Understanding Cabling - Don't Get Stuck Having the Wrong Cables

When you are preparing to give an important presentation, there is no such thing as an unimportant detail. Every component needs to be functioning correctly — the PowerPoint file, the computer it's running on, the projector, the screen, the microphone — and, more importantly, it all needs to work together.

The "nerve system" of your presentation setup is the collection of cables that tie it all together. Power cables bring electricity to the pieces that need it, while other cables route audio and video signals from their sources to the appropriate devices.

Video Connections

If you are setting up for your presentation, it will help you to sketch out the setup. Right now we will assume it is a simple, straightforward setup where you need to present a PowerPoint program with both audio and video.

There are several ways that modern laptop computers make video signals, normally routed to the screen, available to other, external devices. If your laptop has an S-video output, an S-video cable would be needed to carry the video portion of your presentation — and, naturally, that cable would plug into the S-video input on the projector.

If you use the more common monitor out port, you would connect the cable to the projector's RGB or VGA input. All modern projectors have these ports; some have two of them.

The Sound Side

There are a number of ways to amplify the soundtrack of your presentation, but the first step is always the same — getting a 1/8" stereo mini-plug, since this is the standard audio out port for laptops. There are some newer devices that route sound via USB and FireWire connections, but we will take them up in a different, future article.

Now, the A/V panel on your projector is an area with which you should become intimately familiar — everything you will see and hear in your presentation has to connect here somehow. In fact, it is often helpful when determining cabling needs to start at the end, the projector A/V inputs, and work backwards. You will at least become familiar with the kinds of connections your particular projector has.

The fact is, not many of them have 1/8” audio inputs (also called “line in”) so you will most likely need a special cable that has that jack on one end, and a pair (for Left and Right stereo channels) of what are called RCA connectors on the other. These are the connectors used in most consumer stereo gear.

If you want the highest quality sound, of course, you would go digital; if your computer has a S/PDIF digital out, you can attach that via a S/PDIF cable, assuming the projector has a S/PDIF input. The cables can be either optical or coaxial in construction.

Almost Ready for Prime Time

The final connection will be from the projector’s audio out to the speakers. Some projectors have small amplifiers in them than can drive passive (unpowered) speakers, while other would require the use of active (self-amplified) monitors. The projector’s A/V panel or user manual should clarify this.

There are a number of common ways to connect speakers. The first is with a cable that has 1/4" stereo plugs on each end (sometimes called "phone" plugs) and are available in various lengths, or easily made to order. These are the exact same cables used to plug an electric guitar into an amplifier.

Other connections in wide use are old-fashioned speaker wire on the one hand, and banana plugs on the other. You will know from the back of the speakers themselves what is needed; if you see a strange hole that’s not quite right for a phone plug, that’s a banana plug jack. Otherwise, you will most likely see two wiring posts or a ¼” phone jack.

Sight and Sound Check

The most effective way to see if all your cable work was done correctly is to turn everything on and do a “sight and sound check.” Power everything up in order — laptop, projector, active monitors if you have them — and then try the mic. Remember that you want your signal strength (volume) as high as possible coming from your computer, because if you try to amplify a low signal with the projector (or anything else), it will be very distorted.

A few reminders: Cables actually can “get broken” and fail on you. Making too many tight bends of the cable, using too much force on insertion or removal, forcing plugs into damaged or wrong-sized jacks — these can all render a cable useless. And there are quality differences between the cheapest and best, as with any product; if your professional life is being support by A/V cables, make them good ones.

With just a little use, every kind of connector will become familiar to you. As you work more and more with your laptop and projector in tandem, you will look back (soon, perhaps) and wonder just why it was you had to read an “intro to cables” on the Internet!