How to buy Audio for education: How sound systems can make the grade

Old buildings bring acoustic problems, while new-builds can present equally taxing scenarios. This month, AV's audio specialist Roland Hemming answers questions from those wanting to use audio in education

There are two sides to specifying audio systems for the education market. One is the need to have systems for presenting and the other is for students to use them for training purposes, to perform with and to create content. When it comes to presenting, it is critical that people can do so easily and, whenever possible, without technical assistance.

• So when do I need a PA system?

Sound reinforcement for someone's voice isn't really required unless the room or the potential audience is quite large - you might want to consider the option for 40 people or more. But there are other considerations to take into account, such as PC or DVD playback. In this case, even in a very small classroom, a small PA system may be required.

• How do you go about specifying a sound system?

An installation company or consultant should be able to design a system to provide even coverage throughout the room. In most cases this can be done by surveying the space to determine what combination of loudspeakers and coverage will suffice. A larger, more complex project might need an EASE plot.

• So what is an EASE plot?

Almost all professional loudspeakers are measured and their performance is made available as a computer file for the program called EASE. This program lets you import the drawings of your room and input details about the surfaces such as carpet, brick and glass. It will then calculate the predicted performance of the loudspeakers to provide a visual simulation of how the system will perform.

No EASE plot is 100 per cent accurate, but it can give a very good indication of how things will work out and can sometimes show things, such as an odd reflection off a surface, that an indicative design might not have spotted.

• What sort of performance do I need?

In education, flexibility is the key. Even though a lecture theatre may primarily be used for speech, it may also be used for music performances, film screenings and a host of other events.

If budget allows, you should specify it to provide music reinforcement, so some sub bass loudspeakers are probably required. Another consideration is surround sound, which is not necessarily a huge additional cost.

If your budget doesn't run to music or surround sound, I would advise that you at least install the cabling to allow for upgrades in the future.

• When do I need a sound engineer?

In a lecture theatre, it is often good to design the system to work in two modes. A simple mode should allow two or three microphones to be mixed automatically without human intervention. These basic settings can be controlled with a simple wall-mounted remote. However, any event with more microphones is likely to need mixing manually. With modern signal processors, it is easy to design a system that allows either automatic mixing or a manual mixer to be used.

• How do I eliminate feedback?

Feedback is the bane of a sound engineer's life. First of all, before you think about eliminative feedback, you need to design the system so the risk of feedback is reduced. Allow sound designers some flexibility as to where they can locate the loudspeakers. If they are too close, or behind the speaking position, then you are asking for trouble. While many loudspeakers are obtrusive and ugly, if you are too restrictive on their location for the sake of aesthetics, you might have problems.

The other issue is that, even if using microphones, speakers still need to present. If they mumble or stand a long way away from the microphone, no amount of electronics can amplify the sound.

• I've heard that it's best to use line arrays

Not true! Line array loudspeaker systems have become very popular for some audio applications and de rigueur for rock touring, but they are not the ultimate thing in sound. Whether a line array is to be used is completely dependent on the shape of the room, requirements of the system and your budget.

In sound, there are normally several ways to solve the problem. A line array may be better, especially with long rooms, but a very wide room is probably less suitable for one.

• What about video conferencing?

Linking to a video conferencing system is easy. You just send the VC unit a feed from your microphone(s) and accept an audio feed from the VC unit to hear the other side.

The problem comes when you want to use multiple microphones in a room. This is because each microphone in your room will pick up the sound of the remote conference and then try to play that sound back to them. This can lead to an echo as the sound goes back and forth between each site.

It is important, therefore, to have an echo cancellation on each microphone in your system. The echo cancellation unit 'listens' to the remote site audio and then looks for a delayed version of that sound coming into your microphone and cancels it out.

You can't get away with just a mix of all your microphones in your room going into the echo canceller, because each microphone is in a different physical position in your room and will pick up a slightly different version of the sound.

Many digital signal processors have options for echo cancellation cards, so you have plenty of choice.

• What about radio microphones?

Radio microphones are great because they allow the presenter to walk around, but obviously anything people have to hold or wear is more prone to theft and damage. You also have to deal with batteries, though most come with options for recharging in a pod of some kind. Just need to make sure that you have systems in place to properly manage this sort of portable equipment.

• What about other security issues?

Theft can be a problem with most audio equipment. You can buy theft-proof mounts for microphones for putting them into lecterns or tables. You should mount loudspeakers above head height, not only to prevent theft, but also because this is often necessary to give adequate coverage too. Aside from that, the usual precautions apply - tamper-proof screws for racks, security grilles and locating any equipment that doesn't need student access, in a secure room.

• How do we specify systems that can be used as part of students' education?

My golden rule has been to design systems on three levels - for paddlers, swimmers and divers. There are some who just want things to work, while others will want to take an increasingly in-depth view on the equipment.

Do not under-estimate the sophistication of the students. I was amazed on one of my first educational projects when I saw a group of five-year-olds doing a three-camera video shoot with radio mics and vision mixing.

A digital mixer is a boon for education. You can lock users out from complicated settings and recall memories if someone really messes things up. Yet, at the same time, the number of features and settings available can allow the more intense student to tweak, play and learn for as long as they like.

To make equipment last longer I often design systems where the user never actually plugs a cable directly into an item of equipment. They always plug into a connection panel. This lets you restrict students' options so they can't tear the whole system apart; it reduces wear and tear, and also eliminates connection errors.

• Who do I use to design and install?

There are plenty of competent installers out there and many specialise in education. But don't rule out a company where education is not its core business. If it's obvious that the company can competently design and install audio-visual systems, then keep it in mind.

You could employ an independent consultant but the size of job depends on whether you will get sufficient value from doing so - an installer can often do the same work for you.

For installers, education can be a great market to work in. You have clients who are much more likely to pay their bills, more likely to want you to do both the design and build, and are often less affected by the state of the economy. The downside is that education work is often done on a tighter margin.