The answer to your question is "yes" - on material that was recorded for two channel sound, rear speakers can indeed smear the image.
As noted in another thread, the human brain locates the origin of sound in space by comparing the differences in the sound between what is picked up at the left ear versus the right.
There are several main factors involved. First is transient arrival time - a sound to the left of us will arrive at the left ear about half a millisecond before it hits the right ear. A sound directly in front of us will arrive at both ears at the same time.
Next, there is a frequency sensitive volume difference. The right ear will be in the "shadow" of a sound to our left, meaning the high frequencies in particular will be attenuated in comparison to the sound at the left ear.
There is also a phase difference that our brain can detect if the frequency involved is under about 1,500 Hz.
A good stereo image is created when the audio system does a good job of mimicking these spatial clues.
When you place a pair of speakers behind you that are only repeating the same information that comes from your front speakers (even if at lower volume), the result will naturally add confusion to the signals your brain is processing.
Even if the rear signal is somehow processed or derived from the front signal, it is at best a so-so guess or approximation of what the rear signal may have been in real life. It may be pleasant or interesting sounding, but it isn't a realistic recreation of a musical event.
As the original poster noted, there is very little musical material out there that is specifically recorded to capture a true rear image or hall sound. Absent a true signal to feed to the rear speakers I would rather turn them off.
As noted in another thread, the human brain locates the origin of sound in space by comparing the differences in the sound between what is picked up at the left ear versus the right.
There are several main factors involved. First is transient arrival time - a sound to the left of us will arrive at the left ear about half a millisecond before it hits the right ear. A sound directly in front of us will arrive at both ears at the same time.
Next, there is a frequency sensitive volume difference. The right ear will be in the "shadow" of a sound to our left, meaning the high frequencies in particular will be attenuated in comparison to the sound at the left ear.
There is also a phase difference that our brain can detect if the frequency involved is under about 1,500 Hz.
A good stereo image is created when the audio system does a good job of mimicking these spatial clues.
When you place a pair of speakers behind you that are only repeating the same information that comes from your front speakers (even if at lower volume), the result will naturally add confusion to the signals your brain is processing.
Even if the rear signal is somehow processed or derived from the front signal, it is at best a so-so guess or approximation of what the rear signal may have been in real life. It may be pleasant or interesting sounding, but it isn't a realistic recreation of a musical event.
As the original poster noted, there is very little musical material out there that is specifically recorded to capture a true rear image or hall sound. Absent a true signal to feed to the rear speakers I would rather turn them off.