==dB SPL/HL Conversion==

<charter>
title = dB HL vs. dB SPL
size = 800x330
align = center
bgcolor = #ffffff
type = line
dots = 3
XAxisName = Frequency (Hz)
YAxisName = Sound Level (dB)
legendEntries = Hearing Level (HL), Sound Pressure Level (SPL) Free Field
labelSerie = 3

15, 9, 3, -3, -4, 8
0, 0, 0, 0, 0, 0
250, 500, 1000, 2000, 4000, 8000
</charter>

The calculation is based on the frequency the measurement was taken at.

^ Frequency (Hz) ^ dB HL ^ dB SPL FF ^ 
| 250       |          0 |  15|
| 500       |          0 |   9|
| 1000      |          0 |   3|
| 2000      |          0 |  -3|
| 4000      |          0 |  -4|
| 8000      |          0 |   8|

SPL = Sound Pressure Level Free Field
HL = Hearing Level


HL is used for Audiogram representation.  SPL is used for Target Curves representation. The HL chart has the Y-axis origin at the top left corner.  The SPL chart has the Y-axis origin at the bottom left corner.


== Examples ==

=== Audiogram dB HL vs. dB SPL ===
{{:ezfit:ezfit-audiogram-dbhl-vs-dbspl.jpg|Audiogram using dB HL vs. dB SPL}}

=== Audiogram using HL ==

{{:ezfit:audiogram-sample.jpg|Audiogram using HL. Source: Wikipedia, http://en.wikipedia.org/wiki/File:Audio23.jpg}}

Source: Wikipedia, http://en.wikipedia.org/wiki/File:Audio23.jpg

=== Target Curves using SPL ===

{{:ezfit:ezfit-targetcurves.jpg|Sample Target Curves (thick dotted lines) and related Response Curves (thin continuous lines)}}

Source: ezFIT software