Acoustics for Auditorium Spaces

This type of space is apparently the bread and butter for most acousticians – with most non-acousticians being aware of the necessity of acoustical treatment in such spaces. Other spaces are work for us too, but usually only after some problem persists beyond the ‘experienced’ trials of the construction period. Auditoria also suffer from the fact that most are over-treated for music, but just about right for speech. Here are typical acoustical issues that these spaces face.

Large Reverberation Times and Speech Intelligibility 

Reverberation is the fundamental problem that all Paanchvi Pass se Tez people are aware of. You cannot get this wrong and get others right. But while getting this right does eliminate the largest of issues, there are many issues it does not solve. I have worked on projects where a previous ‘consultant’ had set only the reverberation time criteria for spaces, and I had to fight tooth and nail  and evidence and auralization and case studies to prove that speech transmissibility depends on other factors too – which they hadn’t bothered to address. We settled for an inbetween solution – where I gave them both sets of data – for speech intelligibility as well as their beloved Reverberation (for them to do whatever they pleased with the latter).

I am amazed at how many times the Royal Albert Hall is brought up in initial discussions for such large spaces. At the time it was commissioned, it had far too much volume for its seating capacity and the echo was so bad that it was known as the only place where a british composer could be sure of hearing his work twice😀 (reference available😛 ). Later a  number of clouds were hung from the ceiling to provide better early reflections and that fixed it to a large extent.

Getting good early reflections is vital to achieving good acoustics in large spaces. The traditional RT60 analysis is based on some assumptions that don’t necessarily hold good in all spaces.  Also there is a growing crowd of fellows who think a simulation software is all that is needed to get the acoustics right. Yes, these help a lot, but knowing what data is ‘real’ and what part of it is ‘extrapolated‘ is important. I’ve known people who compare two such programs and proclaim that one gives you data down to 63 Hz. May I please add that you might want to take that with a pinch of salt – most diffuse field assumptions are not true at 63 Hz, and so it is tricky to calculate even standard NRC data for that frequency band. Of course, we do measure the response of the LF absorbers we design, but the test conditions are not those typical of measuring NRC data for others. On closer questioning as to how they even managed to procure NRC test data for that frequency band , the program evangelist revealed that they assume that if something provides x NRC at 125, it should give you at least that much at 63 Hz.  So this is added to the overall frequency response to make it look ‘more complete’.

This is just one example – it is vital to understand the limitations of the software. For low frequency analysis, some kind of meshing software will work much better than ray tracing.  Of course, bear in mind that LF issues are much more pronounced in smaller spaces, so with larger volumes, there’s a decent chance we’ll get away with not doing too much to tame the LF. This doesn’t mean we leave it unattended – I’ve seen metro stations  (Delhi) and a 2800-seater auditorium that have low speech intelligibility despite having decent RT60. Fixing the LF in calculated measures will help in such cases.

Also, in many cases, the reverberation values of the spaces are calculated in what is sometimes mathematically more efficient and may not truly model the physical process of sound decay in that scenario.  Multiplying a T10 by 6, or a T20 by 3, or a T30 by 2 may not yield exact results. The actual RT60 could be slightly different. Understanding the physical process and mathematical algorithms and the approximations made are vital to making realistic sense of the data thrown out by these programs.  There’s also another factor – scattering. Calculating with and without scattering co-efficients can actually make a lot of difference. We have to work within limitations of the amount of scattering data that is tested and available.

Background Noise

This depends on factors such as the HVAC equipment and layout, ambient traffic noise, number of windows and their positioning, and in some cases, general MEP equipment nearabouts.  I’ve seen auditoria where an AHU was suspended above the false ceiling of a greenroom – right next to the stage, and there was no door between the two areas. There are other spaces where the green room was only 6 feet away from the compound wall of the venue, adjoining a state highway. Traffic noise freely flowed into the green room and was picked up by the microphones. Our very own Chowdaiah hall here has duct cross-talk issues (sound from music classes in the adjacent rooms comes through to the stage) and also has rain noise infiltration . To Bangalore’s luck, we get rains sharp at 5 in the evening during monsoon – just when all evening events start.


Now apart from letting in noise, there’s a larger issue – most school auditoria will typically be built like a huge wedding choultry – with ample natural light coming in so that they save on electricity. Acoustically, we then have to look at different scenarios – when windows are shut the reverberation is very high, when they are open the reverberation time looks good, etc. An auditorium I worked on had vehicle parking stands closeby, and all those shelters had corrugated sheet metal roof – and this place is on the coastal belt – it rains like mad. The surface area of the shelter is enough to create a fairly loud sound when rain falls.  Sometimes the number of windows is so high ( for example a triple height auditorium with three rows of windows) that our acoustical estimates vary rather widely between the two extremes – and once commissioned, we have no control over many windows will be opened or closed at any time.

Also the other condition these windows create is that of perfect planar reflections – leading to flutter and ringing. Most often, due to symmetric design, windows face each other.  No, curtains don’t solve all issues, although they might be a better option compared to not doing anything at all! The reflectogram has to be carefully studied to understand these aspects.

Coupled Spaces

These significantly affect the speech transmissibility, and it gets very tricky to calculate even reverberation times.  This is especially true of spaces with traditional architecture  – churches and mosques.  In India, many wedding halls and school auditoria have corridors on the sides – these do not form a part of the audience areas, but are coupled with the existing volume.  The effect of the double-slope decay contributed by such spaces can be fairly significant.

Shape of the space(!) 

Uh huh…I’ve worked on one auditorium that was so perfectly fan-shaped that we ONLY had to solve reverberation issues there – the shape took care of all other things! The same architects were, however, also coming up with a completely circular space elsewhere. I was lost for words.  Yes, we can do things to fix that to a good extent but a lot of treatment is then required to just correct issues that are thrown up only due to the shape of the space. Some issues can never entirely be eliminated in such shapes.

Multipurpose Halls

There’s that word again. But really, no space is exclusively optimised for speech – with the current real estate scenario,  and we are very realistic about that.  The extremes of expectations sometimes vary quite a bit – from hosting a world-class basketball court and badminton court, to holding TEDx talks in the same space. Variable acoustics is the key here. There’s no need to buy expensive panels that can be overturned  to increase absorption. It’s far easier and cheaper to construct such panels and most schools have enough manpower to get these mounted or dismantled as required.

To conclude, large spaces typically pose challenges with respect to reverberation, and acoustical simulations of  such spaces can provide very good predictions of the end results post construction.  However a lot needs to be understood about the assumptions, the test conditions, the limitations and the error margins and material data of such software programs.  Empirically or superficially  analysing such data could prove to be risky. Acoustics is a young science, but we seem to have a massive set of failed examples to refer to. Those are invaluable in the insight they provide.  Getting the acoustics of large spaces right is tricky, especially with the amount of straddling across various intended usages that we have to do, but once done right, it is immensely satisfying to see the design take shape as a space that provides warmth, clarity, brilliance, intimacy and envelopment in the desired proportions.










Acoustics for Clubs and Lounges – 2

Great. Now that we’ve largely taken care of soundproofing in the previous post, let’s look at what happens in the interiors.

All Glass 

Glass is something we can’t avoid these days, and the challenge is to ensure that the sound field in a room is sufficiently diffuse, despite perfect planar reflections from large panes of glass all around you. This poses trouble even for the mids and highs, let alone the LF.  How do you introduce time and phase shifts? How do you reduce the spot intensity of standing waves forming peaks and nulls at the same spots ALL the time? Well, clever options are possible if you lay down the fundamentals of the concept/solution to the architect, and let them play with it. They ARE the creative of the species. In Mumbai, a lot of old industrial sheds have been successfully converted into music lounges – despite the theoretical odds.

Mixed Usage

Here’s a very generic scheme of what sound should sound like, for various usages:

Frequency  Movies Live Music Gaming
Bass Loud, but not boomy Tight Loud and Boomy
Mids Short Long, resonant Short
Highs Dead Long, Short

Now lounges have another category    – DJ music. The kind of absorption you need for these scenarios is really different, but we always have to strike a balance. There is always a mixed usage. The kind of bass you need for DJ music is thumping, compared to the kind of tight bass you need for say, smooth jazz. Actually, for those who know their music, within EDM ( Electronic Dance Music), there are so many sub-genres each of which have a typical characteristic feel – all contributed to by the balance of highs, mids and lows.

Now while it’s great to experience this variety, at the design level it is not really possible to alter a room’s response to suit different scenarios. So broad generalizations are made, keeping in mind the primary use, the secondary use, etc. Sometimes the extremes are too far away to bridge – such as one project I’m pitching for where I will need to design for typical lounge music, DJ music, and the space also doubles up as an exhibition area, or ( hold your breath) – a conference room!  The ambience for an exhibition area must be a quiet one  – low noise, piped music, etc, and for speech – deadly quiet. HVAC hum, etc are factors to monitor here. Now for the volume of the space, speech is going to sound terrible if music is to sound awesome. Variable acoustics is the key here. There will have to be additional absorption brought in when there is a speech event going on. The design must be modular, easy to assemble and move, and sturdy.

Such a situation also requires variable sound systems. You can’t be playing piped music through a line array meant for live music. Sound system engineering is also critical for soundproofing. Choice must be made between having a distributed system or a line array-like system. Distributed systems must be chosen to ensure their coverage isn’t much more than needed – to avoid excess sound pressure at the walls. Compared to distributed systems, for the same power configuration, a line array system will beam all energy along the main axis – while keeping smaller amounts of energy in the side lobes. This makes it suitable for long halls, marginally/significantly reducing soundproofing needs for side walls, but surely increasing the soundproofing requirement for the opposite wall. However, low frequency response is nearly similar to that of a distributed system. So soundproofing requirements for LF stays the same.

Mixed usade presents another issue in that seating plays a very important role in acoustics, and we are unable to take that into account for such cases. Seating accounts for a significant absorption, and so does the crowd – we design for 2/3rds occupancy typically. If furniture is going to be modular, to be shifted in and out for various scenarios, our calculations have to buffer for that. Also, the place could have 150 people for a DJ session, and only 25 for an exhibition. The challenge lies in making intelligent estimates, and in knowing the broad ranges of parameters within which these estimates are true.

Concluding each such article leaves me excited about the variety of cases we get to solve in the ever-evolving melting pots that our cities have become.


On Studying Acoustics

I’ve been often asked these questions by a host of people, and considering most of these conversations run into at least an hour if any justice is to be done, I thought writing down the basic information would be useful. This is by no means exhaustive, just a starting point.

Scope of Acoustics 

The most beautiful thing about acoustics is that it is a very multidisciplinary subject. There are fields coming together at all levels – pure math or pure physics, statistics ( perceptual audio and psychoacoustics), electronic engineering ( transducer design – loudspeakers and microphones), mechanical engineering ( noise, vibration and harshness  – NVH), and not to mention music ( tuning spaces for music, musical acoustics etc).  The field that I’m working in is called Architectural Acoustics – I work with architects and builders to design spaces for optimal acoustics and soundproofing. Let’s cover these one by one.

  • Psychoacoustics/Perceptual Audio : This is more research oriented,  and there is very little work being carried out in India on this. ITC Sangeeth Research Academy is one place that does regular research work on this. Audio manufacturers  and mobile phone manufacterers are also interested in this field, but to my knowledge there’s only sales and marketing going on here. Philips has some acoustics-related work here in their product development facility.
  • Electro-acoustics – Commercial/Private Sound System Design: This field has broad applications, and the two companies that actually do product development in India are Sonodyne and good ol’ Ahuja. Most others have manufacturing lines in China or elsewhere and at best hire software engineers to design computer interfaces here. The significant bit is always sales and marketing, and execution – which involves project management, client account management, design, installation, testing and commissioning.
  • ElectroAcoustics – Microphones, etc: This throws up a whole lot of mobile phone manufacturers as potential employers.
  • Electro-AcousticsDIY: This aspect is something that needs highlighting. I know people with fantastic talent in this area. There are plenty of projects to execute if you know the indispensable art of negotiating, project management, and marketing. There is, of course, stiff challenge from the branded products that are sold by equally agressive AV vendors who also offer automation, but there’s always place for talent.
  • Mechanical Engineering: Knowledge in this field will give you an edge when working on industrial acoustics projects. The scale of problem solving is stupendous, as is the cost of basic transducers you need for vibration measurement. I know firms that deal with such a huge variety of problems – from the nanoscale (hearing aid devices) to ocean acoustics. Basic knowledge of finite element modeling, boundary element modeling, meshing etc is vital, and there is investment in terms of procuring some relevant software. Other applications are aero-acoustics, and automotive NVH analysis. With Boeing and plenty of aero-acoustics firms setting up engineering establishments in India now, and with automotive firms moving similar research to India, there’s a big thumbs up for this side of acoustics.
  • Music: Now I started out with this, and my basic love of the sciences. It turns out that the place where you experience maximum music is in live sound acoustics, and electro acoustics, where you test loudspeakers, or even in perceptual acoustics – where you may be playing music to check its effects, etc. Not so in the field I’m in! Now I know a lot of sound engineers who can just listen to sound and and tell you exactly what the problem frequencies could be. Sound engineering, however is different from the study of acoustics, and they have a different skill set. It is important not to mix the concept of music production and sound engineering with the study of acoustics. There is a mild overlap, but the rest of it is quite divergent.
  • Architectural Acoustics: I spend some part of my week taking noise measurements ( – irritating traffic, deafening train horns, machinery noise, stuff that grates on your years), and many of them at night hours. In the other part of the week when I’m on a desk, I look at dry numbers, excel sheets, formulae, impulse responses, CAD drawings, software models etc.It’s REALLY dry – the only music you hear is that on your ipod if you can work side by side – so getting into this profession because of your love for music is a very overrated idea. I do design spaces for sound, but time management tells me that I have to be more interested in running swept sines or MLS sequences, or blasting white or pink noise in a place instead of joblessly hanging around on a site listening to music!   You need to enjoy calculations and analysis to be able to hang around in this field long enough. I’ve climbed 16 storeys of of a building in my third month of pregnancy, assessing noise issues floor by floor, with no place to sit, and debris strewn everywhere (construction sites build lifts after EVERYTHING else is done. The other option was to use a precarious-looking service lift outside the building). Of course, I was all excited and had no complaints, but my folks freaked out, as did my doctor. Long hours of standing on sites is a given. This is true of any construction-related field.
  • Environmental Acoustics: Again, overlaps with Architectural Acoustics and Industrial Acoustics sometimes when it comes to soundproofing projects. Building noise control is increasingly important as residential and commercial zones are overlapping in growing cities.
  • Naval/Ocean Acoustics: This is for the seriously technically inclined. Needless to say, most work locations will be located on coastlines. You can’t choose to live in a place, should you make this choice.

Scope of Working in India

This deserves a first mention because people ask me this before they’ve even thought about why they wish to work on acoustics, and rightly so. The field is still nascent in India.

Acoustical Design is a relatively niche field in India, but things have changed significantly in the last five years alone. When I studied my course, I was still comforted by the fact that I had experience in the IT industry and could always get back to it if I wanted to.  Now there are paid jobs available, and of course the option to do freelance consulting is always there. I chose the consultancy option because it gives me the flexibility I need with a 2 year old toddler.

Salaried Jobs:   A lot of audio video companies are looking for an in-house acoustical designer, and there are acoustical product vendors who also need in-house design services before they can quote for a project – so these are typically the kinds of salaried posts people can expect.

Consultancy: Technical skills are about 20 % of what you need to run your own business. Business skills are equally important. Consultancy has its ups and downs – you sometimes have to spend time recovering money from delayed payments when you’d rather be doing fundoo design, and it can get difficult to plan your finances if you don’t know how to hold your own. Work always needs to be done ASAP, but there are always processes for payments.  Construction itself is a rather unpredictable area – there are unforseen delays and projects rarely get done in time. It takes some getting used to. Also, in the Indian mindset, people like to pay for tangible things – such as products, or installation – it’s rare to find someone who gives importance to design.  But all this takes some getting used to. A few projects down the line, you learn to draw up your set of rules. It is fair to say that while there are enough freeloaders on this planet, there also nice people who think other people’s labour is to be paid for. You learn to tell the difference, but it’s always a trial and error method.

There is also the issue of managing time, especially for women in the Indian context. I’m incredibly lucky to have a fantasic support system, but not every one else can be so fortunate, and this profession has its share of multiple projects landing up together – and this entails nightouts. It also has its share of multiple projects being in a state of execution and your support being sparingly needed. It’s important to stay productive all the time.

Most acoustical consultants I know are not into pure consultancy. I know only a handful ( including myself), who rely entirely on doing only design/problem solving. I couldn’t have done this without my family supporting me till I reached steady levels. One person I know who does pure consultancy( and work with) also works half time with a U.S firm, and that’s his steady source of income. Most others tend to take on turnkey installations ( which means they charge for project management, have margins on materials, etc). Others have ventured into offering a complete auditorium package –  lighting, audio and video, along with acoustical design AND installation, and even audio renting. These are the qualified ones.

While I am a believer of learning on the job, the bulk of acoustical consultants in India are those who can’t tell absorption from isolation. Simply because there is no opportunity to study the science here. Most are forced to offer acoustics as a freebie to clients, while selling either wall panelling, or AV products.  I can count on my fingertips the number of acoustical consultants here who are qualified, who are independent ( do not take commission for recommending products or for vendor referrals), and who do only pure acoustical consultancy. It’s a big decision to take – the turnover is bigger if you take on bigger jobs – simple. Turnkey Interior vendors do business worth crores – it is a very tempting proposition.  As problem solvers, independant acoustical consultants cannot quote their fees as a percentage of the project cost, or on a per-square foot basis for ethical reasons. Instead, we quote for our expertise and time. More on this in a separate page on Independent Consulting.

The upside is that consultancy allows you to work at your own pace like nothing else does. I know how important that can be – on days when the toddler falls sick, or when the babysitter falls sick. I restrict travelling on site visits to two days a week – which helps to ensure that I get uninterrupted periods of time during the other days to get important design work done. Once work starts flowing in, days and nights can get merged into one. Growth is required – you will need assistants for CAD, for site visits, for marketing, report writing, software modeling, measurements, etc.  But I have yet to see a firm that is larger than 6 people.  I haven’t done any marketing so far, but have required help for all others aspects I just outlined. As with any business, you need to ensure you’re covered for a year of regular and random expenses so that you don’t fret or get a panic attack when payments are delayed – as they inevitably will be.

Studying Acoustics in India

In India, the options are fairly limited. A couple of IITs and IISc have some courses in technical acoustics, but I’m not sure of what the entrance criteria is.  Institute of Acoustics has started a chapter in India, and they offer diplomas, but I’m not sure of any further details. I had no choice but to go abroad.

Studying Acoustics abroad

Studying abroad is a great idea. It’s also the rich experience of interacting with people from very diverse backgrounds that helps you become a lot less judgemental, than cocooned home birds. However, one needs to plan finances very carefully before embarking on such a journey. It can get difficult to start out on your own while having an education loan EMI to take care of. I was lucky to get away with 8 % – that doesn’t happen anymore – it’s now at 11 or 12 % – that can get crazy. This made sense earlier when the job markets abroad were good, and acoustics being a rare field, the visa or residentship application for this comes under the category of highly skilled migrant workers in most places. With job markets not doing so good in EU and the US, construction takes a nose dive, and with it, so does construction-related work.  So it makes sense to study abroad only if you are able to manage the finances well.  With my frugal lifestyle ( studying acoustics will usually not leave you with much time to have a life, as the course tutors themselves had advised us🙂  ), a lucky 8 % interest on loan, and the fact that I came back home after finishing my coursework and completed my thesis from here, supported throughout by parents, husband, parents-in-law – I ensured that my loan was only 10 lakhs – course fees, flight tickets, living expenses, combined. This still means an EMI of 17k every month. I knew many even back then whose lifestyles just couldn’t be brought down to less and they had serious issues managing their finances.

At the current rate of interest, and with rents, course fees, etc on their way up since I went there last, I’d say the monthly EMI will easily be around 25-30k a month. Think very carefully about this. Most loans now offer 10 year repayments also, though 7 years is the norm.  To a lot of people, studying abroad makes sense if you can work abroad and make some money for a few years before thinking of coming back to India. The equation is no longer true – due to various factors – general down turn, etc,   it’s not as easy to find jobs as it used to be, stricter immigration laws, significant taxation, higher living expenses to start with, etc.

I must point out that it is easier to get a salaried job abroad than in India – because there the building norms are very clear on the certifications and compliances, and more importantly – they are strictly followed and enforced. Here there is no such thing. People worry about soundproofing only when they are in danger of having their place shut down due to complaints. But even there, acousticians lament that the field is very rare and many just don’t even know such a thing exists. But for sure, organized work is much more easily available there than in India.

Courses Abroad 

I studied at Univ of Salford, and we were privileged to be interacting with the best minds in the field. The course gives a fantastic introduction to the field and we were left in awe at the end of most classes. The course is very intensive and you’d be left with nearly no time to have a part time job, unless you’re a genius and can comprehend lessons in half the time it takes the rest of us to grasp concepts. A strong numeric background is required. You could opt for the audio acoustics module if you’re good with electronics, or the environmental noise modules if you’re interested in noise control. These are two modules each, and the other six modules stay the same. For most current information, please visit the website of the university.

There are many other universities in US, EU, and Australia.

To conclude, the field is nascent in India, and that is both a good and a bad thing, depending how lofty your aims are. Getting into acoustics is a tougher decision to take compared to thinking of other mainstream areas, and this decision takes a good amount a planning. I am personally driven by the joy of experiencing how good a place sounds, but that alone is not enough to keep up a healthy tempo. Though the field is related to music, experiencing music is not really a part of the work – experiencing noise and balloon bursts is🙂.  The romantic illusion that led me to this was that this is the perfect amalgam of my interests in music and sciences. I’d like to burst any such bubble right now.🙂

Things have looked up significantly in the last 5-6 years and there are now firms offering paid jobs in the field for those unwilling/unable to take a plunge into consultancy. I cannot emphasize enough on how unorganized the construction industry is in India, and there are no standards on processes and payments.  It takes serious passion some major family support to keep going forward. To work in architectural acoustics, one must surely have a sense of music, but can do just fine without it, as long as you understand material science and wave propagation well.   Also, consulting works well for women, and it feels good to see things taking shape and the money rolling in – for much less the time you’d spend in a regular 8 to 8 ( 9 to 5 doesn’t really happen anymore, does it). For those willing to endure the rest of what freelancing/pure consultancy entails, it can be a rewarding experience to see a building come up from out of nothing and to hear it sound the way you designed it.


Now this deserves a mention because of the variation that exists here.  I’ve met people who’ve have told me that they’ve never done acoustical treatment at any place they’ve worked in, and their systems have always sounded excellent, and that the software we acousticians use to validate our estimates is only cosmetic, and is only for reporting purposes. I have no issues with their fond opinion. I only have an issue with the notion that it could be an absolute ‘opinion’.

The point is, satisfaction is a classic case of roti kapda aur makaan – how much “more” you want depends on you, and there are no absolute standards. Every construction worker who passes by in front of my house has a pocket radio blaring sickly-sweet bollywood songs from the 90s ( for some reason, their musical taste is stuck in that era – I mean ALL of them – nothing before or after that!). You should come and see how happy those workers are, singing along. I should just start with myself – a pair of Creative 2.1 speakers with a rented computer can arguably contend for one in top five slots for best memories of college days –  I thought the world of them, and have spent wonderful years listening for HOURS daily. What I’m trying to say is that not everyone shares a particular level of discernment.

The field of subjective testing is a very interesting one, and amateur enthusiasts are eagerly getting into it. The field is closely related to Psychoacoustics, and subjective testing methodologies ( AB, Blind AB, etc). It’s a very interdisciplinary subject – it starts with the wonder of biology, and ends up on statistics. There are broad definitions of terms describing music, and many would concur with those, but only when the sample is played in contrast to something that doesn’t fit the definition. I should write another post on the terminology used to describe audio, and what they mean on a physical level. Audiophiles need to understand that for economical reasons, the vast majority of the population is very happy with commercial “low-end” systems.   We will instead try to see what the “discerning” ear looks for. Turns out, there’s a rather huge variation here as well.

Obviously, hisses and crackles and clip sounds are not acceptable. Assuming clear audio quality and no system-induced distortion, we still have a wide range of preference. A lot depends on the genre that’s being played. When I look at home theatres, I necessarily have to ask the client what their main purpose is. A ghazal afficionado will not buy a system that a gaming enthusiast finds awesome, etc. Similarly, room acoustics for a DJ area is not the same as that for alive area, though it seems to be a trend to have both in the same space these days.

Coming back to speakers, this DIY guy I know (Sreekanth) makes bookshelves and tower speakers that have fantastic detailing, and we’ve had a great time trying out the differences between the systems he’s designed! (Exclamation, yes!). The difference in the soundstage between version 1 and version 2 of his bookshelf speakers is stunning. Version 2 is not for everyone. I took some time to warm up to it. But version 1 had me spellbound. Similarly, his tower speakers for the HT setup made me feel like I was right in the middle of those skyscrapers that Batman was planning to jump on. Leave aside brands, and DIY speakers. ( I will discuss about the genuine talent pool that the DIY club of speaker makers is in another post – cannot do justice to that here).

I’ve auditioned enough systems and find some bright, some clear, some mellow, etc. Honestly, before even discussing fidelity etc, we ought to all get our ears tested. Speech and Hearing institutes typically will only test for speech frequencies, though a couple of them may offer extended audiometry upto 12kHz. I’ve been lucky to have checked the full range of my hearing in my labs at my university, and realized that my hearing is acutely sensitive around the female high pitch range. Which is why Lata-ji will grate on my ears if the volume is too high, while others in the room are perfectly happy. When I tune spaces for sound, I depend on readings heavily for this range, and am able to trust my hearing for all other octave bands.

So, there’s stuff for everyone out here – pocket radios, low-end computer speakers, custom handmade speakers, audio engines, AV systems that the aforesaid vendor sells, and let’s just skip a whole lot of stuff to reach close to the top end at Goldmund home theater systems at 2 crores for a set. AV guys will obviously market the products they deal with, but they should be aware that what they’re saying is not the absolute truth most of the times. Owners of such spaces should be even more aware of this fact. Marketing cannot be the only reason why systems can be priced so far apart from each other.  So in summary, what sounds awesome to one conditioned mind may sound terrible to another. For this reason, audio “shootouts” never made sense to me.

To summarise, there’s a certain terminology of description of sound that is fairly standard, but wide variations are possible at the subjective testing level. Blind AB tests must be carefully structured to get the best results out of them. Very few absolute opinions exist beyond a point. But that’s fine no?  There’s a reason why we’re all not clones of each other, so why should we expect our hearing mechanism and preferences to be identical?

Festival Acoustics : Quick Tip

This part of the recommendations is always free of cost. With everyone gearing up for the festive season, I’m only too happy to provide the name of a brand of ear plugs that I’ve found better than most others. 

Db Safe. Made of washable rubber, available at most medical stores for under Rs. 100,  works better than all the inefficient, memory foam stuff doing the rounds these days. Sturdy, washable piece.  

Please note, I’m not being paid by DB Safe or anyone to do this. I’m only writing this to make the reader aware that help is available just around the corner – at your nearest medical store, and it’s not an aspirin. 

Happy festivities! 


Acoustics for Lounges and Clubs – 1

I’ve recently had a chance to look at a few of these projects not six months into my freelancing, and there’s plenty to be said here. Pubs and lounges have integrated themselves into the lifestyles of Bangaloreans for over 10 years now, and plenty of people spend the best part of their weekends catching up with friends and family at such places. This post is for a broad spectrum of audience – aimed at giving general information to people to go to such places, people who design/sell audio, people who own such spaces, and people who live near such spaces.

This post is the first of two, and looks exclusively at operational aspects of such spaces. The second part will go into the technical aspects of soundproofing, interior soundscaping, and sound system engineering.

Why Soundproofing

This is by far the biggest problem required to be addressed for such places, for more reasons than one. For obvious reasons, these places  almost always in the heart of the commercial pockets in various areas in the city, rarely ever on the outskirts. This is usually good news for everyone, because it makes sure they’re not too close to the residences for the most part. Occasionally, when residences have given way to commercial spaces, and some residences are still hanging around on what is now a commercial hub, soundproofing becomes a more critical issue. Like I just said, for more reasons than one:

  • Residents face noise issues. Right , easy to guess that. Only thing, they don’t put up with it these days. There are plenty of groups out there lobbying for noise laws to be stringently implemented, and complaints can lead to spot confiscation of music equipment, and repeat offenders can get their license revoked. This is more serious than it appears – places can get shut down in 3 months of taking off. Full Stop. Anyone who doesn’t believe this can call me on my phone, and I will be happy to put you in touch with people who’re facing this issue.
  • False Threats: There is another aspect to this : It takes all kinds to make a world, and so there are people who can really live with the noise, but choose to make complaints and harass and extort money from owners. Again, there are some famous people who are known troublemakers in Bangalore  –  who give the rest of the genuine anti-noise lobbyists/activists a bad name.
  • Genuine Threats: Residents really do face noise issues : I know this microbrewery that has a reputation for playing extremely loud music. It’s not just residents who face this  (Eg. A glass vendor I was talking to lives about 9 buildings away, and took 15 mins to vent his frustration on how he is completely sleep deprived on weekends because of the loud noise coming all the way from that microbrewery – he said he doesn’t get sleep till they turn off the bloody thing, and has been talking to the welfare association of that layout to press complaints.) Customers also face the same issue – a close friend of mine advised me never to go there with my toddler – her hearing will end up being permanently damaged. She said she their gang of friends couldn’t bear to sit there for even half an hour. Add to it, the place is a metal and glass jungle, the interior acoustics have not been taken care of, and so the music they play sounds bad anyway. I am obviously going to wait for one positive review from trusted sources before I think of going there.

Now, getting an acoustical consultant in early will help owners to relax and run their place happily for years. I’m doing this project where I was roped in rather at the last minute, with tons of changes not possible because many things had already been done. It’s been quite a challenge to work on it, and I cannot assure them that they will comply with the written word of law .That requires measures they’re not willing to implement. So we’ve taken measurements late night, and we’re going to meet ambient noise levels ( which in that space are higher than those stipulated by the law). So we’re really just blending in. However, all measurements are averages, and it is not possible to design for peak noise levels to be contained in. Not the best of things, but with residences right behind them, not doing anything would be far worse.

Why Interior Acoustics

This is the other aspect which is increasingly being paid importance to. With something like 4 restaurants/lounges/pubs opening in Bangalore every month, there’s plenty of competition, and people rely on designer aesthetics, michelin-rated chefs, and plenty of live music and DJ-ing to attract clientele. Now celebrity chefs are fine, but designer aesthetics sometimes don’t allow for even the minimal essential acoustical treatment. The second part of this post will go into detail on what issues we typically see in such spaces.

Why Sound System Engineering 

Now we’ll all just go by our own ears. Fair enough an argument. However, there are also technical factors that go into the design of speaker systems, and while you don’t need to know them in detail, you should still spend time understanding and experiencing the USP of the systems you demo.  My reason for mentioning sound system engineering is that providing the right kind of speakers based on the needs and the type of space will significantly influence the amount of soundproofing and acoustical treatment you will need to spend on. 

Accurate sound system engineering and critical acoustical treatment can make any kind of place sound warm and intimate. Owners of these spaces should take the effort to do plenty of research, because most vendors will usually only try to make the biggest sale they can – that’s their job.  The mid and high end ranges have lots of options, and ideally the sound system should be finalized after the venue has been decided, not the other way round. It seems to be a trend these days to have a DJ space and live area in the same club. The acoustics required are different, but we try to strike a balance between the clear, tight bass needed for smooth music, and the boomy, thumping bass required for EDM.

The next post will discuss the acoustical requirements of such a space.

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!

Thank You For The Music: A Deeper Look At Resonance

We’ve all gone through days when the facts suddenly become too much to handle. That important link between gathering facts and processing them seems to be some kind of bottleneck. That’s when I need to shut out the physical world. I invariably resort to music. It is my first weapon of choice for a mood change.

Why does music make us happy?

Now I’m trying to see if I’m just pleasing my auditory senses here, or if the relaxation happens because of some other factor. True, some good sounds that hold you in rapt attention can take your mind off the reality you just faced. So temporarily, your energies are devoted to something pleasant. Which means, there was something about the real world that made you tired, de-energized, and there’s something about some well harmonized sounds, that ease out your tiredness, and relax those constricted muscles. This could be natural – because music is by definition a collection of sounds that are harmonically related to each other, and even with distortion, can sound quite pleasant.

What about songs that can make you hit the roof with excitement?

That happens when there’s visible gaining of energy … somewhere some resource is being unleashed in your body and as you get absorbed in the rhythm, melody ( or whatever it is you look for in a song)… and as the intensity of the song picks up, you feel your energies returning full strength, and these keep increasing till the end of the song, leaving you on a high.
This intensity of the song, causes your own positive energies to come out and spread themselves on you. This visible gain of energy is worth looking at. It probably doesn’t make sense to rationally analyse these energy transactions, because the very idea of a clinical analysis separates you from that source, but here’s a go at it. Let’s start with the clinical definition of resonance from wikipedia:

In physicsresonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. Frequencies at which the response amplitude is a relative maximum are known as the system’s resonant frequencies, or resonance frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy.

Naada Brahma – The Universe is Vibration

The first idea I’d like to talk about is the Sanskrit phrase – Naada Brahma -which means, the universe is vibration. So you, me, the laptop, the dog, the bridge, the building, are all vibrating bodies. Now we know that this is true at least of structures – structural engineers calculate resonant frequencies carefully. Not doing so results in disasters such as the Tacoma Narrows Bridge – where side winds set up vibrations approaching the resonant frequency of the bridge – and this turned into a self-feeding mechanism that resulted in the bridge swinging wildly with larger and larger amplitude, till it broke at the center. Here’s a video:

Now if seemingly rigid structures can have resonating frequencies, why not the rest of the world? The songs we listen to are all a combination of instrument vibrations, so the song must have its resonant frequency? What about us? Are we resonant ? On at least some tangible level, yes. Some people we ” resonate” best with, are our close friends. We’re on the same “frequency” with them.  Others cancel out our fond beliefs, so we tend to stay away from the likes.  And so, there are songs we like,and songs we don’t. There are people we like, and people we don’t.  “It’s a vibe thing” …

Least Resistance

At this resonant frequency, the two bodies in question have the least amount of resistance between them. And so there is a maximum transfer of energy – no energy is lost in any kind of impedance/resistance.

Manodharma – Expressing the Inner Energy

Now the other idea about why we suddenly gain energy from some kinds of music.

The song is a collaborative effort of a few people who got together and established contact with their inner energies and instincts and expressed whatever they felt then. It could’ve been their rational minds exploring a technique or a scale, or it could’ve been their feelings taking them up and down the scale. Either way, their rational mind or their emotions, contact with something inside has to be established before their skill can express it. Their skill can only express it. The word for this “something inside” is Manodharma . Carnatic musicians use this word to describe an artist’s ability to express themselves completely – this part of the concert is a mix of skill, intuition, feelings, rational intellect. Wikipedia says ” Manodharma plays such a significant role that a capable artiste may never render a raga the same way twice.” There’s a fixed part of a carnatic concert dedicated to this, while the rest of the concert rendering follows rigid rules of structure.

So when I listen to bands that take off on lovely riffs or ones like Shakti, where each person is spontaneously exploring their domain within the framework of the song, I feel that my reaching a high has as much to do with seeing this contact they’ve established with their inner selves, as with appreciating their skillfulness.

I don’t know yet, but on some level, my inner peace gets unleashed, the frown vanishes, the set jaw relaxes, the gaze softens. Some songs build up on intensity instead of just soothing their way till the end. Then I can actually feel my toes and fingers bubbling with energy towards the end. After these visible energy changes, I feel like I just shrugged off those silly inane worries.

When I listen to a classical piece, I can see the singer so much in contact with the feel of the raaga, and yet retaining judgement to express skill within its framework. In fact, our ancestors have classified raagas so accurately according to the feeling they induce, that one wonders how they gauged all this rationally – it really deserves a separate post. Maybe it wasn’t all rational.  Maybe it’s not just music. Maybe it’s directly rejuvenating to see anyone establish a moment’s connection. Music is more instantaneous to me because I posses some basic skill.

But I’d be wrong if I tried to limit all my happy moments to music. Resonance happens with us on many levels. 

It may be a piece of art, it may be a deed of kindness, or it may be a program that worked after you spent all your energy on it trying to make it work, or just something you cooked that turned out well. If we only took time to take a step backwards for just a second, and savour that moment – the very next moment, you’re already smiling.

Music, art, work, anything… they’re all reflective of human thinking, and of human transcendance, and are a direct expression of the vibrational energy that exists around us. Regardless of what moves you –  please take a moment off to step aside and shake hands with it.

Happy Deepavali, everyone!

This is the time of the year all Hindus wait for – houses are spring cleaned weeks in advance, sweets are made, customary gifts are exchanged, etc. Grandiose is the theme of the festival’s new dresses –  people drop in at each other’s places, huge get-togethers happen for Lakshmi pooje performed by women, followed by plenty of feasts. And of course, the crackers. Now I don’t quite know what ancient history or religion has to do with cracker bursting – but we’ve all been mighty excited about it since we were kids – till many of us grew out of it.

The crackers come with a huge story behind them – of the many children forced to work with unsafe materials, working in unsafe factories, of the many fire accidents that are reported, of the many more accidents that go unreported, of the shameful salaries they get, of the heavy price they pay – risking their health, life and limb.  Now if this isn’t enough reason for people to stop using crackers, I don’t know what else could be. Surely, people who burst crackers despite knowing the abovesaid, won’t be dissuaded by the idea of noise pollution, or the distress it causes to humans, and especially to animals. My infant is already being jolted out of sleep – the cracker bursting sometimes starts earlier than the festival itself. The sound scares the living daylights out of her – it’s an explosion, for god’s sake. She wakes up screaming and crying – can’t expect her to understand “it’s merely fireworks”. Given the decent density of infants in any pocket of India – people bursting crackers should perhaps display some consideration. I will not even mention the sheer physical distress that animals must be going through – their range of hearing is much higher than ours, and they hear everything a lot louder than we do.

The number of accidents that happen at this time of the year is shocking – and many more go unreported. Children suffer burns, injuries, scars, and of course, ear injuries. So many children are rendered permanently deaf  – for your ear drum is a tiny, delicate membrane  – stretched taut. I wonder why people think the thrill of lighting crackers is worth the risk. There are toddlers and infants in half the households in India. The lifetime of suffering is not worth the thrill  – and somehow no amount of highlighting this seems to work. There’s always a fresh crop of youngsters, waiting to have their go at the crackers. There’s even some kind of graduation scheme – starting with the small ones – and when you become ‘big’, go for the loud ones. The noise levels in the proximity of such a cracker can be close to 120 -140 dB. How loud is that? Actually, it’s really hard to tell you that without resorting to swear words for accurate expression.  If you think that’s not to worry about –  the explosion is just for a brief second, hear this –  people join such things till this chain extends all around an apartment complex, and then you’ll hear this for 10 mins. Experience your ears ringing after that – and other sounds seem strangely tolerable, because your threshold of hearing just suffered a temporary shift. A few of these in succession, and your hearing will be just a little bit worse off than it was. You’ll only know in your later years.

On a more rational note, clearly, this is a modern phenomenon – this cracker bursting – Prince Rama didn’t have these in his days, I’m guessing. This is more of a social thing – one that really should be done away with.

Now, in case I’m sounding like a doomsday soothsayer, I must clarify – I love festivals myself. I’m very fond of the enthusiasm they bring, of all the sweets and savouries that go around, of all the customary meeting and greeting, of all the new clothes, of people turning up in their finery, of all the long-lost relatives we get to meet, of all the catching up, the feasting and merrymaking, and of course – the holidays! Quite the mood!  I just wish there wasn’t the firecrackers angle. There’s just plenty to enjoy without that one!

So season’s greetings everyone, have a safe festival!

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.