How to evaluate a class room for acoustical renovation

About Classroom Acoustics

Hearing and understanding are important parts of the learning process. A noisy classroom can make these tasks difficult. Noise in the classroom is more than students talking. There are other factors that make it hard to hear and understand in the classroom.

Acoustics is a term used to talk about how sound travels in a room. There are factors in the room design that may make sounds louder or softer. Examples include floor rugs, ceiling type, and air ducts. Classroom acoustics is the term for these issues in schools.

Background Noise and Reverberation

Two things cause poor classroom acoustics: too much background noise and/or too much reverberation.

Background noise is any sound that makes it hard to hear. In a classroom, background noise can come from many places, including the following:

  • Sounds from outside the building, such as cars and lawnmowers
  • Sounds from inside the building, such as students talking in the hallway
  • Sounds from inside the classroom, such as air conditioning units and students in the room

Reverberation describes how sounds act in a room after they first happen. Sounds stay in the room when they bounce off desks or walls. If many sounds do this at once, it can get very loud.

Problems Caused by Poor Classroom Acoustics

When classroom acoustics are poor, it can cause problems with how a student

  • understands speech;
  • reads and spells;
  • behaves in the classroom;
  • pays attention; and/or
  • concentrates.

It is important to keep the classroom as quiet as possible for all children.

Good Classroom Acoustics Helps Everyone

A quiet classroom helps teachers and students. It is especially important to have a quiet room if a student has

  • hearing loss in one or both ears;
  • an ear infection or fluid in the ear;
  • a learning disability;
  • auditory processing disorder;
  • speech and language delay; and/or
  • attention problems.

Teachers also do better if there are good classroom acoustics. Talking in a loud classroom strains the teacher’s voice and may lead to voice problems.

Improving Classroom Acoustics

It is important to think about background noise and reverberation in any space used for learning. Some simple ways to make a classroom quieter include the following:

  • Place rugs or carpet in the room.
  • Hang curtains or blinds in the windows.
  • Hang soft materials such as felt or corkboard on the walls.
  • Place tables at an angle around the room instead of in rows.
  • Turn off noisy equipment when it is not in use.
  • Replace noisy light fixtures.
  • Show students how hard it can be to hear when many children talk at the same time.
  • Place soft tips on the bottom of chairs and tables.

A brochure on The Noisy Classroom is available through the ASHA bookstore.

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The acoustical characteristics of 14 university classrooms at the University of British Columbia were measured before and after renovation—seven of these are discussed in detail here. From these measurements, and theoretical considerations, values of quantities used to assess each classroom configuration were predicted, and used to evaluate renovation quality. Information on each renovation was determined with the help of the university campus-planning office and/or the project acoustical consultant. These were related to the evaluation results in order to determine the relationship between design and acoustical quality. The criteria focused on the quality of verbal communication in the classrooms. Room-average Speech Intelligibility (SI) and its physical correlate, Speech Transmission Index (STI), were used to quantify verbal-communication quality. A simplified STI-calculation procedure was applied. The results indicate that some renovations were beneficial, others were not. Verbal-communication quality varied from ‘poor’ to ‘good’. The effect of a renovation depends on a complex interplay between changes in the reverberation and changes in the signal-to-noise level difference, as affected by sound absorption and the source outputs. Renovations which reduce noise are beneficial unless signal-to-noise level differences remain optimal. Renovations often put too much emphasis on adding sound absorption to control reverberation, at the expense of lower speech levels, particularly at the backs of classrooms. The absorption and noise contributed by room occupants has apparently often been neglected.

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Inferior acoustics is an invisible problem that has far-reaching implications for learning, but is easily solved. Excessive noise and reverberation interfere with speech intelligibility, resulting in reduced understanding and therefore reduced learning. Many educators feel it is important to improve acoustics in classrooms used by children with hearing problems, but unnecessary to do so in those used by students with normal hearing. Yet many populations of students with “normal hearing” also benefit from better classroom acoustics. These include students with learning disabilities, those with auditory processing problems, and those for whom English is a second language.

Another group for whom learning is especially dependent on good acoustics is young children, who are unable to “predict from context.” With their limited vocabulary and experience, if they miss a few words from a teacher’s lecture, they are less able than older students to “fill in” the missing thoughts. Given these considerations, it is clear that a wide range of students benefit from improved classroom acoustics. The best way to solve acoustics problems is to prevent them beforehand, not correct them after the fact. During the design process, acoustics problems can usually be avoided with a bit of forethought and a different arrangement of the same building materials. Renovation of poorly designed classrooms is much more expensive. Even then, the cost of renovation is small compared to the social costs of poor classroom acoustics that impair the learning of millions of children.

What are your classroom acoustics? Take the time to listen to the sounds of your classrooms.

The term “noise” (or variations—background noise, classroom noise, etc.) refers to any auditory disturbance that interferes with what a listener wants to hear (Finitzo-Hieber, 1988). The source(s) of the noise may or may not be within the classroom itself. Most classroom noise sources

  • arise from outside the building and intrude through exterior walls and windows,
  • are generated by heating/ventilating and air-conditioning (HVAC) systems,
  • intrude from hallways and adjacent rooms, and
  • are generated from within the classroom by computers and appliances as well as by the children themselves.
  • American National Standards Institute Standard S12.60 Classroom Acoustics New construction and renovation
  • Reverberation (echo) minimum of 0.4 seconds and maximim of 0.6 seconds for classroom size under 10,000 cubic feet and 0.7 seconds for classroom size between 10,000 and 20,000 cubic feet.
  • Ambient (background) noise less than 35 dBA (weighted scale)

Understanding Sound To better understand how sound, found in the classroom, affects a student’s ability to hear and learn, first become familiar with the attributes of sound. Direct Sound The sound of a teacher’s voice traveling directly from the teacher to the student is direct sound. It is always beneficial in terms of speech intelligibility because it is not affected by anything in the room, making it clear and distinct. Reflected Sound Reflected sound takes longer to reach the listener than direct sound because its path to the listener is longer. Reflected sound can be good or bad depending on the time delay. Reverberation Time The overall effect of reflected sound is called reverberation, and the time required for reflected sound to become inaudible is called reverberation time. Short reverberation times are good for speech intelligibility. Background Noise Any sound that is generated outside the building, such as playground activity, traffic and planes can be considered background noise. It generally intrudes in the classroom by way of the windows. Within the building, an HVAC system and corridor noise can contribute to background noise. Descriptions above provided by Armstrong Commercial & Industrial Ceilings Corp. To further understand the classroom acoustic attributes, watch the video clip entitled “Straight Talk.” Click here to access the web site and then click on the Straight Talk video clip. This is not an endorcement of Armstrong or it’s products.

Steps to Producing a Good Listening Environment

  • that speech intelligibility in many classrooms is 75%, i.e. listeners with normal hearing are missing one of every four words?
  • that up to 30% of primary students have some hearing loss, particularly during cold/flu season?
  • that there is an American National Standard for acoustic criteria and design requirements of classrooms?
  • that classroom noise impacts the academic success of ALL students?
  • that young students, English language learners, and students and teachers with hearing, language, or learning problems are at a greater disadvantage from poor acoustics?
  • that classroom noise impacts teacher absences?
  • that children need the teacher’s voice to be at least 15 decibels (dB) louder than interfering sounds?
  • that classroom sound-field amplification systems facilitate inclusion and response-to-intervention (RTI)?
  • that classroom sound-field systems reduce vocal strain of teachers and reduces absentee rate by as much as 36%?

How do you provide a good listening environment?

1. Provide sound barriers around classroom with partition walls extending all the way to the structural deck (floor above or roof).

2. Use dropped acoustic panel ceiling to reduce sound reverberation (echo).

3. Provide a barrier to exterior noise with double-paned, well sealed windows and solid doors with tight-fitting, sealed frames

4. Provide a “quiet” space, less than 35 dBA of noise from internal sound sources such as ventilating systems, computers, video projectors.

5. Use classroom management strategies to control noise from occupants of the room.

6. Arrange classroom learning centers to provide sound defusion and reduce distraction.

7. Amplify the teacher’s voice to raise the signal-to-noise ratio, which improves speech intelligibility and reduces vocal strain.

Why should you use your classroom amplification system? See the answers!

Posted by Ted W on 05/26/2010 12:40 pm | 8 Comments

Sound quality and understanding speech in a classroom environment is obviously something of importance. If students are not able to clearly hear instruction in a classroom they are not able to learn – or learn nearly as effectively as they should. If this is the case, the room needs acoustical treatment; there is no way around that. But what if the budget for the project is limited – or non-existent? Believe it or not, there are options.

I received a call from a man in California named Jason who reported that he had voluntarily taken on the task of finding out how to control the echo and reverberation of a classroom at his child’s school. I can’t recall whether or not this was being done simply to make the space more comfortable and improve the sound quality and speech intelligibility in the room or whether there was a special needs student that needed this treatment, but either way, something needed to be done in the classroom and there was an EXTREMELY limited budget if there was any at all.

Jason explained to me that these classrooms were common in the fact that they had a hard, VCT tile floor, painted sheet rock walls and a hard sheet rock ceiling. When the classroom was filled with young, noisy and excited children it continued to get louder and louder and louder to the point of discomfort. I’ve been in rooms like this and I know exactly what he was experiencing. I usually refer to problems like this as the “cocktail party effect” where people continue to increase their voice level so they can be heard over the background noise and this causes the background noise to rise which means they have to talk even louder to be heard – and the problem continues.

Because the budget for the project was so limited, there were only a few options. It was decided that the Echo Eliminator panels made from recycled cotton were the only likely choice. Because these panels are made from recycled cotton, they are one of the lowest cost, class A fire rated products on the market. They not only very cost effective but they are also very effective at absorbing sound. Most of these panels are installed by adhering them directly to the structure, but, in this case, the teachers and administrators did not want such a permanent solution. Jason decided that he was going to install some grommets and use some hooks hat he had seen which was a great idea.

Although the Echo Eliminator panels are some of the most cost effective panels on the market, due to the EXTREMELY limited budget for the job Jason and I had to explore some thrifty options. Performance was more important than aesthetics in this case which is why we looked through the available inventory on our Discount Soundproofing website and found a few boxes of product in good enough shape to be used. This inventory fluctuates on an almost daily bases as product is sold or is added and there are often quite a few boxes of product that we have not had time to install yet, but we were able to provide panels at a 50-70% discounted cost for this job which is truly the reason there are sound panels in the room now.

The cotton panels are not the most “finished looking” or “aesthetically pleasing” products on the market, but honestly, third-graders don’t really care. Their understanding of spoken word and physical comfort is, or should be, much more important than how pretty a room is. These panels are not ugly, they are simply not as finished as other products on the market. The teachers and administrators were not a huge fan of the aesthetic at first, but after the panels were installed and they were able to experience the change of the sound quality and feel of the room, all of the sudden these panels weren’t so bad… In fact, I received a call a short time later asking me for a quote on a second set of panels for an additional classroom. I can’t remember the exact dimensions of the classrooms, but twenty-two panels of the 1” #3lb Echo Eliminator were used.

Below is a short E-mail that I received from Jason shortly after the panels were installed into the first room as well as pictures from both. If you have any questions, need any information, or if you would like to discuss a similar situation, please feel free to contact me.

JASON – If you ever read this, you’re awesome! Thank you for the pictures and the little write up, this simple information has the potential to help hundreds of people. Thank you.

The hanging of the panels was a success. The room is glossy paint over plaster and lots of bare walls – it was very BRIGHT sounding. As soon as we did one wall, I noticed a difference on each side – quieter, warmer, less bright, more cozy (?) sounding. Kids, teachers, administrator all noticed a difference. Of course, we could have used more panels, but cost was a factor – so this is a big improvement. Here’s some pics from the job. As you can see, I punched two grommet holes and hung the panels on the walls (you can see all the fire sprinklers on the ceiling.) We used Ook brand picture hanger hooks – they have very slim nails that went straight in and the 30 pound hooks were big enough to hold the 1/2″ grommets. Plus, if there was any alignment issue, we could pivot the hooks on the nails a bit to adjust. (Sorry some of the pics are a little blurry, I was hurrying to get the classroom back to the kids…)

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

The pictures below are of the SECOND classroom that needed treatment. We did not have any more overstock beige panels but we did have enough light gray.

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

How to evaluate a class room for acoustical renovation

Please do not try to adjust your monitor, the swirls are intentional.

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Soft-sensor for acoustic comfort measurements in buildings renovation.

Application of the methodology to a real case study.

Comparison between the KPI evaluated from measured and simulated data.

Uncertainty and sensitivity analyses and impact on the decision-making process.

Identification of the critical input variables to reduce the output uncertainty.


This research presents a methodology for measuring acoustic comfort using a soft-sensing approach to support decision-making for buildings renovation. The soft-sensor provides a measurement system for evaluating indoor acoustic quality of buildings (housing, schools, offices, etc.) in relation to the external noise level. The metric is represented by Key Performance Indicators (KPIs), which quantitatively express the acoustic comfort. Information regarding the current condition of the building (“As-is” KPI) is provided as a normalised value for the simplified quantification of acoustic performance. The knowledge of the “As-is” KPI allows the design team to compare it with the new KPIs obtained from renovation scenarios (“What – if” KPI). A case study is presented to demonstrate the exploitability of the methodology. Sensitivity and uncertainty analyses are performed to establish how the accuracy of the KPI measurement impacts on the decision-making process. The methodology shows promising results in the identification of the best retrofit strategy.

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An assessment model of classroom acoustical environment is proposed.

An evaluation score was calculated from the proposed model.

The weightings generated from the model represented the proportion of alternatives.

The approach can be employed in other assessments of acoustical environment.


In this paper, an assessment model based on multi-layer fuzzy comprehensive evaluation method (FCE) of classroom acoustical environment is proposed. The model classifies five major factors affecting overall assessment model into several subsets alternatives. The weightings of these main criteria and alternatives were collected through questionnaires among students based on analytic hierarchy process methodology (AHP). An evaluation score was calculated from the proposed model with the weightings generated from AHP method. In this paper, classrooms in the Hong Kong Polytechnic University were used to develop the assessment model. The result shows that the evaluation score of PolyU classrooms is about 87.2, which refers to “Good” evaluation set. It indicates that classrooms in PolyU needs to be improved. The weightings generated from AHP method can be considered for the importance of each alternatives. The assessment model can provide proper recommendation to universities for acoustic treatment so as to increase the acoustic quality of the educational environment.

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How to evaluate a class room for acoustical renovation


This acoustical report of MIT Building 10 lobby (a.k.a. Lobby 10) aims to assess the existing conditions of space and provide recommendations for improvements. A computer model is then utilized as one of the tools to evaluate the efficacy of my proposed modifications through the use of Pachyderm (acoustics).

Lobby 10’s grand space, its intersection with the main corridor and three vertical circulation cores (two stair wells and a elevator shaft), and function as a main entrance make it a great place to capture visitors and passersby’s attention. Flexible layout of movable furniture (tables, chairs) makes it adaptive to various temporary events and performance.

According to staff and user-group interviews, there are several events types happening in MIT Lobby 10 space. The primary use of space is to hold daily student club and small networking events with movable furniture during the day due to its high visitor flow. There are also temporary performances including MIT Concert Choir, acrobatics and rehearsal happening in Lobby 10. Visitors and spectators can sit on seats against the wall in the Infinite Corridor.

The uses of space are likely to change and evolve due to its important position at the Infinite Corridor and flexible layout with movable furniture. With improvements and modifications to the room’s acoustics, the acoustic performance of Lobby 10 would better serve its adaptive uses.

My Role

This is an individual project developed in MIT class 4.431 Architectural Acoustics (2020 Spring)

The classroom environment was comprehensively investigated at Florida Agricultural and Mechanical University (FAMU) in Tallahassee, Florida. The purpose of this study was first to objectively measure environmental factors of classrooms at FAMU such as thermal conditions, indoor air quality, lighting, and acoustics and to ascertain if the classroom environmental factors affect academic achievement of students in the college level.

A total of 11 classrooms in the Architecture building and the Education building at FAMU were measured twice to represent the empty classroom and the occupied classroom by students at two different locations in each classroom. The classroom environments at the occupied condition were measured while lectures were ongoing. Thermal conditions such as dry-bulb temperature, wet-bulb temperature and % relative humidity were measured to investigate thermal comfort. CO2 concentration was measured to evaluate the indoor air quality. Light levels were measured in accordance to the style of the lectures. The background noises were measured and compared with NC curves. The classrooms with recent renovation showed relatively better classroom environment in all environmental factors.

keywords: Classroom Environment, CO2 Concentration, Temperature, Lighting, Acoustics