1. Physicality and cost
The first and most obvious difference between speakers and headphones is the absolute signal levels they each put out. Almost everything that makes monitors better for mixing is rooted in the fact that they sit a certain distance in front of you, outputting at volume levels potentially capable of annoying the neighbours; and in the home studio, this can be a very real issue, demanding that you keep the level down to a point that may be counterproductive, or simply restricting the times at which you can make music. Headphones, it goes without saying, are the only solution to this if you don’t want to work at low volume.
The space required to correctly set up a pair of monitors can also be problematic if your room is on the small side, and while there are some superb ultra-compact nearfields available that can be squeezed onto the tightest of desktops, a pair of quality headphones might be more effective in terms of analytical listening. And, of course, their portability also enables you to produce and mix anywhere you can take your laptop, which can be very empowering in itself.
Lastly in this opening summary of physical/literal differentials, although headphones can get very expensive indeed if you look towards the top of the market, by and large, a truly great pair of monitors costs much, much more than a truly great set of cans. However, the fact remains that speakers should always be your primary monitoring system, so as long as noise and space aren’t insurmountable deciding factors, if your budget imposes a choice between middling monitors or fantastic headphones, go for the monitors.
2. The listening environment
To get the best out of any monitors, they need to be correctly placed within a room that’s been acoustically treated so as to best cater to their sonic particulars, and you need to maintain an on-axis seating position in order to keep your ears in the frequency response sweet spot. Once again, headphones sweep those technicalities away, effectively comprising a pair of tiny monitors clamped immovably to your head and sealed off from the reverberant influence of the outside world, and so – assuming your particular model is consistent in its fit from session to session – always sounding exactly how they’re designed to sound, no matter where you are.
3. Stereo imaging and crossfeed
With monitor speakers serving as deliberately positioned sound sources in a physical space, the natural timing and volume differences with which the signals produced by each one arrive at both of your ears (the phenomenon known as crossfeed) yield a realistically representative soundstage, which enables precise and accurate placement of instruments in the stereo field.
Headphones, on the other hand, feed directly into each ear, greatly exaggerating stereo width, and thereby clouding your judgment of panning and stereo effects processing – reverb, delay, etc.
Speaker emulation packages from Sonarworks, Waves, Slate Digital et al can compensate for this to an extent, not only simulating crossfeed in your headphones, but some also using psychoacoustics and head-tracking technology to give the impression that you’re monitoring on any of a variety of particular speaker models in all manner of different rooms. These systems can be nothing short of mind-blowing in their relative realism, but while we’d suggest that they’re good for assistive referencing, we probably wouldn’t feel comfortable working up a mix from start to finish on headphones in a virtual control room just yet.
4. God is in the details
Here’s where things get a bit complicated. Due to their proximity to your lugholes, headphones bring quieter sounds to the fore, which makes them unarguably more effective than monitors when you need to home in on the microscopic details of a mix. Much of the time, this is a positive – indeed, it’s the only thing many pro mix engineers actually use headphones for in the studio – but it can also take you down a rabbit hole of overthinking and correcting for elements that are exaggerated by the cans, but that, ultimately, no one would really notice anyway. The last thing you want is for an unwarranted tweak to have a detrimental knock-on effect on the overall balance of the mix, which is why the aforementioned professionals will only ever reference through headphones for very brief periods: they’re checking the details without giving themselves time to get lost in them.
5. It’s all about the vibe
Last but certainly not least, although a good set of cans can deliver a spectacular listening experience, while at the same time providing a largely accurate representation of frequency response and dynamics, there’s just nothing quite like the vibe and energy of a big old pair of speakers moving air across distance. It all comes down to physics: as well as the stereo imaging limitations of headphones discussed above, a single 50mm driver is simply incapable of matching the trouser-flapping sub-bass and pan-spectrum welly of a full-size woofer/tweeter combination, and that inevitably affects every mixing decision you make with regard to levelling and equalisation.
In conclusion, then, while mixing on headphones is just about within the realms of possibility for the experienced producer, if you do find yourself with no choice but to do so, you shouldn’t consider any mix finished until it’s been addressed on monitors, too. This might entail you hiring out a studio for a day or handing your rough headphones-mixed project to someone else to finish, but whatever it takes, getting your mixes heard and tweaked on high-end speakers in a well-treated space is a necessity, not an option, if you want them to stand up to today’s super high production standards.