xnor
Headphoneus Supremus
- Joined
- May 28, 2009
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The graph seems to me to be as much use as a chocolate tea pot!
Mhhhmm yummie. I want one.
The graph seems to me to be as much use as a chocolate tea pot!
Mhhhmm yummie. I want one.
Decibel is a logarithmic "helper unit" that describes a ratio of power or field quantities (such as sound pressure, voltages etc.).
Logarithmic means that even huge ratios can be described with relatively small decibel numbers.
Examples:
You put 1V into an amp and measure a max output of 5V:
5V / 1V = gain of 5x
20*log10(5) = gain of +14 dB
You put 1V into an amp and the max output is 0.1V (a tenth):
0.1/1 = gain of 0.1x
20*log10(0.1) = gain of -20 dB
As you can see, as soon as the gain factor is lower than 1x you get negative dB. For power you need to use 10*log10(ratio).
Now if some specs say 20 Hz - 20 kHz +/- 3 dB this means that in the whole range the frequency response can vary by 3 dB up or down.
+/- 10 dB is perceived as twice/half as loud.
It gets more confusing since above numbers are completely relative, sometimes written as dBr. There are some common dB units that have a reference, such as dB SPL (reference is a sound pressure of 20 µPa), dBV (reference is 1 V) etc.
Some completely random examples with voltage gain and how to convert it into dB.
You're zooming in on just 18kHz-22kHz. If you look at a conventional scale, from 0-22kHz, you'd probably see a natural rolloff from the bass to the treble as usual?
If you know the headphones' and cable's impedance at 1 kHz you can calculate it like a voltage divider.
For example 20 ohm headphone, 5 ohm cable1, 3 ohm cable2, all at 1 kHz:
20/(20+5) = 0.8
20/(20+3) = 0.8696
20*log10(0.8696/0.8) = +0.72 dB for cable2