It has a fantastic Sound with a very V shape sound so don't expect good mids. If possible get the IE400's from Sennheiser as they're at the exact price as these

With that said, after a few hours of burn in (4-6 hours) they sound less piercing/sharp and is more smooth and comfortable to listen to. modern electronic/pop sounds best with these as well as orchestra music like Nightingale by Yanni. The instrument separation is concise and clear and with some tracks it gives you a kind of mini soundstage although an intimate one. Great buy at 30k Thanks HPZ!

Paired this IEM with Helm Bolt DAC

OMG This just sounds amazing. I cant help but start giggling like a teen whenever i put this earbuds on. Of-course this is a warm sounding which means they are bassy buds but The bass response is super clean, super smooth n super fun. The bass doesnt bleed into the vocals making it sound muffled nor does it sound bloated . Its deep and tight.just like the friendship between dead pool and colossus. Apart from the bass this IEM has nice treble response. But you can definitely notice a roll off at around 10k hz but dont be alarmed there is enough and more detail on the top end. moreover you don't feel the piercing harshness of the highs and this helps you to keep listening for a long duration of time without having ear fatigue . However you can definitely appreciate the shimmer and might i say some exaggerate hissing or “s” noises also known as sibilance . But what it lacks is the emephesis of the frequency range between 2-6k which is responsible for adding presence to vocals and a result the vocals dont shine through whenever the vocalist is surrounded by too many instruments.

But what’s interesting is Despite this boosted bass, the lower mids don’t sound muddy. They have a neutral clean and a linear response. However the overall midrange is not super forward and for context our vocals do fall in this midrange frequency . So this is definitely not an IEM or earbud for those you love their mids.

This is a review of both the IE 300 and the IE 900. I'll copy paste it in both sections.

Firstly, accessories (ear tips and cables) are a massive middle finger from Sennheiser to the buyer. The included silicon tips are absolute bottom barrel trash. They can not seal for me and while pulling one off the IEM it ripped the tip from the stem. The foam tips are useful and help me get a good seal, but I'm using them sparingly, because, like all foam tips they won't be too long lived. Replacement tips?

The cable is sticky, tangly, fights you at all times. The cables of the 900 feel a little softer and less sticky, and there are 3 of them, but still these are far form decent for the price. Sourcing a good replacement cable will be a problem because of the non standard termination. I have bought a replacement cable "Tiandirenhe cable for IE 300, 600 and 900". It feels flimsy and cheap, and I'm not hopeful as to it's longevity, but that cable in feel is a humongous upgrade. I fail to see how a leader in the audio industry is so clueless. I was reading a discussion on a forum where Sennheiser reps., on being asked if they could recommend a replacement cable asked a person what the problem with the stock cable was.

Both the IE 300 and IE 900 are comfortable and after trying different ear tips I've found the best ones for me are the included foamies and Spinfit CP100 plus. It's unfortunate Hpz doesn't sell the CP100 plus. Also sourcing the original foam tips might be a problem. The seal is fidgety and while I can maybe attribute that to my ear shape being wrong, these aren't my first IEMs.

Sound is simple. both of these are basically detailed, pleasant with a good amount of bass. Having said that The IE 900 is FAR better than the IE 300s. More resolution, better imaging/ staging and bass. So much so that IMHO the IE 300 are bad value at their price and the IE 900s, while not good value get a pass because the summit fi section has insane pricing anyways.
In fact I thought my IE 900s were broken and were imaging off centre because of the extreme positioning capability. I sent them in for warranty and they returned them saying its fine. I was still not convinced and as a final resource played tracks on mono. the image was dead centre. Basically when you have multiple vocalists close to centre, the IE 900 can locate them precisely.

This review sounds ranty, and that's unfortunate. The headphones are good but are let down by the absolutely trash accessories. They could learn a thing or two from brands like Fiio. At least the carrying boxes are pretty.

Bottom line. IE 300s, OK, but 10k chi-fi is competitive. IE 900s, GOOD. They know it and have priced them accordingly.