Passive acoustical filters incorporating inserts that reduce the speed of sound
There is disclosed a passive acoustical filter including a first filter element coupled between an ambient and an ear of a listener, at least a portion of the first filter element filled with a material in which a speed of sound is lower than a speed of sound in air.
1. A passive acoustical filter to be coupled between an ambient and an ear of a listener, comprising:
a double-stage low-pass filter comprising a first low-pass filter element in series with a second low-pass filter element, expansion chambers of the first low-pass filter element and the second low pass filter element filled with respective inserts made from a material in which a speed of sound is lower than a speed of sound in air.
2. The passive acoustical filter of claim 1 , wherein the material in which the speed of sound is lower than the speed of sound in air is a reticulated material.
3. The passive acoustical filter of claim 2 , wherein the reticulated material is selected from a plastic foam material, cotton fibers, bamboo fibers, and yarn.
4. The passive acoustical filter of claim 1 , wherein the double-stage low-pass filter is coupled in parallel with a high-pass filter element.
5. A passive acoustical filter to be coupled between an ambient and an ear of a listener, comprising:
a high pass filter element; and
a low-pass filter element in parallel with the high-pass filter element, an expansion chamber of the low-pass filter element filled with an insert made from a material in which the speed of sound is lower than a speed of sound in air.
6. The passive acoustical filter of claim 5 , wherein the material in which the speed of sound is lower than the speed of sound in air is a reticulated material.
7. The passive acoustical filter of claim 6 , wherein the reticulated material is selected from a plastic foam material, cotton fibers, bamboo fibers, and yarn.
8. A passive acoustical filter comprising:
an earbud including a first opening to receive sound from an ambient and a second opening to output filtered sound to an ear of a listener; and
a low-pass filter element contained within the earbud and coupled between the first opening and the second opening, the low-pass filter element comprising an expansion chamber filled with an insert made from a material in which a speed of sound is lower than a speed of sound in air; and
a high-pass filter element contained within the earbud and coupled in parallel with the low-pass filter element,
wherein a cutoff frequency of the low-pass filter element is equal to or less than 200 Hz.
9. The passive acoustical filter of claim 8 , wherein the material in which the speed of sound is lower than the speed of sound in air is a reticulated material.
10. The passive acoustical filter of claim 9 , wherein the reticulated material is selected from a plastic foam material, cotton fibers, bamboo fibers, and yarn.
11. A passive acoustical filter, comprising:
an earbud having a first opening to receive sound from an ambient and a second opening to output filtered sound to an ear of a user; and
a double-stage low-pass filter contained within the earbud and coupled between the first opening and the second opening, the double-stage low-pass filter comprising a first-low-pass filter element in series with a second low-pass filter element, the first and second low-pass filter elements respectively comprising first and second expansion chambers filled with respective inserts made from a material in which the speed of sound is lower than the speed of sound in air,
wherein cutoff frequencies of both the first low-pass filter element and the second low pass filter element are equal to or less than 200 Hz.
12. The passive acoustical filter of claim 11 , wherein the double-stage low-pass filter is coupled in parallel with a high-pass filter element.
13. The passive acoustical filter of claim 11 , wherein the material in which the speed of sound is lower than the speed of sound in air is a reticulated material.
14. The passive acoustical filter of claim 13 , wherein the reticulated material is selected from a plastic foam material, cotton fibers, bamboo fibers, and yarn.