Sound can be described with various
physical parameters e.g. intensity, pressure or energy. These parameters are
very limited to describe the perception of the human ear. A first approach is to
take into account that the ear is less sensitive at lower and higher frequencies.
The research work around 1920 from Barkhausen result into the well known A,B,C
weighting curves. The frequency response of the ear depends on the sound level,
that is the reason for different curves, which are valid for a certain level
only. A pure sine at lower levels e.g. 40dB(A) has the same subjective loudness
over the complete frequency range. However, in practice sine tones are not very
common. For complex sounds and noise, this simple model is not valid anymore.
In most sound pressure meters
available today you will find these techniques, because they are easily to
derive from the physical parameters.
A wideband noise has a different
subjective loudness than a pure tone at the same level measured in dB(A).
Therefore, dB(A) is very limited in its usage although widely used. Zwicker
analyzed various psychoacoustics effects thoroughly. A result was a model for
the human hearing. A famous psychoacoustics effect is acoustical masking. A loud
tone hides quiet tones. Nobody would expect to hear the sound of a mouse during
a symphonic orchestra, although the mouse would audible in quiet phases. A very
famous application of this and other effects are audio compression techniques
like MP3. Only parts of the signal, which are audible according to a model, are
Based on its countless hearing tests,
Zwicker developed a model for loudness measured in sone. For stationary signals
you will achieve much better results than the traditional dB(A). In contrast to
dB(A) sone is a linear parameter. Two sone has double loudness compared to one
sone. The reference level is one sone, which is equivalent to a tone with 1kHz
at a level of 40dB.
As mentioned previously, sone is valid
for stationary signals only. It is ideally in the judgment of air conditioners
or typical PC noise like hard disks of fans.
This measurement describes the
subjective loudness. However, it does not allow distinguishing between nice or
annoying tones. Most people will agree that the sound of a flute is much nicer
than a drill used by dentist although they both might have the same loudness.
The measurement of the loudness is
based on the 1/3 octave analyzer. You will require both the loudness plug-in
(#3010) and the 1/3-octave module (#3004). In addition, you have to calibrate
the system. All psycho acoustic analysis requires absolute sound levels. This
can be achieved with a sound calibrator or a sound pressure meter.
A complete measurement
system for sone contains the following components:
PC/Laptop running Microsoft Windows
WinAudioMLS mind. PRO Version
WinAudioMLS plug-in „1/3 Octave RTA“
WinAudioMLS plug-in „Sone/Loudness“
Soundcard with suitable microphone preamplifier
and phantom power
(A loudspeaker is not required for
WinAudioMLS with Sone/Loudness
measurement. All values are displayed in real-time.
Many sone measurements include
analysis of low noise devices (e.g. beamer, notebooks etc.). The normal
measurement distance is 1m. You can only perform a reliable measurement if the
signal level is above the noise. The noise includes acoustic noise from the
environment and noise in the measurement chain from the microphone or
preamplifier. In a normal office environment at a quiet noise level of 45dBA it
is impossible to analyze a fan with 25dBA. Since the human ear is very
sensitive, such measurements require high quality measurement equipment.
For every measurement, we strongly
recommend to measure the quiet noise first. Simply switch off the measurement
device. The optimum measurement environment is a special anechoic chamber, which
reduces reflections and noise from outside. We strongly recommend switching off
noise sources if possible (windows, air-condition, computers etc.)
Many measurement microphones have a
sensitivity of 30dB, which defines the lower bound for measurements. You can
improve the measurement sensitivity by reducing the measurement distance from 1m
to e.g. 25cm. This increases the signal level by 12dB. This offset can be
corrected with a different calibration factor, which allows WinAudioMLS to show
the measurements results with respect to 1m.
We will explain this with an example.
By reducing the distance to the half,
the level increases by 6dB. With a distance of 25cm the correction factor is
12dB. If you use a sound level calibrator with 94dB, the reference level has to
set to 82dB. A sound level of 82dB will be displayed as 94dB.
This approximation is only valid in the far-field with spherical
radiation. In the near-field you will encounter e.g. diffraction, which has
significant influence on the signal level. Therefore, we strongly recommend
documenting this different measurement distance clearly, because it is difficult
to compare different measurement distances.
With WinAudioMLS you can perform a
loudness measurement either automatically or manually.
With the automatic measurement many
parameters are checked for plausibility to reduce possible sources of error. In
addition, you can enter a reduced measurement distance directly.
The automatic measurement wizard
guides you through all steps. The final results are stored in a comprehensive
Start the measurement with Easy
Measurements->Sone/Loudness from the menu.
Select a folder, where the results
will be stored.
Connect the calibrator to the
microphone and switch it on.
In this picture you can clearly see
the frequency of the calibrator (in this case 1000Hz).
WinAudioMLS helps you to find the
optimum settings. It displays both the input level (RMS) and the distortion (THD+N)
with parameter viewers. If both parameters are within their limits, they convert
Enter the reference level of the
calibrator, normally this is 94dB.
All measurement values are display in
absolute values. Do not change the gain settings anymore.
In the next step enter the measurement
distance. All results are converted to a reference distance of 1m.
By using the automatic measurement,
WinAudioMLS automatically measures the quiet noise. This ensures that the signal
level is significantly above the quiet level. Switch off the calibrator, any
noise sources and the device under test.
In the final step switch on the device
under test and confirm it in the dialog box.
All measurement results are written to
a HTML-report. You can view it with any browser, print it or convert it to PDF.
If the measurement has finished, your default browser will open the report
The following screenshots show an
example of such report.
For a manual measurement you have to
perform the following steps
Start the 1/3-octave RTA
Activate the sone measurement
Weighting should be switched off
display to measure absolute levels.
First, measure the quiet noise.
Finally, apply the measurement microphone to
the device under test.
Start WinAudioMLS with its default
settings and activate the sone measurement with plugins->loudness (Sone) from
The picture shows the uncalibrated
In the next step connect the
calibrator to the microphone.
You can also calibrate WinAudioMLS
with a hand-held sound level meter. This option is less comfortable and is
sensitive to errors. You find more details for calibration in the dedicated
Please pay attention that the level is
between –10dB and –5dB. If this is not the case, please change the gain
settings of the microphone. Distortion and noise (THD+N) should be less than
Start the calibration with
The display shows now the calibrated
reference signal with 94dB.
Place the microphone to the device
under test. The default measurement distance is 1m. Please ensure that the
signal level is significantly above the noise level.
If the signal shows strong
fluctuations, you can apply averaging. In the following example, we average over
10 blocks, which is equivalent to a time interval of 1.8s
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