Campfire Audio IO: Forbidden Love


Today we’re checking out the new IO (Eye-Oh) from Campfire Audio.

Campfire Audio is located in Portland, Oregon and was founded in 2015 by Ken Ball of ALO Audio fame. In the world of high end portable audio they rapidly became a household name thanks to the Andromeda with it’s iconic design language and impressive performance.

The IO that we’re checking out today is one of their newest releases. Along with all-new packaging for the brand, it features a dual armature setup and the same angular design that is shared with many models in their lineup, and that won them great accolades from the community when they first appeared on the scene.

As one of their most affordable models, is the IO a worthy addition to Campfire’s lineup? Let’s find out.


Thanks to Caleb with Campfire Audio for arranging a sample of the IO for the purposes of review. The thoughts within this review are my own subjective opinions based on time spent listening to the IO throughout the last two months. They do not represent Campfire Audio or any other entity. At the time of writing the IO retailed for 299 USD. You can check it out here:

Personal Preference:

I listen primarily to various EDM sub-genres (liquid drum and bass, breakbeat, drumstep, etc.), hip hop, and classic rock. My preferences for earphone tuning are quite relaxed and as such their is no one signature I look for. The HiFiMAN RE800, Brainwavz B400, and Massdrop x MeeAudio Planamic are examples of earphones with wildly varied signatures that are enjoyable for different reasons. I generally listen at very low volumes, so keep this in mind when perusing my thoughts on how an earphone sounds.


Mobile: Shanling M0 alone or with the Periodic Audio Ni amp, ZiShan DSD

@home: TEAC HA-501 with a ZiShan DSD or Asus FX53V acting source duty

The IO is very easy to drive and doesn’t need to be amped. A phone drives it just fine. That said, since it is somewhat bright and quite revealing, it sounds best out of a clean, warm source so I do recommend a decent DAP or DAP/amp combo.


  • Driver: Dual balanced armature
  • Impedance: 26 ohms
  • Sensitivity: 109dB
  • Frequency Response: 5Hz to 22kHz

Packaging and Accessories:

When it comes to packaging, Campfire Audio has changed things up this time around. The spirit of their past designs is still in place as they follow the same astronomical theme, but the format has changed. Similar to the Solaris, the IO comes in a fairly large, shallow square box. Unlike with the Solaris, this box is covered by an exterior sheath, sealed shut by a gold coloured Campfire Audio seal on the back. The front contains a large sticker with a mottled pattern set beneath a high quality image of the IO’s earpieces and the usual company branding and model information. One more sticker is present around the side containing company info and another image of the IO, among other details that may or may not be important to the average consumer.

Breaking the seal, the sheath unfold like the pedals of a flower revealing the main box inside. Lifting out the box, you will notice the inner sheath is printed with the CA logo dead centre, golden rays exploding outwards. It’s quite dramatic. The main box itself contains the same beautiful mountainous scene found on CA’s prior packaging along with more Campfire Audio branding. Lifting the lid you’re greeted by the slogan “Nicely Done” printed on one of the flaps, as well as their new leather carrying case and a smaller cardboard box containing many of the included accessories. Beneath all this is your warranty card and a manual. In all you get:

  • IO earphones
  • Smoky Jacket Silver Plated Copper Litz Cable
  • Final Audio tips (xs/s/m/l/xl)
    Campfire Audio Marshmallow tips (s/m/l)
  • Wire bore single flange silicone tips (s/m/l)
  • Campfire Audio lapel pin
  • Cleaning tool
  • Mesh accessory case (x3)

Overall this is an outstanding unboxing experience, as is always the case with Campfire Audio. But…I still prefer their old packaging. It was smaller and more compact thereby using less material and producing less waste, a big plus for those that toss packaging once they get to the goods within. That said, this packaging still produces a lot less waste than what you get with various other brands (RHA, Dunu, etc.), and everything is recyclable, so take this as more of an observation than a complaint. The new box does look fantastic on display though, a positive for those of us that appreciate brands who put time and effort into crafting unique and attractive unboxing experiences.

Packaging aside, the accessory kit is second to none. Final Audio tips are some of the best in the business and with five sizes included you’re sure to find something that works for your ears. Campfire Audio’s Marshmallow tips are a very high quality foam option. The basic single flange silicone tips are nothing special and are the sort of tip you’d find included with more budget oriented offerings. That’s not to take away from their performance though. They stay attached to the nozzle just fine and consistently seal well, though I’m not a fan of how they sound with the IO. The cleaning tool will be invaluable to those with waxy ears and the inclusion of three mesh bags to keep everything neatly organized is genius. Nicely done.

Build, comfort, and Isolation:

The machined aluminum housings of the IO are adorned with a pale red anodized finish that looks pretty stunning in person. Seems to me that Campfire has improved the quality of their machining and their anodized finish. Compared to the original Polaris, the shells are much smoother. Small bumps and knocks that chipped the finish on the original Polaris have done nothing to the IO. ~10mm long stainless steel nozzles are present and have a prominent lip that does a great job of holding tips in place. These nozzles are very similar to those introduced with the Atlas and Comet and incorporate protective grills into the design. You won’t have to worry about losing a filter when changing tips. Gold plated screws top things off and attractively accent the red colouring, Iron Man style. The IO use’s Campfire Audio’s now familiar and extra durable beryllium/copper MMCX connectors. I say extra durable because that’s what the marketing blurb spouts, but also my now almost two year old and well-loved Polaris has seen tens and tens of disconnects. The MMCX connectors are just as firm now as they were out of the box. Fit and finish is as to be expected, which is to say it is fantastic. Seams are barely visible and everything lines up perfectly without any gaps or off kilter angles.

The IO comes with Campfire Audio’s new Silver Plated Copper Litz cable. It is quite reminiscent in design and thickness to the copper cable that came with the original Polaris, but with a new smoke coloured sheath. The 90 degree angled jack is smartly designed with an extension to permit compatibility with a wide variety of device cases, though strain relief is a little stiff. Less of a worry than it would be on lesser cables. My experiences with Campfire’s cables have shown them to be plenty durable. Within the small, reliefless aluminum y-split, the cable divides sending two strands on each side to the ear pieces. Slotting into the top of the split is a small plastic chin cinch. It moves much more smoothly here than on older Campfire cables and as a result is much more useful. Also much more useful is the move to preformed ear guides. While the memory wire used on past Campfire Audio cables worked, I found the “memory” aspect of that title limited at best which led to the wire straightening out over time. Ditching that entirely and running with preformed guides has resulted in a much more pleasant experience since I’m not constantly rebending the wire to ensure it stays behind my ear. This is a great new cable and I was pleased to see it included with some other new models, like the Polaris v2 and Andromeda v3.

When it comes to comfort you’d be forgiven for assuming Campfire Audio’s iconic angular shell design is a pain in the ear. Maybe for some, but not for me. Ergonomics are just right with the low profile IO conforming quite naturally to my outer ear. That plus the use of lightweight aluminum, a small size that belies the chunky appearance, and a reasonably long nozzle keeps the IO sitting in a way that does not feel out of place. While I find the stubby nozzle of the Andromeda more suitable to my personal ear anatomy, I can still wear the IO for hours without experiencing any discomfort.

The passive isolation of the IO is kinda weird. Low and high frequencies are significantly dulled when I have them inserted, Final Type E tips installed. This is great. Oddly though, vocals come through loud and clear, if not slightly dulled. As a result, I can have a video on in the background at my normal listening volume, IO inserted into my ears with no music playing, and follow along with the host/commentators just fine. This is actually really handy when using the IO in an office setting where you need to be able to hear your colleagues. That is, as long as you’re not using foam tips. Those tend to sop up vocals and muffle everything.


Tips: I found wide bore tips exacerbated the mids and treble making the IO flop over the edge into being overly aggressive. Small bore tips like the included Final Audio E-Type, foams, and other small to medium bore, soft silicone tips (ex. Sony hybrids, Spintfit CP100, etc.) were preferable since they curbed some of that edginess. My testing was done with the included Final Audio medium tips.

The IO has plenty of treble on tap giving it quite a bright presentation. Hi-hats, chimes, etc. are quite vibrant and can get tiring quickly. This was noticeable on King Crimson’s live recording of “Indiscipline” off the ‘On Broadway’ collection. In the first couple minutes the drummer gets to show off his skills and you are assaulted by a barrage of hi-hats. On the plus side, notes are fairly well-controlled with a satisfactory amount of space and air present. This keeps the IO from coming across congested and muddied when a song get busy. Attack and decay are expectedly quick, but not so snappy as to sound unrealistic. Detail and clarity are quite good too and I never felt I was missing out on any fine details, or that the IO was smoothing over imperfections. It sounds quite unforgiving and quite revealing actually.

Vocal presence in the mid-range is somewhat inconsistent. On some tracks, like Tom Walker’s “Now You’re Gone”, both male and female vocalists sound forward and prominent with neither standing out more than the other. Other times, like on Radiohead’s “Weird Fishes”, vocals fall back and sound recessed in comparison to the bassline and high hats, especially in the closing moments. This really only happens with male vocalists and it varies from track to track. The IO certainly feels most at home with female vocalists though. I was somewhat surprised with the IO since it handled Nicki Minaj well. Many earphones with unique mid-range presentations tend to make her sound very nasal, but that isn’t the case here. Running through “Ganja Burn”, her vocals are smooth and sweet, blending in perfectly with the simple instrumentals and background accents. When it comes to guitars and other instruments, timbre is too light but I otherwise enjoy the presentation. Take for example, Havok’s “Covering Fire”. Riffs chug away with a sublime attack and wicked texture. Pianos fall much into the same realm, as heard on the 51 second piano solo opening Supertramp’s “Bloody Well Right”. While the piano doesn’t sound quite right, it still manages to be entertaining and serve its purpose of pulling you into the track to preparing you for the eventual crescendo. The IO’s mid presentation is off, yet it didn’t manage to ruin the immersion of a good track, even one I’ve listened to as much as “Bloody Well Right”.

The IO is fairly light on bass, but it’s some quality stuff. First off, extension is outstanding for an armature with the IO able to reproduce the opening rumble on Kavinski’s “Solli”. While it’s often hard to tell thanks to the lack of emphasis, the IO can certainly provide a satisfying low end experience. Juice Aleem’s “The Fallen” absolutely relies on it’s strong bass line to carry the track and the IO takes it on like a professional. Texture is fantastic too, as evident on Tobacco’s work on his joint effort with Aesop Rock, ‘Malibu Ken’. The IO picks up all the grunge and distortion Tobacco layers onto everything, and tosses it back at you with aplomb. In addition to having plenty of texture, the IO’s low end is pretty quick, as is common with armatures. Each note of the rapid double bass found throughout Havok’s album ‘Time Is Up’ is well defined.

When it comes to sound stage, the IO’s intimate presentation results in a fairly “in-the-head” type of listening experience, with effects and notes dancing off into the distance every once in a while. It really shines in it’s depth portrayal which keeps instruments and effects well layered and separated, and restricts their ability to interfere and blend in with each other. Imaging is quite good with sounds very accurately transferring across channels. I found the IO to be a nice companion when playing competitive games like Counter Strike or PUBG where accurate imaging helps give you an edge in testy situations.

Select Comparisons (volumes matched using Dayton iMM-6):

EarNiNE EN2J (267.00 USD): The EN2J and it’s twin armature setup is much more balanced. Mids and treble are more forward than bass which is quite neutral, but neither steps forward as aggressively as it does on the IO. IO offers better extension in either direction, most noticeable in the bass which rolls off before really offering anything in terms of sub-bass. The EN2J’s bass is impressively quick and articulate, but I can see the lack of presence being a turn off for most listeners, especially given the IO isn’t particularly bassy itself. Mids on the EN2J are less forward but more balanced and slightly more detailed. They also feature that distinct breathy tone characteristic of EarNiNE’s in-house armatures. This unfortunately means it’s timbre isn’t 100% spot on either. While the EN2J’s sound stage is reasonably intimate, it comes across slightly wider but not quite as deep as the IO. Imaging, layering and separation is pretty even across the two with the IO offering slightly improved layering. Between these two, the EN2J does the mid-forward, treble prominent signature a little better. The IO certainly takes the cake in the low end, but I prefer the overall balance and presentation of the EN2J.

In terms of build, the IO is much more impressive. The EN2J isn’t poorly built by any means, but it’s steel housings lack the attention to detail in terms of fit and finish thanks to prominent moulding lines and plastic nozzles that detract from the premium aesthetic they were going for. The brushed aluminum face plate is also very susceptible to scratches, though it does look good. I quite like EarNiNE’s cable. While it doesn’t feel as durable as Campfire Audio’s, the light, flexible sheath completely stays out of the way. I love it. Comfort on both is excellent, though the IO fits me more naturally and remains less intrusive despite the extra size. I think it comes down to the nozzle design which forces the EN2J deep into my ear canal and pressed up against my outer ear. I also find I have to fiddle with it more to regain a lost seal.

ADV GT3 w/ reference filters (299.00 USD): The single dynamic GT3 also has a skewed signature, this time towards a v-shaped sound. Bass doesn’t dig quite as far as the IO’s armature but with the IO’s lack of sub-bass presence it doesn’t feel like it. Mids of the IO are more forward and prominent, upper especially, yet similarly detailed and clear. Timbre is more accurate on the GT3. Treble on both earphones is sharp and crisp with the GT3 sounding tighter and more controlled. The GT3’s peak around 6k gets tiring, though I can say the same for the IO’s peak further up. The IO has a more intimate presentation with a smaller sound stage, but provides a more impressive job of moving sound between channels. Layering and separation is equally good. I prefer the IO at lower volumes while the GT3’s dynamic provides more entertainment at high volumes, though that treble can be unpleasant.

In terms of build both are outstanding with flawless fit and finish, top tier cables, and cool designs. GT3 has a slight advantage in that it brings tuning filters to the party, whereas the IO is more ergonomic. Not only is it heavier, but the GT3 has a very sharp rear end which in some ears will cut into flesh and cause discomfort. I thankfully don’t have that problem during regular listening, but on a few occasions I have forgotten about that edge and when going to lay down jabbed my ear when the iem pressed into the pillow.

BGVP DM7 (299.00 USD): The six-armature DM7 has a more balanced signature with tighter, less aggressive treble, but it lacks the extension and upper treble presence making it come across somewhat numb. Mids on the IO are generally more forward and crisp with better clarity and additional detail, though somewhat artificial and thin when compared to the DM7. DM7 has the lead when it comes to timbre. On select tracks, such as Radiohead’s “Weird Fishes”, vocals on the DM7 come across more prominent in the mix. Bass on the DM7 doesn’t extend as far and sounds heavier, slower, and more mid-bassy. IO has a wider, deeper sound stage and does a better job of portraying various layers to a track, as well as separating individual elements. DM7 sounds more constricted and almost congested in comparison. I prefer the DM7’s overall tune but appreciate the IO’s technical proficiency.

In terms of build, IO is vastly superior. The DM7 is 3D printed which is in itself just fine, but my DM7 is a bit sloppy around the nozzle and in general feels less durable and looks less premium than the IO. There is also that loose MMCX port issue BGVP is currently dealing with, or has already dealt with if you’re reading this well into the future. Speaking of MMCX, both products have very nice cables with the DM7’s being thicker and more impressive looking. I think they’re equally solid, but I will say Campfire Audio has the better preformed guides. BGVP’s are somewhat loose around the cable and when it flexes you can hear ticking as the guide sticks and rubs against the wiring within.

Final Thoughts:

The IO is the kind of product that makes me hate having to put down a score when posting a review to Head-fi. On one hand, I entirely understand the criticism that has been levied at it’s unique tune. It’s bright, it can be tiring, it can be kinda harsh, and it’s not particularly natural sounding. I also found the mid-range inconsistent in it’s presentation across a number of vocalists. On an objective basis, it has issues.

However, enjoyment of an earphone is a subjective experience because everyone is unique. A headphone that measures near perfect, assuming the Harman curve is our target for perfection, will be both loved and hated because there is no one tune that everyone universally considers “good”. The IO isn’t an earphone for the majority, and that’s okay. Those who like it are probably going to like it a lot. It’s a fun, vibrant listen with decent technical prowess, great bass that takes you by surprise, and loads of detail and texture to go around. I wish it was a little easier on the ears and that it’s midrange and treble peaks were more relaxed, but that’s where an EQ comes in, pending you’re not opposed to tweaking your purchases.

While the IO’s sound signature is tuned for a specific crowd, the rest of the package is undeniably, universally fantastic. The unboxing experience is fun and attractive, and once you get inside you are treated to an extensive accessory kit filled with useful tidbits, like Final E tips, multiple mesh bags to organize and store everything, and a fantastic leather carrying case. Criticism has been levied at this case because it looks like something you’d store make up or coins in. I see where people are coming from with that. However, such cases are ergonomic and designed to be carried and interacted with frequently. This new case is just as spacious inside as Campfire’s old cases, but significantly more pocket friendly and easier to get the product into and out of. I think it is a fantastic addition and have no issues with it’s inclusion.

I like the IO, warts and all. If a bright, mid-centric earphone sounds like your jam, give it a shot. You’ll probably like it. It does that sound fairly well. For everyone else, there are lots of other products out there to cater to your specific preferences

Thanks for reading!

– B9Scrambler

***** ***** ***** ***** *****

Some Test Tunes:

Aesop Rock – The Impossible Kid (Album)

Hail Mary Mallon – Are You Going to Eat That? (Album)

King Crimson – Lark’s Tongues in Aspic (Album)

King Crimson – Starless and Bible Black (Track)

Supertramp – Crime of the Century (Album)

Infected Mushroom – Legend of the Black Shawarma (Album)

Gorillaz – Plastic Beach (Album)

Massive Attack – Mezzanine (Album)

Fleetwood Mac – Rumors (Album)

Run the Jewels – Run the Jewels (Album)

The Prodigy – The Day is My Enemy (Album)

Tobacco – F****d Up Friends (Album)

Felt – Felt 2 (A Tribute to Lisa Bonet) (Album)

Michael Jackson – Thriller (Album)

The Crystal Method – Grace (feat. LeAnn Rimes) (Track)

Jidenna – Long Live the Chief (Track)

Skrillex – Ragga Bomb (Track)

Big Grams – Run for Your Life (Track)

Funkadelic – Maggot Brain (Track)

Aesop Rock – Fishtales (Track)

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