What techniques do you use to ensure that a mix translates well across various playback systems, from high-end speakers to smartphone earbuds?

In my experience, testing a mix on a ton of devices is not only impractical and time-consuming but also unreliable. Ultimately, only an optimal acoustic environment with high-quality monitors can provide consistent and dependable results. If you don’t have access to that, it’s wise to have your mix mastered by a professional.

A good mix will sound good on any device, knowing your monitors or headphones is fundamental and above all, trusting your hearing is the best thing you can do.

MK

This is quite simple - test it out and mix on those devices. There are also plenty of plugins that help you emulate the room, device, or platform specs needed. Mix across the board - that way you're sure everything sounds as it's supposed to before publishing the work.

Let's be honest, nothing is going to sound ground-breaking when being played through some laptop speakers or a small phone speaker. The key to ensuring that each mix sounds as good as possible in as many audio environments and systems as possible is balance and testing.

Once a track has been mastered in-house we trial the sound across headphones, smart home speakers, car speakers, etc. to simulate the experience that your listener may have with your sound. We can then use our trained ears to make informed decisions in the mix.

It's no good mastering a piece so that it only sounds good under our conditions. So tonally balancing, gain staging, and dynamic control is all part of our process of creating a well rounded and future-proof master. 

Truth be told theres no easy solution here. But creating space in the mix will often help things translate across platforms.

One thing to bear in mind though is that lots of super sub frequencies often dont translate and can mess other frequencies up when a cheap speaker tries (and fails) to play them. So keeping your low end tight, and even rolling off frequencies under 30hz (or even 40) can help and can even give the impression of there being more bass, not less, as smaller speakers can handle it better.

My least favourite response as a mix engineer though, is "I listened on my phone and I cant hear the bass loud enough". Like, cmon, seriously this is version 9 and its pretty much just bass at this point!

Mix a lot of songs on your monitoring system and get used to how they translate outside the studio. Cambridge MT site has like 600 songs, mix half and you'll get a very good idea on how your monitoring works (for you or against you) 

Unfortunatelly, there's no shortcut here I check each mix on every audio source that is available to me. The better your main monitors though, the more likely the mix will sound good on all other systems.