49:(390 °F) – can destroy the voice coil, but long before that happens the loudspeaker will experience power compression. A voice coil made of copper wire will have its DC resistance increase by about 72% when heating up from 20 °C (room temperature) to 200 °C, and its sensitivity will decrease by 4.7 decibels. Silver wire has a slightly worse problem with power compression, while aluminum wire is slightly better.
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Power compression is usually considered a long-term problem, arising over time with extended strong signal sent to the loudspeaker. However, if the change in resistance is short term, observed as heating up and cooling down with each cycle of low frequency waves, then the loudspeaker will increase in
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as when it is cold. The problem is much greater for hard-driven professional concert systems than it is for loudspeakers in the home, where it is rarely seen. Two main pathways exist to mitigate the problem: to design a way for the voice coil to dissipate more heat during operation, and to design a
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In multi-way systems, power compression is often observed to occur first in one of the low frequency bandpasses. This causes the total system to have an imbalance in frequency response, a reduction of level in one bandpass compared to the others. In passive loudspeakers with internal crossover
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High power audio transducers have a low efficiency, with less than 5% of the amplifier signal turned into sound waves. The other 95% or more of the electrical energy is turned into unwanted heat, which causes the voice coil to increase in temperature. Too much heat – more than 200 °C
64:, metal parts that conduct heat to the outside, increasing the enclosure's internal chamber volume behind the magnet, and electric cooling fans. Another solution is to design a system that increases efficiency, such as by using a
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components, power compression will change the electrical characteristics of the crossover filters, and the crossover point can shift, introducing distortions related to an incorrect crossover filter.
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To counteract power compression, one solution is to increase heat dissipation. Typical methods include cooling fins on the magnet housing, a larger diameter voice coil,
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238:(1986) "The Elimination of Power Compression in Servo Drive Loudspeakers," Presented at the 81st Convention of the AES.
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rather than a direct-radiating design. Or by choosing a transducer other than the voice coil, such as Bruce
Thigpen's
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more efficient transducer that generates less heat for a given sound output level.
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Introduction to Live Sound
Reinforcement: The Science, the Art, and the Practice
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of the voice coil and decreasing the effective available power of the
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in the gap between voice coil and magnet, venting of the
103:"Frequently Asked Questions: What is power compression?"
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198:"Loudspeaker Technology Part 16: Moving Coil Motors"
226:. JBL. Published by the Audio Engineering Society.
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163:"Hot Stuff: Loudspeaker Voice-Coil Temperatures"
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32:heats up under operation, increasing the
28:is a loss of efficiency observed as the
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161:Howard, Keith (November 26, 2006).
76:'s servo-motor subwoofer (1983).
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196:Watkinson, John (May 28, 2018).
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133:. FriesenPress. p. 78.
222:Button, Douglas J. (1992).
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202:The Broadcast Audio Bridge
204:. International Techmedia
82:total harmonic distortion
169:. AVTech Media Americas
255:Loudspeaker technology
127:Boyce, Teddy (2014).
42:sound pressure level
26:thermal compression
101:JBL Staff (2004).
236:Danley, Thomas J.
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167:Stereophile
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208:August 14,
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88:References
74:Tom Danley
72:(1974) or
62:pole piece
58:ferrofluid
30:voice coil
249:Category
179:Link to
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16:In a
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