SPEAKER ENCLOSURE DESIGN FOR EFFICIENTLY GENERATING AN AUDIBLE ALERT SIGNAL

• US 20110095900A1
• Filed: 02/09/2010
• Published: 04/28/2011
• Est. Priority Date: 10/23/2009
• Status: Active Grant

• Current Assignee: InnovAlarm Corporation
• Original Assignee: InnovAlarm Corporation
• Inventors: Lewis, James J., Albert, David E., Smith, Landgrave T.
• Granted Patent: US 8,525,689 B2
• Time in Patent Office: Days
• US Class Current: 340/692
• CPC Class Codes: G08B 17/00 Fire alarms; Alarms responsive to explosion
• CPC Class Codes: G08B 17/113 Constructional details
• CPC Class Codes: G08B 3/10 using electric transmission; using electromagnetic transmission
• CPC Class Codes: H04R 1/28 Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means combinations of transducers with horns, i.e. front-loaded horns H04R1/30

Abstract

Various inventive features are disclosed for efficiently generating regulation-compliant audible alerts, including but not limited to 520 Hz square wave alert/alarm signals, using an audio speaker. One such feature involves the use of a non-linear amplifier in combination with a voltage boost regulator to efficiently drive the audio speaker. Another feature involves speaker enclosure designs that effectively boost the output of the audio speaker, particularly at relatively low frequencies. These and other features may be used individually or combination in a given alarm-generation device or system to enable regulation-compliant audible alerts to be generated using conventional batteries, such as AA alkaline batteries. Various examples of efficiently generated regulation-compliant audible alerts and further enhancing such audible alerts by utilizing speaker enclosure designs are provided.

Claims

1. An alarm device, comprising:

a detector configured to detect an alarm condition and generate a detection signal;

a signal processing circuit configured to receive the detection signal from the detector and in response generate an alarm signal having a fundamental alarm signal frequency; and

a speaker assembly comprising a speaker coupled to an enclosure and configured to receive the alarm signal, the speaker assembly configured to have a fundamental resonance frequency that is substantially equal to the fundamental alarm signal frequency, the speaker assembly as a whole configured such that an audible output of the speaker assembly at the fundamental alarm signal frequency is boosted.

2. The alarm device of claim 1, wherein the speaker is mounted substantially within the enclosure.

3. The alarm device of claim 2, wherein the enclosure comprises a front wall coupled to a rear wall by a side wall so as to define an enclosed volume, the front wall defining an opening to allow passage of the first sound signal from the speaker.

4. The alarm device of claim 3, wherein the side wall comprises a cylindrical shaped wall.

5. The alarm device of claim 3, wherein the rear wall comprises a substantially flat plate.

6. The alarm device of claim 3, wherein the speaker is mounted to the front wall.

7. The alarm device of claim 3, wherein the speaker is mounted to the rear wall.

8. The alarm device of claim 3, wherein the speaker is mounted to the side wall.

9. The alarm device of claim 1, wherein the alarm signal comprises a substantially square wave having a number of periods.

10. The alarm device of claim 1, wherein the fundamental alarm signal frequency is in a range between approximately 400 Hz and 700 Hz.

11. The alarm device of claim 10, wherein the fundamental alarm signal frequency is in a range between approximately 510 Hz and 530 Hz.

12. The alarm device of claim 11, wherein the fundamental alarm signal frequency is in a range between approximately 515 Hz and 525 Hz.

13. The alarm device of claim 11, wherein the fundamental alarm signal frequency is approximately 520 Hz.

14. The alarm device of claim 1, further comprising a boosted Class D audio amplifier coupled to the speaker assembly such that the alarm signal is provided to the speaker assembly via the boosted Class D audio amplifier.

15. The alarm device of claim 1, further comprising a direct current power supply configured to provide power to the detector and the signal processing circuit.

16. The alarm device of claim 15, wherein the power supply comprises one or more AA sized batteries.

17. The alarm device of claim 1, wherein the alarm condition comprises an external audible signal generated by a separate alarm device.

18. The alarm device of claim 17, wherein the audible output of the speaker assembly comprises a supplemental alarm to the external audible signal.

19. The alarm device of claim 17, wherein the external audible signal has a frequency between approximately 2,900 Hz to 3,400 Hz.

20. An speaker assembly for an alarm system, the speaker assembly comprising:

a speaker capable of receiving an input electrical signal having a fundamental signal frequency; and

an enclosure having a front portion and a rear portion coupled by a side wall, the speaker mounted to the enclosure such that at least a portion of the speaker is enclosed by the enclosure;

wherein the speaker assembly is configured to have a fundamental resonance frequency that is substantially the same as the fundamental signal frequency, the speaker assembly as a whole configured to generate an audible signal in response to the input electrical signal, the audible signal having an intensity substantially at the fundamental signal frequency, the intensity greater than what would be generated by the speaker alone.

21. The speaker assembly of claim 20, wherein the fundamental signal frequency is in a range of approximately 400 Hz to 700 Hz.

22. The speaker assembly of claim 21, wherein the fundamental signal frequency is in a range of approximately 510 Hz and 530 Hz.

23. The speaker assembly of claim 22, wherein the fundamental signal frequency is in a range of approximately 515 Hz and 525 Hz.

24. The speaker assembly of claim 23, wherein the fundamental signal frequency is approximately 520 Hz.

25. The speaker assembly of claim 20, wherein enhancement in the intensity of the audible signal at the fundamental signal frequency over that of the speaker aloneis at the expense of a reduction in intensity of one or more harmonics of the audible signal.

26. The speaker assembly of claim 25, wherein at least some of the enhancement is due to contribution from one or more of a resonance of the speaker assembly, an interference effect, or an air resonance effect.

27. The speaker assembly of claim 20, wherein the speaker comprises a substantially circular shaped speaker.

28. The speaker assembly of claim 27, wherein the side wall has a substantially cylindrical shape and the rear portion of the enclosure comprises a substantially flat plate coupled to the rear portion of the side wall.

29. The speaker assembly of claim 28, wherein the speaker is mounted to the front portion of the enclosure.

30. The speaker assembly of claim 28, wherein the speaker is mounted to the side wall of the enclosure.

31. The speaker assembly of claim 28, wherein the speaker is mounted to the substantially flat plate such that the speaker and the front portion of the enclosure define a cavity.

32. The speaker assembly of claim 31, wherein front portion of the enclosure comprises a front wall that defines an opening.

33. The speaker assembly of claim 32, wherein the opening and the cavity are dimensioned so as to facilitate a Helmholtz resonance.

34. The speaker assembly of claim 28, wherein the speaker is positioned relative to the substantially flat plate by a distance that is less than approximately ⅛

of a wavelength corresponding to the fundamental signal frequency.

35. The speaker assembly of claim 34, wherein the wavelength is approximately 66.5 cm.

36. The speaker assembly of claim 28, wherein the substantially cylindrical shaped side wall has an inner diameter that is between about 2 inches and 3.5 inches.

37. The speaker assembly of claim 36, wherein the cylindrical shaped side wall has a length that is between about 1.5 inches and 3 inches.

38. The speaker assembly of claim 28, wherein the side wall and the substantially flat plate of the rear portion are formed from plastic.

39. The speaker assembly of claim 38, wherein the side wall and the substantially flat plate of the rear portion are formed from PVC plastic with respective thicknesses in a range of about 0.100 inch to 0.125 inch.

40. The speaker assembly of claim 28, wherein the side wall and the substantially flat plate of the rear portion are formed from metal.

41. The speaker assembly of claim 40, wherein the side wall and the substantially flat plate of the rear portion are formed from sheet metal with respective thicknesses in a range of about 0.005 inch to 0.020 inch.

42. An alarm device, comprising:

a signal processing circuit configured to receive a signal representative of an alarm condition and in response generate an electrical signal having a substantially square wave form and a fundamental frequency in a range of about 400 Hz to 700 Hz; and

a speaker assembly comprising a speaker coupled to an enclosure and configured to receive the substantially square wave electrical signal, the speaker assembly having a resonance frequency that is within said frequency range of 400 Hz to 700 Hz, the speaker assembly configured to generate an audible alert signal in response to the substantially square wave electrical signal.

43. The alarm device of claim 42, wherein the signal processing circuitry comprises a boosted Class D audio amplifier coupled to the speaker assembly such that the substantially square wave electrical signal is provided to the speaker assembly via the boosted Class D audio amplifier.

44. The alarm device of claim 42, further comprising a detector configured to detect the alarm condition and generate the signal representative of the alarm condition.

45. The alarm device of claim 44, wherein the detector comprises a smoke detector.

46. The alarm device of claim 42, wherein the signal processing circuit is configured to detect an audible alert signal generated by a separate detector/alert device, said audible alert signal having a frequency between approximately 2,900 Hz to 3,400 Hz.

47. The alarm device of claim 42, further comprising a battery holder configured to receive one or more AA sized batteries and provide power to the signal processing circuit.

48. A method for fabricating a speaker assembly for an alarm system, the method comprising:

providing a speaker capable of receiving an input electrical signal having a fundamental signal frequency;

forming an enclosure having a front portion and a rear portion coupled by a side wall; and

mounting the speaker to the enclosure;

wherein the speaker assembly is configured to have a fundamental resonance frequency that is substantially the same as the fundamental signal frequency, the speaker assembly configured to generate an audible signal in response to the input electrical signal, the audible signal having an intensity substantially at the fundamental signal frequency, the intensity greater than what would be generated by the speaker alone.

49. A method for designing a speaker assembly, the method comprising:

selecting a speaker;

obtaining a first set of dimensions for an enclosure having a front cap, the front cap defining an aperture, the first set of dimensions sufficient to allow positioning of the speaker within the enclosure such that the enclosure and the speaker at a first position therein define an inner air cavity in communication with outside of the enclosure via the aperture, the first set of dimensions based at least in part on Helmholtz calculation for the inner air cavity, the Helmholtz calculation providing an estimate of a Helmholtz frequency that the inner cavity is capable of facilitating, the Helmholtz frequency selected to be approximately the same as a desired frequency of sound output of the speaker assembly;

configuring enclosure based on the first set of dimensions and positioning the speaker substantially at the first position within the enclosure;

obtaining a resonance frequency of the enclosure with the speaker positioned therein; and

if the resonance frequency differs from the desired frequency by more than a selected amount, adjusting one or more of the first set of dimensions such that resonance frequency corresponding to the adjusted enclosure differs from the desired frequency by less than or equal to the selected amount.