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Understanding SPL

Tech Talk With Big Tony

SPL stands for sound pressure level and is also commonly referred to as efficiency and sensitivity.  This parameter represents how loud a speaker is.  A higher SPL equates to a louder speaker.

A speaker is placed on a baffle with the cone facing into an anechoic chamber (room designed to stop sound reflections).  A microphone is placed one meter away and centered on the speaker.  Tones at various frequencies from 20Hz-20kHz are played through the speaker during this test.  Eminence uses software called Loudspeaker Measurement System (LMS) to plot the result.  The plot, commonly know as a frequency response graph, shows frequency on an x-axis (in Hz) versus SPL on a y-axis (in dB).

SPL ratings are very useful and well represent speaker output when comparing one manufacturer’s speaker to another model of the same manufacturer.  It can be misleading, however, when comparing two different manufacturer’s ratings.  The problem is that an industry standard method of representing SPL does not exist and we all come up with the published rating a bit differently.  Eminence uses the frequency response curve and considers the usable frequency range of a given speaker for published SPL.  We feel this is most representative of “real world” output.  It is also acceptable to publish an average of the mid-band piston response, an average over the entire 20Hz-20kHz spectrum, or a calculation from T/S parameters.  I often find that other manufacturer’s SPL ratings are lower than Eminence’s, even on ones I know are similar from comparing them sonically. The intent here is not to validate Eminence’s method or accuse others of doing it incorrectly.  It is merely pointing out that there are differences and comparing different manufacturer’s SPL ratings may not be an accurate comparison.

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