When comparing Bose SoundSport (SIE2) vs Audio-Technica ATH-M40x, the Slant community recommends Audio-Technica ATH-M40x for most people. In the question“What are the best headphones?” Audio-Technica ATH-M40x is ranked 17th while Bose SoundSport (SIE2) is ranked 157th. The most important reason people chose Audio-Technica ATH-M40x is:
Sound signature is quite accurate, almost flat. Bass is much more controlled instead of boomy, while there is a slight elevation on the highs, resulting in extra energy and detail up top. These offer a nice middle ground between a fun sound and a more reference/analytical sound signature. This sound quality makes the headphones quite versatile as music enjoyment headphones or studio-use cans.
Specs
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Pros

Pro Engineered for exercise
The SoundSport earpieces are designed to stay in when running or performing other intense activity.

Pro Choice of color (iOS only)
SoundSport earbuds with iOS controls are available in blue, green and orange. The Samsung Galaxy (Android) model comes only in green.

Pro No ambient sound isolation
Because these earbuds are intended for exercise, they let in outside sound so users can remain safe and alert.

Pro Hydrophobic housing
These earbuds are covered in hydrophobic cloth in order to keep sweat or rain out, while still letting sound pass through.
Pro Fairly neutral sound signature
Sound signature is quite accurate, almost flat. Bass is much more controlled instead of boomy, while there is a slight elevation on the highs, resulting in extra energy and detail up top. These offer a nice middle ground between a fun sound and a more reference/analytical sound signature. This sound quality makes the headphones quite versatile as music enjoyment headphones or studio-use cans.
Pro These have a high quality and durable feel
The M40xs feel solid and are known to be quite durable. The plastics used in the build do not easily flex or make creaks, giving the impression that these can last quite a long time.
Pro Can be used in noisy environments
The over-ear, closed back design along with the thick pleather ear pads can block out quite a lot of ambient noise, and will help users to focus in on the music. These make the headphones great for travel or for mixing/monitoring use.
Pro Comes with two detachable cables
The headphones come with a straight cable and a coiled cable, making them useful in the studio or while walking.
Cons

Con No ambient sound isolation
By design, these earbuds do not obstruct outside sound, making them inappropriate for use when isolation is desirable.
Con Incompatible with cables from other brands
Only Audio Technica cables can be used with these headphones.
