Preparing the Listening Environment
I do not want to get into serious sound reinforcement or acoustic treatment here, for the very simple reason that it is a vast subject and one that is so subjective, that even pros debate it all day, with differing views.
I also believe that every room has it’s own unique problems and must be treated as such, instead of offering a carte blanche solution that would probably make things worse.However, to fully understand what needs to be done to a room to make it more accurate for listening purposes, requires that we understand how sound works in a given space, and how we perceive it within that space.
I think a good place to start, without getting technical, is to think of a room that is completely flat in terms of a flat amplitude response.
This would mean the room has almost no reflective qualities and would invariably be too dead for our purposes. The other side of the coin is a room that is too reflective, and that would be worse than a completely dead room.
We need to concentrate on a happy compromise and a realistic scenario.
What we are trying to achieve is to utilize the room’s natural reflective qualities, and find ways to best expose audio, whilst beating the reflective battle.
Whoa, deep statement….
To put it more simply: we are trying to limit the interference of the room with speaker placement and listening position.
The way we determine the location of sound in a given space is by measuring, with our brains, the delay of the sound between our ears. If the sound reaches the left ear first, then our brain determines that the sound is coming from the left. If there is no delay and the sound arrives at both ears at the same time, then we know that the sound is directly in front of us.
This piece of information is crucial in locating sounds and understanding the space they occupy.
Now, imagine a room that has loads of reflections and reflections that come from different angles, and at different time intervals. You can see why this would provide both confusing and inaccurate data for our brains to analyze.
Let us have a very brief look at how sound travels, and how we measure it’s effectiveness.
Sound travels at approximately1130 feet per second.
Now let us take a frequency travel scenario and try to explain it’s movement in a room. For arguments sake, let’s look at a bass frequency of 60 Hz.
When emitting sound, the speakers will vibrate at a rate of 60 times per second. Each cycle (Hz) means that the speaker cones will extend forward when transmitting the sound, and refract back (rarefaction) when recoiling for the next cycle.
These vibrations create peaks on the forward drive and troughs on the refraction. Each peak and trough equates to one cycle.
Imagine 60 of these every second. We can now calculate the wave cycles of this 60 Hz wave.
We know that sound travels at approximately 1130 feet per second, so we can calculate how many wave cycles that is for the 60 Hz wave.
We divide 1130 by 60, and the result is around 19 feet (18.83 if you want to be anal about it). We can now deduce that each wave cycle is 19 feet apart. To calculate each half cycle, i.e. the distance between the peak and trough, drive and rarefaction, we simply divide by two. We now have a figure of 91/2 feet. However, this is assuming you have no boundaries of any sort in the room, i.e. no walls or ceiling. As we know that to be utter rubbish, we then need to factor in the boundaries. Are you still with me here?
These boundaries will reflect back the sound from the speakers and get mixed with the original source sound. This is not all that happens. The reflected sounds can come from different angles and because of their ‘bouncing’ nature; they could come at a different time to other waves.
And because the reflected sound gets mixed with the source sound, the actual volume of the mixed wave is louder. In certain parts of the room, the reflected sound will amplify because a peak might meet another peak (constructive interference), and in other parts of the room where a peak meets a trough (rarefaction), frequencies are cancelled out (destructive interference).
Calculating what happens where is a nightmare.
This is why it is crucial for our ears to hear the sound from the speakers arrive before the reflective sounds. For argument’s sake, I will call this sound ‘primary’ or ‘leading’, and the reflective sound ‘secondary’ or ‘following’.
Our brains have the uncanny ability, due to an effect called the Haas effect, of both prioritizing and localizing the primary sound, but only if the secondary sounds are low in amplitude.
So, by eliminating as many of the secondary (reflective) sounds as possible, we leave the brain with the primary sound to deal with. This will allow for a more accurate location of the sound, and a better representation of the frequency content.
But is this what we really want?
I ask this, because the secondary sound is also important in a ‘real’ space and goes to form the tonality of the sound being heard. Words like rich, tight, full etc. all come from secondary sounds (reflected).
So, we don’t want to completely remove them, as this would then give us a clinically dead space. We want to keep certain secondary sounds and only diminish the ones that really interfere with the sound.
Our brains also have the ability to filter or ignore unwanted frequencies.
In the event that the brain is bombarded with too many reflections, it will have a problem localizing the sounds, so it decides to ignore, or suppress, them.
The best example of this is when there is a lot of noise about you, like in a room or a bar, and you are trying to have a conversation with someone. The brain can ignore the rest of the noise and focus on ‘hearing’ the conversation you are trying to have.
I am sure you have experienced this in public places, parties, clubs, football matches etc.
To carry that over to our real world situation of a home studio, we need to understand that reflective surfaces will create major problems, and the most common of these reflective culprits are walls. However, there is a way of overcoming this, assuming the room is not excessively reflective, and is the standard bedroom/living room type of space with carpet and curtains.
We overcome this with clever speaker placement and listening position, and before you go thinking that this is just an idea and not based on any scientific foundation, think again.
The idea is to have the primary sound arrive to our ears before the secondary sound. Walls are the worst culprits, but because we know that sound travels at a given speed, we can make sure that the primary sound will reach our ears before the secondary sound does. By doing this, and with the Haas effect, our brains will prioritize the primary sound and suppress (if at low amplitude) the secondary sound, which will have the desired result, albeit not perfectly.
A room affects the sound of a speaker by the reflections it causes. We have covered this and now we need to delve a little more into what causes these reflections. Some frequencies will be reinforced, others suppressed, thus altering the character of the sound. We know that solid surfaces will reflect and porous surfaces will absorb, but this is all highly reliant on the materials being used. Curtains and carpets will absorb certain frequencies, but not all, so it can sometimes be more damaging than productive. For this, we need to understand the surfaces that exist in the room. In our home studio scenario, we are assuming that a carpet and curtains, plus the odd sofa etc, are all that are in the room. We are not dealing with a steel factory floor studio.
In any listening environment, what we hear is a result of a mixture of both the primary and secondary (reflected) sounds. We know this to be true and our sound field will be a combination of both. In general, the primary sound, from the speakers, is responsible for the image, while the secondary sounds contribute to the tonality of the received sound.
The trick is to place the speaker in a location that will take of advantage of the desirable reflections, while diminishing the unwanted reflections.
Distance to side wall and back wall.
Most speakers need to be a minimum of a foot or two away from the side and back walls to reduce early reflections. Differences among speakers can also influence positioning, so you must always read the manufacturer’s specifics before starting to position the speakers. A figure-of-eight pattern may be less critical of a nearby side wall, but very critical of the distance to the back wall. The reverse is true for dynamic speakers that exhibit cardioid patterns. In general, the further away from reflective surfaces, the better.
It is also crucial to keep the distances from the back wall and side walls mismatched.
If your speakers are set 3 feet from the back wall, do NOT place them 3 feet from the side walls, place them at a different distance.
Another crucial aspect of the listening position and speaker placement is that the distance from your listening position to each speaker be absolutely identical. It has been calculated that an error of less than ½” can affect the speaker sound imaging, so get this absolutely correct.
Distance to speakers from listening position.
Once you have established the above, you now need to sort out the distance from the listener to the speakers. I work off an equilateral triangle with the seating position being at the apex of this triangle. The distances must all be equal.
The other factor to consider is the distance between the speakers. Too close and you will get a narrow soundstage with the focus being very central. Widening the distance between the speakers will afford you a wider stereo width, but too far and you will lose the integrity of the soundstage.
This is the angle of the speakers facing the listener. There are a number of factors that influence the angle of the speakers.
The room, the speakers themselves, and your preferable listening angle. I always start at an excessive toe-in and work outwards until I can hear the soundstage perfectly.
Tilt is also crucial. Depending on the make of the speakers, most speakers are meant to be level set, but some might require tilting and in most cases, the tilt is rear high. If you have to have the speakers tilted then start off level and work from there.
Personally I prefer a level speaker setup.
You will find that the optimum listening height is that of the speaker’s centre being at exactly ear height.
However, certain speakers have their own specific height recommendations. You will find that with 3-way systems that incorporate top, mid and sub woofers, the listening height is more customized to account for the woofer placements in the speaker cabin or housing.
I find that keeping the seating position 1-3 feet from the boundary wall gives me the best bass response, and because the distance is too short for the brain to measure the time delay and thus locate the source of the reflection.
Please look at the figure below (Fig 1)
The listening position is at the rear of the room with the speakers facing and forming the equilateral triangle setup, and the listening position forming the apex of the triangle.
The elliptical shape denotes the soundstage and as you can plainly see, the side and rear walls do not interfere with the soundstage.
As you can see, I have created this soundstage using the longer walls as the back and front walls, instead of creating the soundstage with the listening position on the shorter walls. This allows me to position the speakers as wide as is sonically possible and thus affording me a wider stereo field.
Place the listening chair near the rear wall, because the distance (1 to 3 feet) is too short for the brain to measure the time delay and locate the source of the reflection. Also, it places you at the room boundary where the perception of bass is greatest.
Please make sure to take care in optimizing your listening environment.
Once this has been achieved, you can mix far more accurately and truthfully.