First I have to say I don't completely buy into this front/rear confusion thing. In my house the '6' speaker sounds very clearly behind me, no question. I've actually had to suppress a duck reflex more than once.

Having said that, the reason 'phantom center' and 5.1 (or 7.1) sound different than single center front or single center rear is simply that your ears hear everything, in a physical sense. So although your mind may process the identical parts of the L&R or 6&7 speakers and convince you it's all one source, each ear gets to hear each speaker. So rather than a single sonic event passing your head and exciting each ear once, you get two similar sonic events passing your head and exciting each ear twice, once per event. Of course your wetware can deal with this and figures it out, but it' not the same.

This is why for most people a phantom center is never as convincing as a real center.

When I bought the ES it had only a 2 year warranty; it changed to 5 years on the ES line shortly after I got it.

The good news is that after taking the cover off the receiver last night I found the two fuses between the AC line and power supply were blown. Hopefully they blew in time to protect everything downstream. Several other fuses on the power supply board were intact. The fuses are of a rather rare size, but I found a source and some are on the way.

The image doesn't appear directly at the back of your head, but you get a sense of it being behind you. Our hearing is not as acute behind us as it is in front of us; that is why there's no problem with a single centre speaker in the front. Using two rear speakers is a good idea, whether they're both playing the same (mono) signal or not.

The problem, really, is that we judge direction horizontal direction based mostly on inter aural time delays; the time it takes a sound to reach one ear vs the opposite ear. When we hear the same sound in both ears (at the same time with the same intensity) we know that the sound is somewhere along our centre line. We can usually tell if it's coming from in front of us or behind us; but not always. This has been demonstrated plenty of times by acoustic researchers.

I've heard this phenomenon myself a couple of times. The last time, ironically, was on a THX Ultra 2 system. A test tone was being played that circled the room; as it went from the side speaker to the rear speakers, the sound momentarily jumped to the front before recovering to the rear. When I looked behind me, I was surprised to see the rear speakers sitting a mere six inches apart (I wasn't aware of Ultra 2 at the time). Spreading the speakers out a few feet really did help get rid of the problem. Fair enough; no need to take my word for it. And keep in mind, I'm not telling anyone not to have a single rear speaker; just informing them of possible problems with that configuration. Meanwhile, here are links to some published information that discuss this phenomenon. While some of these technical papers aren't really all that "technical", they're still a chore to read. Instead, when you're on the page, use the search function to look for the word "reversal". This will allow you to read the relevant passages and skip the boring stuff.

http://www.cyberus.ca/~karen/spatial/readme.txt

http://www.alumni.caltech.edu/~franko/thesis/Chapter4.html

http://www.hitl.washington.edu/publications/hollander/7.html

http://www.auditory.org/postings/2000/20.html

http://216.239.51.100/search?q=cache:tZjU5lJJVMwC:www.khri.med.umich.edu/research/middlebrooks_lab/ewan/icad94/macp_icad.pdf+front-back+reversals&hl=en&ie=UTF-8

Best,
Sanjay

From the 1st ref:



I agree with Charlie: I have had a 6.1 system for almost 2 years now (1st with a DPL processor + 5.1, now with the 950), and I've never had a problem localizing sounds to the front or rear of the room. Maybe I am just lucky!

From the 2nd ref:



So now the plot thickens. NOT just along the center line (front to back). And notice the last phrase: "without additional information." I.e., with the visual cues from the display in terms of where the action is (or isn't), doesn't seem like to me it should be a problem. And ref 2 echos that:



And ref 3 seals it:



So, vertical reversal is more common than front-to-back. Now if you read through the 3rd ref, he mentions he got an average vertical confusion rate of 34% compared to the average rate of 18% that Wenzel got.

So if vertical confusion happens 3.5x more often than fron-to-back, and the averages above are with vertical, that puts the average equivalent rates for front-to-back reversals at 9.7% and 5.1% respectively. Still, with no visual cues, only auditory. Ref 3 goes on to explain that:



So, let me ask a question, and then conclude: Which would you rather use to compare real world performance of a speaker system *by ear*: test tones? Or you favorite CD or movie soundtrack?

With actual music or movie soundtracks, and with the visual cues obvious to the film format, and with *your own* head transfer function (not an average superimposed on the source signal) I still don't see where the problem comes in.

And I suppose it does make me a little sad that a THX Ultra2 setup didn't eliminate this for Sanjay. But then me myself and I: I'd still spread the rears 3 or 4 ft apart anyway. At least on the Anthem, you can specify in the config whether the 2 rears are side-by-side, or spread out.

Got to admit, I know more now than I did before!

I usually use music. Of the many pieces I try, one torture test is Alan Parsons' 'On Air' DTS music disc (a discrete 5.1 mix). The last track starts out with the vocalist in the left side-surround speaker speaker and walks anti-clockwise around the room, ending up in the front centre speaker. As he transitions from the left side-surround speaker to rear speaker, you can hear the hesitation in imaging; for a moment it is hard to tell if the sound is in front of you or behind. On systems where the rears are properly spread out, this problem doesn't occur.

As for the up/down vs front/back reversals; I guess we'll hear more about that when height channels gain popularity. Until then, it doesn't really matter to me if vertical reversals happen more often, because I don't have any speakers on my ceiling (though some room challenged home theatres do have in-ceiling speakers).

Speaking of ceilings... 'We Were Soldiers' was mentioned in the first post of this thread. Bit o'trivia: it is the first movie for which Dolby has encoded an overhead channel. They say it is encoded as an "extension of EX", though they haven't explained further. For home use, experts are saying that the height info may be matrixed in to the 5.1 mix or as additional data in the .1 LFE channel. It may in fact not be a problem for you. It's entirely possible that I'm part of the population that's more sensitive to this phenomenon. Hey, I see a strobing light and want to put on some disco music; other people see a strobing light and have a seizure. Yeah, those two speakers 6 inches apart basically behaved like a single sound source to my ear/brain. Ultra 2 uses some sort of Spatializer-like processing on the rears to give the impression that those speakers are further apart. I'll leave you to guess how effective it was on me. Glad to hear it. As you quoted one of the papers saying, "Judicious choice of room dimensions and listener location also helps to reduce front-back reversals." Reduce, not eliminate. You and Charlie may never ever experience the phenomenon during your lifetimes, but it does exist nonetheless. More importantly, several manufacturers of pre/pros, as well as several designers of surround processing, take front/back reversal into consideration. And I don't think it hurts to be aware of it.

Best,
Sanjay

[This message has been edited by sdurani (edited October 30, 2002).]

I experienced back to front reversal out in the real world 2 weekends ago, (not through a sound system). At a car show the vehicles were put on a dyno in a building with an enormous freight door left open. I was off-axis to the ramp door many yards to the right. When the cars were run up to full revs, I knew that the car was behind me and to my left, yet the sound appeared to be coming distinctly from the front, with distance moved also to approximately a block north.

I knew the walls of buildings in the vicinity were reflecting the sound, but the effect was so pronounced several people commented on it. Very interesting to hear this location jump when you know where the sound originates but your ears are placing the source in a different location.

A little late in this thread, but thought I would throw in my two cents as I didn't see anyone mention this. When I started to build my HT, I had a budget. That budget decided a lot of things. Budget vs. desired end-result taking into consideration what I already had and what needed to be upgraded, ended up giving me a Outlaw 950 as one of the components. I use a 5.1 configuration because it allowed me to use all full speakers. The full size, floor standing speakers give me the sound engulfing feeling that would require many smaller speakers to duplicate given the budget. I use the same system for 5 channel stereo which provides a similar quality, room filling, sound. I would even go so far as to say 4.1 is enough in most budget limited rooms.

[This message has been edited by MeanGene (edited October 30, 2002).]

I'd agree with a few qualifications. First, I played around with placement quite a bit, and although I prefer a narrow angle (40-50 degrees) between fronts for music, for HT I like a 90-110 degree spread. If I do this, the illusion of a phantom center (which is only good in a narrow sweet spot anyway) becomes elusive. The same goes for the rears/surrounds - a wider spread gives a nicer field of sound, but at expense to 'center rear'.

I'm not trying to say 4/5.1 systems can't sound good, or that 7.1 isn't better, but I really think, based on my listening that dimishing returns starts to really set in. One great idea was the concept of 4/5 channels in the front of the room. I think a discrete left and right center would be useful in many cases, and most folks can localize more precisely in front than behind anyway. If I had my 'druthers I'd like to see that implemented by someone.

Charlie- Diminishing returns, right on!

5.1 blows away 2 channel stereo (for movie soundtracks; I'm a solid 2 channel guy for music). I have 6.1, and even though I feel there's a big benefit there, not nearly the magnitude of 5.1 vs stereo. Someday, I hope to go to 7.1, and I'm anticipating another improvement, but maybe not even to the extent of 5.1 to 6.1.

Funny thought: with 7.1, we effectively have 4 speakers behind us, but only 3 in front. Almost seems backwards to me, because we have less acuity for sound behind us than in front. See what I mean? Sort of like we'd get more benefit by putting more speakers where we hear better...

(But I know, in an ideal 7.1 setup, surrounds are to the sides, and rears are to the rear, but I always thought about that seeming contradiction anyway betwen "front" and "back"... )

Well, basically if I'd noticed a problem I'd do something about it, but for whatever reason I've never had any problem with front / rear reversals. Sometimes the center seems to do too good a job of nailing dialog down, for instance if two people are conversing while walking down the street toward you it might be nice to have a bit of left center and right center, not purely so but a bit of directional hinting. But there's not much I can do about that.

My current system has other issues that are real and more pressing, including early reflections and time alignment as two outstanding examples. Once I can treat and correct those I'll either stop and enjoy the music or maybe find something new to worry about.