When a room sounds bad, the instinct is to buy better speakers. In most cases the room is the problem, and modest acoustic treatment delivers more improvement than a far larger equipment budget.
Reverberation above roughly 1.5 seconds destroys speech intelligibility, and no speaker fixes it. Treat the rear wall and first reflection points first. Absorption reduces energy; diffusion scatters it. Most venues need absorption.
| Space type | Target RT60 | Effect if exceeded |
|---|---|---|
| Conference room | 0.4 to 0.6 s | Poor remote call quality |
| Classroom | 0.4 to 0.8 s | Reduced comprehension |
| School hall, speech | 0.8 to 1.2 s | Announcements unclear |
| Worship, mixed use | 1.2 to 1.8 s | Speech blurs, music may suit |
| Music-only hall | 1.8 to 2.5 s | Speech unusable without treatment |
What reverberation time actually measures
RT60 is the time taken for sound to decay by 60 dB after the source stops. It is determined by room volume and the amount of absorption present.
Long reverberation smears consonants into one another. Since consonants carry most of the information in speech, intelligibility collapses well before the room sounds obviously echoey.
A full room has shorter reverberation than an empty one because people absorb sound. Systems tuned in an empty hall frequently sound wrong when occupied.
Absorption versus diffusion
Absorption converts sound energy into heat within porous material, reducing overall energy. This is what most speech-focused venues need.
Diffusion scatters sound in many directions without removing much energy, preserving liveliness while reducing distinct echoes. It suits music spaces where you want reverberation but not slap.
Thickness determines which frequencies are absorbed. Thin panels only affect high frequencies, which can leave a room sounding dull and boomy at once. Deeper absorbers or air gaps behind panels extend the effect lower.
Where to treat first for the biggest gain
The rear wall usually returns the strongest single reflection back toward the audience and the microphones. Treating it typically gives the largest improvement per square metre.
First reflection points on side walls come next, then the ceiling above the stage or lectern.
You rarely need to treat an entire room. Targeted treatment at the worst reflection paths achieves most of the benefit at a fraction of the cost.
Practical treatment in constrained buildings
Heritage and listed buildings often prohibit permanent fixings. Free-standing absorbers, heavy curtains and soft furnishings all contribute without alteration.
In multi-use halls, retractable curtains allow the acoustic to be changed between speech and music events.
Even carpet, upholstered seating and people make a measurable difference. Consider the room in its occupied state when assessing what is needed.