## 1 Introduction
Investigation from [PERSON] et al. [18] showed that for different balloon types, magnitude of deviations below the 500 Hz octave band are on the order of 6-9 dB, well above the ISO 3382-1:2009 limits [2]. The balloon as a sound source radiates mostly toward the direction of needle impact. Similar results about the omnidirectionality have been reported by [PERSON] [19] and [PERSON] [20]. However hydrogen-oxygen balloons seem to show better omnidirectionality [21]. Concerning the question of repeatability, in contrast to [PERSON] [19], [PERSON] [18] have reported that balloon directivity patterns are stable over repetitions if certain criteria are met. Spectra and radiated sound from a balloon were quite constant for a given balloon type with consistent inflation. Also a study by [PERSON] [20] where anechoic recordings of balloon bursts were systematically acquired for various conditions of balloon diameters, puncture location, and inflation pressure, reports that the results are quite consistent when averaged over one-third octave bands. The study reveals that the diameter factor (the ratio between the diameter of the inflated balloon to that of its stated maximum), rather than the overall diameter of the balloon, is a good indicator of the sound pressure level, especially above 200 Hz. Concerning the measurement of reverberation time with the use of balloons, some research shows good correlation compared with the expected RT [22]. Results suggest that balloons as a sound source can be used with almost no influence on the final result if the measured room is large and reverberant [23]. Also the balloon as a sound source does not offer adequate excitation at the low frequencies which also affects the expected results [24]. However, a technique by [PERSON] et al. [25] can improve the expected results by converting recorded balloon pops into full audio bandwidth impulse responses. A gun, as an explosive sound source, is explicitly specified in the standard ISO 354:2003 as a possible alternative. Traditionally, acousticians have used pistols with blank cartridges for acoustic measurements. A gun is an impulsive noise source that is lightweight and small enough to be easily transported. However, firearms are also difficult to transport on airlines and are frightening to audiences for in situ measurements. Concerning the question of directionality, the handgun does not appear to be an omnidirectional sound source [26; 27]. The pistol appears to be directional at low frequencies, where there is a rise in energy from the side [19]. A study by [PERSON] et al. [28] indicates that especially the muzzle blast is directional. Muzzle blast is the most dominant noise source in gunshots. The measured sound levels on axis, ahead of the muzzle, are higher than levels directly behind the muzzle by up to 20 dB. A study on the acoustical characteristics of different guns by [PERSON] [29] showed that the details of the wedge in front of the firing chamber also influenced the directional properties of the gun. Concerning the question of repeatability, [PERSON] [30] states that differences in the noise characteristics between individual cartridges for the same gun are usually small so the impulsive source can be replicated to a high degree. Finally, the frequency spectrum of a gun typically has a peak energy output in the 1 kHz to 2 kHz region [19]. Below this frequency the energy falls off rapidly. A gunshot can also be a preferred alternative when investigating building acoustics and sound insulation measurements compared to conventional steady state noise sources. As an impulsive source offers the possibility of removing flanking transmission, since gun is much more decoupled with a floor, than a heavy loudspeaker [30]. Firecrackers are not used as often as balloons and fire guns, but they do seem to have some extra advantages. Concerning omnidirectionality, [PERSON] et al. states [31] that if the powder charge is exploded directly, the generated impulse is nearly omnidirectional.