Frequency response
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published: Mar-18-2017, updated: Sep-6-2020
Frequency response deviations, as well as phase response, are so called ‘linear distortions’. Phase response is not covered in this topic.
Linear distortion does not produce new (unwanted) signals, contrary to non-linear distortion. When a headphone, speaker, amplifier or DAC has little to no linear distortion the frequency- (and phase-) response is flat.
All frequencies are there in equal amplitude and in the same phase. When this is the case AND non-linear distortions as well as the time-domain issues not being there the reproduction of the original recorded signal is perfectly reproduced.
This does NOT mean the reproduced signal sounds like a real-life recording. In fact a recording may sound quite poor but can also sound extremely nice.
How good a particular recording sounds, under these circumstances, depends completely on the recording itself. ALL aspects of that recording and those are MANY.
Deviations in the frequency response (linear distortion) largely determines the tonal character of a headphone.
Certain linear distortions in the frequency response are often preferred over no linear distortion (flat frequency response) by most listeners. This can depend on factors like:
- taste/preference of a specific sound signature/color
- music genre (also a form of taste)
- listening level (loudness)
- circumstances/surrounding
- mood
Think of preferences like:
- boosted bass
- rolled-off treble
- scooped out mids
- bass light
- elevated treble
Some poorer recordings may sound somewhat better on headphones with a specific coloration such as ones with elevated bass, ‘warmer’ or ‘colder’ sounding headphones or headphones with a dip between 1kHz and 5kHz (takes the ‘edge’ of recordings).
Headphones like that, however, may sound ‘exaggerated’ in certain aspects or ‘veiled’ with well made recordings though.
This thus is a very good reason to own 2 or more headphones with a different tonality so you can pick one based on your taste.
A one headphone does all perfect solution does NOT exist unless all recordings were perfect and all tastes were the same.
One should chase their OWN personal preferences/sound signature and not those of others. What others might find ‘perfect’ may sound as an abomination to others/you.
That being said, my personal preference lies in ‘flat’ with a few dB (sub)bass boost to compensate for the lacking tactile ‘feeling’ of bass. Believe it or not but low frequencies are also picked up by nerves in the skin which ADDS to the low frequencies we hear with the ears. This ‘lack’ of sensory input can be more or less compensated by adding some extra bass. At least for me this helps.
For me otherwise ‘flat‘ (+ that small bass boost) sounds as perfect as can be expected with well made recordings and my personal taste in music. Therefore this is what I chase and hope to find. The plot below thus sounds good to me with well made recordings. When poorer quality sound is heard then I realize it sounds poorer because the recording is poorer.
Sometimes I then reach for a different headphone or skip the song/album.
When a headphone would exist with a flat frequency response as shown below in the plots on this website it has slightly elevated bass in reality.
No headphone nor speaker will ever have a response as shown above. Amplifiers and DAC’s could well have a response as shown above.
All frequencies should be reproduced equally loud when the same amplitude signal is applied. This is something that is easily achieved in the electrical domain by amplifiers, and music sources. At least all good equipment should at least have a range between 30Hz and 18kHz without a deviation relative to a signal of 1kHz smaller than 0.5dB. Differences of 0.1dB are almost impossible to detect. An amplitude step of 0.2dB is detectable by most. A gradual sloping frequency range that drops of a maximum of 0.5dB at the extremes of the range (20Hz and 20kHz) is considered to be indistinguishable by most people. A difference of 3dB is already clearly noticeable and 6dB is a halving of the amplitude. For the human hearing a 10dB difference is considered a halving (or doubling) of the perceived loudness of a signal. Strangely enough a 10dB doubling is not perceived the same as a 10dB decrease in amplitude due to the way our hearing works.
Sonic characterization
Loudspeakers (the better ones) can be reasonably ‘flat’ from 50Hz to 20kHz within +/- 3dB. Top of The Line speakers may even go from 30Hz to 30kHz within +/-1dB when measured in an anechoic room. It is impossible to reach those values is a normal (listening room) though. For headphones it is even harder, if not impossible, to create a flat frequency response over the entire frequency range for many physical reasons.
In reviews a certain terminology is often used when we speak off bass, mids and treble e.t.c. All of these ‘regions’ have a specific band in the audible range. The graph below shows where these sonic descriptions are in the frequency range. This will help to understand how the terminology is used to describe if a certain ‘range’ is lifted (peaks) or is lowered (dips) with respect to the average signal.
25Hz is about the lowest frequency that can be heard. It manifests itself as the deep rumble that can be heard in the movies theater. 32Hz is about the lowest bass note in most music. Only some organs can go lower. Still we can ‘perceive’ even lower frequencies just not as a ‘tone’.
18KHz is about the maximum most people can perceive as a single tone, some younger people might be able to detect up to 20kHz. For most adults about 16kHz is the maximum. This is not perceived as a tone but rather as a ‘pressure’. Some research has shown related harmonics above 20kHz can be perceived by human hearing when single test tones are used.
I am not aware of any scientific sound research that has shown humans have this ability when listening to music which is more complex and the brain might take some ‘shortcuts’. Plenty of anecdotal reports can be found though, but these are only based on subjective findings.
Below a glossary with subjective sound descriptors and a more technical explanation of the origin.
Airy – Describes the sense of space and openness of the music. Best heard in cymbals where the shimmer is realistic. This mostly has a relation with treble extension. It should be mentioned that not all well-extended headphones sound ‘airy’ and some not so well extended headphones can still sound sort of ‘airy’. The superlative (exaggerated) form of an ‘airy’ sound is ‘ethereal‘ where the sound feels very ‘fragile’ and overly ‘delicate’.
Analytical – A term used to describe a product that produces a high level of detail in reference to the music being played back. In technical terms, this means the tonal response is between ‘flat’ and slightly elevated above 3kHz.
Balance – This could mean balance between channels or sometimes people use the term to describe Tonal Balance.
Balance between channels means the stereo image is right in the middle. In some cases, balance can be correct for a certain part of the frequency range and not for higher or lower frequencies. This can be spotted in measurements. In sound, it can lead to a fuzzy position of a stereo image.
Also, one-sided seal loss with headphones can cause this when bass is less prominent in the leaky side. On measurements with a perfect seal this won’t be obvious.
Bassy – This is the lower end frequency of human hearing. Bass can be measured in quantity (heaviness) and quality. Other bass descriptors are muddy, punchy, rubbery, boomy, and fat.
The bass area is between 25Hz and 300Hz but harmonics can go as high as 5kHz. Peaks and dips in the frequency range between 20Hz and 500Hz can make the bass sound different from realistic. For descriptors and the frequency range, they fall into see the chart above.
The opposite of bassy is ‘Lean‘
Bass (Lows) – Can be divided into 4 ranges: sub-bass (10Hz-25Hz) this is not audible as tones or notes but deep rumbles in movies are an example. When it is absent most people won’t miss it. That is once you heard what bass extension does it can add to the musical experience. For instance, with Piano music where pedals are used this lowest part can make the piano sound more real.
Lower bass (25Hz-50Hz) is the part of the bass where the deepest musical notes are. A small and gentle roll-off usually isn’t very audible. A substantial roll-off (-10dB) is quite audible.
Bass (50Hz-120Hz) is the part where most of the ‘body’ of bass instruments is. Sharp dips or peaks and emphasis or subdued parts here can color the bass, make it sound boomy, exaggerated, full, tight, dis-attached or muddy. The best sounding headphones/speakers have a flat response in the area. Some folks prefer substantially more bass than others. When traveling a bit more bass usually is welcome. High-bass (120Hz-250Hz) is where the harmonics of most bass sound-producing instruments are. A small peak there may make bass sound tighter. Too much (>5dB) can make bass sound muddy and boomy. A dip in this area can make bass instruments sound ‘wrong’ or ‘dis-attached’. This is where bass appears to be ‘apart’ from the music. Some people actually prefer a dip, certainly when the lower frequencies are elevated.
Bloat – Bloat is present usually in the mid bass. When frequencies below 400Hz are lifted opposite the mids and highs the bass can sound ‘bloated’ and overdone. When there is a dip around 150Hz this is the opposite of bloated and the bass sounds dis-attached.
Bloated bass often also causes ‘bloom‘ in male voices. In this case the male voice sounds unnaturally bassy/full and lacks clarity.
When only the part below 150Hz is boosted the bass doesn’t sound ‘bloated’.
Bright/Brightness – A small emphasis of upper mids. The frequency band between 1kHz and 7kHz. Brightness is a wider bandwidth form of Clarity + Detail, when exaggerated even more it becomes Shrill.
Clarity – A few dB emphasis between 1kHz and 3kHz can add some clarity for voices and instruments. The opposite (a dip) of clarity (seen a lot in headphones) could be described as Laid back, Sweet, lacking Attack. An exaggerated form is shrill, cold, hard.
Coarse – is another word for Grainy or Gritty and describes uneven treble response with deep dips and peaks. Note that measurements made with measurement gear using a fake pinna can show substantial peaks and dips above 5kHz caused by the fake pinna but may not indicate roughness nor should one try to EQ this out.
Chocolaty – Describes a sweet and lush sound.
Cold – a general upward tilt in the frequency range between 300Hz and 3kHz. The opposite is warmth.
Congestion – Something sounds congested when it the sound is muffled and not very dynamic. It usually is a combination of emphasis in warmth and laid back sound / lacking in clarity.
Compressed – This can mean 2 things. There is compressed data and compressed music. Compressed data means that a file has been shrunk in size. Most people have heard of ZIP and/or RAR where one or more files are smaller in size so they can be sent as an attachment. This is lossless compression where the file can be reconstructed to its original size and then can be used. In Audio there are many lossless formats. The biggest difference with something like ZIP is that a ZIP file needs to be ‘unpacked’ before one can use the file (song or album) where audio files are de-compressed while the song is being played back. One can also compress files by leaving out data which can not be recovered later. The most well known lossy compression files are JPG (for pictures) and MP3 for music but there are many more formats. During the compression (encoding) one can usually select how much one throws away. More compression = more loss of fidelity.
When music is compressed the louder parts in a recording and lowered in volume and/or softer parts of a recording are amplified. Usually this is done in studios to get a more even sound. There is a fine line between this being done craft-fully (usually for each instrument its own compression) and it being overdone in dramatic ways. This sadly is very common for most popular recordings. Search for ‘loudness wars’.
When a headphone sounds compressed it usually is bit bloated sounding and lacks realism/clarity/dynamics.
Crisp – is another description of having clarity, an exaggerated form is shrill. The opposite is laid back.
Dark/Darkness – Describes a gradual downward slope of frequencies above 3kHz often combined with an emphasis on bass/lower mids. An exaggerated form is Muffled. The opposite is Shrill
Decay – How a sound/note/resonance fades away over time. This is not always visible in the frequency response but could be visible in Cumulative Spectral Decay (Waterfall) plots. When there is some clarity and no mid bass emphasis most people describe the decay as fast.
Depth – How far away the instruments spacing is from back to front. In headphones this is not always perceived as such. Sometimes a gradual downward slope between 300Hz and 10kHz can also give a sense of depth imitating a greater distance from an actual music performance.
Detail – When something sounds detailed the frequency band between 1kHz and 3kHz is usually audibly flat or neutral and is more or less flat between 3kHz and 10kHz or has some mild emphasis (a few dB) or a peak in that part of the frequency range. An exaggerated form is Edgy, Sharpness, Sibilant.
Dry – Too little reverb or echo is used. Is also used to describe ‘flat’ and ‘boring’ studio recordings. Opposite of lively
Dynamic – When a headphone sounds dynamic it sounds ‘lively’ and instruments and voices ‘pop-out’ of clearly. It is the opposite of a relaxed, muffled or compressed sound. When a recording is truly dynamic there is a substantial difference between soft sounds and peaks.
You need to play the music loud to hear small details. Funnily enough when you can hear small details already at lower playback levels the sound is actually compressed yet many say, incorrectly, this is a dynamic sound.
The word dynamic is also used to describe a type of headphone driver (the most common type) where a magnet and voice-coil is used to create sound.
Then there is also dynamic range in an electrical sense. This describes how many difference in decibel there is between the signal and the noise and distortion products.
And finally Dynamic Range as in DR-rating. This describes how the difference between the average levels and peak levels in a recording.
Usually the recordings with DR ratings between 10 and 20 sound more realistic than recordings between 2 and 5.
Edgy or Etched – Between 3kHz and 7kHz, as a subset of brightness and Detailed, an exaggerated form of brightness/detail is Edgy, Etched, Sharpness, Sibilant. The opposite (a dip) can be described as lacking Finesse, dis-attached Treble.
Ethereal – Describes a slight treble elevated sound that feels ‘fragile’ and slightly unnatural but otherwise neutral and pleasant.
Finesse – This describes fine and delicate details heard in music. When one can hear small details clearly, realistic and well defined as in not ‘coarse’.
The opposite of finesse is grainy.
Forward – When voices and instruments pop-out. This usually is caused by a mild peak in the 1kHz to 2kHz range. A small peak is usually not very detrimental to the sound at all. The opposite of forward is ‘laid-back’.
Flat – When the frequency response does not deviate in the audible range something is considered flat.
When this word is used with headphones or speakers one usually finds that it doesn’t color the sound (too much). Strangely enough not everyone that describes a sound as flat it actually is flat. So one man’s ‘flat’ can be another ones bassy, boring, mid-rangy, or sharp sound.
Fun – This often describes a sound with elevated treble (>5kHz) and bass (<100Hz), also called ‘U shaped’ or ‘bathtub shaped’ sound.
Grainy – Also called ‘gritty’ and describes a sound that lacks finesse. The finer details are rendered a bit coarse. Often this is caused by lots of sharp peaks and deep dips in the treble area above 6kHz.
Harsh – This describes a sound similar as grainy but more concentrated in the midrange from 1kHz to 5kHz rather than in the treble range. Often distortion levels >1% in the midrange and or sharp peaks in that frequency range are the cause.
Highs – Also called treble, these are the upper frequencies above 5kHz.
Imaging – When a headphone or speaker images well it is very easy to pinpoint where instruments are and that image is stable and ‘sharp’. This requires a flat frequency response that is also matched between the two drivers, and detailed recordings. Slightly angled headphone drivers can have better ‘imaging’ as they make use of the ear-shape.
Laid back – describes a relaxed sound signature and is caused by an audible and rather wide dip around 2-4kHz. It is the opposite of forward and dynamic. Upper mids and lower treble is under-emphasized and is found to be pleasant for longer listening sessions when the dip is just slight (between 5 and 10dB).
Lush – is similar to Laid back. It describes a rich, warm-pillowy sound usually with slightly elevated lower frequencies and rather wide dip around 2-4kHz with a good treble quality that is a bit higher in level than when said to be laid back.
Microphonics – sensitivity to touch. It could be present in some electronic components but in the case of headphones it refers to mechanically ‘conducted’ sounds of the cable. When one touches the ear cups of a headphone one can hear this quite clearly. Depending on how a cable is coupled to the cup touching the cable does a similar thing but attenuated compared to touching the cups directly.
Cloth covered, thick and rigid cables usually are worse in this aspect then softer and thinner smooth surface cables. When microphonics are bad you can hear a cable rubbing against clothes when moving when music isn’t even playing that loud. Some are annoyed others simply don’t mind.
Mids/Midrange – Frequencies between roughly 250Hz and 4kHz. One can divide this in lower mids (250Hz – 500Hz) where the ‘body’ of voices and instruments is. The mids (500Hz – 1500Hz) and upper mids (1.5kHz to 4kHz). In the upper mids the ‘clarity’ of voices and instruments as well as ‘attack’ of musical instruments can be found.
Muddy – Describes the sound of elevated lower mids/upper bass where the bass is not clearly defined and ‘blends in’ with the rest of the music in an unnaturally elevated way.
Muffled – sound is when it would appear as though the sound is coming from a speaker with a wool blanket draped over it. Lacking in clarity and treble. Frequencies above 2kHz are subdued and or rolled-off.
Natural – When a headphone sounds natural all instruments and voices are reproduced in a realistic manner without coloration, a correct stereo-image and with a dynamic sound.
Neutral – and neutral are closely the same but neutral is more about the reproduction of sound not being colored. All frequencies are reproduced at the proper level.
There can be consensus about how a headphone should measure to be considered neutral.
However, there are many people stating a headphone or speaker sounds neutral to them but in reality is quite colored. The term neutral used in subjective reviews thus can be considered a meaningless term unless comparisons are made to known neutral headphones.
Openness – Has little to do with a headphone being open or closed. It usually refers to a detailed and neutral sounding headphone where instruments have a clear separation. Headphones with a good clarity are often described as being ‘open’ sounding.
Punch – powerful bass and drum hits. A small emphasis around 100-150Hz can relatively boost harmonics of bass drum/bass.
Rolled-off – Sound can be rolled-off in the lows and in the treble or both. Rolled-off bass is lacking in lower bass and can have slightly subdued bass as well. When the treble is rolled off frequencies above 10kHz usually are low in amplitude. When this happens usually the sound is not considered airy and lacks sparkle.
Sharpness – An emphasis between 2kHz and 6kHz can give instruments and voices the impression of being ‘highlighted’ and sharply detailed.
Shrill – An exaggerated form of sharpness usually with an emphasis between 4kHz and 10kHz and is unpleasant, shrieky.
Sibilant / sibilance – A sharp peak in the frequency band between 5kHz and 8kHz can emphasize the ‘s’ sounds in words. A high peak (>5dB) can sound piercing and sharp and is usually fatiguing and unpleasant during longer listening sessions. A lower peak between 3dB and 5dB can create an illusion of ‘detail’ in music and ‘sharply’ defined instruments. In the long run also fatiguing.
Signature – the overall tonal balance of a headphone. One could describe a signature in many ways as found in this article.
Soft – can be used to describe the loudness (amplitude as in how loud the sound is) or the ‘texture’ of the treble. For the latter it can describe the amplitude opposite the bass and mids or define treble quality. When treble is not splashy elevated, sibilant or coarse but ‘sweet’ and pleasant it is often described as soft. When the frequency response is quite ‘flat’ between 6kHz and 15kHz without sharp peaks and dips the treble quality usually is good and depending on the relative level can be said to be soft or sweet.
Soundstage – Describes in 3d terms (height, width and depth) where one perceives recorded instruments. For headphones it is very rare to hear instruments ‘projected’ clearly meters in front of you without special recordings or software. In the vast majority of cases sounds are between left and right ear only. For headphones instead of soundstage the word headstage is used.
This describes how well instruments are defined between left and right and how ‘sharp’ they can be pinpointed. One has to realize the stereo image is created in the studio during mixing/mastering process and is artificial in most cases. For headphones there is crossfeed which makes some recordings easier to listen to but this too is just a ‘trick’.
Sparkle – Usually caused by a slight emphasis in the (upper) treble and describes vibrant treble.
Spatial – describes how sounds can be heard all around you. Requires digital trickery to pull this of with headphones. Usually to get spatial sound multiple speakers are required placed around the listening position. Related terms: crossfeed and soundstage/headstage.
Sweet – Corresponds with ‘lush’. It describes a ‘soft’ sound signature usually with slightly elevated lows and soft (not grainy or splashy) highs.
Timbre – The tone of a note from an instrument. Timbre is determined by the ratio between the fundamental tone and its harmonics. Headphones with a ‘flat’ tonal response should have the proper timbre. When the tonal balance is not flat timbre can be affected and changed. This can sometime be for the better or worse and depends on the recording. Do note that in studios timbre of each individual instrument is often adjusted to fit in the recording. This can’t be undone.
Tonal Balance – describes how ‘flat’ a headphone is. When the bass is boosted the tonal balance is bassy, when treble is boosted the tonal balance is ‘bright’. When a headphone is described as tonally balanced no specific frequency bands are popping out or are subdued.
The real snag here is that some owners may feel a headphone is tonally balanced but in reality it may be bassy, bass-shy, warm, cold, midrangy or bright for instance. Tonally balanced = realistic sounding with no emphasis on anything.
Objectively tonal balance is difficult to prove headphone measurements can differ substantially between test-rigs.
Transparent – Similar to clarity it is a clean clear open and detailed quality.
Warm/warmth – a general downward tilt in the frequency range between 300Hz and 3kHz. The opposite is cold.
Even though specifications of headphones always state optimistic figures like ’20Hz to 20kHz‘or even ‘5Hz to 35kHz’ these numbers are often meaningless and should be ignored unless it also states the ‘cut-off’ points.
Those are the points at the extremes of the frequency range where the output signal has dropped by a certain amount of dB’s. Those stating +/- 3dB are the most realistic even though 3dB is already more than barely noticeable. Most headphones, however, are specified at -10dB and those that do not specify these cut-off points usually quote their numbers at -10dB, or -20dB to create more impressive numbers. 10dB is already a halving in perceived loudness and 20dB yet another halving.
No headphone is perfectly flat from 20Hz to 20kHz. The best ones out there may vary ‘only’ +/- 3dB. Most of the headphones around vary MUCH more and can have peaks and dips of over 10dB, even 20dB is not uncommon while the better ones generally keep the variations within +/-6dB. This is the main reason why all headphones sound so different from each other, because of these relatively large differences in frequency response. It is also why the frequency plot reveals the most when it comes to the sonic character.
One of the ‘flattest’ headphones around is the Beyerdynamic DT150 with DT100 pads: 20Hz to 20kHz +/- 3dB (not counting the dip at 3kHz)
Since human hearing is pretty sensitive to human voices a specific part of the frequency range should be pretty ‘flat’ to sound accurate, that is to have a horizontal and not wobbly response in that area. If the lower part of that spectrum is lifted (even just a few dB) with respect to the higher frequencies the voices sound ‘warm‘ (full bodied) sounding. Deep male voices sound that way. If the lower part of that spectrum is lower in amplitude than the highest part of that frequency range we say the voices sound ‘cold‘ (thin sounding). female voices are generally associated with this. When voices sound neutral that specific part of the frequency range is horizontal (flat).
NOTE: the tilted lines are shown exaggerated and less steep sloping plots (less dB difference) will also show this effect. The plot above merely shows the general idea and in reality the slope may differ or look quite different. It is the general idea of a sloping curve in that specific area that counts.
Of course there is also the possibility a headphone is tilted upwards towards the lower and higher part of this band (100Hz to 6kHz) in which a headphone is found to be sounding ‘sucked out in the mids’. The DT990 below is a nice example. Bass is slightly but not terribly elevated as well as the treble. Relatively the mids between 500Hz and 3kHz are lower in amplitude. As the frequency response between 100Hz and 2kHz is sloping downwards the sound is ‘warm’. The part between 3kHz and 6kHz is higher in level again makes it still have good clarity (clarity resides between 2kHz and 6Hz) while still having a ‘warm’ signature.
Also the opposite can be there, tilted downwards in the lower part (300Hz) and lower again in the right part (3kHz) in which a headphone is found to be sounding ‘mid centric’ (a bit ‘cuppy’ sounding). An example below.. a fake MSR7.
In short … NO headphone (nor speaker) is perfectly ‘flat’. The majority of them is even FAR from flat. Therefore ALL headphones add a certain ‘color’ to the sound.
All headphones (even the most expensive ones) thus have a kind of curved (more or less wobbly) frequency response with peaks and dips that may be present at certain point(s) in the frequency range. As long as these peaks and valleys (dips) are gradually sloping and not too big in amplitude (+/- 3dB) they are hard to detect as such. Sharp peaks AND dips are usually the result of a resonance. A resonance is a small part of the frequency range where the driver/cup likes to vibrate by itself.
Sharp and or high peaks (and sometimes a resonance that manifests itself as a dip) is detrimental to the sound quality.
A rather weird phenomenon is that human hearing is less susceptible to (gradual) dips even if they are substantial, yet peaks in the frequency range are easily heard and perceived as coloration of the sound.
The plot below shows where the typical sonic coloration of headphones is located. When the peaks are not too close together in the frequency plot that is. When for instance the part between 4kHZ and 15kHz is raised opposite the part between 200Hz and 4kHz most people will find the headphone to sound ‘detailed‘. It really isn’t in reality, it’s just bright and initially perceived as very detailed but often will be perceived as ‘sharp’ once accustomed to it. ‘Details’ are found in the same region as ‘piercing’ is. A gradual downwards sloping FR from 10kHz is usually described as ‘smooth’ sounding is there aren’t too many sharp peaks and dips. The side effect is that the finer details aren’t as present as when it doesn’t slope downwards in that region.
In short….
dips are not easily noticed and mostly do not harm the sound in a very negative way.
Peaks (of over 3dB) are easily heard and define the sonic character, more often than not in a negative way.
Dips in the 200Hz region for instance will give the sense of a ‘dis-attacted’ bass but generally sounds clear with big bass. A peak, however, will give it a boomy/muddy sound.
A dip in the 2 to 3kHz region will give the headphone a laid-back sound somewhat lacking ‘bite’ and is generally find pleasant where a peak in that same region gives the mids a sharp and ‘shouty’ edge to music.
the importance of scales
When looking at (frequency) plots the first thing to watch for is the used scales.
The horizontal frequency scale should go from at least 20Hz to 20kHz.
The vertical dB scale (and its divisions) varies considerably between different websites and headphones can appear to be very ‘wobbly’ to ‘very flat’ because of this.
When comparing graphs take a good look at the scales and divisions. An example is shown below.
The upper plot has a 5dB/division scale and looks a bit stretched out vertically where the bottom plot is the EXACT same plot except for a different vertical (dB) scale. The bottom plot has 20dB/division.
When looking to buy a headphone I am willing to bet the bottom plot will generate more sales.
It’s also the main reason why lots of people say these plots are meaningless. Graphs, however, are anything BUT meaningless when you know HOW to interpret them and they do tell the biggest part of the story.
Only a frequency plot doesn’t tell the whole story but one needs to take a few different types of plot into account to get the bigger picture of how it behaves.
The scale of the plots I use for frequency and distortion is not chosen randomly.
The chart above bottoms out at around 35dB SPL. Others may have plots down to 0dB or even below it. 0dB SPL is just a value and does not represent no sound pressure.
The reason I chose to use 35dB as the bottom value is not because of one of standards prescribe this but based on experiments I conducted a long time ago.
I found that when listening to music with average levels of 80 to 90dB SPL (which is quite loud) and then attenuating the signal I was unable to hear anything about 60dB below it.
So when testing at 90dB the audible floor would be around 30-35dB SPL. Only when my ears got used to the silence when playing nothing for quite a while I could still hear something when played that soft. The dynamic range of the hearing thus isn’t as big as the limits that are found in labs.
As my mic pre-amp combo starts to clip around 110dB the max. SPL level is set just below 110 dB as well. Headphones peaking above 110dB with 90dB @ 1kHz are unlistenable bright/sharp/nasty sounding anyway.
As we can easily hear a few dB difference but do not want to clutter the graphs with lines the vertical scale is usually shown in 5dB divisions unless noted otherwise.
DIY-Audio-Heaven 