Challenges of acoustic measurements in performance sites

Why a monopole sound source outperforms dodecahedron loudspeakers

A monopole omni-directional sound source will provide the most accurate room acoustic measurements. These can be applied to any type of closed or semi-closed space (e.g. office spaces, apartment buildings but above all, this level of accuracy is most interesting for measurements in theaters, churches, opera houses and concert halls. When conducting measurements in performance sites, monopole sound sources outperform dodecahedron loudspeakers.

Its a real challenge to take measurements inside performance sites where control of sound quality and intelligibility are crucial factors.

These type of room acoustic measurements include:

  • Room Impulse Responses
  • Reverberation Time
  • Speech Transfer Measurements

Qsources Qohm: a high power dodecahedron for a broad range of measurement applications

The Qsources Qohm lightweight omni-directional sound source is also perfectly suitable to take measurements in musical performance sites. The highly uniform sound radiation from the Qohm source allows controlled excitation of the acoustics of small and large sites. The maximum sound power level of 122 dB Lw and a high output at 50 Hz, 97 db Lw makes the Qohm utmost suitable for a broad area of applications such as airborne isolation testing and reverberation testing.

Possible issues using an omni-directional dodecahedron

Studies show that in the frequency bands ranging from 125Hz. to 1kHz. octaves, all types of omni-directional sound sources can be used. However, above 1kHz. measurements might be afflicted by using for instance a 12-speaker dodecahedron sound source*.

The solution: Qoms2 Monopole speaker

Qsources Qoms2 is monopole omni-directional source which include 2 unique Qsources QP4 drivers.
This small & lightweight source is powerful enough for measurements in any type of performance site. In addition, it’s suitable for broadband measurements in wide frequency range (1/3 octaves: 50-16000 kHz.). Next to the output benefits, the light weight (1.25 kg) and the small dimensions (10.6cm) diameter allow this sound source and its measurement amplifier (Qam or Qca) to be taken on site and set up in a stress free and fast manner.

The Qoms2 speaker is designed to conform to amongst other ISO 140, ISO 3382, ISO 16283 and 14275.

The below directivity plots show that Qoms2 provides a smoother output than our high power, dodecahedron speaker Qohm.

The below images also show why the measurements of Qoms2 are more precise than standard omni-directional speakers or dodecahedrons on the market.

When measured in tangential direction, the radial pattern showcases nearly perfect omni-directionality.

In axial position, the directivity is nearly perfect up to 4 kHz. & remains smooth, spherical and balanced in the highest octave bands up to 16 kHz.


In summary, the above directivity results would be impossible to achieve using a standard omni-directional loudspeaker given these will show aspherical patterns above the frequency level of 1kHz. For certain type of measurements where intelligibility and sound control are very important, such as measurements of musical performance sites, the Qsources Qoms2 monopole sound source outperforms dodecahedron loudspeakers.

*Relevant studies include:
Influence of loudspeaker directivity on the measurement uncertainty of the acoustic testing of facades. (Pedrero, Sanchez, Ulin & Diaz; 2011)
Uncertainties caused by source directivity in room-acoustic investigations (San Martin & Arana, 2008)
Uncertainties in measurement of single number parameters in room acoustics (Witew, Behler; 2005)