Originally Posted by ComputerTech0903
If you had 18 inch subwoofers in your rear speakers would they get any use? Do movies have ulf frequencies in the rear channels?
By "rear channels in 5.1 setup" I assume you mean left & right surround
Righto, all main channels including surrounds are full range channels so, in theory, yes there can
be deep bass in the surround channels. In practice however, sound engineers know that deep bass has a better chance of being reproduced with authority if it's placed in the .1 LFE channel or (to a lesser extent) in the three front channels, so that's where deep bass is generally placed. Nobody's holding a gun to their heads, so no doubt there will be exceptions to this.
If you really wanted to get use out of 18 inch subs for the surround channels, you would need to look carefully at your processors bass management implementation. Most processor's bass management will re-direct the LFE channel to all speakers that are set to Large when Subwoofer = None (for example) is enabled in the setup menu.* You just need to ensure that the processors setup allows for Surround speakers = Large in combination with Subwoofer = None and you'll get LFE redirected to your 18 inch surround subs.
* Be aware though that bass management is carried out in the digital domain and for the LFE to be re-directed to main channels, some form of digital attenuation (Dolby call it DRC I think) is enabled to prevent the possibility of a summed signal exceeding 0dBFS. As a result, it won't be as loud for a given master volume setting and may lack some dynamics.
[Hmm... ComputerTech0903 eh, the bloke who started: http://www.avsforum.com/t/1425262/are-audio-companies-all-involved-in-a-huge-conspiracy
? 3000+ posts and a mods nightmare... you legend!