Unfortunately, not true.
1. Olive's resonance studies show resonances as low as 28 dB down (barely a blip on a response curve) can be detectable. I try to target all my crossovers for at least that much rejection.
2. The driver resonances also show up as elevated distortion and this is not detectable in frequency response. You can roll off the resonance 1000 dB with an upstream low pass, won't matter because the distortion is generated in the driver after the filter.
Read
this post Toole wrote on another forum:
Resonances originate in transducers, in mechanical resonances in enclosures, and in acoustical resonances in enclosures. They all exhibit themselves in anechoic measurements and if they are energetic enough we hear them. This 29 year old paper explains it all in great detail:
Toole, F.E. and Olive, S.E. (1988). “The modification of timbre by resonances: perception and measurement”, J. Audio Eng. Soc., 36, pp. 122-142.
Putting an accelerometer on the wall of a cabinet is not a reliable indicator of the audibility of a resonance (sorry John Atkinson). For example, some panel resonances radiate sound effectively and others do not, but both exhibit vibration at a point on the panel. Harman and other advanced designers use scanning laser vibrometers to reveal patterns, polarity and amplitude of panel movement which guides the placement of structural reinforcements to reduce acoustical radiation from the resonance.
When it is below the audible threshold in the anechoic frequency responses all is well (see the paper, or my books). It is not necessary to have foot thick concrete enclosures to eliminate audible resonances, good engineering can do it in rectangular wooden boxes.