Acoustic chamber with low frequency transparency

1. An acoustic chamber, comprising:

an inner wall encompassing an interior of the acoustic chamber and configured to allow acoustic energy to penetrate the inner wall;

acoustic absorber lining an interior side of the inner wall at least in part and having a cutoff frequency below which acoustic energy is not effectively absorbed by the acoustic absorber; and

a perforated outer wall in close proximity to the inner wall, the perforations configured to allow low frequency acoustic energy that penetrates the acoustic absorber and inner wall to penetrate the outer wall and leave the acoustic chamber, the perforated outer wall passing acoustic energy below the cutoff frequency of the acoustic absorber and blocking acoustic energy above the cutoff frequency;

the inner wall, the acoustic absorber and perforated outer wall forming a composite wall having a high pass reflectivity frequency response.

2. The acoustic chamber of claim 1 , wherein the outer wall has a high pass reflectivity frequency response.

3. The acoustic chamber of claim 1 , wherein a frequency response of the outer wall to pass acoustic energy below the cutoff frequency of the acoustic absorber and to block acoustic energy above the cutoff frequency of the acoustic absorber is adjusted by choice of at least one of the size and density of the perforations.

4. The acoustic chamber of claim 1 , further configuring acoustic lining material between the inner wall and the outer wall, the lining material and the inner wall being configured to substantially absorb acoustic energy above the cutoff frequency of the absorber and to pass acoustic energy below the cutoff frequency of the absorber.

5. A method of constructing an acoustic chamber, the method comprising:

constructing an inner wall configured to encompass an interior region of the acoustic chamber; the inner wall being at least partially acoustically penetrable;

lining an interior side of the inner wall at least in part with acoustic absorber, the acoustic absorber having a cutoff frequency below which acoustic energy is not substantially absorbed and above which acoustic energy is substantially absorbed;

constructing a perforated outer wall in proximity to the inner wall, the outer wall passing acoustic energy below the cutoff frequency of the acoustic absorber and blocking acoustic energy above the cutoff frequency of the acoustic absorber;

the inner wall, the acoustic absorber and perforated outer wall forming a composite wall having a high pass reflectivity frequency response.

6. The method of claim 5 , further comprising installing acoustic absorbing material between the inner wall and the outer wall.

7. The method of claim 5 , wherein the acoustic penetrability of the outer wall is frequency-dependent.

8. The method of claim 5 , wherein the acoustic penetrability of the inner wall is frequency-dependent.

9. The method of claim 5 , wherein a reflectivity frequency response associated with the outer wall has a high pass component.

10. The method of claim 5 , wherein the outer wall has a high pass reflectivity frequency response.

11. The method of claim 5 , wherein a frequency response of the outer wall to pass acoustic energy below the cutoff frequency of the acoustic absorber and to block acoustic energy above the cutoff frequency of the acoustic absorber is adjusted by choice of at least one of the size and density of the perforations.

12. The method of claim 5 , further configuring acoustic lining material between the inner wall and the outer wall, the lining material and the inner wall being configured to substantially absorb acoustic energy above the cutoff frequency of the absorber and to pass acoustic energy below the cutoff frequency of the absorber.

13. A method of constructing a composite wall for an acoustic chamber, the method comprising:

constructing an inner wall having an acoustically penetrable surface;

lining an interior side of the inner wall with acoustic absorber, the acoustic absorber having a cutoff frequency below which acoustic energy is not substantially absorbed by the acoustic absorber and above which acoustic energy is substantially absorbed by the acoustic absorber; and

constructing a perforated outer wall in proximity to the inner wall and having a surface that is acoustically penetrable below the cutoff frequency of the acoustic absorber and acoustically impenetrable above the cutoff frequency of the acoustic absorber, the inner wall, the acoustic absorber and perforated outer wall forming a composite wall having a high pass reflectivity frequency response.

14. The method of claim 13 , wherein the outer wall is substantially parallel to the inner wall.

15. The method of claim 13 , wherein the outer wall has a high pass reflectivity frequency response.

16. The method of claim 13 , wherein a frequency response of the outer wall to pass acoustic energy below the cutoff frequency of the acoustic absorber and to block acoustic energy above the cutoff frequency of the acoustic absorber is adjusted by choice of at least one of the size and density of the perforations.

17. The method of claim 13 , further configuring acoustic lining material between the inner wall and the outer wall, the lining material and the inner wall being configured to substantially absorb acoustic energy above the cutoff frequency of the absorber and to pass acoustic energy below the cutoff frequency of the absorber.