## 1 Introduction
Its directivity index is, on average, around 1 dB for the octave bands between 125 Hz and 16 kHz. Concerning repeatability the firecrackers do not guarantee the extraordinary repeatability of techniques based on deterministic signals [7]. However, [PERSON] et al. [32] states their repeatability being better than that of the balloons. The biggest drawback of firecrackers is the low sound to noise ratio obtained for low frequencies and long distances [7]. Firecrackers and other explosive sources are superior to balloons compared by the maximum peak sound pressure level [33]. The spread of the values obtained with firecrackers for acoustic parameters is smaller than that of the balloons. However, the common difficulty for these sources is to satisfy a suitable dynamic range for low frequencies. A hand clap is an attractive acoustic stimulus because it can be produced easily and without special equipment. However it also suffers from poor low frequency content and poor omnidirectionality [19]. Compared with other types of impulse sources, it has the lowest repeatability because the spectral characteristics of the generated impulse vary depending on how the claps are generated. Hand clap lacks the high energy and consistency of other impulse sources, such as pistol shots, but signal processing steps can be introduced in order to improve its performance [34]. A specially designed wooden clapper is an alternative sound source intended to operate as an impulse source for acoustic measurements [35]. However, measurements performed in rooms located in urban environments, where the ambient noise level is high, showed that the dynamic range for the lower octave band might be insufficient and that the measurement results have to be considered valid for the octave band at 250 Hz and higher. Diagrams of directivity show that the clapper has a better uniformity of sound radiation compared to a gun or a balloon burst. If the clapper is operated by a trained person the results of its impulse repeatability are better than those of balloons and firecrackers. Nonetheless, the clapper directivity is worse than that of a standard omnidirectional loudspeaker. The radiation of the wooden clapper is within the limits established by ISO 3382-1:2009 only at higher frequencies. Discharging a shotsell primer down a tube has proved to be a reliable method of producing an impulse sound [36]. It has a peak level of about 145 dB and a useful frequency content varying between 100 Hz and 10 kHz. However the study seems to support that there is lack of omnidirectionality as a sound source. The inverse horn design is a type of omnidirectional sound source, consisting of a loudspeaker feeding a small aperture through a reverse horn for concentrating the acoustical energy. Results prove that careful design makes it possible to construct a very compact omnidirectional sound source satisfying the international standards and involving only one loudspeaker [37]. However, the total sound power available is lower than with traditional omnidirectional sources (dodecahedron speakers): 85 dB in each one-third-octave band between 100 Hz and 5 kHz, 102 dB full band. On the other hand, the directivity diagram is much smoother. The polar response of the proposed design is omnidirectional between well above 5 kHz, making this design more robust at high frequencies than the popular polyhedral designs [38]. With this in mind, there is still a need for an inexpensive, practical, omnidirectional sound source for measuring impulse responses with good repeatability without the use of a dodecahedron speaker. Few researchers have addressed the question of utilizing a common, directional loudspeaker for acoustic measurements [39]. This study set out to explore the suitability of a common, directional loudspeaker for mimicking the sound field created by a dodecahedron speaker for impulse response measurements.