Trevor wrote:
The frequency response plots, as well as the operating characteristics,
come from the marketing department, not the engineering department.
Sure, the speaker will reproduce something below 70 Hz, but as a guitar
player, you probably don't need it. What they want you to believe is
that it will do a good job as a guitar amplifier speaker, which,
hopefully, is why you're buying it.
The raw stated or plotted frequency response of a loudspeaker is more
theoretical than practical, since in the real world, it's a function of
the amplifier, the enclosure, and even the wiring between the amplifier
and speaker voice coil.
You forgot the main thing. The response figure quoted is a function of
what you specify as the limits for acoustic output.
** The OP is talking about *guitar* speakers, not speaker systems, specified as drivers. They are a special case, separate from hi-fi speakers.
See typical example, with plot as well as numbers.
https://celestion.com/product/22/seventy_80/
Note how the " -10dB rule " applies when deriving numbers from the response plot. The plot is obtained with the driver mounted on a large baffle or large volume cabinet and driven with constant voltage input.
In typical use, the speaker or multiple speakers are mounted in an open backed cabinet of modest dimensions and driven with a amplifier that has a high output impedance - anywhere between 8 and 100 ohms. This can dramatically change the response from the published curve.
Still, it is useful for making comparisons between various models.
...... Phil