It may be dependent on the program content or the setup but the addition of surround channels (with specifically encoded material) should enhance the front image. That said, it is likely also to widen the front soundstage and some may mistake that effect for a loss of specificity. (None of these comments apply to synthesized surround modes.)
You should turn the rears down.
Agree your rear speakers are too loud.
To make sure I am understanding you correctly, you are not having this problem with at least some multichannel encoded source material, but are having the problem when listening to 2-channel music with your multichannel system? I do not believe that 4 speakers will necessarily make two channel material sound better. In fact, there are at least several reasons that they should not sound as good as two good speakers on two channel material in a well set up room.
1) If your rears are not being actively driven by the amplifier (with only the fronts driven), they can act as passive radiators absorbing and re-releasing energy from the front speakers like a drum skin - smearing transients. Tap your surrounds' woofer cone and hear what happens, and then put your finger on it when only playing your fronts at higher volume if you don't believe me.
2) If you are having problems when the rear speakers are actively driven, I would monkey with the placement of all your speakers so that they are as close to equal distances from your listening position as possible - as the distance differential away from your ear increases for the fronts and rears, you could start to preceive problems with signal arrival time, resulting in a "smearing" of the signal.
3) With some two channel material played through four channels, you may get phase issues at your listening position, where certain frequencies cancel or add, causing the overall sound to be less coherent.
The suggestions above to turn down your rears may be a quick (but not ideal) fix on the material where you are having problems. This is because actively driving the speakers will tend to resist their passive movements driven by but out of phase with the fronts. And by lowering the volume, you can reduce your perception of any timing or phase issues resulting from poor positioning relative to the front speakers.
I recommend not using your rears for two channel listening at all, and for serious listening, turn your rears around so they face away from the front drivers, or even take them out of the room! for multichannel material, try repositioning your speakers to be as close to the same distance from your ears as possible and run your equalization program for your multichannel processor. If these don't help, then you may have some fatal flaws with room set up or configuration and will need to minimally or radically rearrange the position of your speakers and listening chair, and/or treat the surfaces of your room with accoustic tiles or similar.
I do not listen to multichannel music, but I have noticed that my surrounds diminish the coherence of the front image during movies, even though my processor, like most, delays the signal sent to the surrounds to compensate for variations in the speakers' distances to the listening position.
Because of this, during a recent change of my listening room configuration, I decided to eliminate the surrounds, so now I listen to movies in 3.1. I am an avid movie watcher (1000+ titles on my shelf), but I can honestly say I don't miss the surrounds.
This is, of course, an extreme solution. Knownothing offers very good advice about how to better integrate your surrounds for a more coherent presentation. I would certainly try that first.
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 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.
Not so. It really depends on your choice of repertoire. Among the majority of classical mch releases (SACD and BluRay), the surround is actually and discretely captured at the performance. Proper mch playback is enhanced, in all ways, by its presence.
Whether the number of recordings with true rear ambiance is signifcant or not depends on one's perspective.
I just checked and Amazon shows over 230,000 recordings in the classical genre while they show 305 DVD-A recordings, 3,901 SACDs and 64 Blue Rays.
Certainly those numbers can change a bit with different vendors or the manner in which one searches a catalog, but the point is still less than 2% of classical music material is available in the formats you mention.
In my book, when more than 98% of the available classical cataglog does not offer true rear ambiance, I'd stick with my original assessment. Other's mileage may vary.
Your assessment of the repertoire is correct as stated and, in fact, I agree with the general analysis in your previous post.
However, I was discussing the high prevalence of classical recordings with true rear ambiance compared among the total number of mch recordings.
Of course, all 2-channel stereo recordings lack true rear ambiance.
Why not just set the processor to stereo when listening to music?
Just to clarify things a bit...when I wrote 'rear' surrounds, I was not referring to side surrounds, which I also have, and are not a problem. Rather I was referring to two additional speakers located on the rear wall of the listening room (= 7.1). I have no problems with the side surrounds, and, as I've noted there seems to be almost nothing out there that is truly discrete 7.1. For most other sources, these rears have the problem I have mentioned if I allow the processor to feed them with signal.
Of course. You are letting your processor "mess with" the signals to synthesize rear speaker output. As Rwwear has suggested, just play stereo as stereo (and 5.1 as 5.1).
OK, then 7.1 processors ought to come with a warning!
'WARNING: THE TWO ADDITIONAL BACK SURROUND CHANNELS SHOULD ONLY BE USED WITH DISCRETE 7.1 SOURCES'.
Yup. Print the warning with a skull-and-crossbones!