What Is The First Reflection Point?
The first reflection point is the most discernible echo in a room; it is also the most disruptive. This reflection is the next sound you hear after the direct sound from the loudspeakers. This reflection can confuse the listener because it adds extra information. It also makes it very difficult to distinguish the true sound coming from the speakers.
The first reflection point does this by adding unwanted clutter. After you have controlled the first reflection you can appreciate true stereo imaging. You will hear increased definition and improved accuracy. The treatment of the first reflection point is vital in all rooms where music is to be enjoyed. Rooms such as mixing rooms, listening rooms and home cinema rooms will benefit.
Where is the first reflection point?
The first reflection point is the mirror point between the loudspeaker and the listening seat. These are on the two walls either side of the mixing or control desk. The third reflection point is on the ceiling between the loudspeakers and the listening position. To find the first reflection point you will need a mirror. Depending on the size of the room or distance between the loudspeaker and you, you may may need an assistant.
While sat in your listening position get your assistant to drag a mirror along the left hand wall. The mirror needs to be about head height when seated. When you can see the left speaker through the mirror you have found the first reflection point. Do the same with the right hand side. In most cases this will be same distance from the corner as the left. This does depend on the position of the two loudspeakers in relation to each other though.
The next point to find is the reflection point on the ceiling. From above left speaker get your assistant to drag the mirror along the ceiling towards you. When you can see the left loudspeaker in the mirror you have found the right point. Repeat for the right hand speaker. This will identify the location and size of the first reflection point for the ceiling. Once you have found these three points you have located the most vital positions for your acoustic treatment.
What acoustic treatment should I use?
In these areas you need install clusters of acoustic tiles such as the Tegular Acoustic Tiles. Or you can use product such as our 2ft by 4ft Acousti-Slab Panels. The thickness of acoustic foam you choose is also important. Installing thin acoustic treatment will reduce the bandwidth of frequencies absorbed. By installing thicker acoustic foam the wider the range of absorption and lower it can absorb to. The thickest you would want to install at the first reflections points is 4” (100m) thick. At these points you are only going to absorb from the lower of the mid range frequencies upwards. The panels will absorb the low end frequencies but only a small amount.
After you have treated these three areas you will notice a big improvement in the sonics of the room. You will find that the sound coming from the loudspeakers will be cleaner and more direct. The slap echoes will be removed, widening the soundstage. If you are treating a control room or a mixing room it will give you much more defined stereo image. It will also help you to discern more accurately each channel level. If you are treating a listening room or a cinema room you will widen the soundstage. It will also remove the clutter that comes from those reflective surfaces. This will result in a cleaner sound. In both cases you will bring focus to the room and create a space that works with you. Not against you.
Why don’t I just cover all the walls and ceiling with foam?
This is the last thing you want to do unless you are building an anechoic chamber or a very tight vocal booth. When it comes to treating mixing rooms, control rooms and the like balance is needed. Treatment of the first reflection points and effective bass trapping are sometimes all that’s needed. By treating every surface area with acoustic foam you create a room that is too ‘dead’. A room that is too dead is very difficult to work in or enjoy music in. By removing all the reflective surfaces you take all the life out of the room. This will make the room feel extremely tight and can be claustrophobic.
Are there any other areas that would benefit from acoustic treatment?
Yes there are some other areas that you could treat if you are still having problems. If the room is suffering from to much reverberation it will need further treatment . If you are less then 10ft (3m) from the rear wall some acoustic treatment spaced along the rear wall would help. This will help to reduce the reflections coming back to your listening position. Bear in mind the rear will will not need more than 40% coverage. Another place you could add acoustic treatment is the area between the two loudspeakers on the front wall. Treat this area with a small cluster of acoustic tiles or one or two acoustic panels. This will reduce the interaction between the two speakers. This in turn will improve the stereo imaging of the room.
One area of treatment that must not be ignored but in most cases taken for granted is the use of bass trapping. This is especially important if the mixing room is small. Low end frequencies will congregate in the corners of rooms. This especially occurs behind the loudspeakers. The build up of these low end frequencies can result in the volume inreasing at certain frequencies. This can be by as much as much as 10dB, some times even more. Only by installing bass traps are you going to be able to calm these frequencies. Once you have installed bass traps the room will be more balanced. This is because you will have control along the whole frequency range; not just the mid range upwards.
One of the best places to position the bass traps are behind the two loudspeakers. Another area is on the front wall at the ceiling height in the wall/ceiling seam. The width of the room will determine amount of bass trapping to install. In most cases one or two bass traps along the ceiling will be enough. It is not always necessary to treat the corners behind the listing position. However if the room has particular room modes or severe bass issues treatment at the rear of the room will help. Low end frequency build up is a big problem in small rooms. Quite often we would say that you can’t have too much bass trapping in a room.
We're sure this brief article has helped you to learn what the first reflection points are. You also now know how to find them and more importantly how they can be treated. If you have any questions about this article please don’t hesitate to get in touch. You can contact us at firstname.lastname@example.org.