Impedance curve of a 4 ohm, 120mm speaker

A dynamic loudspeaker driver's chief electrical characteristics can be shown as a curve, representing the driver's electrical impedance versus frequency. A driver is an electro-mechanical transducer using a voice coil rigidly connected to the diaphragm or cone. The voice coil is suspended in a magnetic field provided by the loudspeaker magnet structure. As AC current flows through voice coil From an amplifier), the changing magnetic fields induced in the coil react against the magnet's fixed field and move the voice coil (and so the cone) back and forth, thus producing sound. Image File history File links Size of this preview: 800 × 458 pixel Image in higher resolution (1113 × 637 pixel, file size: 93 KB, MIME type: image/jpeg) This curve was generated with the acoustics simulation software LEAP, and is freely distributable. ... Image File history File links Size of this preview: 800 × 458 pixel Image in higher resolution (1113 × 637 pixel, file size: 93 KB, MIME type: image/jpeg) This curve was generated with the acoustics simulation software LEAP, and is freely distributable. ... A 3. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... City lights viewed in a motion blurred exposure. ...

The moving system of the loudspeaker (including the cone, cone suspension, spider and the voice coil) has a certain mass and compliance. This is most commonly likened to a simple mass suspended by a spring that has a certain resonant frequency at which the system will vibrate most freely. This frequency is known as the "free-space resonance" of the speaker and is designated by F_s. At this frequency, since the voice coil is vibrating with the maximum peak-to-peak amplitude and velocity, the back-emf generated by coil motion in a magnetic field is also at its maximum. This causes the effective electrical impedance of the speaker to be at its maximum at F_s, shown as Z_max in the graph. For frequencies just below resonance, the impedance rises rapidly as the frequency approaches F_s and is inductive in nature. At resonance, the impedance is purely resistive and beyond it -- as the impedance drops -- it behaves capacitively. The impedance reaches a minimum value (Z_min) at some frequency where the behaviour is fairly (but not perfectly) resistive over some range. A speaker's rated or nominal impedance (Z_nom) is derived from this Z_min value (see below). Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Compliance can mean: In mechanical science, the inverse of stiffness (see stiffness). ... Helical or coil springs designed for tension A spring is a flexible elastic object used to store mechanical energy. ... This article is about resonance in physics. ... Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ... Back Emf, or back torque, is an electromotive force that occurs in Electric motors and some generators where there is relative motion between the armature of the motor and the external magnetic field. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) A pack of resistors A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohms law. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... A nominal is a word or a group of words that functions as a noun, i. ...

Beyond the Z_min point the impedance is again largely inductive and continues to rise gradually. The frequency F_s and the frequencies above and below it where the impedance is Z_max/√2 are important in determining the loudspeaker's T/S parameters which are used to design a suitable enclosure for the driver, especially for low frequency drivers. Note that F_s is itself one of the T/S parameters of the loudspeaker. Thiele/Small commonly refers to a set of standard parameters that define how a loudspeaker driver performs. ...

Load impedance and amplifiers

The variation in loudspeaker impedance is a consideration in audio amplifier design. Among other things, amplifiers designed to cope such variations are more reliable. There are two main factors to consider when matching a speaker to an amplifier. The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ... Sound is a disturbance of mechanical energy that propagates through matter as a longitudinal wave. ... The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier. ...

Minimum impedance

This is the minimum value in the impedance vs. frequency relationship, which can sometimes be slightly higher than the DC resistance of the voice coil, ie, as measured by an ohmmeter. Minimum impedance is significant because the lower the impedance, the higher the current must be at the same drive voltage. The output devices of an amplifier are rated for a certain maximum current level, and when this is exceeded the device will, more or less promptly, fail.

Nominal impedance

Due to the reactive nature of a speaker's impedance over the audio band frequencies, giving a speaker a single value for 'impedance' rating is in principle impossible, as one may surmise from the impedance vs. frequency curve shown. The nominal impedance of a loudspeaker is a convenient, single number reference that loosely describes the impedance value of the loudspeaker over a majority of the audio band. A speaker's nominal impedance is defined as: An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ... A nominal is a word or a group of words that functions as a noun, i. ...

The graph above shows the impedance curve of a single loudspeaker driver in free-air (unmounted in any type of enclosure). A home hi fi loudspeaker system typically consists of two or more drivers, an electrical crossover network to divide the signal by freqency band and route them appropriately to the drivers, and an enclosure that all these components are mounted in. The impedance curve of such a system can be very complex, and the simple formula above does not as easily apply. The nominal impedance rating of consumer loudspeakers systems can aid in choosing the correct loudspeaker for a given amplifier (or visa versa). If a home hi-fi amplifier specifies 8 ohm or greater loads, care should be taken that loudspeakers with a lower impedance are not used, lest the amplifier be required to produce more current than it was designed to handle. Using a 4 ohm loudspeaker system on a amplifier specifying 8 ohms or greater could lead to amplifier failure.

Impedance Phase Angle

Impedance variations of the load with frequency translate into variation in the phase relationship between the amplifier's output voltage and current. For a resistive load, usually (but not always) the voltage across the amplifier's output devices is maximum when the load current is minimum (and the voltage is minimum across the load) and vice-versa, and as a result the power dissipation in those devices is least. But due to the complex and variable nature of the driver / crossover load and its effect on the phase relationship between the voltage and current, the current will not necessarily be at its minimum when the voltage across the output devices is maximum - this results in increased power dissipation in the amplifier output stage which manifests as heating in the output devices. The phase angle varies most near resonance in moving coil loudspeakers. If this point is not taken into consideration during the amplifier design, the amplifier may overheat causing it to shut down, or worse, self-destruct as amp output devices fail. To meet Wikipedias quality standards, this article or section may require cleanup. ... Josephson junction array chip developed by NIST as a standard volt. ... In electricity, current refers to electric current, which is the flow of electric charge. ...

References

• Designing, Building, and Testing Your Own Speaker System with Projects by David B.Weems (McGraw-Hill/TAB Electronics, ISBN 0-07-069429-X)
• Loudspeakers, Dynamic, Magnetic Structures and Impedance EIA RS-299-A standard
• Article about effect of speaker impedance on amplifiers