In technical specifications, a lot of manufacturers show the frequency range for headphones. It is believed that within this range, the headphones reproduce all the claimed frequencies. Some users incorrectly assume that the headphones do not play any sound outside this range. In fact, the frequency range shows the frequencies that are confidently reproduced by the headphones, and beyond this range the remaining frequencies are played quieter.
Formally, when we determining the frequency range, we must fix the two interval points for a certain deviation from the mean value. When publishing the frequency range, you must specify the deviation value. On the right graph, two frequency bands are defined and they are both true.
19-13700 Hz -6 dB
8.5-26600 Hz -12 dB
The measurement methods for headphones are much differs from the methods for measuring speaker systems (speakers). Acoustic systems passport parameters assume they are correct for measurements in an anechoic chamber or an open space where there is no echo. Headphones are always measured at the stand, where the frequency response depends directly on its design. Formally, the manufacturer, when specifying the frequency range, should indicate the deviation and write all about the stand itself.
The frequency response of the stands is different, because of that the frequency ranges are directly incompatible with each other. It is possible to compare frequency ranges only from one test stand.
Nevertheless, all the standards recommend using common sense and despite use different stands try to get more or less comparable data. Where the manufacturer assumes the possibility of comparison, the manufacturer adds the EQ setting (HRTF function) or his deviation values to the "universal-standard" frequency range for its stand to the measured frequency response.
We analyzed headphones from different manufacturers (mostly authoritative ones) and compared the passport frequency ranges with our graphs. We have obtained general patterns for the majority of the models analyzed.
Often manufacturers manipulate data. For inexpensive models they indicates narrow range, and wide for expensive ones, applying different criteria for determining the frequency range and of course without specifying it in the characteristics.
Sometimes manufacturers show the frequency range that not based to the drop in frequency response, but the range in which the manufacturer thinks their headphones play well. Thus they define the range is subjective way, without the participation of instrumental analysis.
All specifications for headphones are optional. Each manufacturer decides themselves what characteristics and in what form can be specified in the documentation for the product.
Lower playback frequency
At the lower playback frequency, the spread of the values is high enough from -6 to -20 dB. The low frequency range below 10 Hz is very capricious to vibrations, to external noise and landing headphones. If the headphones have a low 10 Hz drop, the lower frequency can be assigned as 5 Hz. If the fall in the low-frequency region is quite noticeable, then it should be determined at a level of -12 dB.
Though some models of headphones hint at confident playback up to 1 Hz, in reality, at a small volume level, the speaker may not have enough power reserve when playing the infrasound. Thus, the restriction on the lower frequency is determined not by the drop in the frequency response, but by the physical capabilities of the driver. In models with a gentle and long drop in the frequency response, the lower limit can reach 5 Hz (because of the low amplitude, the speaker will not wheeze at this frequency at an average loudness), and for models with a high bass output and without decay on the frequency response, only 20 Hz.
Upper playback frequency
When we deviated downward from the general level at -15 to -20 dB, we obtained close values of the upper frequency bands to frequency bands indicated by the manufacturers. If we used additional EQ in the form of a general rise in the high-frequency range, then the downward deviation might correspond, for example, -3 or -6 dB. In the absence of a single, rigid standard for the measurement of headphones, each manufacturer or test laboratory makes their decision about the use of EQ in the publication of Frequency responce. Thus, if you are looking at graphics, the upper playback frequency can be determined by the level of -18 dB.