Examples an expert would immediately consider:

• Djembe + Cajón: Using both often creates low‑mid congestion because both occupy similar transient and body ranges. An expert may choose one (cajón for tight, boxy pop/folk; djembe for open, tribal energy) unless their roles are clearly separated by pattern, register, or stereo placement.
• Two rhythm guitars in a rock band: Even with the same guitar and tone, one guitarist may play chords in higher fret positions while the other stays in open/low positions. This spreads harmonic content across frequencies instead of stacking it in one range.
• Ukulele vs vocals: Ukulele is often used successfully with vocals because it generally sits above the main vocal body range. Issues arise mainly when dense strumming, strong transients, or constant rhythmic activity mask vocal articulation. An expert may thin the strum pattern, simplify rhythm, or adjust voicing so the instrument supports the voice rather than competing with it.
• Voice + acoustic guitar (real‑world applications using the same principle):
  • Singer‑songwriter folk: Light fingerpicking or broken chords often leave space for vocal phrasing and consonants, supporting intelligibility without heavy processing.
  • Strummed pop ballads: Open‑position strumming works when dynamics are controlled; constant full‑force strumming can mask vocal articulation.
  • Low‑voiced vocal + acoustic guitar: Using higher‑voiced chord shapes or a capo can help separate guitar energy from the vocal body range.

  In practice, success depends mainly on dynamic control, voicing choices, and rhythmic restraint, not on the guitar itself.

  In all cases, success depends less on the instrument itself and more on density, rhythm, and intention.

• Piano + acoustic guitar: Both playing full chords in the same octave often muddies the mix. One is reduced to rhythmic stabs or higher voicings so each instrument earns its space.

These decisions are arrangement choices made before EQ or mastering, and they solve problems at the source.