Validation on speaker placement for 7.1 system - AVS Forum
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post #1 of 11 Old 05-13-2013, 06:30 PM - Thread Starter
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Hi all,
I was finally able to lock down my room layout (seen here) and now am moving on to the speaker layout for that room. I'd like folks thoughts on how to arrange the speakers better, as my first cut using the degree offsets recommended via the DTS / THX sites seems to put the L/R speakers in a strange location, and nowhere near the 'same distance as the center' recommendation.

Assumptions / Notes
  1. Sitting location: Optimal audio location based on room dimensions (from prior discussions)
  2. Channels: 7.1
  3. Screen: Seymour AT type, offset 1 foot from the wall
  4. Receiver: Denon 7.1 channel capable (model TBD)
  5. Speakers: I'm having to reuse the speakers I already have, they are
    • Center: Bose VCS-10
    • L/R/SR/SL/RR/RL: Bose dual cube (like this)
    • Subwoofer: Bose Powered Subwoofer (like this)

Questions
  1. Can I get thoughts on the speaker locations based on the room dimensions (as seen in the picture below, based on the 'proper' degree offsets at DTS / THX)?
  2. The subwoofer I had was previously on a 5.1 setup. The wiring is the bose propriety kind where the inidividual channel wires connect from the receiver and merge into a single connection (that looks like a large VGA connector) which connects into the back of the sub. The sub then powers the speakers which connect to the sub. Can / how can I reuse this in a 7.1 setup?
  3. Some have mentioned a dual subwoofer setup, what is the benefit of multiple subs for a room of my dimensions?


First cut speaker placement
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post #2 of 11 Old 05-13-2013, 06:51 PM
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I'll start this ball rolling with a few points, with the understanding that I won't be able to strike a perfect balance right now, and there will be other opinions and compromises.

First, even though you've linked it, and readers can see this is a small room, it is noteworthy that you're basically building for two seats in one row, with overflow/special use seating in the rear. (please correct that if I'm wrong) That also, IMO is a good reason to stick with the side surround angles you've indicated - there are no obstructions in that part of the room or obstacles on the walls - so sticking with the maximum rearward angle (110 as opposed to only 90) makes the rear seats more reasonable without compromise for the primary LP.

Second, I would not be concerned at all with the equal distance for speakers in the front sound stage. Symmetry is a worthwhile goal, IMO, but the importance of the distance is made virtually zero by the processing in any modern home theater receiver. The processor will account for the distance differences by applying delays to the signals for the closest speakers. Instead, I would position the L and R loudspeakers outside the screen, at it's edge. Will there be adequate space?

Third, the narrow aspect of the room deserves consideration. The first and probably most important is through SBIR (read here for definition) for the front speakers. The second way is through the timing of the first reflections from the L and R speakers. I'm not a ardent believer in absorbing first lateral reflections, but I think in your case it will be important. These aspects may not be something you want to consider at this time, but they should be part of a complete setup and calibration of your system. The complications this brings up should not override any basic layout considerations, it just brings light to the calibration process.
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post #3 of 11 Old 05-13-2013, 07:03 PM
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"Sound radiates from a driver in different ways. Higher frequencies act like a ray and move in straight lines from a point. As you get lower in the spectrum, they begin to radiate more like a sphere. By the time you get below 500 Hz or so, you’re getting pretty spherical radiation. By the time you get to 125, it’s purely spherical."

This is 100% entirely false. Sorry GIK! Ever looked at polar response for speakers before? Good speakers are designed not to beam which is what they are describing here. A 1" dome tweeter is producing "spherical" sound at 10 kHz.

That being said, boundary influence is almost negligible in bass/midbass with the Bose cubes because they don't produce anything below 250 Hz. Also having no tweeters they do in fact start beaming probably around 6-8k.

As far as the front speakers go, putting them behind the screen and inward a little bit, toed in should be good. The Bose cubes are somewhat unique in that the top and bottom are offset by some angle. "Direct/reflecting" they call it.

Anyway, I would move you front speakers back and in, although since it's such a long narrow room I do see what you are doing there.
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post #4 of 11 Old 05-13-2013, 07:16 PM - Thread Starter
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Thanks for your thoughts, my responses below.
Quote:
Originally Posted by HopefulFred View Post

...Instead, I would position the L and R loudspeakers outside the screen, at it's edge. Will there be adequate space?

The visible screen width is 105" and the overall room width is 124" leaving 9.5" on each side - however there is a screen edge (unsure what dimension that would be) and the speaker width would be roughly 4" wide. So it would be fairly close but not sure how close. Couple of questions in that configuration:
  1. That would put the speakers at roughly a 20-25 degree angle, any concerns with the speakers being shallower than the 30 degree recommendation?
  2. Given the tigher spacing, it's possible the speakers would have the screen edge (not the AT screen) between themselves and the listener position, deadening / disrupting the sound?

Quote:
Originally Posted by HopefulFred View Post

.....I'm not a ardent believer in absorbing first lateral reflections, but I think in your case it will be important....
I have been looking at sound and bass traps (I think you alluded to that from this site?.). Once I have the speaker locations I'll confirm the heights for each and then I can start the calcs on the traps needed. If you meant something else please let me know, thanks!
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post #5 of 11 Old 05-14-2013, 08:28 AM - Thread Starter
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Taking the recommendations from above (to move the speakers to the front wall) I came up with the below diagram. It is, actually, roughly to scale. Couple things of note:

  • The screen itself is 105" wide, but the frame will add another 3.5" to each side for a total width of 112"
  • Placing the speakers at the extreme edges of the wall puts that screen frame within the audio 'line of sight' to the listener (red dotted line), potentiall more so when you consider the true position of the dual listeners in that seating position (dotted heads)
  • Moving them in about a foot seems to be the best compromise for the listener locations to avoid the screen frame (green and blue dotted lines). This results in about a 19 degree angle vs the recommended 30.

Questions
  1. So is this more in line with the thoughts of moving the speakers to the front wall? Is 19 degrees vs 30 acceptable?
  2. I'm assuming the Center / L / R are placed at ear height?
  3. And the SL / SR are 2 foot higher than that and directed towards the listener?
  4. What should the height of the RR and RL be?
  5. I currently have one sub in the design, but could place a second under the desk in the second row seating area - is that worthwhile in this modest HT setup of mine?

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post #6 of 11 Old 05-14-2013, 08:43 AM
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You aren't planning on sitting up against the back wall are you??? That's a huge no no for 7.1 surround. I find that sitting 2/3 of the way back the room provides the best mix of optimal audio/video experience at least in my living room and my last living room. I have my front L&R speakers toed in so that the center lines intersect 3 ft behind the Main Listening Position.

I understand that we all have different budgets and that money doesn't grow on trees for all of us. But what I would make sure you do is setup this room that you can swap out the Bose with better speakers. Trust me if you are going to all this trouble and expense to make a theater room with a projection screen, the "little" bose sound won't do it justice. So as time allows you will want to consider upgrading to better speakers.

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post #7 of 11 Old 05-14-2013, 08:50 AM - Thread Starter
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Quote:
Originally Posted by flickhtguru View Post

You aren't planning on sitting up against the back wall are you???

No, sorry that it looks that way, should have been clearer. In the first post I have a picture of the general layout in the room, this was a closeop from the prime listening position to the front wall only. Sorry for the confusion
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post #8 of 11 Old 05-14-2013, 05:21 PM
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Don't put the speakers anywhere that causes them to be obscured. If they need to be in front of the screen, so be it. I don't know that 19 degrees is too narrow a separation, but I expect two things - First, that you should be able to tweak that position enough without changing where and how you wire the room, and second, that you should leave as much room for future larger speakers as possible. Hopefully someone else can comment on the angle considerations.

In response to your other questions more directly:

I don't know if you'll be able to use the sub at all, but I'm not too optimistic that you can use that sub without the rest of the system.

The primary benefit of multiple subs in any home-sized room (an acoustically small room) is minimizing the modal coupling of the LF drivers to the natural modal response of the room (or perhaps more properly, to drive modal waves from multiple positions, to avoid strong coupling - not sure what the best terms are here) . This has two major outcomes - first (and of lesser interest to you) is minimizing the seat-to-seat variation in low-frequency response across the listening area, and second - the ability to strategically locate and equalize the subs/signals to avoid the nulls and peaks associated with modal ringing. Additionally, you can get extra headroom in the system so that global EQ can be more effective. As a side note, and along the lines of what djkest said, the low frequency performance of your small Bose cubes will be very poor. Hopefully the VCS-10 is better - it should be I think, since it has a reflex design it's probably carefully engineered to reproduce normal dialog, which can include frequencies a good bit lower than the 250Hz that djkest sites. This is of mention because many subwoofers are not terribly good to that high a frequency. You might look into something like HSU Research's Subwoofers and Mid-Bass Modules - they could be a high quality and reasonably affordable way for you to bridge your current speakers into a more traditional setup with at least mains with wider usable frequency response.

In an ideal setup, the front soundstage (L/C/R) is ear/eye height, and positioned behind the screen (where appropriate based on both the separation angles for primary listeners and the screen material, obviously). Some compromise may be made to accommodate the various heights of listeners on separate rows.

The height of the surround loudspeakers is generally greater. The reasons for this include avoiding the sound shadow that one listener can cast on another, and minimizing the difference in distance between the speaker and each of the listeners. (Do you see the triangle and how raising the speaker makes the distances more similar?) The distances should be similar to allow for a setting delay and level that is acceptable for both seats. Two feet is a common recommendation and should be appropriate for most small rooms. If it's not possible to aimthe speaker down into the listening area, care should be taken to keep the listeners within the normal on-axis (vertical) listening area for the loudspeaker. I have no idea what the soundcubes' off-axis response looks like, but I would guess that for most surround loudspeakers 15 degrees below the normal axis is a safe maximum (that's a guess).

I personally think more subs is a good upgrade for any common setup, but the proof will be in the pudding. Wire is cheap - why not run some wires to a whole bunch of places? (I'll probably wire for 6 or 8 potential locations in my 12x22 theater, and use two for sure, hopefully 4.)
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post #9 of 11 Old 05-14-2013, 06:08 PM - Thread Starter
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Thanks for the detailed response, that has been a big help. I've incorporated much of that into the design, and made a couple of mods based on your inputs, most notably:
  • I'm going to add in another subwoofer to make a 7.2 system, and place that second sub under the desk just in front of the second row seating position
  • After much reading here, it looks like the idea of trying to leverage my Bose 5.1 into a 7.2 system is a fairy tale tongue.gif So I am looking at other options now in this thread

Thanks again

Updated layout
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post #10 of 11 Old 05-14-2013, 08:01 PM
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The Bose bass module isn't a subwoofer and it us almost completely worthless...and the Bose satellites aren't much better. However, if you need to use them, so be it. In a room that size, you will be best off going 5.1...

Set up #1: EMP e5ti, e5Ci, and SLS Q line Audio surrounds, EMP 10i10i sub
Set up #2: Def Tech SM450, CLR2002, SLS Qline surrounds and Klipsch 12wD sub
Set up #3: JBL130, JBL120C and Klipsch synergy sub
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post #11 of 11 Old 05-14-2013, 08:05 PM - Thread Starter
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Quote:
Originally Posted by Elihawk View Post

The Bose bass module isn't a subwoofer and it us almost completely worthless...and the Bose satellites aren't much better. However, if you need to use them, so be it. In a room that size, you will be best off going 5.1...

I actually updated that speaker choice in the post prior to yours.
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