The acoustic characteristics of the SteelSeries Arctis 9 Wireless are in line with what I've previously heard from other higher-end gaming headsets from the Arctis lineup. The sound output is quite accurate, smooth, and for the most part neutral across the entirety of the frequency spectrum. The mid-range is ever so slightly boosted, which makes vocals stick out a bit, although not so much that they would sound too in-your-face or annoying. The boosted mid-range also helps with spatial awareness and positioning, which makes the Arctis 9 Wireless an excellent choice for multiplayer first-person shooters, as you'll get a ton of information about your surroundings.
Similar to its brethren, the Arctis 9 Wireless isn't very bass-heavy. It doesn't sound lean either, so if you're not a hardcore bass-head (bass isn't the only thing you want to hear), you should be completely satisfied with the low-end reproduction of this headset. Of course, if you want more bass, you can always add it through the system-wide equalizer. The build-in speaker drivers respond well to equalization.
With a strong focus on precision and clarity of sound, the Arctis 9 Wireless holds its own in pretty much every music genre you decide to throw at it. The built-in drivers can keep up with fast drums, guitars, male and female vocals of all ranges, and everything else your playlists may consist of. When considering these for music, don't think about them the same way you'd think about a regular gaming headset. This isn't a headset that's good with games and usable for music. The Arctis 9 Wireless is equally suitable for everything it might be used for, and its aforementioned acoustic qualities are beneficial and pronounced everywhere.
The passive noise isolation is very good. With the ear cushions being marketed as "airy," I was a bit worried that they were going to leak plenty of sound, but they didn't.
DTS Headphone:X V2 Virtual Surround Sound
In the virtual surround sound department, the SteelSeries Arctis 9 Wireless uses the DTS Headphone:X V2 technology. In my time with the Arctis 9 Wireless, it proved to be one of the best virtual surround sound solutions on the market. The surround effect is fairly subtle, which is a good thing as it in turn doesn't ruin everything good about the sound performance of the Arctis 9 Wireless. The sound becomes somewhat wider without added muddiness or artificiality to any part of the frequency spectrum. You can actually listen to music and enjoy it without turning DTS Headphone:X V2 off, which usually isn't the case with competing virtual surround sound solutions.
While it doesn't add much in the sense of spatial awareness or make your virtual targets easier to pick up, it's definitely worth a try. I suggest keeping the Surround Profile option in the SteelSeries Engine 3 on Game, Stereo Profile on Default, and Bass and Dialogue Enhancement on None.