Don’t Get Stampeded By The 7.1 Parade

As a home theater tech critic, I spend much of my time evangelizing for surround sound. I do it unashamedly and with all my heart. I love surround sound and I want everyone else to get as much pleasure from it as I do. But I worry that a lot of people still waiting to dip a toe in the sound-field are turned off by a bunch of seemingly conflicting numbers: 5.1 and 6.1 and 7.1.

I’ve seen this over and over with people who are just getting into home theater as a hobby. When told they have a choice of 5.1 or 6.1 or 7.1 channels, their eyes glaze over and they mumble something along the lines of: “Um, well, I guess I’ll just keep my two speakers and think about it.” When speaking with newbies, I’ve learned to discuss surround as a 5.1-channel medium, which it essentially is, and leave it at that.

Why bug people with a choice that most would rather not make? The expansion of the 5.1-channel standard was born in the movie house, where it’s easier to cover a large space with surround effects if you add a back channel served by speakers in the back of the house.

In film exhibition, 6.1- and 7.1-channel systems make sense. At home, however, 5.1 channels are quite enough. It’s easy to generate a solid sound field in a small space with three speakers in front and two on the rear of the side walls. To me it’s self-evidently nonsensical to have four surround speakers outnumbering the three in front.

Your family’s attention is riveted on the screen and that’s where a home surround system should deliver most of its firepower. Adding more channels gives your surround receiver more work to do. That’s never a good thing. Despite the “100 watts per channel” specs you see in spec sheets, the majority of surround receivers measure at more like 35.

So when an action-movie soundtrack swells up, it drives the receiver into clipping. This might sound like a slight deflating of dynamics. Or the sound may get harsher as it gets louder. In the worst-case scenario, the receiver overheats and shuts down. If you don’t like what you hear when you turn up the volume, clipping is what you’re hearing.

There are two ways to minimize clipping. One is to dump your receiver for separate components – a multi-channel power amp and a surround preamp-processor. This will cost you more money and make your system bulkier and more complex. The alternative is buy speakers with a high sensitivity rating, measured in decibels (dB), say in the low to mid nineties. Unfortunately they’re not always the best-sounding ones. (Klipsch is one of the rare exceptions.)

Clipping is a fact of life in all except the most lavish home theater systems. But the goal should always be to minimize it. And adding needless surround channels makes it worse. When most folks go out to buy a surround receiver, what’s uppermost in their minds is the price point, not the size of the power supply. The slow, sinking feeling comes later – when they turn up the volume and don’t like what they hear.

At this point I should define a few terms. Feel free to skip this paragraph if you’ve just had a heavy meal. Dolby Digital and DTS are the surround formats used on DVDs; Dolby Digital also plays a role in DTV broadcasting. They originated as 5.1-channel formats. Their expanded cousins are Dolby Digital EX, also known as THX Surround EX, since the two companies co-developed it; and DTS-ES. In Dolby Digital EX, the side-surround channels are discretely encoded, while the back-surround channel (singular, though it may be served by two speakers) is derived from the side-surrounds by a technique called matrixing. Or as I prefer to call it, fakery. DTS-ES comes in two forms, Matrix (with the back-channel information faked) and the all-too-rare Discrete (with the back-channel information encoded in its own discrete channel). If you understood what I just said, you’re a fellow drooler; if you didn’t, you’re probably getting annoyed and losing interest, which is precisely the point I’m trying to make. I’ve limited myself to the barest essentials and just look at the length of this graf. Having to reread it makes me queasy.

If you’re worried about missing out on back-channel information in surround soundtracks, I’d advise you not to fret over it. Most DVD soundtracks are either Dolby Digital 5.1 or DTS 5.1. The high-res music formats, SACD and DVD-Audio, are strictly 5.1-channel affairs with no 6.1 or 7.1 equivalents. If you feed a 7.1-channel receiver with a 5.1-channel signal, it will usually fake something for the back-surrounds using Dolby Pro Logic IIx processing. For my own part, I’d rather listen to five (.1) honest channels and dispense with the sonic smoke and mirrors.

With the marketing of 6.1 and 7.1 surround, the industry has decisively outwitted itself. It has convinced many consumers to buy new receivers and more speakers. But it has also undermined the 5.1-channel standard, which is more appropriate for the home, slowing the acceptance of surround sound in general.

All right people, fess up. How many speakers are you using: five, six, or seven? And those of you who “upgraded” from 5.1, do you really feel your system has started sounding significantly better?

Mark Fleischmann is the audio editor of Home Theater and the author of Practical Home Theater (http://www.quietriverpress.com/).

The views expressed here are solely those of the author and do not reflect the beliefs of Digital Trends.

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