Understanding Frequency Response vs sound pressure level

[KEW]

Below it is obvious that this speaker has a fairly consistent FR in the range from 70dB to 90dB. However it has significant deviation in lower frequencies at 95dB.

Chart 4 - Deviation from Linearity at 90dB and Above
Difference @ 90dB, 50Hz - 20kHz (measured @ 2m)

Curve: difference from 70dB at 90dB

Difference @ 95dB, 50Hz - 20kHz (measured @ 2m)

Curve: difference from 70dB at 95dB (sic)

Source:
http://www.soundstagenetwork.com/measurements/speakers/paradigm_signature_s1_v2/

It seems interesting that the greatest deviations are largely at the lower frequencies. The crossover is at 2,100Hz.

I'm just wondering if anyone understands speakers and parameters well enough to conjecture on what source of deviation is likely at play in the woofer and why it might clear up as the frequency increases.

Thanks!

 

[Steve81]

In this case, I'd say the main considerations are the speakers themselves (compact, sealed 2-way monitor w/ a 6" mid/woofer) and the levels they're being driven to, ie 95dB at 2 meters in an anechoic environment or 101dB at 1m. That's simply a lot of output to ask from such a speaker, and a bit of compression, particularly down low as excursion demands rise, isn't surprising.

 

[Steve81]

Also from their "how we test section":
http://www.soundstagenetwork.com/measurements/test_loudspeakers.htm

What it tells you: As volume increases, all frequencies should rise at the same rate. However, as a speaker is stressed, compression will occur at certain frequencies. The stress may be mechanical, thermal or otherwise. This test shows those frequencies at which deviation occurs as a result of compression. Many speakers show slight deviations at 90dB. Most speakers start to show serious deviations at 95dB. Very few speakers can be tested at 100dB without damage.

 

[KEW]

Yeah, I saw the link, but was trying to understand it in the context of these specific speakers.
Thinking about it as high excursions against the air pressure of a smaller sealed enclosure makes sense, just like JL puts big watts into their sealed subs.
Thanks!

 

[utubecomment21]

Not sure how to compare JL to the likes of Sundown X and Z, AD Designs 3000 and 4000 series etc for an evaluation of what is and isn't capable in a sealed enclosure.

YouTube search: sealed subwoofer kings - and see the 3 Playlist by carspeakerreviews