Design & Best Practices: Part 3

Site: QSC
Course: Cinema 101 Training
Book: Design & Best Practices: Part 3
Printed by: Guest user
Date: Sunday, 14 April 2024, 7:38 PM

Description

Video Transcript

00:08
We're back! Let's start back up again.
00:11
Moving on to Loudspeaker Aiming: Horizontal coverage of most cinema screen channel loudspeakers is about 90 degrees.
00:20
For a typical room a best practice is to aim all three screen channel loudspeakers so that they converge at a point about 2/3 into the seating area.
00:30
Front rows are usually well within the coverage angle as long as they are not too close to the screen.
00:36
This achieves the best coverage with good stereo imaging for the most seats possible.
00:42
Even with this aiming, a loudspeaker with a 90 degree horizontal coverage pattern will deliver a lot of energy to the side walls.
00:50
So you can see why it is so important to treat side walls with acoustic absorption.
00:55
Now let’s talk about the location and aiming of Surround speakers.
00:59
These are aimed across the room toward the farthest listener, and should be mounted high enough so that they’re out of reach,
01:06
but not so high that they don’t cover the seating directly below the loudspeaker.
01:11
I’m not going to bore you with the math of calculating loudspeaker height here. You can take a look at the handout.
01:17
It usually ends up between 8 and 12 feet from the floor depending on the width of the room.
01:22
In the smallest rooms, 8 feet keeps them out of reach.
01:26
In large rooms, you don’t want to go much higher than 12 feet, otherwise the listeners below will be too far off axis.
01:34
Also, loudspeakers that are too low reduce the size of the stereo “sweet spot” in the middle of the room.
01:41
Surround loudspeakers are normally installed in approximately the rear 2/3 of the room for 5.1 and 7.1 systems.
01:50
We want to avoid placing the front surround too close to the screen because of potential reflections off the screen and off the open floor area.
01:59
They should be fairly closely spaced – no more than 12 feet apart for the largest rooms. We recommend 8 or 10 foot spacing as a good target for average size rooms.
02:11
The purpose is to create a seamless sound field.
02:15
The loudspeakers should all be mounted roughly the same height from the floor, according to the slope of the seating,
02:21
and they’re are usually configured and wired in groups, or arrays, up to 4 in parallel, per amp channel.
02:27
Along the rear wall of the room above the last row of seats,
02:31
Surround loudspeakers should be mounted high enough so that they can’t easily be reached, at least 8 feet from the floor.
02:38
Lateral spacing should be approximately the same as along the side walls.
02:43
Due to the slope of the floor, rear wall surrounds usually need to be aimed downward more steeply than side wall surrounds.
02:51
QSC makes a special wall bracket that adds another 8 degrees of tilt just for this purpose.
02:58
The number of surround loudspeakers you’ll need in a room is highly dependent on the room dimensions.
03:03
The key factors are room length and width, and the spacing between loudspeakers.
03:09
There’s a formula that works pretty well and we’ve put it in the Downloads section. You’re welcome.
03:15
The exact location of Subwoofers is a little less critical because they are omnidirectional,
03:20
but typically they are located on the floor below the screen, with acoustically transparent draping to hide them from the audience.
03:27
They should be placed slightly off-center to avoid creating a “sound alley” and multiple cabinets should be clustered together
03:35
to take advantage of mutual coupling – which is additional low frequency energy caused by the loudspeakers being placed together,
03:43
without having to pay for additional amplifier power.
03:47
So it’s free. A gift from us to you.
03:53
Alright, let's take a break there and come back when you're ready.

Lesson Description

Learn about aiming screen channel loudspeakers as well as proper surround and subwoofer placement.