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This is specific for 6 string electric guitar amplifiers. The convention appears to be use a resistor equal to the nominal DCR of the intended speaker load, usually 4 or 8 Ω.

What I have found out was, although speakers have both inductance and resistance, the effective resistance is frequency dependent. So why should connect an essentially non-inductive resistor of fixed value to do load testing? According to the chart below for the Jensen 8CR, for example, the impedance rises to 13.7 Ω @ 5 kHz.

However, the guitar program is usually a complex mixture of fundamentals and all kinds of harmonics, so I'm at a loss as to what kind of test signal to use for load testing, or even if simulating a speaker load could be justified. The question arose for me when investigating the various ways to limit power if inadvertently exceeded such as a boosted device placed in the FX loop, or at the input for that matter. A soft-clipping circuit can be used as a dumb limiter, but these could cause other problems, too. Moreover, clipping, especially asymmetrical, of the power amp is be avoided.

Jensen states the inductance of the 8 Ω is 0.43 mH @ 1 kHz if that's any help.

I see that Neureochrome makes an elaborate load tester for headphone amps to check for stability Here. Would a high power version be of any value to load testing?

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    \$\begingroup\$ The better you can approximate the actual speaker load, the more accurate your stability testing gets. You have the impedance curve, which makes it pretty easy to construct a matching test load. \$\endgroup\$ Commented Nov 24, 2022 at 16:45
  • \$\begingroup\$ You can measure the electrical frequency response of a real speaker. \$\endgroup\$ Commented Nov 24, 2022 at 16:54

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A basic model for simulating a speaker is just an RL circuit.

You can add as much components you need to make a model as accurate as you want for some specific speaker, but it basically boils down to the question if the RL is good enough model, and if it isn't, then how detailed model you really need.

Especially if your amplifier must work with all kinds of speakers, so a generic model might be enough.

And it depends also what you mean by speaker. Just one driver element, or actual speakers you can buy from stores with multiple drivers and crossover filters.

If a driver, then the impedance is also affected by how it is loaded by the enclosure it is mounted.

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  • \$\begingroup\$ +1 for RL. When I designed audio amplifiers for a living, a calibrated RL dummy load + AudioPrecesion interface ($$$) was the gold standard for amplifier testing. Cheapo manufacturers would only test with R which simplified the situation for the DUT in question. \$\endgroup\$
    – winny
    Commented Nov 24, 2022 at 17:02
  • \$\begingroup\$ @Justme: Thank you for that commentary. Guitar cabinets almost invariably consist of one, two, or four plain, more or less mid-range drivers, without any crossovers. Complicating this is some are closer to an infinite baffle, a semi-sealed, or fully sealed enclosure. They are usually 8 Ohm total per cabinet, sometime paralleled to 4. In any case, is the model you suggest a series RL ? That's what I envision; fairly easy to construct several. \$\endgroup\$
    – ITPhoenix
    Commented Nov 24, 2022 at 18:06
  • \$\begingroup\$ But doesn't RL completely ignore the large mechanical resonance in the low-mid range? \$\endgroup\$
    – tobalt
    Commented Nov 24, 2022 at 18:39
  • \$\begingroup\$ @tobalt: It appears by the jist of the comments, a fixed driver simulator is completely ignorant of all actual driver dynamics. The interest is maximum wattage at a range of frequencies of which the watt level would be lower in that range. \$\endgroup\$
    – ITPhoenix
    Commented Nov 24, 2022 at 19:19
  • \$\begingroup\$ Correction: the fully sealed cabinet is close to an infinite baffle, i.e., no cancellation resulting in loss of SPL. \$\endgroup\$
    – ITPhoenix
    Commented Nov 24, 2022 at 20:15

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