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:

---

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.

---

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:

---

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.

---

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.