What accuracy should be aimed for when measuring loudspeakers with the Klippel NFS?
The Klippel NFS specification claims +-0.1dB tolerance in direction of of max SPL, which is really impressive. But only if as many test objects as possible are measured and checked against other sources it's ensured that all error sources are excluded.
If you intend to doubt the published measurements of manufacturers, renowned magazines or acknowledged specialists in audio measurement technology (as quite a few have done in the review thread of the Neumann KH 80), you should make sure that your own measurements meet the highest standards.
If not, no real trust can be built. To always claim that others are measuring wrong can only be successful if there is no doubt about your own measurements.
The accuracy should definitely exceed the possibilities of a "bloody" DIY developer who measures in his own living room.
What accuracy is possible for measurements in living rooms?
About 18 months ago a test was carried out among members of a DIY-forum. A small 3-way loudspeaker, equipped with inexpensive drivers and without crossover network, was measured (driver by driver) by the driver manufacturer in the company's own anechoic chamber (RAR) and then sent to 13 interested members for measurement in their own living room (some also made measurements in the garden or in a gym).
The loudspeaker consists of a tweeter, a fullrange driver, which are arranged asymmetrically at the front, and a side-mounted woofer.
The challenge was to measure the individual chassis as accurately as possible without knowing how these chassis were measured in the anechoic chamber by the manufacturer.
The expectations on my part regarding the accuracy of my own measurements were, as you can also think, not very high.
Especially since it turned out that my chosen reference point for the measurement did not correspond to the one for the anechoic chamber measurement. The blue cross corresponds to my chosen reference point for the measuring microphone, the red cross corresponds to the manufacturer measurement.
The test results
My living space measurements are reasonably accurate up to about 300-400Hz. For frequencies that are lower, a near-field measurement has to be added - which I did without. Since I did not know which reference point was used for the RAR measurements, my measurements were taken at a distance of 1.50m, which is unusual for indoor measurements.
First the comparison of the tweeter measurements (in red the anechoic measurement, in blue my measurement):
Same measurements normalized to the anechoic chamber measurement:
Below 800Hz the sound pressure has already dropped too much for an exact measurement in my living room.
In the range 1.5kHz to 4kHz there is different diffraction at the speaker cabinet due to the different reference points.
A better result should be achieved with the full range driver, since the influence of the cabinet edges is less pronounced there (due to the different reference points).
Comparison of the full range driver measurements (in red the anechoic measurement, in blue my measurement):
Same measurements normalized to the anechoic chamber measurement:
Despite the adverse conditions (wrong reference point) it was possible to achieve almost +-1dB accuracy with the indoor measurement compared to a measurement in an anechoic chamber. I found this quite impressive.
To cut a long story short, the demand on the accuracy of the measurements made here in the forum by Amir with the Klippel NFS should be much higher.
The end
The Klippel NFS specification claims +-0.1dB tolerance in direction of of max SPL, which is really impressive. But only if as many test objects as possible are measured and checked against other sources it's ensured that all error sources are excluded.
If you intend to doubt the published measurements of manufacturers, renowned magazines or acknowledged specialists in audio measurement technology (as quite a few have done in the review thread of the Neumann KH 80), you should make sure that your own measurements meet the highest standards.
If not, no real trust can be built. To always claim that others are measuring wrong can only be successful if there is no doubt about your own measurements.
The accuracy should definitely exceed the possibilities of a "bloody" DIY developer who measures in his own living room.
What accuracy is possible for measurements in living rooms?
About 18 months ago a test was carried out among members of a DIY-forum. A small 3-way loudspeaker, equipped with inexpensive drivers and without crossover network, was measured (driver by driver) by the driver manufacturer in the company's own anechoic chamber (RAR) and then sent to 13 interested members for measurement in their own living room (some also made measurements in the garden or in a gym).
The loudspeaker consists of a tweeter, a fullrange driver, which are arranged asymmetrically at the front, and a side-mounted woofer.
The challenge was to measure the individual chassis as accurately as possible without knowing how these chassis were measured in the anechoic chamber by the manufacturer.
The expectations on my part regarding the accuracy of my own measurements were, as you can also think, not very high.
Especially since it turned out that my chosen reference point for the measurement did not correspond to the one for the anechoic chamber measurement. The blue cross corresponds to my chosen reference point for the measuring microphone, the red cross corresponds to the manufacturer measurement.
The test results
My living space measurements are reasonably accurate up to about 300-400Hz. For frequencies that are lower, a near-field measurement has to be added - which I did without. Since I did not know which reference point was used for the RAR measurements, my measurements were taken at a distance of 1.50m, which is unusual for indoor measurements.
First the comparison of the tweeter measurements (in red the anechoic measurement, in blue my measurement):
Same measurements normalized to the anechoic chamber measurement:
Below 800Hz the sound pressure has already dropped too much for an exact measurement in my living room.
In the range 1.5kHz to 4kHz there is different diffraction at the speaker cabinet due to the different reference points.
A better result should be achieved with the full range driver, since the influence of the cabinet edges is less pronounced there (due to the different reference points).
Comparison of the full range driver measurements (in red the anechoic measurement, in blue my measurement):
Same measurements normalized to the anechoic chamber measurement:
Despite the adverse conditions (wrong reference point) it was possible to achieve almost +-1dB accuracy with the indoor measurement compared to a measurement in an anechoic chamber. I found this quite impressive.
To cut a long story short, the demand on the accuracy of the measurements made here in the forum by Amir with the Klippel NFS should be much higher.
The end
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