MULTIWAY SPEAKER SYSTEMS AND ACTIVE BOXES
Introduction:
Multiway loudspeaker systems provide the best possible acoustic performance since each loudspeaker is specially designed and optimized to handle a limited range of frequencies. Commonly, these loudspeaker systems divide the audio spectrum two or three bands.
To maintain a flat frequency response over the Hi-Fi audio range the bands cobered by each loudspeaker must overlap slightly. Imbalance between the loudspeakers produces unacceptable results therefore it is important to ensure that each unit generates the correct amount of acoustic energy for its segments of the audio spectrum. In this respect it is also important to know the energy distribution of the music spectrum to determine the cutoff frequencies of the crossover filters. As an example,a 100W three-way system with crossover frequencies of 400Hz and 3KHz would require 50W for the woofer,35W for the mid range unit and 15W for the tweeter.
Both active and passive filters can be used for crossovers but active filters cost significantly less than a good passive filter using air cored inductors and non-electrolytic capacitors. In addition active filters do not suffer from the typical defects of passive filters:
--Power less;
--Increased impedance seen by the loudspeaker (lower damping)
--Difficulty of precise design due to variable loudspeaker impedance.
Obviously, active crossovers can only be used if a power amplifier is provide for each drive unit. This makes it particularly interesting and economically sound to use monolithic power amplifiers.
In some applications complex filters are not relay necessary and simple RC low-pass and high-pass networks (6dB/octave) can be recommended.
The result obtained are excellent because this is the best type of audio filter and the only one free from phase and transient distortion. The rather poor out of band attenuation of single RC filters means that the loudspeaker must operate linearly well beyond the crossover frequency to avoid distortion.
The proposed circuit can realize combined power amplifiers and 12dB/octave high-pass or low-pass filters. In proactive, at the input pins amplifier two equal and in-phase voltages are available, as required for the active filter operations. The impedance at the Pin (-) is of the order of 100Ω, while that of the Pin (+) is very high, which is also what was wanted.
Transient inter-modulation distortion is an unfortunate phenomena associated with negative-feedback amplifiers. When a feedback amplifier receives an input signal which rises very steeply, i.e. contains high-frequency components, the feedback can arrive too late so that the amplifiers overloads and a burst of inter-modulation distortion. Since transients occur frequently in music this obviously a problem for the designed of audio amplifiers. Unfortunately, heavy negative feedback is frequency used to reduce the total harmonic distortion of an amplifier, which tends to aggravate the transient inter-modulation (TIM situation.) The best known method for the measurement of TIM consists of feeding sine waves superimposed onto square wavers, into the amplifier under test. The output spectrum is then examined using a spectrum analyzer and compared to the input. This method suffers from serious disadvantages: the accuracy is limited, the measurement is a tatter delicate operation and an expensive spectrum analyzer is essential.
The "inverting-sawtooth" method of measurement is based on the response of an amplifier to a 20KHz saw-tooth wave-form. The amplifier has no difficulty following the slow ramp but it cannot follow the fast edge. The output will follow the cutting of the shade area and thus increasing the mean level. If this output signal is filtered to remove the saw-tooth, direct voltage remains which indicates the amount of TIM distortion, although it is difficult to measure because it is indistinguishable from the DC offset of the amplifier. This problem is neatly avoided in the IS-TIM method by periodically inverting the saw-tooth wave-form at a low audio frequency. In the case of the saw-tooth in Fig. 8 the mean level was increased by the TIM distortion, for a saw-tooth in the other direction the opposite is true.
The UTC TDA2030A has an original circuit which limits the current of the output transistors. This function can be considered as being peak power limiting rather than simple current limiting. It reduces the possibility that the device gets damaged during an accidental short circuit from AC output to Ground.
The presence of a thermal limiting circuit offers the following advantages:
1). An overload on the output (even if it is permanent), or an above limit ambient temperature can be easily supported since the TJ can not be higher than 150°C
2). The heatsink can have a smaller factor of safety compared with that of a congenital circuit, There is no possibility of device damage due to high junction temperature increase up to 150°C, the thermal shut-down simply reduces the power dissipation and the current consumption.
Introduction:
Multiway loudspeaker systems provide the best possible acoustic performance since each loudspeaker is specially designed and optimized to handle a limited range of frequencies. Commonly, these loudspeaker systems divide the audio spectrum two or three bands.
To maintain a flat frequency response over the Hi-Fi audio range the bands cobered by each loudspeaker must overlap slightly. Imbalance between the loudspeakers produces unacceptable results therefore it is important to ensure that each unit generates the correct amount of acoustic energy for its segments of the audio spectrum. In this respect it is also important to know the energy distribution of the music spectrum to determine the cutoff frequencies of the crossover filters. As an example,a 100W three-way system with crossover frequencies of 400Hz and 3KHz would require 50W for the woofer,35W for the mid range unit and 15W for the tweeter.
Both active and passive filters can be used for crossovers but active filters cost significantly less than a good passive filter using air cored inductors and non-electrolytic capacitors. In addition active filters do not suffer from the typical defects of passive filters:
--Power less;
--Increased impedance seen by the loudspeaker (lower damping)
--Difficulty of precise design due to variable loudspeaker impedance.
Obviously, active crossovers can only be used if a power amplifier is provide for each drive unit. This makes it particularly interesting and economically sound to use monolithic power amplifiers.
In some applications complex filters are not relay necessary and simple RC low-pass and high-pass networks (6dB/octave) can be recommended.
The result obtained are excellent because this is the best type of audio filter and the only one free from phase and transient distortion. The rather poor out of band attenuation of single RC filters means that the loudspeaker must operate linearly well beyond the crossover frequency to avoid distortion.
The proposed circuit can realize combined power amplifiers and 12dB/octave high-pass or low-pass filters. In proactive, at the input pins amplifier two equal and in-phase voltages are available, as required for the active filter operations. The impedance at the Pin (-) is of the order of 100Ω, while that of the Pin (+) is very high, which is also what was wanted.
The components values calculated for fc=900Hz using a Bessel 3rd Sallen and Key structure are: C1=C2=C3=22nF, R1=8.2KΩ, R2=5.6KΩ, R3=33KΩ. Using this type of crossover filter, a complete 3-way 60W active loudspeaker system is shown as below. It employs 2nd order Buttherworth filter with the crossover frequencies equal to 300Hz and 3kHz. The mid range section consists of two filters a high pass circuit followed by a low pass network. With Vs=36V the output power delivered to the woofer is 25W at d=0.06% (30W at d=0.5%).The power delivered to the midrange and the tweeter can be optimized in the design phase taking in account the loudspeaker efficiency and impedance (RL=4Ω to 8Ω).
It is quite common that midrange and tweeter speakers have an efficiency 3dB higher than woofers.
It is quite common that midrange and tweeter speakers have an efficiency 3dB higher than woofers.
TRANSIENT INTER-MODULATION DISTORTION(TIM)
Transient inter-modulation distortion is an unfortunate phenomena associated with negative-feedback amplifiers. When a feedback amplifier receives an input signal which rises very steeply, i.e. contains high-frequency components, the feedback can arrive too late so that the amplifiers overloads and a burst of inter-modulation distortion. Since transients occur frequently in music this obviously a problem for the designed of audio amplifiers. Unfortunately, heavy negative feedback is frequency used to reduce the total harmonic distortion of an amplifier, which tends to aggravate the transient inter-modulation (TIM situation.) The best known method for the measurement of TIM consists of feeding sine waves superimposed onto square wavers, into the amplifier under test. The output spectrum is then examined using a spectrum analyzer and compared to the input. This method suffers from serious disadvantages: the accuracy is limited, the measurement is a tatter delicate operation and an expensive spectrum analyzer is essential.
The "inverting-sawtooth" method of measurement is based on the response of an amplifier to a 20KHz saw-tooth wave-form. The amplifier has no difficulty following the slow ramp but it cannot follow the fast edge. The output will follow the cutting of the shade area and thus increasing the mean level. If this output signal is filtered to remove the saw-tooth, direct voltage remains which indicates the amount of TIM distortion, although it is difficult to measure because it is indistinguishable from the DC offset of the amplifier. This problem is neatly avoided in the IS-TIM method by periodically inverting the saw-tooth wave-form at a low audio frequency. In the case of the saw-tooth in Fig. 8 the mean level was increased by the TIM distortion, for a saw-tooth in the other direction the opposite is true.
The result is an AC signal at the output whole peak-to-peak value is the TIM voltage, which can be measured easily with an oscilloscope. If the peak-topeak value of the signal and the peak-to-peak of the inverting sawtooth are measured, the TIM can be found very simply from:
TIM = Vout / Vsawtooth * 100
In Fig.8 The experimental results are shown for the 30W amplifier using the UTC TDA2030A as a driver and a low-cost complementary pair. A simple RC filter on the input of the amplifier to limit the maximum signal slope(SS) is an effective way to reduce TIM. For example if an anti-TIM filter with a cutoff at 30kHz is used and the max. peak to peak output voltage is 20V then, referring to the diagram, a Slew-Rate of 6V/μs is necessary for 0.1% TIM. As shown Slew-Rates of above 10V/μs do not contribute to a further reduction in TIM. Slew-Rates of 100V/μs are not only useless but also a disadvantage in hi-fi audio amplifiers because they tend to turn the amplifier into a radio receiver.
POWER SUPPLY
Using monolithic audio amplifier with non regulated supply correctly. In any working case it must provide a supply voltage less than the maximum value fixed by the IC breakdown voltage.
It is essential to take into account all the working conditions, in particular mains fluctuations and supply voltage variations with and without load. The UTC TDA2030A(Vsmax=44V) is particularly suitable for substitution of the standard IC power amplifiers(with Vsmax=36V) for more reliable applications.
An example, using a simple full-wave rectifier followed by a capacitor filter. A regulated supply is not usually used for the power output stages because of its dimensioning must be done taking into account the power to supply in signal peaks. They are not only a small percentage of the total music
signal, with consequently large over dimensioning of the circuit. Even if with a regulated supply higher output power can be obtained(Vs is constant in all working conditions),the additional cost and power dissipation do not usually justify its use. using non-regulated supplies, there are fewer designee restriction. In fact, when signal peaks are present, the capacitor filter acts as a flywheel supplying the required energy.
In average conditions, the continuous power supplied is lower. The music power/continuous power ratio is greater in case than for the case of regulated supplied, with space saving and cost reduction.
It is essential to take into account all the working conditions, in particular mains fluctuations and supply voltage variations with and without load. The UTC TDA2030A(Vsmax=44V) is particularly suitable for substitution of the standard IC power amplifiers(with Vsmax=36V) for more reliable applications.
An example, using a simple full-wave rectifier followed by a capacitor filter. A regulated supply is not usually used for the power output stages because of its dimensioning must be done taking into account the power to supply in signal peaks. They are not only a small percentage of the total music
signal, with consequently large over dimensioning of the circuit. Even if with a regulated supply higher output power can be obtained(Vs is constant in all working conditions),the additional cost and power dissipation do not usually justify its use. using non-regulated supplies, there are fewer designee restriction. In fact, when signal peaks are present, the capacitor filter acts as a flywheel supplying the required energy.
In average conditions, the continuous power supplied is lower. The music power/continuous power ratio is greater in case than for the case of regulated supplied, with space saving and cost reduction.
SHORT CIRCUIT PROTECTION
The UTC TDA2030A has an original circuit which limits the current of the output transistors. This function can be considered as being peak power limiting rather than simple current limiting. It reduces the possibility that the device gets damaged during an accidental short circuit from AC output to Ground.
THERMAL SHUT-DOWN
The presence of a thermal limiting circuit offers the following advantages:
1). An overload on the output (even if it is permanent), or an above limit ambient temperature can be easily supported since the TJ can not be higher than 150°C
2). The heatsink can have a smaller factor of safety compared with that of a congenital circuit, There is no possibility of device damage due to high junction temperature increase up to 150°C, the thermal shut-down simply reduces the power dissipation and the current consumption.
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