I bought one monitor speaker (Behringer Truth B1030A) but I think this device has a problem. I play a music but this speaker does not play some sounds. I play this music by (Boss BR 600).
Source music: Listen
But I listen this on speaker: View
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It sounds to me like you have accidentally inverted the phase of one stereo channel when you produced the mono signal for your single Behringer speaker.
I verified that by recording your mp3 into Audacity, inverting the phase of one channel, and playing the result mixed down to mono.
It didn't sound "exactly" the same, but your mp4 of the Behringer is re-recorded from the speaker using an unknown quality of mike, and in a different room environment to mine, so that's not surprising!
If you just connected the two "live" wires from the stereo audio output to the two terminals of the Behringer, and ignored the one (or two) "neutral/earth" wire(s), that would cause this mistake. That is giving you the difference between the two stereo channels, not adding them together.