Originally Posted by mdameron
How is a 120hz LFE sound any different than a 120hz regular sound, and why would you want either coming out of a subwoofer?
I think that, in some respects, there really isn't a difference, except that the subwoofers are intended to play the LFE content. The bass content could actually be the same in some cases, where both the regular channels and the LFE channel are playing the same low-frequency effects, such as an earthquake or a helicopter. But, as long as you have subwoofers in your HT system, the LFE content (which is 10db louder than the content in the regular channels) will be played by the subwoofers and not by any other transducers. So, if you want to hear that content it will need to come from your subs.
Most good subwoofers can play 120Hz content with no issues, so having those sounds coming from the subwoofers would be no problem at all, unless it contributed to localization. The point that Mark was making is that, if you are running your subwoofers hot, as most people do, then all of the frequencies from 10Hz (or whatever) up to 120Hz (and slightly above) will be boosted equally. And, due to the way our hearing works, the 100Hz and 120Hz frequencies may now sound comparatively louder than they should. But, it is tied in part to your bass boost, and to how significant it is.
If you don't boost your bass frequencies to start with, and if there is no localization of the subwoofer, then there may be no reason to ever use anything other than a 120Hz LPF of LFE. But, we don't hear low-frequencies as well as those in our more normal hearing range, which is why most of us need to add bass, after calibrating, if we are watching movies at below Reference levels. Movies are recorded to have frequencies in equilibrium at Reference volume levels. In a home theater, somewhere between about -5 MV and -8 MV may be equivalently loud to what we would hear in a commercial theater. So, bass frequencies could still be in relative equilibrium a little below Reference, although I'm not sure how much below.
But, most of us don't watch movies at -5 MV. I think that the average listening level is much more likely to be around -15, or lower. At those listening levels, the bass frequencies will not
be in equilibrium with what the film mixer and director intended. (This is due to the Equal Loudness Contours which illustrate the way we hear. Our ability to hear lower frequencies, at equivalent loudness, decreases as the frequencies drop--especially below ~120Hz.) So, most of us boost our subwoofers to compensate for our below Reference listening levels.
And, of course there is also a healthy portion of personal preference involved. Some of us may not hear low-frequencies as well as others, or we may just like more bass (or TR) than others. According to what Mark is saying, the more we boost our bass, the more we may want to selectively bring down the upper bass frequencies in the LFE channel, especially if we are using ~80Hz crossovers for the regular channels. That way, we will be restoring some equilibrium between the lower bass frequencies and >80 Hz frequencies. But, it's strictly a YMMV issue. We may hear a positive difference with a lower LPF, and we may not.
I wrote this to go well beyond your original question, but I thought that a slightly more complete explanation of why most of us may boost our subwoofers to begin with might also be helpful in the context of discussing the LPF of LFE. Ultimately, I believe that there is really no right or wrong way to do any of this. To me, audio is an entertainment hobby, and whatever is most entertaining to a particular individual is perfectly legitimate, as far as I'm concerned. But, I think that understanding some of the reasons why
we might wish to change certain settings in our audio systems enables us to engage in better-informed experimentation.