The Acoustics of the DG/ Backup Power Area

Usually, acoustic engineers are never consulted for this part of the design – we all think this has only to do with the Electrical contractors for the building, and all we need are specifications on how much power backup a building needs – which determines the number of DG sets for which to provision space.

Manufacturing Specification

Even more so, because all DG sets now come with an acoustical enclosure. The mandate below, out in 2002, clearly states that DG sets must come with their own enclosure. This actually mercilessly threw a lot of people out of business – these guys used to be design and build contractors for DG set enclosures. I know one of them personally. Very depressing times for them. Now they’ve all been forced to look for livelihood elsewhere. Click on the image below for a larger view of the text. 

Excess Noise in Residential Layouts

The funny part is, this mandate does not take into account the fact that DG sets confirming to 75 dB of noise at 1 m is only good for commercial or industrial areas. Residential areas need them to be quieter than 60 dB during daytime, and 45 dB during night time. Who on earth is now responsible to fill that gap? 

Case Study: This was exactly one of the cases we handled – a fertility clinic had opened up in the heart of a residential layout. The layout is one of the most beautiful, well planned layouts –  planned by the legendary Sir. M. Vishweshwaraiah, no less! – with lovely boulevards lining one of the most beautiful, tree-lined roads in Bangalore, and the layout on both sides of it. The residents refused to put up with the noise levels  – given that Bangalore faces a lot of power cuts in summer – the DG was required to be in use for good portions of the day. The Clinic people contacted us, and we asked them to move the DG set to the terrace, build a 4-inch thick enclosure around it, leaving enough open for ventilation, but blocking line of sight from nearby houses – what they don’t see daily won’t seem obvious to complain about. :).

Heating and Ventilation Issues

Now the other problem with DG sets in mid-size to large buildings may again seem unrelated to acoustics These large buildings could be office spaces, commercial outlets or residential buildings. I know of a case where a 17-storey residential complex wasn’t able to sell the houses in the ground floor of a building, because their DG area was located in the basement below that. The noise was so deafening that while taking measurements, my colleague and I had to use sign language to indicate dimensions to the other person to write down. We couldn’t hear ourselves shout over it!

What exactly is the problem? 

Now DG sets in buildings are almost always considered a necessary evil. Nobody wants to provision the space they really need, because it means giving up precious car parking space. As a result, these are often crammed into some corner of the basement, mostly as an afterthought.

But as it stands, correct provision must be made for the emitted hot air to be vented out either by giving space around it, or by providing artificial ventilation. Merely standing around such a DG set will tell you how hot these can get, and that you will feel most comfortable nearly 2.5 metres away from it. Not in the stipulated 1m space around it. Now usually, nobody affords that kind of space around a DG set these days – which means that in the absence of a ventilation system, these sets heat up and the DG operator walks over to the set and opens the door of the enclosure to let some air in for cooling. Now what’s the purpose of the acoustical enclosure again? Here is where a heating and ventilation issue becomes an acoustical issue. 

Now basements are usually bare bones by design, and provide ample empty space and bare walls for the sound to echo and reverberate in. I’ve heard huge basements echo with large amounts of noise, annoyingly audible 3 floors up. Three hotel floors up. Acoustical engineers are then required to design secondary enclosures based on the noise reduction needed.The good part is, unless you have staff sitting in the basement, you’re okay with having decent amount of noise there.

To summarise, noise is not the primary issue, but becomes one after a few months of the building’s commisioning.  The life of the engine is affected by these design decisions. The owner of the building spends time maintaining the set, replacing parts, etc, long after the building is up. In terms of acoustics, you only need to ensure that the sound reaching your compound wall and your building interiors is within the specified limits. This is easy to do, but is best done in foresight, not in hindsight.


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.

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.

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!

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. 🙂