Does your system have a subwoofer? Shouldn't your main monitors be able to handle the bass?
It is a law of nature that loudspeaker design is a three-way trade off. You can have any one of these features, or a compromise of any two, but you cannot have all three...
- High-fidelity sound quality - the sound the speaker produces corresponds very closely to the input signal.
- Loud, with deep bass and plenty of it.
- Compact and convenient size.
Very few speakers are as big as they need to be to produce the lowest frequencies our ears can hear at anything approaching an adequate level. And the vast majority are far too small.
Nearfield monitors struggle to get down to 70 Hz and below, and since our ears are sensitive down to 20 Hz, and various bodily organs even below that, plainly we are not hearing everything we really ought to be entitled to hear.
The best answer is simply to make speakers bigger. It really is that simple. But current preferences dictate that manufactures concentrate on compact loudspeakers, particularly for domestic use, so we need an alternative.
An alternative is to dedicate one speaker to low frequencies, so the two (or more in a surround system) conventional speakers can handle their own preferred frequency range.
Only one low frequency speaker is necessary because the ear isn't particularly sensitive to the directionality of low frequencies, nor to their stereo content. So the low frequencies of the two channels (or more for surround) can be mixed together and fed to this special speaker, known as the subwoofer, sometimes simply as the 'sub'.
For domestic purposes, this really isn't a bad compromise. And since the subwoofer can go anywhere in the room, it doesn't have to be all that small (behind the TV in the corner is common).
However, the problem is that the output from the subwoofer has to be closely matched to the conventional speakers, so where the conventional speakers are starting to roll off in the bass, the subwoofer is smoothly taking over. This doesn't happen all by itself, but by careful alignment of amplifier power.
For domestic purposes, it's not that much of an issue - people are not that bothered. However, if you were to use a subwoofer for monitoring in the studio, then it is vital that the output is well matched, and the overall frequency response is flat.
Otherwise your mixes will end up with too little or too much bass to compensate for the errors of your monitoring system.
To rely solely on a subwoofer system for monitoring would be a risky practice, but as one of a selection of monitoring systems, it could provide an additional perspective on the way an increasing number of people listen at home.