ARTA measurement box

[JMB]

OK,

Been building speakers for almost 2 decades and I feel pretty confident with doing so and what I have produced and measured. I built the ARTA measurement jig (at the ARTA website v2 of the Measurement Jig) some time back, have used it to measure with ARTA, Soundeasy (with reversed leads), and REW. Now, as I was looking at the Measuring Jig in the ARTA manual that I have faithfully used for many years, I began to wonder how the (zener) diode values were arrived at.

Here I am likely showing my diodic ignorance. 4.1 volts is more than one might want a sound card to handle though my logic is likely off here (and is not a common value so how would one arrive at a rationale to go to 3.9 or 4.3?). What is the method to calculate the needed diode value in the circuit for the ARTA Measuring Box? I think that I understand breakdown voltage plus the 0.7 volt pass when diodes are back to back and I am reading up on this but having trouble understanding how to calculate necessary zener values in the ARTA circuit.

Thanks in advance.
Jay

 

[John Mulcahy]

From a circuit safety point of view want to avoid reverse biasing any supplies from signals fed to the input, device absolute maximum input voltage rating is usually the same as the supply voltage. The supplies were typically 5V back in the day, so the zener value was likely chosen with that in mind. 3V3 is a more common supply voltage nowadays, mind, with 1.8V to 3.6V a range often encountered in low power devices for portable applications.

 

[JMB]

Thanks John. That makes a lot more sense to me. I was trying to figure out if they looked at RMS or half wave, etc.
Jay