[JohnR]

This is a "fact-finding" thread about speaker distortion. If you find useful information on distortion in loudspeakers (or drivers) please post it here!

I'll start. Seas seems to be one of the few driver companies who publishes unadulterated measurements of their drivers. The W18EX001 is widely considered to be a low-distortion driver, the spec sheet is here:

http://www.seas.no/excel_line/excel/E0017.PDF

This is the driver used in the Ellis 1801, which appears to be universally loved by owners. So this is not some garden variety driver used as a bad example; this is a VERY GOOD driver. Here's the distortion graph:



"Operating power" is defined elsewhere in the datasheet to be the power required to reach a nominal 96dB SPL, or 6.3 Watts. The curve is a bit fuzzy so here are the main features. Second-harmonic distortion dominates through most of the spectrum. Between about 150 Hz and 1500 kHz, distortion levels are around 0.3%. Below 150Hz, distortion rises, being around 0.8% at 100 Hz, 3.5% at 50 Hz, and reaching 10% around 35 Hz.

Remember, this is with 6 Watts input, not at rated power.

JohnR

[JohnR]

Here, for comparison, is the W15CY001. This is a 6" driver in the same series, same cone material (magnesium).



It's reasonable to assume that the quality of the cone and the motor in this driver are just as good as the W18. Above 400 Hz and below breakup, distortion levels are about the same (0.3%). However, below 400 Hz, distortion rises much earlier than the W18; specifically, 1% at 200 Hz, 3% at 100 Hz, and 10% around 60 Hz.

This is why a smaller driver can never be as good as a larger driver. To produce the same SPL it has to move further and inevitably generates more distortion due to the limitations of the motor and suspension.

This graph is at 10 Watts input (again, a nominal 96 dB SPL).

[JohnR]

To prove that this correlation between driver size and distortion in the bass area is not a fluke, here is the curve for the W26FX001, a 10-inch driver.



Distortion is 0.5% at 100 Hz, 2% at 50 Hz, and reaches 10% at around 25 Hz.