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: http://www.restaurantnoise.com/restaurant_article.html.

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!

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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:

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.

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. 🙂

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. 🙂