DE2046776A1 - Interference loudspeaker system for stereophonic reproduction - Google Patents

Description

I NTE RFERE NZLAUTSP RECH E RSYSTEM FOR STEREOPHONE REPRODUCTION Factig area: Electrical engineering - stereo acoustics applicationO The interference loudspeaker system is suitable for the acoustic stereophonic reproduction of performances.

It can be used with advantage in stereophonic "loudspeakers" Small appliances.

It can be used in normal stereos to improve the depth effect the sound image can also be used.

Purpose and task: The main purpose of the loudspeaker system is to to enable stereophonic playback in a relatively simple way - without two Having to use speaker boxes! -It must be ensured that amplitudes- and transit time differences occur at the ears of hearing as they occur at the location of the Stereo recording microphones were available; that a spatial dissolution for the listener the virtual sound sources is made possible - also the sound sources far next the speaker system. The original directions should appear. pre-condition it may be that the performances were recorded using a stereo microphone, whose overall characteristics correspond to those of the human ear.

Current stereophonic playback: A sound source is located by volume and transit time differences "(E.G. Neibmann: Phys.u.techn. Akustik) Both features are used in normal stereophonic playback when the Handset is equidistant from both speakers.

If a signal is only transmitted in the right or left channel, then the sense of direction is natural: for the listener, the sound comes from that direction of one loudspeaker, and the virtual place of origin agrees with the real one match: with that of the speaker. A further deep view is only possible if the other loudspeaker also emits a corresponding signal. You can see from If there are further reflections in the playback room, the natural impression is created slightly falsifies the fact that one ear has a weaker amplitude (through Diffraction dependent on frequency), delayed signal from the loudspeaker of the other Page also perceives. The one formed from the transit time and amplitude difference This slightly falsifies the impression of depth.

This corruption can be avoided by means of the interference loudspeaker system are reduced1 the impression of depth can be improved; the direction information is also conveyed. It is necessary that the listener directs himself in the broadcast ng of the speaker system. An electronic control allows the optimal Adaptation of the sound image to the distance of the listener from the loudspeaker0 Solution: The task at hand can be solved. Speakers (two or more) can be in one relatively small level offset are arranged and controlled that on Location of the listener approximates the desired sound image.

Fig. 2 and Fig. 3 show two possibilities found, the most possible require little effort. The individual loudspeakers are arranged side by side.

If more speakers are used, analog ones can of course be used Specify options. A well-bundled, forward-facing radiation of the Loudspeaker seems advantageous here - to avoid additional reflections from the side To reduce objects in the room.

Let R, L be the signals of the right and left channels, respectively. Divided by two speakers arranged next to each other, working in phase opposition, controlled by p (w) (L - an interference wave image is generated, this is the suitably emitted Signal (L + R) superimposed acoustically. Both are superimposed in such a way that at the place of the The listener has almost the same sound image that prevailed on the stereo recording microphone.

1.Example: (See Fig. 1) The one on the left ear of the listener incoming signals can be represented in the form: L '# p (w) # i # sin wto # (L - R) + ½ (L + R); p (w): Frequency response of the "L - R" channel, w: circular frequency to: to = # I / 2c , c: sc% allspeed; Let b «« 1; then the following applies approximately: t0c = ba = Wl Ur a = 15 cm, b = 25 cm, 1 = 200 cm, for example, # = 0.46 cm. 3 Let the frequency response given by p (w) = iwtS11 (realizable by means of an RC element); then will for the usual Frequency range (up to 18 kHz) approximately L '= L and R' = R.

Choose # = 0.3 cm, that means b = 0.08 1 and get approximately a limit frequency f0 = 18 kHz, with FO = 1/2 # to.

2nd embodiment: The example shows the use of two loudspeakers the execution of the interference loudspeaker system, as it is for small devices particularly suitable.

According to certain idealizations, which are tacitly also in the 1st example were made, we get: L = p (w) -i.sin wt; CL - R) t cos wt (L + R) And for b «I results again after a few approximations L * = L and R = R.

In this arrangement, however, it is recommended that the ratio b / l to choose smaller - about 0.05 to 0.08.

This example is sketched in Figure 2.

Remarks: With the sizes Lund, the left and right are signal amplitudes of the usual stereo channels, with p (w) (L -R) and (L + R) the signal amplitudes referring to the loudspeaker cones. The sizes L'and R do not directly indicate the Sound intensity at the ears; however, they can be frequency-dependent Convert proportionality factor. p (w) indicates the frequency response of the channel "(L - Rr 'opposite the channel "L R" up to the loudspeaker membrane: acoustic couplings the loudspeakers among each other are therefore included.

The mathematical relationships themselves finally describe partly only sensibly chosen idealizations and approximations - what kind is the Recognize readers immediately. They should emphasize the principle effect: explain the essentials in a clear manner. The real acoustic conditions deviate more or less from the representation depending on the arrangement (diffraction, Dispersion, no point sources of sound) For the realization: Because of the necessary high gain differences at lower frequencies in the channels "L- R" and "L + R" - but below 300 Hz may be p (w) = 0 - seems to be the first Realization to be difficult.

However, experiments show that the acoustic coupling is used the loudspeaker and the dispersion characteristics - by taking the latter into account if R and L are presented a little differently - satisfactory results can be achieved, especially with the 1st exemplary embodiment. The loudspeakers working out of phase S 1 and S2 can also be used here below 300 Hz: You can use frequency softening circuits be driven in phase with S 3 and to the required more powerful radiation contribute to the low frequencies.

The best sound image at the distance from the listener to the loudspeaker sets men by changing the gain of the channel "L - R" versus "L + R ". For higher demands the frequency response p (w) has to be corrected as well. It is recommended to provide devices with an adjustment device with a distance scale.

If the distance I remains fixed, you can change this Amplification ratio the width and depth impression of the sound image slightly vary.

The author provides further information and empirical values if required like to.

Achievable Benefits: The number of stereophonic broadcasts is today so big that it is already perceived as a disadvantage, still on with small receivers having to do without stereophonic playback. It can be done here - as in others Playback devices - replace the loudspeaker with a pair of loudspeakers as an interference system. In the case of broadcast receivers, only a simpler stereo decoder is required for this purpose ; one only needs to amplify the demodulated additional signal L -R.

The additional use of the interference loudspeaker system for normal stereo set up in the middle of the two speakers and equidistant away from the listener like this, improves stereophonic playback, increases the Depth effect of the sound image. Careful adjustment and installation of the system however, care must be taken here! For rooms that are not suitable, two loudspeaker boxes in them set up, the loudspeaker system described offers a welcome replacement.

Claims (1)

Patent claims: 1.) For interference loudspeaker systems intended for stereophonic reproduction (especially circuits according to Fig. 1 and 2), i.e. a combination of mini, two Loudspeakers, characterized in that they are essentially in one plane arranged offset, the signals p (w) (L - R) and -p (w) (L - R) emit separately and the signal q (w) (L + R) is superimposed - by means of the same loudspeakers or more. Meaning of the symbols: L, R: signals of the left or right stereo channel L = ## A # eiw # t, R = ## B # eiw # t; w = 2 # f # f: frequency; p (w), or: frequency responses of the respective transmission channels, considered up to the loudspeaker membrane; these are to be selected according to the system so that in front of a certain distance the speaker is given the stereophonic impression to a listener. p (w) and q (w) should not both be constant at the same time. An essential feature of the interference loudspeaker system is that that for the listener the virtual sound directions also next to or far from the Loudspeaker area, 2.) interference loudspeaker systems according to 1.) whose loudspeakers emit in phase below 300 Hz. Blank page