5.1 audio - why?

[EvilBiker]

I've gots a question!

What is it with this "5.1" audio form factor? Reason I ask is that I'm considering buying a DVD player, and I want to set up a nice home theatre system, but can't see myself buying another sound system just to implement 5 channels.

I've got a pretty decent system for my PC - I built up a four channel 100W amp for my sound card, and searched around to find second-hand hi-fi speakers for it, eventually tracking down two pairs of Mordaunt Short boxes, which work nicely. I didn't bother with a subwoofer channel, as I thought that there would be enough residual bass in the other 4 channels to do without the 5th. Silly me, it seems.

After discussion with a geek friend of mine, I discovered that the bass channel is pretty necessary for real "punch". Bah, means I have to build up a little circuit to recombine the bass into the other 4 channels. No real problem, but it got me thinking - why did they split off the bass?

My initial thought was that it was an economic decision. Sell a sub-standard sound system (low wattage) with only one powerful channel needed to supply the bass. Four channels only need tweeters and maybe some midrange, speakers are small. However, my friend said that it was more than that - apparently the bass channel is extremely powerful, more so than in normal home audio systems. I have no idea why, besides the obvious need to deal with higher sound pressure needed to distribute low frequency sound properly.

Taking a look at some audio system specs, I noticed that power output for the subwoofer for highish-end systems is in the region of 70W, with a frequency response down to 30 Hz, if you're lucky. Nothing special, really - my little home-built can do 30 Hz no problem.

So what's the big deal? If I have an amp that can handle 4 channels with a bass response down to 30 Hz for all those channels, why the hell do I need a subwoofer?? Surely combining the bass from all channels into one degrades the surround effect? OK, low frequency does not add as much to the positional effect as higher frequencies do, but isn't this still a copout?

EB

 

[shanek]

What is it with this "5.1" audio form factor? Reason I ask is that I'm considering buying a DVD player, and I want to set up a nice home theatre system, but can't see myself buying another sound system just to implement 5 channels.

I can only presume you've never heard it...Especially when your DVD player and receiveer both support DTS (which is MUCH better quality than Dolby Digital), the sound is crisp and clear with pinpoint accuracy. You can pick out every single voice in the baptism scene in O Brother, Where Art Thou? for example.

After discussion with a geek friend of mine, I discovered that the bass channel is pretty necessary for real "punch". Bah, means I have to build up a little circuit to recombine the bass into the other 4 channels. No real problem, but it got me thinking - why did they split off the bass?

To get better definition. There are problems with combining the bass from the other channels, which is that, depending on how they're mixed, sometimes you might be doubling-up the bass sound from two other channels, and that might overpower a bass from another channel that's supposed to be as loud.

So what's the big deal? If I have an amp that can handle 4 channels with a bass response down to 30 Hz for all those channels, why the hell do I need a subwoofer??

If your speakers can already handle the frequencies, then the only issue might be one of placement. A subwoofer allows you to place the bass output for optimum response since you're more worried about how the sounds travel around the room than you are what direction they're coming from.

Surely combining the bass from all channels into one degrades the surround effect?

Not if you filter out frequencies above 100-200Hz. Your ears cannot distinguish direction well at lower frequencies.

OK, low frequency does not add as much to the positional effect as higher frequencies do, but isn't this still a copout?

No, it's a very real effect. As I said, positioning it for optimum sound has a greater effect than any positioning you can get. You just don't notice which sound the direction's coming from, and so your brain considers it to be coming from the same direction as the companion signals in the higher frequencies coming out the other speakers.

 

[Bikewer]

I'm no audiophile, but the big advantage to surround sound in gaming is that you can tell which way the enemy is coming....

The subwoofer makes nice explosions....but my wife complains.

 

[WildCat]

Just listen to the opening battle in "Saving Private Ryan" in 5.1 and you'll understand.