REVIEW / MEASUREMENTS: KZ ZSN Pro - very inexpensive dynamic + balanced armature IEM. (And the importance of the audiophile "low end" and meaningful succession.)

Since I believe much of high-fidelity audio is already "mature" technology, these days a lot of what I find interesting are products that either present new features for the music lover (and audiophile), or devices that are of high value. In a present era of inflation and energy price shocks, "value" I think for most people has become even more important into the foreseeable future. As discussed in the past, the price of luxury items is usually a reflection of non-utilitarian benefits rather than actual sonic fidelity; that is basically the epitome of the "high end" moniker, behind which, much snake oil is allowed to thrive.

In this post, let's have a look and listen at an IEM which I think absolutely represents a member of the "high value" class of products! At less than US$25, the KZ "Knowledge Zenith" ZSN Pro IEM is at a price point that anyone can afford if you're in the market for some wired headphones these days (funny the designation "Pro" for something in this price point!). Considering the wide range of prices for headphones, it's the kind of thing you can throw in your travel bag and not worry if they get damaged.

The question of course is how do these sound!? Let's take a deeper dive into this...

Notice that I have the blue colored earphone here. They come in different colors with black, grey, gold, and purple options as well.

Here's a look at the open box and accessories these come with:

Nothing fancy in the box but build construction is good and it comes with 4 sets of single-flange ear tips - not bad for less than US$25! The 1.2m cable tangles and knots up quite easily which is not uncommon with this kind of design. Microphonics are not too bad and in fact better than the 1MORE Quad Driver or Etymotic ER-4B. Notice I got the one with the integrated microphone (white plastic controller button for mute/play, the variant with no microphone can be had for $5 less). The zinc-and-plastic earpieces feel sturdy and the transparent plastic siding looks quite nice with a glimpse of what's inside.

Internally, each earphone consists of a single 10mm dual magnet dynamic driver for the bass and mids, supplemented by a single small high-efficiency balanced armature driver (Knowles 30095) for high frequency extension. As one would expect, historically (and still used today), the little balanced armature drivers were developed for hearing-aid applications.

0.75mm 2-pin detachable cable (QDC / C PIN). There's a Bluetooth cable available. As well as non-microphone replacement cables. Note the 90° 3.5mm phono connector.

Make sure to connect the right and left sides appropriately. As far as I can tell, there's no right-left indicator as the sides are implied based on the orientation of the ear loops. Have a look at the image at the front of the box to make sure the orientation is correct. Even at this low price point, we can find IEMs with detachable cables which would have been nice with the 1MORE Quad Driver. The size of the ear pieces were comfortable for me but I can imagine them being a little large for some.

Total weight of the headphones including cables came out to 30gm.

Here's a closer look at the earpiece with tip being replaced:

Tip: notice I inverted the rubber "Starline" ear tip so I can fit the stem into the nozzle of the earphone easier.

The default ear tip size worked quite well for me achieving a good fit. You'll know the fit is too loose if the bass sounds lacking due to poor seal. The smaller ear pieces worked well for my kids.

This kind of ear-loop (pre-formed ear guide) design works well for me and the earphone will stay in place even when I'm out jogging. It's also quite comfortable over hours. No complaints on the ergonomics.

For the measurements, I'll use the standard ear piece that came attached when I opened the box; I think it's a reasonable size for the average adult ear.

I. Measurements

Can be a little tricky getting a good seal. When the seal is poor, the bass response droops.

As you can see above, here's the "big graph" of core headphone measurements. The frequency response portion in the top left I think shows us quite clearly the type of sound to expect. The two channels are close at about 1dB difference - excellent channel balance at this price point. It's a bit "V" shaped with strong bass which extends all the way to 20Hz. There's a mild recess into the midrange but no major valleys here to muddle vocals. And the treble frequencies have a "zing" to them. ;-)

That elevated treble will divide listeners depending on one's preference. If you like your high notes crystal clear - to the threshold of excessive brightness - these are the headphones for you!

These are low impedance headphones measuring 24-25Ω across most of the audible frequencies (specs say 24Ω). Sensitivity is high at 101dB/0.1V or around 105dB/mW measured - official specs say 112dB/mW but I'm measuring a result more like the ZSN non-Pro which is spec'ed at 104dB/mW. I had no problem achieving deafening output levels on my mobile devices.

The waterfall plot is interesting. Most striking is the resonance around 6kHz, a particular area of excess energy.

Distortion is primarily <0.5% 2nd order harmonic with output at 95dB SPL. This is relatively high total harmonic distortion but the 2nd order nature is innocuous and possibly even "euphonic". I confirmed this distortion amount with both right and left ear pieces.

Moving along, let's have a peek at the 100Hz square wave:

We see a bit of overshoot and ringing likely representative of the high frequency accentuation in the frequency response and waterfall graphs.

Noise isolation is quite good; obviously there will be some variation depending on the quality of the seal in the ear and the type of ear tip you use:

-25 to -30dB from 2.5+kHz is similar to the 1MORE Quad Driver and not as good as the Etymotic ER-4B with its triple-flanged ear tips providing even better isolation.

As for sound leakage:

At ~100dB SPL playback, 100-10kHz average leakage level is around 60dB SPL at 1" or 38dB SPL at 1', again very similar to the 1MORE Quad IEM. As usual, it's the higher frequencies that leak. At normal listening levels, this should not be a problem unless someone is sitting nearby in a quiet library.

II. Listening impressions...

These are good!

I knew that the reputation for these IEMs are quite good based on a quick online search, but was still surprised when I first had a listen. I did not notice any "break in" using these over the first couple of weeks by the way (as usual, other than maybe larger speakers, I don't believe "break in" happens generally with most electronic devices or smaller headphones after maybe an hour or two, don't even mention cable break-in ;-).

I find it funny when audio reviewers compare based on price point (as if there's some kind of "standard" sound for $100, or $500 headphones) since I think we're beyond that these days. I don't think there's a close correlation between price and performance fidelity anymore with many electronic products (especially things like DACs). All I can say is that these earphones produce seriously impressive sound and would compete with products at multiple times the price.

These KZ IEMs sound great with pop/rock where the combination of strong bass and clarity of the high frequencies really bring out the excitement in something like Kylie Minogue's DISCO: Guest List Edition (2020, DR6). I love the remix of "Real Groove" with Dua Lipa.

The excellent sub-bass performance accentuated the low frequency synths on Soft Cell's "What?" off The Very Best of Soft Cell (2002, DR8) or "Surface Pressure" off the Encanto (2021, DR9) soundtrack. Although the bass is strong, as usual with headphones, it's not the same experience as an actual subwoofer in the sound room as there's no visceral "thump" to the chest.

While dynamically rich and detailed, I think these headphones are not the best for "natural" acoustic recordings. For example, on TakéDaké & Neptune's Asian Roots (1998, DR13), I'm hearing a metallic edge to the bamboo flute on "Ocean Motion" compared with some of my better headphones. I did not notice any issues with other "audiophile" music like say Jennifer Warnes' "Way Down Deep" on The Hunter (1992, DR11). If you want to hear the effect of those treble peaks and how they accentuate certain tracks, have a listen to the overly crystal clear ring of the triangle (? maybe it's a synth) on Warnes' "I Can't Hide".

Due to the bright higher frequencies, these are not the most enjoyable headphones for some early digital recordings like Donald Fagen's Nightfly (1982, DR15) which I've always found to be already too thin-sounding with neutral gear.

The microphone (in-line right channel cable) was surprisingly good with voice calls over my phone using the inexpensive Soditer USB-C DAC adaptor previously examined (similar to this inexpensive adaptor); certainly sounds better than most wireless headphones I've come across. Just be careful with wind noise.

The only issue I ran into was with higher power desktop headphone amps like my Drop + THX 789 where I can hear a little bit of buzzing due to the sensitivity of the IEM, more in the right channel with the integrated mic/controller (I suspect no issues with the non-mic version). With highly sensitive IEMs >100dB/0.1V, very low noise headphone amps like the IEM output of the RME ADI-2 DAC are recommended.

III. In Summary

Are there better IEMs out there than the KZ ZSN Pro? Of course, there must be a ton of great ones out there these days at all kinds of price points!

But honestly, for the purpose of mobile applications to use when out and about, these <US$25 headphones sound good, the mic works well, they loop around the ears without falling off, and look fine even if generic. The dollar-to-performance value is phenomenal and like it or not, this "class" of low-budget IEM must be taking away business from companies selling headphones starting at many times the price!

If you've never owned or tried an IEM of this variant, this might be right for you. These headphones can give you a taste of what the modern hybrid dynamic + balanced armature combination can accomplish without in any way breaking the bank, nor shedding tears if broken in active use. Since preferences are subjective in nature, I bet for many listeners, the quality one gets from something like these would in fact be more than "good enough" for one's needs. From here, you can consider way more expensive options if you become a connoisseur in multi-driver IEMs!

I see that there is the newer KZ ZSN Pro X which is a few bucks more. According to this article with measurements, the X bumped up the upper frequencies even more! Considering that for my taste, I'm already close to the limit of how "bright" I want my headphones to sound with the ZSN Pro, any extra treble would be excessive.

As for EQ then, here's a setting that works for me listening in Roon:

Simple, narrow -6dB Q 2.5 attenuation at around 6kHz to just take the edge off the treble frequencies a bit without dulling the sound. On the old Stax The Space-Sound-CD (1988, binaural, DR12), this high frequency attenuation definitely improved the tonality of the violin on tracks 17 & 18, removing much of the metallic-like harshness (reminds me of the excess harshness in some metal tweeters). Since there are even higher frequency excesses, I'll leave it to you whether you might want to add something like a -3dB high shelf from 9kHz like this:

As usual, experiment! Our ears are all a bit different and likewise, preferences will vary.

I've heard that some folks use a layer of toilet paper under the ear tip to dampen the high frequencies. So I cut out some ~0.75cm x 0.75cm single layer tissue and using a blunt toothpick, carefully stuffed it under the ear tips making sure the center portion was only a single layer:

0.75cm x 0.75cm single-ply toilet paper. Carefully stuffed over the nozzle and under the ear tip.

And remeasured for change in frequency response:

Yeah, indeed we see that the "tissue hack" (it's not even a proper "tweak") does tame some of the high frequencies - about -3dB at 6.3kHz where the cursor is. At the same time, there's a relative increase in bass frequencies below 200Hz by about +1dB SPL. I had a listen and it does reduce the high frequencies in a positive way.

While this works, I would not recommend doing it in daily listening simply because I worry that the tissue paper will dislodge and get stuck in the ear. Digging out a small piece of toilet paper with tweezers deep in the ear canal would not be pleasant! Maybe there's a better way than naked toilet paper.☺ (I did not try, but maybe felt like what I used with the Dekoni Blue mod would work without too much dampening.)

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To end, I think it's interesting as audiophiles to consider very inexpensive devices like this and evaluate the sound quality one can achieve with little expense! I doubt you would ever see a product like this mentioned or tested in the pages of Stereophile, or The Absolute Sound, or even in many of the ad-supported websites. No doubt, if I were the manufacturer of expensive luxury items, I would be a bit threatened by the existence of such products and just how good they can sound. Enough to avoid spending advertising dollars to a magazine or website if the writers also gave exposure to this "cheap" stuff.

Regardless of how magazines might select products to review and highlight, in principle, I believe a vibrant audiophile community needs not worry about being open with hobbyists. This is how we, as consumers, push the envelope on value and sound quality. After experiencing something like this at US$25, we can calibrate our expectations for the kind of sound quality we expect when companies are demanding multiples of that price for yet another wired headphone. And in turn, "luxury" brands do need to consider just what they are bringing to the table to entice consumers; is it truly better sound quality, better build and materials, style and design, accessories, features?

Even if grey-haired audiophiles might be unaware of earphones like this, I don't think it's stopping younger music lovers. To cover this price point is to embrace the younger folks who are already exploring products of good fidelity without breaking the bank. I think it would be wise for the audiophile media to make sure they explore the "low end" of MSRP. Whether blatantly consciously aware or not, there is often an air of arrogance on audiophile websites and forums that need to be called out and addressed. There are places on the Internet (like Mono & Stereo, or ridiculous people like Peter Qvortrup, and more we'll talk about next week) where this arrogance is simply nauseating. The implied correlation between price and sound quality that's used to justify the expensive "high end" IMO has broken down all over the place (from DACs to amplifiers to digital streamers to speakers and headphones). 

In every long term venture, we must consider legacy as well as making sure that there is a path to succession. I've often wondered leafing through the pages of various magazines what they would look like in 10 years if they're catering to the "high end" hobby. Would we still have large glossy ads about expensive cables that likely make no difference, be treated with front-page reviews about speakers that cost >$100,000 (inflation adjusted of course in 10 years), expensive audiophile streamers and servers that are really nothing more than dressed up computers a hobbyist can DIY, unnecessarily expensive amplifiers with questionable objective performance, and mere turntables with people talking about amazing sound quality from an archaic spinning plastic medium? All this while tending to exclude the average younger folks, those who want to prioritize finances elsewhere, or perhaps pragmatic (even "rational") audiophiles who look at the nice CNC metal fascia and see nothing but hype rather than sound quality improvements.

My belief is that the mainstream audiophile magazines as they exist today and the "high end" have already well begun their decline as a subgroup among the greater audiophile hobby. This will not harm hobbyists with the desire of achieving "high fidelity" audio; in fact, it might spur greater interest as a result of attitude changes that are more inclusive, less pretentious, and frankly more objectively honest. Audiophilia in pursuit of fidelity as a philosophy will live on regardless of the health of the "high end" Industry and no doubt there will always be hobbyists to discuss opinions and engage in healthy, if not heated, debates with.

That's all for now, dear audiophiles. Until next time, I hope you're enjoying the music. Happy Easter weekend.