# Review of Acoustic Sources Alternatives to a Dodecahedron Speaker
## 2 Acoustic Source Alternatives to a Dodecahedron Speaker
### Firecracker
Furthermore, the sound-to-noise ratio (SNR) between 1 and 8 kHz was found in a study [26] to be higher compared with measurements with dodecahedron speaker utilizing MLS and ESS signals. In an extensive work by [PERSON] et al. [96], sound pressure levels were measured for many different categories of firecrackers (ground shots, aerial shots and garland type) in an anechoic chamber and in a test site. There are also many kinds of research that have been conducted regarding sound pressure levels of firecrackers [94; 96; 97; 98], related to the effect these levels have on hearing. It should be noted that because firecrackers cause high-pressure levels, care must be taken for the selection of a suitable microphone in acoustic measurements as well as appropriate precautions for the risk of hearing loss. Relating to frequency response, results presented in various research [68; 93; 94] indicate that most energy emitted is concentrated in the frequency range from 500 Hz to 2 kHz with a roll-off below 1 kHz. [PERSON] et al. [26] stated that the biggest drawback of firecrackers is the low sound-to-noise ratio obtained for low frequencies. The same was denoted by [PERSON] et al. [93], that the spectral power of a pseudo impulsive source (firecracker) is not sufficient in the low-frequency range. However, studies by [PERSON] et al. [94] and [PERSON] et al. [68] presented frequency spectra for different firecrackers showed that the maximum of energy is shifted towards lower frequencies with the increase of amount of explosive. The largest firecracker measured by [PERSON] et al. [68] exceeds 100 dB in the low-frequency range. This observation leads to the conclusion that in order to satisfy the ISO 3382-1 sound pressure level requirements (45 dB SNR) at low frequencies, the selection of the appropriate firecracker is necessary. Hence the utilization of firecrackers as an acoustic source in the low-frequency range should be exercised with caution and in conjunction with knowledge of the background noise levels for the optimal firecracker selection. In regard to the measurement of acoustic parameters, [PERSON] et al. [26] present the most comprehensive research. Impulse response measurements across different halls performed with firecrackers (ten explosions) and two commercial dodecahedron speakers. The authors state that if both techniques are applied correctly, similar values are obtained for the acoustic parameters. In the same research, the STD for T\({}_{30}\), C\({}_{80}\), and G was also compared for the two sources (firecracker, dodecahedron speaker). The STD was found to be greater for the firecracker in the low-frequency range for T\({}_{30}\) measurements across different enclosures. However the STD is remarkably higher for the dodecahedron speaker for C\({}_{80}\) and source strength (G) in the high-frequency range across different enclosures. In a study by [PERSON] et al. [93] acoustic measurements were performed with a firecracker. In the study it is stated that \"average values for EDT were practically identical to those obtained with two other recent techniques\" (however the techniques were not identified in the study). Also in a study by [PERSON] et al. [75] measurements of acoustic parameters were performed with firecrackers, but they were only compared with measurements performed with balloons. In conclusion, the firecracker as a sound source can potentially meet the ISO 3382-1 requirements concerning omnidirectionality. Research needs to be carried out according the ISO 3382-1 measurement procedure to certify that the firecracker can cover this requirement. Concerning the sound pressure levels requirements of ISO 3382-1, as stated in the introduction, they need to be at least 45 dB above the background level in the corresponding frequency band. Whether this condition is met depends on the firecracker used and the sound level that it creates in the low-frequency range, as well as the background noise in this frequency range.