25 JANUARY 2017

written by Mike

Acoustics

How To Soundproof a Room

Acoustics is an art of measuring space and treating it with appropriate materials. Acoustic panels or acoustic foam are an easy example.

The minute you decide you want to pursue a career (or just a hobby) in sound and music, a question comes to a mind.

How to soundproof a room? Answer is:

Acoustics.

The subject of acoustics is colossal and requires years of in-depth studying and experience. Try to think about it beyond soundproofing a room or recording studio. Soundproofing affects every underground metro station, every shopping mall, school or office. It is noise pollution, reverberation, and general ruckus that we are fighting.

City halls, churches, conference rooms. Architects design all these buildings with acoustics in mind.

If you want to get deeper into the subject, check

Architectural Acoustics by Marshall Long

This book is useful if you are serious about studying acoustics. It starts with a history of acoustics and human perception. But it also goes into a great detail of different kinds of buildings and designs. It is a heavy, around 800 pages volume. Not a bedtime read.

Why is it so rare to see an open-air orchestra? Or open-air opera?

One answer, there is no acoustics outside.

Ok, but what about these old theaters where people sat outside?

Yes, these places were (and still are) open air. Architects designed them with acoustics in mind too.

Music halls are exceptional in their design. These rooms must deliver the best sound possible. But, for example, think of hospitals.

How can soundproofing be important there?

We build hospital rooms with patients’ comfort in mind. Especially surgery rooms that need to minimalize outside distractions. To become an acoustician, you must learn physics of the sound, mathematical equations, computer programs and specialized measurement equipment. I want to introduce you to some basic concepts of acoustics. I will try to ignite in you a deeper interest in this subject.

I’m not going to lie; it is a bit of a challenge.

MEASURING A ROOM

Measuring a room is not as easy as it sounds. The size of the room is important, but you also need to think about orientation and functionality of the place. And don’t forget about the volume of the room. Here comes the math.

The perfect solution would be to build the room from scratch. Rod Gervais writes how to transform room into a recording studio in

Home Recording Studio Build It Like the Pros, 2nd Edition

Great book for people, who are not as good in math or physics. Easy to understand text, full of pictures and easy to read graphs. And it goes step by step, from start to finish. There is a cool ‘acoustics myths’ chapter at the end too.

First thing that most people would do is to measure the frequency curve. It will show you what kind of acoustic treatment the room needs. For this task, you will need one of these weird looking microphones.

As critical as it is, think about other variables too. What is the isolation from the outside world? What about the spill from other rooms? How will the room be lit, powered and air-conditioned? Where are you going to put your desk? Also, the room will sound different with all the equipment inside.

So remember to take more just one measurement. Take a note of these few basic requirements that you will need to think about:

frequency balance, acoustic isolation, and separation, reverberation and cost.

Before committing to anything, do your research and analyze results of your measurements. Don’t rush it. There is a cool program that you can you use for your acoustic adventures called SketchUp. I used it for my school acoustics projects. We designed a home recording studio with one of my colleagues. It is easy to use and fun. I suppose it is sort of like Sims.

Without actual Sims.

ACOUSTIC TREATMENT

Treating a room is much more complicated that just putting some egg cartons on your ceiling and walls. And by the way, these are quite ineffective so do not waste your money or time on doing that. Acoustic treatment will make you think about the state of the doors, windows, walls and floor in your room.

How isolated are they?

Is it possible to enhance their effectiveness on a low budget?

It is also important to analyze frequency balance of space.

You will need to invest in some materials that will absorb, diffuse and trap the unwanted sound frequencies. Acoustic panels and acoustic foam are something to consider buying.

That’s where sound absorption coefficient charts come in handy

http://www.sengpielaudio.com/calculator-RT60Coeff.htm

http://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm

I know. These are fascinating to read.

The aim is to have frequencies balanced as much as possible. It means that whatever you mix in your room will sound good in other spaces. For small rooms like a bedroom, unwanted bass frequencies will pose the biggest threat. Do your research but making your bass traps can also be a great and a low-cost option to consider.

REVERBERATION

Reverberation is a big part of acoustics.

What is it?

Every time you make a sound (in a room) it reflects and bounces off walls, floor, and ceiling. You can have early or late reflections, depending on a journey of the sound. Imagine sitting in front of the speaker. 

The sound that hits you first is called direct signal. There is nothing between your ears and speaker’s cone that could block it. Beyond that, you have your sidewalls and maybe your ceiling. Some frequencies will reflect off these surfaces and then hit your ears. These are short reflections.

Late reflection is the sound that will travel to the wall at the end of the room and then travel back to you; you hear it after everything else.

How long can the sound bounce around like that?

Definition of reverb.

It is a period in which a sound diminishes to a millionth of its original intensity. You can calculate it with an RT60 equation of 60dB decrease over a certain time duration.

RT60 = Vx0.049/AS

V is the volume of the room

A stands for absorption coefficient of the room. That is the amount of acoustic energy absorbed rather that reflected

S is the total surface of the room

This formula can explain the reason sound lingers in a big cave.

You can calculate it here.

http://www.sengpielaudio.com/calculator-RT60.htm

Accurate measurement of reverberation will help you to design your space for the best possible result. As you can see acoustics is a vast and deep subject. We haven’t even scratched the surface and already there are some equations to remember.

Boring!

But consider this. If you want to build a small studio, space to record your online video channel or even just a home cinema, consider soundproofing your room. You will realize it is not as scary as it sounds.

Well, unless you want to design a concert hall or something.

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