Not all the very best, most expensive and most lusted-after headphones use planar magnetic technology. Some are electrostatic, and some are even dynamic. But many of the best do use this tech. So what are we to make of FiiO’s new JT7 planar magnetic headphones, which sell for less than $200 in Australia?
Table of contents
- Specifications and price
- What is “planar magnetic”?
- About the FiiO JT7 headphones
- Headphone output dependencies
- Listening with the FiiO JT7 headphones
- Who are the FiiO JT7 headphones for?
FiiO JT7 specifications and price
| Weight | 329.6 grams plus cable |
| Impedance | 18 ohms |
| Sensitivity | 92dB, 1mW@1kHz, 109dB, 1Vrms @ 1kHz |
| Frequency response | 7 to 40,000 hertz |
| Colour | Black Champagne Gold |
| Accessories | 1.5m cable with 3.5mm plug 3.5 to 6.25mm adaptor 1.5m cable with 4.4mm balanced plug Soft carry bag |
| Price (RRP) | $189 |
| Official website | FiiO |
| Local retailer | Addicted to Audio (includes local warranty) |
What is ‘planar magnetic’?
First, a little explanation. The great majority of headphones use ‘dynamic drivers’. These are just like small loudspeaker drivers. They use a diaphragm or cone – typically round and 40mm to 50mm in size, although that may vary – with a coil attached to a cylinder in their centre. The coil is immersed in a magnetic field. Apply a signal to the coil, and it interacts with the field, driving the cone forwards and backwards.
A planar magnetic driver has no coil as such. Instead, it has a conductive ‘trace’ – typically metal – attached to the surface of the diaphragm, wound over its face in such a way as to cover most of its surface. That is placed between two rows of magnets, one row in front and one behind. Again, the current through the conductor interacts with the magnetic field, making the diaphragm move.
So what’s the difference? The coil in a dynamic driver is attached to a relatively small part of the diaphragm, while the trace in a planar magnetic driver is spread over most of the diaphragm. In order to ensure even movement of the diaphragm, and no flexing (which causes distortion), the diaphragm in a dynamic headphone driver must be reasonably stiff, which adds weight. There’s no such requirement for planar magnetic drivers.
So, for example, the 95mm by 86mm diaphragm of the JT7 headphones is only 3mm thick. That is micrometres (aka microns), or thousands of a millimetre. And that exceptional lightness allows it to move extremely responsively.
One other difference is that the coil in a dynamic driver acts, electrically, like an inductor. So, along with some inevitable capacitances and the mechanics of the driver, there are resonances. This impacts the actual signal delivered to the headphones by some devices. Planar magnetic headphones have a vanishingly small amount of inductance, so they’re relatively immune to that problem. I dig into that below.
About the FiiO JT7 headphones
To be clear, the FiiO JT7 headphones are passive. No amplifiers, no Bluetooth. They connect to a device with wire. Which I say is great, because even the best Bluetooth codecs are inferior to wire.
They are over-ear, open-back models. They have large openings with soft padded earcups. These fully surrounded my ears, placing their modest pressure on my head without compressing my ears at all. I have a largish head, so most people should find them comfortable.
Open-back means that there is a grill on the back, not a closed container. Compared to closed-back headphones, open-backed ones tend to have a more open, airy sound. The downside is that they provide little isolation from environmental noise. Virtually all noise-reducing headphones are closed-back for that reason. Also, open-back models allow much more sound to escape to those around you. For commuting, always use closed-back headphones!
The cups have plenty of swivel and a good range of up/down adjustment. I can’t imagine them not fitting most people. The structural part of the headband is spring metal. Most of the other structural parts look to me like ABS plastic, although it can be difficult to tell. FiiO says that the various hinges are made with a “high-strength fibreglass material” and that they tested the expansion and twisting of the headphones over 10,000 times. I must say, these headphones do not feel like cheap headphones. Nor do they sound like them in one very important way: they never made creaking or cracking noises when I was using them. They deliver the music without any mechanical intrusions.
Two cables are provided. Both are about 1.5 metres in length, and both have a pair of 3.5mm TS (tip-sleeve) plugs at the headphone end, one for each side. That means that the cable is easily replaced or upgraded. One of the cables has a stereo TRS (tip-ring-sleeve) 3.5mm plug at the other end. This one is supplied with a 3.5mm to 6.25mm adaptor. That cable will work with just about any source device.
The other cable has a balanced stereo TRRRS 4.4mm plug. Balanced headphones use completely separate conductors for the left and right channels. Normal connections (3.5mm and 6.5mm both) share one “return” wire. After years of ad hoc ways of providing balanced connections, 4.4mm (aka Pentaconn) has finally settled in as the standard. Most modern digital audio players and higher-end desktop headphone amplifiers should support 4.4mm.
The headphones can fold up into a fairly compact package and come with a soft bag to carry them in.
The JT7 headphones are “Hi-Res Audio” certified. That’s a quality certification overseen by the Japan Audio Society and the Consumer Technology Association. With wired headphones, all it really requires is a measured frequency response out to at least 40kHz, an octave beyond the generally accepted 20kHz limit of human hearing. (That upper limit is for young, healthy people. Codgers like me have typically lost at least the top octave: 10kHz to 20kHz).
Headphone output dependencies
Well, ain’t that a weird subheading! But it’s actually quite important for sound quality for headphones, yet it’s something that’s not much mentioned in most writing on these matters. Here’s the thing: there aren’t any official standards, but in the real world, we’re gradually converging on some.
You may have noticed that in my reviews of the FiiO M21 DAP and the FiiO DM15 R2R CD player, I mentioned the output impedance of the devices. There were both under two ohms. That’s a good value. Some devices push things further, to under a single ohm. Why?
When you apply power to some gadget, the output voltage is split between the gadget and internal resistance of the thing supplying the power.
So what? Well, there are three consequences for headphones.
First, if the internal resistance of the source is high, less voltage is applied to your headphones. If the output resistance is, say, 500 ohms, and the impedance of your headphones is 250 ohms, they’re only going to receive one-third of the power. But most headphones have a much lower impedance. The FiiO JT7 headphones have a rated impedance of only 18 ohms, so in this case they’d get less than 4 per cent of the available power!
Second, the impedance of most headphones varies across the frequency range. Dynamic headphones tend to have an impedance peak somewhere in the bass, and lower impedance in the higher frequencies, due to those resonances I mentioned. If the device driving them has a high internal impedance, then the voltage supplied to the headphones will also vary by frequency. This can be a few decibels variation in some extreme cases. The problem isn’t so much that this happens, but that the results are quite unpredictable because this is rarely specified for headphones and, in most cases, headphone outputs on amplifiers.
Third, any electromagnetic device designed to produce sound – such as a headphone – is also a kind of microphone. If you vibrate its diaphragm externally, this will generate a voltage back into its input cables. And the same applies where the diaphragm of a headphone is not responding exactly to the signal. That will cause a back voltage into the driving circuit. The lower the resistance to that voltage, the more the untoward motion is physically resisted.
That might not seem obvious, but it’s true. A low driving resistance actually provides better control over the movement of the diaphragm, which means higher quality sound: less distortion and fewer other non-linearities.
So, why do I blather on about all this? The second and first are importantly influenced by the characteristics of the headphones.
The FiiO JT7’s 18 ohms impedance is quite low for over-ear headphones. You may find yourself having to turn the volume knob up a long way with some equipment. And, yes, some gear approaches 500 ohms in output resistance. That includes several well-known brands of home theatre receivers. To be fair, I haven’t measured any of them for about six years, so maybe they’ve reformed their ways. But the otherwise-excellent stereo preamplifier I use in my main system has 100 ohms of output impedance. I have to turn it up a long way with these headphones. Fortunately, it does go a long way, so volume level isn’t a problem.
That is not the case with my fairly new Lenovo Yoga notebook computer. Even at maximum volume, the Yoga didn’t manage to produce an engagingly loud level with these headphones. So I measured its output. It turns out that, at best – using test tracks which are almost as loud as is technically possible with digital audio (they are sine waves that peak at 0dBFS) – the Yoga can produce a maximum output of a little over 1Vrms. According to the FiiO JT7’s specifications, that’s enough for 109dB of output, so it should be fine. Except that the Yoga has, according to my measurements, an output resistance of 69 ohms. So the maximum it can deliver into these headphones is just over 0.2 volts, or less than 3mW, which means that they can produce a maximum of no more than 97dB with these headphones. And that’s using a maxxed-out track. With regular music, they’re much quieter.
The JT7 headphones were fine, however, with my MacBook Air M4. Its maximum output is just under 3 volts, and even into a 16-ohm load, it manages 1.5 volts just before clipping. That’s 160mW and, with these headphones, a theoretical 115dB. In large part, that’s because the Air’s output resistance is just 0.3 ohms.
It’s funny how a computer company can do audio gear so well. The waveforms produced by the Air on my oscilloscope were amongst the cleanest and most stable I’ve ever seen.
I solved the Lenovo Yoga problem by using an external DAC. I tried the headphones out with AudioQuest Dragonfly Red and Cyrus SoundKey USB sticks, and the sound was more than adequate (19mW, 105dB and 65mW, 111dB respectively). Even an old Asus USB-C to analogue audio dongle managed similar output levels to the Dragonfly.
In reality, the Lenovo was the only device I used that seemed inadequate. Even an old iPod Nano (7th Gen) was fine.
On the other hand, though, the FiiO JT7 headphones use planar magnetic technology. As explained above, they should be immune to the frequency response variations of dynamic headphones. I measured the voltage applied to the JT7 headphones with 466 ohms in series across the full audio range, and it varied by less than 0.1dB! That’s nothing. These headphones are immune to that kind of unpredictable frequency balance variation.
That was the case, even with the 100-ohm output resistance of my pre-amp. I had to turn it up louder, but it made no difference whatsoever to the tonal balance of the headphones.
Listening with the FiiO JT7 headphones
I used these headphones with all manner of gear, including that AudioQuest Dragonfly Red DAC plugged into the Windows computer, the Macbook Air (directly), a couple of FiiO digital audio players, including the M21, a couple of FiiO portable CD players including the DM15 R2R, an iFi Zen Can headphone amplifier, a fairly expensive Topping DX9 headphone amplifier/DAC combination, and of course my RMA ADI-2 Pro FS R Black Edition ADC/DAC. The very best performance was available from the last two, given their enormously capable output stages with stacks of available power and extremely low output impedances (around 0.3 ohms for each).
And mostly I used the 4.4mm balanced cable (except on the RME, because the wiring was too complicated).
To start, I spun up The Police’s final album, Synchronicity, in the FiiO DM15 R2R portable CD player. “Wrapped Around Your Finger” was superbly realised. Sting’s bass is prominent in the mix and the lower frequencies are properly reproduced by the headphones. Along with all the rest of the mix. The sound was clean and with no apparent distortion.
The JT7 headphones have a slightly prominent upper midrange. Not to the point of being irritating, but they can bring out any roughness in the recording. But they also sometimes enhance the sound by disclosing details that more precisely balanced headphones might recess.
I was intrigued by the bass. I pulled out a Telarc CD of Michael Murray playing Bach’s “Passacaglia and Fugue in C minor” on the Methuen Memorial Music Hall organ. The lowermost C on a grand piano has a fundamental frequency of 32.7 hertz. On this mighty organ, the lowermost C on the pedal has a fundamental frequency of 16.35 hertz.
The performance was stunning. It wasn’t just that the low frequencies were properly reproduced, but when the sound swells by something like ten decibels at the Passacaglia’s climax, everything is held together with enormous clarity. All those pipes were delivered without breakup or confusion. Superb.
For a total change, I spun up the dual LP of Chuck Mangione, Live at the Hollywood Bowl, on an Audio-Technica SoundBurger record player, the output of which was plugged into the iFi Zen Can headphone amp. Yes, I have better turntables, but for close headphone listening, the SoundBurger tends to paper over the clicks and pops, making for a more enjoyable experience. And enjoyable it was. The performance was tight, controlled, with the five-piece quartet (go figure) and the 70-piece orchestra rendered very nicely indeed. The only downside was the applause after each track, which was widely separated into the two earcups. That’s a mixing problem, less noticeable from speakers.
Who are the FiiO JT7 headphones for?
I was worried for a little while: had the couple of thousand dollars I paid for my Final Audio D8000 headphones been a complete waste? No, when I switched to them, the bass was even cleaner, as was everything else. Slightly.
But the sad truth is that for a couple of hundred dollars, you can get ninety per cent of the way to that kind of performance with the FiiO JT7 headphones. Well, sad for me. Pretty exciting for those who are just getting into quality sound.
Just remember, with their low impedance, they may not produce decent sound volumes with some gear, particularly computers.
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