Can back surrounds smear the front image?

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.

Mlsstl wrote:
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.

Kal

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.

Kal