The HISO is a departure from the typical style that Heir has stuck with for the rest of their lineup. While it certainly isn’t cheap by any means, the HISO is actually the most “budget friendly” IEM currently offered at Heir Audio coming in at a cool $329. Can Heir Audio pull off an IEM that competes in this price-range? You can find the HISO for sale here on Heir’s official website.

Disclaimer: This unit was provided to me free of charge for review purposes. I am not affiliated with Heir Audio beyond this review. These words reflect my true, unaltered, opinion about the product.

Preference and Bias: Before reading a review, it is worth mentioning that there is no way for a reviewer to objectively pass judgment on the enjoy-ability of a product: such a thing is inherently subjective. Therefore, I find it necessary for you to read and understand what I take a natural liking to and how that might affect my rating of a product.

My ideal sound signature would be an extended sub-bass with a leveled, but textured, mid-bass. The mids should be slightly less pronounced than the treble, but still ahead of the bass. I prefer a more bright upper range.

Source: The HISO was powered like so:

Nexus 6P -> earphones


Hidizs AP100 3.5mm out -> FiiO A5 3.5mm out -> earphones


HiFiMAN SuperMini -> earphones


PC optical out -> HiFiMe SPDIF 9018 Sabre DAC 3.5mm out -> earphones

All music was served as MP3 @320Kbps or as FLAC.

The HISO scaled nicely with all my sources, and didn’t change too much when used on cold or warm sources. As such, I did most of my testing on my most sensitive IEM-friendly DAP, the HiFiMAN SuperMini. I tried a wide variety of tips with HISO as I was having a hard time finding one that fit my left ear. I discovered that foam tips heavily impact the sound. Do not use foam tips with the HISO. It makes the bass far too woolly and overbearing.

Sound Signature

Initial Impressions:

The HISO is fairly neutral in terms of outright emphasis, but does fall on the darker side of the sonic spectrum. That’s not to say that the upper mids and treble are neglected. Rather, the treble and upper mids are preserved quite well, just aren’t the focus. I find the other parts of the mids and mid-bass to be more forward while still being courteous of the other elements of sound.

Put simply, the treble is slightly ahead of the upper mids, the lower mids are slightly ahead of the mid-bass, the mid-bass is ahead of the sub-bass, and the lower mids are ahead of the upper mids by a slight margin.

Treble: Songs used: 'In One Ear', 'Midnight City', 'Outlands', 'Satisfy'

Electric synths such as those in the intro of 'Midnight City' were distinct, textured, and had good decay. Heir Audio claims that the HISO’s new crossover design enables it to have a greater level of detail and texture than it’s predecessors, and I don’t think that’s entirely hyperbole. There is something different between the 4 Ai S, which has four drivers, and the HISO in terms of treble texturing. The HISO is less smoothed out and does seem to have some extra textural cues that the 4 Ai S misses out on. However, I think that this subtle difference is something that could go either way in terms of pros and cons based on the preferences of the listener.

The treble extension of string instruments such as violins is quite good. A sense of airiness does develop in Outlands and many of its companion songs on the TRON:Legacy soundtrack.

The HISO’s treble is entirely without hiss or sibilance. Even the sharpest and least-behaved songs such as 'Nero’s Satisfy' are tamed well by the HISO. No complaints here.

Mids: Songs used: 'Flagpole Sitta', 'Jacked Up', 'I Am The Highway', 'Dreams'

One might expect the mids of the HISO to be scooped out due to the fact that they don’t have a dedicated driver. This is resoundingly not the case. The upper-mids are open and expressive, while the lower-mids are hearty and full. This expresses itself well with songs that have a drier production style, as the HISO revitalized them and imbued them with a sense of vibrance. Harvey Danger’s 'Flagpole Sitta' is an excellent example of such as song. While the guitars weren’t as well fleshed out as with the more expensive 4 Ai S, the HISO does perform admirably, especially with 3D-placement cues.

Pianos have a very satisfying timbre to them on the HISO. 'Jacked Up'’s pianos in particular had a great edge to them in terms of hardness, indicating a very competently-tuned attack and decay. Guitar distortion and vocals both sounded great as well. Vocal enunciation is above average, but still not quite like some other options in this price-range that offer more upper-mid and treble-centric sound signatures.

There is a lot of detail present in the mids as a whole. There are some smaller details that I missed on other songs that I am starting to notice now as I listen to my music library on shuffle, which is always a welcomed experience.

Bass: Songs used: 'Moth', 'Gold Dust', 'In For The Kill' (Skream Remix), 'Leave Me'

The HISO’s bass surprised me. I absolutely did not expect it to be as pronounced as it is, as the 4 Ai S (which has two “lows” dedicated drivers) was rather subtle in this area. The HISO shattered this ill-conceived preconception the moment I played back 'Moth' or '(Girl We Got A) Good Thing' by Weezer. The bass guitars were able to express their deep chugs quite well, enabling them to set the tone and pace of their respective songs.

Listeners of electronic music will appreciate the HISO’s take on a dual-BA configuration. Mid-bass quantity and control are both among the best I’ve heard from balanced armature IEMs. The bass is toned very well giving Gold Dust a great level of wetness, impact, and rumble. While it doesn’t quite get to where some of my dynamic-driver IEMs can get to, it’s commendable in its own driver-configuration class.

The HISO does try to push down into the sub-bass frequencies but has a hard time. While the HISO does have the tonality of a bona-fide sub-woofer, it doesn’t quite have the ear-vibrating properties that other basshead IEMs have. That’s okay, as I doubt this IEM was targeted at that audience anyways. Check out my Rose Cappuccino Mk. II review if you are interested in a truly basshead-friendly IEM.

Packaging / Unboxing

The HISO’s packaging is more substantial than Heir’s other offerings despite being the cheapest of their lineup. It’s appropriately sized and makes effective use of space, something I appreciate as someone who tends to keep the boxes of the products he uses.

Construction Quality

The HISO is built from a transparent plastic, different from the type used with the 4Ai S. Inside the plastic lies a face-plate with a design varying on the type that you order. There are the three variants, all of which I find to be quite cool.

The nozzle is short, giving the HISO a very shallow insertion depth. Expect that you will have to test out new types of eartips or sizes that you might not expect as a result. The HISO utilizes a two-bore nozzle design, so make of that what you will. This, in theory makes the sound more clear. While there’s no real way for a consumer to test these claims, I don’t think it’s the kind of baseless snake-oil that other manufactures try to sell.

The HISO’s cable is detachable and uses the 2-pin standard. My unit’s cable is stuck in there pretty good, so I haven’t yet disconnected the cable, though I’ve seen others who have.

The cable itself is of the four-core plastic variety and uses a twine-style braid. It’s identical to the cable used in the 4 Ai S, so if you have any experience with that model you pretty much know what you expect here. The cable is light and bendable. It has almost no body to it, making it quite easy to untangle in the rare event that it actually does get mixed up a bit. The microphonics are minimal, but will be noticeable to someone who greatly cares about such things. The cable terminates in a plastic-housed right-angled 3.5mm jack. There is adequate stress relief, and I’m not concerned at all with the longevity of the cable.

The cable does have a memory-wire-like ear-guide that is decent. I don’t have any comfort issues with it, and it keeps the HISO well-secured to my ears on brisk walks. It is made from a clear plastic, so from a visual perspective the ear-guide is unobtrusive as well.


The HISO is reasonably comfortable. While I found that I wished the nozzle was longer, I didn’t have too many concerns once I found a good set of eartips to use. Finding a pair that worked was harder than with other IEMs (as I couldn’t just cave-in and use foams due to the sonic ramifications of those eartips), but not so much that I’d let that be a deciding factor when deciding to buy this IEM.


Heir Audio seems to have changed things up a bit with the HISO. It doesn’t come with the usual black plastic carrying case. Instead you can find a circular brushed-metal carrying case. I personally prefer the HISO’s case to the other standard Heir Audio case, but again, this is all preference.

Inside the box you will find:

1x cleaning tool

9x spare eartips

1x metal carrying case

I really like this case. It is functional, visually-appealing, and easy to carry around. I feel that a lot of little details are often overlooked by headphone makers, so it’s nice to see a company pay so much attention.


The HISO is a great addition to Heir Audio’s lineup. It is a departure from the bass-light style of the 4 Ai S and provides a much-needed sonic-variety to the bottom-end of Heir’s price structure. While there are certainly a lot of competitors in this price bracket, I think that buyers of the HISO won’t be disappointed.