Acoustics of Restaurants

Actually, there’s no single view to take on this topic. Restaurants are theme-based, these days, and ambiance of older restaurants become their “theme” after a period of time.  Let’s talk about a few ‘themes’, and then we’ll look at some common  acoustical issues at such places.

Eerie Places

I once  went into a restaurant called Gufha. The word means “cave”. True to its name, I walk into seemingly absolute darkness, one bright sunny afternoon. After my eyes got used to the darkness, as the door closed behind me to shut out outside light completely, I realized the whole place has undulated, brown-coloured plaster work all over the walls – made to look like a huge cave we’re entering. The waiters were all dressed like Shikari Shambu.

The undulations on the wall provide for ample diffusion of sound and there are no sharp echoes, no sound of clutter – which is so unlike most restaurants  where “sleek” is the theme. The only downside was that the place had piped music being played – not sweet-sounding chirps, babbling brooks, gushing water etc,  but eerie night-time noises from the jungle. Crickets, the occasional distant roar – what have you. The place provides good quality acoustics, and good quality food, I must add. But you don’t exactly feel appetized listening to sounds of creepy crawlers. The acoustic ambiance is not just about reducing echo and reverberation, and preventing noise going out/coming in. The choice of music goes a long way in attracting certain types of clientele.

The other example I can think of is Cafe Coffee Day at Jayanagar 4th Block. It played such loud music, on such crappy speakers – high on treble, low on bass, and in a room where NO thought had been spent on acoustics, I had to take a disprin at the end of an hour. This was years before I studied acoustics at UK, and so I didn’t imagine bad music could do so much damage. I have sworn not to go into a CCD since.

Noisy Places

Restaurants can be deafeningly noisy – Koshy’s for instance. This one also comes under the category of “Quaint old places, best left untouched”. There are railway canteens that sound quieter than this one! But that’s the ‘theme’ at Koshy’s – old world charm, nostalgia, noise of people, noise of cutlery, noise of the kitchen, bright chequered tablecloth, old fashioned cutlery, etc. There are old, analogue loudspeakers mounted on the corners on top, with cobwebs on them. No point in playing them anyway. 😉 This one should stay as is. 🙂

However, newer places that are deafeningly noisy don’t get the discount of old world charm. Toit micro brewery in Indiranagar is a good example. The weekend I went there, we couldn’t hear ourselves shout. It was so noisy. Of course, noisy restaurants are a sign of good times for the restaurant owners, but I’m not so tempted to go there again if I have to spend a couple of hours shouting myself hoarse over the din for having gone there.

Quiet Places

On a regular basis, we expect “quiet” to be a standard part of a fine dining experience. To provide this feature, the restaurant owners have to make sure the kitchen door isn’t leaking noise, and if the kitchen wall is a lightweight gypsum construction, it shouldn’t leak out noise into the dining area either. Also, the place is to be carpeted for sure – footfalls are irritating when you’re looking for quiet. The other issue we see is a high roof, usually made of gyp, with various designs for diffused lighting. Designs are good – we acoustical engineers are not very fond of flat, parallel surfaces, but high roofs can lead to cutlery noise being amplified. Fine dining places must have heavy upholstery on the furniture, and plenty of carpeting in the open corridor spaces – sleek chairs, smooth floors, high roofs are a bad idea.

Places with Live Music

This one clearly needs specialized acoustical treatment. Thumb rules like the ones mentioned above can backfire rather badly. We’re always talking about money wasted, when we design in hindsight. Such spaces have to be optimized for clear speech, as well as live-sounding music. Too much carpeting will help speech, but kill the high notes, and too little of it will make conversational noise and music mingle with each other unintelligibly. Treatment is not always essential. Hard Rock Cafe in Bangalore is a lovely example. The place is located in an ancient stone building that once housed the Bible Society of India. As was prevalent during that time, the stones of the building  have a natural irregular finish, and so there’s ample scattering of sound at least in the HF range. The various artifacts displayed also help in scattering some mids. It works for speech as well as music.

Common Acoustical Issues

So, it’s not really possible to have a standard view here about acoustical issues, but let’s make an attempt to generalize. For a quick peek into the possible acoustical problems in restaurant spaces, here’s a good read:

HVAC: In general, the HVAC duct acoustics must be carefully calculated – certain critical distances can cause them to turn into roaring resonators. That’s not good for any kind of place – noisy, or quiet.

Kitchen Noise: These areas must be strictly isolated, with double doors spaced a few feet apart at the minimum. That way, when one door is open, the other will be shut. The doors must be acoustical doors – 6mm glass will not do much.

Foot falls: Contrary to what you may think, this doesn’t just imply treatment on the floor. It also implies isolating the ceiling from the noise on top, depending on the kind of space above. If the floor above contains a gym, or another restaurant, or an office space, care needs to be taken to isolate that sound.

DG set noise: Seems unrelated? Nearly every restaurant has one, usually right outside the main door. Nobody provisioned space for these things even 5 years back. Now it’s the norm to have one outside. The good news is, road noise will sometimes help to mask it.

Road Noise: At other times, road noise is the problem itself. Glass doors that are not framed, glazing that isn’t thick enough, will cause some noise to filter in. We’re not looking for studio-like quietness, so it’s okay to hear some, but occasionally, it’s bad enough to drown out conversation, especially on rooftop restaurants that aren’t really very high up. The Coffee Day at Jayanagar 5th block is located on the first floor, at the corner of one of the worst traffic signals in that part of town, and they’ve placed tables and chairs outside the room, in the balcony overlooking the signal.  I haven’t bothered to go in, but I can’t imagine myself sipping coffee, inhaling vehicular smoke, and shouting over traffic.

To summarise, for places that solely rely on good user experience for clientele, acoustics can be a big factor to determine how much time people spend at such spaces. Plenty of easy solutions are usually possible, and they don’t have to interfere with the theme that an architect or an interior designer has in mind. And if you thought architects and interior designers were the more creative of the species, I happen to know a couple of really creative acoustical engineers, who’ve worked with the interior designers to come up with spectacular looking furniture, with lighting inside them, which also work as tuned LF resonators to trap bass booms in the room! So there’s always room for some wonderful creativity that accommodates fantastic aesthetics, functionality, and science!


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.  🙂

Acoustics and Aesthetics

These two words have more than a few letters in common, contrary to what some architects probably believe. And no, they need not be conceptual antonyms of each other

The variety of finishes available these days would leave most interior designers with no room for complaint. Choose from vinyl, fabric, leather, or just good old perforated gyp or wood. There’re also products that are actually transparent, and can be used on glass. The only constraint is usually related to how dust free a place really is. I can provide case studies of how we’ve worked with the concepts provided by the interior designers and architects, and provided  unobtrusive treatment that maintains the look and feel they have in mind for the space.  Here’s one case study:

A spa located on top of a mall, on a noisy road, with 3 mosques nearby, and a noisy AC chiller embedded into the structure needed a quiet, relaxed environment within, and a very open  and spacious look and feel. This meant we could not wall out the loudspeakers of the mosques. We had to work with glass, so that the view of the expansive sky is maintained, but the sound from the traffic below, or the mosques (200 meters away) does not come in.  We provided glazing specification strong enough to drown out the measured amount of noise, and worked with the structural engineers to ensure that the span is adequately supported. The thickness of the glass was enough to block out most frequencies, but not enough to block out the amplified, low frequencies of male voices singing out prayers 5 times a day, almost simultaneously from 3 mosques. The solution was to provide a torture path between glass panels all along the edge of the building. The torture path for the sound was designed according to the wavelength of the lowest frequency we needed to block.  This account does not provide the other site requirements and designs – the point is to illustrate that the look and feel was not tampered with, despite walling being the easiest option.

Similarly, there are enough other projects, where one of the primary things we ascertain from the architects/interior designers are the finishes they have in mind, and we design our acoustical treatment in accordance with those.  Acoustical treatment, unlike little girls, must be heard, not seen. 🙂