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Originally Posted by mporettim

All of that is controllable though and building a box is fairly cheap.

And for sure measuring the resistance immediately after testing would be best. I'm curious as to how much heat will affect the resistance.

While it's true a box is cheap. 200' of magnet Wire is cheaper. The effort in making a box vs wrapping the wire around a suitable former and encasing it is probably similar.

I don't 100% agree on it being controllable. With an ideal port yes, but things aren't ideal. If there was no resistance to the air flowing through the port it would be a perfect solution. But that resistance to the airflow will show up as a rise in impedance.

It's definitely not a bad solution though. I just think it would be better to use essentially a Power resistor for benching amps.


As far as how much does temperature rise affect copper wire?
Temperature is in Celsius (25C is roughly room temp)
RT2 = RT1 * (1 + α(T2 - T1))
R25 =1Ω
R200 = 1Ω * (1 + 3.95E-3(200 - 25)) = 1.69Ω

To figure out where the DCR doubles
2Ω= 1Ω * (1 + 3.95E-3(T2 - 25))
2= 1 + 3.95E-3(T2 - 25)
1+25*3.95E-3=3.95E-3T2
T2=(1+25*3.95E-3)/3.95E-3=278C (532F)

So if your VC hits 278 degrees Celsius, the DCR will double. Also a lot of bad things happen at this point. Check out the site below for more info.
Anyways this needs to be accounted for in either the power resistor or subwoofer method of benching the amp. As the DCR rises less current will flow, and an easier load will be presented to the amp. Luckily it takes time for the temperature to rise, (no I'm not going to get into heat equations that's waaaaaaaay beyond this thread), so if you are quick enough with the measurement it shouldn't matter too much.





I modified it for 1 ohm, originally was for 6:
Power Handling Vs. Efficiency