173_58300000002379_ara_en_j.doc – 29.04.14
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2.10 Noise measure from customer
Hint
The information about the noise level in the product info helps the
customer to compare cooling appliances themselves. Like the
Information about the fuel consumption on Cars.
The noise level according to DIN (Norm IEC 60704) is measured and
confirmed in
laboratory
.
To measure again in household with noise-meter or programs /
software like app´s for smartphone
or similar is
not possible.
Background
More frequently the customer service faces complaints from the
customer measuring noise level of appliances by using a smartphone
application. Often high differences between the measured numbers
and the labeled numbers are observed. Below arguments are given to
explain such differences.
Explanation
For the determination of noise the declaration value manufacturers
have to follow exactly described rules. They are defined in the
international standard IEC 60704. The procedures and boundary
conditions described in this standard cannot be fulfilled in a regular
household environment and by technical equipment of a smartphone.
Out of that errors and deviations must be expected when doing a
noise measurement with a smartphone in a living environment. Main
arguments are:
1. The manufacturer’s declared noise level is a sound
power
level.
Smartphone apps only measure sound
pressure
level. Both may not
be mixed up.
2. The used equipment – a smartphone – does not have the required
precision.
3. The application does not apply all needed post processing
procedures as required in the standard IEC 60704. Especially the
required time average for a clearly specified time frame is not done.
4. It must be expected that the applied algorithms in the app are faulty.
Usually such apps are not certified or created by hobby programmers
who do not know about all required specification. Thus errors must
be expected.
5. Kitchens, living rooms or apartments in general do not fulfill the
requirements for standardized test room as described in IEC 60704.
By not fulfilling these requirements measurements at home cannot
give the right and comparable measurement result.
To 1.)
A smartphone-app only can measure the sound pressure at the
position in space where the smartphone has been placed. By varying
the position the sound
pressure
level changes. The customer can
check it easily by repeating measurements at different positions at
home.
But the stated noise level on the label is a sound
power
level. This
sound power level is independent from the microphone position. It is a
method to compare product in an equal way. But it needs well defined
test procedures, high-precision test equipment and a standardized
test environment. The sound power is a number describing the totally
radiated sound of an object, e.g. home appliances. It characterizes an
appliance allowing a comparison of appliances with each other. This is
not possible to be realized at home!
To 2.)
A smartphone does not use a precise microphone and the electronics
causes a high background noise versus the measurement signal. Also
the sensitivity of the smartphone microphone is not good in every
relevant frequency range. These negative properties reduce the
accuracy of test result. Usually these microphones also have different
sensitivity depending from the direction the noise is coming from.
Therefore depending from the angle the smartphone is hold the test
result will vary. Again a deviation from the real noise level must be
expected.
To guarantee the accuracy of the test results microphones have to be
calibrated on a regular basis. For smartphones this is not possible.
Thus the accuracy is low.
