Sound sponge for loudspeakers
View Patent ↗The specification and drawings present a new method and apparatus for reducing loudspeaker size by partitioning the back cavity of the loudspeaker using a sound sponge block. The sound sponge block is an array of narrow ducts (e.g., parallel ducts, or parallel round cylinders of a small diameter) made of a pre-selected material with predetermined dimensions (e.g., the diameter and length) formed within a single block which is placed behind a loudspeaker diaphragm but not in a direct contact with it. The sound sponge block, comprising the multiple very narrow ducts (e.g., with duct diameters on the order of microns) substantially absorbs the sound waves radiated from a rear side of the diaphragm in the backward direction due to significant drop in the impedance for very narrow tube diameters.
1. A sound sponge block, comprising:
multiple ducts made of a pre-selected material, said multiple ducts being substantially equal in length and having predetermined geometrical dimensions, configured to substantially absorb the sound waves from a rear side of a diaphragm in a backward direction when said sound sponge block is placed behind said diaphragm without physically touching said diaphragm,
wherein said diaphragm is configured to provide an acoustic signal by a way of vibrations in forward and backward directions.
2. The sound sponge block of claim 1 , wherein said multiple ducts are round cylinders.
3. The sound sponge block of claim 2 , wherein said round cylinders have a diameter between 0.1 and 10 microns.
4. The sound sponge block of claim 1 , wherein ends of said multiple ducts furthest from the diaphragm are sealed and have an infinite specific termination impedance.
5. The sound sponge block of claim 1 , wherein said multiple ducts are parallel to each other.
6. The sound sponge block of claim 1 , wherein said multiple ducts are substantially perpendicular to a surface of said diaphragm.
7. The sound sponge block of claim 1 , wherein a cross section of said multiple ducts comprise 90% or less of a total cross section area of said sound sponge block.
8. The sound sponge block of claim 1 , wherein the sound sponge block has a real part of an acoustic impedance substantially constant in a predetermined frequency range.
9. The sound sponge block of claim 8 , wherein predetermined said frequency range is from 10 Hz to 10,000 Hz.
10. The sound sponge block of claim 1 , wherein ends of said multiple ducts furthest from the diaphragm are sealed and have an infinite specific termination impedance.