# What is the point of a frequency response higher than 20 Hz to 20 kHz?

According to Dr. Mike Hewitt the writer of Music Theory for Computer Musicians:

"The general range of human hearing extends from about 20 Hz to 20 kHz, although this can vary depending upon the sensitivity of the individual ear".

What is the point, for example, of a pair of headphones like the Sennheiser HD 800 that has frequency response of 8 Hz to 51 kHz? Wouldn't any frequency higher than 20 kHz (give or take, depending on the "... sensitivitiy of the individual ear" as Dr. Hewitt pointed out) be impossible to hear?

• I've migrated this to Sound.SE since headphones aren't computer hardware or software, and the question isn't about interfacing with computers either. Feb 13, 2014 at 21:11
• I think this may be useful to solve the mystery en.m.wikipedia.org/wiki/Nyquist-Shannon_sampling_theorem Oct 2, 2017 at 1:12

The point is to have the necessary frequency response or usual power output requirements well within the nominal spec for the product, thus minimising distortion or other unwanted non-linearity.

With microphones the point is also to provide extended frequency response to recordists who plan on manipulating the sounds later.

With audio software plugins the point is to minimise rounding errors, provide better response curves for e.g. compressors, or better frequency response for e.g. EQs and spectrum analysers.

With sound reproduction equipment (e.g amps or speakers) the aim is to avoid the edge areas of non-linearity in frequency response.

Finally that way you can be sure that even if the marketing department have asked engineering to measure within -10dB (as opposed to -3dB), the range you're interested in will be intact.

It's interesting to note that the Sennheiser HD 800 is specified as : -

Frequency response (headphones) 14 – 44100 Hz (- 3 dB)

Is it a coincidence that they specify the frequency of 44.1kHz - this is the sampling frequency of digital audio in CDs! It's also quite interesting that there appears to be no published graph of frequency response when tested in the normal way: -

The pictures of the testing are there to be seen but i can't find a frequency response graph that goes above 20kHz anywhere on the web. The ones that I have seen show typical mid/high range anomalies that all headphones seem to have BUT stop at 20kHz.

So, is it marketing hype? I suspect that it is. Having a frequency response exactly specified at 44.1kHz is totally bogus to me. It's trying to impart "stuff" to the potential "soft" buyer that is irrelevant. 44.1kHz (as a signal), sampled at 44.1kHz produces (due to aliasing) a frequency of exactly 0 (zero, zilch) hertz i.e. dc!!

As for the mechanics, there are plenty of mechanical structures (speakers included of course) that have a decent frequency response up to a certain point then it falls away at about 12 dB per octave (error fixed now) - this is a standard 2nd order characteristic of mechanical items like speakers (techy phrase is spring-mass-damper systems).

Have you ever read the instructions on how to use a graphic equaliser??

They say that cutting the volume of the bass sounds can increase the clarity of vocals and indeed higher pitch sounds like flute.

So, knowing from those experiences that lower frequencies can affect higher ones why do you think that stops below or above the Audible range ??

It is still the same air molecules vibrating at a certain speed despite being slower or faster than our ears can hear..

So if you accept that cutting low frequency on a graphic equaliser can make the higher ones sound better... Why not adjusting the ones outside the range of hearing make the ones above that sound clearer.

You might not hear those frequencies but if you consider their effect on the ones your ears are sensitive to, those will change even though you didn't directly change that exact frequency but rather the one beside it.

A specification for equipment doesn't mean that no sound is produced outside the spec, but rather that it has lowered below a quoted value. Knowing that the response extends outside the hearing limit means that not only will it produce sound linearly within the quoted frequency but it will also not degrade in volume until so far away from the human hearing limits that even the aforementioned harmonics wount affect the fundamentals you're listening has.

• I believe that you are somewhat mixing (no pun intended) acoustics with psychoacoustics a bit. The effect of increasing clarity with dropping the bass is used quite often but in my opinion it is mainly due to psychoacoustic reasons. This has more to do with how we perceive sound than how some frequencies affect others. In the linear regime, at which spend most our audio time, different frequencies do not affect each other. This may happen (not only in air but inside audio equipment) when non-linearities strike in. Not sure you are referring to that though. Would you care to clarify a bit? Mar 29, 2021 at 22:38

Here is an interesting article that can give some insight on this.

http://blog.lhyeung.net/lang/en-uk/2010/03/06/picking-earphones-and-speakers-a-guide-to-better-audio/

Specifically to your question, here is a section that relates to this.

The sounds that are “beyond” the human range of hearing and ones that you can only feel. They are known as “harmonic frequencies” which are musical notes that can reach outside the “hearing range” while the ones you can hear are known as “fundamental frequencies“. Instruments in particular have a great variation in harmonic frequencies as the frequency for each note is different on each instrument allowing you to tell they are well… Different instruments.

Thus if your earphones/headphones/speakers have a wide frequency response and you are using lossless files, music should sound better – especially orchestral recordings.

• I don't buy that, really. Most music is sampled at 44.1 kHz. The highest frequency that can be represented without aliasing is ~22 kHz (see the Nyquist theorem). You cannot "feel" high frequencies the same way you can feel low frequencies—you simply don't hear them.
– slhck
Feb 13, 2014 at 21:00
• Note that the “44kHz” you see displayed in your digital audio player (DAP) is not the sound frequency of your music files. This is the “sample rate” the music was recorded at i.e. how many times a sound wave is captured per second. Generally the higher this sample rate, the higher quality music or sound will be.
– kobaltz
Feb 13, 2014 at 21:02
• Yes, that's what I said—most music is sampled at 44.1 kHz. The highest frequency you can sample with that is 22.05 kHz. The fundamental frequencies of music instruments mostly lie within the audible range. Those that are outside cannot be heard—or felt, for that matter.
– slhck
Feb 13, 2014 at 21:06
• I read people say things like "most music is sampled at 44.1 kHz" & I think, when you make music, have you never, ever played a sample at half speed? Its only a one octave pitch shift.... If so, then that half speed element just became a 22.05k sample rate & its highest freq response is 11.025k... think you can hear that?
– user49
Feb 13, 2014 at 22:44
• just some little corrections: fundamental frequencies are not 'the ones you can hear'. Fundamentals are the base frequencies of a note, anything beyond that is a harmonic (1st,2nd,etc). Yes, harmonics can outreach our hearing (keys jangling anyone?), but there is more interesting stuff beyond 22kHz than just harmonics (bats, insects, etc). "Thus if your earphones/headphones/speakers have a wide frequency response..snip..especially orchestral recordings. Well the following article has a good scientific response to this statement: xiph.org/~xiphmont/demo/neil-young.html Feb 14, 2014 at 8:15

The 'frequencies you can feel' argument is arguable, and probably valid to some degree.

However, there's another argument, which is easier to support with physics and acoustics, to do with the ways in which the response of headphones is measured. Speakers with a 'response' from 20Hz to 20kHz cannot have a nice linear response (same output power for same input level, which is what you want for accurate reproduction of sound) across that range of frequencies, and then immediately drop to no output at all at 19Hz and 20,001Hz. The frequency characteristics of speakers are determined by the frequency characteristics of materials and electronic components, and there's no way to have a steep 'roll off' of this sort, without distorting the frequency response within the wanted range as well.

Any frequency filtering (whether done electrically, digitally, mechanically, or acoustically) will affect a large range of frequencies - theoretically all frequencies (though to a very small degree, far away from the filtered frequency). Likewise, all speakers will probably produce sounds from 1Hz to 100kHz (and beyond) - just not linearly for a given input level.

If a speaker is deemed to have a response from 6Hz to 51kHz, this is probably the range with a reasonably linear response - probably something like +/- 6dB. This will mean the audible range from 20Hz-20kHz can be made lovely and linear, with increasingly poor response between 6Hz-20Hz and 20kHz-51kHz, and worse response still outside that range. If the published range is 20Hz-20kHz, however, you can be pretty sure that at the 20Hz and 20kHz points, the measurement is at the limit of the +/-6dB point, meaning that there will be colouring of the sound, probably from 20Hz-100Hz, and from 15-20kHz, which would be audible to human ears!

• On a related note, audio equipment sometimes generates unwanted frequency content which is above the range of human hearing, and the presence of such frequency content may adversely affect the reproduction of sounds which are in hearing range. For example, if an amplifier were driven by a switching power supply that injected noise into its output at a frequency that warbled 120x/second between 24,900 and 25,000, such noise should be inaudible; if a pair of headphones had the right kind of resonance at 25,000Hz, however, that could cause distortion which... Dec 8, 2014 at 18:02
• ...would be modulated at 120Hz. Headphones which are even remotely clean up to 50Khz will be free of any such effects below that frequency. Dec 8, 2014 at 18:03

I would hazard an uneducated guess that it more to do with how well they reproduce the frequencies between 20Hz and 20kHz. If they had a response of between 20Hz and 20kHz then the frequencies towards the upper and lower limits wouldn't sound that good, as the quality would start to tail off. But with a response of between 6Hz and 51kHz the frequencies to the upper and lower response limits won't sound that good (if you could hear them) but they 'can' reproduce them, however, the human upper and lower frequencies that they reproduce, would be produced very well? I think it's about the scale. If they could 'only' produce audible frequencies, they would sound shit because as you get to the limits of audible frequencies so too are they getting near their response limits which you would be able to hear as poor quality.

An analogy would be an F1 car. On an infinite straight, they would hit a much higher top speed than they do on a track, they are never going to reach that limit on the track. Likewise, they can go very slow, but never need to, and don't do it well. So they are designed to work exceptionally between the limits of the track. There's no point designing a car that has a maximum top speed and minimum speed required for the track, as the performance would be very limited between those limits.

Or maybe your dog would like to use them? :)

• That analogy does not seem accurate... Aug 3, 2016 at 0:52

Its simple really. Headphones are designed with components to sound the best in the audible frequency range. Sometimes certain headphone designs result in a frequency response that is above or below the audible spectrum.

But why would a manufacturer go out of their way to limit this frequency response for no reason? A particular headphone design might yield a frequency response high than 20000hz....does that matter? No. Why would that matter? The manufacturer did not go out of their way to engineer for this frequency response, but when they ran the test, that was the result.

So when they post the specs, they post the honest results of their tests. If that happens to be > 20000hz.....so be it.

Simple right?

This isn't the most scientific answer but neither is this the most Sound Design question. Its also Christmas.

The audiophile answer is probably that the higher (20k+) frequencies have some discernible effect on the lower frequencies. And that the -20Hz frequencies probably add 'warmth'

I've got to say however that in my mind, most music is sampled at 44.1KHz anyway which means that sweet 50Khz tone wouldn't even be reproduced to affect your lower frequencies and anything below 20Hz should ideally be killed in any mix imaginable. And even if there are 10Hz tones they are definitely not being produced at adequate amplitude by a set of 1 inch headphone drivers to effect you in the way 'Infrasound' is allegedly supposed to.

So the answer to what's the point? Nothing really just bigger parameters on a tech spec I'm guessing. Either that or they're earphones for cats and elephants.

I disagree. There must be something else around here that we dont know yet. Perhaps an engineer could help, i dont know. What do i know is this: Last two days i broke my Pionner at 8 - 22 khz 108. Last songs i was listening was heavy metal at flac and wav. Yesterday i bought a Sennheiser at 17 - 21 khz 118. And guess what... i hear some songs different than before! I did my research and it seems that i could not hear the bass of Trujillo. I set the equalizer in the player at maximum, the 20 hertz of course. And... nothing.

I return to my PC, and here at home i really got the equipment for monitoring audio, with panasonic headphone and soundblaster inside among other beauties. So... i am crazy? no... i test the song and there it was, the bass, clear as a bell. No need to touch anything. So... unplug panasonic and jack my news sennheiser 17-21k, and... no more bass.

A magnified in the adobe and the audacity, i SEE the frecuency going, but just a little noise in the headpiece.

So my friends. That low frecuency in the devices, DO something. I dont know what it is. But there is some.

My adivce ? When buying something and spend half of you monthly payment haha, pick a device that can get the long and best RANGE in frequency. If it starts at 8 would be better than 17, if its starts at 6, would be even better, and so on. I learn from my mistakes, and i worte this so you dont fall in the same, that frecuency thing... is NOT marketing.

Lem.

• The human hearing range can extend down as low as 12hz for some individuals in some environments, so your experience doesn't necessarily contradict that. There are also differences in the level of response that you get when a headphone covers a particular range. Just because it can barely squeak out a 20hz signal doesn't mean it reproduces that range well. There are many other factors that could be at work in your anecdotal situation. Best bet would be to artificially cut the lower frequencies and see what the change is on the headphones with good bass response. Aug 4, 2016 at 5:54
• Yeah, what @AJHenderson said, plus, another thing to consider is that consumer headsets colour the sound to give you a better experience, Cheaper headsets tend to drown you in bass, because this gives the illusion of a nice sound. Usually a "Rock" - type frequency response is desired. This can detract from how the real "uncoloured" song sounds. So when you then hear the song on flat response headset, or a tighter low-end response headset, it can make you think something is missing.
– n00dles
Aug 4, 2016 at 13:47

Headphones have comparably small moving parts and low loudness. They need to reproduce low frequencies with "enclosures" that have no relation whatsoever to the wavelength of the sound and it is actually the "closed" side where the listener is rather than a wide open space. So there is no similarly important low frequency threshold like the resonance frequency of bass speaker enclosures: loudspeakers need to be efficient for low frequency production, headphones not so much.

The wavelength of sound at 20kHz is still about 17mm (or .675in) meaning that soundwaves do not have much of a chance to become incoherent in relation to the ear canals. The tricky thing is to straighten the frequency response in the vicinity of the resonance of the ear cup. But that's the middle rather than the extremes of the hearing range.

So excessively large ranges tend to be not much work (if at all) over good in-hearing ranges. However, speakers (and also headphones) are usually the parts in the sound reproduction chain most susceptible to non-linear distortion. So if you are listening to a combined broadcast for earth worms, humans, and bats, the quality of the human part may suffer if the others turn up the equalizers for their parts (which should be inaudible to you in a perfect world) too much.

• That doesn't seem to answer the question at all.
– n00dles
May 10, 2017 at 5:20