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Loudspeaker Placement
The question that I was asked most frequently at audio shows was: "Why are the speakers placed so far out into the room and so close together?" My speaker placement is indeed unique. Instead of positioning them close to the front wall, as far apart as the room allows and toe-in towards the listener, I put mine almost flat towards the guests and very close together so that the speakers are as far away from all room boundaries as possible.
The demonstration rooms at audio shows are quite small. When the speakers are located almost in its middle, audiophiles are forced to listen at a rather uncomfortable distance of a mere 7-8 ft (2.1-2.4 meters) away from the speakers. This gives the false impression that my speakers are designed for near field monitoring inside the recording studio, not for enjoying music at home.
Those guests who sat down to listen were impressed. The music is 3-dimensional, a sensation most of them have never experienced before. There is a sound stage with width, depth, and height. Good recordings resemble live performances.
Why do so many hobbyists question my speaker placement? The answer is simple. Audiophiles generally pay no attention to room acoustics, or have very little interest and understanding of it; except putting lots of sound absorbing materials inside the audio room.
How can the speakers project a 3-dimensional sound stage? To answer the question, a detailed explanation of the physics behind is necessary.
Very few of us realize as much as 50% of the sound that we are hearing in a typical room are reflected sound: sound waves bouncing back to our ears after hitting a surface.
There are two kinds of reflected sound. Sound waves reflected once are called single reflected sounds; multiple reflected sounds are those reflected more than once.
All reflected sound waves have to travel a longer distance than the direct waves (those going directly from the speakers to our ears). This means that they arrive at our ears later than the direct waves. The delay in time is proportional to the number of times that the wave had been reflected. When a wave hits a surface, a portion of it is absorbed, therefore, all reflected waves are weaker than the direct waves.
When music is reproduced indoor, there are a trillion combinations of the direct and reflected waves, which are changing continuously in accordance with the flow of music. How does the human brain process such complex sounds?
When the time delay is long enough, the reflected sounds are interpreted as distinct echoes of the direct wave, but when the time delay is short enough, the reflected waves are perceived as a tail trailing behind the direct wave. The brain is fooled into recognizing them as the music's ambience, much like the halo surrounding a light bulb. All these effects combine to give the illusion of a room filling 3-dimensional sound stage behind the speakers having depth, width, and height. The sensation of depth is created by reflections from the front wall (the wall behind the speakers), width from the side reflections, and height from the ceiling. Up to a limit, the farther the speakers are from the walls, the larger and more vivid is the sound stage.
When the speaker is placed very close to a wall, the time delay of the reflected waves are so short that our brain fails to separate them apart for the direct waves. There is no dimensional sensation in the music as a result. All we could hear are tones without a definate position in space, an experience very different from a live performance. This is unfortunatley the kind of sound that most audiophiles are listening to everyday.
A simple experiment to demonstrate how direct and reflected sounds work together is to listen to a favorite song at the normal listening position a few times and then go to listen at the back of the speakers. Please use a pair of front radiation speakers for the experiment. The same is true when listening to music out-door because there are very little reflected sounds.
Reflected sounds alter the frequency response of an audio room tremendously. This is produced by the phenomenon termed "comb filtering". Since the reflected waves have to travel longer distances than the direct waves, according to the pathway, they may arrive at our ears in-phase, or out-of-phase. When two waves are in-phase, there is amplification. When out-of-phase waves meet, a complete cancellation occurs. Waves can also be partially in-phase or out-of-phase. When the position of the speakers in the room is changed, the "comb filtering" effect is also changed.
The room dimensions, interior decorations, and furniture also distort the sound in a big way. Resonance enhances sound waves having a wavelength equal to or are multiples of a room dimension. Parallel surfaces generates waves bouncing back and forth between them (standing waves). Different materials absorb and reflect sound waves in very different ways. How the interior decoration and furniture change the sound is determined by their size, their material, and their positions inside the room. Therefore, indoor music reproduction is a very complex and dynamic situation involving interactions bewteen the environment and the equipment, a situation too complex to be calculated accurately by the computer.
All these enhancements and cancellations effects add up to create a frequency response very far from linear. A variation of 12-18 db is normal in our audio rooms. Please remember that 3 db represents a 100% power difference.
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It is now clear whether a room sounds good or not is determined mainly by how it reflects sound. How a system performs, besides the quality and matching of the components, is governed by the loudspeakers' position.
If room acoustics and speaker placement are so crucial in audio reproduction, what is the role that they play in the recording process? The answer is: they are equally important.
During a recording session, microphone or microphones convert the sound waves into electrical signals which are either stored on magnetic tape or as undulating grooves on a disc. The process is reversed during playback.
The majority of our reference recordings were made in the early stereo era from the late 1950s to the late '70s. The analogue electronics available at the time were a lot more difficult to make sound adjustments than the digital devices of today. The acoustics of the recording hall and microphone placement were the two most powerful tools that the engineers had at those days. The best recordings of classical music were made by only a handful of outstanding engineers. The most famous were Kenneth Wilkinson and James Lock of Decca, Gunther Hermans of DG, Lewis Layton of RCA, Christopher Parker of EMI, and Bob Fine of Mercury. They were all innovators and masters of microphone placement.
There are also very few halls in the world possessing acoustics suitable for recording music. The best is the Kingsway Hall in London, the Symphony Hall in Boston, the Old Orchestral Hall in Chicago, and the Golden Hall in Vienna. Even though these halls have excellent acoustics, engineers still have to spend months, or even years, to find the sweet spot or spots to place their microphone or microphones. In some cases, when the acoustics of the hall is less than ideal, modifications in the form of partitions, baffles, reflectors, or curtains have to be used during the recording session.
Just like microphone placement, loudspeaker placement is an art even though the principle behind is acoustics. The reason why it is still not a science is because we know very little about how the human brain processes sound. The use of computer analysis and graphic equalizer never worked. Out of ignorance, we are always trying to adjust the frequency response of the room. Rendering it flat is meaningless: our ears are accustomed since birth to rooms having a frequency response resembling the cross section of the Swiss Alps. Few audiophiles are aware of the fact that microphones used for recording music also do not have a flat frequency response. Moreover, the human ear is not a linear device. It is most sensitive around 1K Hz. There is a sharp decrease in sensitivity above and below this frequency. If we look at the Equal Loudness Contour of our ears, it is very far from being a straight line. In addition, there are high frequencies hearing losses as we age.
What is correct loudspeaker positioning? It is the placement of the speaker (speakers for stereo) at the exact spot on the floor to achieve a perfect blending of direct and reflected sounds; a tedious job requiring patience, experimentation, and ingenuity. Moving speakers around will bring sonic improvements quicker than changing equipment.
We also must bear in mind that we are using recorded music as the tuning tool. As we are not present when the recording was made, how should it sound? This requires a vivid memory of how good recordings sound, a good knowledge of music, imagination, and a lot of common sense.
How to remember sound? Although very few of us are born with such an ability, whenever you are listening to music, pay attention to its sonic signature while enjoying the performance. While it is more difficult than piano tuning, with a lot of practise, everybody can become a golden ear.
As questions, do experiments to prove your idea is the way towards audio Nirvana.
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