Stereo Imaging – Multiple early reflections from different directions cause a “fogging” of the sonic image and a shift in apparent position of where the sound is coming from. Without reflections, a well-balanced system will provide a tight, bright, white-hot dime sized image when fed a coherent dual-mono signal. But where is it located?
Level Matching: Centering the Image
Psychoacoustics and the anatomy of the ear dictate that our image shifts towards the louder source. The ear is sensitive enough that even 1 little dB of level difference will cause an image shift toward the louder speaker!
To experience the music as intended, get the output levels of your speakers matched. But before grabbing your RadioShack SPL meter, let’s look at the other reflections that shift image position and apparent speaker level. Remember, here is our goal:
Room Effects: Flying Images
In real rooms, there are objects that reflect different frequency sound because of their size, shape, and location. Speakers beam high frequencies but as frequency lowers, the beam widens. If your image seems to shift, drift, fly, and dart around through different passages of music, the following graphic shows the resultant image shift caused by several common room object reflections.
Run a Sweep
Run a slow sweep through your system from about 4kHz down to the sub range. Watch that image dance around!
Use a pair of treble range absorbers laid against your mains like shown. The absorbers should overhang the front baffle by about 6 inches.
The frequency sweep took your system through the full range of beam-widths and illuminated all of the reflective objects in your room at some point. The addition of shadow casting blinders reduced the illumination of objects in the room and stabilized the image position. Now you might have an idea of which objects in the room are causing the most interference with your image, and also an idea of your system’s potential for stereo imaging.
Adjust the position, tilt, and toe-in of your mains to alter the room illumination character. Move furnishings, hang drapes & tapestries, reposition acoustic devices.
A Better Solution
After you have had some fun tinkering with your room’s acoustics, the best long-term solution is the installation of properly engineered sound absorbers at the right locations. The ASC products most suited to image control are the StudioTrap (for shadow casting) and the SoundPlank (for traditional wall-mounting). TubeTraps in the corners can extend the pinpoint imaging down well into the omnidirectional* bass range.
In the meantime, please stay safe and healthy, take a break and enjoy some beautiful music with your fine sound system. You deserve it!