JPH0136314B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to equalization and amplification, and more particularly to high power level stereo power amplification particularly useful in automobiles, in which signal spectral components are Provides relatively low cost through novel circuit techniques including novel dynamic equalization that varies the equalization characteristics in frequency ranges that can cause overload while maintaining equalization characteristics in other frequency ranges. Regarding things.

In automobiles, it is common practice to power stereo power amplifiers directly from a 12 volt DC power supply. DC power supply to loudspeaker
To prevent biasing the diaphragm off-center, these amplifiers typically require large, expensive capacitors connected between each amplifier channel and each loudspeaker. Also, when equalization is used, the amplifier can be overloaded when receiving spectral components that are significantly boosted by the equalization circuit, thus creating undesirable audible distortion and Limit sound power output.

Accordingly, an important object of the present invention is to provide improved amplification and/or equalization.

Another object of the invention is to achieve the above objects while increasing the ratio of audible distortion-free power output to cost.

Another object of the present invention is to achieve the above object while performing equalization.

Another object of the invention is to achieve the above objectives while reducing the volume and cost of the capacitor.

Still another object of the present invention is to achieve the above objects with a dynamic equalization that maintains the desired equalization curve while excluding those portions of the frequency range where spectral components are amplified and create audible overload. It is.

According to a feature of the invention, in a system having first and second loudspeakers energized by left and right power amplifiers, between the first and second power amplifiers; first and second loudspeakers coupled in series; and a capacitor connected between a reference or ground terminal and a connection point of the first and second loudspeakers to block DC from both loudspeakers. configured. Preferably, the first and second power amplification devices cooperate with a loudspeaker, the loudspeaker being driven at low frequencies by the signal sum provided by the first and second power amplification devices; Above a predetermined crossover frequency related to the capacitance and impedance of the loudspeaker, a bridge is formed in cooperation with the loudspeaker driven by respective signals from the first and second power amplifiers.

The present invention will be described in detail below with reference to Examples.

Referring to FIG. 1, a block diagram illustrating the logical arrangement of an apparatus according to the present invention is shown. In Figure 1, one output coupling capacitor is omitted and another coupling capacitor performs the function of DC blocking and is of very small value, thereby reducing size and cost compared to conventional This is lower than either of the two blocking capacitors normally used in the device. The apparatus includes left and right channel amplifiers 10 and 11 coupled in series with the outputs + and - of left and right channel amplifiers 10 and 11 to left and right loudspeakers 12 and 13, respectively, and other outputs. The terminal is grounded. The blocking capacitor 14 is connected to the left speaker 12.
and the connection point between the right speaker 13 and the ground. The left and right loudspeakers 12 and 13 are of substantially the same impedance, and the left and right channel amplifiers 10 and 11 are constructed of substantially the same and in the absence of an input signal.
No DC flows through either loudspeaker and the voice coil remains in the center of the air gap. When a low frequency signal below the cut-off frequency appears, the capacitor 14 effectively becomes an open circuit and the potential at the ungrounded output terminals of the left channel and right channel amplifiers 10 and 11 rises and the series connected left A current flows through the right speakers 12 and 13, drives the diaphragm in phase, and supplies a monaural low frequency signal. Since low frequency signals are naturally omnidirectional and do not produce appreciable stereo effects, this circuit configuration does not audibly change the stereo feel perceived by the listener.

At higher frequencies, capacitor 14 effectively grounds the junction of left speaker 12 and right speaker 13, so that the speakers are driven independently at higher frequencies to provide left and right signals to the listener, creating stereo make you feel the sensation. The crossover frequency at which the response is 3 dB lower than the range above the crossover frequency where the response is approximately constant corresponds approximately to the frequency where the capacitive reactance of half the capacitance of the capacitor 14 is equal to the impedance of the loudspeaker 12 or 13. For a speaker with an impedance of 0.5 ohm at a crossover frequency of 600 Hz (typically achieved by having 1 ohm front and rear speakers for each channel connected in parallel), the capacitor 14 value is
1000 MFD, and in the past a value one tenth of the two blocking capacitors was typically used.

Referring to FIG. 2, a block diagram illustrating the logical structure of a dynamically scalized loudspeaker system in accordance with the present invention is shown. The loudspeaker device 21 receives an input signal from an input terminal 22,
Reproduction at a relatively high sound level without audible distortion caused by overloading the power amplifier 23. An operational amplifier is connected to the input terminal 22, to which is added a fixed parameter equalization circuit 24 shunted by a variable parameter element 25 in the feedback path from the output of the amplifier 26 to the summing point 27. Power amplifier 23 transmits the feedback signal to LED 32 via feedback path 34, providing light to photoelectric converter 25 with an intensity proportional to the magnitude of the feedback signal provided by power amplifier 23.

Next, the operating principle will be explained. In equalized loudspeaker systems, the power amplifier is typically overloaded in response to signal spectral components in the frequency ranges (usually the bass and treble regions) where the equalization gain is highest. Prior art solutions incorporate compressors and cascaded static equalizers to uniformly increase the gain of the transmission channel independently of frequency as the signal level increases, independent of the spectral component response that creates the rotational loading. reduce Consider the case where a singer is accompanied by a bass drum, and without a compressor the bass drum signal would overload the system. To prevent overload, prior art compressors reduce the gain of the channel to reduce not only the loudness of the bass drum but also the loudness of the singer's voice. The present invention lowers the bass drum level to prevent amplifier overload, while leaving the singer's perceived sound level essentially the same.

The present invention achieves the above results with the apparatus of FIG. Maximum equalized gain occurs at the frequency where the conductance of the feedback circuit around amplifier 26 is maximum. The photoelectric converter 25 has negligible conductance in the dark, and equalization is determined by the fixed equalization circuit 24. When LED 32 is energized in response to an overload on power amplifier 23, the conductance of photoelectric converter 25 increases enough to reduce the equalization gain until the overload is removed. In the limit of attempts to severely overload the device, the photoelectric converter 25
is so high compared to the conductance of fixed equalizer circuit 24 that the frequency response of the channel is constant and the device acts as a constant response amplifier and compressor.

Referring to FIG. 3, a graph showing the response of the equalizer is shown, where curves A, B, and C are 0 and 0, respectively.
These are the characteristics when compressed by 5db and 20db. Curve B, which shows 5 dB compression with a photovoltaic converter 25 resistance of 100K ohms, is only about 1 dB lower than response curve A without compression from 200 Hz to 8000 Hz, but 50
6db lower at Hz and 8db lower at 15KHz. Photoelectric converter 2
Curve C showing 20db compression with 4 resistors at 10K ohms.
In this case, the frequency response is almost constant from 50Hz to 15KHz.

Referring to FIG. 4, a circuit diagram illustrating a preferred embodiment of the present invention is shown. Since one skilled in the art will be able to practice the invention by assembling the circuit of FIG. 4, the following description will be limited to the extent that it is helpful in understanding the principles of operation.

Transistor Q1 and associated circuitry include means for providing a suitable DC potential to the circuit arrangement. Terminal P
16 is normally connected to a program source, such as an associated car radio tuner, and is normally non-conducting when the source is turned on.
1 to provide the appropriate energizing potential to each circuit and to prevent the potential at the collector of transistor Q1 from exceeding the 16 volts established by Zener diode D4. Since the left and right channels are equal, only the right channel is shown in detail.

Transistor Q203 is normally non-conducting except when the power amplifier is overloaded. When it becomes conductive, current flows through the LED 32, illuminating the photoelectric converter 25 in proportion to the degree of overload.

The particular output circuit connections shown are to accommodate the front or A loudspeaker and the rear or B loudspeaker, the left and right speaker pairs being connected in parallel. The positive (+) terminals of the left channel loudspeaker driver are connected together to the collectors of the output transistors, while the negative (−) terminals of the right channel loudspeaker are commonly connected to the collectors of output transistors Q206 and Q207. Ru. The - terminal of the left loudspeaker and the + terminal of the right loudspeaker are both connected to a capacitor 14 . The capacitor 14 is
Typically 1000MFD as shown,
600 to approximately 0.5 ohm impedance by a pair of 1 ohm loudspeakers connected in parallel.
Establish a half-power crossover frequency in Hz.
The preferred loudspeaker driver style is
Used in the BOSE901(R) series loudspeaker system and also has a US patent
4061890. There is a high input for high level sources such as tuners, and a low input for low inputs such as tape heads.

Thus, novel devices and techniques have been presented that provide high acoustic power output with relatively inexpensive and compact circuitry. The circuit reduces multi-output coupling capacitors and maintains a good balance between different reproduction tones with almost inaudible distortion, allowing the amplifier to operate close to its maximum when a wide variety of program components are required. make it possible to It will be apparent to those skilled in the art that modifications can be made to this embodiment without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a power amplification system according to the present invention. FIG. 2 is a block diagram of another power amplification system according to the present invention. FIG. 3 is a graph showing equalization responses to various types of compression. FIG. 4 is a circuit diagram of a preferred embodiment of the present invention. (Explanation of symbols), 10: Left channel amplifier, 1
1: Right channel amplifier, 12: Left speaker, 1
3: Right speaker, 21: Loud speaker, 2
3: power amplifier, 24: fixed parameter equalization circuit, 26: amplifier.

Claims (1)

[Claims] 1. A common terminal and a first terminal for supplying first and second audio signals corresponding to the first and second audio input signals.
and a second loudspeaker device, and first and second power amplification devices amplifying the first and second audio input signals, respectively, wherein: between the first and second power amplification devices; said first
and a device for interconnecting a second loudspeaker device, and a capacitive device for DC blocking connected between the common terminal and a connection point of the first and second loudspeaker devices, the first and preventing DC from flowing through the second loudspeaker device at a frequency above a predetermined crossover frequency determined by the values of the capacitive device and the first and second loudspeaker devices. In the
a capacitive device for passing spectral components corresponding to the first and second audio input signals through the first and second loudspeaker devices, respectively, to the common terminal; said first within the frequency range of
and a power amplification system in which the first and second loudspeaker devices are interconnected to radiate spectral components of a second audio input signal as acoustic energy in phase. 2 the first and second loudspeaker devices are directly connected between the first and second power amplifier devices;
2. The power amplification system of claim 1, wherein the power source for the power amplification system includes a terminal for connecting to a DC power source of a vehicle and means for directly coupling the DC power source to the system. 3 indicated by each of said loudspeaker devices.
Claim 2, wherein the DC impedance is on the order of 1 ohm or less, and wherein said capacitive device cooperates with said first and second loudspeaker devices to establish a crossover frequency of approximately 600Hz. Power amplification system as described. 4. The power amplification system of claim 3, wherein the value of the capacitive device is approximately 1000 microfarads.