I hadn't considered the cutoffs different engineers might choose to use and how that could impact playback, I just always assumed whatever cutoff was above my crossover setting. On my system where the sub carries a bulk of the low end load, this probably translates positively to having a fuller/richer bottom end when no crossover is used, but I do wonder if it hypes some of the frequencies that overlap with the other channels on those same systems that don't use a crossover.
Chances are there 's always a crossover in use in your system, somewhere.
On typical systems with a subwoofer, there is a strong low pass filter (LPF) function in the AVR that operates only on the LFE channel before the signal goes to the sub This filter is often called the '
LPF for LFE' in AVR user manuals. Typical default setting is 120 Hz (which is also the bandwidth of the LFE in Dolby 5.1 mixes), though some AVRs give users a choice of settings. Denons offer settings from 80 to 250 Hz.
(NB this is NOT the bass management setting -- usually recommended to be 80 Hz. That's the freqency at which the AVR splits bass out from the 'small' front and surround channels, to be sent to the subwoofer. A different thing! And a different setting in your AVR, see below.)
Thus, for a typical system with a subwoofer, it doesn't much matter what higher frequency content above ~250Hz the mixer sticks
into an LFE track. It gets filtered out by the LPF for LFE.
Of course in a bass managed system, in addition the LFE content, the subwoofer
also sees redirected bass from 'small' main and surround channels, eg. content below 80z (the usual recommended setting). This crossover can ALSO be set higher in the AVR...as high as 250 Hz on Denons (and as low as 40 Hz).
And finally
on top of all that, the subwoofer itself will have a built-in low pass filter, usually a variable 'crossover' dial. Usually it's best to turn this 'off' if possible. The subs I've owned never had an 'off' switch for theirs, so best practice is to set it as high as it goes. Which is usually again....~250 Hz. The subwoofer only 'allows in' content below this.
So, the interaction between LPF for LFE setting, bass management crossover, and the subwoofer's own low pass filtering, is something to consider when pondering what will be coming out of your subwoofer.
The upshot is that:
- the subwoofer itself will
never output much content above (at most ) 250 Hz. At some stage, virtually everything above that, from any channel, gets filtered out by one means or another ('much' and 'virtually' because filters aren't necessarily brick walls, they are steep roll-offs).
- But allowing, e.g., 250Hz instead of 120Hz into subwoofer output, certainly could make a sonic difference. That's a whole octave of audio.
- But keep in mind, the stronger the >80Hz content of the subwoofer output is, the more likely you are to 'locate' the subwoofer in the room, which usually you don't want to do.
What I'm not sure of is what happens to LFE in systems that run full range speakers, no subwoofer. There, to hear the LFE content, it needs to be folded into main channels. Does LPF for LFE act then? I don't know!
