This is a question that seems to come up quite often, so here are my thoughts and some recommendations for mixing with headphones. First thing is that it is OK to mix with headphones. Lots of great albums have been mixed on headphones and you can get a professional sound. For many DIY musicians and home studio engineers, the mixing room is not always optimal for sound. A decent pair of headphones will give you a more accurate presentation of your mix.
Now here is a main factor to consider, the quality of your headphones really does matter. Not all headphones are created equal. Some headphones are designed specifically for the studio and others are designed for listening and playback. So how do you know what is the difference between headphones? Most studio headphones actually put on the packaging that they are studio headphones. But words don't necessarily mean that you will get the quality needed to mix properly. It is always advisable to listen to a pair of headphones before you commit to buying them. I don't recommend buying headphones because of the name brand or because someone famous endorses them. Companies are in the business of selling their product, so you can't just take their word or reputation for granted.
I've owned lots of different headphones over the years and some are good for recording, some good for mixing, and some good for listening and enjoyment. Every pair of headphones I've owned have had their own strengths and weaknesses. It just takes time for you to get used to sound your headphones provide so that you can be productive in your mixing choices. If mixing with headphones is the route that you plan to take for your post-production, I'd suggest getting a decent pair of headphones. Many of the headphones in the $99 - $199 price range will give you a decent representation of your mix. Let me give you my experience with a few different models that are out on the market.
When I was starting out, I used Sennheiser HD280headphones for recording and mixing. These are great headphones for all applications and music. They have rich detail in the low-mids and don't get too harsh in the upper frequency range. That's a bit of good news for your eardrums. These headphones are comfortable and do collapse down for easy transport from one place to another. I'd say the big plus for these headphones is the price. At under $100, these are some of the most affordable professional headphones you can buy. Especially if you're on a budget and would rather spend your money on gear or mics. The ear pads can be replaced when they get old and worn out, so you can keep the feel of these headphones in a feels-brand-new fashion at any point.
I moved on to a pair of Beyerdynamic DT 770 Pro studio headphones. I was initially impressed with the comfort, quality, and sound of these headphones. I demoed a pair at a local pro audio shop and a few minutes later walked out with a brand new pair for the studio. Now these are a bit more price-wise, but you get quite a bit for your money. The large ear pads are extremely comfortable and they don't squish your ears against your head. This was a huge plus right off the bat for me. For $199, I felt like I purchased a quality pair of headphones that would give me many great hours of recording and mixing. I used these headphones for about 2 years and mixed some of my favorite albums with them. Yet as the years went by, I started to be a little more critical of my mixing and felt that these headphones were not giving me enough detail on the high-end. This was frustrating, so I went back to search for a new pair of headphones. However, I do still use these headphones for recording and mixing from time to time. I still like the comfort and the relaxed feel they provide. Most of my clients prefer this pair of headphones when they're tracking and I agree that these are headphones that you can wear for a long period of time and not get too fatigued.
After some research and field testing of some different headphones, I decided to go with the Shure SRH840 professional studio headphones. There are a few reasons I chose this pair of headphones and I still feel like these are the right pair for most studio applications. The ability to easily replace the ear cushions and the cable are big advantages, so I'm already a little happier. This is just the tip of the iceberg. The sound quality of these headphones is transparent and dynamic. The drums that I've mixed with these headphones are crisp and punchy without being too muddy or boomy. I've also been able to get a better vocal balance in my mixes with these headphones. Having a good vocal balance can really make or break a song. You have to have faith in your headphones to give you a clear representation of your mix. To be able to trust your ears and rely on your headphones is crucial. These headphones are comfortable for short periods of time, but a long studio session can be rude to your ears and neck. These headphones are a little heavier than some other pairs I own and I notice that my neck can get cranky if I rock the headphones for too long. Overall, these are the best pair of headphones that I could find under $200.
Now one thing to keep in mind is that I don't solely use headphones to work on my mixes. I also use the studio monitors, but I regularly check my mixes with headphones. I recommend taking regular breaks if you are using headphones. Give your ears some time to recover and unwind from the constant noise that is only inches from the eardrum. These are just a few of the headphones that I own and/or have used in my career as a musician and producer. There are so many options out there and manufacturers keep improving on the designs, but I stand by my original statement that you need to go out and actually put the headphones on and listen to them for yourself.
Sometimes it is good to use earbuds to check your mix. You may be asking yourself, "Why would I use earbuds to check my mix?" Well, good question. The main reason is that your mix will most likely be heard on earbuds by the majority of listeners. Mobile music is the new trend and everyone has earbuds with their phones and MP3 players. So get in the game and make sure you are covering all your bases.
I did just purchase a pair of the Focal Spirit Professional headphones as a personal pair for my own listening enjoyment. I haven't had enough time to evaluate them, but my first impression is that they are on par with the BOSE noise-cancelling headphones. The ear cushions are quite snug and I don't know if I would use them for mixing. When I have more experience with them, I'll post my thoughts.