Why does 7.1 sound better than 6.1?

[nightflier]

I know it's a silly question, and I can sort of hear the difference myself, but there really is no logical explanation, is there? After all in a 7.1 setup, the rear speakers are just a matrixed mono signal of the 6th channel, right? So what's going on with the sound between these two speakers that is so different from the single speaker?

[GMichael]

It fills a larger room better.
Also lets more than one location hear sounds from what seems like directly behind them. With just the one, you can hear that it's coming from a direction that is a little "off of" directly behind you.

[kexodusc]

I think the big reasons is it provided versatility over 6.1.
In a 6.1 system, you have a very localized, pin point source in the rear which tilts the sound field towards the rear center rather sharply.
In 7.1 the rear can be pinpoint when necessary, but can also be more diffuse and better blends in with the side surrounds, creating a better panning experience.

[GMichael]

That's what I meant to say.

[nightflier]

So then wouldn't a speaker in the center rear with a wide dispersion work? Maybe a dipolar speaker?

[kexodusc]

So then wouldn't a speaker in the center rear with a wide dispersion work? Maybe a dipolar speaker?
Sure, IMO, 6.1 works better than 5.1 at creating a convincing surround experience...a dipolar/bipolar speaker with good dispersion would create a diffuse rear presence.
I don't think it will pan as well from right, to rear right, to rear left, and thus not blend as well as 2 separate speakers. Again, the larger, and wider your room, the more this would be apparent.
I would expect in smaller, more narrow rooms, the need for the 7th speaker diminishes.
Also, dipolar speakers would sacrifice imaging compared to direct radiators - a lot of the time it wouldn't matter, but some cues are intended to be pinpoint in nature. Guess it's the old trade-off again, but if you don't have dipolars in your system already you probably made that choice awhile back.

[s dog]

I know it's a silly question, and I can sort of hear the difference myself, but there really is no logical explanation, is there? After all in a 7.1 setup, the rear speakers are just a matrixed mono signal of the 6th channel, right? So what's going on with the sound between these two speakers that is so different from the single speaker? My room is only 11ft wide so one rear speaker does a nice job. Im useing a Klipsch SS1 surround speaker.