleaning, let’s keep this focused on practical, actionable steps you can take to freshen up your classroom sound.
Declutter Your Speaker Coverage
Too many overlapping speakers can do more harm than good. Use the fewest number of speakers necessary to evenly cover the space and avoid blasting the same signal from all directions.
Pro Tip: Less is often more. If every speaker targets the same area, you’re inviting phase issues.
Dust Off Those Delay Settings
If you’re using multiple speakers, please ensure your DSP properly time-aligns them. Even a few milliseconds of misalignment can cause destructive interference.
Delaying the audio so that sound from all speakers arrives at the listener’s ear in sync can make a world of difference. Don’t trust your ears? Trust your eyes. If you’re doing a lot of voice lift in your spaces, consider investing in a Smaart setup. Tools like this let you visualize the delay misalignment and tune accordingly.
Re-Aim and Reflect (Literally)
Take a moment to inspect where your speakers are aimed. Avoid pointing them directly at hard surfaces like whiteboards, windows, or glass walls; these reflect sound and can create unwanted interference. Also, don’t aim speakers at each other.
A minor tweak in speaker aim can yield a significant improvement in clarity.
Tidy Up with the Right Speakers
Speaker selection is a whole topic of its own, and there’s no such thing as a one-size-fits-all speaker—no matter what the marketing brochures say.
That said, one of the most significant issues I see in higher ed installs is the use of mismatched speakers from different eras or manufacturers. If your space is stuck with a Frankenstein setup, consider upgrading to speakers with better dispersion control. Wide-coverage ceiling speakers or steerable column arrays can dramatically reduce overlap and help clean up your soundscape.
Don’t let old gear clutter up your audio.
Wrap-Up: Clear the Air (and the Sound)
A little attention to speaker placement and delay timing can take your classroom audio from “good enough” to “Wow, that sounds great!” And that’s a win for everyone—students, faculty, and your support team.
So, as you’re organizing cables, labeling racks, and refreshing signage this spring, take a few minutes to clean up the sound, too. Your students’ ears—and your help desk—will thank you.