I didn’t create it. There was no instrument used, those can be created from various techniques; sweeping frequencies, white/pink noise, impulses, etc, But it is a common way to report frequency response.
You also need to know how to read them as there’s a few ways to report it. For example, that one is not as bad as it looks - note that it is not 0-based. It does not roll off to 0; it simply has lost 40dB of volume down between 100 and 30 Hz. Now, that’s a lot, but it doesn’t mean the fundamental is gone; it just means that increasingly, you are hearing higher harmonics as the volume decreases.
That’s presumably the internal cab speaker.
But it’s pretty common speaker/amp measuring and reporting method, you can find those for most amps and speakers.
