I would like to introduce you to Lucien MOATTI, a doctor who is perhaps a bit of a noisemaker in his spare time.
Indeed, he is the inventor of a pack of 4 sound toys (about 100€) which are to be returned, like moo boxes...
But why ? It is, in fact, a hearing screening test intended for pediatric examinations of children from 6 to 24 months!
Each of the 4 "moo boxes" generates the cry of an animal, at a level of 60dB at 2 meters (same as voice), and are to be turned over one by one, without the child seeing them: the cow (250Hz), the sheep (500Hz), the cat (1000Hz) and the bird (more than 2000Hz).
They make it possible to test the good perception of speech frequencies by the child, from 250 to 3000 Hertz. All that remains is to interpret the reaction of the child tested: curious, surprised? He heard them!
More info: www.testmoatti.com