Compression driver: Difference between revisions

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{{Short description|Type of loudspeaker}}

A '''compression driver''' is a type of [[loudspeaker]] driver which uses the technique of "compression" to achieve high efficiencies. In this context compression refers to the fact that the area of the loudspeaker diaphragm is significantly larger than the aperture through which the sound is radiated. Compression Drivers are most commonly used in high [[sound pressure]] level applications. They are normally used in conjunction with [[Horn (acoustic)|acoustical horns]]. Horn-loaded Compression Drivers can achieve extremely high efficiencies compared to direct-radiating loudspeakers. They are almost universally used for high frequency reproduction in high power sound reinforcement loudspeakers.

{{multiple image

| align = right

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| header =

| image1 = KlipschK400.jpg

| caption1 = A compression driver ''(cylindrical box at rear)'' on a midrange horn speaker used in a home audio system

| image2 = Horn loudspeaker animation.gif

| caption2 = A compression driver ''(A)'' in a horn loudspeaker consists of a metal diaphragm ''<span style="color:blue;">(blue)</span>'' vibrated by the audio signal current in a coil of wire ''<span style="color:red;">(red)</span>'' between the poles of a cylindrical magnet ''<span style="color:green;">(green)</span>''. The sound waves pass out through an acoustic horn ''(B)''.

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A '''compression driver''' is a small specialized diaphragm [[loudspeaker]] which generates the sound in a [[horn loudspeaker]]. It is attached to an [[horn (acoustic)|acoustic horn]], a widening duct which serves to radiate the sound efficiently into the air. It works in a "compression" mode; the area of the loudspeaker diaphragm is significantly larger than the throat aperture of the horn so that it provides high sound pressures. Horn-loaded compression drivers can achieve very high efficiencies, around 10 times the efficiency of direct-radiating cone loudspeakers. They are used as [[midrange driver|midrange]] and [[tweeter]] drivers in high power [[Sound reinforcement system|sound reinforcement loudspeaker]]s, and in reflex or folded-horn loudspeakers in [[megaphone]]s and [[public address systems]].

==History==

== History ==

In 1924 Hanna, C. R. and Slepian, J.

<ref>

In 1924 C.&nbsp;R. Hanna and J. Slepian<ref>

{{cite journal

| last = Hanna

| first = C. R.

| coauthorsauthor2 = Slepian, J.

| date = September 1977

| year = 1977 (originally published 1924)

| monthorig-year = September1924

| title = The Function and Design of Horns for Loudspeakers (Reprint)

| journal = The Journal of the Audio Engineering Society

| volume = 25

| pages = 573–585

}}

</ref> were the first to discuss the benefits of using a large radiating diaphragm with a horn of smaller throat area as a means of increasing the efficiency of horn loudspeaker drivers. They correctly surmizedsurmised that this arrangement results in a significant increase in the radiation resistance (and therefore increased efficiency), because the loading mismatch between the vibrating transducer surface and air is largely corrected, thus allowing for much better energy transfer. In the Hanna and Slepian proposal the compression cavity is directly connected to the throat of the horn.

</ref>

were the first to discuss the benefits of using a large radiating diaphragm with a horn of smaller throat area as a means of increasing the efficiency of horn loudspeaker drivers. They correctly surmized that this arrangement results in a significant increase in the radiation resistance (and therefore increased efficiency), because the loading mismatch between the vibrating transducer surface and air is largely corrected, thus allowing for much better energy transfer. In the Hanna and Slepian proposal the compression cavity is directly connected to the throat of the horn.

The next innovation came from E.&nbsp;C. Wente and A.&nbsp;L. Thuras in "A High-Efficiency Receiver for a Horn-Type Loudspeaker of Large Power capacity" in the Bell System Technical Journal, 1928.<ref>

<ref>

{{cite journal

| last = Wente

| first = E.

| coauthorsauthor2 = Thuras, A.

| yeardate = March 1978 (originally published 1928)

| monthorig-year = March1928

| title = A High-Efficiency Receiver for a Horn-Type Loudspeaker of Large Power Capacity (reprint)

| journal = The Journal of the Audio Engineering Society

| volume = 26

| pages = 139–144

}}

</ref> They devised a plug placed in front of a radiating diaphragm to control the transition from compression cavity to horn throat. They found that the bandwidth of the transducer could be extended to higher frequencies using their [[phase- plug]]. They also outlined criterioncriteria for the design of the channels in the plug and suggested a path-length based design approach to maximize the bandwidth. Significantly, their plug moves the coupling point between the cavity and horn away from the axis of rotation. This change significantly improves the transducer response as the effect of the acoustical resonances in compression cavity is reduced. The paper described the first generation compression driver with a field coil magnet and phase plug, It used an aluminum diaphragm with an edge wound aluminum ribbon voice coil.<ref>{{Cite web |last=Dunker |first=Thomas |title=More references on horn loudspeakers |url=http://invalid.ed.ntnu.no/~dunker/refs02.html MORE|url-status=dead REFERENCES|archive-url=https://web.archive.org/web/20181211003245/http://invalid.ed.ntnu.no/~dunker/refs02.html ON|archive-date=Dec HORN11, LOUDSPEAKERS2018}}</ref>

</ref>

They devised a plug placed in front of a radiating diaphragm to control the transition from compression cavity to horn throat. They found that the bandwidth of the transducer could be extended to higher frequencies using their phase-plug. They also outlined criterion for the design of the channels in the plug and suggested a path-length based design approach to maximize the bandwidth. Significantly, their plug moves the coupling point between the cavity and horn away from the axis of rotation. This change significantly improves the transducer response as the effect of the acoustical resonances in compression cavity is reduced. The paper described the first generation compression driver with a field coil magnet and phase plug, It used aluminum diaphragm with an edge wound aluminum ribbon voice coil.<ref>http://invalid.ed.ntnu.no/~dunker/refs02.html MORE REFERENCES ON HORN LOUDSPEAKERS</ref>

The first commercial compression driver was introduced 1933 when Bell Labs added a Western Electric No. 555 compression driver as a mid-range driver to their the two-way "divided range" loudspeaker which was developed in 1931.<ref>http{{Cite web |last=Plummer |first=Gregg |date=May 2, 2007 |title=The Short History of Audio/Video Technology |url=https://amplioaudio.blogspot.com/2007/05/short-history-of-audiovideo-technology.html The|url-status=live Short|archive-url=https://web.archive.org/web/20220314035723/https://amplioaudio.blogspot.com/2007/05/short-history-of-audiovideo-technology.html History|archive-date=Mar of14, Audio/Video2022 Technology|website=Ampliozone}}</ref>

In 1953 Bob Smith made the most significant contribution to modern phase-plug, and hence compression driver design, with his paper published in the Journal of the Acoustical Society of America<ref>

<ref>

{{cite journal

| last = Smith

| first = B.

| year date=March 1953

| month = March

| title = An Investigation Of The Air Chamber Of Horn Type Loudspeakers

| journal = The Journal of the Acoustical Society of America

Line 49 ⟶ 56:

| pages = 305–312

| doi = 10.1121/1.1907038

| issue = 2

}}

</ref> in which Smith analyzed the acoustical resonances occurring in the compression cavity and devised a design methodology to suppress the resonances by careful positioning and sizing of channels in the phase-plug. This work was largely ignored by his contemporaries and was only later popularized by Fancher Murray.<ref>

</ref>

in which Smith analyzed the acoustical resonances occurring in the compression cavity and devised a design methodology to suppress the resonances by careful positioning and sizing of channels in the phase-plug. This work was largely ignored by his contemporaries and was only later popularized by Fancher Murray

<ref>

{{cite journal

| last = Murray

| first = Fancher

| year date=October 1978

| month = October

| title = An Application Of Bob Smith's Phasing Plug

| journal = Presented at the 61st conventionConvention of the Audio Engineering Society

| volume = preprint 1384

}}

</ref> Today the majority of compression drivers, either by inheritance or design, are based on the guidelines outlined by Smith.

</ref>.

Today the majority of compression drivers, either by inheritance or design, are based on the guidelines outlined by Smith.

The suppression technique of Smith has been recently extended<ref>

<ref>

{{cite journal

| last = Dodd

| first = M.

| coauthors author2= Oclee-Brown, J.

| year date=October 2007

| month = October

| title = A New Methodology for the Acoustic Design of Compression Driver Phase-Plugs with Concentric Annular Channels

| journal = Presented at the 123rd Convention of the Audio Engineering Society

| volume = preprint 7258

}}

</ref> using a more accurate analytical acoustical model of the compression driver geometry. From this work improved phase plug design guidelines have been deduced to completely eliminate all traces of acoustical resonance in the compression cavity. Interestingly, inIn this work SmithsSmith's derivation is confirmed using Finite[[finite Elementelement Analysisanalysis]], a luxury that was unavailable to Smith.

</ref>

using a more accurate analytical acoustical model of the compression driver geometry. From this work improved phase plug design guidelines have been deduced to completely eliminate all traces of acoustical resonance in the compression cavity. Interestingly, in this work Smiths derivation is confirmed using Finite Element Analysis, a luxury that was unavailable to Smith.

==Compression driver protection==

In some [[Sound reinforcement system|sound reinforcement]] and [[studio monitor]]s the high frequency drivers are protected withfrom damage by current sensing / self-resetting circuit breakers. When too much power is provideddissipated toby the driver, the circuit breaker trips.interrupts the Afterflow aof shortelectric timecurrent. of acceptableThe power, thecircuit breaker resets itself after a brief interval. An older circuit protection technique which was used by [[Electro-Voice]], [[Community Professional Loudspeakers|Community]], [[UREI]], [[Cerwin Vega]] and others is a is a light bulb putplaced in series with the driver whichto actsact as a "current-to-light" conversionvariable circuitryresistor. The Asresistance of the powerbulb appliedfilament tois theproportional driverto increases,its thetemperature filamentwhich inincreases theas lightcurrent bulbflow heatsthrough upthe andfilament emits lightincreases. The Asnet the currenteffect is increased,that as the resistancepower ofincreases the filament alsoconsumes goesan upincreasing asshare itof heatsthe up.total power Thisthus in turn causeslimiting the lightpower bulbavailable to dissipatethe morecompression of the currentdriver.<ref>{{cite web |url=http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/seaandland.pdf |title=Sea & Land's Speaker Protection Devices |accessdate=2009-01-17 |url-status=dead |archiveurl=https://web.archive.org/web/20090407131736/http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/seaandland.pdf |archivedate=2009-04-07 }}</ref><ref>{{cite web |url=http://www.patentstorm.us/patents/6201680/description.html US Patent 6201680 - |title=Adjustable high-speed audio transducer protection circuit - US Patent 6201680 Description |website=PatentStorm |accessdate=2009-01-17 |url-status=dead |archiveurl=https://web.archive.org/web/20090216174010/http://www.patentstorm.us/patents/6201680/description.html |archivedate=2009-02-16 }}</ref>

==References==

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==External links==

* [{{cite web |url=http://www.audioanthology.com/audio1.html |title=WESTERN ELECTRIC speakers] |website=Audio Anthology}}

{{DEFAULTSORT:Compression Driver}}

[[Category:Loudspeaker technology]]