Resistive absorbers are impractical at low frequencies because quarter-wavelengths are huge

Evidence

If resistive absorption is to be useful, it must be at a distance from the room boundary—the portion of it that is adjacent to the boundary is doing nothing, and the effectiveness increases with distance from the boundary, or the thickness of the material, up to a maximum at the 1/4-wavelength distance where the particle velocity is maximum (Figure 4.21d). Look at Figure 4.19 and divide those wavelengths by four to get an idea of why resistive absorbers are not attractive solutions at low frequencies—even at a mid-bass frequency of 100 Hz the quarter-wavelength is 2.8 ft (0.86 m), which seriously intrudes on expensive real estate. — , Toole, Floyd E - Sound reproduction-…, 481

Categorization

• DEFINE: Explains why particle velocity peaks at 1/4-wavelength from a boundary — the mechanism that makes resistive absorbers thickness-dependent.
• XREF: connects to: Resistive absorbers only work where air particles move, which pushes them to high frequencies; A resistive absorber behind the listener solves reflective-wall problems where diffusers fail; Even quarter-wavelength diffuser depths are too large for low frequencies (+1 more)

Broader Connections

• Even quarter-wavelength diffuser depths are too large for low frequencies #corroborates (0.95)
• Porous sound absorbers work best when positioned at a quarter wavelength from a wall #contradicts (0.80)