[HiFi1972]

I am looking to give my kid one of my more sturdier headphones for him to use (we've bought a couple of pairs of those "kids headphones" that aren't as loud as other headphones but they break easy).
 
What I'm looking for (to further educate myself on using resistors) is a way to figure out the value of resistors I need based on decibels (if possible). For example, if I would like to decrease the levels of a particular set of headphones by -10dB, and knowing the impedance of the headphones (45ohms), what calculation do I need to figure out what value of resistors I would need to decrease the level of the headphones by -10dB (or approximately).
 
Thanks for any help!

 

[wakibaki]

OK.
 
To convert from dB to ordinary numbers, take the number of dB, put it in the Windows calculator, divide it by 20, click the tickbox for Inverse (inv) and click log.
 
10 > 0.5 > 3.16. Call it 3. 
 
dB = 20(log n)
 
n = antilog (dB/20)
 
It's minus 10dB, so you're dividing by 3 to get 1/3 or 0.3333.
 
The headphone impedance is 45R, so the total impedance required is 3 * 45 = 135R. The resistor needs to be 135 - 45 = 90R.
 
Now 2/3 of the volume appears across the resistor and 1/3 in the headphones.
 
w

 

[HiFi1972]

Most awesome. Thank you!

 

[HiFi1972]

Just one question on the calculation - would you always divide the first number (dBs) by 20? Or is it simply double the dBs' value (20 in this case because it was 10dBs I wanted to work with?) Again, thank you (especially for helping to prevent hearing loss for my child!)

 

[wakibaki]

When you're working with voltages, you always divide by 20, regardless of the number of dB. If you're working with power (Watts) you divide by 10.
 
Children? I love 'em. I've eaten dozens.
 
w

 

[HiFi1972]

LOL! Thanks again!!