How to Reduce Reverberation in a Room: Echo vs. Reverb Explained

How to Reduce Reverberation

If a room sounds loud and muddy, with voices that seem to hang in the air, you’re probably hearing reverberation. People usually call it echo, and in everyday speech that’s fine. But the two are different, and in most rooms the one you need to fix is reverberation.

Quick answer To reduce reverberation, add sound-absorbing material to the room’s hard surfaces, such as acoustic wall panels, ceiling clouds or baffles. Spread them across more than one surface, and size them to the room. An echo is a distinct repeat of a sound, while reverberation is many reflections blending into a lingering tail. Heavier walls won’t help with either one inside the room.

Echo vs. Reverberation: What’s the Difference?

Both are sound that bounces back off a surface. The difference is timing. A reflection that arrives about 50 milliseconds or more after the original can be heard as a separate sound, which is an echo. Anything sooner blends with the original. Simpler explanations, like The Physics Classroom, use 0.1 seconds.

	Echo	Reverberation
What you hear	A distinct repeat	A continuous, fading tail
Timing	About 50 ms or more	Many reflections, too close together to separate
Where it happens	Canyons, empty gyms, long halls	Almost any room with hard surfaces
How it’s measured	Delay	RT60, in seconds

A true echo needs distance, with a reflecting surface about 28 ft or more away. That’s why you don’t get one in a small office, but you can still get plenty of reverberation there. Our sister company Commercial Acoustics has a longer guide to echo vs. reverberation if you’d like more detail.

What Is Reverberation Time (RT60)?

Reverberation time, or RT60, is how long a sound takes to fade by 60 dB after it stops. Longer times make speech harder to follow, because each word runs into the tail of the one before it. The right number depends on the room. Here are general ranges from Commercial Acoustics, though a specific project may aim a little higher or lower:

Room	RT60
Recording studios and vocal booths	Under 0.3 seconds
Offices, classrooms and conference rooms	0.3 to 0.5 seconds
Restaurants and libraries	0.5 to 0.8 seconds
Lecture halls and speech-led worship	0.8 to 1.2 seconds
Gymnasiums and large worship spaces	1.2 to 2.0 seconds
Concert halls and cathedrals	Over 2.0 seconds

How to Measure Reverberation in a Room

• The clap test. Clap once and listen. A ring or lingering tail tells you there’s a problem, but it won’t give you a number.
• A phone app. RT60 apps give a rough reading, good enough to compare a room before and after treatment.
• A calculation. The Sabine formula estimates RT60 from the room’s size and surfaces, as shown below.
• A professional test. Worth paying for in large or critical rooms, or when you need numbers to show someone.

An empty room usually reads higher than a full one, because people and clothing absorb sound. Measuring it empty gives you the worst case.

What Reduces Reverberation: Panels, Clouds, & Baffles

Reverberation comes from sound reflecting off hard surfaces, so the fix is to swap some of those surfaces for absorbing ones:

• Sound absorbing wall panels: the usual starting point. Ours are 2 in fiberglass, rated NRC 1.05. See how to hang acoustic panels.
• Acoustic ceiling clouds: a good choice when windows, shelves or glass leave little wall space.
• Acoustic ceiling baffles: these hang on edge and absorb on both faces, which suits high, open ceilings.
• Soft finishes: carpet, rugs, drapes and upholstered seating all help, and they’re often enough for a mildly bright room at home.

Where you put them matters too. Treat more than one surface, including walls that face each other and the ceiling, instead of filling one wall. For room-specific advice, see our guides to conference rooms, coffee shops and gyms.

Real project: 1.1 seconds down to 0.7 Cena, an Italian restaurant in Tampa, had tall ceilings, full-height windows and painted drywall, and it measured 1.1 seconds, too long for guests talking across a table. Commercial Acoustics added 2 in fiberglass ceiling clouds and wall panels in fabric matched to the decor, and the room measured 0.7 seconds afterward. The project cost under $6,000 turnkey, and the install took one afternoon.

How Much Absorption Do You Need?

A good rule of thumb is panels equal to 15–25% of the floor area. To get closer, use the Sabine formula: RT60 = 0.049 × room volume in cubic feet ÷ total absorption in sabins.

Say you have a 20 ft × 25 ft room with a 10 ft ceiling, which is 5,000 cu ft, and it measures 1.2 seconds:

• Now: 0.049 × 5,000 ÷ 1.2 = about 204 sabins of absorption.
• Target of 0.8 seconds: 0.049 × 5,000 ÷ 0.8 = about 306 sabins.
• The gap: about 102 sabins to add.
• One 4 ft × 4 ft panel at NRC 1.05: 16 sq ft × 1.05 = about 16.8 sabins.

That works out to 6 or 7 panels, which at $259 each is $1,554 to $1,813 before shipping. It’s an estimate, not a guarantee, since the formula is less reliable in very large or oddly shaped rooms. Commercial Acoustics has a full walkthrough of how many panels a room needs.

What Doesn’t Fix Reverberation

• Soundproofing materials. Mass loaded vinyl blocks sound from passing through a wall, but it doesn’t absorb much. The reverse is true as well: panels reduce reverberation, but they won’t stop neighbors hearing you.
• Thin foam tiles. These mostly absorb high frequencies, so a room can end up sounding dull while the lower part of voices and music still rings.
• Egg cartons. They don’t absorb enough to matter.
• Diffusers alone. Sound diffusers scatter reflections, which can make a room sound better, but they won’t lower reverberation much by themselves.

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