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Help with monopole surrounds for 5.1


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7 replies to this topic

#1 of 8 Kevin Co

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Posted April 29 2003 - 02:30 AM

I need some last minute advice on placing my rear surrounds in my 5.1 setup. They are inwalls, so I only have one chance to get it right. I’m hoping that some of you with monopole surrounds will chime in here. I have my fronts separated by 90 inches (tweeter to tweeter) and my listening distance from the front plane of the speakers to my ear is 11 ft. Now for the ugly part. My sofa is only 6 inches away from the rear wall. I have only one side wall and I can’t use stands because of my toddler. So, this relegates my surround placement to the rear wall behind the sofa. Has anyone tried a similar arrangement? What I need to know is the recommended distance between the surrounds. From reading some of the posts here, It seems as though aiming them directly at the fronts would be the popular choice. My dilemma is due to the fact that I’m sitting so close to the rear wall. Should I spread them out more so that the sound isn’t so direct? Or, should I move them in closer together because there is not enough distance between myself and them (approx. 20 inches) to get any diffusion? The speakers are Boston 361’s which seem to have pretty decent off-axis response (feel free to contradict this statement as I am by no means an audiophile). I’m hoping some of you have similar experiences to share.

#2 of 8 Brian L

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Posted April 29 2003 - 03:26 AM

Unfortunately, there is no easy answer, but you really have two choices; rear wall, or ceiling.

FWIW, my layout sounds identical to yours, but my child is 5, so I was able do stand mounted bookshelf speakers slightly behind and just beyond the edges of the couch.

Another factor is what you want to optimize for; music or movies?

For films, much (but not all) of the surround stuff is ambiance, so you want a diffuse radiation pattern. In my previous home, I had a pair of the Polk's (they are those wedge shaped speakers) high up on the side walls, and aiming at the ceiling. That was great for movies, but terrible for music.

In the new home, I could have opted for wall mount (as you proposed) but I wanted better sound for music (I have MC SACD and DVD-A now), so I went with a pair of KEFs on the stands.

It is somewhat hampering that you have in-walls. A small book-shelf would have given you some options with aiming.

BGL

#3 of 8 Rich Malloy

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Posted April 29 2003 - 03:34 AM

You have to go in-wall, right? I'm assuming so...

And these are not "rear surround" speakers, but rather the left and right surrounds (sometimes referred to as "side surrounds")? I presume so since you say this will be a "5.1" setup (as opposed to 6.1/7.1).

For a system with monopole rears, I've found the best setup is the ITU Standard described here: http://www.timefordv...m/ref/ITU.shtml

I changed from the more common "side surround" setup (see here: http://www.dolby.com.....html#chapter3) when I upgraded my speakers and decided to go monopole rather than dipole for the surrounds. IMO, this was an improvement in everyway, both the monopole speakers and their placement.

Note that while the ITU setup moves the surround speakers more to the rear of the listener (conversely, the dolby labs setup recommends dipoles placed directly to the sides), they are not behind the listener and most definitely not aimed directly toward the fronts. You will get some freaky imaging from this placement, with sounds that should be placed to the side as your surrounds image laterally with your fronts seeming to hang in the middle of the room instead.

Not knowing more about your room, my recommendation would be to move your listening position forward as far as possible, preferably such that it is the same distance from both of your main speakers as your main speaker are from one another. This is the ideal "near-field" setup. Place your center speaker directly in-between and slightly recessed (again, ideally the same distance from your listening position as your main speakers). Toe-in your main speakers until you get a solid center image, but without collapsing the width of your soundstage too much (I have mine aimed directly at a point about a foot or two behind my head). Find the right compromise and remember that tiny changes (as little as an inch in any direction) can make all the difference. Now, place your surround speakers as close to the ITU standard as possible, behind you and more to the sides of the room rather than the rear. Also toe these in toward the listening position (mine are aimed just barely behind ear level). If you set this up just right for your room, you should get excellent imaging across the front, sides, and rear of your room.
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#4 of 8 Kevin Co

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Posted April 29 2003 - 07:12 AM

Thanks for the info guys. Rich, you are right in assuming that I am incorrectly referring to the L & R surrounds as "rear surrounds". My existing setup is Prologic, so old habits die hard I guess. I have seen the ITU diagram before and am in total agreement that it makes sense. My problem however, is that I am pretty well stuck with using the inwalls on the rear wall for surrounds. I am also stuck with the couch on the rear wall. This room is primarily intended to be a family / play room, so the couch in the middle of the room won't fly I'm afraid. Posted Image

#5 of 8 Brian L

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Posted April 29 2003 - 07:52 AM

Quote:
Note that while the ITU setup moves the surround speakers more to the rear of the listener (conversely, the dolby labs setup recommends dipoles placed directly to the sides), they are not behind the listener and most definitely not aimed directly toward the fronts.


Rich,

I will buy the 2nd part (speakers not aimed forward), but how can they NOT be behind the listener? Unless they are at 90 degrees (left and right) to the listening position (assuming the center is 0 degrees), wouldn't 110 degrees be slightly behind?

In my room, I am using a sort-of ITU arrangement. I am at less than 110 degrees (I too have the couch against the wall, which kind of screws the pooch on a true ITU set-up), but the speakers are ever so slightly behind me.

BGL

#6 of 8 Kevin Co

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Posted April 29 2003 - 11:56 PM

Assuming that my primary concern is HT not 5 channel music, and that I can't toe the surrounds in, is there any way I can make this setup sound decent? In other words, is there a location for the surrounds on the rear wall facing forward that is better than another? What if were to apply the ITU standard to my room with the couch in its present location? When I draw this, the two 110 deg. axes for the surrounds intersect my rear wall with 110 inches of separation. Since this is wider than my front speaker separation, would it serve to lessen some of the weird imaging problems that Rich described?

#7 of 8 Rich Malloy

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Posted April 30 2003 - 02:53 AM

Quote:
I will buy the 2nd part (speakers not aimed forward), but how can they NOT be behind the listener? Unless they are at 90 degrees (left and right) to the listening position (assuming the center is 0 degrees), wouldn't 110 degrees be slightly behind?
That's exactly right, behind and to the sides, but not directly to the rear.

Kevin, having your surrounds wider than your fronts will help, but aiming them towards the listening position is even more important. Obviously, you're going to have to find the best compromise for your room, but the only way to really do this is trial and error. You have to get them up there and listen, move them a little bit, listen some more, etc. You may even find that mounting them in the ceiling is better. Not having that side wall makes things really difficult, but if you can spread those speakers wide along the rear wall and aim them in toward the listening position, then you might find an angle where everything falls together (if not perfectly, at least sufficiently to create a believable soundstage).
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#8 of 8 Brian L

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Posted April 30 2003 - 02:56 AM

I guess the best I could suggest is bringing them down lower (perhaps a foot over ear height), and moving them in toward the listening position (but still have them outside the edges of the couch).

That would perhaps allow them to do a better phantom image between the two surrounds. As for developing a decent phantom between the Front/Rear pairs, I don't see that happening, but for the most part, unless you are in the WSR Test Lab, who DOES get correct imaging between each pair?

All that said, you hands are somewhat tied. No point obsessing over it. If you want an optimized set-up, you are not going to be able to do it with in-walls (IMHO), so just do the best you can.

When you child gets older, get a decent pair of bookshelves and stands. Thats what I had to do, and I can assure you that even in my poorly laid out first home, I still enjoyed the heck out of my system.

BGL





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