Soundstage, Ambience & Accuracy

The three basic characteristics of what you hear when you use your high fidelity sound system are accuracy, soundstage, and ambience. (One can find dictionaries which have dozens of words to describe the audio experience, but let's keep things simple.) Accuracy is the ability of the system to reproduce sounds precisely so a violin sounds like a violin, a trumpet like a trumpet, a piano like a piano, and so on. Secondly, it allows you to distinguish such subtleties as the fact that two violins are playing a melodic line, rather than just one violin. With good accuracy, you can hear the mallet striking the skin of the drum, and not just the boom of the drum. A guitar pick touching the string is heard, and not just the note being played. One speaker can produce this characteristic, so stereo is not necessary.

The soundstage is the left to right, and front to back (depth) placement of the instruments or voices. At least two speakers and separately recorded channels (stereo) are necessary for a soundstage (unless you can be satisfied with a soundstage as wide as only one speaker, if you only have just one). The left to right concept is easy enough to understand, since the sound is being reproduced through at least two microphones, one each for the stereo channels. Front to back is a little more complicated. This phenomenon (front to back soundstage) is a result of how close the microphones were to the instruments, and the relative volume (loudness) that different frequencies are reproduced by the speakers. If the speakers have a strong midrange, then instruments in that frequency range (clarinets) would sound "forward", whereas if the speakers are very strong at the high end of the spectrum, piccolos and cymbals would sound forward. If the midrange frequencies are not as strongly reproduced, then the clarinets would sound "recessed" into the background. Imaging is a term used to describe the placement of the instruments on the soundstage.

The third characteristic, ambience, is a factor not only of the speakers, but the room in which they are placed. Ambience is essentially made of echoes (reflections or reverberations), and it gives you a feeling that "you are there". If you listen to a concert live, the ambience is a result of the sound of the instruments bouncing off the ceiling, walls, floors, other people, and anything else in the symphony hall. This goes onto the recording along with the original sound of the instruments. In your home, the original ambience comes through, filtered somewhat by the fact that you are listening to the music through two windows (stereo speakers), but careful listening will reveal the reverberant characteristics in many recordings, telling us something either about the environment where the recording was made, or the studio techniques used to fake an environment. The ceiling, walls, floor, doors, windows, and furniture in your listening room add to this ambience, which can make up for some of the loss caused by having only two speakers.

Ambience is also emphasized in surround sound. In fact, that is one of its main functions. You can get this ambience in a Dolby Surround system, and you can also achieve it to a certain degree by simply adding two speakers in the rear that duplicate the front stereo speakers, without using any surround processor, although this compromises the ability of a system to create a "focused" center image in front, as it will wrap sound around you homogenously. Further ambience is achieved by using dipolar or bipolar speakers (enclosure has drivers on opposite sides) which aim the sound in several directions, bouncing it off numerous surfaces, totally enveloping you with sound. Many rear channel surround speakers are of the dipolar or bipolar design, and you should audition some of them. Most of these methods for increasing ambiance from two-channel sources aren't accurate in terms of reproducing the recording, but it can make the experience more pleasant, and in some cases, for some people, more subjectively realistic. Digital surround sound, such as Dolby Digital (DD, AC-3) and DTS, have the potential for tremendous, more accurate ambience, since each channel is discrete from the others and can offer a more detailed and deliberate surround experience.

Once you have purchased the speakers, experiment with their placement before you mount them permanently. Consider how your particular speaker's radiation pattern interacts with your room. Typically, you need to sit directly in front of them (on axis) to hear all the frequencies clearly. Many "home theater" speakers made for the front channels are designed with wide dispersion patterns, so that you can sit anywhere in the room to watch a movie, and hear the sound clearly from all the speakers, even if you are off to one side. However, because time arrivals play a key role in our perception of depth and image, there will only be one ideal listening location in any room, so make sure you have it. Try to match speakers as closely as possible in a surround sound setup, paying particular attention to the center channel, where an identical match (with the left and right) would be ideal.