Acoustics for Malls

This note is for mall owners / mall managers. Let’s start with looking at a few aspects of the mall.  The first is about the kind of crowds that come in.  At least in the Bangalorean context, with gardens and parks being turned into parking spots for malls (ironically),  play area and lung spaces are fast disappearing. People have no place to go if they just want to go out and get some air, and get a feel of the city’s mood.  This is quite unlike a few places in other countries I’ve seen – there are vast areas in the city center, meant for people to just sit around and bask in the sun (when they do get some).  You’re not compelled to be visiting shops there – you can go there without a shopping list, and just hang around.

In Bangalore, Lalbagh and Cubbon Park used to be those kind of places, and people went to regular markets/santhes/petes for their shopping needs. Parks and churmuri were the mainstays when it came to relaxing outside.

Now malls have become those places where people just go and hang out, as well as shop.  I think more than 80 % of the crowd that goes to mall does so for socializing. Most don’t have shopping on their list. Shopping is usually only incidental. I personally prefer the local shops for my grocery shopping – those kids can do fractions in their head! But being this new mom, sometimes I want all my work to get done in one place, so malls are useful there.

So what are the acoustical issues at malls?

Now here we hardly worry about acoustics – malls are fundamentally supposed to be abuzz with noise, quiet malls are a sign of bad times! But you’ll be surprised to know a few things.  A visit to the mall might be a thrill or a nightmare, depending on how sensitive to sound you are.  I know people who can’t handle the weekend buzz in malls, and finish all their shopping during weekdays – not just to beat the rush. My own husband is such an example – wild horses can’t drag him to a mall on weekends. 🙂

From an acoustical perspective , the expected sources of noise are:

• noise from conversation
• noise from events run by companies – more during weekends
• noise from toys meant for children – play horses, play cars, etc – placed outside shops
• noise from bowling alleys
• noise from kids play areas – soft zones
• noise from the PA system
• noise from the food court
• and rarely, noise from the HVAC ducts and vents.

Now, this post assumes that the cinemas, gyms and spas have been acoustically treated and there isn’t noise leaking in and out of those sites. So we’ll only discuss noise sources  listed above.

Why is noise a problem again?

It won’t kill anyone, yes. But people can choose how much time they want to spend at a place that sounds like a huge bathroom. As mall owners/product marketing guys, you’d would like them to hang around and witness publicity events.

Any studies conducted on mall noise? 

Here are a few:

• Page 29 of this talks about mature customers rating noise as one of the negative experiences at a mall. The customers suggest carpeting – not at all feasible in the Indian context.  Acoustical treatment can reduce noise levels without having to resort  to such high maintenance options.  http://173-254-37-135.bluehost.com/JSCR/2006_07_Articles/Hu%20and%20Jasper%202.pdf
• This post talks about a user not wanting to spend time at a mall due to irritating piped music being played there.  http://www.brw.com.au/p/sections/focus/few_shoppers_sold_on_mall_mediocrity_7pFgD7969w83v6ofLuxUNI
• This one’s about the disasterous consequences of installing HVAC without caring for its acoustics. Professional acoustical consultants can analyse all this before it happens.  http://www.greenprophet.com/2012/01/green-shopping-mall-israel-ungreen/

If you really want to study this before you take a decision, contact me and I’ll be happy to provide more sources to you.

So what happens to customer experience at a noisy mall?

The problems are

• low speech intelligibility
• ringing sounds
• general clamour

Low Speech Intelligibility

People will often strain their ears trying to listen to some DJ or someone on the mic trying to engage the crowd.  Most might just find it easy to move away to a quieter place.  But for having organized the show, mall owners/ product marketing managers would want people to hang around to ‘engage’ them.

One of my projects was based on such a case – the mall owner who approached us was convinced he could drive up the revenue on weekends by almost 40%  if we could just take care of the speech intelligibility. You hear lots of noise everywhere – all around you – you hear people talk, but despite high amplification (high enough to drown out ambient crowd noise), you can’t make out what they’re saying.

Ringing Sounds

Stand around one of those events, and you’ll hear music unevenly – even if you’re right in front of the huge speakers put up. Some notes hang on forever, muffling others. The bass sounds muddled and is usually all over the place, merely adding to the noise. Hearing bands perform at malls has never been anything but torture for me.  My favourite guys have played at malls close to my place, and I’ve had to turn back and come home because their words, lines, songs blended into one another due to echoes.

General Clamour

There are people who don’t hang around watching those events, but do go to malls to have a cup of coffee with friends  -such people might find themselves shouting over the din. The noise does get to them after a while.  My husband, for instance, forever prefers quiet, fine dining to eating at the food court. Typically high roofs provide for ample space for reverberation – so the sound energy tends to just hang on forever, in the absence of anything to absorb it. People do absorb noise, and we acousticians take that into account when designing auditoria, but in malls, they’re also the source of noise :).

That seems common across malls. What causes this? 

Smooth interior finishes – huge glass showrooms in most places, smooth gypboards everywhere else. Large empty spaces waiting to get excited with sound and echoing on forever.

Right. The solution is…?

The best part is, the acoustical treatment need not be seen.  These days, there’re so many products available, and for malls with a tight budget (if there’ such a thing 🙂 ) local carpentry is always an option. If some of the treatment areas are unavoidably conspicuous, they can be used for publicity banners.

The amount of treatment must be carefully calculated – a dead-sounding mall is as uninviting as a painfully noisy one.  Here’s a study actually recommending a decent amount of buzz.  http://www.retailcustomerexperience.com/article/196427/Study-Background-noise-inspires-innovative-purchases

So in summary, all other factors remaining the same, the time people spend at a mall is a function of how comfortable they are with the ambient noise – among other things.  And it’s so easy these days to make a mall  sound  more chirpy and less like a glorified, reverberant bathroom – without marring the interiors.   People would spend more time catching up with each other on the food court if those didn’t all sound like “noisy railway canteens.”. I quote because a friend once described Koshys that way. Now some quaint old places just have to be noisy. I won’t have them any other way.  🙂 But our malls could do with not sounding like deep, bottomless, echoing wells.

Festival Noise Pollution

This post was long in the making – the seeds of it sown during the recent Ganesh Chaturthi  celebrations, and now culminating in the Durga Pooja celebrations. This note is for the organizers of such festivals. Having been on both sides of the fence, I expect this post to be a balanced view.

Indians love noise. 

Let me begin by Indianizing the context – we love noise during festivals. Bustling preparations that set the whole household abuzz a week before the festival contribute majorly to the excitement – and they’re all needed to take one away from the drone of daily routine. All this has been happening for thousands of years – and frankly, not just in India – festivities involve huge preparations all over the world – and are always accompanied by noise/music/gatherings/storytelling/rituals, etc.

Festivals are ages old. So is noise. Why this hue and cry about Noise Pollution now?

So why this brouhaha about noise pollution now? What’s changed is that loudspeakers now transmit sounds over long distances, and communities are more widely spread out than they used to be.  This means there’re always a mixture of people living around you – some who don’t share that festival with you, and some who do.

What can one or two days of noise do to you anyway?

We’re talking noise 24/7 on those days.  Eight hours of exposure to 85 dB of noise can be the beginnings of permanent ear damage. And noise at a loud dandiya hall,  or near some cultural programme can exceed 100 dB on an average. In general everyone faces irritation and annoyance, students face anxiety due to their inability to concentrate, and  some exam or the other is always looming near, the older folks face raised blood pressure, the infants are  repeatedly startled out of deep sleep, and disturbed sleep makes everyone cranky – infants and adults alike.

The Legal Angle

A little bit of consideration can save you from legal action. These days people don’t take things lying down, and there are android apps available for every passer by to measure the noise levels leaving your venue.  Along with GPS mapping to pinpoint location, it’s easy to gather proof and lodge a police complaint.

Any solutions here? 

I’ve mentioned enough about what noise pollution can do to your health, so here let me only speak of the solutions we can think of.  There are strict mandates by the courts of law about acceptable noise levels in urban areas being less than 55 dB uptil 10 p.m., and less than 45 dB after 10 p.m. Organizers of the events are bound by law to adhere to these norms.  Here are some things they should do  – these will ensure

• that you enjoy your festival while not causing physiological distress to others who don’t share your festive mood
• that you don’t get on the wrong side of the law.

To start with,

1. Ensure that noise levels at the boundary of your event is less than 55 dB. This is easily possible these days, and it doesn’t have to cost you an arm and a leg. Talk to an acoustical consultant. Solutions can be easier and cheaper than you think, and they may cost you less than a  twentieth of the average budget for such events.
2. Tilt your speakers. Rock shows use line array speakers which are tilted at an angle – this ensures that the main beam of sound coming out of a speaker does not run parallel to the ground, but will surely hit the ground at some point, minimizing the direct energy leaving the area.  The reflected sound leaving the venue is easier to contain with barriers. Your sound engineer or acoustical consultant can help you with this.
3. Cut out celebrations at 10 p.m .  Everyone needs their shut eye after a tiring day. Ask tired moms whose infants wake up 4 times an hour thanks to your mood. The solution is simply to celebrate during the day. If you can’t do that, please spend more from your budget on soundproofing. It’s not as expensive as you think, and a lot of features of the venue can be used to mitigate sound after a certain boundary.
4. Avoid mounting horn loudspeakers on streetlamp poles for half a mile on each side. In other words, there’s no need to tell the whole town about your celebrations. Use posters/hoardings to publicize, if you have to. Keep all your loudspeakers within your venue.
5. Use ear plugs yourself. Quite honestly, your ears aren’t made of sterner stuff  compared to those who get disturbed by noise at a distance.  Before you find out the wrong way, please do things to protect your hearing. You will be able to dance quite well to the music despite ear plugs in your ear – they only reduce the direct sound hitting your ear. Try it.

So is it really possible to contain noise in such venues? 

The simple answer is yes. Distance does a great deal to help attenuate, so if the venue is large, it is more easily possible to contain sound at the edges. I was once posed with a client’s requirement – they wanted me to think of some kind of enclosure that tests audio setups for live sound. So this enclosure is to have about 50 dB of sound on the outside, while the inside sound levels would be about 120 dB. The catch is, because this enclosure tests live sounds, it has to be completely modular – one should be able to dismantle, transport, and assemble it.  Now THAT’s a difficult project. Only heavy mass can block sound over short distances.

So, controlling noise levels from leaving a fixed area meant for large gatherings is decently possible.

Acousticspeak : Things You Will Hear Acousticians Saying

Acousticians speak physics. They don’t speak convenience. :). But here’s a post outlining the basics of what you’ll hear them talk about.

Loudness
Yes, I know you know what loudness is. You may even know that we measure this in decibels. But what you should know is that the human ear perceives loudness logarithmically, not linearly. What does that mean to you? It means that we humans therefore use a logarithmic scale to measure loudness. And that means, that a 10 dB increase in noise levels means a doubling of the noise you hear. Similarly, to bring down noise to half of what you’re hearing, you need a 10 dB loss.

Frequency
This is roughly the ‘pitch’ of the sound you hear. Buses, bass guitars, bass drums, and all rumbles in general are ‘low’ pitches. Most vocals figure in the ‘mid’ frequency range. Shrill voices, instruments, female opera singers figure in the ‘high’ pitch range. Generally, if you have a piano before you, low pitch is to the left, and high pitch is to the right.

Why do you need to know this? When you get a room acoustically treated, you must know that high frequencies scatter more easily and predictably around a room. Low frequency sounds tend to bend around life-size objects such as chairs, sofas, etc, producing irregular shadow regions. Absorption helps kill most high frequencies, but it can’t keep the low frequencies from bouncing around the room. Trying to ‘absorb’ low frequencies would eat up most of the space you have – around 3 feet on all sides.

Reflection
Of course, this is about how sound bounces off walls. High frequencies bounce off walls and surfaces like light does. Low frequencies have a mind of their own. They bend around objects, ignore most wall treatment, and pretend that your single partitions don’t exist. These are what your neighbours will most often complain about. Quite simply, sound acts like a particle at high frequencies, and like a wave at low frequencies.

Absorption
This really needs a separate post, but we’ll stick to the definition for now. So absorption is the fine art of reducing sound energy in a room. Absorber materials are essentially porous in nature – sound goes where air goes, and then while passing through a maze of pores, being  in frictional contact with maximum surface area, sound energy gets dissipated into miniscule amounts of heat.

Diffusion
This is the process of scattering sound around a room. Egg crates work here, only for high frequencies, though. Nowadays, there are products available which absorb as well as diffuse.  Again, space constraints in most site conditions make it difficult to build diffusers for low frequencies. These constraints are sometimes marginally overcome by making the opposite wall surfaces non-parallel.

Reverberation
This is a measure of how long it takes for sound to die out in a room. Well, not exactly die out – reduce by a certain amount.

Isolation This may seem too elementary to define, but the number of times people confuse this with reverberation treatment makes this worth mentioning. Isolating is to prevent sound from leaving a certain space.  Materials that ‘absorb’ sound seldom ‘block’ it.

There are plenty of other terms – depth, clarity, speech intelligibility, etc. There are also terms describing what sound sounds like – warm, cold, bright, mellow, intimate, etc. These will be dealt with in another post.  For now,   the above terms should lessen some of the the geek (!) and latin in your conversations with your consultant. 🙂

Acoustics for Speech and Hearing Institutes

I’ve only just started freelancing on my own. Unlike the initial  romanticised impression of acoustics being the perfect mix of music, maths and physics, I really spend most of my day listening to noise :). So I thought I should get my hearing tested for two reasons:

1. To have a point of reference for a ‘before’ and ‘after’ scenario of my hearing sensitivity.
2. To understand what frequencies I am sensitive to, and any hearing losses I may have for other frequencies – so that I can accurately tune listening spaces.

I went to this institute near my place and found out two things that didn’t suit my needs.

1. I could hear road noise very clearly inside their listening room! This is past 3 doors, no less – the entrance door, the door to the audiologist’s room, and the door of the listening booth.
2. They test only 5 frequencies from 250 Hz to 8 kHz, because this is primarily for old people to hear speech.  For my purpose of tuning spaces for music, I need to be tested for a much wider range – 50 Hz to 18 kHz.

Anyway, I went ahead and turns out my hearing is normal, but I suspect it won’t stay so for long. I am a tad sensitive to vocal high pitches – the Lata Mangeshkar types – playing those at normal volumes can grate on my ears. But I did have difficulty in listening to low pitches – the 250 Hz thing. This would’ve been critical information for me to have found out – except that I will have to take it with a pinch of salt, pending more accurate tests. There was plenty of low noise infiltration through the doors, and I could hear them despite the on-ear headphone.

Anyway, the point is, that critical spaces such as these must not have any type of noise coming in. They had even used thermocol for acoustical isolation. Thermocol, styrofoam are easily and cheaply available, but they are not acoustical materials at all – they can at best be used for impact isolation.  There was also some masking effect happening due to road noise intrusion. I could clearly tell the sound of an auto, a bike, a bus, and some local vegetable vendor hawking at a loud voice.  This is also because the glazing they had used was rather thin. It is critical for listening booths to have glazing because they are to be closed, and the only way for the audiologist to know that you are able to hear a certain test frequency, is when you raise your hand. They have to be able to see you. Glazing itself is not a problem, but the right thickness must be used. Also for such applications, either in-ear earphones, or supra-aural earphones must be used. On-ear headphones are not very effective for blocking out sound.

These and many other defects can be solved right at the design stage.  Eventually, the kind of hearing aids that are prescribed are primarily influenced by the extent of the patient’s hearing loss, and the budget.  The first factor – the extent of the patient’s hearing loss can be accurately gauged if external interference is zero. In this case, it is critical to avoid masking effects.

The right technical advice will take into not just that, but also the hum of your HVAC, the type of earphones you must use, the influence of nearby buildings and their DG sets, etc.  It should also prescribe materials from a rough-use point of view (for instance, the rubber linings of the door had peeled off – leading to a compromise in sound isolation). For a place primarily meant for accurate testing of hearing loss, the noise constraints posed by the location can be easily overcome with correct acoustical diagnosis, testing and recommendation.

Soundproofing Studios

Studios are critical listening spaces. The noise levels have to be as low as 10-20 dB.  The hum of the HVAC, the rumble of the ceiling fan, the structural vibrations of all the houses/buildings nearby, the rumble of trucks on the road, the cross talk through the HVAC duct, the hum of the machines, all make a rather big difference to the quality of the sound. Also, since most studios are rather small spaces, the the bass response must be carefully evened out.

One of the projects I worked on involved two studios (A and B), located one above the other. Both A and B were located on top of a full fledged household. So the ceiling fan of the house was hung from a metal hook, and that ceiling formed the floor of Studio A. That made a rather audible rumbling noise, despite carpeting in Studio A. The glasswool in both studios was filled in more than 15 years ago, and was clearly sagging. When you played sound loud in Studio A, it could be heard in Studio B’s recording room. This is otherwise not a problem, only, in this case, when they increased the gain of the mic for singers with feeble voices, the sound coming out of the other studio got recorded.

Both studios were built with good isolation in mind, with double doors, corridors lining the rooms, etc. But the structural vibrations caused by the HVAC unit on top of the terrace was a problem, as was the motor run by the next house for pumping water to their overhead tank.  The recording room in studio B was exactly 11 ft along one size, and the bass frequency formed clear dips and peaks in the room. Any surprise that the problem frequency was exactly 100 Hz? The monitor speakers were placed at accurate angles, but despite that, the recording console had a big dip, and right behind that, where the producer of the movie and his cronies sit, there was a boom.  They were also not able to use the air conditioning when the recording was in progress. They only used it for post production. So in terms of scope of work, it was a rather big project. But as with all acoustics projects in Bangalore, the budget was rather limited 🙂

The purpose of outlining this scenario is to mention common issues faced by a lot of studios in this area. Structural vibration is the biggest grouse. And increasingly, pavements are laid joining the road and residential areas. This, despite there being a mandate not to do so for longer than a certain width ( wide enough for your car to roll out of your house). This leads to added coupling.

That said, in India, the advantage is that most structures are still brickwork/RCC, unlike gyp/wood partitions in the west. Internal walls are usually 4 inches wide, and external walls are 8 inches. Older houses have thicker external walls.  So, a decent amount of isolation exists between rooms, if you ignore flanging.

All this is was about the sound isolation bit. Now when it comes to reverberation treatment, and the frequency response of the room,  studios again are the most critical sound spaces.  It is vital to avoid shadow zones for bass frequencies, and diffusers must be optimally used. Faulty room acoustics leads to the sound engineer falsely believing the sound spectrum to be something it is not, and equalizing to correct what they think they’re hearing.

Sound technical help should make sure that you avoid all these pitfalls, and the expensive corrections they entail. The right treatment should make the ambient sound crisp and clear, with accurate and predictable colouration from the room.   The quality of sound you hear can then safely be subject only to the quality of the equipment. I have a personal affinity towards sound studios, because these test so much of our skills, and these are also the places where some of the best works of art are immortalized. As someone whose interest in music primarily led her to acoustics, I do have a thing for these little rooms.  🙂

Soundproofing Jamming Rooms

 

That gap on top of this post is intentional. Air Gaps are your friend when it comes to soundproofing!

Every band dreams of practicing freely in a room without neighbours dropping in with a scowl on their faces. Similarly, every studio hopes to record the most subtle aspects of music without worrying about the surrounding urban noise.  These two places need soundproofing for opposite reasons – jamming rooms must prevent sound from going out, and studios need to prevent sound from coming in.

This post discusses the soundproofing requirements of jamming rooms, and lists some loopholes to watch out for. Soundproofing for studios requires a separate post.

Jamming Rooms generate noise levels equivalent to around 100-110 Db – close to twice or thrice the loudness you hear at a noisy traffic signal. This can get distressing because by definition, practice implies long hours. Involuntary listening for long hours can get disturbing – leading to annoyance, irritation, headaches, raised heart rates, and raised blood pressure. A sustained elevated heart rate is good for a workout – staying in such a state for long causes a dip in your longevity.

How much soundproofing do these rooms need?

The good news is, there’s no need to have a zero output concept here. Urban noise is expected to be at least 60 db during daytime, and around 43 db during night time in residential areas. What’s even better news, our ears perceive loudness logarithmically, and so the decibel scale is logarithmic. That means if you reduce the sound even by 10dB, you perceive it as only half as loud.

Soundproofing projects are always more challenging than those which require acoustical treatment for reverberation, or fine tuning. This is because heavy mass is needed to block sound, and most venues do not afford space. A room within a room is the best option, but when that’s not possible due to structural constraints (or in the absence of permission to make structural changes to a building), alternatives must be carefully calculated.

The common mistake here is that while gypboard constructions can be used for isolation, the calculations must be for that purpose alone. Expecting gypboard configurations that work for absorption, to also work for isolation, is a folly here – one that I see all too often around me. Rockwool or glasswool will do nothing to absorb sound at low frequencies if you don’t stop them first.

A word of caution to DIY guys.

• All soundproofing materials come with numbers that tell you how much transmission loss they give. Do not assume that simple arithmetic will give you accurate results. The materials come with a clever line “All joints to be properly sealed and caulked”. Here lies the whole game.

• Also, the materials are tested under lab conditions – the numbers will vary rather widely under different site conditions.
• Further, they come with instructions on how to construct. If structural constraints or budget force you to make variations, discuss them with an acoustical consultant, not the vendor.
• While heavy absorption helps in transmission loss if carefully designed, careless use of absorption materials will make your drum kit sound dead. A drum kit produces a wide range of frequencies – 50 to 15kHz. The high frequencies will sound dead almost immediately, while low frequencies will painfully linger on if you provide too much absorption in the room.  

The other important thing to watch out for are leakages due to site constraints, or plain human error. Every soundproofing project has a leakage fixing phase. A 1 mm gap is enough to turn a 99 % success into a 100 % failure. Also, the most important thing to watch out for is leakages due to structural contacts. You may come up with a clever design, but if you drive nails or screws through to hold things together, that’s a short circuit route. Acoustical caulks must be carefully chosen. I know carpenters who use metal paste to block leaks. It’s rather difficult to convince them of the structural coupling it provides.

Lastly, a note about budgeting. Soundproofing materials are more expensive than absorption materials. All choices must be based on calculations, with generous discounts on the claimed performance, keeping site conditions in mind. While budget constraints are understandable, it is vital to have a talk with an acoustical consultant to understand what part of it can be DIY, and what part of it must be professionally installed.

The funny part is, road traffic noise can be a blessing for such projects. I have two precisely opposite cases on hand – one project next to a noisy road, and one located in a quiet residential layout. Needless to say, the sound reduction needed in the latter was huge, and with structural changes not being an option, I had many sleepless nights reading quoted transmission loss numbers and separating the grain from the chaff.

If there’s a choice of location, try to choose a noisy location, so that you don’t stand out. Low frequencies and structural vibrations are the toughest to isolate, but there are clear laws defining how things work, so in the right hands, your project can be a decent success even with budget constraints. Happy Jamming!

Home Theater Acoustics

Now while we solve seemingly more complicated problems in large auditoria, integrated commercial and residential complexes, and critical listening spaces such as audiometric rooms and studios, home theaters deserve a mention because of the challenges presented by small rooms.

There are two aspects to acoustical treatment for home theaters.

1. Noise Isolation: To ensure there’re acceptable levels of sound going in and out of the HT room.
2. Sound Colouration: The other is to treat the room to reduce colouration of sound due to the room response, reverberation, standing waves, etc.

In this article, we will deal with only the latter. Noise Isolation can only be dealt with on a case by case basis, and some aspects of it will be covered in an article on Residential Noise treatment, coming up soon. For now, let’s look at some problems that small rooms share with larger halls.

1. Reverberation Treatment : For music, and movies, a reverberation time of 0.8-1.0 second is ideal.  This can be controlled to a great extent by room furnishings – but there’s a scientific basis to that. The number of myths surrounding this is so large, that I’ll have to write another post to quell those.
2. Flutter Noise: This happens between two parallel surfaces.
3. Ringing : The room’s response amplifies some frequencies and suppresses others. This is unique to each room.

Measurements and calculations will tell us exactly where the problem spots are, and precisely which frequencies sound sore. There are many thumb rules going around, but the scientific principles on the basis of which some of these originated must not be forgotten. There’re enough myths to bust on this, but I’ll do that in another post. For now, it is important to remember that despite thumb rules that seemingly work, there are always exceptions, and that’s why each case is a unique experience.

There are challenges unique to small rooms. The dimensions of most of these rooms are equivalant to the wavelength of low frequency waves – 8ft to 20 feet.

• Room Modes: The foremost of them is to even out the bass frequencies in the room. The dimensions of a small room can  sometimes be exact multiples of the wave whose wavelength is an integral multiple of any one side of the room.  Room modes are an important part of the colouration of sound in a room, and calculations can help in this area. While many modes are possible in theory, not all of them will have an effect on the sound.  Designing bass traps can help for some of the problem frequencies.
• Diffraction: Bass frequencies have wavelengths long enough for the wave to bend around life-size objects such as sofas, or chairs. This leads to irregular shadow zones, and amplified sound in some areas. The reason for mentioning this is that the peaks and dips are very clearly audible.
• Harsh, unnatural colouration, with amplified sound. Human ears can hear speech and music very clearly upto 10s of meters. Small rooms should ideally not have amplified sound, and especially not amplified speech. Too much of this in a day will temporarily shift your hearing threshold, making you lose sensitivity to softer, subtle sounds. Unless a room is acoustically treated, amplified sounds in small rooms tends to sound  harsh and unnatural, and lead to auditory fatigue – over time.  This is especially an issue when we deal with practice rooms for drummers. Fatigue and annoyance have been widely studied, and good advice should make sure you don’t experience them too early into your movie. The final commissioning of a room must always be done after testing it for amplified sound.

For acousticians, home theaters are ripe grounds for understanding the behaviour of low frequencies in small rooms.  Each case can be a challenge depending on the site constraints.

How much treatment is really needed?

Once the frequency response of the room has been “smoothened” out after treatment, the real issue we see around us is an over treated room. Small rooms can sound very dead if treatment is not accurate. I will need to write another post on various aspects of sound – tonality, warmth, brilliance, etc. These are measurable quantities, to some extent, but these are more critical for large auditoria. For home theaters, these are generally looked at only if the room doesn’t sound right.  So, for home theaters, the right amount of reverberation must be present in the room.  For a room this small, it is vital to first ascertain the interior decoration of the room – the kind of upholstery, the number of sofas, the type of carpeting, etc.  These can unfavourably tilt the balance post the treatment.

However there are no hard rules on what a room should sound like. People enjoy a wide amount of variations, and at least in the Indian context, people contact acoustical consultants only when there is a “problem”, which is to say, that enough times there isn’t a “problem”. :). Thankfully, factors such as individual preferences play an important role beyond fancy room treatments. The key is to be aware of what your home theater consultant is doing with your room’s response. Treatment is expensive, and much of it is sometimes unnecessary.

The Commercials

I know of enough home theater vendors here, who also undertake to do acoustical treatment, mostly as a business perspective here.  I’ve been asked to provide consultation by vendors who then proceed to bill the client 4 times what I charge them. I’m not saying that’s wrong – no one’s here for charity, and vendors have overheads, unlike consultants. But the choice of hiring a qualified consultant rests with the buyer.

In the Indian context, with not enough places teaching acoustics as a dedicated subject, most AV vendors provide generalized, thumb-rule-based acoustical treatment for each project. In fact, many of them offer it ‘merely’ as an added service. That surprises me because many of them started out as audiophiles themselves,   and they talk about precise soundstage, and terms like that. But when it comes to precise acoustical treatment, a lot of them think thumb rules-based acoustical treatment is good enough. Sure. So is watching a movie on a laptop. You won’t miss the story, I promise. Next, I also know DIY enthusiasts who like to “EQ out” a room’s faults. Now I do resort to parametric equalization to kill the odd bass boom when all other things fail, but depending on equalization to substitute for accurate acoustics is not just foolish, it is cumbersome. You’ll have to change settings for each song you play.

Thankfully, there is a growing set of people who appreciate the science that acoustics is, and give it due importance in their scheme of things. There’s a growing crowd of AV vendors who are not just trying to make a sale, they’re trying to provide a good overall experience – which is significantly influenced by the acoustics of the room. Also, there’s a growing crowd of people who can tell good sound from bad. There’s just so much happening in the audio scene in Bangalore alone!

A fraction of the money spent on one such project will get you correct technical advice from a qualified acoustical consultant, on what’s really necessary, and even get you unbiased options for installation, keeping in mind your budget and aesthetic preferences.

To conclude,  home theaters are vital spaces for quiet time, noisy time, music time, game time, movie time, family-bonding time, and the quality of your time spent in this room can be significantly enhanced by precise treatment that makes your room sound clear, intimate and warm.  And I’m not reeling adjectives here.  The last three are measurable quantities.  🙂

Myth Busting : NRC, and its cosmic significance

Here, many unsuspectingly enter into a spot. There are acoustical tiles available, whose “NRC” ratings are x, and people blindly assume higher the rating, more the absorption.  That is only true to an extent.  NRC itself is an average of the absorption at 4 different frequencies, and  inevitably, the performance of the acoustical tile at low frequencies is poorer than the stated NRC value.  Further, lab reports show that the shape of the tile has significant effect on the NRC value. I am writing this as caution to the hordes of professionals in the audio industry who rely entirely on NRC values for judgement.

Lab reports sometimes show NRC of 1.3. This should baffle most people who go by accepted definition that NRC is roughly the percentage of the sound absorbed by a tile. So does it mean that a tile of NRC 1.3 absorbs 130 % of the sound incident on it? Where is the extra sound coming from?

If this isn’t enough ambiguity, the fact that lab tests are always more ideal than real life situations should be enough to make you think again. There’s flanging, there’s external noise, there’re differences in performance depending on the way the tiles are mounted, ..etc.

Acousticians have answers to all this, and beyond a point, their value lies in their sheer experience with products.  Add to this, many products are touted to be acoustical in nature, and very few have been clinically studied and experimented with.

With so many factors affecting the way a room sounds – the interiors, the decor, the upholstery  the positioning of speakers and listeners, the sound transmission properties of the surrounding walls, the noise from surroundings,  the mounting and installation of products, the very shape of the room, etc., it is vital to have some scientific basis as a starting point before giving in to the variables.

The lucky part is, a wide variation  in ambience is tolerated and enjoyed rather well by human ears.  Plus the variations in “perception” of music are profoundly influenced by many factors – physiological, cultural, environmental, etc. So regardless of accurate or faulty calculations, home theaters continue to sound acceptable to some, and unacceptable to others, always. Hallelujah!

Acoustics for Schools and Colleges

I’m going to structure this post in an FAQ format.

Q: We never had a problem with acoustics when we were growing up. Despite not having acoustically treated classrooms, we heard our teachers just fine.  Why worry about classroom acoustics now?

Educational Institutes earlier did not have a few issues that they face now. Here’s what’s changed:

• Diminishing Playgrounds: The school I studied in had place for football, basketball, tennis, garden, swings for children, a huge auditorium, and even a mini-zoo. The classrooms were in a central building, separated by the main roads by these sports areas, and the school as such was located in a residential area. In contrast, these days, with land prices shooting through the roof, there are plenty of schools in Bangalore with no playgrounds, let alone garden spaces. They either just don’t have one, or they use a municipal ground nearby as their own. I’ve taught in a 30ft long class, at the end of which was 4 ft of external corridor, and then (gasp!) the main road. With the last benchers being 4 feet away from traffic, and 30 ft away from the voice of their teacher, I wonder what they managed to learn. They strained their ears all day above the muffling effect of traffic noise.
• Road Traffic Noise: The above problem is compounded by the fact that roads are no longer quiet. There is more traffic, more honking, and louder horns than ever.
• Air Traffic Noise: If anything, air traffic has increased in the 20-odd year span that has passed since I went to high school. All the big cities, some of the smaller cities have all got airports. I’ve sat in the most beautiful lung space in Bangalore – the Lalbagh – and watched 15 flights go above my head in one hour. It’s a bigger problem than we think.
• Changing Interiors Trends:  These days, the interiors are all sleek, with vitrified tiles commonly in use,  with tables and chairs also having sleeker, smoother finishes. These surfaces reflect much more than materials that were used in older buildings.

Q: So what problems (that I need to worry about) do these building environments cause?

Reverberation:  This is a double edged sword. Too much of it, and the room sounds forever noisy, noise just doesn’t die down, the mood is abuzz, instead of calm. The room makes some voices stand out more than others.  Too little of reverberation, and the room sounds dead. Everyone tends to strain to speak louder.  In both cases, at least the teacher ends up with a raspy voice at the end of the day. It doesn’t just stop with throat irritation ( that persists even during non-teaching hours).  When you’re in a chaotic environment, your heart rate’s always higher. This means your body doesn’t feel calm. You lose quality of life right there, let’s not even talk about after-hours fatigue. Teaching ceases to be enjoyable right then.

Poor audibility : Teachers often have to shout to be heard over the ambient background noise. This volume is often too loud for the front benchers, and usually not enough for the back benchers – leading them to be distracted and disengaged. Teachers are all too familiar with the buzz of conversation in the back benches, when they’re distracted.

Extra boominess : In the same room, some pitches sound very loud, and some pitches sound very soft.  Male teachers with low pitched voices will often find that, there are sometimes spots in the room where their voice sounds too loud, or faint.

Low speech intelligibility: You hear the teacher’s voice booming around you, but you can’t make out the words very clearly. There’s enough research out there for you to look up, and that’ll make you realize that there are schools where students miss out on close to 50% of the speech.  There’s a nervous irritability that sets in when students are not able to understand despite their focus.

Q: This is tricky ground. You could easily be talking through your hat. Is there any way to know for sure that learning is impeded by poor acoustics? Is there proof?

It is true that the concentration ability of all students is not the same – there are always those who concentrate well, and those who get distracted easily. However, organized studies have been conducted – some for as long as three years – to obtain unbiased proof of the effect of bad acoustics on learning – all other factors remaining the same. There is a genuine link because the act of ignoring the existence of a noise source also uses up cognitive power.  A few if them are listed below for those interested. I will not go into explaining what each one says, because these only substantiate what I’m saying.

1. http://news.bbc.co.uk/2/hi/uk_news/education/487721.stm : This study by the BBC conducted as early as 1999 was conducted for nearly three years.
2. http://download.contentx.ch/160/new%20zeeland.pdf : This study speaks of vocal strain,  classroom acoustics, and substantiates it with measurements conducted before and after acoustical treatment.
3. http://www.centerforgreenschools.org/docs/acoustical-barriers-to-learning.pdf
4. http://www.speechandhearing.ca/en/consumer-info/children/classroom-acoustics/classroom-acoustics-studies-materials-and-resources : This last one contains a set of articles regarding current standards recommendations.

Q: How can acoustical treatment help?

In places where the spoken word is the main purpose, acoustical treatment should be considered as important as other aspects of building design. But to keep things short, the improved hearing experience will surely bring benefits – some obvious, and some intangible but important nevertheless.

• Less vocal and physical strain, more quality of life for teachers.
• Better comprehension, less disengagement, more active participation
• Better behaviour due to less frustration. The social effect is the most important, and the least readily tangible.

Q: I don’t understand acoustics. What does a 10dB loss mean? Can I hear some examples please?

The links below have sound samples that tell you what some classrooms sound like, and what they should sound like.

A wonderful talk by Prof. Trevor Cox, speaking of what just a 10 dB reduction in noise levels can do for your understanding.

Another talk by Julian Treasure, discussing the academic, physiological, and social implications of better acoustics in classrooms.

The cost implications of treating a room is surely smaller than the huge profits that many schools in Bangalore rake in. The benefits are huge. I will post another article on the kind of treatment required for speech enhancement. For now I hope people reading this are at least aware that acoustical treatment can significantly enhance the listening experience at places that exist entirely for this purpose.

A quiet environment allows the mind to freely explore ideas, thoughts, and form quirky connections in the head. A noisy environment disturbs not only the mind, but also the body.

Thunderclaps in Your Ears

There is one rather disturbing aspect of road noise on the rise. It is that the soundscape in India has drastically changed in the last ten years alone, never mind my growing years. Post liberalization, and 10 years post that, with increasing affluence,  there are plenty of SUVs on the road. While engines have grown quieter (and dangerously so – I can’t hear cars creep up behind me on the road!),  horns have grown increasingly louder. It is not unusual to hear an SUV honk at 110 dB to a guy standing just 2 feet away.  Yes, on some roads in India,  cattle, people, cyclists, SUVs still go shoulder to shoulder.  Just to give you an idea of how loud 110dB can be, imagine standing next to a jet engine, or in a loud discotheque. Of course, imagine that you stood only for 2 seconds, because that’s how long the horn lasts. But I must confess, at my seemingly young age, my ears ring for 5 seconds after I experience such inconsiderate honking.  To make matters worse, there are articles like this :  http://jalopnik.com/5896859/audi-is-designing-extra-loud-horns-for-india

Now this rant is entirely based on that article I read. I am assuming it is true. I am hardly feeling rational and sane right now, but I’ll attempt to be. So I understand the need for a foreign automobile company to design mechanically sturdier horns for the Indian scenario, given that lane discipline is rare and horns are a necessity here. But why “louder” horns?. I think the engineers who came up with this thought are shortsighted, to say the least.  I really wish to go honking near their homes with this very horn they’ve designed. 

Someday in the not-so- distant future. I will move a petition, with the eventual hope of seeing it implemented as a legislation – to force automobile manufacturers to have two different volumes for horns built in. Just like high beam and low beam for lights. Shouldn’t be difficult for them to do this, and it would make our cities that much quieter. All this hullabaloo wouldn’t be necessary if temporary deafness was an immediate effect. The sad truth is, it only sets in later.