AVS Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
178 Posts
Discussion Starter #1 (Edited)
First up, I am sorry for the long post

I am constructing a dedicated home theater room with the dimensions of 23.95 ft (l) x 19.8 ft (w) x 14.6 ft (h). I have planned for only one row of seating and I would like to place the seats/subwoofers at their most ideal locations to get a great low frequency response across all the seats. I am also planning to implement BOSS riser to achieve a good tactile response. Being a rectangular sealed room with solid brick walls all around having multiple subwoofers, I am hoping to determine the potential subwoofer placement locations before the room is constructed.

This would also help me to determine the right location of the theater entry door along the rear wall of the theater. I don't want to end up with a door at the best subwoofer location for my room. Unfortunately rear wall is the only wall where I could put the door.

I have attached the sketch of the building and planned theater room layout. Theater entry door location indicated on the sketch/layout is just a possibility and it could be moved anywhere along that wall.

I am going to use 4 Rythmik FV18 paper cone subwoofers in my build. It would be great if you could please throw some light on a couple of things.


1. With multiple subwoofers in hand, please let me know if I can go with a 3 seat configuration (with center prime seat) or if I need to look at 4 seat configuration instead (without a center seat to avoid width mid point mode). I would be using only 3 seats though even if I go with a 4 seat configuration.

2. For one row of seats, experts seem to suggest 2 subwoofer locations and not 4. I can stack 2 subwoofer at each location if this is the ideal approach for a single row. Please confirm.

3. I believe mid wall placement of subwoofers is supposed to be the best placement option for multiple subwoofers to get a good output coupled with even low frequency response across seats. I tried to do a room simulation of mid wall placement of subwoofers using REW. For some weird reason, I am not getting a flat response for both 2 subwoofer and 4 subwoofer mid wall placement for my room - with the seating put at 2/3rd length from the front wall. I have attached the results from REW room simulator. Please let me know if I am missing something or if I need to tweak the delay or something for the mid point placement to work. Weirdly, when I reduce the ceiling height of the room to 8 ft or less, low response becomes very flat. I was wondering if the mid point placement of multiple subwoofers is not applicable for rooms with high ceiling. Please clarify.

4. If mid wall subwoofer placement is not going to work for my room, I would like to put the theater door in the mid rear wall location to maintain symmetry. But if I still need to reserve this spot for subwoofer(s) despite poor results from REW, I can do that as well. Please advice.

5. Please let me know if there could be a need to put the subwoofers at rear corners or rear wall quarter points for a single row of seating. If these locations are never going to be used for a single row theater, I can put the door in these locations as well. Kindly confirm.

6. If I cannot get the mid wall subwoofer placement working in my setup, please let me know the next best location(s) I need to look at.

7. Since the rear wall of the theater isn't constructed yet, I still have the privilege to move the wall slightly (a foot or two). Kindly let me know if the length of 23.95 ft works or if I need to tweak it to get a better low frequency response in my room.

8. While using REW, I hope I don't have to worry about the response beyond 100 Hz. Let's say if I have a dip at 120 Hz, I was wondering if I need to work on correcting that dip. Generally the response curve isn't staying flat after 80 Hz for almost all subwoofer placements when I simulated using REW.

Please feel free to share any other advice to achieve the best chest slam and lift off in my new setup at every seat :)
 

Attachments

·
Registered
Joined
·
1,299 Posts
Simulate subs at 1/4 and 3/4 positions along the front/rear walls as well. Keep in mind, simulation is not reality, but it'll be close. The 4 sub response is much better than the 2 sub response in the simulation, as it should be.

You're going to need a MiniDSP 2x4HD or the like to EQ the bass regardless of how many subs you have, but you should definitely play around with the simulator and try subs all over the place.

The room sim only vaguely resembles reality in my room, FWIW...
 

·
Registered
Joined
·
28,981 Posts
With multiple subwoofers in hand, please let me know if I can go with a 3 seat configuration (with center prime seat) or if I need to look at 4 seat configuration instead (without a center seat to avoid width mid point mode).
If you blow across an empty bottle, you can make the air in that small chamber resonate (make that boooooh sound). If you enlarge that small chamber to the size of your room, the air in there will still resonate (of course at different frequencies than the bottle).

Your 19.8' room width will result in resonances (room modes) at certain problem frequencies: 28Hz, 57Hz, 85Hz, 114Hz, 143Hz, 171Hz, etc. The first 4 of these width modes are mapped on the graph below, with each problem frequency in a different colour, so you can see where it's peaks & nulls fall across the width of your room:



As you can see from the graph, every listener will be sitting in a different combination of peaks & nulls, making for a very inconsistent experience from seat to seat. The worst place to sit would be the midpoint of room width, where the problem frequencies are either loud peaks or quiet nulls (all extremes, no moderation).



Unfortunately, the worst location (midpoint of room width) also happens to be the money seat. Since nulls cannot be equalized away, they have to be addressed with subwoofer placement. Turns out that centering a pair of subs at the ¼ and ¾ points of room width will cancel the first 3 width modes (28Hz, 57Hz, 85Hz), minimizing ALL the peaks & nulls associated with those modes. Explanation from Floyd Toole:



Getting rid of the width modes in the subwoofer range allows you to have an odd number of seats (3 or 5) with the sweet spot at the midpoint of room width (formerly the worst location). Best part: it's free (doesn't cost anything to move subs). Will give the room correction system in your receiver a big head start.
 

·
Registered
Joined
·
178 Posts
Discussion Starter #4
Simulate subs at 1/4 and 3/4 positions along the front/rear walls as well. Keep in mind, simulation is not reality, but it'll be close. The 4 sub response is much better than the 2 sub response in the simulation, as it should be.

You're going to need a MiniDSP 2x4HD or the like to EQ the bass regardless of how many subs you have, but you should definitely play around with the simulator and try subs all over the place.

The room sim only vaguely resembles reality in my room, FWIW...
Getting rid of the width modes in the subwoofer range allows you to have an odd number of seats (3 or 5) with the sweet spot at the midpoint of room width (formerly the worst location). Best part: it's free (doesn't cost anything to move subs). Will give the room correction system in your receiver a big head start.
Thank you Sorny and sdurani. I am planning to get a MiniDSP 2x4HD for managing the subs :)
I tried simulating for 1/4 and 3/4 positions and it isn't as flat as the corner placement of two subwoofers. Please see the attached images.

When I simulated with 4 corner placed and quarter point placed subs, the response doesn't seem to be as flat as 2 corner placed subs for some reason. Could you please post the room simulator's screenshot with 4 subs in place. Thank you!
 

Attachments

1 - 4 of 4 Posts
Top