Since it is often claimed here in the forum that replacing cheap sand-cast resistors with low-inductance resistors would lead to clearly audible improvements, and since it's no use pointing out that the sound change (unless it's completely imagined) is very likely due to slight deviations in the resistance values, I'm now so annoyed that I want to get to the bottom of it

UPDATE: Also check out "Capacitor upgrade in crossover - Is it audible?".

Considered are a 20W sand-cast resistor with about 3.28 Ohm and a low induction 4W metal oxide resistor with about 3.29 Ohm - - I could not find a better pairing among my resistors.

The resistance measurement results:

As expected the measurement curves of the two resistors are practically identical.

UPDATE: The 20W sand-cast resistor (instead of e.g. a 5W) was chosen for comparison to create a worst-case scenario (big "bad" sand-cast resistor against "short" metal oxide resistor) and because only for this resistor a metal oxide resistor with exactly the right impedance was available.

First of all it should be checked if the MOX resistor is really low inductance compared to the sand-cast resistor.

For this purpose we first look at the impedance at 5kHz for both resistors.

Arta-Limp reports for the sand cast resistor that the measured impedance has a resistive part of 3.28 ohm and that the imaginary part is inductive with a value of 675 nH.

For the low-inductance MOX resistor Arta-Limp provides for the impedance as resistive part 3.29 ohms and for the imaginary part 183nH - so much less than for the sand-cast resistance.

Next we look at the impedance/induction of the two resistors against the entire audible frequency range:

The manufacturer's data are correct, the MOX resistor is indeed low inductance compared to the sand-cast resistor.

A test will provide information on this.

The test setup is very simple. Since the inductive component is noticeable at high frequencies, we measure the effects on the frequency response of a tweeter.

The tweeter is measured in the near field. Every resistor is connected in series to the tweeter.

We use the SB21RDC tweeter from SBAcoustics and a calibrated iSEMcon EMX-7150 as measuring microphone.

The measured frequency response of the tweeter with the respective resistors looks as follows:

Of course, you're kidding! That's just twice the same measurement with different colours - isn't it?

Unfortunately no, that's really the effect when exchanging a cheap sand-cast resistor for a low-inductance MOX resistor.

But it must be possible to detect an effect, otherwise your test is simply faulty.

Let's have a look at the frequency response measurement for both resistors with a finer scale:

There are very small differences. To be able to show it better, we'll normalize to the frequency response of the MOX resistor and look at the deviation of the sand-cast resistor. For this purpose, we resolve the scaling to 0.01dB:

Now we see the effect of the higher inductive part of the sand-cast resistor, because at high frequencies the frequency response drops slightly compared to the low-inductance resistor - up to 20kHz by as much as 0.02 dB!

Even if the effects should increase at higher resistance values, even 5 times the value is inaudible.

UPDATE: Also check out "Capacitor upgrade in crossover - Is it audible?".

Considered are a 20W sand-cast resistor with about 3.28 Ohm and a low induction 4W metal oxide resistor with about 3.29 Ohm - - I could not find a better pairing among my resistors.

The resistance measurement results:

As expected the measurement curves of the two resistors are practically identical.

UPDATE: The 20W sand-cast resistor (instead of e.g. a 5W) was chosen for comparison to create a worst-case scenario (big "bad" sand-cast resistor against "short" metal oxide resistor) and because only for this resistor a metal oxide resistor with exactly the right impedance was available.

**Is the MOX resistor really low induction?**First of all it should be checked if the MOX resistor is really low inductance compared to the sand-cast resistor.

For this purpose we first look at the impedance at 5kHz for both resistors.

Arta-Limp reports for the sand cast resistor that the measured impedance has a resistive part of 3.28 ohm and that the imaginary part is inductive with a value of 675 nH.

For the low-inductance MOX resistor Arta-Limp provides for the impedance as resistive part 3.29 ohms and for the imaginary part 183nH - so much less than for the sand-cast resistance.

Next we look at the impedance/induction of the two resistors against the entire audible frequency range:

The manufacturer's data are correct, the MOX resistor is indeed low inductance compared to the sand-cast resistor.

**Is this difference audible when playing music over loudspeakers?**A test will provide information on this.

**Test Setup**The test setup is very simple. Since the inductive component is noticeable at high frequencies, we measure the effects on the frequency response of a tweeter.

The tweeter is measured in the near field. Every resistor is connected in series to the tweeter.

We use the SB21RDC tweeter from SBAcoustics and a calibrated iSEMcon EMX-7150 as measuring microphone.

**Measurement results**The measured frequency response of the tweeter with the respective resistors looks as follows:

Of course, you're kidding! That's just twice the same measurement with different colours - isn't it?

Unfortunately no, that's really the effect when exchanging a cheap sand-cast resistor for a low-inductance MOX resistor.

But it must be possible to detect an effect, otherwise your test is simply faulty.

Let's have a look at the frequency response measurement for both resistors with a finer scale:

There are very small differences. To be able to show it better, we'll normalize to the frequency response of the MOX resistor and look at the deviation of the sand-cast resistor. For this purpose, we resolve the scaling to 0.01dB:

Now we see the effect of the higher inductive part of the sand-cast resistor, because at high frequencies the frequency response drops slightly compared to the low-inductance resistor - up to 20kHz by as much as 0.02 dB!

Even if the effects should increase at higher resistance values, even 5 times the value is inaudible.

**The effects of replacing a sand-cast resistor with a low-inductance resistor are practically zero.**
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