# Review of Acoustic Sources Alternatives to a Dodecahedron Speaker
## 2 Acoustic Source Alternatives to a Dodecahedron Speaker  
This chapter will present fifteen acoustic sources alternatives to a dodecahedron speaker (Table 3). The list includes only sources for which relevant publications were found in the literature. The most common alternative acoustic sources with the most references and practical applications are the balloon, gunshot, firecracker, handclap and inverse horn design. These sources are going to be presented first. The next sources in the list (wooden clapper, shotshell primer, rotation of directional speaker, ultrasound piezoelectric transducer, ring radiator, explosive mixture of acetylene gas with air and compressor nozzle hiss) have a smaller number of references in the literature. Directional speakers which are next in the list are not alternative sources to a dodecahedron speaker since they are not omnidirectional. However, they are used as such and therefore have been included in the list. There is a considerable amount of literature concerning the application of lasers in acoustics. However, a laser-induced breakdown is a relevant new acoustic source with potential for practical applications. Finally, electric spark sources have been mainly used for the simulation of acoustic phenomena using scale models. However, there are some publications where they are used as an alternative source for acoustic measurements and they are therefore included in this review. Emphasis will be placed on features such as omnidirectionality, repeatability, frequency response, adequate sound power, accuracy in measurement of acoustic parameters and fulfillment of ISO 3382-1 sound source requirements. The reason why these features were chosen to be presented in is because they are the most commonly studied features to be found in the literature and they also define the acoustic behavior of acoustic sources. Source omnidirectionality is one of the two sound source characteristics required from the ISO 3382-1 standard. Omnidirectionality ensures uniform space excitation necessary for correct impulse response measurement. The directivity of the source influence the measurement of impulse responses and acoustic parameters of spaces [24; 25]. For each source, we have collected various research that have investigated the directivity of the source in accordance with ISO 3382-1 or with more general criteria. Source repeatability ensures that the same sound filed is produced from the sound source for each measurement and hence similar impulse response and acoustic parameters are measured. Source repeatability is considered to be given for acoustics sources that utilize electrodynamic speakers (e.g., dodecahedron speaker). However, for sources of the impulsive type (e.g., handclaps and balloons) repeatability is not certain and may involve large variations. For each source we have collected relevant data from the literature. \begin{table}
\begin{tabular}{l r} \hline
1. Balloon & 7 \\
2. Gunshot & 9 \\
3. Firecracker & 10 \\
4. Handclap & 11 \\
5. Inverse horn design & 13 \\
6. Wooden clapper & 14 \\
7. Shotshell primer & 15 \\
8. Rotation of a directional speaker & 15 \\
9. Ultrasound piezoelectric transducer (spherical distribution) & 16 \\
10. Ring radiator & 17 \\
11. Explosive mixture of acetylene gas with air & 18 \\
12. Compressor nozzle hiss & 18 \\
13. Directional speaker & 19 \\
14. Laser-induced air breakdown & 20 \\
15. Electric spark source & 21 \\ \hline \end{tabular}
\end{table} 
Table 3: List of acoustic source alternatives to a dodecahedron speaker. Adequate sound pressure levels (according to ISO 3382-1) ensure that there will be no contamination in the acoustic measurements by background noise. Sound pressure levels should be studied in conjunction with a frequency response of the sound source since ISO 3382-1 requires source level at least 45 dB above the background level in the corresponding frequency band (if synchronous averaging is not available).