DE1270614B - Device with an amplifier and a loudspeaker connected downstream - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H04b

German KL: 21 a2 - 16/01

Number: 1270 614

File number: P 12 70 614.8-31

Filing date: June 23, 1964

Opening day: June 20, 1968

The invention relates to a device with an amplifier and with a loudspeaker connected downstream, whose membrane is connected to a transducer that accelerates the membrane supplies corresponding voltage fed back to the amplifier input in the sense of a negative feedback. In the following, the term "membrane" is used to refer to the moving part of the loudspeaker which radiates the sound vibrations. This membrane can, for. B. the shape of a flat Disc, have a conical shape or a double conical shape. Such a device is for example from U.S. Pat. No. 2,860,183.

Such a device makes it possible to have such a device over a relatively wide frequency range Move the speaker cone to get that sound pressure or the root of the sound energy is proportional to the input signal. In particular, a piezoelectric element is used as the transducer a certain mass used, so that the mass forces caused by the membrane movement generate the relevant negative feedback voltage at the transducer electrodes. Compared to devices in which by means of a part that does not move with the loudspeaker membrane Vibration sensor, the movement is measured relative to this part, results from this Measure the advantage that scattered vibrations of various kinds between this part and the speaker membrane make themselves noticeable in the generated negative feedback voltage, whereby the risk of parasitic vibrations is particularly high.

It turns out that with relatively high values of the negative feedback factor, it is absolutely it is not easy to keep such a device free from vibration. This swing occurs as soon as the Loop gain for the system: amplifier, loudspeaker, negative feedback circuit, equals 1 and has experienced a phase shift of 360 °. To prevent this phenomenon, on the one hand mechanical Problems are solved so that it is ensured that the electrical Vibrations correspond exactly to the vibrations of the loudspeaker membrane; on the other hand have to electrical filters ensure that at the frequency at which the negative feedback voltage is 180 ° in the Phase is shifted so that positive feedback would occur, the loop gain below the Value 1 has dropped.

Since the aim is to achieve the highest possible correspondence between the sound pressure of the generated vibrations and the input signal to device with an amplifier and with a downstream loudspeaker

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. H. Auer, patent attorney,

2000 Hamburg 1, Mönckebergstr. 7th

Named as inventor:
Stephanus Hendrik de Koning,
Eindhoven (Netherlands)

Claimed priority:

Netherlands of June 26, 1963 (294 600)

one would prefer to use the highest possible negative feedback factors. As a result of the above-mentioned risk of self-excitement, this wish can generally not be easily fulfilled. In addition, it turns out that at the high frequencies (at which the loudspeaker membrane no longer vibrates as a whole), namely at vibrations with a wavelength smaller than half the circumference πD (D = diameter) of the loudspeaker, provided that the loudspeaker is is located in the wall of an otherwise closed housing, a correction is still required. It has been found that the sound pressure of the vibrations generated decreases in inverse proportion to the frequency with constant acceleration of the membrane.

The invention has the purpose of creating an amplifier arrangement that meets high requirements in with respect to freedom from lag and fidelity.

It is characterized in that a first between the amplifier input and the loudspeaker Network is connected, the one favoring the frequencies below the loudspeaker resonance Has transmission characteristic, and that in the negative feedback path between the converter and a second network is connected to the amplifier input

809 560/352

is that above a frequency whose wavelength is equal to half the loudspeaker range, a the transmission characteristic attenuates the high frequencies.

The invention is based on the following knowledge:

By using the second network, the desired frequency characteristic between the root from the radiated sound energy and the input

Vei stronger with high impedance input and lower impedance To switch output impedance.

The invention is explained below with reference to the drawing neari.

F i g. 1 shows a basic circuit diagram according to the invention;

F i g. Figures 2 to 5 show frequency characteristics of the various networks used in Figure 1; F i g. 6 Shows an elaborated execution

signal are obtained, whereby this network is an io example according to the invention, The negative feedback which attenuates the high tones in this way. 1 will be the

tion voltage provides that the risk of a signal oscillation undesired self-excitation occurring at an input terminal 1 in the high tones is passed through a network 1 and then reduced to one. This danger remains, however, if amplifier 2 is fed to the output of which the speaker 3 is 15 if the negative feedback factor is too high. With the membrane of the speaker 3 is. Although by the mere application of the
mentioned converter and the mentioned second network already the desired frequency characteristic

between the sound pressure and the input signal

a transducer 4 is connected, which supplies a voltage proportional to the acceleration of the membrane. This voltage is fed to a network II via a cathode amplifier 5 and then in the sense of a

is obtained, the first network 20 negative feedback is still fed back to input terminal 1.

plant in the transmission circuit within the negative feedback loop switched, since with the help of this network a considerable reduction in the non-linear Distortion of lower audio frequencies can be achieved

can. This distortion supplies the largest 25 loudspeakers. It is assumed that Contributing to audible unwanted overtones and membrane itself in the rest of the wall of one

F i g. 2 shows the root of the radiated sound energy E of the loudspeaker 3 as a function of the frequency (plotted on a logarithmic scale) / with a constant input voltage this

Difference tones. The combination of these two measures can therefore be used with a moderate value of the negative feedback factor for the midrange nevertheless cause the linear, the nonlinear and the Transition distortion as well as the risk of acoustic feedback within the playback frequency range stay low. For frequencies below or above the audibility limits can

Enclosed housing is located and that this membrane vibrates as a rigid whole in the entire tone range. Above the frequency Z _1, the air in this housing vibrates as a rigid mass; below this frequency the air flows out of the housing. At frequency / ₂ the loudspeaker membrane is in resonance, above frequency / ₃ the radiation resistance for the membrane is almost constant;

If necessary, a band filter with a wavelength corresponding to this frequency can be used, which prevents acoustic feedback outside about half of the loudspeaker range, in that of the playback frequency range.
The negative feedback voltages increase in frequency

influence is for example from the Swiss

In practice, / i is close to a few Hertz ,, / ₂ at almost 100 Hz, / ₃ between 1000 and 2500 Hz.

The transducer 4 supplies a voltage which is known over the patent specification 238 929 as well as from the German patent 40 whole frequency range proportional to the Schleuscript 853 298. In the case of the speaker membrane from the first mentioned slope. Above the arrangement known from the patent _{specification, however, the square root of the sound energy of the loudspeaker diaphragm takes a coil which is arranged at frequency / 3} , reversed with constant acceleration of the diaphragm and such an arrangement shows the above-mentioned proportionally to the frequency. Conversely th difficulties that lead to parasitic oscillations 45 so that with constant sound energy the can lead. The same applies to the voltage generated by the converter 4 above the frequency / _{a increases} with the frequency _s as shown in FIG. 3. '- ^

According to the invention, the networks) and II 50 almost matches the transfer characteristics that are in the F i g. 4 and 5 are shown. Next, these networks are in the form of minimum phase networks executed, d. h ,, that 'that structure with inductors, capacitors and resistors was chosen Digit 55, is 7 where the phase angle of the transfer function is minimal.

Above frequency / 3, network II a falling transfer characteristic. In this way, the rising characteristic of F i g, 3 is eliminated.

is compared according to a further feature of the invention for 60, so that above the frequency / ₃ this frequency range also a direct feedback voltage with constant strength of the negative feedback while bypassing the loudspeaker sound energy remains almost constant. Since this network * and the converter applied. . plant lies in the negative feedback circuit, and in the

In a device according to the invention dei could take that the product of the gain factor and Negative feedback circle of the oscillations below 65 of the negative feedback factor is large compared to 1

Arrangement according to German patent specification 853298, because there is also a coupling coil on the voice coil of the loudspeaker or its supporting body arranged.

In the foregoing, it has already been explained in detail by what means and in what manner the known arrangements occurring difficulties can be eliminated, so that a closer look on the known devices on this does not appear necessary.

Since the first network is usually a proportionate brings about strong favoring of the noise components below the audible frequency range,

of the audible frequency range on the first-mentioned network. It can also be useful between the converter and the second network

thus only by this measure a reproduction characteristic is achieved that is almost independent of the Frequency is. Nevertheless, the network I is still

Claims (1)

5 6 intended. This network has the loudspeaker 3 at the first of these very low frequencies Place the special function below the Fre- reach. quenz / _{a is} the product of the gain factor and to increase the negative feedback factor significantly, so Ia were a practical embodiment that the distortion of the low audio frequencies 5 dimension the switching elements as follows: is considerably reduced, since the products of these p «..- _Q ""j _1ft -nsQnn Frequencies are in the audible range and thus are particularly annoying. The network also improves transistors 20 2N2386 Werk I the phase characteristic of the element 1, resistor 14 82 kO 2, 3, 4, 5, II formed loop and thus the stability io the device. Resistance 16 561 <Ω F i g. 6 shows a practical embodiment of the resistor 17 1.8 kO Device according to the invention. The input signal wka ^ o + ^ a tt isnn
at terminal 1 is amplified with the help of a cascade amplifier, which contains the tubes 9 and 10, 15 resistor 23 2.7 kü its output voltage via network 1 to resistor 24 500 ΜΩ high-resistance input, e.g. of 1 ΜΩ, of the end Amplifier 11 arrives. The series branch of the network resistance 25 10 Ul Work I contains the parallel connection of an inductive resistor 28 1.5 ΜΩ activity 12 and the series connection of a condenser 20 wi / Wct »« /! iq 1 <; \ * n sators 13 and a resistor 14, while the Cross branch of the network I the series connection resistor 30 150 kΩ a resistor 17 and one through a further resistor 32 1 ΜΩ Resistor 16 bridged capacitor 18 holds. The capacitors 15 and 19 act as a ₅ capacitor 13 3900 pF Isolating capacitors for the audio frequency oscillation capacitor 15 2μΈ ^ SP ¹¹ '- AA ι · α β α ♦ - ι n capacitor 18 5600OpF The m the output circuit of the power amplifier 11 switched speaker 3 is again with a wall capacitor 19 0.1 μΡ ler 4 provided, the one of the acceleration of the mem- 30 capacitor 26 10000 pF bran provides proportional voltage. This tension ν α ti c the control electrode of a field effect transistor 20 capacitor 27 1 μ * fed in a manner similar to a cathode capacitor 31 3300 pF amplifier a corresponding voltage down to inductance 12 900 H
set impedance level at its output ^{electrode 35}
21 generated. The input impedance of this field effect transistor can be particularly high, z. B. several claims:
10 ⁹ Ω, so that the piezoelectric transducer 4 1. device with an amplifier and with almost no load; its output impedance to a downstream loudspeaker whose meme can e.g. B. of the order of some 40 bran with a transducer connected to be one of the hundred ohms, for which purpose the re-acceleration of the membrane corresponding, in the stands 22, 23 and 24 are attached. The switching sense of a negative feedback to the amplifier input elements 20 to 24 are preferably supplied with the returned voltage, thereby converter4 built into the loudspeaker, so that the marked that between the danger of the occurrence of hum and other 45 strength input (1) and the loudspeaker (3) noise is reduced. The output signal of the transistor 20 is fed to the frequencies below the loudspeaker resonance network II, which has as an integrating network-favoring transfer characteristic, and works for oscillations with frequencies higher than / ₃ that in the negative feedback path between which is executed. For this purpose, its longitudinal converter (4) and the amplifier input (1) contain a branch, the resistor 25 and its transverse branch, the second network (II) is connected above the capacitor 26. A frequency whose wavelength is equal to the output signal of the Network II is supplied to the control electrode of the amplifier 9 over half of the loudspeaker circumference. The 55 line has. Resistors 28 and 29 are large compared to the second device according to claim 1, thereby ge-amplifier input resistance 30. indicates that the amplifier also has a direct negative feedback for Schwinhalb to reduce the noise components the audible frequency range is still a little below the audible frequency range Another negative feedback circuit attached to the 60 bypassing the loudspeaker and the wall capacitor 31 and the resistor 32 and lers is provided. Via which the output signals of the network I with the third device according to claims 1 and 2, Frequencies below the limit of audibility, e.g. B. characterized in that the negative feedback of about 10 Hz, to the input electrode of the circle of oscillations below the audible Stronger 9 are fed back. This negative feedback frequency range on the first-mentioned network lungsweg thus bypasses the speaker 3 and attacks. Converter 4; due to the presence of the condenser 4. Device according to one of the preceding sators 19 can almost no vibrations with claims, characterized in that between the transducer and the second network a transducer connected to the built-in loudspeaker Amplifier with high-resistance input and low-resistance output impedance switched is. Considered publications: German Patent No. 853 298; Swiss Patent No. 238 929; U.S. Patent No. 2,860,183. 1 sheet of drawings 809 560/352 6.68 © Bundesdruckerei Berlin