Sounds Like? An Audio Glossary Sidebars: 5-6
The ideal stereo soundstage for a large performing group will center the performers across an area of about 2/3 to 3/4 of the distance between the loudspeakers, and will audibly separate the front rows from the receding rows (layering). There will be an awareness of the reflective boundary walls of the acoustic space behind and to the sides of the performers, and the spatiality of the hall itself will extend a considerable distance beyond the distance between the loudspeakers. The ideal is achieved only from suitably miked recordings.
Specific phantom images will often appear beyond the speakers when the performing group was wider than the axis lines of a coincident pair of microphones, or if the recording has been specifically encoded with recoverable ambient surround information. Such "beyond-the-speakers" imaging, however, is only audible from the sweet spot. [If a pair of loudspeakers has very poor phase performance, or very loose crossover tolerances, or produces strong specular reflections, it can produce strong "beyond-the-speakers" imaging, which may be very pleasing. This, however, is a distortion of what is encoded on the recording.---Ed.]
Surround-encoded recordings, played on a properly implemented surround-sound system, can cause the hall ambience to "wrap around" to the rear, completely enveloping the listener as in an actual concert hall, and can even place instruments in any direction around the listener. So-called "derived-ambience" decoders can extract the ambient spatial information from unencoded recordings, but cannot place phantom images at the sides or rear.
Sidebar 6: About Vowel Colorations
The audible effects of these can be illustrated in two ways: vocally, or by means of a pink-noise signal source---track 4 on Stereophile's original Test CD or track 15 on our Test CD 2 will do nicely---and a 1/3-octave equalizer.
For the vocal simulations, shape the tongue and lips as if pronouncing the vowel sound, and breathe out through the mouth.
With the generator and equalizer, set all controls to Flat and raise the band closest to the vowel sound's center frequency by 6dB or so. (The effect will be more noticeable if you can switch the equalizer in and out of circuit without changing the level, allowing you to compare Uncolored with Colored.) Then play some program material to get a handle on what the same coloration does to the sound of music. Each time, restore the equalizer's response to Flat before raising the next band.
Try lowering each band, and you will observe that, even though the effect of the dip is audible, it is much less so and is much more difficult to describe.