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If you want to measure eiser a box or a complete loudspeaker, the first thing to do is to place your microphone on the right place as shown below :
This way, you can do a far field measurement either of each loudspeaker separately or of the entire box. Measuring each loudspeaker separately is interesting in order to design the crossover, where as measuring the whole box is interesting to see the result, once your crossover is alredy made. The best place for the microphone is aligned inline with the box horizontally, and somewhere in the middle between the tweeter and the medium or just above it vertically (ideally 2/3 vs 1/3, see below). You cannot moove the microphone between each measure if you measure the three loudspeakers independantally if you want to have an accurate phase and frequency response.
Once everything is installed, you have to record the audio files. It is not possible to record the files with Sofmea, you will have to use another software such as Audacity. The advantage of that is that you can record a file on the computer you want, even if Sofmea is not installed, and use the audio files on another computer when you want. The format to use is the standard format WAV.
You have to choose the source for the operation, for example you CD player or your computer (if you have a full duplex sound card). Then, the microphone is connected directly to the sound card (or better : to the pre amplifier). The best way to have a good phase information is to have the microphon on the left or right channel of the sound card and a copy of the source signal on the other channel. If it is not possible to do this dual recording, you will have to compute the phase with the Hilbert transform and estimate the distance between the acoustical center of the speakers approximately.
If you are using Audacity to record the sound, open the MLS signal file, don't forget to check the box "Play other tracks while recording new one" and finally click on the recording button.
How to determine precisely the height of the microphone ?
There is a way to compute this value as follow... The idea is to have the same phase difference when you measure your box and where you are listening to your box in your room... Yes, you need to know approximately the listening point to get the best place for your microphon, but jno, you don't need to measure the box at the listening point because if you do so, you won't be able to get rid of the refexions on the walls and the floor. As shown on the scheme under here, the phase difference between medium and tweeter is linked to distance difference between medium-micropohone and tweeter-microphone.
The equation obtained is
Let say your ear is exactly on the same high as the tweeter, and at the distance L of the box as shown on the scheme :
The phase difference is linked to distance difference between medium-ear and tweeter-ear. In this case, the equation you get is
The global equation is also
In my example, L (listaning distance) is 3m, h (distance medium center - tweeter center) 14 cm, L1 is 1m. If you solve it numerically, you will get x = 9,2cm which is approximately 2/3 of h which is 14 cm ! I tried to take into account the fact that the acoustical center of the boomer is behind (in my case I took 4 cm) and I got less than 1mm difference in the result, so don't worry about it. I think I will build a new module inside Sofmea to be able to compute the height of the microphone.
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