Boundary-layer recording: why the capsule belongs close to the surface

When a microphone sits some distance above a table, stage, or floor, sound from the same source reaches the capsule once by the direct path and again by the reflected path. The delayed signals add and cancel at different frequencies, producing comb filtering. Moving the capsule close to the boundary reduces that path difference at the source instead of trying to guess an EQ correction after the recording.[1][2]

As the panel becomes small relative to wavelength, sound bends around its edges and the low frequencies behave less like they are meeting an infinite boundary. Shure likewise notes that the reflecting surface must be large relative to wavelength and that low frequencies diffract around a small boundary.[2] The current D-PZM specifications list a panel size of 24.7 × 17.8 cm.[5] That dimension is useful for planning the physical footprint, but it cannot by itself prove equal boundary gain from 20 Hz to 20 kHz. Any detailed response claim requires measurements from a defined placement.

For boundary-layer recording, keep the capsule as close to the panel as practical and place the panel on a stable, hard support. Thick carpet, soft pads, lifted edges, or a cavity beneath the panel can change both reflection and structural vibration. If a small panel must sit on a larger table or floor, also check whether the step between the panel edge and the surrounding surface creates another reflection. A sweep or segmented listening test with the actual source is more reliable than judging the setup from a placement photo alone.[2][3]