Understanding Room Acoustics and Sound Treatment: A Primer Guide

This guide is intended to introduce to you the world of room acoustics, and how you can enhance your listening environment by taming sound issues that studio owners face. Thus, improving your recordings.

The goal is very simple – we want to get the sound from the speakers to your ears with the least amount of reflection and distortion. This is really just a matter of what becomes of the sound after it passes your ears.

Introduction

In a perfect world the ideal studio would be placed in the middle of a large field, ensuring that nothing would interfere with the frequencies hitting your ears; otherwise known as a reflection free zone (RFZ).

Because this is not always possible we have to contend with sound reflections from walls, floors, furniture and ceilings. These are all factors that will change the way we hear things in a listening environment. Therefore, we have to deal with the possibility that the sound we are listening to isn’t always as it seems.

Part 1 – Soundproofing VS. Sound Absorption

There is a very commonly misconstrued idea that soundproofing is the same as sound absorption. However, they are completely different topics to discuss.

*SOUNDPROOFING

SOUNDPROOFING is when you want to stop the transfer of sound from your studio to another room, and SOUND ABSORPTION is what you want to do when you want to improve the acoustics within your studio. Implementing both will ensure best results.

Products that are designed to BLOCK SOUND from entering or leaving a space are almost always found INSIDE the wall construction. These products are heavy, dense, cumbersome, or designed to decouple the wall so that one side of the wall doesn’t have hard surface contact with the either.

*SOUND ABSORPTION

Sound absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to sound energy that material reflects or conducts.

Products that are designed and intended to ABSORB ECHO within a room are soft, light, fluffy products. They will generally feel soft to the touch. They are designed to soften up the surfaces that are in the room and reduce the echo within that space.

*SOUND CAN PASS THROUGH ANY MEDIUM. In fact, it travels through solid objects better than through air. Much like water, it doesn’t have a form and molds to its surroundings. It can be absorbed by some materials and contained by others.

(Above: Sound Absorption Panel)

Part 2 – Early Reflections: The Destruction of Proper Stereo Imaging.

The first issue we want to address are called early reflections. This is when a sound hits your ear after bouncing off an object creating a very small delay effect and our brain cannot distinguish this as a separate sound source.

For example, the sound coming from your left monitor hits the right wall next to you and as a result bounces into your right ear. This means you are actually hearing some frequencies twice! This is not good.

Instead of distinguishing the delay as being separate from the original source, our brain interprets it as the same sound coming from different directions.

When you pan a sound left or right you will have a harder time distinguishing the balance between the two. Similarly, a sound that is in the center might sound more left or right. If this is familiar you might be dealing with effects of early reflections.

The image above shows an example of early reflection points.
The red lines represent the sound you do not want to hear.
Keep in mind these reflections also occur from the back wall, floor (including large desks and large mixing boards below your monitors), and ceiling.

*HOW TO FIND EARLY REFLECTION POINTS

A simple and effective way to find early reflection points is to position yourself in your normal listening position and have a partner move a mirror flat against the sidewalls at ear level starting from the front of the room to the back of the room.

ANYWHERE YOU CAN SEE YOUR TWEETERS is where you should place sound absorption panels. Once the sidewall reflection points are located you should do the same thing on the floor, back wall and ceiling. It’s best to place absorption panels all around the areas of reflection for best results.

Part 3 – Standing Waves: Controlling Your Room.

You don’t have to understand the science of standing waves to understand what they are. To put simply, standing waves are when the sound combines with a reflecting source in mid-air. This can occur between reflected sounds and the original sound source and also between reflected sounds themselves.

When this happens frequencies will sometimes over power other frequencies and cancel them out causing nulls or dead space within a room and vice-versa where frequencies will expand giving the impression that your music sounds louder.

Ever notice when you stand near the corners of your room and the low frequencies seem almost too much? Or move to another position and the instrument you thought sounded great just isn’t there anymore?

Or, how about when you eat something that’s just been microwave and you realize some parts didn’t get cooked enough and other parts got too hot? Much like sound in a room, this is caused by standing waves.

– Dealing with standing waves.

Because mid and high frequencies are easier to treat this particularly happens more often with lower frequencies. One of the most effective ways to deal with standing waves is by having an angled ceiling. Unfortunately this is not the case for most of us.

This is where room acoustic treatment comes in. By applying low frequency absorption to the corners, walls and ceilings, we reduce the amount of sound waves being reflected back into the room.

These absorbers that focus on the low-frequencies are commonly referred to as Low-End Noise Reduction Devices, or LENRD. More commonly they are referred to simply as “bass traps.”

(above: LENRD Bass Trap)

By placing LENRD’s in your studio you can prevent unwanted low frequencies from gathering in your room that can lead to standing waves and acoustic interference.

Part 4 – Monitor Positioning: Where Room Treatment Really Begins.

While there are a ton of articles to be read about monitoring position and speaker placement, we will keep things basic and stick to some key rules.

– Generally, the more symmetrical the room the better (minus a slanted ceiling for getting rid of standing waves).

– In a room that is more elongated it is better to position your speakers facing the long way so the back wall is further behind you. That way the sound has further to travel behind you before reflecting back to your ears. This is important when working in most home studios and smaller recording spaces.

– For listening position, you want to make sure you form an equilateral triangle between you and your monitors. The distance between your monitors and your ears should be equivalent to the distance between your monitors.

– It’s good practice to have your tweeters at ear level.

– Lastly, if your monitors are on their side, make sure the tweeters are positioned on the outside.

Part 5 – Diffusion: Optimizing Your Sweet Spot

Diffusers are used to treat sound aberrations such as echoes. They are an excellent alternative or complement to sound adsorption because they do not remove sound energy, but can be used effectively to reduce distinct echoes and reflections while still leaving a live sounding space.

(above: wooden sound diffusor)

Compared to a reflective surface, a diffuser will cause the sound energy to be radiated in many directions, hence a wider more open sounding environment, including your sweet spot. DIFFUSION CAN MAKE A SMALL ROOM SOUND LARGE AND A LARGE ROOM SOUND LARGER.

Final Notes

• Soundproofing is NOT to be confused with sound absorption.
• Using the mirror method to find early reflection points is a good start to treating your studio.
• By placing LENRD’s in your studio you can prevent unwanted standing waves and acoustic interference.
• In a room that is more elongated it is better to position your speakers facing the long direction so the back wall is further behind you.
• The distance between your monitors and your ears should be equivalent to the distance between your monitors.
• It’s good practice to have your tweeters at ear level.
• Lastly, if your monitors are on their side, make sure the tweeters are positioned on the outside.

Helpful Video Demonstrations

 

For more info on acoustic treatment products please visit www.ProSonicAcoustics.com