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I have always been a movie buff since my childhood days. But it was only nine years ago that I bought my first home theater in a box system. That’s when I really started paying attention to the ‘movie experience’.
A few months later I got into DIY acoustic panels and bass traps for my room. The difference that it made to the quality of sound overwhelmed me.
At the time that I first built my own acoustic panels and bass traps, I only had a basic idea about where to place them in the room.
But, after experiencing the benefits of treating my home theater room, I dove deep into research to find ways to further enhance the quality of sound in my home theater room.
In this article, I share what I have learned from experts, forums, and other resources on the internet.
Why Do We Need Room Acoustics?
You can have the best of audio/video equipment, but in a room with poor acoustics, your speakers will sound bad.
On the other hand, in a well-treated room, a not so great AV set up can sound good. That’s the importance of room acoustics.
We require room acoustics to get the best performance out of our speakers whether it is for watching movies, listening to music, or recording music.
When you are trying to improve the acoustics of a room, there are many issues that you will be dealing with. If you understand what these are, your DIY acoustic panel and bass trap project is more likely to be fruitful.
This article is for both DIY bass traps and acoustic panels because you will be most likely building both together. There is no point in having separate posts for both as the principles are more or less similar.
About DIY Bass Traps and Acoustic Panels in This Article
Bass traps are designed for controlling low frequencies.
There are different types of bass traps but for simplicity, this article is restricted to the broadband type which caters for a wide range of low frequencies.
Acoustic panels are designed for mid and high frequencies.
Broadband bass traps and acoustic panels are similar in design and vary only in thickness.
Bass traps are four inches or thicker whereas, acoustic panels are normally about two inches thick.
The recommended insulating material for bass traps as well as acoustic panels is rigid fiberglass insulation of high density.
High-density insulating material is more effective for sound absorption because more the fibers, more the absorption.
Reflections are easy to understand and thankfully easy to fix for certain sound frequencies.
At the listening position, you will hear direct sound coming from your speakers as well as the sound being reflected from walls, ceilings, and floors.
You will obviously want to listen to only the direct sound coming from your speakers because the reflected sound can really mess up the sound quality. This mixing of direct and reflective sound waves which causes muddled sound is known as comb filtering.
Acoustic or sound absorbing panels placed at the reflection points will absorb the sound and try to prevent it from reflecting back onto the listening position.
Low Frequencies- the Biggest Challenge
Taming mid and high frequencies in a room is fairly easy and that you can do with acoustic panels.
It is the low frequencies that are very difficult to control. Bass traps are used for low frequencies but they are effective only for a limited range.
Acoustic panels and bass traps will absorb only those frequencies whose wavelengths are commensurate with their thickness.
In simple words, a thin sound absorbing panel can absorb sound waves of shorter wavelengths whereas a thick panel is capable of longer wavelengths.
To better understand this, let’s go over the relationship between frequency and wavelength.
Frequency = Wave Speed / wavelength
As we can see, frequency is inversely proportional to wavelength which implies that higher the frequency, shorter is the wavelength. That is why higher frequencies are easier to tame because their wavelengths are short.
In the lower frequency range, the problem is that the wavelengths increase exponentially with a reduction in frequencies.
In the subwoofer range at 80 Hz and below, the wavelengths are so long that you will have to create bass traps that are several feet in thickness. This is too impractical.
However, bass traps are definitely beneficial in smoothening out the bass response of the room and that is why they are very much required.
How Thick Should Your Bass Traps Be?
As brought out by Ethan Winer in this article, a four-inch-thick bass trap with rigid fiberglass insulation placed sufficiently away from a wall will be very effective at 125 Hz and below.
The gap between the bass trap and the wall is beneficial. A four-inch bass trap placed four inches away from a wall will be as effective as an eight-inch bass trap.
Therefore, the minimum thickness of a bass trap should be four inches and should be placed a few inches from the wall or ceiling for maximum effectiveness.
How Much Absorption is Required?
The amount of sound absorption will depend on the type of room.
The requirement of rooms with drywall is lesser as compared to concrete walls. Drywall rooms are less reflective and have a better low-frequency response whereas concrete walls are just the opposite.
Room size is also a factor. The square room or room with equal dimensions will have a lot of peaks and nulls. Peaks and nulls are related to interferences of reflected sound waves.
Without being too technical, peaks cause the bass to sound ‘boomy’ while the nulls would make those frequencies inaudible or weak.
So, for a square-shaped room, you will require more sound absorption in comparison to a rectangular room.
You don’t want to have excessive absorption though. Ideally, you want a mix of absorption, diffusion, and reflection for a room for balanced sound quality.
How Many Would You Need?
Acoustic or Sound Absorbing Panels
You will need to place acoustic panels at the reflection points on the walls and ceiling. The reflection points are those points from where sound reflects on to the listening position.
Each speaker in the room will have its own set of reflection points. In a typical 5.1 home theater, we have the center speaker, two front speakers, two surround speakers, and a subwoofer.
We discount the subwoofer for determining reflection points because low frequencies are omnidirectional and will thus have multiple reflection points. Moreover, as seen earlier, it is pointless to use low thickness acoustic panels for low frequencies of the subwoofer.
Mid and high frequencies from the other speakers are unidirectional and will have a set number of reflection points. Each of these speakers will have first reflection points and second reflection points on the walls, ceiling, and floor.
Many DIY enthusiasts prefer to have bass traps placed at the first reflection points as these are the closest to the speakers and would require most absorption.
You will need sound absorbing panels for all the remaining reflection points. You may want to consider extra absorption at some places where you feel absorption is required, such as the rear sidewalls and back wall.
Rear sidewalls and back walls are areas where interference of sound waves take place quite a bit, so it is a good idea to place acoustic panels in these spaces.
Ethan Winer recommends diffusors for the rear parts of the wall as you would want the sound to be bright around the listening position.
If you don’t have the budget for diffusors, placing sound absorbing panels would be better than no acoustic treatment at all for the rear sidewalls and back wall.
Note: The placement of acoustic panels as described is applicable for one listening position only.
For a dedicated home theater with multiple seating, Dennis Erskine of Erskine Group (creators of home theater spaces) strongly recommends that the walls should be covered from ground to ear height with 1” rigid insulation and the remaining with diffusing material like cotton batts. In fact, most of the DIY home theater rooms are built on this concept.
However, if your home theater is in the living room or bedroom, covering the entire wall with insulation and cotton/polyester batts is not always practical. So, the acoustic panel route is the only way to go.
There is no defined number of bass traps that are enough for a room. The more you have, the better.
You will need bass traps at corners and places where the walls meet the ceiling. Maximum bass accumulation takes place here.
The best way to go is to cover the four corners of the room from floor to ceiling and then place as many bass traps as you can at wall-ceiling interception points.
How to Find the Reflection Points
The method for finding the reflection points of a room is by a ‘mirror trick’ which is explained well in this article.
You will need another person to help, you can’t do this alone. The step by step procedure of the mirror trick is as follows:-
Make sure that your speakers are correctly positioned where you want them.
Clear the area of furniture that is too close to the walls. We don’t want any obstructions during this process.
Give your friend a handheld mirror and a masking tape.
Sit in the listening position and ask your friend to place the mirror flat on the wall close to the left speaker.
Ask him to move the mirror on the wall till you see the reflection of the left speaker. That is one reflection point.
Ask your friend to put a piece of masking tape on the reflection point which you have just discovered.
Repeat the process to find all reflection points on the walls, ceilings, and floors for each speaker. Each speaker will have one reflection point on each.
Note: While you will be placing bass traps and acoustic panels on the walls and ceilings, the same is not practical for floors. You can place a rug or thick carpet at the reflection points on the floor.
Where to Place Bass Traps
As I had brought out earlier, bass traps should be placed in the corners of the rooms and intersection points where the floor meets the ceiling.
But, this is a general rule. Every room is different and treatments required vary.
It would be best to measure places in the room in which bass tends to be maximum so that you can place bass traps there.
The simplest way for this is as shown in this video by GIK Acoustics.
After you build your bass traps and acoustic panels, you will want to know how to mount them. On the flat wall, you can hang them like you hang picture frames.
The eye hooks will go on the back of the acoustic panel or bass trap. Fix the eye hooks on the frames 12 inches from the top and on both sides as shown.
Cut two six-inch pieces of picture hanging wire and insert them in the eye hooks. Make loops out of the wires so that they can be hung on the hooks.
Measure and mark the places where the hooks will go and fix them. After that, you can just hang the panel with the wire onto the hooks.
For straddling the bass traps at the corners of the room, the wire and hook combination makes it easy to mount.
Mounting Acoustic Panels on the Ceilings
Mounting panels on the ceiling can be a bit of a task and you will need to make sure that they are sturdy enough not to fall down.
You will need to install four of these for each corner of the panel. Once installed in the ceiling, one end of the S hook will go into the eye hook of the panel. The other end of the S-hook along with the panel will go into the eyelet of the ceiling.
Placing the Acoustic Panels Away From The Wall
We have discussed earlier in this article that if a bass trap or acoustic panel is placed with a small gap from the wall, the benefit is increased.
While you are straddling a bass trap on the corners, that gap is automatically created. However, for flat wall surfaces and doors, you will have to place a spacer in between the panel and the wall.
A great way to do this is explained in this article by Realtraps. In the article, a post base is used to create the gap between the bass trap and the wall.
Some Questions Answered
Before closing, it would be best to answer some of the frequently asked questions with regard to acoustic panels and bass traps.
As a small disclaimer, I take the liberty to state that I’m not an expert but the answers to the questions below are based on the knowledge I have gained from authority figures in the field of acoustics.
Will acoustic panels block noise from my neighbors’ television?
You will first need to know the difference between sound absorption and soundproofing before this question can be answered.
Sound absorption is trying to prevent sound from reflecting off the surfaces of the room.
Soundproofing is trying to prevent sound from entering or leaving the room. We can absorb sound with insulating material but insulating material does not block sound.
Hence, acoustic panels will not block noise from your neighbor’s television.
If I don’t have acoustic treatment, are there any other household items that absorb sound, such as mattresses?
Mattresses do nothing and are a waste of effort. It does help to have furniture, rugs, bookshelves, etc which would be better than an empty room.
However, there are not many household items that can be used for acoustic treatment of a room.
Does it do any good having foam panels?
Foam panels are an option for sound absorption but have limited capabilities for low frequencies.
They can be used on the walls as acoustic panels for mid and high frequencies. For bass traps, it is better to stick to fiberglass and rockwool.
Are acoustic treatments worth it?
I would say, most definitely. I first started treating my home theater room about nine years ago. Now, I cannot do without sound absorption.
I know that I’m not alone and can assure anybody who has this question in mind, that acoustic treatments are definitely worth it. And they do not cost much if you are building your own bass traps and sound absorbing panels.
What is the best DIY sound absorbing bass trap for a small room?
Super chunk bass traps are the best. These are large triangular pieces of rigid fiberglass stacked one on top of the other. As compared to the bass trap straddling corners, these absorb more.
However, making these will require a lot of insulation material and hence, will cost more. On the other hand, the straddling bass trap is the best bang for the buck.
What is the recommended thickness of a bass trap?
The minimum thickness of a bass trap should be four inches. If you have the space in your room, thicker the better.
Bass traps should be placed leaving a small gap from the wall for increasing their effectiveness. You can also build super chunk bass traps which are the best but end up being more costly.
Should you build triangular or rectangular bass traps?
Each has its purpose and has to primarily do with where it is going to be installed. For tri-corners, you will want to build triangular traps that will cover them nicely. For other places in the room, the rectangular ones are the ones to go for.
Is it possible to build DIY Bass Traps without wooden frames?
It is possible to build bass traps and acoustic panels without wooden frames. You can get the most rigid fiberglass boards and just cover them with fabric.
Unfortunately, you will have to be really careful with them. These types of bass traps and panels will not be durable and can look terrible.
Hence, building these is possible but not recommended.
Why does the bass from my home theater subwoofer sound powerful in some parts of my listening area, yet weak in others?
As brought out in this article earlier, this is because of peaks and nulls created in an untreated room.
The peaks cause the subwoofer to sound powerful and the nulls cause it to sound weak. One of the benefits of bass traps is that they reduce the peaks and nulls in the room.
Thanks for reading! Before you go, take a minute out and check out the best insulation materials for soundproofing and acoustics which I highly recommend.