Hi, I am upgrading the caps and resistors in a crossover with the same values but better parts. My question is, can I replace the 3.9 ohm 7 watt sandcast resistor with a 4 ohm? The resistor is in the tweeter circuit.
I plan on using a Mills or Vishay-Mills 4 ohm 10 or 12 watt resistor.
Thanks,
Larry
I plan on using a Mills or Vishay-Mills 4 ohm 10 or 12 watt resistor.
Thanks,
Larry
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Probably is a volume attenuator which is not critical to the frequency. If series to the tweeter, yeah. Series some other element, inductor or capacitor, accuracy is more critical.
However, unless it is off value I wouldn't bother. 3.9 ohm resistors don't have a lot of thermal noise. $ spent replacing electrolytic caps with polyprophylene film give a lot more bang for the buck. Note measurements taken @ 3.9 ohms with the average DVM depend a lot on the state of the battery. Better use a known accurate resistor in that range as a calibrator. Then add of subtract the difference you get from the reading on the known resistor versus what you get on the 3.9 subject.
However, unless it is off value I wouldn't bother. 3.9 ohm resistors don't have a lot of thermal noise. $ spent replacing electrolytic caps with polyprophylene film give a lot more bang for the buck. Note measurements taken @ 3.9 ohms with the average DVM depend a lot on the state of the battery. Better use a known accurate resistor in that range as a calibrator. Then add of subtract the difference you get from the reading on the known resistor versus what you get on the 3.9 subject.
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Well also consider the tolerance. 10% 5%? Likely not 1%. A 5% 3.9 ohm resistor could measure anywhere from 4.1 to 3.7 and still be in spec. Your 4 ohm if also 5% could range from 4.2 ohm to 3,8 ohm and be in spec. Your 4 ohm resistor could be 3.8 ohms and be smaller than a 3.9 ohm at 4.1 ohms
If your resistors are 10% tolerance it gets even more sloppy.
SO really 3.9 and 4 are effectively pretty much the same. How precise are the rest of the parts?
And if you are really jonesing for accuracy, remember your meter probes have a small resistance as well. SHort them together and see what the meter reads. Always subtract that amount from the reading on low resistance work. A half ohm meter probe matters little when measuring a 10k resistor. But if you are sweating 3.9 ohms, then it does.
If your resistors are 10% tolerance it gets even more sloppy.
SO really 3.9 and 4 are effectively pretty much the same. How precise are the rest of the parts?
And if you are really jonesing for accuracy, remember your meter probes have a small resistance as well. SHort them together and see what the meter reads. Always subtract that amount from the reading on low resistance work. A half ohm meter probe matters little when measuring a 10k resistor. But if you are sweating 3.9 ohms, then it does.
4r parallel with 156r is 3.9r exact. If 7W was enough, then the 156r only needs to be 0.2W.
However I too am quite sure no speaker component needs to be this "precise".
And I suspect the "3.9" is really "nearest standard value" for a 4 Ohm concept. https://en.wikipedia.org/wiki/E_series_of_preferred_numbers
