I've noticed several times that ASR and S&R measurements differ.
Here is just one example, but you could find many others.
To be able to really compare the measurements, some preconditions have to be checked:
- Was the microphone position identical in relation to the baffle?
Amir always points the measurement microphone at the tweeter center, S&R takes into account the manufacturer's specifications (as far as I know), which often means that the mic is aligned halfway between the tweeter and the bass-midrange chassis.
- Was the measurement distance identical?
In
@amirm's reviews the description of the simulated measurement distance is missing, AFAIK the distance (at least in the current measurements) is simulated for a distance of 2m (the NFS measurements can be transferred to any measurement distance) and the SPL is converted to 1m (as required by the CEA/CTA-2034 ANSI).
The measurement distance for S&R's ground-plane measurements depends very much on the loudspeaker dimensions. Thus, measurements are very often made at a distance of 4m to fully capture the influence of the baffle.
A large measurement distance also reduces the effect of phase shifts on the frequency response caused by the distance between the different chassis.
But possible temperature fluctuations affect the phase behavior at large measuring distances (which is not a problem with the NFS due to the near-field measurements).
If the temperature in Amir's garage is around 20°C, the resolution of the measurements in the low bass should be superior to those of S&R.
S&R's anechoic chamber does extend down to 100Hz, but the "gating" of the measurement smooths out the frequency response somewhat at low frequencies. Below 100Hz it depends on how well the various near-field measurements of woofers, possible ports and the influence of the baffle
is simulated are calculated to an approximation of the frequency response below 100Hz.
If the S&R ground-plane measurements are performed very carefully, they should be superior to those of Amir's NFS in the frequency range above 10kHz, since the conversion of the frequency responses measured in the near field to user defined distances becomes less accurate towards very high frequencies (or needs a lot of data points and time to be accurate up to 20kHz, e.g. 7h measurement for one speaker).
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