The First Reflection Point
Last week we discussed the importance of treating listening rooms and cinema room for bass anomalies. This week we are going to briefly look at another very important aspect of the room first reflection point treatment.
What Is The First Reflection Point?
The first reflection point is the most discernable 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 in the direction of the listener and makes it very difficult to distinguish the true sound projecting from the speakers because it adds unwanted clutter. It is only after you have eliminated this first reflection or minimized the affects it has that can you truly appreciate stereo imaging and soundstage and achieve a clean sound. After the first reflection has been removed you will appreciate increased definition, enhanced accuracy and better timing. The treatment of the first reflection point is vital in listening rooms and home cinema rooms.
Where is the first reflection point?
The first reflection point is the mirror point between the loudspeaker and the listening position. These are on the two walls either side of the system. The third reflection point is found on the ceiling between the loudspeaker and the listening position. To find the first reflection point you will need a mirror and an assistant. While sat in your listening position get your assistant to drag a mirror along the left hand wall starting from the position of the loudspeaker. When you can see the left loudspeaker through the mirror you have found the first reflection point for the left channel. Do the same with the right hand side. In most cases this will be same distance from the corner as the left but depends on the position of the two loudspeakers in relation to each other. The next point to find is the one of the ceiling. Directly in front of the listening position get your assistant to drag the mirror along the ceiling until you can see the two monitors in the mirror. If you only have a small mirror you may have to do each channel separately. Once you have found these three points you have the most vital positions of your acoustic treatment.
I have multiple channels what then?
The other channels in a home cinema system still have first reflection points and these still need to be treated using the same principle as described above. If you have a number of listening positions and you entertain others in your cinema room then this will need to be taken into consideration also. In a cinema room more acoustic treatment will be required than in your 2 channel listening room as there are more reflection points to content with.
What acoustic treatment should I use?
In these areas that you have found you need install acoustic panels such as our Wall Sound Trap Panels or Symphonic-R Acoustic Panels. If you require something freestanding as opposed to wall mounted then the Wall Orbis Acoustic Panel is a popular option. The thickness of acoustic foam you choose is also important. If you only install thin acoustic treatment then there is a smaller and higher frequency range that is going to be absorbed. The thicker the acoustic foam the lower it can absorb to. The maximum thickness you would want to install at the first reflections points is 4” (100m) thick. At these points you are only going to effectively absorb from the lower of the mid range frequencies upwards. The panels will absorb the low end frequencies but only a small proportion will be absorbed. The panels we have developed and mentioned above have been specifically designed and developed for this application. They offer the perfect comprise between performance and acceptability. 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 emitting from the loudspeakers will be cleaner and more direct. The slap echoes will be totally eradicated enabling you to better distinguish between each channel. By treating a listening room or a cinema room in this way treatment of the first reflection points will widen the soundstage and remove the clutter that comes from over reflective surfaces giving you a cleaner sound. You will bring focus to the room and create a space that works with 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 listening rooms and cinema rooms and the like the basic treatment of the first reflection points are, apart from bass trapping, usually 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 enjoy music in. By removing all the reflective surfaces you take all the life out of the room which means you have built a room the is very 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 suffering from excessive reflections or echoes. If you are less then 10ft (3m) from the rear wall then you would benefit from a little acoustic treatment spaced along the wall to reduce the reflections back to your listening position, however you will not require more than 40% coverage. Another area that could be considered for treatment is the area between the two loudspeakers on the front wall. By treating this area with one or twoacoustic panels you will reduce the interactions between the two speakers and so improve the stereo imaging of the room.
One area of treatment that must not be forgotten but is in most cases taken for granted is what we discussed last week, the use of bass trapping. This is especially important if the listening room is small. Low end frequencies will congregate in the corners of rooms especially behind the loudspeakers. The congregation of these low end frequencies can result in the level of certain frequencies being raised by as much as 10dB. Only by installing bass traps are you going to be able to calm these frequencies. Once you have completed the installation of the bass traps the room will be more balanced as you will have absorption along the whole frequency range and not just mid range upwards. The best places to position the bass traps are behind the two loudspeakers and also on the front wall at the ceiling height in the wall/ceiling seam. Depending on the width of the room depends on the amount of bass trapping to install but in most cases one or two bass traps along the ceiling will be sufficient. It is not absolutely necessary to treat the corners behind the listing position however f you have the budget for it the treatment o these two corners will be of benefit to the room. Low end frequency is a big problem in small rooms and it is quite often that we would say that you can’t have too much bass trapping in a room.
Hopefully this brief article has helped you to learn what the first reflection points are, when and how they can be found and more importantly how they are to be treated. If you have any questions regarding this article please don’t hesitate to contact the author at the following email address: firstname.lastname@example.org.