DE102004023054A1 - Spatial-filter for headsets e.g. for playback of CDs, reduces cophasal sound components in both ears - Google Patents

Abstract

A spatial filter for reduction of in-head localization of sound sources during reproduction by headset, is achieved by reducing extensive cophasal sound components in both ears. This is achieved by means of a parallel circuit including a fixed coil and capacitor and a potentiometer used to produce a null setting.

Description

The Spatial filter presented here for reducing in-head localization of sound sources when headphones are playing belongs in the field of electroacoustics.

at The localization of sound sources is the chronology of the the two (human) ears reaching sound important. In-phase (naturally corresponds at the same time, sound that hits both ears can be heard while the headset is playing lead to an apparent location of the sound source in the head of the listener. These possible In-head localization of sound sources in headphone playback is in the electrical Recording of acoustic signals or further processing of the recorded Signals through z. As electronic amplifiers are generally not considered. With the help of the here presented, very simple and only out passive components built Spatial filter is a reduction the in-head localization of sound sources when playing through headphones. The level reduction sufficiently in-phase sound components can be controlled by a potentiometer be adjusted, thereby providing a controllable reduction in in-head localization possible is.

Either the usual electrical headphone outputs from Audio devices, as well as the usual ones (Jack) connector of (mostly dynamic) multichannel (stereo) headphones generally a common ground connection of the different playback channels (left-right) on. In the Spatial filter for headphones presented here, the current flow of (almost) in-phase signal components of the various playback channels in the ground path so inhibited that one reduced sound radiation of these signal components can be achieved can.

Of the Advantage of this spatial filter for headphone is that at the reproduction usual Audio recordings over commercial Audio equipment (eg CD player) and commercially available (dynamic) headphones a reduction of possibly occurring and common as unpleasant in-head localizations of sound sources can be achieved.

The basic circuit of the Spatial filter for headphones is in (1) shown. The circuit consists of a resistor or potentiometer 'R', a coil 'C' and a capacitor 'L', which are interposed in parallel in the common ground connection of the headphone. The properties are described in more detail below.

Electrical properties of the principle circuit (1)

The resistance or the potentiometer R of the spatial filter off (1) in the common ground path reduces the current flow sufficiently in-phase signals of the same frequency f through the built-in headphones in the headphones (K1 and K2 in (1) ). This happens because the total current through R for in-phase signals of the same frequency is greatest and leads to an increased voltage drop across R. Since headphones are usually operated on constant-voltage amplifiers, the headphone drive voltage U _K1 or U _K2 decreases, as a result of which the sound emission of the headphone speakers is correspondingly reduced. By changing the resistance value of R, the reduction of the sound radiation can be adjusted.

The human ear is particularly sensitive to phase differences in the frequency range around 1000 Hertz, since the average ear distance in this frequency range corresponds approximately to half a wavelength of the airborne sound. The coil L of the Spatial filter off (1) avoids the lowering of sufficiently in-phase, lower frequencies for which the hearing is relatively insensitive to phase differences. The capacitor C of the spatial filter off (1) avoids the lowering of sufficiently in-phase, higher frequencies, for which the phase relationship becomes ambiguous at short wavelengths relative to the ear distance.

The frequency f _min , at which the lowering of sufficiently in-phase signals of the spatial filter is greatest, is approximately calculated

The value of the inductance L should not be too large, so that the frequency range in which the Lowering sufficient in-phase signals occurs is sufficiently narrowband.

At f _min , the terminal impedance Z of the headphone used and the resistance of R form a voltage divider. The achievable level reduction .DELTA.P therefore depends on the ratio of Z and R and is calculated approximately from

For | Z | = R is given by equation (2) z. B. an achievable level reduction of 6 decibels.

measurement setup

To determine the in-head delocalization properties of the spatial filter, the in (1) constructed circuit and connected between the headphone output of a CD player and a commercially available dynamic stereo headphones with 50 ohms terminal impedance. The value of the inductance L used was 3.3 × 10 ^-3 Henry, the value of the capacity C was chosen to be 6.8 × 10 ^-6 Farad. For the resistor R, a potentiometer with R = 50 ohm was used. As input voltage test signal U _E , white noise was reproduced from a measurement signal CD. The headphone drive voltage U _K was measured at the connector of the headphone used.

Measurement results

(3) shows a largely frequency-independent, constant course of the level of the headphone drive voltage U _K between 100 hertz and 10000 hertz at zero position of the potentiometer (R = 0 ohms).

(4) shows a maximum reduction of the level of the headphone drive voltage U _K in the range of 1100 Hertz by about 5.5 decibels at maximum position of the potentiometer (R = 50 ohms).

rating the measurement results

The course of the measured headphone drive voltage U _K at zero position of the potentiometer ( (3) ) shows the expected, unaffected, almost constant course. The decrease above 9000 hertz is essentially due to filtering in the measurement signal detection.

The course of the measured headphone drive voltage U _K at maximum position of the potentiometer ( (4) ) has approximately the expected according to equation (2) level reduction of 6 decibels in the range of approximately the equation (1) expected frequency of 1062 Hertz. Because of the ohmic resistance R _{L of} the copper wire of the coil used (R _L = 4 ohms) and the relatively low phase differences of low signal frequencies occurs in comparison to (3) also below about 400 Hertz a significant level reduction of the headphone drive voltage. The decrease above 9000 hertz is essentially due to filtering in the measurement signal detection.

One subjective hearing test the Spatial filter with the headphones used showed depending on the potentiometer position and heard Music program material a more or less noticeable reduction the perceived as more or less unpleasant in-head localization, without the overall soundscape changed significantly would have.

Claims (1)

Spatial filter to reduce in-head localization from sound sources in headphone playback through Reduction of both ears, largely in-phase Sound components.