Production

Why You Should Use a Direct Box

A discussion about direct boxes might seem like a terribly simple concept for some. But to be honest, this topic confused me for at least one or two seasons as a new live sound tech.

In order to address the reason why we should do something or use some tool or technology, we need to know what we really plan to accomplish. When it comes to audio, first and foremost we want it to sound good. A good direct box can help you achieve that goal. Let me explain.

In live sound, there are two general types of analog audio signals that we work with: line level & mic level. (Yes, there are nuances to this, but let’s keep it simple for this discussion.)

Mic level signals, like those generated from a microphone, are generally low impedance (LoZ) balanced signals transmitted over a 3-conductor shielded wire. This type of signal and cable is very effective at transmitting audio over long distances and with minimal electrical interference.

Line level signals can come from things like guitars, keyboards, CD/MP3 players, and other equipment. This signal is often a high impedance (HiZ) unbalance signal transmitted over a 2-conductor shielded wire. This type of signal and cable is typically only good for distances up to 20’ before you run the risk of greater electrical and signal interference.

NOTE: Some professional audio equipment will send out a balanced line level signal that can be transmitted longer distances than unbalanced cables. When it comes to distance and quality, the big issue is the unbalanced or balanced signal transmission, not line or mic level concerns.

So now we know that balanced “mic level” signals are better for distances over 20’.

Well, then…How do we get a high quality signal from the unbalanced line level output of an acoustic guitar or keyboard back to the mixing console?

We use a direct box.

A direct box contains a small electrical transformer that converts the unbalanced “line level” high impedance signal to balance “mic level” low impedance. This allows you to transmit the audio from an instrument to the mixing console with minimal interference.

And the added benefit is that most live sound mixing consoles predominantly have balanced microphone inputs, so this one signal conversion on stage at the instrument location works perfect!

Here’s a good rule of thumb to follow: If your cable has a ¼” connector and only has two segments (Tip & Sleeve), then you’re dealing with an unbalanced line level connection. If your cable has a 3-pin XLR connector, then you’ve probably got a balanced low impedance connection.

You can save a lot of stress and bad sounding audio by using a direct box, also called a DI for “direct input”, by converting signals from unbalanced to balanced.

And here’s something else you should know about direct boxes: there are two types – Active and Passive.

Active direct boxes require phantom power from the console, battery, or other power supply. This power is used to run the electronic circuits contained in an active direct box.

Passive direct boxes do not require power to operate.

There are advantages and disadvantages to both types of DIs.

While active DIs need extra power, they often sound better, since they add some extra signal processing and can provide a little boost to the audio signal. But even though a passive DI doesn’t have any fancy electronics inside, a quality DI with a good transformer can sound just fine and work for years.

If you’re in the market for a new direct box, I’d recommend trying out a few different types and see what works and sounds best in your application. Just don’t forget to turn on phantom power for any channels using an active DI.

I’ve personally always found that Radial and Whirlwind provide reliable and quality direct boxes. In fact, Radial has a really slick online tool that helps you select the right direct box for your needs: http://www.radialeng.com/roadmap.php

And remember…The ultimate answer to your audio Why? should be: “Because it sounds better!”

JAMES WASEM

Author / Audio Engineer
Great Church Sound | Missoula, MT
greatchurchsound.com

James Wasem has been fascinated by sound and electricity from an early age. His love of music and technical gear made sound engineering and systems integration a natural pursuit. James has spent the last 20 years performing and touring in bands as a drummer, mixing live sound for churches, schools and theatres, and working as an audio systems installer and designer.

Though involved in highly technical fields, James has a passion for making things simple to understand and easy to use. It was from this passion that the book Great Church Sound – a guide for the volunteer was born. James believes that technical ministry volunteers provide a critical service for their congregations and should be well equipped with quality tools to help them grow in craft, skill, and spirit.

James and his wife Kate (who also provided the illustrations for Great Church Sound) live in the beautiful Rocky Mountains of Missoula, Montana.