SPL measurement

[Avezzano]

So, AFAIK (very little!) the Sound Pressure Level measurement is done placing a mic at 1 m / 1 kHz / 1w (please correct me if I am wrong) in front of the cab. I would like to know how much (how little?) this measurement is actually meaningful for a bass cab, since a few reflections:

1) at 1 kHz, a 1x10 cab result "should" (?) not be much different from a 2x15

2) if the measuremnent was done in three regions 50, 500, 1000 Hertz instead...

3) some cabs have the port (hole) in front, some on the rear, some even on the bottom (having wheels or casters)

4) what is the point, from a manufacturer point of view, in indicating the loudspeaker SPL on the datasheet, when this same speaker can end up in literally endless possibilities (small cab, multispeaker cab, big cab, ported, closed etc.)

Thanks to the experts for answering V.

[bongomania]

The unfortunate reality is that the published number means very little, not just because of the reasons you mentioned, but because the tests are done in different-sized rooms with different amounts of reflection.

On the other hand, we have to be grateful for whatever scraps of information they give us, no matter how flawed.

[johnk_10]

most speaker manufacturers just use 1k@1w/1m to give you a 'general' idea of a given speaker's sensitivity for comparision, although JBL's spec ratings are over a much wider range like 500hz-2.5Khz.

[Avezzano]

thanks. So, the SPL figure is just to be "loosely aware"...

[johnk_10]

i think that it's helpful and important, but you have to look at all of the other specs (like xmax, frequency response, QTS, FS, etc) to determine its real capability.

[billfitzmaurice]

Originally Posted by Avezzano

So, AFAIK (very little!) the Sound Pressure Level measurement is done placing a mic at 1 m / 1 kHz / 1w (please correct me if I am wrong)

SPL measurements are taken at every frequency, not one. Measuring at one frequency is of no value whatsoever.
As for the SPL figure on a raw driver datasheet, rightfully that's not a measured result. That figure is the Transfer Function Magnitude, is calculated from the T/S specs, and directly correlates with the electric to acoustical conversion efficiency of the driver.

[will33]

Most the spl charts you see on data sheets are done in an anechoic chamber with the driver mounted in the wall at one end I believe. Those charts are full 20-20k sweeps. Drivers that can go to 40-50 hz still look like they fall off at 100 because there's no box behind them. The box has a lot to do with what happens below 200 hz, above that not so much. When you model box designs, the model is to predict what will happen below 200hz or so, then splice that together with the response graph for above 200hz response.


You can measure a finished cab the same way but most of them don't publish it.

[Avezzano]

thanks!

V.