Below is a cut and paste on my initial thoughts of the 4.AI from the Heir Audio Appreciation Thread. As there have been some questions on isolation I will add that they isolate very well and better than most IEM's I have had. They actually come pretty close to my original comfort version 4.A.
The build quality of the 4ai is nothing short of spectacular. They simply scream to other iem's look at me I am breathtakingly sexy. None of the other IEM's that I have had the pleasure to own even come close and I would be surprised if anything in the future from a company other than Heir would even come close. They are built and adhere to the same strict standards that Heir builds their ciem's to.
As I have previously stated the 4a's are simply the best sq that I have heard to date (that statement was made proor to receiving my 8a's, more on those in a future post) and since the AI version utilizes the same components it should be no surprise that the 4.AI sounds identical to its fraternal twin brother the 4.A. Out of the two my preference would goto to the 4.A's younger sibling as now I am able to share the masterpiece that is the 4a with friends and family.
These iems are by far the most comfortable that I have ever worn and they truly disappear into your ears and in no time you will forget that you are even wearing them. This is by no means a small feat as the Wizard can attest to my small ears and canals.
It is incomprehensible to me that a company can put out such an outstanding IEM that is not only hand built with a stellar build quality but also possesses a sound quality that is equally astonishing for such a low price. And to boot they include a removable cable that is interchangeable with most standard socket ciem's.
It is easy to recommend the AI line to anyone solely based upon the product as described above. When you through in the unparalleled commitment to the customer it becomes a no brainer; Heir Audio and their products stand alone at the pinnacle of the industry.