# Review of Acoustic Sources Alternatives to a Dodecahedron Speaker
## 2 Acoustic Source Alternatives to a Dodecahedron Speaker
### Handclap  
Handclap, the production of sound by striking the hands together, is an attractive source for acoustic measurements. It is common for acousticians to excite a room with a handclap in order to assess the quality of the space. It can also be used to detect unwanted acoustic phenomena such as echoes and flutter-echoes [26]. Sound generation by a handclap was the focus of some studies [99; 100]. Research by [PERSON] et al. [99] examined the underlying physics in order to explain the sound variations from a dull that through a low-frequency pulse to a sharp high-frequency snap. Possible simplified geometries of a flat impact and a domed impact were examined. It was shown that a shock wave is generated for configurations of the hands that produce a loud sharp sound. The addition of a Helmholtz-type resonance is involved in the case of domed impacts. An impulse response of a handclap is presented in the same research. Schlieren imaging was used in a study [73] in order to depict shock waves from a handclap. In a study by [PERSON] [100], the different sounds of a handclap were categorized in eight clapping modes according to hand configuration. A description and a figure for each configuration can be found in the research. The author states that additional variations may derive from such factors as hand curvature, stiffness, fleshiness of the palms, tightness of the fingers, precision and striking force. Relevant research by [PERSON] et al. [101] presents an analysis for synthesizing hand clapping sounds. Some research utilized the handclap for acoustic measurements through the use of a smartphone as a sound recorder [102; 103; 104]. Measurements with a handclap were used mainly as a survey method for these studies to monitor room acoustics. Considering omnidirectionality, a study by [PERSON] [71] showed that a handclap has directional characteristics. Measurements in different directions revealed differences of more than 15 dB in certain frequency ranges. Therefore the handclap does not fulfill ISO 3382-1 requirements for omnidirectionality as expected. Concerning repeatability, the handclap may have one of the lowest among acoustic sources. The reason being that the slightest variation of hand configuration may alter the generated impulse and spectral characteristics [100]. Also, there is considerable variability in spectral shapes of handclaps across individuals. In the same research, the amplitude standard deviations ranged from 0.7 to 5.2 dB across subjects. However it was found that it is possible to improve the repeatability of a handclap if it is produced by the same individual utilizing the exact same hand configuration every time. Regarding sound pressure levels, a study measured the handclap to be 75.8 dB [102]. In a study by [PERSON] and [PERSON] [103] the handclap averaged 26.4 dB above the background level (in a concert hall) with a standard deviation of 4.4 dB across measurements. In the same study however it was noted that signal processing steps can be introduced in order to improve its performance as a sound source. However, the handclap as a sound source does not fulfill ISO 3382-1 requirements for sound pressure levels. Relating to frequency response, the handclap can be generated in different ways which result in different frequency responses. As stated before, eight clapping modes according to hand configuration were presented in a study by [PERSON] [100]. It can be seen in all frequency responses that a roll-off is evident below 500 Hz. The same is reported in a similar study [102] and is in accordance with [PERSON] [71] which states \"handclaps suffer from poor low-frequency content\". In a study by [PERSON] [99], measurements of the sound of nominally flat and cupped natural handclaps were made in an anechoic environment. The author states that \"a flat clap produces broad-band sound that typically extends to about 10 kHz while the spectrum of a domed clap usually has a subsidiary maximum somewhere below 1 kHz and then declines with frequency more rapidly than does the flat clap\".