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- While designing multiband earphones, there are used the same methods as for designing the multiband acoustic system. The only difference is the size of cases where it is necessary to place the drivers and electrical components. In the case of custom earphones, the internal dimensions of the shell are limited by the size of the human ears. Therefore, frequency division can be carried out by the simplest passive electric crossovers (frequency filters). As usual, these are passive filters of low and high frequencies of the first order. Capacitors and inductors of various ratings are used as passive elements in such filters. These filters perfectly fulfill the role of limiting a frequency band of drivers, they have a transition band sharpness, linear Frequency Response (hereinafter referred to as FR) in the transmission range, and, most importantly, are easy to implement! This allows you to get a smooth FR of multi-band custom earphones. However, it is worth to note that the smooth final FR of the earphones will not be perceived as “smooth” by ear and this is the main problem of applying such filters. This is due to the fact that the simplest passive filters, having a linear FR in the transmission zone, have a completely non-linear phase frequency response (hereinafter referred to as PR), i.e. the time it takes for the signal to pass through the filter is frequency dependent. Thus, some frequencies at the junction of the filter bands are “delayed” / “ahead” in time relatively to others. When you compose music from different frequency bands, there are audible “mismatch” of the boundaries of drivers playback with the human ear in the overall picture. As a result, while listening to a tone picture becomes “fragmental”, “crumbly” or “non-coherent”. This may explain the difference between the earphones sound with the same FR but different electrical phase distortion. Each manufacturer of multiband earphones in its own way corrects the phase distortion of the earphones, but, to achieve an ideal harmonization of the frequency bands in the phase domain, unfortunately will not work with this approach. To solve problems with frequency bands phase matching of multi-driver earphones, Ambient Acoustics laboratory has developed a new unique design approach. The separation of frequency bands is carried out without the use of electric passive filters, but due to the natural blockage of the AFC of each driver. And also with the help of various acoustic load of the oscillating circuit of the system of sound guides for drivers and acoustic rejective filters. This allowed us to avoid the parasitic effects of using capacitors and inductances in the structure of the earphones, thereby increasing the linearity of their impedance and the electrical phase in the entire frequency range! This, in turn, increased the "fusion" and "coherence" of the sound of all MAD series models, and the impedance linearity almost completely removed the influence of the dependence of the sound source on their sound pattern! Back