I would like to agree with that. Without measurements, one should be cautious about making predictions about how loud or dynamic a loudspeaker can play without "significantly" (this has yet to be defined) changing its timbre - i.e. dynamic compression.
Small 2-way speakers are always dynamically limited in the low frequency range. The short-time dynamic measurements (at 76, 86, 96, 102 dB) of
@hardisj are very informative, because they introduce an objective measure for the dynamic capability.
To get an idea of the dynamic compression of the JBL 4309, I simply compared the frequency responses of the HD measurements at 86dB and 96dB.
Since these are most likely performed without changing the position of the microphone, it can be assumed that repeated measurements should result in almost identical FRs - or let's assume it was and let's further assume that the amplifier voltage was meticulously adjusted to 10dB difference .
Around 0.5dB sound pressure level difference I would define as dynamic compression, since such a level change, with a correspondingly small Q, is perceptible as a tonality change - this is simply my definition to be able to compare loudspeakers.
(I made small sound pressure level adjustments by hand, e.g. +-0.02dB)
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Thus, the dynamic limit of the JBL 4309 would already be clearly exceeded in the low bass around 40Hz. The human voice range starts at about 100Hz, around 120-180Hz the 4309 reaches a deviation of 0.5dB and would thus also be dynamically at the limit in this frequency range.
In comparison, the ASR Directiva, which by this objective standard (as I said, assuming Amir's measurements are comparable) has less dynamic compression and actually only sags a bit in the frequency range above 6kHz. However, it also just reaches the limit of dynamic compression at 40Hz.
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