Acoustic Treatment
Fixing how a room sounds, before the sound system is asked to fight it
OBAV surveys, specifies and installs acoustic treatment for restaurants and hotels, offices, churches, halls and schools across London and the South East, so a room controls its own sound instead of throwing it back at the people in it. It is most often designed alongside a sound system, and it stands on its own.
Absorption rated to a class, specified with a fire classification that is valid for the surface it is fixed to, and no more of it than the room needs.
Acoustic treatment for commercial buildings across London and the South East
From East Sussex we work across London, East Sussex, Kent, Surrey and the rest of the South East, travelling further for larger projects.
The rooms people complain about are always the same rooms. A dining room that gets louder as it fills. An open-plan office where nobody can concentrate. A hall with a hard floor and a high ceiling where speech smears into echo before it reaches the back.
We treat rooms in restaurants and hospitality, in the churches and heritage buildings we are known for, in schools and education where hall acoustics decide whether a lesson is heard at the back, in public buildings, and in bars and late-night venues. It sits alongside our other services and is usually specified in the same design as the AV install.
Acoustic treatment is not soundproofing
This is the first thing worth settling, because the two words get used as if they meant the same thing and they solve opposite problems.
Treatment changes what happens to sound inside a room. Insulation stops sound getting from one room to another, or out to the neighbours. BS 8233:2014 puts it bluntly: most types of absorber do not provide high values of sound insulation. Lining a wall with absorption will make the room sound better and will do almost nothing for the flat next door.
Approved Document E splits along the same line. Requirements E1 and E2 cover resistance to sound passing between spaces. Requirement E3 is the one about reverberation. Different requirements, different remedies, usually different contractors.
So if the problem is a noise complaint, a planning condition or a licensing condition, that is an insulation and noise breakout job and it needs an acoustic consultant’s report. We will say so early, and we are happy to install the treatment such a report calls for. If the problem is that the room itself sounds wrong to the people in it, that is our work.
Why turning the system up makes it worse
Most rooms that sound bad get treated by adding more sound to them. A restaurant fits a louder music system, diners raise their voices over it, and by half past eight nobody at a table of six can hold a conversation. A hall turns the volume up until the echo arrives with the words.
The physics is against it. Reverberation acts as a filter on the rise and fall of speech, smearing the gaps between syllables that carry the meaning. Turning the system up raises the direct sound and the reverberant tail together, so the ratio between them barely moves and intelligibility barely improves.
The Diocese of Chelmsford’s own guidance on church sound systems reaches the same conclusion in plainer words: in a building with a lot of inherent reverberation, amplifying speech can only increase the echo and create loss of clarity.
Treatment works the other way round. It changes what the room does with sound before the system is asked to fight it. A treated room usually needs a simpler system, not a bigger one.
What the right acoustic treatment gives you
In a treated dining room a table can talk at normal volume on a full Saturday night and the music sits under the conversation. That is often the difference between guests staying for another course and asking for the bill.
In a treated meeting room a video call sounds like the people in it instead of the room around them, so the far end stops asking for things to be repeated.
In a church the spoken word carries to the back without the music losing the reverberation that makes the building sound like itself. That tension is real in heritage work and we would rather name it than pretend it away.
Every room gets its own target, because a nave, a classroom and a boardroom all want something different.
What gets measured, and how well
Reverberation time is the number that matters most, and it gets measured instead of judged by ear. The method is BS EN ISO 3382-2 for ordinary rooms, which covers classrooms, offices, halls and restaurants, with BS EN ISO 3382-1 for performance spaces.
Two details in that standard matter before anyone quotes you a figure. First, the quantity is not what consumer audio calls RT60. The standard measures decay over a 30 dB range and reports it as T30, or over 25 dB as T20. School guidance uses Tmf, the average of the 500 Hz, 1 kHz and 2 kHz octave bands. Second, the standard defines three accuracy grades by how many source and microphone positions are used: at least two for survey, at least six for engineering, at least twelve for precision.
That second point is the useful one commercially. A single reading taken on a phone app is not a precision measurement, an engineering measurement, or even a survey measurement. It is one reading.
We also measure across the frequency range and not at one frequency, because a room can be acceptable at 1 kHz and hopeless at 125 Hz, and work out where the reflections that blur speech are arriving from. The wall people expect to be the culprit often is not.
[[CONFIRM: what acoustic measurement does OBAV carry out in house, with what equipment, and to which BS EN ISO 3382-2 accuracy grade? This section currently claims measurement across the frequency range as a capability. If measurement is brought in from a consultant, the wording needs to say so plainly.]]Absorption is rated in classes, and NRC is the wrong number
Absorbers are rated under BS EN ISO 11654, which converts absorption across the frequency bands into a single figure and a class from A to E. Class A is roughly 0.90 and above, class C runs from 0.60 to 0.75, class E from 0.15 to 0.25. Approved Document E names that standard directly when it sets out how to specify an absorber, so it is the rating a building control officer expects.
If a data sheet quotes NRC instead, it is an American number. NRC comes from ASTM C423 and has no standing in the Building Regulations. It usually means the supplier has handed you a US test report.
The class number has a limit worth understanding, and the standard says so itself. Its rating curve stops at the 250 Hz octave band, so the rating is not appropriate below that. It also says the single figure is not appropriate where a room needs careful acoustic design, and that only full absorption data across frequency will do. Which is a standards committee’s way of saying that buying panels by their class alone will get you a room that measures well on paper.
Bass is a depth problem, not a panel-count problem
Thin absorption works at the top of the range and does very little at the bottom. That is not a matter of quality, it is a matter of wavelength. A porous absorber needs to be roughly a tenth of a wavelength thick to absorb usefully. At 100 Hz the wavelength is about 3.4 metres, so a tenth of it is around 340 millimetres. Fifty millimetres of foam is about one seventieth.
The government’s own figures make the same point. Approved Document E’s table of absorption coefficients gives carpet on a concrete floor as 0.03 at 250 Hz rising to 0.40 at 4 kHz, a factor of thirteen across the range.
That is exactly how a room ends up dull and still boomy. Somebody carpets it and hangs thin panels, the top end disappears, the low end is untouched, and the room now sounds worse in a different way.
Where low frequency genuinely has to come down, the tools are depth, an air gap behind the absorber, or a tuned panel or membrane absorber working against a sealed cavity. All three take space, so the conversation belongs at design stage and not after the finishes are signed off.
The fire classification question, which almost nobody asks
This is the part of acoustic treatment where getting it wrong matters most. It is also the part the online panel market is worst at.
Approved Document E, the acoustics guidance, hands the question straight over: the choice of absorptive material should meet the requirements of Building Regulation Part B, fire safety. Approved Document B then sets what a wall or ceiling lining has to achieve. In buildings other than dwellings the general requirement is class C-s3,d2 in rooms and class B-s3,d2 in circulation spaces, which are the routes people escape along.
Three things follow that are worth checking on any quotation.
An untested product has no classification. Approved Document B is explicit that products which have not been tested cannot be classified under BS EN 13501-1. Bare polyurethane studio foam bought online usually arrives with no classification report at all, so there is no route to showing it complies anywhere in a public building. The HSE’s own guidance on cellular plastics notes that most are fire hazards, may be ignited easily with a small ignition source, and produce thick, black, toxic smoke.
Class 0 is no longer a thing. The national reaction to fire classes, Class 0 and the BS 476 Part 7 classes, were removed from Approved Document B on 2 March 2025. European classes are now the sole route to specification in England. A panel still advertised as Class 0 is being sold against guidance that no longer exists.
A classification belongs to a build-up, not to a panel. Approved Document B states that a classification achieved in testing is only valid when the product is used in that same field of application, meaning fixed to a substrate of the class it was tested against. A panel tested on plasterboard and then glued to bare masonry may have no valid classification at all.
We specify absorption with a current European classification that is valid for the surface it is actually being fixed to, and we would rather lose a job than staple unclassified foam to the wall of a village hall.
[[CONFIRM: this section commits OBAV to specifying only absorbers with a current BS EN 13501-1 classification valid for the actual substrate. Confirm that is the policy, and that the classification reports get passed to the client at handover. This is the strongest differentiator on the page and it needs to be true.]]Too much treatment is also a fault
Covering every surface costs more and leaves a room sounding dead, and there is official backing for saying so. Approved Document M asks for an acoustic environment that is neither too reverberant nor too absorbent, so that announcements and conversations can be heard clearly.
Churches are where this goes wrong most often, usually with soft furnishings rather than panels. The Diocese of London’s guidance warns about over-absorption near the source and notes that even an aisle carpet can be bad. The Diocese of Chelmsford records a church that introduced so much extra carpeting that its original sound system became ineffective.
The other common error is putting everything on one wall. Absorption on the rear wall of a hall answers one specific problem, slap-back off the back wall, while the front wall and much of the ceiling usually want to stay reflective so the talker’s voice is projected forward. The Institute of Acoustics design guide for schools makes the general point: what matters is a reasonable distribution of absorption around the room, and the ceiling is usually the most practical place to start.
So we sometimes specify less treatment than a room has already been quoted for. That is not us being modest about the scope, it is what the room needs.
Churches, chapels and listed buildings
A masonry church is the hardest acoustic problem we get asked to solve, so here are the numbers. Published research puts English parish churches at around a second of reverberation for speech and one and a half to two seconds for music, with large cathedral spaces running very much longer. St Paul’s measures around eleven seconds at 500 Hz when empty.
You will not bring a listed nave down to office figures, and you should not want to. The building’s reverberation is part of what it is, and organ and choral music were written for it. So the answer in a church is usually not blanket absorption. It is a distributed sound system with each loudspeaker covering a defined area, so speech reaches people directly instead of arriving as a wash off the stonework, with targeted absorption only where a specific reflection is doing damage.
At Galeed Baptist Chapel in Brighton the reverberation in the high ceilinged chapel was the whole problem, and the way through it was a larger number of smaller loudspeakers each serving one area, so that sound went to the congregation rather than bouncing off windows and walls. At Christchurch in Little Heath the cabinets were mounted off the wall plates and angled down for the same reason.
One practical detail almost nobody mentions: a church measures considerably longer empty than full. Published measurements put the difference at around eight tenths of a second on average. A survey taken in an empty building on a Tuesday is not what the congregation hears on Sunday, and the target has to allow for it.
On consent, the current rules are the Faculty Jurisdiction Rules 2015 as they have effect from 17 May 2024. Installing or altering a sound reinforcement or loop system sits in List B, needing the archdeacon’s written notice. Adapting an existing system can fall under List A, but in a listed church only if no alteration is made to existing fixings or cable runs, which in practice means the moment you drill a new hole List A stops covering you. Fixed acoustic absorption appears in neither list, so we work on the basis that panels in a listed church need a full faculty and we check with the DAC before anything is specified. Historic England’s guidance on changes to heritage assets is that new work should be reversible where possible, and that is how we detail fixings in these buildings.
[[CONFIRM: that fixed acoustic panels require a full faculty is our reading of Lists A and B (2024) by absence, since neither list mentions acoustic absorption. It is sound but it is an inference. Worth confirming with a DAC before this is stated as settled, and it is a good thing to be seen checking on every church job.]]Schools, and the numbers a hall has to meet
School acoustics are the one sector with hard published targets, so there is no argument about what good looks like. Requirement E4 of the Building Regulations covers acoustic conditions in school buildings, and the normal route to satisfying it is Building Bulletin 93, currently the February 2015 edition.
BB93 sets maximum reverberation times as Tmf. A new-build primary classroom is 0.6 seconds and a secondary classroom 0.8, with refurbishment allowed 0.8 and 1.0. An open-plan teaching area is 0.5 either way. An assembly or multi-purpose hall sits in a band of 0.8 to 1.2 seconds. A teaching space specifically for pupils with hearing or communication needs is 0.4 seconds averaged across 125 Hz to 4 kHz, and no more than 0.6 in any octave band in that range. Sports halls scale with floor area up to 2.0 seconds.
One nuance worth getting right, because school business managers notice. BB93 is the guidance route to satisfying a Building Regulation, not a regulation itself. The speech transmission index duty for open-plan teaching spaces, at least 0.6 within a group, comes from the School Premises Regulations instead, and those cover performance in use as well as design.
In practice the halls we are called into are the ones being used for assemblies, performances and exams, where the reverberation was never treated and the sound system has been asked to compensate for years.
Restaurants, hotels and dining rooms
A loud restaurant is not usually a music problem. It is a hard-surfaces problem with music on top. Bare floors, plaster, glass, stone counters and timber chairs hold each sound long enough that the next one lands on top of it, the room climbs all evening, and nobody touches the controls.
There is less published guidance here than people assume, so it pays to be precise about what exists. BS 8233:2014 gives design ranges for indoor ambient noise, putting a restaurant at 40 to 55 dB and a nightclub or public house at 40 to 45, and it explains why reverberation matters. It does not set a reverberation target for a restaurant. Anyone quoting you a BS 8233 reverberation figure for a dining room has invented it.
The one UK standards-body figure we can point to is PAS 6463:2022, the BSI guide on designing for neurodiversity, which recommends a maximum of one second Tmf for a large dining room or restaurant and 0.6 seconds for a small one. It is guidance and not regulation, and it is the best published number available.
There is an access argument too. RNID’s policy work on cafes, pubs and restaurants found that nearly four in five respondents with hearing loss had difficulty holding a conversation in restaurants because of background music, and identifies hard surfaces and hard furniture as what makes room acoustics much worse. Its recommendations include absorptive wall and ceiling panels, soft furnishings, and the least glamorous fix on the list, rubber caps on chair and table legs.
In a finished dining room the treatment usually has to disappear, which means ceiling rafts, fabric-wrapped panels chosen with the designer, upholstery, planting and joinery all counted as one scheme rather than panels bolted on at the end.
Bars, clubs and the staff who work in them
In a late-night venue acoustic treatment stops being only a comfort question and becomes a duty of care one. The Control of Noise at Work Regulations 2005 have applied to the music and entertainment sectors since April 2008. The lower exposure action value is 80 dB A-weighted, the upper is 85, and the exposure limit value is 87, with peak values of 135, 137 and 140 dB C-weighted. Bar staff, front of house and engineers are all in scope.
The HSE’s own guidance for these sectors, Sound Advice, recommends acoustic panelling and sound-absorbent materials and calls the treatment highly cost effective. Its nightclub case study is a good description of what actually works: absorbent tiles on the ceiling, durable absorbent coatings low down where things get knocked, mineral wool behind perforated steel higher up, and narrow-directivity loudspeakers mounted above the dance floor pointing down.
The same guidance carries a warning that costs venues money every few years. Do not redecorate existing acoustic treatments, because it can reduce their effectiveness considerably. Painting a perforated ceiling closes the holes, and a closed perforation absorbs nothing.
Noise breakout to neighbours is a different problem again, and where a licensing or planning condition is involved that work belongs with an acoustic consultant.
Where our work ends and an acoustic consultant’s begins
Acoustic treatment controls sound inside a room. It is not sound insulation between rooms, and it is not noise breakout work for a planning condition or a complaint from the neighbours.
Those are different problems with different remedies, and pretending otherwise wastes a client’s money. Where a scheme needs a consultant’s report, for planning, licensing or Building Regulations, we say so early and work alongside it, installing the treatment the report calls for.
Where the question is simply that a room sounds wrong, we survey it, measure it and specify for it.
[[CONFIRM: whether OBAV want to offer measurement and reporting as a standalone paid service, or only as part of an installation]]
Specified with architects, interior designers and main contractors
Acoustic treatment costs least and shows least when it is designed in early. It costs most retrofitted into a room whose surfaces have all been signed off.
We are most useful at design stage, working from the drawings with the architect and interior designer, so ceiling rafts, panels, upholstery and soft furnishings all count as one scheme instead of competing for the same budget later. Depth for low-frequency absorption and the substrate a panel will be fixed to are both far easier to resolve on a drawing than on site.
We are comfortable on a cat B fit-out and on public-sector and education work. Where a project needs the electrical installation as well, we work alongside our sister company Lake Electrical, which makes larger contracts easier to tender where the AV, the acoustics and the electrical sit together.
We set out the full scope and cost from the start.
Accreditations
OBAV is SafeContractor approved and certified to ISO [[NUMBER: exact ISO standard to confirm]]. Copies of both certificates go out on request.
[[NUMBER: SafeContractor registration number, the ISO standard, certificate number and certifying body]]
OBAV is the trading name of Old Barn Audio Ltd, company number 06040735.
The engineers who survey and install are employed by OBAV rather than subcontracted, and most have long service behind them, so the person who stood in the room and listened to it is the one who specifies the treatment and comes back to check it.
We are not the cheapest and we do not pretend to be. You are paying for the survey, the measurement and a specification built for the room instead of a quantity of panels.
Rooms where the acoustics drove the design
What clients say
[placeholder, acoustics client review 1]
[placeholder, acoustics client review 2]
[placeholder, acoustics client review 3]
Acoustic treatment questions answered
Is acoustic treatment the same as soundproofing?
No, and they solve opposite problems. Treatment changes how sound behaves inside a room, reducing reverberation and improving intelligibility. Insulation stops sound passing between rooms or out to neighbours. BS 8233:2014 states plainly that most types of absorber do not provide high values of sound insulation, and Approved Document E keeps the two in separate requirements. If the problem is a noise complaint or a planning condition, that is insulation work and it needs an acoustic consultant.
Do you survey and measure the room before quoting?
Yes. We visit, listen to the room at the time of day it is actually used, measure what the reverberation is doing across the frequency range and work out which surfaces are causing it, then specify from that instead of from a photograph and a floor area. BS EN ISO 3382-2 defines accuracy grades by the number of source and microphone positions used, from two for a survey up to twelve for a precision measurement, which is a useful reminder that one reading on a phone app is not a measurement of anything.
How much does acoustic treatment cost?
It depends on the size of the room, how hard its surfaces are, how much absorption it actually needs and, most of all, the finish. A fabric-wrapped panel in a colour chosen with your designer costs more than a standard one, and low-frequency absorption costs more than mid and high because it needs depth. We price after the survey, not from a rate per square metre.
Does acoustic treatment have to look industrial?
No. The grey foam tiles people picture are one option among many and rarely the right one for a dining room or a boardroom. Treatment can be specified in fabrics, colours, timber slats and printed finishes chosen with your designer, built into ceiling rafts or joinery, or concealed behind acoustically transparent finishes so the room sounds better with nothing obvious to look at.
Is acoustic foam a fire risk?
Bare polyurethane studio foam bought online usually arrives with no fire classification report, and Approved Document B is explicit that an untested product cannot be classified under BS EN 13501-1. In a building other than a dwelling the general requirement is class C-s3,d2 in rooms and class B-s3,d2 in circulation spaces, so unclassified foam has no route to compliance. Note also that Class 0 and the BS 476 national classes were removed from Approved Document B on 2 March 2025, so a panel still advertised as Class 0 is quoting guidance that no longer exists.
Will thin panels fix a boomy room?
No. A porous absorber needs to be around a tenth of a wavelength thick to work usefully, and at 100 Hz that is roughly 340 millimetres. Fifty millimetres of foam is about a seventieth. Thin absorption takes the top off a room and leaves the bottom alone, which is how a room ends up dull and still boomy. Low frequency needs depth, an air gap, or a tuned panel or membrane absorber, and all three need space agreeing at design stage.
Can you treat a listed or heritage building?
Yes, regularly, and it needs the consent process building in from the start. Treatment has to be reversible, fixed with as little intervention in historic fabric as possible and sympathetic in appearance. On consent, installing or altering a sound or loop system in a church sits in List B of the Faculty Jurisdiction Rules and needs the archdeacon’s written notice, while fixed acoustic absorption appears in neither List A nor List B, so we work on the basis that it needs a full faculty and check with the DAC first.
What reverberation time should a school hall have?
Building Bulletin 93 sets 0.8 to 1.2 seconds Tmf for a new-build assembly or multi-purpose hall, and 0.8 to 1.5 for a refurbishment. Classrooms are tighter, at 0.6 seconds for a new primary classroom and 0.8 for secondary. A teaching space for pupils with hearing or communication needs is 0.4 seconds averaged across 125 Hz to 4 kHz and no more than 0.6 in any octave band in that range.
If we treat the room, do we need a smaller sound system?
Usually a simpler one, not a smaller one. A treated room does not waste energy on reflections, so a system need not be driven hard to be understood and you generally need fewer loudspeakers doing less work. It is one reason we design treatment and system together, and why treating first can take money out of the equipment budget.
Can a room have too much treatment?
Yes, and Approved Document M says so, asking for an environment that is neither too reverberant nor too absorbent. Over-absorbed rooms feel dead and oddly tiring, and in churches over-treatment usually arrives as soft furnishings rather than panels. The Diocese of London warns that even an aisle carpet can be bad. We sometimes specify less treatment than a room has already been quoted for.
Arrange a site survey
If a room is too loud or too echoey, the next step is a survey and a set of measurements, so the treatment is designed for the room you have.
Tell us the building, what the room is used for and what people are complaining about, and we will tell you what surveying it involves.
Where treatment is going in alongside a new sound system, raise both at once. The two cost less and work better together, and treating the room first often takes money out of the equipment budget.
Our wider work covers AV installations, PA and voice alarm, hearing loops and home cinema, and completed projects are in the case studies.
Old Barn Audio Ltd
Unit 15 Wylands Farm
Powdermill Lane
Battle
East Sussex TN33 0SU
01892 752246
enquiries@oldbarnaudio.co.uk
We work across London, East Sussex, Kent, Surrey and the rest of the South East, and travel further for larger projects.
[[NAP: this address and phone still need confirming. Unit 15 Wylands Farm is the address Lake Electrical publishes, Wylands Farm’s own site lists Old Barn Audio in Unit 1, the Companies House registered office is Highlands House, Boreham Street, Hailsham BN27 4SD, and oldbarnaudio.co.uk publishes no postal address. Separately, 01892 is the Tunbridge Wells code and Battle is on 01424.]]