AES Europe 2026

The Zylia ZM-1 (19 MEMS capsules, spherical array, 88 mm
diameter, 3rd-order); Harpex Spcmic (84 MEMS capsules,
planar array, 230 mm diameter, 5th-order capable) represent
two distinct geometrical approaches to higher-order
Ambisonics capture. Despite widespread adoption in research
; production, systematic comparison of their performance
in real-world recordings remains absent from published
literature. This case study presents a controlled
comparison through simultaneous recordings of piano
recitals in the same concert hall.

Two arrays—Zylia ZM-1; Harpex Spcmic—were mounted on a
single stereo bar (17 cm apart) ensuring acoustically
identical capture positions. Recording sessions occurred in
Aula Politechniki Gdańskiej (370-seat hall, RT60 = 1.97 s)
on two dates: August 15, 2024 (Franck: Prélude, Choral et
Fugue; Prokofiev: Piano Sonata No. 4, 35.6 minutes
total); April 30, 2024 (Ginastera: Sonata No. 1, Op. 22,
15.4 minutes). Both arrays recorded simultaneously; files
were processed through manufacturer A-to-B conversion
software; peak-normalized to −0.5 dBTP. The Spcmic was
encoded to both native 5th-order; truncated 3rd-order
formats for direct comparison with the ZM-1.

Four metrics were analyzed: (1) W-channel spectral
response, (2) integrated loudness (LUFS-I per ITU-R
BS.1770-5), (3) spatial energy distribution across
Ambisonics orders,; (4) first-order directional
component ratios.

Spectral analysis reveals the ZM-1 exhibits 5–8 dB
elevation at 200–600 Hz relative to the Spcmic. Loudness
measurements show the Spcmic 3rd-order yields 2.3–3.3 dB
higher LUFS-I than the ZM-1 despite identical peak
normalization.

The primary finding concerns spatial energy: the ZM-1
exhibits 27.4 dB attenuation from 0th to 3rd order, while
the Spcmic shows only 8.4 dB—a 19 dB difference despite
both producing "3rd-order Ambisonics" format. Analysis of
both recording sessions confirms consistency across
different repertoire (romantic, 20th-century,
contemporary). Directional analysis shows the Spcmic
exhibits stronger first-order components (X/Y/Z ratios
0.68–0.83) versus the ZM-1 (0.42–0.55).

Results demonstrate that nominal Ambisonics order
inadequately characterizes spatial resolution in real
recordings. The substantial higher-order energy deficit in
compact spherical arrays has implications for reproduction
quality, decoder design,; archival standards. Arrays
with steeper rolloff may require order-dependent gain
compensation to match spatial impression of larger systems.

This case study complements existing anechoic validation by
demonstrating performance differences in authentic
recording conditions. Recordings are part of a publicly
available HOA corpus (Gdańsk University of Technology
repository).