+1 @ieales … another #metoo attempt, and this time trying to sneak in panels as a heat stroke sufferer.
Thermal Distortion your loudspeaker most likely suffers from it. But do you care?
Thermal Distortion is much more serious than just a maximum power handling limitation or side effect.TD is overlooked by most manufacturers as there is no easy (low cost) solution and TD is audible and measurable most of the time at most power levels. TD is caused by the conductive metal (aluminum, copper, or silver) voice coil getting hotter when you pass electrical energy through it. The more power you pass through it the hotter the metal gets. The hotter the metal gets the more the electrical resistance increase. The efficiency goes down and you need to ram in more and more power for smaller and smaller increases in SPL. It can be the reason you get fatigued while listening. If you are running massive power you are creating more TD in your transducers. But do you care? And is it a reason some prefer horn-loaded designs or SET-powered systems since they have the least problems with TD?
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Back when tubes were king, high efficiency speakers were very common because tube power was (and continues to be) expensive. When solid state amps were commonplace, speaker efficiency started to go down. The problem here is that it never helps to have an amplifier drive a speaker that is a difficult load and in particular low efficiency. The result will be higher distortion from the amplifier if nothing else, and that distortion usually manifests as higher ordered harmonics, to which the ear assigns the tonality of 'harsh and bright' and is keenly sensitive to their presence since it uses them to sense sound pressure. So we've been hearing 'harsh and bright' for 50 years now. Some is the fault of amplifier design of course, but difficult to drive speakers don't help. So inefficient and low impedance speakers should be avoided if you want to get the most out of your amplifier dollar investment.
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It's a question of balancing speakers and amplifiers. If speakers are 86dB/2.83v/1m, then you better have at least 200wpc and preferably 400w good, clean undistorted power @ speaker minimum impedance. Professional studios may have 1000wpc driving horn multiway speakers, usually without power eating passive XO. Sadly, too many today have zero understanding of basic fundamentals and buy faceplates.
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Modern high powered amps (400+ watts) that can run into a 1 ohm load can certainly burn pretty much any low impedance device up. How much heat is developed depends entirely on current flow which depends in part on the impedance of the load, lower impedance devices being more likely to heat up. How fast depends on the amount of heat sink is available for the device and how well it is ventilated. The most significant problem is not thermal distortion but failure of the device. Modern voice coils with Kapton formers are surprisingly tolerant. Although resistance does increase with temperature the effect is minimal. It might skew the frequency response of the speaker a little and decrease output or available power but it will not cause IM or Harmonic distortion. You can read about the effect here https://www.cirris.com/learning-center/general-testing/special-topics/177-temperature-coefficient-of-copper and here, https://en.wikipedia.org/wiki/Power_compression#:~:text=In%20a%20loudspeaker%2C%20power%20compression,power%20of%20the%20audio%20amplifier. Thermal compression can be a problem in large commercial concert systems. It is not a significant problem in home HiFi systems. It would best be characterized as inaudible. The sky is not falling and you need not go looking for 16 ohm loudspeakers. Take a deep breath and say,"OOOOOOOOHMMMMMMMM....
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