kirasd69 a écrit :Sachant qu'Hiby a aider à concevoir nombre de baladeur d'autres marques, ça paraît étrange qu'ils aient négligé ce point
Tout à fait. Mais c’est le cas quand même !
10 ohms et « régle des 8 fois l’impédance » * : rien ne passe (
du moins, sans en changer la signature globale) à moins de 80 ohms. Exit tous les Intras et une grande partie des casques nomades. Pour un DAP, c’est ballot !!
*
Headphone & Amp Impedance http://nwavguy.blogspot.fr/2011/02/head ... dance.html
THE SHORT VERSION: All you really need to know is most headphones work best when the output impedance is less than 1/8th the headphone impedance. So, for example, with 32 ohm Grados the output impedance can be, at most, 32/8 = 4 ohms. The Etymotic HF5s are 16 ohms so the max output impedance is 16/8 = 2 ohms. If you want to be assured a source will work well with just about any headphone, simply make sure the output impedance is under 2 ohms.
WHY DOES OUTPUT IMPEDANCE MATTER?
It matters for at least three reasons:
- The greater the output impedance the greater the voltage drop with lower impedance loads. This drop can be large to enough to prevent driving low impedance headphones to sufficiently loud levels. A real world example is the Behringer UCA202 with a 50 ohm output impedance. It struggles with some 16 - 32 ohm headphones.
- Headphone impedance changes with frequency. If the output impedance is much above zero this means the voltage delivered to the headphones will also change with frequency. The greater the output impedance, the greater the frequency response deviations. Different headphones will interact in different, and typically unpredictable, ways with the source. Sometimes these variations can be large and plainly audible.
- As output impedance increases electrical damping is reduced. The bass performance of the headphones, as designed by the manufacture, may be audibly compromised if there’s insufficient damping. The bass might become more “boomy” and less controlled. The transient response becomes worse and the deep bass performance is compromised (the headphones will roll off sooner at low frequencies). A few, such as those who like a very warm “tube like” sound, might enjoy this sort of under damped bass. But it’s almost always less accurate compared to using a low impedance source.
THE 1/8th RULE: To minimize all three of the above problems, it’s only necessary to keep the output impedance less than 1/8th the headphone impedance. Or, put another way, just divide the headphone impedance by 8 to get the maximum output impedance without potential audible degradation.
C’est une faute inadmissible comme l’a dit Fab.