To start - a ready example: bass harmonics, heard through a phone. Press Play, switch “Unprocessed” on and off, and hear the difference. Then switch the speaker: the graph shows what reaches it.
Bass on the phone−58 dB → −19 dBOn the laptop−42 dB → −9 dB
The bright fill is what is left of the bass after the speaker. The shaded part on the left is what the speaker does not play.