Will I need a dedicated headphone amp for planar magnetics?

[Bautastein]

Hi,

I’m considering getting a pair of magnetic planar headphones for music production. In particular the HifiMan Edition XS has caught my attention, but also the Sundara and the cheaper HifiMan HE400se are on my radar.

I am currently using the headphone output of an Apogee Quartet audio interface. The info I’ve found on it is that its maximum output is +19dBu, which equates to 7 Vrms, and output impedance is 30 ohms. The recommended listening levels for mixing is 65 dB SPL, and for mastering is about 80 dB SPL (average), but some go a bit higher. And sometimes you wanna have some fun and play really loud, but not most of the time. Equalization will be used for a neutral sound, so bass may be boosted a bit.

I see many reviewers indicate that the Edition XS, and almost any planar magnetic, will require a powerful headphone amp. I’m not sure whether the amp in my audio interface is up for the task. According to HifiMan, the sensitivity of the headphones is rated as 92 dB @ 1mW, and its impedance is 18 ohms.

Some say the impedance of the headphones must be at least eight times the output impedance of the amp. In that case the amp in my audio interface would be hopelessly inadequate. However, I thought maybe that didn’t matter since the impedance of planar magnetics is constant.

I know I could just try it out and hear for myself, but since I haven’t bought the headphones yet, it would be good to know whether I’m likely to have to factor a headphone amp into the budget. It may also affect my choice of headphones. Also, for all I know, the shortcomings of an inadequate headphone amp might be something you need practice to hear. I might attribute to the headphones or music something that is actually caused by the headphone amp.

 

[oleg87]

However, I thought maybe that didn’t matter since the impedance of planar magnetics is constant.

You are correct in that it won't change the FR, though you will lose some output level to the output resistors.

If you're not intending to crank it, it's likely fine, but Apogee’s specs are not really sufficient for any certainly about how loud it can go. Audio interfaces are often not great at driving more demanding low-impedance loads.

 

[DVDdoug]

And sometimes the published impedance spec for a headphone amp is the minimum headphone load, and the actual output impedance is lower.

The recommended listening levels for mixing is 65 dB SPL, and for mastering is about 80 dB SPL (average), but some go a bit higher.

Who's recommending that?

There are really no standards unless you are using the K-System. You'd have to figure-out how to calibrate your headphones. It's normally done with monitors and an SPL meter.

Here are some excerpts I've collected about mixing & mastering with headphones (most pros recommend against it).

This is from Recording Magazine "Readers Submissions" where readers send-in their recordings for evaluation:

As those of you who have followed this column for any length of time can attest, headphone mixing is one of the big no-no's around these parts. In our humble opinion, headphone mixes do not translate well in the real world, period, end of story. Other than checking for balance issues and the occasional hunting down of little details, they are tools best left for the tracking process.

And this is from a mixing engineer, also Recording Magazine:

Can I mix on headphones?

No. But in all seriousness, headphones can be a secret weapon and it really doesn’t matter what they sound like…

Over time, after constantly listening back to my work from different studios on those headphones I really started to learn them. They became sort of a compass. Wherever I went… It became a pattern for me to reference these headphones to see if what I was hearing was “right”…

I learned them, I knew them, I trusted them. It didn’t matter whether or not I loved them…

So, can you mix on headphones? Probably. I just think you really need to put some time into learning them first…

This is from Floyd Tool's book, Sound Reproduction

Headphones entertain masses of people. Professionals occasionally mix on them when conditions demand it. Both rely on some connection to sound reproduction, that is, loudspeakers in rooms, because that's how stereo is intended to be heard. Stereo recordings are mixed on loudspeakers.

This is from Ethan Winer's book, The Audio Expert:

(Headphones) are not usually recommended for mixing music because you can hear everything too clearly. This risks making important elements such as the lead vocal too soft in the mix. Mixes made with (headphones) also tend to get too little reverb, because we hear reverb more clearly when music is played directly into your ears than when it's added to natural room ambience...

...It is good practice to verify edits using (headphones) to hear very soft details such as clicks or part of something importing being cut off early.

 

[Bautastein]

Who's recommending that?

Justin Coletti from SonicScoop-dot-com is one. I have not been following this guideline before, I have not even been looking for guidelines on it. However, since I needed some numbers to indicate to the forum about expected listening levels, I did a search on the topic.

Here are some excerpts I've collected about mixing & mastering with headphones (most pros recommend against it).

I know it's generally frowned upon. However, it beats a horribly treated room like mine, and I have neighbours who complain as well. As you may have guessed by now, I'm not a pro. More like a happy amateur. And for my kind, more and more pros have come out and said (admitted) that headphones are probably the way to go.

Investing in a pair of great headphones is a helluva lot more economical than spending tons of money on renting or buying a studio, plus room treatment, acoustic isolation and you-name-it...

 

[Vincent Kars]

Maybe try a cross feed, it makes STEREO on a headphone sounds like Stereo.

I thought maybe that didn’t matter since the impedance of planar magnetics is constant.

Indeed a damping ratio of 10 or better is recommended. In case of a fluctuating headphone impedance, you have a fluctuating demping ratio, in case of a planar a constant demping ratio and your case a 18/30 a horrible one.
A major reason why there are headphone with 300 Ohm or higher is indeed that one can combine them headphone out of 30 ohm and still have a decent damping ratio.

 

[AnalogSteph]

As mentioned:

If you're not intending to crank it, it's likely fine, but Apogee’s specs are not really sufficient for any certainly about how loud it can go. Audio interfaces are often not great at driving more demanding low-impedance loads.

Without some data points of max output voltage for various different load impedances, it'll be very hard to tell.

Either way, you wouldn't need anything terribly expensive in terms of amp. Run the headphone out into one of the usual $99-140 candidates from Sabaj / JDS Labs / Topping / Schiit, and you should be fairly well-prepared.

 

[solderdude]

Some say the impedance of the headphones must be at least eight times the output impedance of the amp. In that case the amp in my audio interface would be hopelessly inadequate. However, I thought maybe that didn’t matter since the impedance of planar magnetics is constant.

Correct for planar magnetics and other headphones with a constant impedance, at least for what possible changes in tonality is concerned.
However, due to voltage division and current limiting the max. output level for low impedance headphones with a low sensitivity will be low,

 

[ExPerfectionist]

I recently got the Hifiman Edition XS. They sound "fine" paired with my iPhone and standard Apple dongle. The cord is a bit old and sometimes cuts out, so I got a spare from JSAUX on Amazon, also under $10. A better dongle with more might sound better?

On my work laptop, where I listen to a lot of music during the day, I use USB out to a DAC > Marantz AVR > speakers. I also have a Focusrite Scarlett Solo gen 3 DAC/mic/headphone unit that I use for podcasting, and use the Hifiman headphones with this hooked up to the work laptop.

I was also worried about enough "power" from this, like you OP, but I looked up the amount of headphone power needed ( https://www.headphonesty.com/headphone-power-calculator/ ) using the Edition XS stats, and about 1 volt is enough for them. My Scarlett Solo puts out that much, so it's got enough power, I assume.

 

[solderdude]

using the Edition XS stats, and about 1 volt is enough for them. My Scarlett Solo puts out that much, so it's got enough power, I assume.

Actually the Edition XS is 14 ohm and thus the solo will only put out 0.53V so reach 103dB peak (80-90dB average).

 

[Bautastein]

Indeed a damping ratio of 10 or better is recommended. In case of a fluctuating headphone impedance, you have a fluctuating demping ratio, in case of a planar a constant demping ratio and your case a 18/30 a horrible one.
A major reason why there are headphone with 300 Ohm or higher is indeed that one can combine them headphone out of 30 ohm and still have a decent damping ratio.

Thank you. While I had already figured out about the voltage divider effect, from my rudimentary electronics knowledge, I didn't know about the damping factor. So, as I gather, the headphone amplifier with lower output impedance will be more in control of the driver diaphragm, making it stop when it needs to stop and reduce unwanted resonances, which could lead to a clearer sound. Pretty much all info I could find about the effect takes for granted that the headphone drivers are dynamic, so I reached out to HifiMan support with the following two questions:

1) Does the same concern about electrical damping also apply to planar
magnetic drivers, like they do to dynamic drivers?

2) Does the new very thin diaphragm of the Edition XS alleviate or
perhaps even remove the need for a high damping factor, due to lower
inertia?

The answer from tech support (which came as fast as anyone could possibly answer a question like that) were as follows:

1.Electrical Damping in Planar Magnetic Drivers vs. Dynamic Drivers:
Electrical damping in dynamic drivers (which use a voice coil attached to a cone or dome) is crucial because it helps control the motion of the diaphragm by dissipating excess energy, thus reducing unwanted resonances and improving sound quality. In contrast, planar magnetic drivers have a flat, thin diaphragm with conductive traces that interact directly with magnetic fields. The mechanical properties and the way these drivers operate mean they rely less on electrical damping and more on the physical design of the driver itself, including the strength and configuration of the magnets and the tension and material properties of the diaphragm. Thus, while electrical damping is still relevant, its role and impact are different compared to dynamic drivers.

2. Impact of Very Thin Diaphragm in Edition XS on Damping Needs:
The new very thin diaphragm introduced in headphones like the Edition XS is designed to reduce mass and inertia, which can indeed affect the need for high damping. Lower inertia means the diaphragm can start and stop more quickly in response to audio signals, potentially leading to better transient response and clarity. However, whether this alleviates or removes the need for a high damping factor depends on several factors including the specific materials used, the design of the magnetic structure, and the intended application. While a lower inertia diaphragm might reduce some forms of distortion related to excessive movement, effective damping is still important to manage other types of resonances and ensure clean sound reproduction. Therefore, while the thinner diaphragm does contribute positively to performance, it doesn't entirely negate the importance of having an appropriate damping strategy.
In summary, both electrical damping and mechanical design play critical roles in optimizing the performance of audio drivers, regardless of their type. Innovations such as thinner diaphragms in planar magnetic designs aim to enhance performance.

I guess this still leaves out the question of whether I can actually hear the difference, but if the damping ratio of 18/30 is "horrible", I suppose I can.

 

[Bautastein]

I was also worried about enough "power" from this, like you OP, but I looked up the amount of headphone power needed ( https://www.headphonesty.com/headphone-power-calculator/ ) using the Edition XS stats, and about 1 volt is enough for them. My Scarlett Solo puts out that much, so it's got enough power, I assume.

Thanks, that was a nifty tool. I'd like to take the opportunity to confuse you some more.

All good music has a certain dynamic range. For this reason, streaming services like Spotify, Apple Music etc., play the music at reduced average levels, to allow for volume differences in the audio stream, which translates to peaks in the output voltage much higher than the average RMS level. Spotify plays the music at about -14 dB LUFS, while Apple Music plays it at -16 dB LUFS to allow for even more dynamics.

This makes me curious about these output voltage specs given for various headphone amps: Are they absolute, momentary limits, or are they averages over longer time periods, allowing for short bursts of higher amplitudes? For popular music like I listen to (meaning not classical), the bursts of higher amplitude peaks are often snare drum hits. Since they are already a chaotic mess of frequencies, it may not matter of you get some clipping at higher listening levels.

Nevertheless, the calculator doesn't seem to specify whether the output loudness you specify is an average level, or a maximum short burst level. If it is the maximum short burst level, you might have to bump up your numbers in the input field to allow for some dynamics.

 

[ExPerfectionist]

Actually the Edition XS is 14 ohm and thus the solo will only put out 0.53V so reach 103dB peak (80-90dB average).

I got the 1 volt number for the Scarlett Solo gen 3 from here:

Teardown, few basic measurements and personal thoughts of the Focusrite Solo Gen3

I recently purchased the Scarlett Solo 3rd Gen and couple of mics, mostly for podcasting and audio measurements. The new generation seems to be better than the previous one regarding on how it measures; feel free to compare...

www.audiosciencereview.com

"the built-in headamp is able to deliver over 1V RMS with a good audio quality (THD+N of 0.004%)"

 

[Bautastein]

OK, I went to a hifi store today, and came back with a pair of Sundara headphones. The Edition XS had an amazing out-of-head experience, I could not believe it was actually coming from a pair of headphones, and the sound felt very spacious and detailed. Also the bass was fantastic, with total control. Nevertheless, the Sundara had a more coherent sound to my ears, due to having more midrange. It was an easy choice for me. The guy in the store had a background as a mixing and mastering engineer, and while he actually preferred the Edition XS, when describing the Sundara he said the magic word, my favourite word of all time: "neutral". I was sold.

It sounds great on my Apogee Quartet interface, but I have to crank the volume up high, almost to the top, to hear it loud enough to be fun. I'm using headphone correction EQ from autoeq based on oratory1990, and they indicate a pretty large negative gain, and on top of that mixing is typically done at a very low audio level to begin with, at maybe -21 dB avg RMS level or so. So the sound in the digital domain, before reaching the DAC, is already rather attenuated. I guess I don't need the negative gain of those correction EQ profiles for my use case.

The Sundaras are rated as 32 ohms impedace, with a sensitivity of 92 dB @ 1mW.

Nevertheless, I can't help but wonder whether I could make it sound even more fantastic with a headphone amp, although it already sounds fantastic to me...

 

[SuicideSquid]

OK, I went to a hifi store today, and came back with a pair of Sundara headphones. The Edition XS had an amazing out-of-head experience, I could not believe it was actually coming from a pair of headphones, and the sound felt very spacious and detailed. Also the bass was fantastic, with total control. Nevertheless, the Sundara had a more coherent sound to my ears, due to having more midrange. It was an easy choice for me. The guy in the store had a background as a mixing and mastering engineer, and while he actually preferred the Edition XS, when describing the Sundara he said the magic word, my favourite word of all time: "neutral". I was sold.

It sounds great on my Apogee Quartet interface, but I have to crank the volume up high, almost to the top, to hear it loud enough to be fun. I'm using headphone correction EQ from autoeq based on oratory1990, and they indicate a pretty large negative gain, and on top of that mixing is typically done at a very low audio level to begin with, at maybe -21 dB avg RMS level or so. So the sound in the digital domain, before reaching the DAC, is already rather attenuated. I guess I don't need the negative gain of those correction EQ profiles for my use case.

The Sundaras are rated as 32 ohms impedace, with a sensitivity of 92 dB @ 1mW.

Nevertheless, I can't help but wonder whether I could make it sound even more fantastic with a headphone amp, although it already sounds fantastic to me...

Take care to protect your hearing.

 

[solderdude]

I got the 1 volt number for the Scarlett Solo gen 3 from here:

Teardown, few basic measurements and personal thoughts of the Focusrite Solo Gen3

I recently purchased the Scarlett Solo 3rd Gen and couple of mics, mostly for podcasting and audio measurements. The new generation seems to be better than the previous one regarding on how it measures; feel free to compare...

www.audiosciencereview.com

"the built-in headamp is able to deliver over 1V RMS with a good audio quality (THD+N of 0.004%)"

yes, but not in 14ohm

 

[Bautastein]

yes, but not in 14ohm

Perhaps there is a confusion about the impedance of the Edition XS? According to HifiMan, it should be 18 ohm.

Headphones & portable audio - HIFIMAN.com

 

[solderdude]

I measured it at 14ohm.
Efficiency: 91dBmW
Sensitivity: 109dBV

Specs from HIFIMAN are often incorrect.

 

[oleg87]

Nevertheless, I can't help but wonder whether I could make it sound even more fantastic with a headphone amp, although it already sounds fantastic to me...

If you've got the money to spare it won't hurt.
Something like the Topping L50 might be a good choice to run them off the TRS outputs of your interface.