Author: Karsten Hein
Category: High Fidelity
The term ‘sound stage’ describes the acoustic impression of width and depth that resembles a live-stage setting, observed from the position of the audience. It is mostly used in the context of two-channel stereo setups but can also be found in three-channel stereo and two-channel mono discussions. A solid sound stage is the result of many important and correct decisions when setting up a HiFi system, and it is difficult, if not impossible, to achieve this without observing most of the ground rules laid out in the twenty two points of the ‘High Fidelity’ section. The sound stage is a result more than it is a ‘thing’ to be done, but in order to describe it and identify flaws in it, we need to make sure that we agree on some basics.
The picture shows the current 2-channel setup of our Hafler XL280 and Tannoy XT8F system. The loudspeakers are positioned 90cm from the front wall, measured from the front of the driver and the center axis of the speaker. When discussing the distance to the front wall, we refer to the distance between driver and front wall, rather than the back of the cabinet, as this changes with the dimensions of each new speaker. The reason for this method is simple: It is the driver that reacts with the room, not so much the speaker’s cabinet. Based on the circumstances found in our specific room, the distance between the speakers results in only two meters, again measured from the driver’s centre axis.
We have positioned our listening chair to assure that the listener’s ears are at level with the tweeters, which is usually the manufacturer’s advised position. Since the Tannoy speakers are of coaxial (or dual-concentric) design, tweeter and midrange share the same axis, making the correct level of the ears even more attractive. Furthermore, to assure ideal listening conditions, the distance between the ears and the drivers should form an isosceles triangle with the distance between the speakers. As in many domestic environments the distance to the listening position needs to span the full depth of the room, it is advisable to place speakers and listening position on opposite sides along the wider walls of the room. This setup offers the additional benefit of minimising first-order reflections from the room’s side walls.
In our setup, we have turned the speakers towards the listening position by 5 degrees. The resulting angle is called ‘toe-in’. Depending on room conditions, speaker distance, and speaker design, more or less toe-in will be preferable. It is therefore advisable to begin on a slight toe angle and to increase and decrease the angle while repeating the same song. This is most quickly achieved with a friend, or even better two friends, one at each speaker. While changing the angle, it is important to maintain the exact distance to the front wall. Even one centimetre of forward or backward movement will have a strong impact on sound.
There should be three discernible positions from which the music emanates. The left speaker, the right speaker, and the centre between the two speakers. The centre image results from mono signals in the recording, and since there is no visible speaker in this position, it is often called the ‘phantom’ centre. Speaker toe-in and listening position should be such that the music creates one seamless stage, panning from left to right. If there are holes in the stage, the speakers probably need more toe-in. If the stage is too narrow or compressed, the toe angle should be decreased. When positioning speakers in this way, you are looking for believability, i.e. a position in which the stage appears to be most natural.
In most forums, the vast majority of people discussing the merits of equipment have not even taken this basic step to assure fidelity. What they are discussing, therefore, is a random overlapping of frequencies. This becomes clear when they post images of their rooms and their setup. Based on their observations, they proclaim that speakers matter or that amps matter more. Little do they know that moving the speakers a few inches will transform their systems more profoundly than any new speaker or amp could ever do for them. No wonder, they cannot hear the difference between HiFi racks (in their ability to absorb micro-vibrations), or the merits of different cables (in their ability to protect and time-align signals), for as long as simple acoustic laws are not being observed.
If the speakers are set up correctly, listeners will be able to discern the three positions, but they may find that the music does not free itself from the speakers, so that the width of the channels, or that of the centre, or both, is very narrow still. The channel width can be fixed by making sure that ground potentials between the HiFi units are minimised. This is usually done by checking the polarity of the AC plugs. This is however not applicable in countries with fixed polarity plugs, unless you have a faulty AC outlet, power cord, or your unit has been meddled with internally. The centre image becomes narrow, for instance, if electrical interference affects the audio signal, either through HF interference, or through touching or crossing RCA/cinch interconnects. When the signal is received in a pure and clean fashion, the centre will be wide and pleasant.
When music is recorded, natural instruments such as piano, guitar, and drums are picked up indirectly with the use of microphones, rather than being directly connected via the use of cables. This means, music is captured in two ways: Directly from the source of the signal, and indirectly, when reflected from walls, floor, ceiling, and objects in the room of the recording. When sound waves are reflected, they are delayed and/or inverted. Our brain calculates the amount of delay and inversion and from this derives a sense of room dimension, material property, signal location, and distance. In a two-channel setup, it is therefore possible to hear music coming from positions to the far left and far right of the actual speaker positions. This is called stage extension.
On a proper setup, we can also sense elements of music that seem located nearer to us and elements that seem to be further away. The impression of stage depth is the result of recording choices, but the recreation of this stage in our listening environment is just as much dependant on our choices in setting up the system. Speakers that are pressed into the corners of rooms or standing too close to the front wall will not be able to deliver the same intact quality of imaging as speakers that are placed properly. And as timing has an electrical as well as acoustic dimension, proper speaker placement will enable you to identify HiFi units and cables that have frequency dependent timing issues.
I hope to have explained my findings well. Although I have read extensively about the subject of soundstage in recent years, the image and explanation I have shown here is based on my own findings as audiophile listener. If you feel that an important aspect of sound stage is missing from this description, I would welcome your input. Feel free to leave your comment below or contact me directly.
Enjoy your music.