Resistor Inductance

Hi Folks!

Are non-inductive resistors worth it?. What would be the difference between buying a 1 Ω wire wound resistor at my local Radio Shack to put in series with my tweeter, as appose to buying the "audio grade" type? How much inductance are we talking about? Also, is there any sonic differences between attenuating resistors in series and using them in a L-Pad configuration?

Thanks,

John.
 
You want to discuss whether the difference between something that costs pocket change, and something that costs a little more pocket change is worth it?

From Solen here in Canada a cement wirewound 10W resistor costs 23 cents and a metal oxide 10W resistor costs 53 cents. Radioshack in the states wants $2 for a 10W cement resistor (according to their website) and the values are very limited. The difference in price is pocket change, especially when compared to the cost of an entire speaker project, so why not?

I think the point I'm trying to make here is that you'll save much more money by simply not shopping at Radioshack then you will from using a slightly better metal oxide resistor.

And yes there will be a significant difference between simply adding a resistor in series and using an L-pad. Take a look at an impedance response plot and think very hard about what will happen in either circumstance. The L-pad will apply a uniform attenuation over frequency, but the series resistor will not because the impedance of your speaker will change over frequency. Sometimes this can be benificial.
 
I measured a number of the inexpensive sand cast resistors from Parts Express and some more expensive Mills resistors, using my LAUD set up, and none of them showed any inductive behavior. I think the audible differences that some people claim to hear between these two types of resistors has more to do with slight differences in actual resistance values and not so much to do with some inductive behavior.

The comments above about the relative cost differences are exactly correct. I usually buy the Mills resistors and spend a little more assuming the construction is of higher quality. The cost difference is not significant compared to the other components in the speaker design. But if I was truely looking to pinch some cost out I would not hesitate to buy the sand cast resistors.
 
I wouldn't worry about the inductance that much for the tweeter resistor. Comparing to the inductance of the voice coil of the tweeter the inductance in the resistor is so small and you can completely ignore it. It will only affect very high frequencies way beyond human hearing capability. If you are talking about the resistor in some other circuitary that will be a different story. No worries for the tweeter resistor.
 

bastek

Member
2005-12-21 5:20 pm
NY
With my inductance meter, a white sand cast resistor of 20 ohms, measures 0.4 mH, which is almost the inductance of the tweeter (0.35mH). A mills 20 ohm resistor measures 0.4 mh also, so there is no benefit in using it.
Now, what happens if you put this resistor in parallel to the tweeter?
 
bastek said:
With my inductance meter, a white sand cast resistor of 20 ohms, measures 0.4 mH, which is almost the inductance of the tweeter (0.35mH). A mills 20 ohm resistor measures 0.4 mh also, so there is no benefit in using it.
Now, what happens if you put this resistor in parallel to the tweeter?

I'm surprised that they measured so high. Were they very large resistors?

Did you measure the inductance of the shorted probes, too, as a baseline?
 
With my inductance meter, a white sand cast resistor of 20 ohms, measures 0.4 mH, which is almost the inductance of the tweeter (0.35mH). A mills 20 ohm resistor measures 0.4 mh also, so there is no benefit in using it.

Do you believe those results? Do they make sense? Look at the size of a 0.4 mH coil and compare it to the Mills resistor, I am sorry but your results don't make sense to me.
 
gootee said:


Not wanting to "pile on", but, 0.003 mH seems extremely high, for just the probes shorted, too.

Sorry. On second thought, it's not terribly high. If we assume a rough estimate of 25 nH per inch of wire, it would only take 10 feet of wire to get to 3000 nH = 3 uH = .003 mH. So it's right in line with what might be expected for two 5-foot probe wires.