Editing Loudspeaker (section)

==Specifications==
[[File:Eltax Silverstone 200 loudspeaker label.jpg|thumb|Specifications label on a loudspeaker]]

Speaker specifications generally include:
* '''Speaker or driver type''' (individual units only){{dash}}[[full-range]], woofer, tweeter, or [[Mid-range speaker|mid-range]].
* '''Size''' of individual drivers. For cone drivers, the quoted size is generally the outside diameter of the basket.<ref>EIA RS-278-B "Mounting Dimensions for Loudspeakers"</ref> However, it may less commonly also be the diameter of the cone surround, measured apex to apex, or the distance from the center of one mounting hole to its opposite. Voice-coil diameter may also be specified. If the loudspeaker has a compression horn driver, the diameter of the horn throat may be given.
* '''Rated power'''{{dash}}[[Audio power|power]], and peak power a loudspeaker can handle. A driver may be damaged at much less than its rated power if driven past its mechanical limits at lower frequencies.{{Citation needed|date=April 2024}} In some jurisdictions, power handling has a legal meaning allowing comparisons between loudspeakers under consideration. Elsewhere, the variety of meanings for power handling capacity can be quite confusing.
* '''[[Electrical impedance|Impedance]]'''{{dash}}typically 4&nbsp;Ω (ohms), 8&nbsp;Ω, etc.<ref>EIA RS-299 "Loudspeakers, Dynamic; Magnetic Structures and Impedance"</ref>
* '''Baffle or enclosure type''' (enclosed systems only){{dash}}Sealed, bass reflex, etc.
* '''Number of drivers''' (complete speaker systems only){{dash}}two-way, three-way, etc.
* '''Class''' of loudspeaker:<ref>{{cite book |last=McCarthy |first=Bob |title=Sound Systems: Design and Optimization: Modern Techniques and Tools for Sound System Design and Alignment |publisher=CRC Press |date=2016 |page=70 }}</ref>
** Class 1: maximum SPL 110–119&nbsp;dB, the type of loudspeaker used for reproducing a person speaking in a small space or for [[background music]]; mainly used as fill speakers for Class 2 or Class 3 speakers; typically small 4" or 5" woofers and dome tweeters
** Class 2: maximum SPL 120–129&nbsp;dB, the type of medium-power–capable loudspeaker used for reinforcement in small to medium spaces or as fill speakers for Class 3 or Class 4 speakers; typically 5" to 8" woofers and dome tweeters
** Class 3: maximum SPL 130–139&nbsp;dB, high-power–capable loudspeakers used in main systems in small to medium spaces; also used as fill speakers for class 4 speakers; typically 6.5" to 12" woofers and 2" or 3" compression drivers for high frequencies
** Class 4: maximum SPL 140&nbsp;dB and higher, very-high-power–capable loudspeakers used as mains in medium to large spaces (or for fill speakers for these medium to large spaces); 10" to 15" woofers and 3" compression drivers

and optionally:
* '''Crossover frequency(ies)''' (multi-driver systems only){{dash}}The nominal frequency boundaries of the division between drivers.
* '''[[Frequency response]]'''{{dash}}The measured, or specified, output over a specified range of frequencies for a constant input level varied across those frequencies. It sometimes includes a variance limit, such as within "± 2.5&nbsp;dB."
* '''[[Thiele/Small|Thiele/Small parameters]]''' (individual drivers only){{dash}}these include the driver's ''F''<sub>s</sub> (resonance frequency), ''Q''<sub>ts</sub> (a driver's ''Q''; more or less, its [[damping factor]] at resonant frequency), ''V''<sub>as</sub> (the equivalent air compliance volume of the driver), etc.
* '''[[Sensitivity (electroacoustics)|Sensitivity]]'''{{dash}}The sound pressure level produced by a loudspeaker in a non-reverberant environment, often specified in <sub>SPL</sub> measured at 1 meter with an input of 1 watt (2.83 volts RMS into 8&nbsp;Ω), typically at one or more specified frequencies. Manufacturers often use this rating in marketing material.
* '''Maximum sound pressure level'''{{dash}}The highest output the loudspeaker can manage, short of damage or not exceeding a particular distortion level. Manufacturers often use this rating in marketing material—commonly without reference to frequency range or distortion level.

===Electrical characteristics of dynamic loudspeakers===
{{Main|Electrical characteristics of dynamic loudspeakers}}

To make sound, a loudspeaker is driven by modulated electric current (produced by an amplifier) that passes through a ''speaker coil''  which then (through [[Electrical inductance|inductance]]) creates a magnetic field around the coil. The electric current variations that pass through the speaker are thus converted to a varying magnetic field, whose interaction with the driver's magnetic field moves the speaker diaphragm, which thus forces the driver to produce air motion that is similar to the original signal from the amplifier.

The load that a driver presents to an amplifier consists of a complex [[electrical impedance]]—a combination of resistance and both [[Capacitance|capacitive]] and [[Inductance|inductive]] [[Electrical reactance|reactance]], which combines properties of the driver, its mechanical motion, the effects of crossover components (if any are in the signal path between amplifier and driver), and the effects of air loading on the driver as modified by the enclosure and its environment. Most amplifiers' output specifications are given at a specific power into an ideal [[resistive]] load; however, a loudspeaker does not have a constant impedance across its frequency range. Instead, the voice coil is inductive, the driver has mechanical resonances, the enclosure changes the driver's electrical and mechanical characteristics, and a passive crossover between the drivers and the amplifier contributes its own variations. The result is a load impedance that varies widely with frequency, and usually a varying phase relationship between voltage and current as well, also changing with frequency. Some amplifiers can cope with the variation better than others can.

Electrical models of loudspeakers are available that address these effects in detail.<ref>{{cite journal
  |title=Application of electric circuit analogies to loudspeaker design problems
  |author=Locanthi, Bart N
  |journal=IRE Trans. Audio
  |volume=6
  |pages=15
  |year=1952
  |url=https://www.aikenamps.com/images/Documents/speaker.pdf }}</ref>

===Electromechanical measurements===
Examples of typical [[loudspeaker measurement]] are: amplitude and phase characteristics vs. frequency; impulse response under one or more conditions (e.g. square waves, sine wave bursts, etc.); directivity vs. frequency (e.g. horizontally, vertically, spherically, etc.); [[harmonic distortion|harmonic]] and [[intermodulation distortion]] vs. sound pressure level (SPL) output, using any of several test signals; stored energy (i.e. ringing) at various frequencies; impedance vs. frequency; and small-signal vs. large-signal performance. Most of these measurements require sophisticated and often expensive equipment to perform.{{Citation needed|date=July 2024}} The sound pressure level (SPL) a loudspeaker produces is commonly expressed as [[Sound pressure#Sound pressure level|decibels relative to 20 μPa]] (''dB<sub>SPL</sub>'').

===Efficiency vs. sensitivity===
Loudspeaker efficiency is defined as the [[sound power]] output divided by the electrical power input. Most loudspeakers are inefficient transducers; only about 1% of the electrical energy sent by an amplifier to a typical home loudspeaker is converted to acoustic energy. The remainder is converted to heat, mostly in the voice coil and magnet assembly. The main reason for this is the difficulty of achieving proper [[impedance matching]] between the [[acoustic impedance]] of the drive unit and the air it radiates into.{{efn|At low frequencies, improving this match is the main purpose of speaker enclosure designs.}} The efficiency of loudspeaker drivers varies with frequency as well. For instance, the output of a woofer driver decreases as the input frequency decreases because of the increasingly poor impedance match between air and the driver.

Driver ratings based on the SPL for a given input are called ''sensitivity ratings'' and are notionally similar to efficiency. Sensitivity is usually expressed as the SPL (''dB<sub>SPL</sub>'' by common usage meaning ''dB relative to {{val|20|ul=μPa}}'') at 1&nbsp;W electrical input, measured at 1 meter,{{efn|A different measurement technique{{specify|date=July 2024}} is used for headphones.}} often at a single frequency. The voltage used is often 2.83&nbsp;V<sub>RMS</sub>, which results in 1&nbsp;watt into a nominal 8&nbsp;Ω speaker impedance. Measurements taken with this reference are typically quoted as dB<sub>SPL</sub> with 2.83&nbsp;V @ 1&nbsp;m.{{Citation needed|date=August 2024}}

The sound pressure output is measured at (or mathematically scaled to be equivalent to a measurement taken at) one meter from the loudspeaker and on-axis (directly in front of it), under the condition that the loudspeaker is radiating into an infinitely large space and mounted on an [[infinite baffle]]. Clearly then, sensitivity does not correlate precisely with efficiency, as it also depends on the directivity of the driver being tested and the acoustic environment in front of the actual loudspeaker. For example, a cheerleader's horn produces more sound output in the direction it is pointed by concentrating sound waves from the cheerleader in one direction, thus ''focusing'' them. The horn also improves impedance matching between the voice and the air, which produces more acoustic power for a given speaker power. In some cases, improved impedance matching (via careful enclosure design) lets the speaker produce more acoustic power.

Typical home loudspeakers have sensitivities of about 85 to 95&nbsp;dB<sub>SPL</sub> for 1&nbsp;W @ 1&nbsp;m—an efficiency of 0.5–4%. Sound reinforcement and public address loudspeakers have sensitivities of perhaps 95 to 102&nbsp; dB<sub>SPL</sub> for 1&nbsp;W @ 1&nbsp;m—an efficiency of 4–10%. Rock concert, stadium PA, marine hailing, etc. speakers generally have higher sensitivities of 103 to 110&nbsp; dB<sub>SPL</sub> for 1&nbsp;W @ 1&nbsp;m—an efficiency of 10–20%.{{Citation needed|date=July 2024}}

Since sensitivity and power handling are largely independent properties, a driver with a higher maximum power rating cannot necessarily be driven to louder levels than a lower-rated one. In the example that follows, assume (for simplicity) that the drivers being compared have the same electrical impedance, are operated at the same frequency within both driver's respective passbands, and that power compression and distortion are insignificant. A speaker 3&nbsp;dB more sensitive than another produces very nearly double the sound power (is 3&nbsp;dB louder) for the same electrical power input. Thus, a 100&nbsp;W driver (A) rated at 92&nbsp; dB<sub>SPL</sub> for 1&nbsp;W&nbsp;@ 1&nbsp;m sensitivity puts out twice as much acoustic power as a 200&nbsp;W driver (B) rated at 89&nbsp; dB<sub>SPL</sub> for 1&nbsp;W&nbsp;@ 1&nbsp;m when both are driven with 100&nbsp;W of electrical power. In this example, when driven at 100&nbsp;W, speaker A produces the same SPL, or [[loudness]] as speaker B would produce with 200&nbsp;W input. Thus, a 3&nbsp;dB increase in the sensitivity of the speaker means that it needs half the amplifier power to achieve a given SPL. This translates into a smaller, less complex power amplifier—and often, to reduced overall system cost.

{{Anchor|Hofmann}}<!--"Hofmann's Iron Law" redirects here.-->
It is typically not possible to combine high efficiency (especially at low frequencies) with compact enclosure size and adequate low-frequency response. One can, for the most part, choose only two of the three parameters when designing a speaker system. So, for example, if extended low-frequency performance and small box size are important, one must accept low efficiency. This [[rule of thumb]] is sometimes called '''Hofmann's Iron Law''' (after [[J. Anton Hofmann|J.A. Hofmann]], the H in [[KLH (company)|KLH]]).<ref>{{Cite web |url=http://ldsg.snippets.org/appdx-a.php |archive-url=https://web.archive.org/web/20080305171316/http://ldsg.snippets.org/appdx-a.php |title=Hofmann's Iron Law |archive-date=March 5, 2008 }}</ref><ref>{{cite web |url=http://www.salksound.com/wp/?p=56 |title=Sensitivity and Hoffman's Iron Law, or 'Why You Can't Have Hour Cake and Eat It Too' – Audioblog |website=SalkSound.com |access-date=April 14, 2018 }}</ref>