Does acoustic treatment really work? What research shows about results before and after the work

More comments keep reaching the head teacher: in the first-floor rooms it is hard to hold a conversation, two teachers complain of vocal fatigue, pupils increasingly ask for instructions to be repeated. Someone suggests buying sound-absorbing materials and “soundproofing” the worst rooms. But the decision to buy answers neither of the two questions everything depends on: what exactly is the problem here, and how will we know the work has succeeded? Because “is it quieter?” can be asked after any refurbishment - and after any refurbishment the answer can be “a bit, I think”. So how do you tell a genuine improvement in conditions from the impression that things feel nicer after the works?

First establish which problem you are solving

The sentence “you can’t hear properly in this room” can describe at least ten different situations, each calling for different action. Too long a reverberation time is one. Sound coming through the door and wall from the corridor is another. Street noise through the windows is a third. Humming ventilation or other services, a fourth. Noisy furnishings, chairs and tables without protective feet, a fifth. A large number of people speaking at once during group work, a sixth. The way lessons are organised, a seventh. Poor speech intelligibility, which may follow from several of the above at once, an eighth. Most often it is not one problem but an overlapping combination of them.

The consequence is simple and expensive: a solution right for one problem can be useless against another. Sound-absorbing material on the ceiling shortens reverberation time - but will not stop noise coming in from the corridor, which is a job for the building fabric: door, wall, seals. Replacing a door with a heavier one improves insulation - but will not change the fact that words spoken in the room overlap one another. Replacing a fan lowers background noise - and touches neither reverberation nor insulation.

Four terms used interchangeably in conversations about schools describe different things. Acoustic treatment means shaping the sound conditions inside a room - controlling reflections and reverberation. Sound insulation concerns the transmission of sound between spaces or from outside. Reducing services noise is a separate technical task, concerning equipment. And the everyday word “soundproofing” is not a term at all - it blurs all of the above and should therefore not appear in documentation or in a request for quotation. If these concepts merge in conversation with a contractor, that is the first warning sign.

What should be measured before and after

Assessing effectiveness requires a reference point. Without a measurement before the change there is no way to say whether anything improved - only an impression. Which parameters to use depends on the problem and the room’s function, but it is worth knowing what each of them describes.

• Reverberation time - how fast sound decays after the source stops; the basic indicator for interior treatment, reported separately for frequency bands.
• Background noise level - sound in an unoccupied room: services, street, corridor. It tells you what the teacher’s voice has to compete with.
• Sound level in use - how much there really is during a lesson; it also depends on the number of people and the type of activity.
• STI or another measure of speech intelligibility - how faithfully the room transmits the features of the signal that carry legibility.
• Signal-to-noise ratio - the voice’s advantage over the background; the parameter that decides whether a message can be received.
• Insulation of the building fabric - how much sound passes through walls, floors, doors and windows.
• Services noise - measured separately, because it calls for separate solutions.
• Differences between places in the room - conditions at the board and in the back row can be incomparable, and a reading from one point will not show it.

Two methodological notes. A measurement in an empty room and a measurement during lessons answer different questions: the first describes the room itself and allows comparison with requirements, the second says what happens in it in real use. Both are useful and neither replaces the other. And the second: a phone app may suggest that a room is worth checking properly, but it will not confirm compliance with a standard or produce a result on which an investment decision can rest.

Objective measurements and users’ views

The best assessment combines two sources of data. A professional measurement describes the room’s acoustic properties. Teachers’ observations, pupils’ views, ratings of vocal effort, how often instructions have to be repeated, tiredness after lessons and how people actually use the space - these describe the users’ experience. They are two different layers of information and neither replaces the other.

Two conclusions follow, and they are easily confused. An improvement in parameters need not be noticed to the same degree by everyone: some will feel the difference from day one, some will not notice it at all, and others will notice something the measurement did not cover. And conversely: favourable user opinion after a refurbishment does not confirm technical compliance - why, we explain later in this text.

Technical, organisational or educational intervention

Research on improving acoustic conditions in schools shows three recurring kinds of action - and the fact that they rarely occur separately.

Technical measures cover changing the properties of interior surfaces, reducing sound transmission through the building fabric, improving services, changing furnishings and making furniture quieter. These are what change a room’s measurable parameters.

Organisational measures mean changing the break timetable, separating the noisiest activities in time, ordering how pupils move around the building, rules for using spaces and how groups are distributed. They do not change a room’s parameters, but they change how much sound is generated in it.

Educational measures are workshops for pupils and teachers, explaining how noise affects learning and communication, agreeing rules together, observing sound sources and building users’ awareness.

This three-way split has an important methodological consequence. In many studies - and in most real school projects - several kinds of measure are introduced at once. That makes sense from the school’s point of view and is awkward from the point of view of evaluation: if things are better after a refurbishment combined with workshops and a new break timetable, there is no telling which element is responsible, or in what proportion. It is worth bearing in mind while reading the findings we now turn to.

What the research shows

What technical refurbishment changes

A comprehensive intervention in a Polish school (Polewczyk and Jarosz, 2020). In the Polish context this study comes closest to the question in our title: what changes in a school after acoustic treatment [1]. In one primary school, measurements were taken before and after work covering a large part of the building - equivalent sound level (LAeq), reverberation time and the speech intelligibility index STI. Users’ assessments were collected in parallel: 378 pupils and 44 teachers completed the ACFS-S and ACFS-T questionnaires. The starting point was difficult: reverberation time before the treatment was very long. After the work the acoustic parameters improved, and participants reported changes in understanding instructions, concentration, work pace, tiredness and - for teachers - perceived vocal effort.

The limitations should be named plainly, because they matter. Some results come from questionnaires and participants’ own ratings, not from measurements. It was not a randomised study and had no control group - it is a “before and after” comparison in a single school. The work covered a large part of the building, so the contribution of individual elements cannot be separated. Results from one school do not transfer automatically to others with different architecture and different patterns of use. And an important point: rating “I concentrate better” on a questionnaire is not a neuropsychological test and does not measure cognitive function - it measures how a pupil rates their own experience.

Classroom refurbishment and teachers’ perceptions (Kristiansen et al., 2016). A Danish team examined how acoustic refurbishment of classrooms affects teachers’ perception of their noise exposure and the noise-related symptoms they report [2]. The study was conducted in two schools, comparing conditions before and after the changes. Reverberation time and sound levels during activity were measured; in parallel, teachers provided ratings of perceived exposure, information about disturbances (including from furnishings) and about symptoms linked to noise. The refurbishment was associated with lower reverberation times and lower sound levels during lessons, and some of the teachers’ ratings changed favourably.

Two things must be kept apart here. Lower reverberation time and sound level are a measured result. A change in teachers’ ratings is a self-reported result. The first speaks about the room, the second about people’s experience - and they should not be merged into a single sentence about “improvement”. Not all reported symptoms improved unambiguously. The numbers of classrooms and teachers, the exact reverberation values and the detailed questionnaire results require verification in the full text, which is why we do not quote them.

When several fronts are tackled at once

Technical, organisational and educational intervention (Taborda et al., 2021). A Brazilian team evaluated a programme covering all three kinds of action at once [3]. Sessions on the effects of noise were held with school administrators, teachers, pupils and families; the organisation of breaks and the way pupils left the building were changed; furnishings were maintained and technical changes made to the building. Measurements covered 11 classrooms and 4 outdoor spaces, and the signal-to-noise ratio was measured in 3 classrooms; questionnaires were collected before and after. The annoyance index fell from 0.78 to 0.59, and the mean signal-to-noise ratio rose from +7.5 to +8.4 dB.

The study does, however, contain a finding that does not fit a simple success story - which is precisely why it repays careful reading: after the intervention, reports of tinnitus increased. This should be neither passed over nor interpreted hastily. Several explanations are possible and the study does not settle between them: participants had attended educational sessions on the effects of noise on hearing, which may have increased attention to their own sensations and their willingness to report them; the propensity to report at the second measurement may itself have changed. Above all the result shows why it is wrong to select from a publication only the data that support an expected thesis. A further limitation: because several interventions were introduced simultaneously, no effect can be attributed to any single one.

Treatment plus a workshop (Pirilä et al., 2020). A Finnish study combined an acoustic intervention in two primary-school classrooms with a subsequent workshop on controlling noise, then collected participants’ experiences [4]. Two teachers reporting voice symptoms and 50 pupils took part. Listening experiences and vocal ergonomics were assessed, and the design allowed what followed the technical change to be separated from what followed the workshop. The value of this work lies precisely in showing that changing the space and working on users’ behaviour can complement each other.

The limitations here are very serious and must be read together with the result. The sample was minimal - two teachers. There was no substantial control group. Some data are subjective ratings. No conclusion about effect size can be drawn from such a study, nor transferred to other schools. One thing must be said plainly: a workshop is not a substitute for technical work. Talking about noise does not change reverberation time.

What shows up over a longer period

Long-term monitoring (Kotus et al., 2010). A Polish team ran continuous measurements of the acoustic climate in two schools for about 16 months, some eight of them before the acoustic treatment of the corridors [5]. This is a rare and valuable design: it allows conditions before and after the change to be compared not on the basis of a single measurement day but over a long period covering different seasons, different weeks and different attendance. The significance for schools is methodological: a one-off measurement may happen to fall on an atypical day, whereas long observation shows conditions as they actually are.

Two caveats. The study concerned the acoustic climate and measurements, not a full assessment of users’ health or pupils’ educational outcomes - so it does not answer what the treatment changed about learning. And the detailed numerical results require verification in the full text, which is why we do not give them.

A finding that calls for caution: not all absorption helps

Panels and listening effort (Amlani and Russo, 2016). In our set this publication is the most important safeguard against the simple message that “more absorption = better” [6]. The experiment compared a room without acoustic panels with the same room with panels. STI was measured, different seating positions were tested, and 27 third-grade pupils aged about 8-9 took part. The task was word recognition, and an additional memory task served as an indicator of listening effort. The result was surprising: in some conditions effort increased after the panels were installed, and distance from the speech source mattered - the seats furthest away suffered most.

The paradox is instructive. After the work the room may have met particular recommendations for reverberation time while, in this experiment, signal transmission and performance on some tasks got worse - especially towards the back of the room. The explanation is physical, not ideological: early reflections reinforce audibility further from the speaker, and excessive or badly placed absorption can weaken them. The person who loses out is the one sitting furthest away.

What does not follow from this study is that absorbing materials are harmful - what follows is that the design matters. Placement matters. Quantity matters. How the solution behaves across frequency bands matters. And a solution must not be chosen solely on how much it will shorten reverberation time - speech intelligibility has to be assessed at different places in the room, including those furthest from the teacher.

What the evidence looks like as a whole

Systematic review (Mercugliano et al., 2025). A current review of how the acoustic quality of classrooms affects pupils’ perception and wellbeing shows three things relevant to our question [7]. First, the outcome measures vary widely - studies measure different things and define them differently, which makes comparison harder. Second, the number of studies on pupils’ subjective experience remains limited, especially for the youngest. Third, results depend on the educational level, the type of room and the method used. The authors point to the need for better-designed intervention studies. Caveat: the review is not evidence of the effectiveness of any particular treatment - it organises the evidence and shows its gaps.

What a “before and after” result really means

In school conditions a before-and-after comparison is often the only feasible design and has real value - but it is worth knowing what it does not settle. The point of this section is not to undermine intervention studies, but to read their results honestly.

In a before-and-after study the same object is measured twice: before the intervention and after it. Without a control group - a comparable school or room where nothing was changed - the effect of the intervention cannot be separated from what would have changed anyway. A separate phenomenon is the Hawthorne effect: people change their behaviour when they know they are being observed. Teachers and pupils aware of taking part in a project may for a time speak more quietly, keep to the rules and use the space more carefully - regardless of what was done to the ceiling.

More prosaic factors come on top. The sound level during lessons depends on the number of people in the room, and class sizes change. The season matters: conditions with the windows open differ from December. The school’s organisation may change at the same time as the refurbishment - a new timetable, different room allocations, a different rhythm of breaks. Novelty affects questionnaires: a freshly renovated interior is rated more favourably. And finally: improving two acoustic parameters does not automatically confirm an improvement in educational outcomes - that is a separate question requiring separate research. This is why long-term observation, as in the study by Kotus and colleagues [5], is stronger than a single check a week after the works are handed over.

When the measurement improves and the user does not feel it

This happens more often than one might think, and usually has a concrete explanation. Reverberation time was shortened, but noise still comes in from the corridor - the treatment was improved without touching insulation. Door and window insulation was improved, but the room still has unfavourable reverberation - the reverse case. The average sound level fell, but sudden sounds still occur and interrupt work regardless of the average. The improvement is clear near the teacher and absent in the back row. Users need time to change how they use the space - old vocal habits persist long after the works. Or - the costliest scenario - the intervention simply did not match the real source of the problem.

An important caveat: the absence of felt improvement does not prove the measurement was wrong. It means one thing was measured while something else is the obstacle - or that the effect is real but smaller than expectations.

When users feel an improvement and there are no measurements

The reverse case is equally instructive. After the refurbishment the ratings are clearly better, but nobody measured either the starting point or the end state. Such opinion is valuable and should not be dismissed - but it is worth remembering that a refurbishment usually changes more than acoustics. The interior has been renovated and simply looks better. New furnishings have appeared. The organisation of work has changed. The problem has become a focus of attention, so people started talking about it and keeping to the rules. Participants feel they took part in a project about their own working conditions. Other environmental conditions have changed too - lighting, ventilation, temperature.

This does not mean users’ views matter less than a meter reading. It means that a change in ratings alone does not say how much of it is down to acoustics - and that information is needed when deciding whether to repeat the same solution in the next ten rooms.

Not every room needs the same thing

Requirements depend on a room’s function, and that varies drastically within one building. An ordinary classroom, the after-school room, the canteen, the sports hall, a corridor, the library, the music room, a specialist office, an open-plan space and a room intended for pupils with particular hearing needs - these are ten different acoustic tasks, not one repeated ten times.

A music room needs different treatment from a reading room, because in one sound is the content and in the other an interference. The canteen and the corridor are spaces where nobody gives a lecture but where sound levels escalate and there is nowhere to rest. Rooms for pupils with particular hearing needs require more favourable conditions than an average classroom - we write about this in the article on reverberation and speech intelligibility, where we also discuss the standards that differentiate requirements by a room’s purpose.

Hence two negative recommendations. There is no single universal reverberation time that is right for all school spaces. And a value obtained in one study - in one room, with one function - should not be transferred to every type of room in the building.

What the research cannot yet tell us

The evidence on the effectiveness of acoustic interventions in schools is markedly weaker than the evidence on the effects of noise itself. Many studies cover one or two schools. Some have no control group. Interventions differ so widely in scope that the word “treatment” in two publications can describe completely different undertakings. Very often several elements were changed at once, which makes attributing an effect to one action impossible. Some results come from questionnaires and self-report.

There are thematic gaps too. Not all studies measure educational outcomes - most stop at acoustic parameters and user ratings. A short observation after a refurbishment does not say whether the effect will hold over years of use. Schools differ in architecture, building age and how their spaces are used, so a result from one is not a forecast for another. Not every favourable result can be attributed to absorbing materials alone - and as Amlani and Russo’s study shows [6], not every use of them improves conditions for receiving speech throughout the room. And finally: the publication of a single case study is no guarantee that the same result will recur elsewhere.

Summary

Let us return to the school from the start of this article - the one where conversation is hard and someone proposes buying sound-absorbing materials. The question “is it quieter after the change?” is too narrow to base a decision about public money on. It can be quieter for ten reasons, some of which have nothing to do with the refurbishment. And it can be both quieter and harder - as in rooms where excessive absorption weakened the reflections the back rows needed.

An effective acoustic intervention should leave behind not only new interior elements but also a measurable change in conditions and a better experience for the people who use the room every day. One without the other is incomplete: measurement without users’ views does not say whether the change matters in practice, and views without measurement do not say whether it can be repeated in the next room.

And one last thing: even a favourable change deserves an honest account of its limits. A school that can say “we improved reverberation time and speech intelligibility, teachers report less vocal effort, but we did not study the effect on pupils’ results and we do not know how it will look in three years” knows more about its building than one that announces a success. On how a room’s acoustics translate into the daily load on the person teaching, we write in the article on the vocal load on teachers.

References

1. Polewczyk I., Jarosz M., Teachers' and Students' Assessment of the Influence of School Rooms Acoustic Treatment on Their Performance and Wellbeing, „Archives of Acoustics” 2020; 45(3): 401-417. DOI: 10.24425/aoa.2020.134057.
2. Kristiansen J., Lund S.P., Persson R., Challi R., Lindskov J.M., Nielsen P.M., Larsen P.K., Toftum J., The Effects of Acoustical Refurbishment of Classrooms on Teachers' Perceived Noise Exposure and Noise-Related Health Symptoms, „International Archives of Occupational and Environmental Health” 2016; 89(2): 341-350. DOI: 10.1007/s00420-015-1077-3; PMID: 26259727.
3. Taborda R.F., Gomes R.F., Rocha C.H., Samelli A.G., Evaluation of Noise Reduction Interventions in a School, „Folia Phoniatrica et Logopaedica” 2021; 73(5): 367-375. DOI: 10.1159/000509332; PMID: 32829342.
4. Pirilä S., Jokitulppo J., Niemitalo-Haapola E., Yliherva A., Rantala L., Teachers' and Children's Experiences after an Acoustic Intervention and a Noise-Controlling Workshop in Two Elementary Classrooms, „Folia Phoniatrica et Logopaedica” 2020; 72(6): 454-463. DOI: 10.1159/000503231; PMID: 31639814.
5. Kotus J., Szczodrak M., Czyżewski A., Kostek B., Long-Term Comparative Evaluation of Acoustic Climate in Selected Schools Before and After Acoustic Treatment, „Archives of Acoustics” 2010; 35(4): 551-564.
6. Amlani A.M., Russo T.A., Negative Effect of Acoustic Panels on Listening Effort in a Classroom Environment, „Journal of the American Academy of Audiology” 2016; 27(10): 805-815. DOI: 10.3766/jaaa.15096; PMID: 27885976.
7. Mercugliano A., Corbani A., Bigozzi L., Vettori G., Incognito O., The Effects of Classroom Acoustic Quality on Student Perception and Wellbeing: A Systematic Review Across Educational Levels, „Frontiers in Psychology” 2025; 16. DOI: 10.3389/fpsyg.2025.1586997; PMID: 40861365.

This article is for information only. It is not an acoustic treatment design, and it does not replace a measurement taken in a specific room or technical advice on choosing a solution.