Headphone Measurements Explained - Frequency Response Part Two

Target Response
In Part One of this article I introduced a bunch of concepts that resulted in a target headphone response curve (as measured at the ear drum) that looks something like the black plot above. (The green plot is what speakers, equalized to be flat in the room, look like at the ear drum.) To some extent, it's necessary to memorize certain aspects of the curve above in order to be able to mentally compare it to the raw frequency response plots when you look at headphone measurements. The first thing to do is establish a 0dB reference level, which should be the lowest point, or the average level, of the mid-range (~200hz-1kHz) on the raw frequency response plots. These are the characteristics you should look for:

  • +4dB rise in the bass, starting no higher than 200Hz and at full level by 60Hz.
  • From 200Hz to just over 1kHz, you should have a gentle 3dB rise.
  • The main peak of the plot should be at 3kHz +/-500Hz ideally. If the peak starts getting too high in frequency the sound can get quite piercing in nature.
  • Although the curve can get fairly noisy above 3kHz, it should generally follow the profile shown and be roughly back to 0dB at 10kHz. And a less noisy frequency response curve is generally better sounding.
  • Above 20kHz the plot should continue to fall off to about -13dB below baseline.

The above curve is right out of Sean Olive's paper "Listener Preferences for In-Room Loudspeaker and Headphone Target Responses" and my notes above are for that curve. My personal sense is that it's close but not quite right. So here are a few variables to consider:

  • I think the bass may be high by a small amount, I'd rather see 3dB in the bass. I do agree that the bass emphasis should all be below 200Hz, any higher at all, and you start to hear the lower mid-range start to thicken up unnaturally.
  • The 3dB rise from 200Hz to 1.2kHz is so rare that I really can't say much about whether it's right or not. This rise mainly comes from the head and torso interaction that is bypassed by headphones, so I would think it's something that should be there on headphones, but it might be very difficult to achieve.
  • I think +12@3kHz might be a a few dB high. I'd say you want this peak between 10dB-12dB, but not higher lest there be daggers in your ears.
  • Although headphone measurements may be noisy and have lots of peaks and valleys above 3kHz, on average it is good to see the level back to between 0dB and 3dB at 10kHz. It is very common to have a peak in response near 10kHz due to an ear canal resonance; this peak being higher than the average level can be okay if nearby frequencies remain near the target curve level on average.
  • It is very difficult to get a real sense of where the levels are above 10kHz since measurements are so noisy and plagued with resonance artifacts, but my sense is the Harman response curve shows too much roll-off. I think that while levels above 10kHz should continue to fall, the drop should be more like -10dB.

Okay, lets take a look at headphones that approach the above curve, and some that don't, and what that means when relating measurements to the listening experience.

Later, will also look at some of the characteristics of ear pads that can be seen in the frequency response curves; characteristics that are unique to in-ear monitors; and a few other odds 'n ends that can be seen in the frequency response plots of headphone measurements.

Historical Headphones Relative to the Target Response Curve
The point of this section is not only going to be identifying headphones that approach the target response, but also noting how they deviate from the curve and what character it might give the headphones apart from sounding neutral. Remember, we're going to be talking primarily about the lower gray curves that are the raw frequency response measurements from the dummy head with microphones at the ear drum position. (The upper blue and red curves are compensated.)

Lets start with a few headphones that have historically been considered "good" sounding.

Sennheiser HD 580
Headphone101_InterpretingFrequencyResponse2_Graph_HD580 For this plot, we'll call the -25dB line the 0dB reference. You can see that the peak at 3.3kHz and +12dB over baseline is just about right when compared to the target response curve at the top of the page. The fall above 3kHz is somewhat too steep with the peak at 10kHz just reaching the 0dB line, and the average falling significantly below. This would cause the HD 580 to sound somewhat laid back, and, of course, this headphone is famous for having very good, but "veiled" sound.

You'll also note the bass is not accentuated but is, in fact, rolled-off in the low bass. Fifteen years ago headphone enthusiasts really didn't complain of the HD 580 not having enough bass; that kind of response in headphones was the norm. We were used to it.

AKG K701
Headphone101_InterpretingFrequencyResponse2_Graph_AKGK701 Another old favorite is the AKG K701, which generally considered a brighter headphone than the HD 580 but still fairly neutral when it was first introduced. Here you can see there is no well defined peak at 3kHz and that area only rises about 8dB above baseline. More importantly, above 3kHz it continues at +8dB to 5kHz before beginning to descend to baseline around 10kHz. There's quite a bit more treble energy in the K701 than the HD580 above 3kHz relative to each other.

You'll also notice the broad mid-range hump is centered at about 300Hz, while it's centered at 120Hz on the HD 580—that's more than an octave higher in music, it's quite a bit of difference in the overall center of emphasis. This makes the the bass sound just a bit warmer on the 580 than the overall cooler sounding K701. The point here is that the K701 and HD 580 clearly sound different while there measurements are not that dramatically different. Subtle interpretation is important to get things correct.

Beyerdynamic DT 880
Headphone101_InterpretingFrequencyResponse2_Graph_BeyerDT880 We might as well have a look at the Beyerdynamic DT 880 as it joins with the first two as the triumvirate kings of the headphone hill for quite a while. Here you can see that the DT 880 has quite similar response to the HD 580 to 3.5kHz. Above 3.5kHz the DT 800 remains high and the 10kHz peak is at +10dB relative to baseline, with an average level at about +3dB at 10kHz. Energy above 10kHz is about 5dB higher than either the HD 580 or K710. The DT 880 was a bit brighter sounding than the K701.

Denon AH-D5000
Headphone101_InterpretingFrequencyResponse2_Graph_DenonD5000 Another old school headphone that had a strong following for its good sound is the Denon AH-D5000...and its siblings D2000 and D7000, which were similar. While it doesn't have the step up in the bass of the target response curve it at least does rise about 5dB from baseline, which gave this headphone a sense of heft and body the the first three lacked, and which was broadly appreciated by enthusiasts.

Unfortunately, while the 3.5kHz peak is in a good place 12dB above baseline, it subsequently looses little energy and remains 5dB above baseline to about 13kHz before dropping. This made these headphones somewhat too hot in the treble for some listeners (me included), and was particularly noticeable on the D2000.

Sennheiser HD 800
Headphone101_InterpretingFrequencyResponse2_Graph_HD800 Introduced in 2009, and remaining still one of the finest reference headphones on the planet, the Sennheiser HD 800 shows some improvements over the HD580/DT880/K701, but also some troubling features. The bass response doesn't roll off as fast as the first three, which gives the HD 800 a stronger punch down low. The rise to 3kHz is good and the subsequent response has fairly good shape without excessive peaks and valleys. However, everything above 3kHz is also about 3dB too high as well, making these a headphone that can be too bright for comfortable listening.

Audeze LCD3
Headphone101_InterpretingFrequencyResponse2_Graph_AudezeLCD3 Then about five years ago we started hearing planar-magnetic cans and people were immediately drawn to their powerful and tight bass response. The graph above shows the LCD-3 with a wonderfully flat bass extension. Even though it's below the target response, it's much flater and better extended in to the lowest notes than anything that preceded it. People love planar magnetic headphones for their well extended bass response. I have to say though, after having spent some time now with headphones that more closely conform to the base boost of the target response, I do feel that it's more pleasing, and a more subjectively accurate representation of neutral.

The plot above is from one of the earlier LCD-3s that were considered somewhat lush in the mids and polite in the treble. In the plot above we do see a slight rise from 200Hz to 800Hz, which gives the sense of strength and character to the vocal harmonics. But the subsequent dip before the peak at 3.5kHz puts the LCD-3 a little off the pace in the presence region—the sound of spit on the lips or saliva on the reed of a sax is going to sound a little laid back. Also, above 3kHz it falls too quickly and, other then the level of the 10kHz peak, is about 5dB below the target curve. All this might make for a headphone that is too polite in sum, but the treble above 10KHz actually rises above the target and somewhat makes up for the slightly too dark treble otherwise.

Two things to note here. First, this is where the value of measurements end, and only experience can fill in the blanks. Yes, the LCD-3 is a bit too low in the low and mid treble (though the peak at 3kHz is the right height), and a bit too hot in the top octave above 10kHz, but it's not too far off. The question is: does that sound bad or good? Because it can go either way. And second, we're only looking at the FR measurements and not able to analyze all the other plots. There are further hints about sound quality gained by looking at transient and distortion characteristics, but there again there are limits to how much information about the quality of the listening experience that can be gleaned through measurements.

Stax SR-007
Headphone101_InterpretingFrequencyResponse2_Graph_StaxSR007 Last old school headphone that needs to be viewed would be a Stax electrostatic. Many would say the SR-007 shown above is the best of the lot.

I'm not certain, but I would assume the drop in the bass is due to a pad resonance. Electrostatics have a reputation of having poor punch in the bass, but I think that's a bit of an overstatement. I think there has been some problems with pads and how they fit historically, and I do think that larger electrostatic panel speakers may have had poor bass impact, but from what I've heard and can tell from measurements, electrostatic headphone have fairly good bass response; certainly as good or better on average than open dynamic headphones.

Above 200Hz the curve does have a nice rise to 1kHz, but subsequent rise to 3.5kHz is a bit of a roller coaster and on the low side of optimal at 8dB over baseline. The fall after 3.5kHz starts off about right but at about 8kHz begins to gather about 5dB of energy and keeps that emphasis for the remaining treble. Like the LCD-3, Laid back in the lower treble ranges, hot in the top treble ranges, but overall close. It's just how it all comes together in you ears that will determine wither it's good or bad for you.

Current Headphones Close to the Target Curve
The next group of plots will be from current headphones that I've measured and appear to come close to the target response curve. They all sound fairly good, in my opinion. That's not to say there arent good sounding headphones that farther off the target curve, or headphones that may be close to the curve but sound poor, I'm just saying the headphones on the target curve seem to have a pretty good probability of sounding good.

NAD VISO HP50
Headphone101_InterpretingFrequencyResponse2_Graph_NADVISOHP50 The first headphone that I've measured that had a raw response very close to that of the target response curve is the NAD VISO HP50. Paul Barton designed this headphone with a very clear picture of the acoustics and studies surrounding the development of target response curves in general. He went straight to the drawing board with his own target response curve using the trademarked term "RoomFeel." The result is a headphone with a very pleasing and fairly neutral sound, and a measured performance quite close to the Harman target response.

In the plot above, you can see that though the bass has a very typical broad hump characteristic of dynamic headphones, there is an overall rise of about 5dB over baseline. The transition upward into the bass starts at about 400Hz, which is a bit high in frequency and will typically cause a bit of thickness to appear in the low mids. From 500Hz up to 3.5kHz we see a beautiful profile that very closely fits the target response and indeed the HP50 does a very nice job of rendering vocals with a natural timbre. Though there's a dip at 6-7kHz and a small peak at 10kHz, the overall profil of the upper treble on the plot matches the target response well.

It's probably a good time to note that a dip somewhere between 5-8kHz in response might actually be preferred to the Harman target response in the region. Work by Philips on the X2 headphone suggested to them that a notch in this region is subjectively preferred. Too much energy in this area can be quite abrasive to the ears. I don't know this for sure, but if you see a dip in the 5-8kHz region it might be a good thing.

Another thing to start noticing as we look at cans that have good matching with the Harman curve is the shape of the compensated curve. As I mentioned in part one of this article, I use the "Independent of Direction" compensation provided by Head Acoustics, which is quite similar to the "Diffuse Field" response. One thing you'll notice is that if a headphone closely matches the Harman curve, it results in a relatively featureless sloping line that gradually drops of faster as you go higher in frequency. The one exception is the peak at 10kHz, which can be overemphasized by the compensated curve.

Focal Spirit Professional
Headphone101_InterpretingFrequencyResponse2_Graph_FocalSpiritProfessional While the Focal Spirit Pro plot below 3kHz is a little smoother than the HP50, it doesn't do quite as good a job of producing the long linear rise from the mids to the 3kHz peak. It's more liquid and coherent sounding bass through mids, but it's also a tad polite in the presence region sounding a bit more laid back than the more correct to my ears HP50.

Headphone101_InterpretingFrequencyResponse2_Graph_FSPHD600SquareWavesThe valley at 6-8kHz, peak at 10kHz, and subsequent peaks and valleys are not optimal, but after having looked at hundreds of headphone frequency response plots I've found that this feature is surprisingly common and often fairly benign. I'm going to break my rule about remaining with frequency response plots only, and show the 300Hz square wave for the FSP and HD600 (which has a similar look to its FR plot). You can see that rather than a clean initial step there is some ringing. I don't know for certain, but I think this may be a fairly natural result of ear canal resonances due to the way some headphones acoustically interact with the ear, and it might be that the auditory perception system knows how to ignore it. In any case, when you see the a frequency response plot with three big peaks at 3kHz, 10kHz, and 15kHz, and the triple ringing front end of the 300Hz square wave, it's a good bet that while the treble may not have superb transient response it will probably sound okay. This measured feature seems to look worse than it sounds.

Shure SRH1540
Headphone101_InterpretingFrequencyResponse2_Graph_ShureSRH1540 At first glance the Shure SRH1540 looks quite a bit like the target response curve. The bass boost is nicely placed with a start to the boost at 180Hz, but at +8db over baseline at 50Hz is a tad excessive. The peak at 3.5kHz is of proper height, but lacks the long slope upwards from 200Hz, causing it to loose some presence and richness of vocal overtones. The decent of the treble above 3kHz has fairly good shape, but should probably fall of a little faster and be down another 3-5dB at 20kHz.

In short, it's got a bit too much bass and high treble, and lacks a bit in the mids—a mild "U" shaped response, and that's exactly the way it sounds. One thing worth mentioning here is that while a "U" shaped response may be too exciting for some (me included) at solid listening levels, it tends to sound great at lower volumes as it delivers a bit more bass and treble, just like Fletcher and Munson prescribe. So, if you listen a lot at low levels (as I often do) this is a terrific headphone.

All the headphones above are around-the-ear, sealed headphones, which seem to be the most likely type of can to get close to the target response—especially in the bass—but there are a few headphones of other types that get close.

Philips X2, circumaural, open
Headphone101_InterpretingFrequencyResponse2_Graph_PhilipsX2 Open, dynamic driver headphones have a much tougher time getting the bass extension of sealed dynamic headphone, and you can see that the X2 does fall off at about 6dB/octave below primary driver resonance at about 60Hz. However, unlike the three open headphones at the top of this article, the mid-range is not a broad hump but rather is flat with a hump only below 200Hz. This is a fairly good approximation of the target response for an open headphone.

The mid-treble peak has about the right level, but centered at 4.5kHz is a bit high. However, this headphone was designed with a lot of feedback from trained listeners, and it was determined that a notch at 6-8kHz makes for better listening. This notch could very well have required a bit more energy both before and after to help compensate for the loss of treble energy in the notch. The result is a nice, warm, friendly sounding headphone, but I think all the tuning to get the curve into the desired shape has caused the response to lack a little smoothness and, as a result, sounds a bit grainy to me.

V-Moda XS, on-ear, sealed
Headphone101_InterpretingFrequencyResponse2_Graph_VMODAXS The XS has a somewhat excessive bass response that bleeds too far up into the mids giving them a bit of thickness to the sound. But the fact that the rise to 3kHz starts below 1kHz, and the fall above 3kHz (though starting off a bit fast) has good proportion makes for a really lovely sounding headphone.

V-Sonic GR07 Bass Edition, dynamic driver, in-ear
Headphone101_InterpretingFrequencyResponse2_Graph_VSonicGR07BassEdition This is a headphone I heard only briefly after measuring it and seeing such good measurements, so I really can't comment in depth. ljokerl can however, and in his GR07 review on TheHeadphoneList.com he gave the GR07BE a 9.1/10 in sound quality.

One thing I will point out however is the peak at 5kHz being equal in level to the one at 3kHz, which might skew these headphones into sounding a tad bright. ljokerl's comment at the end of the review has him pointing to "Mildly sibilant on some tracks" as one of the GR07BE's cons.

Here are a few more IEMs that measure relatively close to the target response. I'll just post them without comment.

Headphone101_InterpretingFrequencyResponse2_Graph_MOESS01

Headphone101_InterpretingFrequencyResponse2_Graph_MonsterLadyGaga

Headphone101_InterpretingFrequencyResponse2_Graph_SteelseriesFluxInEarPro

Headphones a Little Farther Off the Mark
The above headphones are about all there are that are very close to the target response curve. Let's look at some fairly good sounding headphones that are a little farther off the curve and see if their failings match their deviations from the target.

Beats Solo2
Headphone101_InterpretingFrequencyResponse2_Graph_BeatsSolo2 A big round of applause for Beats getting this damn close to the target response, the new Beats Solo2 is a good sounding headphone—WAY better than the first Solo. However, you can see that the bass boost goes all the way up to 500Hz, which causes the low mids to sound quite thick. And while the peak at 3.5kHz and subsequent drop to 10kHz look fairly good, the drop between 10kHz and 20kHz is far too excessive, causing the headphones to lack a sense of spaciousness.

AKG K267 Tiesto
Headphone101_InterpretingFrequencyResponse2_Graph_AKGK267 The K267 has a switch on the earpieces that changes the internal acoustical tuning to adjust the bass to three different settings. In the "Club" setting it does a fairly good, if a bit rough, job of mimicking the target response, especially in the long rise to the 3.5kHz peak from ~300Hz. It has a fairly wide notch above 3.5kHz, which may sound okay, but it does seem a bit too wide to me. Above about 8kHz the curve looks good.

Musical Fidelity MF100
Headphone101_InterpretingFrequencyResponse2_Graph_MusicalFidelityMF100 When I first saw my measurement system draw out the plots for the Musical Fidelity MF100 I was giddy with excitement, it looked like it was very close to the target response. But as you look at it a little more closely, you'll see the 3.5kHz peak is about +3dB too high, and the subsequent run up too 10kHz remains far too high in level. In listening this headphone sounded mostly good but somewhat piercing to me, and caused me to put more credence on Philip's idea that taming the 6-8kHz area might indeed be a good idea. The MF100 is a bit hot there and suffers dearly for it. You may also want to take a peak at the full measurements to see how this treble boost made for a very significant leading edge spike. So, close, but no cigar.

Audio Technica ATH-M50x
Headphone101_InterpretingFrequencyResponse2_Graph_ATHM50x Though pretty rough looking due to some pad bounce artifacts between 80Hz-300Hz, the M50x response is quite close to the target curve from 20hZ to 4kHz, especially between 300Hz and 3kHz, and this is indeed a good sounding headphone. Above 4kHz is a notch probably too large, but response is in place above 10kHz. Overall, the tonality of these headphones is excellent, but, as evidenced by the herky-jerky response, they aren't particularly refined or liquid sounding.

Okay, that's probably enough on the target response curve, let's turn the page and look at some of the other things that can be seen in the raw frequency response measurements.

ARTICLE CONTENTS

COMMENTS
Inks's picture

I'm surprised you didn't include:
Sony MH1C [though based on results compared other graphs, I think this unit is one of those off-units that tend to pop up once in a while].
Lg Quadbeat: bass is excessive but it follows it quite well in certain areas

To note, insertion depth and tips plays a huge role with IEMs. Insert certain tips [long narrow bore] on something like the KC06 and those two last peaks on it's plot are gone and it's overall following the plot well. Same goes for DUNU DN1000 and 2000. K3003 are considered top of the line, yet don't seem like much on it's on raw measurement........

Two IEMs that I feel will follow the curve very well are the Aurisonics Rockets and the budget Zero Audio Tenore.

love these articles. Seems like frequency response is finally getting looked into more, like it should have been.

zobel's picture

Those last three headphones look to be broken! woah.
Some questions;

1) Do you measure and graph at a reference voltage at a certain frequency, allowing the sensitivity of the cans to be displayed, or do you adjust input power to achieve a reference dB at a certain frequency?

2) Does a headphone response curve change at different power levels?

3) All over the ear cans seem to have a peak at about 3.5 kHz with a very similar dip at twice that frequency, about 7 kHz, that if you draw a line through the middles of, from about 2 kHz to 10 kHz, you would get the smooth curve, like the model. Why are the peak and dip an octave apart? Is the peak due to the closed tube resonance of the ear canal? Is the dip also a resonance response?

Again, Thank you for being so diligent and helpful, and giving us something to chew on. Shouldn't be too tough to come up with a true compensation curve from your raw data, since we are doing that mentally now anyway.

zobel's picture

is useless isn't it? I also think the Oliver curve should include the dip around 7 kHz. Since your raw data looks so good below 1 kHz, no compensation needed right? Could it be possible to take all the data on headphones that sound right above 1 kHz and closely follow the Oliver curve, with the addition of that dip around 7 kHz, and come up with your own target raw curve with that dummy head of yours?

Seth195208's picture

It's Gulliver.

zobel's picture

Hmmmm.

marab's picture

Thank you so much for this (and previous)article! I learned so much!
Now, a question - seems like Focal Spirit One S have quite right frenquency response, don't they? I would like to buy something sounding "right", meaning it follows to a degree the perfect response curve described in this article, but also is a bit fun - meaning slightly enhances bass (but still very tight). I could buy Focal Classics but they are supposed to be very mellow, right?
I like the segment of portables that can succesfully act as home closed headphones - such as Momentums Over Ear, Focals, Fidelio L2, NAD VISO, Beoplay H6 etc.

Long time listener's picture

My opinion is that IEMs need to show a stronger low bass response on the graphs in order to sound subjectively right. The lack of in-room resonance (as with speakers), or ear-cup resonance (as with over-ear or on ear models) suggests that, subjectively, they won't sound as bassy without boosting the bass slightly higher. Of course what I hear may be due to other factors as well.

So the IEMs that sound best to me include ones that have been characterized on this site as being too bassy: the Philips TX1 and the Beats Tour 2.0, as well as the NHT Superbuds and the Nuforce NE-600X.

Please don't try to force everyone to meet your target curve--you'll be ruining the experience for some of us.

Hjelmevold's picture

In my opinion, trying to simulate room (bass) resonance using amplitude adjustments is a pipe dream. While room resonances cause resonant peaks in amplitude (and importantly: also nulls!), resonances are primarily a time-domain effect - something that amplitude adjustments cannot adequately simulate on their own.

Hjelmevold's picture

What listening level was used in the experiments that have led to the Harman Target Response Curve? Could it be that the bass boost in these curves is to compensate for experiments done at a low listening level?

Studio monitors that measure more or less flat are usually designed for listening levels at around 85dB SPL, which is a great monitoring level when I'm doing 8-hour long studio mixing and mastering sessions. But the sound becomes considerably more bassy at levels that I've witnessed that my clients enjoy, say 110dB SPL. A simple hypothesis is that this is a more "fun" and emotionally engaging listening level / frequency response. Perhaps the listening level in the Harman study was lower than what the test subjects were used to, and that the test subjects were trying to compensate for this, by preferring a response curve with bass boost?

Rillion's picture

In the following paper Olive et al (page 6) used 78 dB B-weighting.

http://www.aes.org/e-lib/browse.cfm?elib=16768

At 110 dB SPL, your clients are risking serious hearing damage. If the damage is already done, then they might only be able to hear bass.

In an Airo study referred to at
http://headwize.com/?page_id=266%C2%A0 , listeners preferred 69dB SPL (don't know what weighting) average level on headphones in a quiet room. The link to that study is missing now.

Even sustained 80 dB SPL (C-weighting) seems awfully loud to me. However, I understand when recording music you want to have the best signal-to-noise ratio that you can get with your gear.

Hjelmevold's picture

Thanks for finding the data on the levels that were used!

I don't want to conclude that those levels were the reason for a bass boost in the compensation curve, as the proper scientific way to find out would be to repeat the experiment at a louder listening level. But I do have my suspicions that it does matter quite a lot.

69 dB SPL (if used correctly, dB SPL means no weighting at all) is quite a low listening level, given that many living rooms in an urban environment have a background noise level at 40-45 dB(C) because of outside traffic, ventilation/A.C., refrigerators... It is surprising to me that 30 dB dynamic range would be an average desirable listening level, so I suspect that the testing room must have been significantly quieter than the more typical 40 dB(C) background noise. This could have led to participants accepting a lower listening level compared to a real-life situation, and at lower levels, a greater bass boost is desired. But this is just my theory.

For motion picture sound, the traditional Dolby standard has been to calibrate for 85 dB SPL, and although there are different standards, this has been adopted in many pro audio studios as well. But I don't know if this has anything to do with the fact that ISO 226 and other equal-loudness contours seem to flatten out a bit at around 85 dB SPL...

I don't think musicians and other clients in the studio wanting to listen much louder than this is so much about signal-to-noise ratio (you hear worse if you get ear fatigue!), but rather that people want to be blown away, almost literally.

zobel's picture

When you refer to 85 dB level for monitoring recordings, are you talking about average levels or peak levels?

Hjelmevold's picture

Technically, it's neither. Originally it was just a reference level for calibrating VU meters. According to the original Dolby standard, 85dB SPL is meant as a reference level for 0vu in analog mixing desks, which means that while dialog usually is played back much lower than 85dB SPL, occasional transients like gun shots could be as loud as +20vu (105dB SPL).

In music studios however, the "85dB limit" is followed mostly in order to protect against hearing loss, as 85dBA is accepted by many sources as just about what can be tolerated during 8-hour long sessions without inducing hearing loss. Thankfully, a mixing engineer is typically only exposed to music 20-50% of the time on a job.

But to try to give a simple answer to your question: The measurement is done RMS (one method of calculating average), and not peak level, which allows for occasional transients to be louder than this. Typically, during tracking (recording), 85dBA is set to equal -18dBFS digitally due to the dynamic nature of raw audio. But when doing mixing/mastering, I would work at levels around 80-85dBA RMS depending on how much dynamic compression was applied to the music.

But practices differ. The mastering engineer Bob Katz has recommended music to be calibrated for 6dB lower than the film standard.

zobel's picture

I didn't know how much headroom was above dBFS exactly before. I have been trying to get maximum s/n by keeping levels as high as possible, and with my meters, uncompressed acoustic sources, especially close mic'd percussion has to be at a lot lower ave dB, or RMS levels than other sources. The Tascam 8 track I use has kind of hard to read meters compared to those on my mixer/pre-amp or on my CD recorder. Sure is easy enough to hear when the levels get too high though, since distortion slams in on peaks.
I think I tend to work at about 80 dB mostly too, but with some stuff, I can let it ride at 0 VU a lot, or 85 dB RMS.
I'm still learning and really appreciate the link and discussion!

zobel's picture

headroom there is to dBFS from 0 dB. I have LEDs that signal over load on my Tascam machine, and LCD bar graphs for monitoring levels, but there are no over load indicators or peak level markings on those, so you're supposed to keep the bar graphs from remaining at top position very long, whatever that means.

I like the LED displays that are calibrated on the CD recorder and on the mixer much better! I have been learning to read those LCD bars just by experience, and practice.

Thanks again!

Inks's picture

One thing to add is that these bluetooth IEM seems to be the first IEM to be actually tuned with that curve, by Harmon Kardon. It follows it quite well, I just wonder how it's distortion figure looks....
link: http://en.goldenears.net/en/files/attach/images/108/170/056/24d9c649bb7d...

zobel's picture

Yeah its.. Sean Olive, not Olive Oil, not Oliver, and not Gulliver,
and you doesn't has to calls him Johnson.

Seth195208's picture

.

Claritas's picture

This is best article on headphone measurements to date. Thanks so much Tyll for sharing your expertise.

I would note, however, that HP50 and FSP did *not* sound very similar to me, which is unfortunate for HP50. (It's possible that my HP50 was defective, but that sounds like a bad excuse to me.) I hope that Focal develops a truly over ear model with even better sound. The demand is definitely there.

gatucho's picture

I believe that some of the interpretations made based on how the FR "looks" are rather simplistic and lead to bias when assessing a HP performance. For instance take this conclusion made by some hearing researchers for comb filtering in speakers:
"Two speaker mono was considered superior to the one speaker, one path mono. A reflection from a vertical surface was barely audible but a horizontal reflector was more audible. An electronic delay comb filter was highly audible and annoying" found here http://www.madronadigital.com/Library/RoomReflections.html

And this is only for the subject of comb filtering, which I always have found to be misunderstood.
Measurements are accurate, our hearing isn't; however, music pleasure is not made with scopes but with our ears which are not even closely modelled with a simple "ideal" FR. Sorry Olive and company

Overheat's picture

Would you be able to subtract the target curve from the measured curve to easily identify at what frequencies the headphones response is emphasised or lacking? I think that would be easier to read. What do you think?

Tyll Hertsens's picture
Yes, it can be done. I tried it here.

Eventually I'll develop a good curve and when I have an on-line automated way to display the data that compensation curve will be available. Until then I need to stick with the current method on the spreadsheets as I can't go back and change the hundreds of spreadsheets I have. So for consistency sake I won't be changing until the on-line tool is available.

markanini's picture

Apple IEMs are pretty close to Harman target too.

markanini's picture

Polk ultra focus, Shure SRH440 in the 300-3k range.

markanini's picture

Koss Porta pro and KSC75, and AKG K81DJ Are pretty close above the bass range.

keyser's picture

For the last couple of months I have been an avid reader of your reviews and background articles. I've learned a lot and I would like to thank you for that! Based on your recommendations I ordered a pair of NAD HP50's, which are expected to be delivered next week. I'm really excited and would love to compare them to my good ol' Sennheiser HD600!

In the above article you discuss the 300 hz square wave of the Focal Spirit and the Sennheiser HD600. You say you wonder why there is ringing in them. Look at the step response and you'll notice that there are almost four little peaks in one millisecond. Four cycles per millisecond equals 4000 hertz. That means that there is an indication of a resonance just below 4 khz. Both headphones indeed do have a response peak at about 3.5 khz, so this is most likely the cause of the ringing.

Because the peak in the response is supposed to be there, the ringing in the 300 hz step response is perfectly normal.

Badder's picture

Thank you for the amazing overview of headphone measurements you provide in this and the other articles, it's been a great learning experience.

One question though - all the freq. response graphs in this article include vertical lines marking the logarithmic frequency scale, which is very helpful for those who like me can't still visualize the frequencies in a graph without that aid. Why are these omitted from the headphone measurement results pages and what is the meaning of the vertical and horizontal lines one sees there instead?

Thanks!

Badder's picture

I'll answer myself as it turned out to be a PDF renderer issue.

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