What Do Those Surround Sound Number Specs Mean?

What Do Those Surround Sound Number Specs Mean?

Taryn Williford
Feb 7, 2011

Not since 4-8-15-16-23-42 have numbers been so confusing. Although these digits aren't on a mysterious-island-based network TV drama, they're on the displays and packages of sound systems as you walk through the aisles of your local big box retailer. 2.0 Stereo? 4.1 Surround? 5.1 Side? But what does it all mean, Basil? Here's your quick guide.

So What Does 5.1 Really Mean?

If you're looking for a quick, one-sentence answer as to what those numbers on sound system packages mean, here you go: It's the number of speakers, with a ".1" added if the system has a subwoofer.

But really, it's more complicated. The number actually indicates the number of channels, not speakers, although for many consumer systems it's the same thing.

For example, a "5.1" system, the most common living room surround sound setup, includes 5 full-range channels plus one "Low Frequency Effects" (a.k.a. LFE, a.k.a. "the subwoofer") channel.

What the Heck is this Slash Mark?

Sometimes, you'll see system specs with slashes in them, indicating the positions of the speakers in the room.

Reading the number from left to right, as we're so apt to do in the English language, you'll read the number of full-range channels in front of the listener, separated by a slash from the number of full-range channels beside or behind the listener, separated by a decimal point from the number of limited-range LFE channels.

For example, system noted as 3/2.1 is technically the same as a 5.1, but it's telling you that the system has 3 front channels, 2 side channels and an LFE channel.

And Specs with Colons?

A notation with a colon is expanded to include matrix decoders.

Again, the number before the slash is the number of front channels. But then the numbers directly before and after the colon indicate the number of rear speakers and the number of channels in the rear in total, respectively.

Sound confusing? It's really not. Dolby Digital EX, for example, has only 5 regular speakers, but also has a sixth full-range channel incorporated into the two rear speakers with a matrix. It's specs are noted as 3/2:3.1, meaning there's 3 channels in the front, plus three more coming through the rear 2 speakers, plus the subwoofer.

Still Confused?

Here's a great chart from Wikipedia that shows you which channels are included in many popular specification notations. Print it out and take it with you when you're shopping. It beats flagging down a sales guy.

(Top Image: Flickr member Sujay T. licensed for use under Creative Commons)

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