Plug your ears, you studio monitor lunatics! Or maybe I'm the lunatic, and you're the norm.
I've been mastering on and off for about 15 years, and just as any other engineer will attest it's been a a lot of work over that time to make everything perfect in every way. From the quality of the source mix, to the room, to the speakers, the analog chain, plugins, and my own ears. I can say with certainty having a set of mastering ears is the single most important tool an ME has, bar none! Yeah, I said that. Ears even preclude speakers or a well-treated room.
What I mean is without a set of trained ears, even the best speakers, equipment, and room isn't going to tell you what to do next to a mix. Say what you will about a poorly treated room and tiny desktop speakers but, if you have the ears for this I believe you can actually produce quality work--albeit, you need to test it elsewhere. Much like a photographer who uses a Smartphone. Drop a Canon 1D Mk IV with an "L" series Canon 70-200mm IS lens into the hands of an amateur and you're very likely going to see amateur results. Drop an old iPhone 5S into the hands of a professional photographer and the results will still be eye watering.
I want to bring up a subject that's been in discussion on mastering forums and groups: Mastering on headphones. Eww!! WHY would you! Or more to the point, Artist: "I'm paying you good money from an exhausted budget, why did you waste your time mastering our best album ever on headphones? Every engineer on the planet says never use headphones!" ME: "Did it not sound good?" Artist: "Well, yeah, it sounds awesome, but I bet it could have sounded better if you used speakers!" I suppose, but could I have done a better job on my speakers? Perhaps. To be fair to myself this didn't actually happen but I performed a test on a master. I mastered a song on my speakers. Then, after 2 days of not hearing the tune, I mastered it again on headphones. I honestly wanted to see which was better. The results were a bit ironic. In an A/B blind test the headphone master sounded better. The only thing I would go back and adjust is to not boost the highs quite as much on the headphone mix as I did. It was subtle and merely an ear-training issue. I was impressed that I could make something on headphones sound as good, if not better than my main speakers!
Now, there is a caveat here. One thing speakers can do that headphones simply cannot is tell you how a master will translate across a room. Believe it or not, even air-conditioning blowing in the background can have an effect on the master. The air blowing across the room from the side (if enough) can dull the highs. Ever watch a concert in a stadium? Notice how the sound warbles at times and the highs seem to come and go throughout the performance? Is that a terrible mix engineer? No. That's the atmosphere and wind causing that. Did you know air blowing inside your house can also affect WiFi? Nevermind, too much of a tangent.
Speakers have a way to do something headphone cannot in ways you may not expect. But this doesn't necessarily mean they're better. It's quite subjective. Headphones can subtract all that, for what it's worth. But speakers can bring you into the room more than you might expect. Unfortunately, most consumers aren't listening to speakers anymore.
Audeze Deckard Class A 4-Watt headphone amp
I've spent some time training my ears to a set of Shure SRH-1840 headphones powered by an Audeze (Aw-diz-ee) Deckard Class-A headphone amp, a really great piece of gear--surprised Audeze no longer produces it. These headphones are not the top-of-the line Audeze LCD-4 planar cans, no, and they're not the industry standards such as the Sennheiser HD-600.
Shure SRH-1840 correction with SonarWorks Reference 4
The Shure SRH-1840, incidentally has a very flat frequency response, even flatter than the amazing Audeze LCD-4 above 1khz. It doesn't mean they'll sound better, but they're flatter. Has Shure altered the frequency response to make these headphones flat at the cost of accuracy, clarity, and transparency? I honestly don't know, but they do sound natural to me. If you use Sonarworks Reference 4 the Shure's require less correction than the LCD-4. But this isn't to say the LCD-4 is worse---not even! The LCD-4 sound amazing. They do! I find the Shures to sound flat and less exciting, but they still work. The point is, you can master on either and produce excellent results (if you know how).
An aspect of expensive headphones, and to the fact that I don't use the most expensive available: Most consumers don't, either. In my opinion, there's a danger with using the absolute best of the absolute best, same with speakers. Your ears might be more prone to accept a width and depth of a mix when you still really have more work to do. This is why even mastering engineers will check their mixes on ear-buds, a mono speaker, and at times, in a car. Don't get mad at me for saying that, because if I owned a set of LCD-4 cans, I'd damn sure use 'em! Mastering engineers do use them. They just have to understand them.
EDIT: About 2-3 months after I wrote this blog post, I purchased a set of Meze Empyrean headphones which are powered by a Benchmark HPA4 Headphone amp. I made this choice because, although I do respect and value the use of my speakers in the room there may be times when I need to work on headphones. Should that be the case I'm here to say, so far...what a FABULOUS combo! Still, the Shure SRH-1840 headphones and Audeze Deckard are still quite excellent.
All that said, I want to describe something that happened to me, recently that just blew my mind. I was building a walk-through video for a client to show exactly what I did for the master (I do this upon request if I have time). During the recording of the video on my Samsung S8, I had the client's music playing on my speakers in the video while I talked. Upon playback, when the music kicked in, I could swear I heard the music, not in the headphones, but through my speakers! I had to take the headphones off to be sure. The audio came from the front of the room as if the speakers were playing right along with me watching the video!
I suppose that's also a testament to the S8's microphone, but the Shure headphones fooled me into thinking the speakers were on. The frequency response is pretty flat in both the speakers and headphones and they do sound quite similar. I'm impressed and I see the headphone market only getting better. If Elon Musk were to somehow get a set of earbuds to produce sound directly to the brain I'd suggest one day we'll all buy Audeze planar implants and just tune in! With companies like Audeze, Meze, HiFiman, Focal, Grado, Shure, Sennheiser, Sonarworks, and a few other game-changers, I've no doubt I could one day master on hearing aids!
Until then, will I master on speakers or headphones? It depends. There are times I'm not in my room and headphones on a laptop are working well. It also depends on the mix. While I can produce an excellent master on a laptop and headphones I largely still prefer the room and my speakers. Also, some mixes truly benefit from the analog treatments I have to offer. So, if I master on headphones the master typically isn't ready until I've passed it on my main speakers and heard what I need to hear. It's about the results, not the gear!