378333
This phase plug directed sound waves into the horn throat from the center of the diaphragm and from a ring around the perimeter of the diaphragm , by way of center hole and annular slot , for the purpose of improving " the transmission characteristics " of the loudspeaker " at the upper portion of the sound frequency range . "
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None