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Adding material to lengthen Shofar: 
If any material was added to lengthen the size of a Shofar in a way that the sound passes through this addition, the Shofar is invalid. This applies even if the Shofar was already Kosher, containing the minimum required measurement, prior to adding the material to lengthen it. It applies whether the added material is made of horn or of other matter. It applies whether the material was added to the narrow end or the wide end. [It applies even if the sound of the Shofar did not change at all due to the addition and even if the material was only added to the thickness of the end of the Shofar in a way that it slightly added to its length.]
 The reason: The reason for this is because the sound of the Shofar protrudes through the added material and the Torah validated only the sound which protrudes from a single Shofar and not from two Shofros. [586/10]
 586/17; Admur writes “even if it was added to the wide part by the thickness of the Shofar in a way that it lengthened in size”. Simply this means that one added material to the wide end as opposed to the narrow end. This law was already states in 586/11. Perhaps however it also refers to the top part of the wide end of the Shofar that extends more than then the opposite side of the wide end and hence the novelty is that an extended coating even in that area is invalid.