COMPARSION: Old & New Test Setup

In the essay 'The Meaning of the Measurements' under the 'Measurements and Methods' section the case is made that very large loudspeakers cannot be measured in a way so as to simulate 'Free Field' response in typical livingrooms. Below is the proof of that matter in an overlayed plot of four separate frequency responses. Two of the responses are from the earlier measurement position, at 2 meters distance, and the other two are from the latest measurement position, also at 2 meters distance.

In the earlier case the rear wave of the dipole baffle is allowed to interact with the room, and in the current case, attempts are made to both absorb and dissipate the rear wave. In neither case does significant room or wall reflections appear in the data sample analyzed! Below is the 1/3 octave smoothed overlay of four 2 meter frequency responses of the '3&SQ' baffle. This is the 'Rosetta Stone' for comparing the One-Sided and Two-Sided 2 meter frequency responses.

The WHITE and YELLOW traces are from the earlier test condition, and the BROWN and GREEN traces from the new. Three of the traces represent the 'BG54' driver, but the GREEN trace is that of the 'BG55' driver. It clearly has a slightly different frequency response than does the BG54 driver. This was documented earlier in the Two-Sided Baffle section.

If we compare the frequency response envelopes of the two measurement conditions it is clear that there are seemingly large differences. Yet the basic shape and trends of the frequency response remains from one condition to the next. Even more dramatic changes seem to appear in the 1/12 octave smoothed individual plots. The area around 1000Hz is much less smooth than in the earlier measurements. Is this a result of attempting to absorb and dissipate the rear wave of the baffle? Or, just a measurement anomaly resulting from a change of baffle and microphone position?

Let us jump ahead and look at a more 'difficult' overlayed plot. This plot contains two of the same frequency responses as above, but this time they are 1/12 octave smoothed. Thing look a bit different! The same BG54 driver is used in each case: There is the old and new 2 meter responses of the '3&SQ' baffle, and the new '1S9T' baffle, also at 2 meters. The '1S9T' baffle has been selected as the best of the tested One-Sided baffles.

Three things to note with the '1S9T' baffle: The remainder of the cavity resonance at about 6KHz is lower, the low-frequency rise is tamed, and the output around 1000Hz is much increased - compared to the '3&SQ' baffle at 2 meters. There is more work to be done, wouldn't you say?


Room Test Setup - 1m, 2m, 3m & 3.5m.
Comparison: Edge Effects.
Listening Room Measurements Menu.
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