Acoustic treatment is the best way to minimize sound reflections in a home theater room for improving its sound quality. But, how many acoustic panels do you need which will do the job?
There is no definite answer to this question because room acoustics cannot be generalised. Every room is different and each room would have different requirements for acoustic treatment.
A minimum ballpark figure for a standard rectangular room is 18 acoustic panels but there are other factors to consider as well.
If the room has concrete walls or has a large number of windows and doors, the requirements would increase. Square shaped or L-shaped rooms will require more treatment. Hence, the number of acoustic panels will depend on the room in which the home theater is installed and that is why there is no standard figure that can be defined.
However, after reading this post, you will learn some fundamental principles through which you can determine how many acoustic panels you would require for YOUR room.
Acoustic Panels For Sound Absorption
A home theater room without any acoustic treatment will have sound waves reflecting from all surfaces of the room.
Ideally, you want to hear only the sound which is coming directly from your speakers and not the reflected sound from walls, ceilings and floors. The direct sound from the speakers when mixed with the reflected sound from the surfaces of the room creates muddled sound. This is popularly known as comb filtering.
Comb filtering cannot be eliminated but minimizing it can make a huge difference in the perceived sound quality. To keep the sound reflections to a minimum, sound absorption is required and that is where acoustic panels figure in.
Acoustic panels are panels containing sound absorbing material that will help in reducing the sound reflections in a room.
I would like to subdivide acoustic panels into two categories based on the types of sound frequencies they absorb for a better understanding of their functioning.
- Sound Absorption Panels – For mid and high frequencies.
- Bass Traps – For all frequencies but bass traps are specifically designed to cater for low frequencies.
Thickness of Sound Absorption Panels
Treating mid and high-frequency sound reflections are not too difficult. Hence, sound absorption panels can be only two inches thick.
Thickness of Bass Traps
On the contrary, controlling low-frequency sound reflections in a room by any means is not an easy task. In fact, it is virtually impossible to treat a room for very low frequencies.
The reason for this can be best understood by the relationship between frequency and wavelength.
Wavelength is inversely proportional to frequency which implies that lower frequency sound waves will have longer wavelengths. Longer the wavelength, thicker the bass trap required to prevent reflections.
Hence, bass traps have to be more than four inches thick.
Dimensions of each acoustic panel (sound absorption panels and bass traps) would be approximately 48″ x 24″. The thickness, as mentioned, would be two inches for sound absorption panels and four inches or more for bass traps.
Reflection Points In Your Room
Sound will bounce off from every point on your walls, ceiling and floors. But, you’re only concerned with those reflections that will affect you at the listening position.
For each speaker, there will be one reflection point on each wall (except the one behind it), the floor and the ceiling amounting to a total of five. The wall behind the speaker will be ignored as speakers are normally shielded from behind.
In a typical 5.1 surround system, there will be a total of 25 reflection points for the front, center and surround speakers (five speakers). You would need to treat these points for mid and higher frequencies. We’ll get to the subwoofer later.
How To Find The Reflection Points
Finding the reflection points for the five speakers is pretty easy. All you need is a small mirror, some masking tape and a family member or friend to assist you. The detailed procedure has been explained in detail here.
Have your family member or friend hold the mirror against the wall and move across till you see the reflection of the speaker. That is the reflection point for that particular speaker on that particular wall. Do this for all surfaces for each speaker and mark all the reflection points with masking tape. These are the points which need to be covered by sound absorption panels.
What About The Subwoofer?
The low-frequency sound waves from the subwoofer are omnidirectional and hence, their reflection points are not easy to determine.
However, as a general rule, bass reflects mostly from the corners, wall-ceiling and wall-floor intersection points in a room. Maximum bass is reflected from the tri-corners of the room. You will need to place as many bass traps as possible in these places.
How Many Acoustic Panels Do You Actually Need?
It is obvious that a home theater room requires substantial acoustic treatment. However, if budget is a constraint, then it is important to prioritize so that you get the most from the limited number of panels that you can afford.
Priority 1 – First Reflection Points
The first reflection points also known as ‘early reflection points’ should be the top priority. These are the reflections from the two side walls.
You will need to worry about the first reflection points of your center and front speakers from which most of the music and dialogue play out. That makes it three sound absorbing panels of two inches thickness for each side wall amounting to a total of six.
The surrounds can be ignored as they are mostly for ambient sounds in a movie.
Acoustic panels required so far – 6 sound absorption panels and nil bass traps.
Priority 2 – Bass Traps In Front Corners
Bass traps of four thickness or more can be straddled across the corners, from floor to ceiling. The front corners are a priority as the maximum bass is reflected from there.
Assuming that you need two bass traps for each corner, the total requirement for front corners is four.
Acoustic panels required so far – 6 sound absorption panels and 4 bass traps.
Priority 3 – Bass Traps In Rear Corners
The next priority is to cover the rear corners of the room as a lot of bass is reflected from there too. Another four bass traps would be required for the rear corners.
Acoustic panels required so far – 6 sound absorption panels and 8 bass traps.
Priority 4 – Reflection Points On The Front And Back Wall
The front and back wall should also be treated. The back wall for reflections and the front wall for a better sound stage. Place at least two sound absorption panels on each wall.
Acoustic panels required so far – 10 sound absorption panels and 8 bass traps.
Priority 5 – Reflection Points On The Floor
It is not possible to put acoustic panels on the floor, but some amount of sound absorption is necessary. Placing throw rugs at the reflection points on the floor is a good idea.
Acoustic panels required so far – 10 sound absorption panels and 8 bass traps.
Priority 6 – Reflection Points On The Ceiling
Placing sound absorbing panels on the ceiling will definitely help. I have prioritized this a bit lower because the speakers are farther from the ceiling as compared to the walls and the floor.
Strategically place two panels on the ceiling that will cover the reflection points of the center and front speakers.
Acoustic panels required so far – 12 sound absorption panels and 8 bass traps.
Priority 7 – Go Crazy With Bass Traps
Ethan Winer of Real Traps in this article says that there is no such thing as too much bass trapping. The more you have the better.
Apart from the corners of the room, other places where bass tends to reflect most are the points where the walls and ceiling/floor intersect. Placing bass traps in these places will enhance the sound quality in your home theater room.
Acoustic panels required so far – 12 sound absorption panels and 8+ bass traps.
The Number of Acoustic Panels That I Would Recommend
Personally, I would go up to Priority 5 and that is what I have implemented in my home theater room.
I left out the ceiling, not due to budget constraints but only because it is such a pain to fix them up on the ceiling. Moreover, you need to be doubly sure that they are securely fixed and there is no risk of them falling.
If you go for a similar set up such as mine, you will need 10 sound absorption panels and 8 bass traps. That makes a total of 18 acoustic panels.
You can reduce the number of bass traps in the corners if you need to. However, ensure that some portions of the corners are covered with the highest priority given to the tri-corners.
Some Handy Tips
In conclusion, here are a few useful tips that I would like to share from experience.
- For the sound absorption panels, you can go for rigid fiberglass boards or acoustic foam panels. However, for bass traps, avoid foam as it is not good for absorbing low frequencies.
- Use a spacer between the sound absorption panel and the wall. The gap in between will act as an additional insulating layer and will hence, increase the effectiveness of the sound absorption panel.
- Straddle the bass traps across the corners. The gap will increase the effectiveness of the bass trap.
Thanks for reading!