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Acoustics 101: Acoustic Treatment Guide For Home Music Recording Studios

by | Studio Acoustics | 0 comments

Do you have trouble mixing your tracks and making them sound good?  A primary element is first making sure your room sounds good acoustically.  This guide covers the basics of acoustics and sound components for home studios. You’ll learn which acoustic phenomena causes problems with your room’s sound, and how to correct them.

Do your mixes usually sound muddy or too bass heavy?

Are your mixes lacking punch and power?

Do your recordings compare favorably to what you hear on records or the radio?

If you want to make your recordings and mixes sound better and more professional, the quickest way to do this is to improve your studio’s acoustics!

More than buying the latest and greatest mastering plugins or virtual instruments, proper acoustic treatment will provide the highest return for your money.

It’s the most overlooked aspect of having a recording studio, and the one thing that will pay lots of dividends for years to come.

What You’re Going To Learn

This Acoustic Treatment Guide For Home Recording Studios is going to walk you through the basics of how to get your studio sounding better by applying acoustic sound treatments.

I’m going to start with a little acoustic sound theory (but not enough to put you to sleep!)

You’ll learn how soundwave phenomena like room modes and standing waves affect how you hear your music, and if left untreated will compromise all the work you do in your studio.

If you’ve been struggling with getting the bass right on your mixes, this is what has been causing the issue!

AND, if your studio has flutter echo, comb filtering, or room ring issues, (and all untreated studios do!) it will be tough to produce broadcast-quality tracks in your studio.

The truth is this:

Insufficient or incorrect use of sound treatments jeopardizes your investments in high-quality studio monitors and other gear. You simply won’t get maximum value out of your studio’s equipment.

I hope you see that acoustic treatments are worth the investment.

To help you, I’ll go through the various types of acoustic sound treatment products you’ll need to improve your studio’s acoustics.

And finally, you’ll discover some really valuable FREE SERVICES that will help you analyze your room and determine the amount and type of products you’ll need.

If you’re ready, let’s start!

Acoustics 101

Acoustics is a very complex field and is actually part science, part art.

For example, the acclaimed Hollywood Bowl outdoor venue in Los Angeles has had its stage and sound system redesigned multiple times over many decades to fix ongoing acoustic issues.

Though dealing with sound and acoustics can have its challenges, some basic principles govern how sound moves through air.

Sound travels in two ways:

  • As direct sound to your ear or a microphone
  • As reflected sound that bounces off walls, ceilings, or other surfaces

It’s important to know that reflected sound arrives later to your ear or a microphone because it has farther to travel than direct sound.

It is this reflected sound that causes most acoustic issues in studios, especially in smaller rooms.

There are two reasons for this…

Sound Reflections

The initial sound that is reflected off a wall or ceiling is called the first reflection.

BUT, that first reflection also gets reflected off walls, etc. creating what’s called the 2nd reflection.  This continues for 3rd reflections, 4th reflections, etc.

AND, each reflection is delayed a little from the previous one.

All this creates very complex sound waveforms that hit your ear or microphone.

These multiple reflections can create what is known as destructive interference, which is the source of problematic room acoustic phenomena such as flutter echo and comb filtering (explained later in this article).

The following short video illustrates these concepts with some nice visual touches:

How Sound Works (In Rooms)

Sound Components

This next part gets a little techie, but hang in there, it’s important to understand…

Sound travels in wave cycles and is composed of three components:

  • Amplitude – the strength of the wave, commonly known as the loudness of a sound.
  • Frequency – the number of wave cycles per second, which is heard as the pitch of the sound. Frequency is measured in Hertz or Hz.  For example, the note A used for concert pitch is 440 Hz, which means it has 440 waves cycles per second.
  • Wavelength – the distance between the wave cycles.

A sound’s wavelength is of particular importance in studio acoustics.

The low E on an electric bass guitar has a wavelength of 41.2.  Measured in feet, this note is 27.425 feet long!

With wavelengths this long filling a room and having nothing to absorb the sound energy, it’s no wonder acoustically untreated studios have problems getting the low end of mixes right!

Room Modes

Every room has what is called room modes based on the interaction of the room’s dimensions and sound frequencies.  These modes are caused by sound bouncing off the room’s surfaces.

Room modes can be clearly heard in studios by walking around to different parts of the studio while a music track is playing.  You’ll notice that the bass may be loudest in the corners and almost non-existent 2 feet away.

What causes this is peaks and nulls (dips) in the waveforms within the room.   These are created when the waveforms meet and interact. If the waves are in phase at a particular frequency, they combine into making that frequency louder.

Conversely, if the frequencies are out of phase with each other, they combine into making that frequency softer.

Another example is when you’re playing an electric bass, and on some notes the room suddenly seems to resonate or buzz.  Those notes are exciting the room’s resonant frequency based on one of the room’s modes.

Standing Waves

Standing waves cause problems in most studios.   They are frequencies that are exactly one-half (or a whole multiple of) a room’s dimension.  Standing waves cause the bass response to be very uneven, just like you learned with room modes above.

The following short video illustrates this concept:

What Are Standing Waves In Rooms?

Unlike other waves that bounce around the studio, standing waves known as axial modes remain stationary and occur at specific physical locations in a studio.

Axial Modes

Axial modes are a primary source of acoustic problems in a studio.  They are a room’s standing waves that are bouncing between two opposite parallel walls.

You’ve probably heard that having parallel walls in your studio is a no-no; axial modes are the reason why.

Axial modes bounce back and forth between these parallel surfaces, creating sound pressure that has nowhere to go in your room.  It causes peaks and nulls in the low frequencies.

Flutter Echo And Comb Filtering

There are two final acoustic phenomena I want to go over that are common in studios, especially home studios:

  • Flutter echo
  • Comb filtering

Flutter Echo

Flutter echo is a rapid series of echoes created by sound bouncing between two parallel surfaces like walls.  The result is a metallic “rattle” that can easily be heard if you clap your hands in a room without acoustic treatment.

Flutter echo will ruin both vocal and instrumental recordings, as the singer or player will sound like they were recorded in a terrible sounding room due to these reflections hitting the microphone.

Comb Filtering

Because most home recording studios are located in small rooms, comb filtering can become a problem.

It is created by sound bouncing off nearby walls or the ceiling that are physically in close proximity to the microphone.

These short reflections create a series of peaks and nulls that result in a hollow boxy sound on your recordings.  Not good!

Larger studios can usually avoid the comb effect by recording vocals and other featured instruments in their larger rooms where the reflections are spread out.

OK with theory out of the way, let’s focus now on solutions to these acoustic problems.

Creating A Great Sounding Studio

A good recording space provides an acoustically desirable ambiance that enhances recorded sounds.

A great sounding studio should not sound too live or too dead.  It is created by a balance of:

  • reflective surfaces
  • absorbent materials
  • diffusive materials

Reflective Surfaces: Hardwood Floors

Most professional studios will have their main recording room include a hardwood floor.  Hardwood floors are a desirable reflective surface that livens up sounds without making them too reverberant.

AND, hardwood floors can be dampened if necessary by placing rugs on the floor as needed.

As you’ve learned, sound travels from one location to another both directly and as reflections off a building’s walls, ceiling, and other surfaces.  The complex sound waves created by these reflections are the primary cause of most studio’s acoustic problems.

Absorbent and Diffusive Materials:  Acoustic Products

There are three main types of acoustic sound products that are used in recording studios to absorb and diffuse sound:

  • Acoustic panels
  • Bass traps
  • Diffusers

Acoustic Panels

Acoustic panels are made of a special foam and are designed to absorb mid to high frequencies.  They do not have much effect on low frequencies.

They are effective at reducing reverb and early reflections that come from sound bouncing off walls and ceilings.

There are two types:

  • Wall mounted panels used for overall studio acoustics improvement.
  • Gobos, or moveable baffles used for partition off a vocalist or instrumentalist for isolation.

To get specific product recommendations and placement instructions, check out my article: 11 Best Acoustic Wall Treatment Panels For Home Recording Studios.

Acoustic Panels

Acoustic Diffusers

Unlike acoustic panels that are designed to absorb sound, acoustic diffusers act to diffuse and scatter sound.

They interrupt echoes created by sound reflections bouncing off of walls and ceilings and are used to deal with the effects of comb filtering, standing waves, first reflections and flutter echo.

When properly used, diffusers will help retain the positive acoustic qualities of your room while reducing or eliminating those common issues.

To get specific product recommendations and placement instructions, check out my article: 11 Best Acoustic Wall Treatment Panels For Home Recording Studios.

Diffuser Panel

Bass Traps

Bass traps are made either of a special foam or fiberglass insulation and are designed to absorb low frequencies.

Because of their size and mass, they also help absorb mid and high frequencies to some extent.

Bass traps are placed in corners of a room and also along areas where the walls meet the ceiling.

To get specific product recommendations and placement instructions, check out my article: 3 Best Bass Traps For Home Music Recording Studios Guide.

Bass Traps

Studio Sound Treatment Guidelines

Studio design should follow these general guidelines:

  • The ceiling should be Sound absorbers provide significant help here because they minimize sound reflected back down that many times results in either flutter echo or thin-sounding recordings.
  • The side walls should employ both absorbent and diffusive treatments such as acoustic sound panels and sound diffusers to eliminate flutter echo and comb filtering.
  • The wall behind your studio monitors should be a combo of acoustic sound panels and bass traps to reduce bass buildup and reduce flutter echo, comb filtering, and first reflections.
  • All corners and ceiling/ wall meeting points should employ strategically placed bass traps to reduce bass buildup.
  • The floor should be reflective to provide life and presence to recordings.

By using acoustic products correctly and in the right amounts, you should be able to eliminate or reduce flutter echo, comb filtering, first reflections, standing waves, room modes, and other issues.

How To Evaluate Your Room’s Acoustics

Here are three quick things you can do right now to assess your room’s acoustics for common issues:

  • Check your room’s size, dimensions, and structural elements
  • Do a flutter echo test
  • Run a low-frequency room response test

1) Check Your Room Size, Dimensions And Structural Elements

Size does matter… as far as studios go!

Small rooms tend to exhibit more acoustic issues than large rooms. This is because sound waves in small rooms have less time to decay and thus end up creating more destructive interference.

Ideally, your room’s length and width will be irregular lengths that are not divisible into each other with a round number.   These dimensions create fewer issues with room modes.

For example, a room that is  11’ x 17’ would fit the bill, while a room 12’ X 8’ would not.

Try to avoid using a square room like 10’ X 10’ for your studio. Equal width and length dimensions tend to amplify acoustic problems with room modes and standing waves.

Even worse is a cubed room, like 10’ X 10’ x 10’.  Any issues you have in a square room will be multiplied.  Many acoustic engineers will tell you to find another space to work in, as fixing the acoustic problems you face will be very problematic.

Structural elements that break up a room’s dimensions are desirable.  Ceilings that are higher in one part than another or a closet or wall feature that breaks a straight wall line will help your studio’s acoustics, especially in a square room.

A room without parallel walls helps greatly with acoustics, as sound waves cannot build up and bounce back and forth between walls as easily as with non-parallel walls. Unfortunately, most bedrooms and other home rooms almost always have parallel walls, but architectural elements such as built-ins or alcoves can help immensely by breaking up soundwaves.

2) Do A Flutter Echo Test

To check for flutter echo, clap your hands in the middle of your studio and listen for the characteristic “metallic” ring of flutter echo.

Audio Example: Flutter Echo Demo

Courtesy www.marktaw.com

Flutter Echo Demo

If you’re lucky, flutter echo will be at a minimum, implying that your studio already has some degree of absorption and diffusion.

Even if you hear really strong flutter echo, it is one of the easier acoustic issues to fix with diffusers and acoustic panels.

FYI, bookcases make great diffusers as the varying book sizes and layouts help diffuse sound.

3) Run A Low-Frequency Room Response Test

This test requires you to play back some audio test tones in your studio.

Download the file first by right-clicking to download it to your computer, or play it directly below:

Low-Frequency Sine Tones

The audio file is a chromatic scale of sinewaves that runs from 24 Hz to 262 Hz.

IMPORTANT NOTE: Always keep you volume low when playing back test tones.  High volume can damage your speakers.

How To Use The Test Tones

This file will let you hear the effect of room resonances and room modes on your room’s low-frequency response.

Stand in the spot you use (or will use) to listen to your monitors while you play back the file.

In most untreated rooms you’ll find that some tones will stick out in higher volume, while other tones may almost disappear.

The following chart, taken from Mike Senior’s excellent Mixing Secrets For The Small Studio book, lists the frequency and pitch of each test tone.  Write down which frequencies stand out or disappear the most – this will be very useful info when you get a room analysis done.

These three test will give you a good start on determining your studio’s acoustics strengths and weaknesses.

Free Room Acoustics Analysis!

Auralex, Ultimate Acoustics, and ATS Acoustics, three leading acoustic sound product makers, offer free room acoustics analyzer programs.  You can use them to determine how much sound treatment you need for your studio, their layout in your studio, plus tips on where to place everything.

Of course, all three companies want you to purchase their products once they provide their analysis, but you are under no obligation to do so.

Auralex

Auralex provides two excellent free tools to help you evaluate your studio in more detail:

  • Room Layout xXpress – an automated studio room layout app that is designed to give instant recommendations for small rooms.
  • Auralex Free Studio Evaluation Service – a free personalized analysis of your room with recommendations of specific products and where to place them. This service is the most comprehensive and you get the ability to ask questions specific to your situation.  Highly recommended!

ATS Acoustics Free Online Room Acoustics Analysis

ATS provides a free online room acoustics analysis.  You provide your room’s dimensions and surface info, and they determine how much acoustic treatment is needed for your room.

Ultimate Acoustics’ Room Analysis App

This free iOS app (available in the Apple Store) will help you determine the right amount of acoustic treatment you need for your studio.

My Own Studio Analysis

I’ve used Auralex’s Studio Evaluation Service twice when I moved my studios.  I use their acoustic panels and diffusers in my studio, and these products are on my recommended product lists.

Here’s the drawing I submitted:
(Click to enlarge)

Here is a diagram of the treatment suggestions I received:
(Click to enlarge)

Below are the notes I received from Auralex regarding product and placement recommendations:

Thank you for turning to Auralex® Acoustics, Inc., for your acoustical needs. I have attached a diagram of treatment suggestions for your project studio. The diagram is a top view of the room with the walls “folded out” showing specific placement of the suggested products.   Please do keep in mind that the suggestions are prepared off-site, based on the information supplied, and the combined experience of Auralex Acoustics.

In your room, I have suggested a Pro Plus Roominator™ Kit, which includes: (12) LENRD® Bass Traps, (36) 2” Studiofoam® Wedge 2’x2’ panels, (8) T’Fusor™ Diffusor Panels, and the necessary (8) TubeTak Pro Adhesive to affix it all. Please refer to the attached PDF for specific placement suggestions on all of the advised implements.

The Studiofoam® Wedge Panels are placed as shown to reduce excessive reverberation. Notice that the panels are placed in a non-symmetrical, offset pattern across opposing walls to reduce slapback and flutter echo, and the LENRD® Bass Traps are placed in each of the corners where possible can help to reduce bass build up where it tends to occur most. The T’Fusor™ Diffusor panels can help keep some of the sound energy in the room so it does not become too dry or “dead” sounding. You may also backfill the T’Fusor Diffusors with loose insulation for added absorption.

For the windows in your room, you might consider thick, dense curtains wide enough to fit loosely in front of the windows and have folds in the material when drawn.  This can help reduce unwanted reflectivity.

Our ISO Series products can help isolate speakers, amps, and drum kits from the floor.  Decoupling these instruments eliminates sound transmission and resonance that occurs when resting on a hard surface, which decreases discoloration and increases clarity. Check out our MoPADs™GRAMMA™ Series, HoverDeck™ Series, and our Aural X•Panders™ for more information.

The treatment shown in the layout should improve the sound quality within the room.


To get your free room analysis, please go to their Personalized Room Analysis Form.  You will need to create a drawing of your studio’s layout and dimensions, and attach it to their online form.

Conclusion

I’ve covered the basics of acoustics for home recording studios, and you’ve seen how you can do some simple tests to uncover acoustic issues in your space.

Finally, you can use the four different free room analyzers to give you a lot of information on how to fix acoustic problems in your studio.

As always, please leave any comments or question below.

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