What RT60 and C50 Tell You
RT60 (reverberation time) is how long a sound takes to fade away after the source stops. C50 (clarity) is the ratio of early, useful sound energy to the later, reverberant energy that blurs speech. Together they tell you whether a room is too live and whether the people in it will understand each other.
There is no universal target. A classroom aims for an RT60 around 0.4 to 0.6 seconds, a conference room a bit more, and a worship space longer to support music. Memtech Acoustics measures the room, then tunes it to the right range for how it is used.
Whether the space is a classroom, a courtroom, a conference room, or a worship space, RT60 and C50 are the metrics that decide whether speech is intelligible in it.
There is no universal target. A classroom aims for an RT60 around 0.4 to 0.6 seconds, a conference room a bit more, and a worship space longer to support music. Memtech Acoustics measures the room, then tunes it to the right range for how it is used.
Whether the space is a classroom, a courtroom, a conference room, or a worship space, RT60 and C50 are the metrics that decide whether speech is intelligible in it.
A room with the wrong reverberation causes:
- Speech that is hard to follow
Reflections blur the words, so listeners strain, mishear, and tune out. - Listener fatigue
A live room wears people down over a long class, meeting, or service. - A PA that fights the room
Adding volume in a reverberant room adds reflections and makes clarity worse, not better. - Spaces that miss their criteria
Classrooms, courtrooms, and conference rooms have target ranges they are expected to meet.
Measuring RT60 and C50 gives you the data to treat the room precisely instead of guessing at panels.
How We Measure It.
In the Field.
Memtech Acoustics measures RT60 and C50 from the room's impulse response, captured with a calibrated source and a Class 1 analyzer across multiple source and receiver positions, following ISO 3382.
Impulse Response Capture
We excite the room with a calibrated source or interrupted broadband noise and record the full decay, the basis for both metrics.
RT60 by Octave Band
Reverberation time is derived per frequency band, because a room can be controlled at speech frequencies yet still live in the low end.
C50 and Speech Clarity
Multiple Positions
We measure several locations across the room, because reverberation and clarity vary with where a listener sits.
Reporting Against Target
Results are reported per octave band against the design target for the space type, with the treatment direction where a target is missed.
Our Process
STEP 1
Discovery & Qualification
Memtech Acoustics starts with a collaborative process to understand the room, how it is used, and what people are experiencing, whether that is echo, poor speech clarity, or a space that is simply too loud.
We confirm the target RT60 and C50 for the room's purpose, identify the surfaces driving the problem, and align on whether the goal is a measurement baseline or a full treatment plan.
We confirm the target RT60 and C50 for the room's purpose, identify the surfaces driving the problem, and align on whether the goal is a measurement baseline or a full treatment plan.
Here are the types of questions we typically ask:
How is the room used, and is the main complaint echo, understanding speech, or overall loudness?
What are the room's hard surfaces (glass, drywall, exposed deck, hard flooring), and roughly how large is the volume?
How many people use the space at once, and is speech reinforced with a sound system?
Has any acoustic treatment been tried before, and what was the result?
How will the results be used: a design target, LEED or WELL credit documentation, or resolving a complaint about an existing space?
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STEP 2
On-Site Measurement
Memtech Acoustics measures the room as it actually performs, during a site visit, not from a drawing.
The room's impulse response is captured with a calibrated source, and the decay is recorded across octave bands from 125 Hz to 8 kHz.
All measurements use a Class 1 sound level meter, calibrated before and after the session, which is the standard required for defensible engineering reports.
Readings are taken at multiple source and receiver positions so the result represents the whole room, not one spot.
Background noise is logged as an NC or RC rating at the same time, because a noisy background lowers speech clarity even in a well-tuned room.
The room's impulse response is captured with a calibrated source, and the decay is recorded across octave bands from 125 Hz to 8 kHz.
All measurements use a Class 1 sound level meter, calibrated before and after the session, which is the standard required for defensible engineering reports.
Readings are taken at multiple source and receiver positions so the result represents the whole room, not one spot.
Background noise is logged as an NC or RC rating at the same time, because a noisy background lowers speech clarity even in a well-tuned room.
STEP 3
Analysis & Reporting
Memtech Acoustics calculates RT60 by octave band, along with the C50 and STI clarity ratings, from the measured decay curves.
Results are compared against the target for the room's use, and the absorption needed to reach that target is modeled using established room-acoustics methods.
We then deliver a clear report that states the measured performance, the target, and what it will take to close the gap.
Results are compared against the target for the room's use, and the absorption needed to reach that target is modeled using established room-acoustics methods.
We then deliver a clear report that states the measured performance, the target, and what it will take to close the gap.
STEP 4
Actionable Guidance
Reports are written to support real decisions, with measured numbers and a defensible method behind every recommendation.
Each report includes:
- Measured RT60 by octave band at each position
- C50 and STI speech-clarity ratings, with the NC or RC background rating
- Comparison against the target for the room's use
- A modeled treatment plan and product placement when Memtech handles the full package
STEP 5
Verification & Re-Test (Optional)
After treatment is installed, Memtech Acoustics can return to measure the room again and confirm it now meets the target.
When Memtech controls the engineering, materials, and installation as a full package, the measured result is backed by a written performance guarantee.
When Memtech controls the engineering, materials, and installation as a full package, the measured result is backed by a written performance guarantee.
We provide:
- Post-treatment re-testing to confirm RT60 and C50 reached target
- Before-and-after comparison of the measured room acoustics
- Documentation for LEED, WELL, or owner sign-off
- Performance guarantee on full engineered packages, remediated at our cost if the result misses target
The Memtech Difference
At Memtech, noise is our business. Our engineers oversee every step, ensuring that each project is properly delivered, on-time and within budget. This integrated approach delivers predictable results and protects your investment.
Certified Acoustic Professionals
Testing conducted by certified engineers and acoustic specialists, not general contractors or “safety consultants.”
National Standards Alignment
We follow OSHA 1910.95, NIOSH criteria, and ANSI S12.19-1996 methods for noise exposure assessment. Measurements are conducted via ISO procedures or per academically accepted methods.
Engineering Expertise
Noise measurements, analysis, modeling and installation support are overseen by professionals who understand acoustic theory, as well as the implementation of practical solutions.
High Responsiveness, Proven Reliability
We are your trusted local partner providing on-demand support and dependable project execution. Michigan-based with regional reach and national* shipping capabilities.
Confidential & Detailed Reporting
We don’t just submit a report. You are provided with complete documentation, delivered in easy-to-understand language with accurate data and comprehensive drawings.
*Shipping available across the continental USA, and international; installations are offered in select regions.
NOTE: We do not stock custom products in our U.S. warehouse. Ask us about lead times for your project.
NOTE: We do not stock custom products in our U.S. warehouse. Ask us about lead times for your project.
Frequently Asked Questions (FAQs)
What is RT60, and what does it measure?
RT60 is reverberation time: the time it takes for sound to decay by 60 decibels after the source stops. It is the most common metric in room acoustics. A high RT60 means a room is live and echoey with poor speech clarity; a very low RT60 can mean a room feels dead. Memtech Acoustics measures RT60 by octave band, because a room can perform well in one frequency range and poorly in another.
What is C50, and how is it different from RT60?
C50 is the clarity index: the ratio of early sound energy (the first 50 milliseconds) to the late energy that arrives after it, measured in decibels. Higher C50 means clearer speech. RT60 tells you how long sound lingers; C50 tells you how intelligible speech is in that room. Both are derived from the same impulse-response measurement, and Memtech Acoustics reports them together with an STI rating.
What is a good RT60 for my space?
There is no universal target; it depends on how the room is used. Classrooms are held near 0.4 to 0.6 seconds under ANSI/ASA S12.60, conference rooms around 0.5 to 0.7, open offices around 0.6 to 0.8, and worship spaces higher, often 1.5 seconds or more to support music. Memtech Acoustics sets the target from the room's purpose, then measures and models to reach it without over-deadening the space.
How does Memtech Acoustics measure RT60 and C50 in the field?
Memtech Acoustics captures the room's impulse response with a calibrated source and a Class 1 sound level meter, calibrated before and after the session, following ISO 3382. Measurements are taken across octave bands from 125 Hz to 8 kHz at multiple source and receiver positions. RT60, C50, and STI are calculated from those decay curves, and background noise is logged as an NC or RC rating because background level affects clarity.
What spaces need RT60 and C50 testing most?
Classrooms, lecture halls, conference and training rooms, restaurants, worship spaces, gyms and multipurpose rooms, and open offices: any room where people say speech is hard to understand or the space feels loud and echoey. Memtech Acoustics also tests to set a baseline before treatment and to verify the result after.
Will acoustic treatment make my room sound dead?
Not when it is engineered to a target. Over-treating a room drives RT60 too low and makes it feel lifeless. Memtech Acoustics models the absorption needed to reach the target for the room's use, then specifies engineered noise control in the right amount and the right places, rather than covering every surface and hoping.
What do I get in an RT60 and C50 report?
A clear report with measured RT60 by octave band at each position, the C50 and STI clarity ratings, the background noise rating, and a comparison against the target for the space. When Memtech Acoustics also handles the treatment, the report includes a modeled treatment plan and product placement. Assessment reports are typically delivered within about 15 business days of data collection.
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