April 12th - Is a 7.1 System Worth it? - AVS Forum
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post #1 of 8 Old 04-11-2013, 11:01 PM - Thread Starter
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Today's Show:
We recently received an email from a listener who was asking whether a 7.1 system was something that he should wire his home with. This got us thinking that there are probably a few listeners that may benefit from a discussion on whether a 7.1 system is worth it for them.

We also discuss:
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  • Panasonic has developed its 'last plasma panel,' but television sales to continue
  • Sony Announces Price And Availability Of Its New XBR 4K Ultra HD LED TVs, 4K Media Player & Distribution Service
  • Boxee Cloud DVR
  • The number of cord cutters is steadily growing


and a lot more...

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post #2 of 8 Old 04-12-2013, 12:05 PM
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The 7.1 discussion got a few things right (e.g., need space behind the seating to be effective), but unfortunately started from the mistaken premise that a 7.1-speaker layout is somehow tied to discrete 7.1 content, when that hasn't been the case historically.

Fosgate started selling consumer 7.1 pre-pros in 1986, Lexicon in 1988. By comparison, discrete 7.1 content didn't show up until 2006 (two decades later). Heck, even 5.1 content didn't show up (on laserdisc) until the mid 1990s. So the number of channels in the source material had nothing to do with the number of speakers used for playback.

Even in the Pro Logic era, content was 2 discrete channels, carrying 4 matrix encoded channels, typically played back over 5 speakers. Again, the number of channels (matrix or discrete) had nothing to do with the number of speakers.

Many of us have who have been going to movies since the '70s have seen commercial theatres go from 1 surround channel (Dolby Stereo) to 2 surround channels (discrete 5.1) to 3 surround channels (Surround EX) to 4 surround channels (discrete 7.1), all while maintaining the same number of speakers in their surround arrays. Again, the number of surround speakers those theatres used had nothing to do with the number of channels in movie soundtracks.

Considering that history, it was odd to hear consumer 7.1-speaker layouts (which have been around for a quarter century) discussed in terms of something as recent as discrete 7.1 content, when that's never been the point of a 7.1 configuration.

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post #3 of 8 Old 04-13-2013, 06:36 AM
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Quote:
Originally Posted by sdurani View Post

The 7.1 discussion got a few things right (e.g., need space behind the seating to be effective), but unfortunately started from the mistaken premise that a 7.1-speaker layout is somehow tied to discrete 7.1 content, when that hasn't been the case historically.

Fosgate started selling consumer 7.1 pre-pros in 1986, Lexicon in 1988. By comparison, discrete 7.1 content didn't show up until 2006 (two decades later). Heck, even 5.1 content didn't show up (on laserdisc) until the mid 1990s. So the number of channels in the source material had nothing to do with the number of speakers used for playback.

Even in the Pro Logic era, content was 2 discrete channels, carrying 4 matrix encoded channels, typically played back over 5 speakers. Again, the number of channels (matrix or discrete) had nothing to do with the number of speakers.

Many of us have who have been going to movies since the '70s have seen commercial theatres go from 1 surround channel (Dolby Stereo) to 2 surround channels (discrete 5.1) to 3 surround channels (Surround EX) to 4 surround channels (discrete 7.1), all while maintaining the same number of speakers in their surround arrays. Again, the number of surround speakers those theatres used had nothing to do with the number of channels in movie soundtracks.

Considering that history, it was odd to hear consumer 7.1-speaker layouts (which have been around for a quarter century) discussed in terms of something as recent as discrete 7.1 content, when that's never been the point of a 7.1 configuration.



Sanjay,


"(e.g., need space behind the seating to be effective)"



I have a room that is 12'6" wide and 21 feet long.

Would an ear to back wall distance of 6 feet be effective enough for Back Surround speakers in a 7.1 setup? confused.gif

Also, the spacing of my Dipolar Back surrounds would be 2 feet from the center of each speaker to the side walls. Basically, 8 feet from center of Left Back Surround to center of Right Back Surround. I am locked into this approxiamately 8 feet between speakers and 2 feet from the wall due to prewiring. Will this also be effective enough? confused.gif

Thanks!


...Glenn smile.gif
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post #4 of 8 Old 04-13-2013, 11:51 AM
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Glenn,

6 feet distance from the back wall is plenty. You should get excellent rear vs side separation in the surround field.

The 8-foot spread for the rear speakers will be helpful, letting you hear stereo separation behind you, where our human hearing isn't so good. Instead of a mono-ish blur back there, which can happen when the rear speakers are too close together, you will clearly be able to discern sounds over your left shoulder vs sounds over your right shoulder.

The only suggestion I would make, albeit minor, is to move your seating forward a foot. Frequency response variations (peaks & dips) tend to be smaller at 1/3 divisions of room dimensions. So if you could move your seating to 1/3 of room length (7 feet from the back wall), it will help give smoother response. Remember to move your side speakers forward so that they are in line with your seating.

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post #5 of 8 Old 04-23-2013, 03:20 PM
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Originally Posted by sdurani View Post

Glenn,

6 feet distance from the back wall is plenty. You should get excellent rear vs side separation in the surround field.

The 8-foot spread for the rear speakers will be helpful, letting you hear stereo separation behind you, where our human hearing isn't so good. Instead of a mono-ish blur back there, which can happen when the rear speakers are too close together, you will clearly be able to discern sounds over your left shoulder vs sounds over your right shoulder.

The only suggestion I would make, albeit minor, is to move your seating forward a foot. Frequency response variations (peaks & dips) tend to be smaller at 1/3 divisions of room dimensions. So if you could move your seating to 1/3 of room length (7 feet from the back wall), it will help give smoother response. Remember to move your side speakers forward so that they are in line with your seating.

Try this... sit in front of a nice two-channel stereo. Cue up a good album, something with really great stereo separation and imaging. Find the "sweet spot." Now, turn around 180 degrees and keep listening. The same separation, the same imaging—it's all there. Even the volume sounds about the same.

 

Humans will hear exactly as much stereo separation behind their heads as they will in front. It is the sides that are a relative "blur" because we don't have ears on the fronts and backs of our heads. 


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post #6 of 8 Old 04-23-2013, 06:51 PM
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Originally Posted by imagic View Post

Now, turn around 180 degrees and keep listening. The same separation, the same imaging—it's all there.

Humans will hear exactly as much stereo separation behind their heads as they will in front.
Relative localization accuracy is ±1-2° in front of us and ±6-7° behind us, so it is definitely not "the same separation, the same imaging".

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post #7 of 8 Old 04-23-2013, 07:23 PM
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Originally Posted by sdurani View Post


Relative localization accuracy is ±1-2° in front of us and ±6-7° behind us, so it is definitely not "the same separation, the same imaging".

 

My mistake, I made an absolute statement that is likely wrong. It is believable that sound localization is not as accurate when the source is behind your head, although I had a hard time finding the numbers you cite. I was really trying to convey the fact that you can hear a lot of detail in the sound field, even when the stereo source is behind you. Localization on the sides is far worse, with 15° accuracy. 5 or 6 degrees  is enough that when the sound combines with reverberant ambience, it is remarkable how many directional cues can be picked up. It was a Krell Foundation demothat I went to a couple of weeks ago— which really opened my ears to how detailed a rear sound field could be. 


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post #8 of 8 Old 04-23-2013, 08:36 PM
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Quote:
Originally Posted by imagic View Post

It is believable that sound localization is not as accurate when the source is behind your head, although I had a hard time finding the numbers you cite.
Even though our ears are at the side of the head, they 'face' forward. So, for example, sounds coming from in front are not obstructed by ear flaps they way sounds from behind are. This is why sounds from behind appear lower in volume, at least between roughly 1200Hz to 8000Hz.

The numbers were from 'Spatial Hearing' by Jens Blauert.

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