I let the HM9 to burn in for about 80 hours. I didn't note any dramatic differences between the out-of-the-box and burnt sound, with the exception of the treble, which became smoother and more pleasant to the ear.
Overall, the headphones feature a deep, laid-back, warm and slightly dark sound signature, quite forgiving to lower-quality recordings. Unlike similarly priced Audio Technica's ATH-M50, or Sennheiser's HD558, this is not a neutral pair of cans. Quite the contrary, it features a warm and bassy signature.
However, I don't have many problems with this signature.
Why? Because it does the sculpted sound well. Yah, the bass is proeminent, but not overpowering or overly colored, like the one on Sony's MDR-XB300. There's a bit of noticeable bleed, but it doesn't damage the overall audio experience.
I have to say, for the amount of rumble HM9 features, I was expecting a bit more punch. It's boomy at times, but it carries a nice texture to it, and the detail / clarity is impressive for headphones at this price-point.
Alas, there's a bit of bass bleed into the mid-range, and that may feel muddy, depending on what music genre you're listening to.
HM9 comes with warm, smooth and heavily forgiving mids. There's noticeable veil, especially with instruments, but underneath that theres a lot of detail, layering and depth. It's a rich sound, extended but slightly dark.
Detail between the lower and upper mids is rightly balanced, so you might get a smooth, responsive experience of almost all mid-range. The pronounced bass might take away from the audition, but despite it, the richness and detaill still adds a lot to passive instruments, and vocals aren't far behind either.
The treble is toned down, relaxed, but still very much active. It's lagging behind the bass and mid-range, but only by a small fraction. Extension is about average, with detail and clarity adding a great deal of sparkle and airiness in the upper portions. It's really impressive, especially considering the signature is somewhat dark.
HM9 delivers great highs when you have songs that put that frequency to the test, however with lower-highs the sound is again, veiled.
BrainWavz HM9 features a broad and deep soundstage, with proper channel separation.
For a closed-back design, the sound-stage is interesting, especially when it comes to center-depth, where it truly excels.
This is yet another one of those cases where a music pair of cans is considerably better than most gaming headsets. The sound is sculpted enough to give that oomph that most gaming headsets are going for, but it also has a lot of detail and clarity to offer. Not only that but the soundstage is well defind, with great stereo imaging, which lets itself to great audio accuracy.
If you ever focused on sound while playing a game, using to pin-point the exact location gun fire in the distance or footsteps of someone sulking around the corner, then know that BrainWavz HM9 delivers more than headsets who promise exactly this.