I used to think that the ability to make fine adjustments to the left/right balance for different material was absolutely necessary for best realism in my home reference rig. I still find that left/right and front/back balance is highly critical in an auto environment, basically because the driver's seat isn't in the middle of the left/right and front/back speakers, and driving positions vary much from driver to driver.
For my home two-channel set-ups, however, in recent years I have found that the best solution--one which cannot be matched by fiddling with the balance control--is to acoustically match the left and right channels by very careful speaker and listener placement in a room designed for left/right structural symmetry, and even-handed acoustical treatments of the left and right side of the room.
I try to get the speakers to match in distance from the listening position to within 1/16 inch. That is tough, but can sometimes be done with patience and the right tools. Certainly 1/4 inch is achievable. Equalizing the degree of toe in and other aspects of physical positioning is also important. While some folks try de-centering both the speaker and listening positions with respect to the left and right walls in order to avoid the effect of room mode nulls which occur at the center position, in my experience, in a small to moderate sized listening room, this is less important than keeping the speakers and listener equi-distant from side walls in order to maintain proper left/right balance.
The main reason that balance controls don't work as well as you might at first think is that while they can change the relative amplitude of the left and right channels, they cannot correct for phasing, time of arrival, or tonal balance shift problems. The best stereo imaging and staging requires very close matching of these three factors as well as amplitude in the sound from the left and right speakers. See here for an easy-to-understand discussion of how we perceive space from recordings and in concerts.
I use a simply miked centered speaking voice or announcer to make final judgments for this aspect of system set up. A single monophonic mike pickup in an acoustically dead control room atmosphere is ideal, such as the announcers on my local classical station, WFMT, or the announcers on any number of test disks, including the Stereophile Test CD2, Test CD3, and the Sheffield/XLO Test and Burn-In CD.
Once your set up is correct, such sources are truly centered and occupy a very small subtended angle in the center of the stage without smear to the left or right, up or down, or front to back. Done properly, a simply miked announcer's position will not change at all if a stereo/mono switch is flipped back and forth.
In my book, if you find that you routinely use the balance control at an off-center position of the control, there is something wrong with your equipment, your ears, or your room/room treatment. But once set up the way I have done it, sure, you will hear small (or not so small) left/right shifts of announcers and program material, but it really doesn't help the realism to attempt to correct these flawed program sources with an electronic balance control. Yes, the left/right balance can be made more equal, but for the reasons mentioned above and explained at the link, you lose other important aspects of realistic staging and imaging and the overall effect is no better and usually not as good.
By the way, some feel that a simply miked recording of an announcer in which the left and right channels are recorded out of phase is the best test for getting the left/right balance correct, the goal being to maximize the "diffuse and directionless quality" of such program material. I disagree. I find it much easier to judge the tightness of center focus than the degree of diffuseness and directionlessness of the same source. Until you really hear what a great set up can do in terms of a centered mono image, you will probably have no idea what a maximally "diffuse and directionless" quality played back in stereo should sound like.
For those who want to try using an out-of-phase source as a test, let me tell you that on something like the track 3 of the Sheffield/XLO Test and Burn-In CD, with proper set up the voice should be so diffuse and directionless that the location of the voice cannot be determined in the front/back or up and down dimensions, much less left and right. Slight head movements can shift the apparent source anywhere in the room, including anywhere behind you.
For my home two-channel set-ups, however, in recent years I have found that the best solution--one which cannot be matched by fiddling with the balance control--is to acoustically match the left and right channels by very careful speaker and listener placement in a room designed for left/right structural symmetry, and even-handed acoustical treatments of the left and right side of the room.
I try to get the speakers to match in distance from the listening position to within 1/16 inch. That is tough, but can sometimes be done with patience and the right tools. Certainly 1/4 inch is achievable. Equalizing the degree of toe in and other aspects of physical positioning is also important. While some folks try de-centering both the speaker and listening positions with respect to the left and right walls in order to avoid the effect of room mode nulls which occur at the center position, in my experience, in a small to moderate sized listening room, this is less important than keeping the speakers and listener equi-distant from side walls in order to maintain proper left/right balance.
The main reason that balance controls don't work as well as you might at first think is that while they can change the relative amplitude of the left and right channels, they cannot correct for phasing, time of arrival, or tonal balance shift problems. The best stereo imaging and staging requires very close matching of these three factors as well as amplitude in the sound from the left and right speakers. See here for an easy-to-understand discussion of how we perceive space from recordings and in concerts.
I use a simply miked centered speaking voice or announcer to make final judgments for this aspect of system set up. A single monophonic mike pickup in an acoustically dead control room atmosphere is ideal, such as the announcers on my local classical station, WFMT, or the announcers on any number of test disks, including the Stereophile Test CD2, Test CD3, and the Sheffield/XLO Test and Burn-In CD.
Once your set up is correct, such sources are truly centered and occupy a very small subtended angle in the center of the stage without smear to the left or right, up or down, or front to back. Done properly, a simply miked announcer's position will not change at all if a stereo/mono switch is flipped back and forth.
In my book, if you find that you routinely use the balance control at an off-center position of the control, there is something wrong with your equipment, your ears, or your room/room treatment. But once set up the way I have done it, sure, you will hear small (or not so small) left/right shifts of announcers and program material, but it really doesn't help the realism to attempt to correct these flawed program sources with an electronic balance control. Yes, the left/right balance can be made more equal, but for the reasons mentioned above and explained at the link, you lose other important aspects of realistic staging and imaging and the overall effect is no better and usually not as good.
By the way, some feel that a simply miked recording of an announcer in which the left and right channels are recorded out of phase is the best test for getting the left/right balance correct, the goal being to maximize the "diffuse and directionless quality" of such program material. I disagree. I find it much easier to judge the tightness of center focus than the degree of diffuseness and directionlessness of the same source. Until you really hear what a great set up can do in terms of a centered mono image, you will probably have no idea what a maximally "diffuse and directionless" quality played back in stereo should sound like.
For those who want to try using an out-of-phase source as a test, let me tell you that on something like the track 3 of the Sheffield/XLO Test and Burn-In CD, with proper set up the voice should be so diffuse and directionless that the location of the voice cannot be determined in the front/back or up and down dimensions, much less left and right. Slight head movements can shift the apparent source anywhere in the room, including anywhere behind you.
