For those interested in the somewhat esoteric world of High End Audio....I offer some links to speaker simulators
Note: Speakers are not nice stable loads, even a single speaker rated at 8 ohms might be 8 ohms a some frequency, mount it in an enclosure and the impedance will be extremely different depending on the type enclosure.
A closed box will behave on way, a single port another, a transmision line speaker (yes they do exist) will have yet another set of impedances.
And the impedance will be a mix of inductance, coil resistance and any resonances of the cone as modified by the enclosure.
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This is one test load
https://www.stereophile.com/reference/60/index.html
Note the Zobel Netork on page 2, they can be critical in some situations.
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This site covers some of the interaction between speaker cables and real world speakers.
Loudspeaker Cable Characteristic Impedance
https://sound-au.com/cable-z.htm
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Passive crossovers
https://sound-au.com/lr-passive.htm
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Loudspeaker Enclosure Design Guidelines
https://sound-au.com/articles/enclosures.htm
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Phase Angle Vs. Transistor Dissipation
https://sound-au.com/patd.htm
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Driving a 4 or 8 ohm resistive load is easy peasy, driving any real world speaker is fraught with possibilities. Some speakers present loads that cause some very high quality amplifiers to oscillate.
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I worked part time at an electronics shop. The owner sold high end audio equipment to the demented. Great American Sound offered Son of Godzilla. And amp that would drive damn near anything, we used it to make a drill variable speed. [Hey we were bored] However when connected to a pair of KEF studio reference monitor speakers, the GAS amp went insane, destroyed the speakers in about 4 seconds. KEF withdrew that set of speakers and it isn't listed in their history. KEF claimed that speaker had constant phase correction.
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Those KEFs sounded good with my Sansui AU555A, a rather mediocre amp by any definition.
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Effects Of Source Impedance on Loudspeakers
https://sound-au.com/z-effects.htm
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At some point everything in an audio chain has an influence. And it is next to impossible to pinpoint every variable.
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Audio Wattmeter - Measures?True?Power!
https://sound-au.com/project189.htm
Shows some speaker electrical characteristics.
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DIM/TIM (Dynamic or Transient Intermodulation) Some older references call it SIM (Slew rate intermodulation)
From https://www.aes.org/par/i/#IM
"DIM/TIM (dynamic/transient intermodulation distortion)?A procedure designed to test the dynamic or transient behavior, primarily, of audio power amplifiers. The other IM tests use steady-state sine wave tones, which do not necessarily reveal problems caused by transient operation. In particular, audio power amplifiers with high amounts of negative feedback were suspect due to the inherent time delay of negative feedback loops. The speculation was that when a rapidly-changing signal was fed to such an amplifier, a finite time was required for the correction signal to travel back through the feedback loop to the input stage and that the amplifier could be distorting seriously during this time. The most popular test technique consists of a large amplitude 3 kHz square wave (band-limited to ~20 kHz). [Historical Note: This test proved that as long as the amplifier did not slew-limit for any audio signal, then the loop time delay was insignificant compared to the relatively long audio periods. Thus, properly designed negative feedback was proved not a problem. Subsequently, this test has fallen into disuse."
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Note: I can make any audio amplifier display TIM, but not with any music, even the cannon fire in the William Tell Overture has a fairly slow rise time.
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Now a 9mm pistol shot captured with a condenser microphone on a 96K digital recorder and played back into an audio amp might cause TIM. I'm not sure the microphone's rise time would capture the actual event's risetime...and the blast might destroy the microphone.
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This might be worth reading
https://sound-au.com/articles/distortion+fb.htm
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On balance, just buy a decent audio amp and speakers and use your time for more productive projects. Unless of course understanding the subtleties of high performance audio amps is your thing.
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And just when you think you've seen every crazy idea on earth....
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My friend's dummy load has inductors and capacitors with large wattage resistors to simulate a 'regular' spkeaker.
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BTW, the problem is in the driver stage of the AF power amp.
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