Sennheiser CX 300S In-ear Monitor Black

 All I can say is WOW!!!!!!!
i have had the opportunity to listen to the "high end" Shure E2, E5 as well as the "entry level" Sony's. These are UNBELIEVEABLE!

these cx-300's sound every bit as good as the "high end" models!!! the bass is LOUD and natural. the mids and highs are also very clean and detailed.

they are very comfortable and do an excellent job of blocking out unwanted exterior noise.

if you have a chance to pick these up at 39.99, like a lot of us have, BUY THEM. they are a steal at this price. you will be amazed!

 Amazing...
First of all, I am not what you would call audiophile. I am generally not picky about sound quality, as long as they are not obviously terrible.

That said, I wanted a new ear plug because when I got my Archos AV500, I found the one that came with it uncomfortable. I was looking around $20 range, but they were mostly with mixed reviews. After several weeks of search, I bumped into this. It came with incredible reviews everywhere. Although it costed more than I was going to spend ($40), I was assured by many online that it's worth it, especially since many places sell it for $70.

I just received it yesterday and had chance to try it out. All I can say is, Wow! I didn't realize the ear plug can make such difference. Songs, especially those that are encoded with high bps, came to life like I didn't expect. It sounded full and rich. I didn't know it's supposed to sound like that. Just for the giggle, I put the old plug back in and listened the same song. Now that I experienced cx300, it sounded like an old Nintendo 8 bit music.

I was also amazed with the volume it outputs. I had to turn down AV500 quite a bit compared to when I was using the other ear plug.

 CX 300S
Excellent IEM's...for the money! As good if perhaps not better than the super.fi 3S at almost twice the price. Good going, Senn and Amazon!

 Forget Etymotic and Shure - buy this Sennheiser instead
Sennheiser CX 300 series was formerly launch into the professional musician market as Sennheiser IE4 In-Ear Monitor.

Sennheiser IE4 sold at ~150 US Dollar (Suggested Retail Price). As a competitor of Etymotic Er6 and Shure E3c.

Following the product's success in the professional market now it is time to harvest from the vast consumer market.

So the marketing description of this product now change from "the high accuracy reproducing of the sound" into the new hype "the bass driven sound".
Very common marketing trick. :-)

Sennheiser IE4 was a rebranding of the highly acclaim "Sharp MD33".
Sharp MD33 is one of the most succesfull IEM in the world.
It also described as a "giant killer".

After it got wide reputation around the world Sharp MD 33 was rebranded into Creative ep630 (which can be found in Asia) and Sennheiser IE4 (which goes directly to the most demanding professional musicians market.

Sound of this Sennheiser/ Sharp/ Creative IEM is solid and very clear.
Bass is decent, mid and high are details.

It need less maintenance comparing with Etymotic or Shure since it cleverly use metal grills instead of direct filter.
Once a month scrap your earwax out of the metal grill is enough to keep this decent IEM working for years.

Silicone ear tips are interchangeable with Sony's ex series ear tips.
If you want to do some experiment you can try Shure's ear tip on them.
Even somebody have suggested Shure's Ultra Soft Flex Sleeve (PA749M) on this IEM but I would like to suggest Shure's PA757M Flex Sleeves instead. (Please change the size according to your ear size)

With Shure PA757M Flex Sleeve this Sharp/ Creative/ Sennheiser IEM sounds as if the sound stage become expanded without deterioration in sound quality.

If you live in US this Sennheiser IEM is worth your money. And sound quality is much better than many expensive IEM.

 Unbelievable Performance at a Great Price! The IEMs to own.
I have been using both the Sony Fontopia 51s and 71s for a few years now. After recieving one set of these, and comparing the Senns to the Sonys, I immediately ordered 2 more sets. Incredible sound. And the price of $40 is 50% cheaper than the retail price, and $70 is the common selling price. I doubt they'll last at this price. $70 is a fair price for the sound quality. $40 makes this a steal.

I have been comparing the offerings of both Etymotic and Shures, and the constant complaint in a variety of reviews has been a lack of bass response. I considered this unacceptable and stuck with my Sonys. Prior to this I looked at the Shure e2c, e3c, Etymotic 6i. Each had some major deficiencies that made me avoid a purchase (constant comfort complaints for the e2cs, and lack of bass for the e3cs and the 6is). Each of these also cost significantly more than the Senns.

Enter the Sennheisers. Bass response is just as good as the Sony earphones, but clarity is vastly improved, and the mids and highs are incomparable. Music sounds spectacular. Are the most expensive headphones probably better? Maybe, but a) they will certainly be many times more expensive and b) they may lack the bass response desired.

Finally, while I can't speak as to durability, the 2 year warranty is fantastic.

In short: I highly recommend these.

 Wow, just as good as Super.fi 5 Pro!
I love the Super.fi 5 Pro. I've owned two pairs in the last few months, returned one because of irritation with UE. When I saw the new Senns were available I decided to A/B the two.

Well, for $150 less these guys are amazing! I have to push the volume up just a bit, but the tips are are comfy, the earpiece itself is discreet and easily maneuvered, and the sound is excellent - not too bassy like the cheap Sony IEMs. There's a soundstage! These are worth at least twice the price. My Super.fi's are going back to Headroom.

Test tracks:

1. "Naked Mole Rap" by Ron Stoppable and Rufus
2. "Le Jazz Hot" from Victor/Victoria
3. "Sentimentale" by Claude Bolling.

All three genres were marvelous. I can feel the piano keys tinkling. Buy these.