If you’ve ever measured sound in your building, decibels are probably the metric you know best. A decibel reading measures how much sound energy is in a space, usually adjusted to match how the human ear hears and averaged over a set period of time.
But that reading isn’t enough on its own to understand how a space sounds or how it affects the people in it, because it says nothing about what the sound is made of, how it changes through the day, or why two rooms at the same level can feel completely different. Those missing details determine whether or not people are able to focus on their work, which is why a space can look fine on paper and still generate noise complaints.
Here's what a decibel reading actually captures and what it leaves out, how frequency and variability change the way a space affects occupants, and why measuring many aspects of sound together is what it takes to achieve acoustic comfort.
Decibels aren’t enough because a single decibel figure reports overall loudness and nothing else. It can’t tell you which frequencies make up that sound or how the level changed while it was being measured, two factors that often shape how people experience a space more than the sound level itself.
Picture two meeting rooms that both read 45 dBA. In one, the sound is the steady hum of air moving through the vents. In the other, it's quiet until a phone call starts on the other side of the wall, then quiet again until a door bangs shut down the hall. When you measure the average decibels over time, the two rooms are identical. In practice, only one of them is easy to think in, but the decibel reading can't tell you which.
Researchers have documented the same gap in real offices. When they followed 31 employees who moved from private offices into an open-plan layout, the measured sound level stayed around 39 dBA in both settings, yet the productivity loss employees attributed to noise doubled.
The conversations around them weren’t any louder, just easier to understand. Speech you can follow pulls your attention with every new word, and a decibel reading has no way to capture that. Going by that number alone, the new office looked no different from the old one.
A decibel reading measures sound pressure (the tiny fluctuations in air pressure that reach your ear) after running it through three processing steps:
Loudness doesn't capture what kind of sound fills a space (whether it's an annoying high-pitched ring or a low rumble) or how much it swings between quiet and loud (whether it's distracting or helps you focus), which is why you also need to measure frequency and variability.
Those two factors are what separate the two meeting rooms at 45 dBA: one has a low, steady hum that you can easily concentrate in, and the other has the stop-and-start of voices and doors that constantly breaks focus.
Level, frequency, and variability together are the three measurements that describe how a space actually sounds.
|
Measurement |
What it describes |
Common metrics |
What a single dBA reading misses |
|
Level |
Overall sound energy and its peaks |
LAeq, LAmax |
When peaks happen and how often |
|
Frequency content |
How sound energy is spread across low, mid, and high frequencies, from rumble to hiss, including single tones like a whine or buzz |
dBA and dBC levels, one-third-octave band spectrum |
Low-frequency energy that A-weighting turns down, and narrow tones that add little to the average |
|
Variability |
How much and how often the level swings |
LA10, LA90, noise climate |
The difference between a steady room and a swinging one |
Building standards already treat sound as more than one number. For HVAC background sound, ASHRAE's design guidelines pair each dBA target with two more numbers: a Noise Criteria or Room Criteria (NC/RC) rating, which checks how the sound is balanced across frequency bands against a reference curve, and a dBC ceiling, which caps low-frequency energy.
The WELL v2 Sound concept does the same for a room's whole acoustic environment, with separate requirements for background noise, sound insulation between rooms, reverberation time, and sound masking. The acceptable office noise levels it sets are only one piece of the acoustic picture.
Frequency changes how comfortable a room feels because people respond differently to low rumble, mid-range voices, and high-pitched tones, even at the same overall level. The low drone of a rooftop unit tends to fade into the background, a nearby conversation at the same volume is much harder to tune out, and a faint electrical whine can end up being the most irritating sound in the room.
Lab research shows how big that difference can be. In a listening study, participants rated ventilation-like background noise played at the same A-weighted level but with different mixes of low and high frequencies. Versions with more high-frequency energy were rated more annoying at all three levels tested, even though their decibel readings matched. In the same team's earlier experiment, spectrum shape alone added an annoyance penalty of more than 10 dB, roughly the difference between a sound and one twice as loud.
Two measurements show what a dBA reading can’t:
Tones are where the gap between reading and experience gets widest. Research presented at ICBEN found that a clearly audible mid- or high-pitched tone can carry an annoyance penalty of 8 to 12 dB compared with steady sound at the same level. That's why tonal noise from a quiet whine can bother occupants more than a louder, even hum.
Variability matters because people tune out steady sound but notice every change. If you've ever worked in a busy coffee shop, you've probably found the steady buzz easy to ignore. But if you've ever tried to focus in a quiet library while someone drops a book every 30 seconds, you know each thud pulls you out of your work, even though the library is quieter on average.
Research on how sound disrupts thinking points the same way. Across 70 cognitive-disruption experiments, a single measure of how much a sound fluctuates explained 55% of the variance in how disruptive it was, correctly predicting the outcome in 63 of the 70 cases.
Cognitive psychologists see a related pattern in the changing-state effect: sound that keeps changing, like the shifting syllables of nearby speech, disrupts memory far more than steady or repetitive sound. Because an LAeq average smooths those changes out, variability needs its own statistical levels:
Sound level and variability together make up a room's acoustic profile. Plotting one against the other sorts spaces into four broad types:
Unlike air quality or light, sound has no single correct target for a workplace, only general recommendations and safety limits. A profile that suits a cafeteria would fail in a quiet zone, so the real question for each space is whether its sound matches what the people using it need (i.e., acoustic comfort).
Finding out where each space stands is the first step in the measure, treat, mask approach, because it tells you how far off target a space is, and which solution is likely to fix it: acoustic treatment, masking, or both.
Continuous, multi-parameter monitoring is the only way to track level, peaks, variability, and frequency together over time. Of the ways to measure office noise, it's the one that shows how those properties change across a full workday.
A continuous sound monitor like Kaiterra's reports A-weighted, C-weighted, and unweighted average levels, maximum level, LA10, and LA90 every minute, plus sound energy across 31 one-third-octave bands every five minutes. That gives facilities and workplace teams a record of when a space gets loud, how much it swings, and which frequencies dominate, instead of a single spot reading taken on a quiet afternoon.
That ongoing record lets you benchmark a space's sound over time and gauge its acoustic comfort as people actually use it. This measure-first approach helps you make the changes that will do the most for occupants, and confirm they worked, instead of trying several fixes that may or may not solve the underlying problem.
Measuring sound doesn't have to mean recording conversations, but that comes down to how the sensor is built. Anything that measures sound uses a microphone, because it has to turn sound pressure into an electrical signal before it can calculate anything, even a single decibel level. Whether that microphone works as a recording device depends on how it is recording the sound and what happens to the signal next: whether audio is stored or sent anywhere, or processed into numbers and discarded.
At Kaiterra, our sound sensor is designed so it cannot function as a recording device. The microphone is only turned on for 8.7 milliseconds every second, which is far too little audio to follow a conversation. Each snippet is processed into numbers as soon as it’s captured, and the audio is discarded without ever being stored. Only numeric values like sound level and frequency-band energy leave the sensor.
All of this happens on a standalone sensor with its own processor, separate from the rest of the monitor. It can’t be reached over the network or reprogrammed, so no one can change how often or how long it listens.
Just like any other aspect of indoor environmental quality (IEQ), sound requires continuous, multi-parameter monitoring to understand how each space is performing and what it needs to deliver acoustic comfort. Reach out to Kaiterra today to learn more about how you can measure sound securely in your building and enhance your occupants’ health, well-being, and overall experience.