Introduction:
If an in-ear manufacturer introduces a new in-ear with a dynamic driver that has a (nano) coating that has not yet been used by any other manufacturer, this is usually greatly exaggerated in marketing terms and advertised as a special, extremely innovative feature that, how would it be different, significantly improves the sound.
If those newly developed in-ears had crystal receivers, the manufacturers would probably somehow be able to advertise them as exclusive and of high quality as well.
Flashback: Years ago I bought a used Super 8 film camera including the original leatherette bag and the manual. It wasn't until about 2013 that I noticed that there was a small ear canal phone in one of the side pockets, namely the Sony ME-21 piezo-electric crystal in-ear to which this review is dedicated.
Due to the age of the in-ear it was even unknown to Sony Japan and it was no longer possible for them to give me any information about the earphone with the sound-generating crystal due to the piezoelectric effect, because archive material about that time (1970s, possibly a little earlier (late 1960s)) does not exist at Sony anymore, according to their own statement.
The functional principle of such a piezo-electric crystal driver, which in-ears still rely on this technology today (RHA, Radius), and how the Sony ME-21 sounds, is what I have compiled in this review.
Delivery Content:
Since the ME-21 is the first and only headphone I ever bought used (and I happen to have bought it even without knowing it), I can't tell if it was ever sold separately or if it was only included with detector receivers, film cameras and other electronic devices from that time. Whether it was equipped with accessories, such as ear pieces in different sizes, is therefore unknown to me (I'm guessing "no"). In the leatherette case of my Super 8 camera, there was only the ME-21 with that amber-colored tip.
Nevertheless, I was kind enough to make a protective, padded storage box for the in-ear and put it on my in-ear shelf.
This and That:
The type of cable used (very thin and very fragile appearing), as it is still used at Sony, as for example also on my Sony XBA-C10, has a long tradition, because the cable of the old ME-21 doesn't differ clearly from my much newer in-ear except for the color and is qualitatively also quite thin, although it has a better kink protection than some of Sony's new cheap models (which doesn't say much, because the ME-21's kink protection is only rather basic and the cable generally looks very cheap and fragile).
On the angled jack plug you can see the names "Sony" and "ME-21".
The grey plastic shell with the "Japan" lettering on the inside, corresponding to the colour of the cable, looks relatively stable, although it largely follows the cheap feel of the cable and looks rather thin.
An optically welcome contrast is provided by the surrounding black stripe, which connects the two halves of the shell.
The nozzle of the ear canal receiver has a notch that ensures that the amber-coloured ear tip with angled sound canal fits perfectly and without rotating.
It is not unlikely that the crystal receiver was delivered with only one ear piece at the time, which means that the number of people who are ideally suited to this rather small standard size and have a correct seal in their ears is probably quite small.
I have very large ear canals, for which the small, amber-coloured tip is definitely too small. But if I use the ME-21 turned by 180°, with the cable running upwards over the ears, it is the housing of the in-ear itself that interestingly achieves a very good seal for me, which makes an exact evaluation of the in-ear possible in the first place.
Since the cable is very thin and light, there is no cable noise.
Logically, the overall isolation is not particularly high due to the fact that only one earphone sits in only one ear, but the noise isolation is even better than average in the ear in which the Sony is sitting with the good seal I reach in my ears.
Sound:
In an in-ear with piezoelectric crystal receiver, unlike in "normal" headphones, no classical membrane with magnet and voice coil is responsible for the sound reproduction, but a high-impedance crystal (e.g. quartz) that is able to reproduce tones through the piezoelectric effect - if a voltage is applied, which is logically supplied by the source device the in-ear is connected to, the crystal is deformed. Since the voltage is an alternating voltage, the crystal begins to oscillate. This oscillation is then transmitted to a simple, electrically conductive membrane, which makes the oscillations audible.
So it is a very simple, cheap, easy to produce technology, which was used decades ago in cheap crystal receivers like my Sony ME-21, but is still used in some cheap loudspeakers, although not exclusively, because with know-how and more development effort you can also produce tweeters with good measurement results for loudspeakers. However, the main field of application still lies in the cheapest possible applications - such as the sound transducers in melodic greeting cards or smoke detectors.
By the way, the tweeter in the RHA CL-1 is also a piezoelectric driver... The Japanese manufacturer Radius, whose models seem to have a much more even and natural treble than the CL-1 according to various reports, also uses such a tweeter with piezoelectric principle in its hybrid in-ears.
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Since the amber-coloured tip is way small for my large ear canals, I have to use the case of the ME-21 itself to achieve a seal (which fortunately is quite ideal).
Another possibility is of course the use of modern silicone earpieces in my size - such as the SpinFit Tips, which I usually don't like very much and which, admittedly, harmonize quite well with the ME-21.
Nevertheless, for the next sections I used the in-ear mainly with the original amber attachment, while the shell of the in-ear itself served to achieve a seal in my large ear canals.
Tonality:
The sound of the ME-21 can definitely be described as a little "telephonic" and bright, so it has a raised upper midrange and a somewhat uneven treble.
The level rises slightly from 900 Hz to 2 kHz, but only slightly. Directly after this, at 3 kHz, follows a rather narrow, powerful peak, followed by another, somewhat weaker, albeit still bright, emphasis at 5 kHz. At 7 kHz the next peak follows; above it, the level rolls off (editor's note: if you use the SpinFit tips, everything stays practically the same, but there is an additional emphasis at 9 kHz and less restrained super treble extension).
Accordingly, voices are on the somewhat brighter side, a tuning preferred by some Asian in-ears to give singers clarity and make the sound appear clearer and airier.
Due to the uneven treble it unfortunately appears quite sharp and harsh, which can be fixed with a good software EQ, if you are willing and able to do it.
Cymbals sound damped by the rolling off level above 7 kHz, but this doesn't necessarily have to be considered negative because of the already existing sharpness.
(Editor's note: if I use the in-ear without any tips at all and only use the shell to achieve a seal, the intensity of the peaks decreases and the treble therefore appears somewhat less bright and more even and natural in comparison.)
A very positive surprise is the bass and fundamental range of the in-ear, but only if you reach a very good seal. Without a good seal there is practically no bass and fundamentals, and the sharp treble and bright midrange are all you hear.
Provided you manage to achieve a very good seal, the ME-21 rewards you with a bass and fundamental range that is almost perfectly diffuse-field neutral like an Etymotic ER-4S/ER4SR. Only at 100 Hz there is a small resonance (which is amplified when using the SpinFit Tips).
Up to 40 Hz the level remains constant and 30 Hz are still audible. Only the vibrations at 20 Hz are no longer really perceptible.
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With a more even, less bright treble, the Sony ME-21 could have come very close to the diffuse-field target curve, so it is one of the few in-ears that actually aims for such a flat, diffuse-field-neutral bass range. However, its uneven treble destroys it all.
Resolution:
Overall, the detail resolution, as one could expect, is rather low. The detail level is sufficient for most mainstream pop and electronic recordings, but the ME-21 struggles (heavily) with more complex, multi-layered recordings in terms of separation of the individual tonal elements, which is sometimes also due to its distortion levels that rise quite quickly with increasing volume.
While for people who usually listen at low volume, like myself, the playback is still relatively clean, the in-ear already begins to distort at increasing volume levels, which for many represent an average room level. At what most people would call normal volume/high volume, the distortion is already very noticeable.
The resolution in the midrange is fine for a canal phone that could be classified in the cheap segment, but does not have particularly high texture or fine speech intelligibility/resolution (fine nuances in the voice are somewhat lost).
For such an old earphone, the level of detail, although a bit grainy, is still quite neat and still a good deal higher than that of an over-ear headphone from the time of the Second World War, which I was able to audition a few years ago and which sounded quite horrible.
Separation of individual notes/instruments is present in the treble, although definitely not particularly noteworthy or even outstanding.
And again, it is the bass range that provides a positive surprise, because it is pleasantly tight, fast and well controlled - all that however only at low to lower average volume levels.
Here (, if used at low volume,) the Sony outperforms most in-ears in the low price segment quite noticeably, even though it doesn't quite approach the strength and speed of my Fostex TE-02, although it manages to beat my Logitech/Ultimate Ears UE200 audibly beats in this discipline.
Only a moderate dullness and a rather weak texture can be attested to the bass, which by the way reacts well to moderate EQ adjustments without becoming muddy.
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All in all, the Sony ME-21 is definitely a low-end in-ear, even though it has a nicely tight and crisp bass, which is rarely encountered in this performance range.
Although the in-ear doesn't come close to good budget models in terms of detail resolution, it's still better in this discipline than many cheap earbuds and in-ears of the well-known manufacturers for $10 to 35 from an electronic store or some of the older in-ears of Knowledge Zenith.
Someone like me who usually listens at low volume can get along with the ME-21, even when playing music, but the majority of people who don't listen to music at low volume are very unlikely to.
Soundstage:
The ME-21 is a mono-in-ear with only one earpiece, so there is no soundstage.
Conclusion:
The old Sony ME-21 has an extremely cheap cable, won't achieve a correct seal in most people's ears (although this can be fixed quite easily with most modern silicone attachments), isn't particularly level-resistant, a bit too sharp in the high frequencies and uneven, and offers a level of resolution only suitable for the beginner's range.
Nevertheless, it can be used for listening to music, although preferably with EQ adjustments, so it has a nicely fast and tight bass range that follows the diffuse-field target (provided you get a good seal), responds well to the equalizer, and is not worse than rather decent budget models - as long as you use it at low to moderate volume.
But ultimately there really is no point in listening to music with only one mono earpiece.