While audio manufacturers may extol the technical virtues of their products, the real differentiator in high end IEMs is their sound signature. That said, we still expect the tech specs to be up to scratch and the Aero's are with a frequency range of 20Hz – 18KHz, impedance of 19.7 ohm and sensitivity of 116 dB SPL (at 1mW). When it comes to that sound signature, though, it will provoke a love/hate reaction depending on your choice of music.
Much like Etymotic and GenevaSound, Unique Melody opts for a signature focused on accuracy. This makes the Aero's superb for classical music, jazz, indie and 'unplugged' music. It is possible to hear the detail within track arrangements, isolating particular instruments or honing in on the vocals. Settle down with some Duke Ellington, Philip Glass or Belle & Sebastian and you'll be in heaven.
Where the Aeros run into problems though is when you switch to music with a greater focus on bass. Pick any big beat artist, heavy metal (or even rock) band or some dance and the sensation is the Aeros are holding back. Certainly it is possible to tweak the sound through an equaliser, but this isn't desirable on a regular basis and many modern MP3 players/phones don't offer this functionality in any case.
This development is something of a surprise since the Aeros pack triple balanced armature drivers with a passive three-way crosser (Single High/Mid, Dual Low) - on paper more than enough to power through whatever material you throw at them. Part of the problem is amplification. More drivers require more power and the Aeros seem particularly power hungry. Plug them into a laptop or a decent amp and the problem is reduced, but it doesn't go away completely.
The schizophrenic nature of the Aeros is perfectly born out in a track such as The Dresden Doll's 'The Mouse and the Model'. The delicate piano of the intro and soft vocals are delightfully detailed, but when the military-esque drums kick in around the minute mark you're suddenly left cold and this is further accentuated as the six minute track folds in the guitars and bass, and the vocals switch to their staccato conclusion.
Don't get us wrong, Unique Melody has not created a poor sound signature and we appreciate that some people do prefer a more trebly output. What's more the quality of the Aeros is not to be doubted - the detail and soundstage can be phenomenal. It's just that they are specialists which excel at particular music types. Given these monitors are custom moulded they only need to suit your music tastes and no-one else so if that fits your bill then go for it. Then again if you're music collection is diverse you'll be in trouble.
Which brings us to another significant talking point: the nature of hard shell custom moulds themselves...