Then my speakers should be measured minimum 153cm distance.
Microphone distancing is absolutely critical. It is also a complex subject! There is no single mic distance that will work for every measurement. The first thing you need to realize is that high frequencies are corrected to the anechoic response. Low frequencies are corrected to the in-room response. So you have to ask what you are trying to measure.
The first thing to do is calculate your Schroder frequency (Fs), because this tells you the limit where you need to take an anechoic or quasi/anechoic measurement. Read
this before proceeding. The transition zone is up to 4Fs. You can decide if you want to do in-room bass correction up to Fs or 4Fs or something in between. The typical Schroder frequency is 100-200Hz depending on your room, so 4Fs is 400Hz - 800Hz. If you decide on 2Fs, that will be 200Hz - 400Hz. 200Hz has a 1.7m/5.6ft wavelength.
Now you need to decide if you want to measure your drivers, or your entire speaker.
If it is the entire speaker, you will need to measure in the acoustic nearfield, which is either the greatest dimension of the speaker (usually its height) or the lowest wavelength of interest, whichever is greater. If you decide on measuring down to 2Fs, you place your mic 1.7m away.
If it is individual drivers, you have additional considerations. Upper frequencies are influenced by the baffle diffraction step (BDS), so must be measured from 2x baffle width away at minimum. The BDS is a volume loss of about 6dB that occurs over 4 octaves. You can calculate the centre frequency of the BDS f3 with 115824/W (W = width in mm) 4560/W (W = width in inches). The upper limit of the BDS is 2 octaves above f3, and the lower limit is 2 octaves below f3.
As you can imagine, measuring further away means greater risk your measurement will be contaminated by reflections. The closer the reflective surface (usually the floor or ceiling), the higher the risk. You can calculate the lowest reflection-free wavelength with this formula:
This is why people take their speakers outside and elevate them on stands to obtain quasi-anechoic conditions.
Taking measurements alone requires a book to explain. It is very poorly explained in typical DSP user manuals. "Measure from 1m away" is completely arbitrary, yet it is the standard recommendation in most manuals. If you can take a 1m measurement under anechoic conditions - great! But many people can't!
