Acme Thunderer 560 referee whistle plastic black Small. Two high tone frequencies for loudness close to the whistle and a lower one for the distance that all sound at the same time. Recommended for referees especially in the large stadiums. Loudest whistle in the world, used in FIFA. The bulletless whistle has two frequencies for tone generation. With a slowly increasing sound, this tone penetrates even large crowds of spectators. - Material: plastic - Stands out from background noise - Blowing difficulty: Easy to blow - Blowing sound: Very high volume - Blowing tone: High - Size: 560 (Small) - Dimensions: 4 x 2 x 2.2 cm