Loudspeakers Jared Bench ECE 5320 Spring 2004 Image: galaxyaudio.com

2/33 Loudspeakers Jared Bench 2/33 Loudspeakers Jared Bench Sound Basics Types of Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics Applications Conclusions Contents Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

3/33 Loudspeakers Jared Bench 3/33 Loudspeakers Jared Bench References SoundRecordingandReproduction.cfm /article_503_en.html howtheywork.htm speaker_tech.htm Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

4/33 Loudspeakers Jared Bench 4/33 Loudspeakers Jared Bench Further Reading New Developments:  article_698_en.html Modeling in a Control System:  AcousActu.pdf Speakers:  speaker_tech.htm   speaker_impedance.html/ ANC:   Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

5/33 Loudspeakers Jared Bench 5/33 Loudspeakers Jared Bench Definition of Sound What is Sound? Sound is a mechanical vibration transmitted by an elastic medium. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

6/33 Loudspeakers Jared Bench 6/33 Loudspeakers Jared Bench Sound Basics Sound is generated by vibration of an object or surface. The vibrating surface radiates pressure waves into the adjoining medium. Examples:  Speaker cone  Violin body  Human vocal cords  Turbulent airflow  Many others! Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

7/33 Loudspeakers Jared Bench 7/33 Loudspeakers Jared Bench Acoustic Actuators An acoustic actuator converts electrical signals into sound waves Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions Image: pathwayoflight.org

8/33 Loudspeakers Jared Bench 8/33 Loudspeakers Jared Bench Types of Acoustic Actuators Analog Loudspeaker  Dynamic Loudspeaker  Electrostatic Loudspeaker  Magnetic Ribbon (Planar) Loudspeaker Digital Loudspeaker (In Development) Acoustic Piston Devices Piezoelectric Materials Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

9/33 Loudspeakers Jared Bench 9/33 Loudspeakers Jared Bench Electrostatic Loudspeakers Electrostatic loudspeakers use the principle that like charges repel and opposites attract A thin plastic membrane is stretched over a rigid frame of some sort. It is then coated with a low mass electrically conductive substance like graphite power or metal flake. Two stiff, flat, electrically conductive structures called the stators are then made. Each stator has the same area as the thin membrane. The stators are connected to a power supply to provide the voltage to charge them. They are mounted on either side of the diaphragm, at a point exactly equidistant between the two stators. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

10/33 Loudspeakers Jared Bench 10/33 Loudspeakers Jared Bench Planar Magnetic Loudspeakers Planar magnetic speakers are similar to electrostatic loudspeakers. Unlike electrostatic speakers they do not need an external power source to charge metal plates. Operate by passing a current through a metal ribbon. As the current passes along, the ribbon is attracted to or repelled from the magnets surrounding it, generating sound waves. Used for high and mid frequencies. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

11/33 Loudspeakers Jared Bench 11/33 Loudspeakers Jared Bench Electrostatic and Planar Speakers Advantages:  Detailed high and mid frequency performance in a wide arc around the speaker.  Drivers are very relatively efficient. Disadvantages:  Can be expensive  Less durability  Wide frequency performance can be very expensive  Very little low frequency reproduction  Electrostatics must have an external power source to charge the stators  Stators and membranes can come into contact with each other, causing a short-circuit (and smoke). Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

12/33 Loudspeakers Jared Bench 12/33 Loudspeakers Jared Bench Digital Loudspeakers! This piezoelectric array is a prototype digital loudspeaker made from a ceramic strip. It translates an electrical voltage into physical movement of the ceramic strip due to electrical field. Image: 1 Limited Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

13/33 Loudspeakers Jared Bench 13/33 Loudspeakers Jared Bench Dynamic Loudspeakers A dynamic loudspeaker consists of a diaphragm suspended in a magnetic field Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions Image: electronics.howstuffworks.com

14/33 Loudspeakers Jared Bench 14/33 Loudspeakers Jared Bench Dynamic Loudspeaker Operation Current flows through the coil of the speaker, inducing an alternating magnetic field in the coil. As the polarity of the magnetic field alternates, it is alternately attracted to and repelled by the permanent magnet. This causes the coil to vibrate. The vibrating coil causes the attached cone shaped diaphragm to vibrate and reproduce the sounds generated by the original source. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

15/33 Loudspeakers Jared Bench 15/33 Loudspeakers Jared Bench Dynamic Loudspeaker Model Can be split into three primary groups:  Voice Coil Electrical Properties: Voice Coil DC Resistance Voice Coil Inductance  Equivalents of Mechanical Components: Suspension Compliance – Inductor Cone Mass – Capacitor Suspension Loss – Resistor  Radiated Sound Radiation Impedance Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

16/33 Loudspeakers Jared Bench 16/33 Loudspeakers Jared Bench Dynamic Loudspeaker Model Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

17/33 Loudspeakers Jared Bench 17/33 Loudspeakers Jared Bench Effect of Enclosure One can construct a similar branch for the enclosure, using the lumped parameters  Port mass – Capacitor  Enclosure Compliance – Inductor  System Losses – Resistor  Port Radiation Impedance Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

18/33 Loudspeakers Jared Bench 18/33 Loudspeakers Jared Bench Enclosure Model Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

19/33 Loudspeakers Jared Bench 19/33 Loudspeakers Jared Bench Combined Model Complete Driver + Enclosure + Electrical Model: Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

20/33 Loudspeakers Jared Bench 20/33 Loudspeakers Jared Bench Typical Driver Characteristics 0 Hz – Impedance is completely dominated by the DC resistance of the voice coil 0 Hz to Fundamental Frequency – Suspension compliance begins to dominate and is inductive in nature. At Fundamental Frequency – Impedance is purely resistive (phase angle = 0), determined by the series combination of the voice coil resistance and the suspension loss. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

21/33 Loudspeakers Jared Bench 21/33 Loudspeakers Jared Bench Typical Driver Characteristics Above Fundamental Frequency – Impedance drops (phase angle < 0), and is capacitive in nature. Midrange – Impedance approaches DC resistance of the voice coil. Typically about 10 to 20% higher than the voice coil resistance. This impedance is specified by manufacturers as “nominal impedance”. Higher Frequencies – Inductance of the voice coil begins to influence impedance. *Over the majority of the range of operation, the voice coil resistance dominates. The impedance NEVER becomes purely inductive, or even remotely close. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

22/33 Loudspeakers Jared Bench 22/33 Loudspeakers Jared Bench Impedance Characteristics Typical two-way loudspeaker, showing electrical impedance magnitude (solid trace) and phase (dashed trace) plotted against frequency in Hz. (Image: stereophile.com) Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

23/33 Loudspeakers Jared Bench 23/33 Loudspeakers Jared Bench Dynamic Speaker Disadvantages Disadvantages  Cannot reproduce entire frequency spectrum on their own  Large Mass (Not smooth or uniform)  VERY Inefficient  Performance declines sharply for off- axis applications Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

24/33 Loudspeakers Jared Bench 24/33 Loudspeakers Jared Bench Active Noise Control (ANC) Active control is sound field modification, particularly sound field cancellation, by producing a mirror image of the offending sound. In theory, the disturbance is thus cancelled, and the net result is no sound at all. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

25/33 Loudspeakers Jared Bench 25/33 Loudspeakers Jared Bench Passive vs. Active Noise Control Passive noise control includes:  Insulation  Silencers  Vibration mounts  Damping and absorptive treatments Works best at mid to high frequencies but is difficult at low frequencies. Active noise control is more practical for low frequencies. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

26/33 Loudspeakers Jared Bench 26/33 Loudspeakers Jared Bench Benefits of Active Noise Control Low-frequency quieting that would be too expensive, inconvenient, impractical, or heavy by passive methods alone. Improve performance and/or efficiency (i.e. a less restrictive muffler passage) Increased material durability and fatigue life Lower operating costs due to reduced facility down-time Reduced operator fatigue and/or improved ergonomics Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

27/33 Loudspeakers Jared Bench 27/33 Loudspeakers Jared Bench Types of Active Noise Control Active noise cancellation (ANC)  Control of acoustic disturbances Active structural-acoustic control (ASAC)  Control of vibration of a flexible structure ASAC is distinguished from ANC only in how it is applied Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

28/33 Loudspeakers Jared Bench 28/33 Loudspeakers Jared Bench Aircraft interior noise by use of lightweight vibration sources on the fuselage and acoustic sources inside the fuselage. Helicopter cabin noise by active vibration isolation of the rotor and gearbox. Noise radiated by ships and submarines by active vibration isolation of interior mounted machinery and active reduction of vibratory power transmission along the hull. Internal combustion engine exhaust noise by use of acoustic control sources at the exhaust outlet or by use of high intensity acoustic sources mounted on the exhaust pipe. Industrial noise sources such as vacuum pumps, forced air blowers, cooling towers and gas turbine exhausts. Lightweight machinery enclosures. Tonal noise radiated by turbo-machinery and aircraft engines. Low frequency noise propagating in air conditioning systems. Electrical transformer noise. Noise inside automobiles using acoustic sources inside the cabin and lightweight vibration actuators on the body panels. Active headsets and earmuffs. Active Noise Control Applications Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

29/33 Loudspeakers Jared Bench 29/33 Loudspeakers Jared Bench Active Noise Control Headphones Cancel low-frequency noise while passing mid and high frequency sounds such as conversation and warning sirens. Used extensively by pilots. NOISEGARD HMEC 300 HEADSET Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

30/33 Loudspeakers Jared Bench 30/33 Loudspeakers Jared Bench Active Exhaust Mufflers Several automobile manufacturers are now considering active mufflers for future production cars. Image: Katholieke Universiteit Leuven Department of Mechanical Engineering Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

31/33 Loudspeakers Jared Bench 31/33 Loudspeakers Jared Bench Industrial Fan Noise Reduction “Speakers placed around the fan intake or outlet not only reduce low- frequency noise … but they also improve efficiency to such an extent that they pay for themselves within a year or two.” - SignalSystemsCorp.com Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

32/33 Loudspeakers Jared Bench 32/33 Loudspeakers Jared Bench Automobile Interior Noise Active noise reduction systems are available to automobile manufacturers for reducing low frequency noise inside car interiors. These systems use the car speakers to superpose cancellation signals over the normal music signal to cancel muffler and tire noise and other sounds. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions

33/33 Loudspeakers Jared Bench 33/33 Loudspeakers Jared Bench Conclusions Loudspeakers can be used in many applications, not just to create noise, but to reduce it! In addition to noise reduction, vibrations can also be reduced, increasing fatigue life. Sound Basics Acoustic Actuators Loudspeaker Basics Loudspeaker Model Loudspeaker Characteristics ApplicationsConclusions