How to Reduce Echo and Reverb in a Studio

October 8, 2019

In the small walk-in closet (vocal booth) at my parents house, lined wall-to-wall with blankets, I remember my 16-year-old self thinking, “It’s getting a little hard to breathe.” I had deadened not only every sound, but every bit of creative vibe that had existed in that room. A cramped, dead-sounding room is not ideal for letting the creativity roll in a recording session. There are better, simpler ways. The ideas I’ll show you will help you transform any room into a studio.

Although deadening a room with blankets kills echo, it also kills the natural, comfortable environment required for a good recording. The sound and feel of a vocal booth is unnatural and sterile. Some of the best ways to improve the acoustics of your studio are totally free and require much less work than hanging blankets wall-to-wall. 

Although deadening a room with blankets kills echo, it also kills the natural, comfortable environment required for a good recording. The sound and feel of a vocal booth is unnatural and sterile.

What Are Bad Acoustics?

It may be helpful to learn the basics of how sound works if you’re trying to treat your room for better acoustics. For a quick lesson on audio basics, read this article by Audio University.

Generally speaking, when a room sounds bad, it is because the sound waves are interfering with their own reflections. 

To understand how to reduce sound interference, let’s quickly explore what causes it.

Polarity and Phase

Sound exhibits constructive and destructive interference. In other words, sound waves that interact in a room sometimes work  with one another and other times work against one another.

Constructive Interference

Take a look at the following sound waves. The waves are the exact same size, or loudness. They are also in phase, meaning the waves go up and down in loudness together. Because they are in phase, they add together perfectly and create a sound wave that is double the original size. It’s like 1 + 1 = 2.

Destructive Interference

However, in the following image, the sound waves are perfectly out of phase. This means that when one wave goes up in loudness, the other goes down. The waves are the same size and perfectly out of phase, so the result is a complete cancellation. These two sounds add together to equal nothing. It’s like 1 + -1 = 0.

It’s rare that the two waves are ever lined up perfectly in phase or perfectly out of phase. Usually, they are slightly offset as you see below. 

In most cases, there is a combination of constructive and destructive interference. 

Comb Filtering

When we place a microphone in front of a vocalist or instrument, the sound waves take more than one course to the microphone.  Some waves go to the microphone directly, and some bounce off of a surface and then head towards the microphone. 

By the time a sound wave on the two paths (direct and reflected) has reconverged with itself at the microphone, the two copies have traveled different distances. Thus, they are slightly out of phase, and various cancellations and summations of the sound waves will occur, resulting in some frequencies being doubled, and some being cancelled.  

This phenomenon is called comb filtering, because it looks like a comb when seen on a graph. The graph shows the frequency on the x-axis and the loudness on the y-axis.

I wrote an article all about comb filtering and phase cancellation. If you’re planning your studio, I recommend checking it out.

What Causes Echo in a Studio?

Flat Surfaces

Spectral Reflections

If a sound hits a flat surface, a near-perfect copy of the sound is reflected. This is called a spectral reflection. Spectral reflections are dangerous, because they cause comb filtering and echo.  

Our main focus in acoustically treating a room will be to reduce the amount of flat surfaces in our room so that we can avoid spectral reflections.

Reflective Surfaces

Echo and Reverb

Reflective surfaces aren’t always a bad thing. We are used to hearing people speak in rooms with reflective surfaces. However, there is a problem with only having reflective surfaces in your studio. The problem is that the sound takes a lot longer to go away, or decay. This is why some rooms are very reverberant. 

When sound hits an especially hard material, the reflected wave is almost as loud as it was before it hit the wall. When sound hits a soft, heavy material, a lot of energy is absorbed. A wave reflected off of a soft, heavy material is much quieter than before hitting the wall.

Parallel Surfaces

Standing Waves

Most rooms are built with parallel walls.  Every room has what is called room modes. A room mode is a specific frequency that resonates between parallel surfaces. 

Based on the distance between two parallel walls, there will be one frequency which is much louder than other frequencies. It sounds boxy and unnatural. We will try to break up the reflections which cause these.

Flutter Echo

A flutter echo can also occur between parallel surfaces, too. This is usually when the surfaces are further away from one another. A sound will bounce back and forth, creating a fast echo.

We often think of room modes and flutter echoes occurring only between walls, but don’t forget that the ceiling and floor are parallel, too!

How To Improve Acoustics In A Room

Absorption

Most absorptive materials only remove mid and high frequencies and reflect low frequencies back into the room. Air particles are lightweight. When waves moving through the air interact with heavier materials, energy is absorbed. However, unless you use very thick absorption materials, only mid and high frequencies are absorbed. This will ultimately cause a buildup of low frequencies, making the room sound dull.

Place Absorptive Materials In Corners

The angle of almost all residential corners is 90-degrees. If a sound wave enters a 90-degree corner, it is always reflected back to the source of the sound wave. That means that if you are practicing good microphone technique and speaking close to the microphone, your voice will travel to every 90-degree corner in the room and reflect back into the microphone. 

How can we absorb the energy before it reflects back to the microphone? Try this:

Coat Rack Holding Blankets

Hanging heavy blankets on a coat rack will help to absorb the sound reflected in the corner. The lightweight air particles will try to move the heavy blanket particles, and will lose a lot of energy trying. The energy will be absorbed, and the result will be no reflection. If you don’t have a coat rack, use a tall shelf and drape heavy blankets or cloth over it. 

Soft Furniture Along The Walls

Remember that vertical corners and horizontal corners can be problematic. Corners between the walls and the floor can be treated by placing soft furniture to break up reflections.

Sound Absorption Panels

In all honesty, I do not use any sound absorption panels, because I find it easier and more economical to employ the above techniques using things I already own. Sound absorption panels can be good tools for treating locations that are not able to be treated with the above methods.

Corner Panels

It is more difficult to treat the corners between the walls and the ceiling with furniture. In these areas, it is worth it to use acoustic panels for absorption. I’ve done some research, and I’ve found these corner panels to be affordable and easy to set up. The link will take you to the Amazon product page. The corner panels are easy to install and will help reduce the mid- and high-frequency reflections in the higher corners of your room that furniture cannot treat.

Wall Panels

If you are trying to absorb sounds that reflect off of a flat wall, these wall panels are an affordable option. The link will take you to the Amazon product page. These panels will help reduce the high frequency sounds from reflecting off of the surface and back into the microphone. 

However, read the next section before you go with absorption panels for flat surfaces, because there is a better way to address these reflections.

Diffusion

Diffusion is not an attempt to absorb the energy. Diffusion is an attempt to reflect the energy into many directions, rather than reflecting it directly back to the source. Using the terms learned above, diffusion attempts to break up spectral reflections. A diffusive surface consists of various depths and angles.

The angle of incidence is the angle of reflection.  

That means that if a sound hits a wall at 90-degrees, it will reflect at 90-degrees. It would look like this:

If a sound hits a wall at 45-degrees, it will reflect 45-degrees in the opposite direction. That would look like this:

Place Diffusive Materials Along Walls

Think about the various paths sound will take from the source to the walls and back to the microphone. Prioritize diffusing the reflections that travel the shortest distance.

Bookshelves

Bookshelves are great diffusers! Just make sure that you mix in small books with large books, so that sound waves will hit many different depths. You can also place other objects on bookshelves to reflect sound in various directions. The more variety, the better.

Round Surfaces

Round surfaces are the best diffusers. When sounds hit a round surface, they are evenly reflected into different directions. You can place round objects on shelves or select furniture with rounded surfaces. 

Diffusive Artwork

There are some really cool pieces of artwork out there that are specifically made to diffuse sound waves. 

You can make your own if you have a woodworking shop available to you. This article offers clear instruction on how to make your own acoustic diffusion panel. If you would like to see a great premade option, check out these wooden diffusion panels. The link will take you to the Amazon product page for my favorite diffusion panels. You can buy as many sections as you need and place them on the walls or ceiling. 

Remember, although sound takes millions of routes from a source to the microphone, it’s most important to place diffusion to break up the shortest routes.

Acoustic Treatment With Character

Acoustically treated rooms don’t have to be stuffy and lifeless. In fact, if you can find a way to use the diffusive materials you already have strategically, you can maintain a studio environment that is expressive of your personal character. When a room has character, musicians can feel more comfortable expressing themselves.

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