Axiom Home Page Forums General Discussion Advice from Axiom Owners Rear surrounds - rear or...sides?

I was looking over Alan's article on Dolby's recommended speaker positioning and came up with the following for my room:

http://www.mts.net/~joanlh/theater_room.pdf

The shaded areas represent the speakers' direct radiated sound to what I guess would be considered the "sweet spot".

Does this make sense or do you think I would be better off with W2s at the back of the room? If located at the back of the room they would have to be closer together. I thought that this might yield better imaging.

Room area specs: Area: 267 sq.ft. (Volume: 1779 cu.ft. - yes I know, low ceiling, but we like to watch our movies sitting down), Length: 22'-8", Width: 11'-11"

Reason for my question is I am mounting the speaker terminal boxes in the walls and running the inwall speaker wire (currently only outside walls are constructed, no interior partitions yet). Worst case scenario is that I run two extra speaker plates at the back of the room anyway but I think an extra set of unused speaker terminal plates would be a waste of materials.

I wouldn't worry too much about imaging unless it's in front of you. As long as there's enough distance between two speakers behind you for you to be able to tell if a sound is coming more from the right or left, you'll be fine.

About your last paragraph, I'm not sure it would be a waste of material to wire for 7.1 now. If you don't do it and want to upgrade later, you'll think it's a waste of material to have to cut and re-patch your drywall. Also, if you wire both rear locations now, you'll be able to experiment and choose the location that sounds best to you.

Hi BruceH,

Looking at your diagram, I wondered why the two extra surrounds (for 7.1?) aren't located behind the seating area, which is where they are intended to go if you are running 7.1.

But perhaps you are running 5.1 with multiple surrounds for better coverage? If the latter, I don't think you'd need to angle the rear QS8s towards the listening area. Their very broad dispersion depends on reflections from a variety of room surfaces. Try it both ways.

Regards,

In reply to:

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Looking at your diagram, I wondered why the two extra surrounds (for 7.1?) aren't located behind the seating area, which is where they are intended to go if you are running 7.1.

But perhaps you are running 5.1 with multiple surrounds for better coverage? If the latter, I don't think you'd need to angle the rear QS8s towards the listening area. Their very broad dispersion depends on reflections from a variety of room surfaces. Try it both ways.

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Yes, it is supposed to be a 7.1 system. I was wondering about the placement of the rears on the sides to the back. I was going with the sound pattern using the degrees of separation as shown in your article (courtesy of Dolby Labs?). In retrospect, I guess that is not the best idea.

My thinking (there I go again) was that I could attain better separation on the rear channels by getting them further apart and thus placing them on the side walls where the shaded sound field indicated, versus placing them closer together on the back wall.

The other concern would be whether or not QS8s (or likely QS4s would be adequate) or W2s would be best for the rear channel application. If I went with W2s for rear surrounds, would that mean I would have to mount them at "seated ear level" versus close to the ceiling? Comments?

Hi Bruce! I'm speculating here. What I would do in your situation is put QS8's on the back wall. I think their dispersion characteristics are going to give you the best effect.

Is there a lot of discrete 7.1 content out there now? My understanding was that most material you would put through a 7.1 system is actually native 5.1 or 6.1 that is matrixed by your processor to derive the other channels. However, the world has passed me by in many other areas

In reply to:

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Is there a lot of discrete 7.1 content out there now? My understanding was that most material you would put through a 7.1 system is actually native 5.1 or 6.1 that is matrixed by your processor to derive the other channels.

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You are likely correct in this statement. My main objective is to "future-proof" the speaker setup so the wife does not have to go through the mental stress of upgraditis. If it is there from the beginning, she can't complain.

Hi Bruce,

I don't know if the diagram in Alan's article was for 5.1 or 7.1, but here's Dolby's diagram for 7.1.



My first thought was that your rear surrounds aren't placed in the 135 to 150 degree arcs indicated by the diagram, BUT they are far enough behind the listening position that they very well might be. I can't tell, for sure, one way or the other. If you haven't got one handy you can print a protractor, and use your eye, a laser pointer, or a laser level to get an idea of where your proposed rear surround positioning relates to Dolby's diagram.

I agree with Alan that you don't need to angle the QS8s toward your listening position, but can if experimentation indicates you should.

Bruce, your diagram is clear and raises a point which you illustrated but didn't discuss: when there are two rows of seats do you optimize the surround placement for the front row(where daddy and mommy sit?)or do you adopt a compromise location? In theory, when the setup is 7.1 the side surrounds should be directly to the side of the listening position to maximize the side effect, since being slightly farther back to provide a phantom back effect isn't necessary when there're actual rear speakers. Of course, with very wide dispersion speakers such as the QSs this is less critical.

My thought is to optimize the front row by moving the sides a foot or so farther forward. The back surrounds should be separated by as least as much as the distance they are behind the seats and wider is better than narrower. So I don't think that a deeper and narrower back wall location would be as good. The location you show for the back surrounds is good; possibly a foot farther back even better.

There's no 7.1 material, but using processing such as DPLIIx and Logic 7 to extract ambience contained in two and five channel material and sending it to the back where it belongs can be quite effective.

I have a very similar situation as yours Bruce. My sides are in about the same location as to accomodate 2 rows seating. However, I think you need to move your rears closer together along the back wall, they appear to be to wide and close to your left/right surrounds, reducing the seperation you would want. just my 2 cents.

This is an old picture, but if you look you can see that my rears are closer.

QS4's would be accurate enough I think.

No one upholds them as much as the QS8's. I really don't think there is that much of a difference.

Yes the idea was to optimize the sound for the front row. I almost had it optimized for one seat in the ultra-sweet spot but the wife would have none of that so it is a compromise sweet spot (what the heck, she makes me popcorn for every movie ..no not microwave, too many hydrogenates).

My main goal was to keep the wire runs to the wall plates as short as possible but worst case scneario is that I end up using painted flat wire to hide most of the length.


If I stick with Dolby Digital EX then the rears are likely fine where they are. If a lot of 7.1 material happens to appear on the market then a wider rear channel separation would seem to be best. At least with using wall plates, I have the flexibility of adding as much wire as I need and moving the speakers to where they will end up sounding the "best".

Bruce, you may want to experiment with the height of the rears and sides as well before making final decision. In my experience getting them lower improved things considerably. I ended putting them just barely above the ear level, maybe 15cm or so above ears when seated. The sound change from vertical adjustment was more than the change from moving them laterally. I would also experiment with moving the sides a bit further back so that they are not as much in front of the back seat. but rather at most directly to the side of it - at least in line with the front edge of the seat. Again "my experience" has been that placing side channels anywhere ahead of the listening position destroys the surround "magic".

Good point. Did you have to mount your QS8s to the studs? If they can not be mounted to the drywall through the use of wall plugs, I may have to plan for some extra braces in the wall to give me some lateral movement flexibility instead of every 16".

Love your setup, by the way. Very simple and clean. Did you use component video to the projector or S-video?

One of my QS8s is tied in to a stud, the other is in drywall, no problems at all.

Both of my 8s are in the drywall on the T bracket. No problems.

Woo Hoo! That's great. I did not want to compromise the insulation in my exterior wall by throwing in a stud brace.

Thanks guys!

My Qs are just attached to the dry-wall - no studs. I just made sure to add some dry-wall anchors and place plenty of screws in the T-Bracket to spread out the load.

Shoot - I mounted my plasma on the bare dry-wall without any studs - I just bought some freakishly haevy-duty dry-wall anchors. No problems here so far.

One of my QS8s was screwed to that cheap thin wood panelling, no stud. I used about 5 screws to distribute the load.

The other was on soup cans. Works but looks ugly.

At least some of the T-bracket holes align with the studs, the rest use plastic drywall screw plugs. The rubber bumpers do a great job of silencing the link - no rattles or any hint of instability. One of my QS8's is now mounted on the room door - suboptimal but that was the only place that was not too far behind or not too far front. The wire went inside the door so it is not visually too ugly. The door is of basic variety and regular screws seem to do the job - although I am definitely not trying to load test it or slam the door

>> Did you use component video to the projector or S-video?
Component DIY cable that goes up the back wall (behind the paint) and above the ceiling tiles. I have the S-video cable thrown in for redundancy but I am not using it as Marantz upconverts everything to component.
The cable has 5 shielded coaxes inside and I am using one of them to get the signal from the FM antenna that is also hidden above the ceiling tiles back to the equipment rack in front. I used a Radio Shack 24db or so FM amp - also in the ceiling to boost the poor reception in the basement. One coax is unused and the remaining 3 provide for component video connections.

A little late to this post but i can also say that using only regular floor screws (deeper threads) that the QS8s can be mounted right into drywall and remain quite firm.
The one problem we had awhile back was with the speaker cable running to the backside of the surrounds. Because the QS8 was tight against the wall, the plastic cable jacket ended up sticking to the paint which cracked and peeled during the removal of the surround speakers when we moved.
The rubber feet did something similar although i managed to keep the paint from peeling off the wall.

As for your system Bruce, we also prefer having the side surrounds slightly to the rear of our seating position (see recent pics link again).
Our rear surrounds will go directly behind us in the near future.
In your situation, if you do not hang the QS8s directly behind your seating area, then your alternate idea of using direct radiating speakers aimed right from the back wall should work equally well. Another alternative is to mount something like M2s in the positions you noted on your drawing and then angle them forward. You would of course need something like the FMB to do this, but at least you could locate the speaker wires on the side walls rather than trying to run more wire to your back wall.