The Design of Active Crossovers>
This book deals with the design of active crossovers for multi-way loudspeaker systems. It is, to the best of my knowledge, the first book that concentrates wholly on the subject. It is a unique collection of detailed information on crossover design. It will contain a lot of wholly original information that I have worked out over the last twelve months. A detailed synopsis of the chapter contents is given below.
THE DESIGN OF ACTIVE CROSSOVERS by Douglas Self Chapter 1: Active crossover basics Chapter 2: How loudspeakers work Chapter 3: Crossover requirements Chapter 4: Crossover types Chapter 5: Notch crossovers Chapter 6: Subtractive crossovers Chapter 7: Lowpass and highpass filter characteristics Chapter 8: Designing lowpass and highpass filters Chapter 9: Bandpass & Notch Filters Chapter 10: Time-delay Filters Chapter 11: Equalisation Chapter 12: Passive components for active crossovers Chapter 13: Opamps for active crossovers Chapter 14: Crossover system design Chapter 15: Subwoofers and their crossovers Chapter 16: Line Inputs Chapter 17: Line Outputs Chapter 18: Power supply design Chapter 19: An active crossover design -------------------------------------------------------------------------------------------- Chapter 1: Active crossover basics What a crossover does Why a crossover is necessary Beaming and lobing Active crossover applications Bi-amping and bi-wiring Loudspeaker cables The advantages and disadvantages of active crossovers The advantages of active crossovers Some illusory advantages of active crossovers The disadvantages of active crossovers The next step in hifi Active crossover systems Matching crossovers and loudspeakers A modest proposal: popularising active crossovers Multi-way connectors Subjectivism Chapter 2: How loudspeakers work Sealed box loudspeakers Vented boxes Reflex (ported) loudspeakers Auxiliary Bass Radiator (ABR) loudspeakers Transmission line loudspeakers Horn loudspeakers Diffraction Modulation distortion Further reading Chapter 3: Crossover requirements General crossover requirements 1: Adequate flatness of summed amplitude/frequency response on-axis 2: Sufficiently steep rolloff slopes between the output bands 3: Acceptable polar response 4: Acceptable phase response 5: Acceptable group delay behaviour Further requirements for active crossovers 1: Negligible extra noise 2: Negligible impairment of system headroom 3: Negligible extra distortion 4: Negligible impairment of frequency response 5: Negligible impairment of reliability Linear phase Minimum phase Absolute phase Phase perception Target functions Chapter 4: Crossover types All-pole and non-all-pole crossovers Symmetrical and asymmetrical crossovers All-pass and Constant-Power crossovers Constant voltage crossovers First-order crossovers First-order Solen split crossover First-order crossovers: 3-way Second-order crossovers Second-order Butterworth crossover Second-order Linkwitz-Riley crossover Second-order Bessel crossover Second-order 1dB-Chebychev crossover Third-order crossovers Third-order Butterworth crossover Third-order Linkwitz-Riley crossover Third-order Bessel crossover Third-order 1dB-Chebychev crossover Fourth-order crossovers Fourth-order Butterworth crossover Fourth-order Linkwitz-Riley crossover Fourth-order Bessel crossover Fourth-order 1dB-Chebychev crossover Fourth-order linear-phase crossover Fourth-order Gaussian crossover Fourth-order Legendre crossover Higher-order crossovers Determining frequency offsets Summary of crossover properties Filler-driver crossovers The Duelund crossover Crossover topology Crossover conclusions Chapter 5: Notch crossovers Elliptical filter crossovers Neville Thiele MethodTM (NTM) crossovers Chapter 6: Subtractive crossovers Subtractive crossovers First-order subtractive crossovers Second-order Butterworth subtractive crossovers Third-order Butterworth subtractive crossovers Fourth-order Butterworth subtractive crossovers Subtractive crossovers with time delays Performing the subtraction Chapter 7: Lowpass and highpass filter characteristics Active filters Lowpass filters Highpass filters Bandpass filters Notch filters All-pass filters The order of a filter Filter cutoff frequencies and characteristic frequencies First-order filters Second-order and higher-order filters Filter characteristics Butterworth filters Linkwitz-Riley filters Bessel filters Chebyshev filters 1dB-Chebyschev lowpass filter 3dB-Chebyschev lowpass filter Higher-order filters Butterworth filters up to 8th order Linkwitz-Riley filters up to 8th order Bessel filters up to 8th order Chebyshev filters up to 8th order More complex filters- adding zeros Inverse Chebyshev Filters (Chebyshev Type II) Elliptical Filters (Cauer filters) Some lesser-known filter characteristics Transitional filters Linear-Phase filters Gaussian filters Legendre-Papoulis filters Synchronous filters Other filters Chapter 8: Designing lowpass and highpass filters Designing real filters Component sensitivity First-order lowpass and highpass filters Second-order filters Sallen & Key second-order filters Sallen & Key lowpass filter components Sallen & Key second-order lowpass: unity-gain Sallen & Key second-order lowpass unity-gain: component sensitivity Sallen & Key second-order lowpass: equal-capacitor Sallen & Key second-order lowpass equal-C: component sensitivity Sallen & Key second-order Butterworth lowpass: defined gains Sallen & Key second-order lowpass: non-equal-resistors Sallen & Key third-order lowpass in a single stage Sallen & Key third-order lowpass in a single stage: non-equal-resistors Sallen & Key fourth-order lowpass in a single stage Sallen & Key fourth-order lowpass in a single stage: non-equal-resistors Sallen & Key fifth and sixth-order lowpass in a single stage Sallen & Key highpass filters Sallen & Key second-order highpass: unity-gain Sallen & Key second-order highpass: equal-resistors Sallen & Key second-order Butterworth highpass: defined gains Sallen & Key second-order highpass: non-equal-capacitors Sallen & Key third-order highpass in a single stage Sallen & Key fourth-order highpass in a single stage Linkwitz-Riley with Sallen & Key filters: loading effects Lowpass filters with attenuation Bandwidth definition filters Bandwidth definition: Butterworth versus Bessel ultrasonic filters Bandwidth definition: subsonic filters. Bandwidth definition: combined ultrasonic & subsonic filters Distortion in Sallen & Key filters: highpass Distortion in Sallen & Key filters: lowpass Mixed capacitors in low-distortion Sallen & Key filters Noise in Sallen & Key filters: lowpass Noise in Sallen & Key filters: highpass Multiple feedback filters Multiple-feedback lowpass filters Multiple-feedback highpass filters Distortion in multiple-feedback filters: highpass Distortion in multiple-feedback filters: lowpass Noise in multiple-feedback filters: highpass Noise in multiple-feedback filters: lowpass State-variable filters Variable-frequency filters: Sallen & Key Variable frequency filters: state-variable second-order Variable frequency filters: state-variable fourth order Variable frequency filters: other orders Chapter 9: Bandpass and Notch Filters Multiple feedback bandpass filters High-Q bandpass filters Notch filters The twin-T notch filter The 1- bandpass notch filter The Bainter notch filter The bridged-differentiator notch filter Boctor notch filters Other notch filters Simulating notch filters Chapter 10: Time-delay filters The requirement for delay compensation Calculating the required delays Signal summation Physical methods of delay compensation Delay filter technology Sample crossover & delay filter specification All-pass filters in general First-order allpass filters Distortion & noise in first-order allpass filters Cascaded first-order allpass filters Second-order allpass filters Distortion & noise in second-order allpass filters Third order allpass filters Distortion & noise in third-order allpass filters Higher-order allpass filters Delay lines for subtractive crossovers Variable allpass time delays Lowpass filters for time delays Chapter 11: Equalisation The need for equalisation What equalisation can and can’t do Loudspeaker equalisation 1) Drive unit equalisation 2) 6dB/oct dipole equalisation 3) Bass response extension 4) Diffraction compensation equalisation 5) Room interaction correction Equalisation circuits HF-boost and LF-cut equaliser HF cut and LF-boost equaliser Combined HF-boost and HF-cut equaliser Adjustable peak/dip equalisers: fixed frequency & low Q Adjustable peak/dip equalisers: variable centre frequency & low Q Adjustable peak/dip equalisers with high Q The bridged-T equaliser The biquad equaliser Capacitance multiplication for the biquad equaliser Equalisers with non-6 dB slopes Equalisation by frequency offset Equalisation by adjusting all filter parameters Chapter 12: Passive components for active crossovers Resistors: values and tolerances Improving accuracy with multiple components: Gaussian distribution Resistance value distributions Improving accuracy with multiple components: uniform distribution Obtaining arbitrary resistance values Resistor noise: Johnson and excess noise Resistor non-linearity Capacitors: values and tolerances Capacitor shortcomings Non-electrolytic capacitor non-linearity Electrolytic capacitor non-linearity Chapter 13: Opamps for active crossovers Active devices for active crossovers Opamp types Opamp properties: Noise Opamp properties: Slew-rate Opamp properties: Common mode range Opamp properties: Input offset voltage Opamp properties: Bias current Opamp properties: Cost Opamp properties: Internal distortion Opamp properties: Slew-rate limiting distortion Opamp properties: Distortion due to loading Opamp properties: Common-mode distortion Opamps surveyed The TL072 opamp The 5532 and 5534 opamps The 5532 with shunt feedback 5532 output loading in shunt feedback mode The 5532 with series feedback Common-mode distortion in the 5532 Reducing 5532 distortion by output stage biasing Which 5532? The 5534 opamp The LM4562 opamp Common-mode distortion in the LM4562 The LME49990 opamp Common-mode distortion in the LME49990 The AD797 opamp Common-mode distortion in the AD797 The OP27 opamp Opamp selection Chapter 14: Crossover system design Crossover features Input level controls Subsonic filters Ultrasonic filters Output level trims Output mute switches, Output phase-reverse switches Control protection Features usually absent Metering Relay output muting Switchable crossover modes Noise, headroom, and internal levels Circuit noise and Low-Impedance Design Using raised internal levels Placing the output attenuator The amplitude/frequency distribution of musical signals, & internal levels Gain structures Noise gain Active gain-controls Filter order in the signal path Output level controls Mute switches Phase-invert switches Distributed peak-detection Power amplifier considerations Chapter 15: Subwoofers and their crossovers Subwoofer applications Subwoofer technologies Sealed (Infinite baffle) subwoofers Reflex (ported) subwoofers Auxiliary Bass Radiator (ABR) subwoofers Transmission line subwoofers Bandpass subwoofers Isobaric subwoofers Dipole subwoofers Horn-loaded subwoofers Subwoofer drive units Hifi subwoofers Home entertainment subwoofers Low-level inputs (unbalanced) Low-level inputs (balanced) High-level inputs High-level outputs Mono summing LFE input Level control Crossover in/out switch (LFE/normal) Crossover frequency control (lowpass filter) Highpass subsonic filter Phase switch (normal/inverted) Variable phase (delay) control Signal activation out of standby Home entertainment crossovers Fixed frequency Variable frequency Multiple Variable Power amplifiers for home entertainment subwoofers Subwoofer integration Sound-reinforcement subwoofers Line or area arrays Cardioid subwoofer arrays Aux-fed subwoofers Automotive audio subwoofers Chapter 16: Line inputs External signal levels Internal signal levels Input amplifier functions Unbalanced inputs Balanced interconnections The advantages of balanced interconnections The disadvantages of balanced interconnections Balanced cables and interference Balanced connectors Balanced signal levels Electronic vs transformer balanced inputs Common mode rejection ration (CMRR) The basic electronic balanced input Common-mode rejection ratio: opamp gain Common-mode rejection ratio: opamp frequency response Common-mode rejection ratio: opamp CMRR Common-mode rejection ratio: Amplifier component mismatches A practical balanced input Variations on the balanced input stage Combined unbalanced and balanced inputs The Superbal input Switched-gain balanced inputs Variable-gain balanced inputs High input-impedance balanced inputs The instrumentation amplifier Transformer balanced inputs Input overvoltage protection Noise and balanced inputs Low-noise balanced inputs Low-noise balanced inputs in real life Ultra-low-noise balanced inputs Chapter 17: Line outputs Unbalanced outputs Zero-impedance outputs Ground-cancelling outputs Balanced outputs Transformer balanced outputs Output transformer frequency response Transformer distortion Reducing transformer distortion Chapter 18: Power supply design Opamp supply rail voltages Designing a ±15V supply Designing a ±17V supply Using variable-voltage regulators Improving ripple performance Dual supplies from a single winding Power supplies for discrete circuitry Mutual shutdown circuitry Chapter 19: An active crossover design Design principles Example crossover specification The gain structure Resistor selection Capacitor selection The balanced line input stage The bandwidth definition filter The HF path: 3 kHz Linkwitz-Riley highpass filter The HF path: time delay compensation The MID path: topology The MID path: 400 Hz Linkwitz-Riley highpass filter The MID path: 3 kHz Linkwitz-Riley lowpass filter The MID path: time delay compensation The LF path: 400 Hz Linkwitz-Riley lowpass filter The LF path: no time delay compensation Output attenuators and level trim controls Balanced outputs Crossover programming Noise analysis: input circuitry Noise analysis: HF path Noise analysis: MID path Noise analysis: LF path Improving the noise performance: the MID path Improving the noise performance: the input circuitry The noise performance: comparisons with power amplifier noise Conclusion Appendix 1: Crossover design references Appendix 2: Loudspeaker design references Douglas Self London Jan 2011