Design & Best Practices: Part 4

Cinema 101 Training : Design and Best Practices

1 ) Introduction

5m 33s

3 ) Product Catalog

21m 41s

Video Transcript

Design & Best Practices: Part 4 6m 46s
Welcome back! Let's pick up again where we left off.
Once a system is installed, it’s time for calibration and tuning.
Using a decibel meter set to the C-weighted setting Pink Noise is run through each loudspeaker individually,
or in groups of surrounds, which we’ll cover here in just a minute.
The most critical loudspeakers in the sound system are the Left, Center, and Right Screen Channels.
This is where most dialogue, music, and effects are localized. All three loudspeakers should be well-matched.
Any inconsistencies in these loudspeakers– especially in the human voice frequency range – can get really distracting for the audience.
Let’s look at the basic SPL targets for each loudspeaker type starting with these.
For each screen channel, the level should be set to achieve 85 dB C weighted at the 2/3 distance from the screen.
For surrounds in a 5.1 system, each Left and Right array should be set to 82 dB.
For a 7.1 system, Left side channel plus the Left rear channel, and Right side plus the Right rear channel should be set to 82 dB also.
For subwoofers, don’t use the SPL meter.
If you were to use a typical SPL meter, the narrow bandwidth of the subwoofer would read too low compared to a full range signal.
SMPTE Recommended Practice RP200 specifies a method using a Real Time Analyzer to set the subwoofer level.
Look at the level of the center channel on the RTA at mid frequencies and set the subwoofer level to be 10 dB higher.
The result is that the subwoofer ends up with the same level in its passband as the screen channel loudspeaker.
The most common calibration tool used in Cinema is the Real Time Analyzer, the RTA.
Most RTA’s use 4 or more microphones positioned in the seating area, a pink noise generator, and a multiplexer to create a “spatially averaged” measurement.
For screen channel loudspeakers, response should approximate the industry-standard “X curve”, which is defined in SMPTE standard 202.
You can see that the X curve has plus and minus 3 dB tolerance.
The good news is that for a properly designed, well-behaved loudspeaker, the high frequency loss due to sound through a typical perforated screen
along with the loss to natural “air” attenuation already approximates the X curve – without the need for a lot of equalization.
If a loudspeaker seems to require a lot of equalization – say, more than a few dB – there is probably something else wrong with the room acoustics,
the wiring of the loudspeakers, or maybe even the loudspeaker itself. In any of these cases, equalization will not fix the problem!
A high quality screen channel loudspeaker should look roughly like this on an RTA screen.
The Yellow line is the X curve, and the Red lines are the 3 dB tolerances.
This particular loudspeaker is a popular QSC model with our own Intrinsic Correction processing – and it required no additional equalization to approximate the X curve.
Now let’s take a look at how it all goes together in a system design.
This is just one example of a Basic 7.1 Sound System for a medium sized room, let’s say about 300 seats.
Three bi-amplified screen channel loudspeakers at Left, Center and Right. Two dual-driver subwoofers. And 18 surround loudspeakers.
Let’s assume this will be a fully-networked Q-SYS application, which provides all loudspeaker signal processing and routing,
and network control and monitoring of all of our system parameters.
Since we’re using our Q-SYS network amps, this entire system can be powered by just two 8-channel amplifiers.
Now let’s add some interconnections.
QSC recommends wiring the Left and Right loudspeakers together on one amplifier, and the Center loudspeaker on the second amplifier.
In the very rare case that an amplifier might fail, you can still have sound coming from the screen so it doesn’t ruin a show before the amp can be replaced.
The Center channel is powered by two channels of the second amplifer.
If there are multiple subwoofers, as we would recommend for this example room, you would also separate the subs onto the two amplifiers for the same reason.
Note that in this example, the subwoofers are each powered by two amplifier channels in parallel mode.
And we’ll use the same idea for the surround arrays.
The six rear wall surrounds can go on two channels of the first amp.
Surrounds for a 7.1 format system should be grouped and wired in parallel – and you can easily put 3 or 4 surrounds per channel on QSC amplifiers.
The remaining channels on the second amp feed the Left and Right wall sound arrays.
And you’re done! A simple and elegant, high performance 7.1 cinema sound system using just two amplifiers, with complete signal processing, control and monitoring.
Only possible, by the way, with the Q-SYS Ecosystem.
Once the products are selected, and the system is designed, installed, and calibrated - then it’s time for commissioning and final checking.
Always play some familiar content and walk around the entire room. Listen to every loudspeaker.
Listen to the dialogue. For even coverage around the room, for reflections and echoes, for noises that shouldn’t be there like buzzes, and rattles.
Look for any bright metallic surfaces from construction materials, or light sources through the perforations of the screen.
We realize that any room that is not designed as a purpose-built cinema will present a number of inherent challenges
that might make it impossible to adhere to all of these guidelines and best practices.
But the closer you can get to these guidelines, the better overall audio and visual experience you’ll be able to deliver.
And finally, don’t forget to check out the resources we’ve put in the Links & Downloads section.
Alright, that's a lot - I know. Let's take a break for now and come back again when you're ready.

Lesson Description

Design & Best Practices: Part 4 6m 46s

Specifics regarding system calibration and commissioning are covered along with interconections of a basic 7.1 system using Q-SYS.