An introduction to commercial audio
In the first part of a series for the residential installer starting out in the field of performance spaces and commercial audio applications, Jason Allen looks at the new issues and challenges that you’ll face and how to get the resources, education and help you’ll need.
If you’re thinking about expanding your business from primarily residential installation to more commercial jobs such as school halls, churches and other performance spaces, you’re going to start coming across a lot of new issues and requirements. And the biggest part of the learning curve is going to be finding out what these are and how to deal with them. There’s no central resource for you to sit down and absorb this information, so you’re in the classic situation where ‘you don’t know what you don’t know’.
All of the principles of sound reproduction, inputs and outputs, control systems and video that you’re familiar with in a complex domestic environment scale up pretty neatly to a performance space like a small auditorium. Sources come in, audio gets processed, sent to an amplifier and then to a loudspeaker. All of this remains the same, it’s just the equipment that does the job that changes.
The most pervasive difference between a domestic entertainment system and a small PA is how people interact with it. PA systems have more human contact, involvement and input at every step of the signal chain than a domestic system. This causes huge variables, and it’s the nature of the human interface that is the biggest design and implementation challenge.
The differences start at the sources; a domestic system typically has static line sources like Blu-ray players and iPod docks. A PA has these as well, but with the added complication of microphones. This is where the variables start – what kind of microphone do you need? What’s it being used for? Does it move? And because it’s people that use the microphones, you can guarantee that some won’t know the best way to use it, the best place to put it or what they should avoid doing with it. Line sources like computers and synthesisers will need DIs.
Get on the mic
Next up is how to deal with the inputs. You’re going to need to mix them, process them, and send the results on to amplifiers and then to loudspeakers. Sounds straightforward, but there are a multitude of ways to accomplish this that all hinge of the basic question of who is using the system and for what.
Let’s take the example of a school hall. The school wants to use it for assemblies (one lectern microphone and CD player), parent committee meetings (lectern mic, roving radio microphones for Q&A) and musical performances (three or four vocal mics, line sources from keyboards and other electronic instruments, maybe some instrument mic’ing). The big question here is who will be operating the system? Will it be someone with knowledge of how to use a mixing desk or do you need to look at an automated solution? Sometimes, the system will need to be capable of doing both – automated mixing in a DSP unit for the meetings and assemblies, plus the capability to switch over to mixer input when they want to put on a musical.
In or out of the box?
Choosing a mixing desk, DSP unit or combination of both is going to depend on a few factors. There’s the number of and type of inputs to count up, number of outputs needed (which depends on the number of individual mixes that need to be distributed) and functionality. Is there an operator? How knowledgeable are they? If you’re looking at using a mixing desk, do you want to go down the digital path so that you have a combination of simple presets combined with the ability to take complete control?
DSP and other ‘in the box’ solutions are generally a good choice for an environment that needs sound reinforcement but doesn’t have specialist staff. Options in the market range from fixed architecture units that are essentially mixing desks without controls, in which the signal path is through a set series of processors, to open architecture units with almost limitless processing and I/O options. Open architecture units are programmed via computer, and the designer can implement any kind of processing in any order they want, as well as have it change states on command.
The one thing the fixed and open architecture processors have in common is that they are designed to be controlled from separate control panels, usually wall mounted. These can be proprietary accessories with a couple of buttons and a screen, or full-blown touch screen control systems from AMX or Crestron. The general rule seems to be that the simpler the operation becomes for the user, the more programming and setup needs to be done in the background.
Power ‘em up
After all this audio has been mixed, bussed and sent to an output, we then come to the amplifiers. These could be rackmounted back-of-house and connected to the mixing desk via copper multicore, or they could be built-in to the loudspeakers and on the end of a Cat5 run. For smaller systems, they could even be amplifier ‘cards’ inserted into a modular DSP unit, feeding smaller surface mount speakers. All of this will depend on the target performance for the space and the resulting loudspeaker choice.
The Speaker of the House
Loudspeaker choice, based on the power, performance and coverage needed, is a decision that will dictate what amplification you need and what capabilities your mixer, DSP unit or loudspeaker system processor will have to have. If you’re doing a large, irregularly shaped hall, you might need to add additional loudspeakers to cover side areas that the main left and right can’t reach. If there room is long, you’ll need delayed speakers to keep up levels near the rear. If it’s a theatre style auditorium, you’ll most likely need a left-centre-system flown quite high with additional front fill.
These requirements will dictate how many busses your mixer needs, and how many outputs your DSP and/or system processor requires. Every loudspeaker that is not part of the main left-centre-right array will need to have its signal delayed to ensure time alignment and phase coherence. That’s an individual output for each delay. If you’re using left-centre-right, you’ll want your mixer to have that capability. If you’re using subwoofers, either your DSP or system processor will need to handle the crossover and separate outputs.
Predicting the Future
Determining whether or not a loudspeaker system will be able to achieve the coverage and volume required is thankfully a lot easier than it used to be. Though there is no substitute for experience, there are a lot of software products on the market that can help you predict performance and figure out the optimal way to install the system.
Some software, such as EASE, is astonishingly complex and expensive, and is mainly used by consulting engineers. A lot of loudspeaker manufacturers have their own, usually free, predictive software tools that let you model your room and its behaviour with their products. And that’s the difference – an open platform like EASE lets you model anything in any space you can design, whereas a manufacturer’s free tool is usually limited to basic room shapes and only that manufacturer’s products.
Tune it Up
Once you have the system installed, there’s the need to tune, optimise and sometimes document its performance. Again, there are a variety of hardware and software tools on the market to help you accomplish this. Rational Acoustic’s Smaart software, paired with a decent analysis microphone and computer audio interface, is a widely accepted optimisation and measurement tool in the industry. If there’s a contractual to provide documentation on commissioning, Smaart will most likely be accepted. If the contract isn’t that rigorous, there are even free apps for iOS devices available that can be helpful aids to tuning by ear.
In some public spaces, the system might be required to achieve a particular STI score. That’s Speech Transmission Index, and is an international standard that quantifies how intelligible any voice announcements are in a particular environment through a particular PA. As you can imagine, this is important for any system that might have to carry evacuation or emergency announcements. STI is measured on a scale of 0 to 1, 0 being terrible and 1 being perfect. Minimum STI in public places is usually required to be at least 0.5. Again, this can be designed for and verified with specialist tools.
I Fought The Law…
Another legal requirement that you will almost certainly encounter is the need for hearing assistance. The Disability Act mandates in law that “A hearing augmentation system must be provided where an inbuilt amplification system, other than one used only for emergency warning, is installed..” and goes on to clarify that this means in any “auditorium, conference room, meeting room, room for judicatory purposes, or a room in a Class 9b building.”
A Class 9b building is defined as any public assembly building. So that’s basically every church, school and theatre in Australia.
The legislation goes on to state what the acceptable performance criteria are to satisfy these requirements. For most rooms, this means installation of a copper hearing induction loop under the floor. These can be difficult to retrofit, so there are other receiver/transmitter based solutions if a loop is not an option. The act then dictates how many receivers/transmitters per person you need dependant on the capacity of the room.
Call the IT guy
As the world has gone digital in almost all of media delivery, the commercial end of the market is also turning digital for its signal distribution. Audio signal distribution via standard Ethernet switches and Cat5 cabling is becoming more prevalent. It’s cheaper, easier and more flexible than analogue. Buying and running a 24 microphone input, eight output copper multicore from a stage to a mixer can cost thousands. The equivalent amount Cat5 will cost maybe $20, and carry hundreds of channels.
While there are many technologies available that carry multi-channel audio over Cat5, there are currently two competing for market dominance. The first is the newer, as yet not completely IEEE ratified AVB (Audio Video Bridging) and the second is Dante, a suite of tools from Sydney company Audinate that has been massively internationally successful. Dante carries audio and control signals only, and interestingly, can run on an AVB network. It can run on any old managed Ethernet switch, as long as it’s 1GB. AVB carries audio, video and control, but needs AVB compatible switches, which aren’t common yet. Both make life much, much easier for the tech-savvy installer.
Now hear this…
This has been an overview of the many different parts of a PA system and how decisions about one section affect the other. There are a huge amount of variables, hoops to jump through and things to learn if you’re just starting out. If you can pick the brains of an experienced integrator, fantastic. But you’re really going to learn by doing. You need someone who’s got your back while you’re doing it.
Supply and Demand
Your biggest asset and most important resource if you’re trying new markets that require new skills is going to be your supplier. You need to develop a relationship with a well-regarded commercial audio supplier that can provide most, if not all, the equipment you need for the job but most importantly, the knowledge and back-up to make it all work.
A good supplier employs technical specialists that will help you quote on jobs, design systems and install and commission them properly. It’s worth their while to train you to competently use their products as it means business for you and sales for them. As you do more jobs and expand into more complicated gear, they will be there to teach you, help you and make sure you’ve got everything you need to do the best possible job. You will never have a better business partner than a dedicated supplier.