Patent Description:
Typical building fire alarm systems include a number of fire detectors positioned throughout a building. Signals from those detectors are monitored by a system controller, which, upon sensing an alarm condition, initiates operation of one or more notification devices to provide an audio or visual alarm indication to persons within the building. Speakers or horns used in notification devices are typically required to be relatively compact, but capable of producing sound with a suitable intensity within the hearing range of the human ear. The sound output level and current draw are key performance metrics for such a sound generation device.

A piezo sounder is a high intensity sound source usable in a notification device. The piezo sounder is both cost effective and power efficient. However, piezo sounders may experience an adverse loss in sound level as the temperature of the notification appliance departs from a nominal temperature of about <NUM>. More specifically, the resonance and drive frequencies associated with operation of a piezo sounder are designed to match at the nominal temperature. However, these frequencies tend to drift apart as the temperature deviates, both increases and decreases, relative to the nominal value. The greater the mismatch between the resonance and drive frequencies, the greater the loss in sound pressure level generated by the piezo sounder.

<CIT> describes a sound reproduction device including a modulator having an output terminal for outputting a modulated carrier wave signal. The ultrasonic wave source is configured to output the carrier wave signal such that the signal output from the differential amplifier unit is constant. This sound reproduction device can reduce deterioration of sound quality even is temperature changes.

The method of operating a sound generation mechanism according to claim <NUM> includes determining a temperature of the sound generation mechanism, identifying a resonant frequency of the sound generation mechanism associated with the determined temperature, and communicating an excitation frequency to the sound generation mechanism. The excitation frequency is selected in response to the resonant frequency associated with the determined temperature. The sound generation mechanism is operated to produce one or more sounds.

In addition to one or more of the features described above, in further embodiments the excitation frequency is generally equal to the identified resonant frequency associated with the determined temperature.

In addition to one or more of the features described above, in further embodiments the excitation frequency communicated to the sound generation mechanism varies based on the determined temperature.

In addition the features described above, the excitation frequency is selected to minimize a difference between the identified resonant frequency associated with the determined temperature and the excitation frequency.

In addition to one or more of the features described above, in further embodiments determining the temperature of the sound generation mechanism includes sensing a temperature of an environment surrounding the sound generation mechanism.

In addition to one or more of the features described above, in further embodiments determining the temperature of the sound generation mechanism includes sensing a temperature of one or more components of the sound generation mechanism directly.

In addition to one or more of the features described above, in further embodiments determining the temperature of the sound generation mechanism includes inferring a temperature of the sound generation mechanism from other available data.

In addition to the features described above, identifying the resonant frequency of the sound generation mechanism associated with the sensed temperature includes selecting a stored value of the resonant frequency from a database.

In addition to one or more of the features described above, in further embodiments identifying a resonant frequency of the sound generation mechanism associated with the sensed temperature includes calculating the resonant frequency in response to the determined temperature.

In addition to one or more of the features described above, in further embodiments the sound generation mechanism is a piezoelectric sounder and communicating the excitation frequency to the sound generation mechanism further comprises communicating the excitation frequency to a piezoelectric diaphragm of the piezoelectric sounder.

In addition to one or more of the features described above, in further embodiments comprising a sound driver for communicating the excitation frequency to the sound generation mechanism.

The notification device according to claim <NUM> includes a sound generation mechanism configured to generate sound waves and a notification horn circuit including a sound driver operable to supply a voltage to the sound generation mechanism to generate one or more sound waves. An excitation frequency associated with the voltage supplied to the sound generation mechanism is selected based on a resonant frequency and the resonant frequency is determined based on a temperature of the sound generation mechanism.

In addition to one or more of the features described above, in further embodiments the excitation frequency is selected to maximize a sound pressure level of the sound waves at the temperature.

In addition to one or more of the features described above, in further embodiments the excitation frequency is selected to reduce a difference between the resonant frequency and the excitation frequency at the temperature.

In addition to one or more of the features described above, in further embodiments the excitation frequency selected is generally equal to the resonant frequency at the temperature.

In addition to one or more of the features described above, in further embodiments the sound generation mechanism is operable over a range of temperatures.

In addition to the features described above, the sound generation mechanism includes a piezoelectric sounder.

In addition to the features described above, it is comprising a module for determining the temperature of the sound generation mechanism.

In addition to the features described above, the module for determining the temperature of the sound generation mechanism includes a temperature sensor.

With reference now to <FIG>, an example of a piezoelectric sounder <NUM> of a notification device (not shown) is illustrated. The sounder <NUM> includes an outer curved wall <NUM>. One or more curved inner walls <NUM> disposed inwardly of the outer wall <NUM> form a boundary of a resonant chamber <NUM>. The sounder <NUM> additionally includes a cover <NUM> oriented generally perpendicular to the outer wall <NUM> and the inner wall <NUM>. As shown, the cover <NUM> forms the top wall of the resonant chamber <NUM>. A sound port <NUM> is formed in the cover at a central portion of the resonant chamber <NUM>. Mounted adjacent an opposite surface of the resonant chamber <NUM> is a piezoelectric diaphragm <NUM>. In an embodiment, the piezoelectric diaphragm <NUM> forms a narrow point of contact with the inner wall <NUM>, illustrated at <NUM>. In an embodiment, this narrow point of contact may be located at a central portion of the piezoelectric diaphragm <NUM>, such as at a location about <NUM>% of the radius of the diaphragm for example, and may extend around an annulus.

As best shown in <FIG>, the sounder <NUM> includes a piezoelectric diaphragm <NUM> including a piezoelectric material <NUM> positioned in overlapping arrangement with a plate <NUM>. The piezoelectric material <NUM> may include any suitable material having piezoelectric properties, such as a piezoelectric ceramic for example. The plate <NUM> may be formed from any suitable material, including but not limited to a metal, such as brass for example. As shown, the piezoelectric material <NUM> is disposed centrally on the plate <NUM> and is suitably secured thereto. An electrode <NUM> may be positioned in overlapping arrangement with a portion of the piezoelectric material <NUM>, such that the piezoelectric material <NUM> is at least partially sandwiched between the electrode and the plate. In such embodiments, the plate <NUM> is configured as a second electrode and electrical input lines 48A, 48B extend from the first and second electrodes <NUM>, <NUM>, respectively. A voltage is applied to the piezoelectric material <NUM> via the electric input lines 48A, 48B.

When a voltage having a first polarity is applied to the piezoelectric diaphragm <NUM>, the diaphragm <NUM> bends in a first direction. Similarly, when a voltage having a second polarity is applied to the piezoelectric diaphragm <NUM>, the diaphragm <NUM> bends in a second, opposite direction Accordingly, when an oscillating electrical signal is applied to the piezoelectric diaphragm <NUM>, the piezoelectric diaphragm <NUM> vibrates in a repeated bending mode, causing the piezoelectric material <NUM> to change shape and generate sound waves by this movement. The sound waves generated will travel from resonant chamber <NUM> into the atmosphere via the sound port <NUM> formed in the top wall <NUM> of the resonant chamber <NUM>. The chamber <NUM> allows resonance to occur at certain frequencies based on the chamber volume, port volume, and the mass and resilience of the fluid within the chamber. It should be understood that the sounder <NUM> and the piezoelectric diaphragm <NUM>, illustrated and described herein are intended as an example only and that other configurations of a piezoelectric sounder for use in a notification device are also within the teaching of the disclosure.

With reference now to <FIG>, an example of a notification horn circuit <NUM> for operating a piezoelectric sounder, such as sounder <NUM> for example, is illustrated. As shown, the notification horn circuit <NUM> includes a sound engine <NUM> operable to generate and form an acoustic signal and a sound temporal pattern generator <NUM> responsible for generating one or more frequencies. In the illustrated, non-limiting embodiment, the sound temporal pattern generator <NUM> includes a temporal code generator <NUM> and a module for generating acoustic roughness <NUM>. The temporal code generator <NUM> is configured to generate a temporal code to indicate the presence of an alarm. In an embodiment, the code includes a combination of acoustic pulses separated by pauses or periods of silence, and each of the pulses and pauses may last for identical or varying lengths of time. An example of a code generated by the temporal code generator <NUM> includes a "fire pattern" consisting of a first pulse on for a half second, a first pause for a half second, a second pulse on for a half second, a second pause for a half second, a third pulse on for a half second, a third pause for a half second followed by a <NUM> second pause. Alternatively, the code generator <NUM> may generate a continuous "alarm tone.

The code generated by the temporal code generator <NUM> is communicated to the acoustic roughness module <NUM>. Within the acoustic roughness module <NUM>, a special modulation of the code is performed. This modulation is intended to enhance the ability of the sound wave being generated to attract attention. In an embodiment, the acoustic roughness module <NUM> is configured to modulate the waveform to mimic that of a human scream by including an additional low frequency into the temporal pattern.

A signal including a combination of the code and the acoustic roughness to be applied thereto is provided to a power control module <NUM> in communication with the sound engine <NUM>. As shown, the power control module <NUM> receives an input current from a notification appliance circuit <NUM> of an alarm system and communicates a drive current to a sound driver <NUM> of the sound engine <NUM>. In addition, the acoustic roughness module <NUM> simultaneously communicates the combination of the temporal code and the acoustic roughness to an excitation frequency generator <NUM> of the sound engine <NUM>.

The excitation frequency generator <NUM> typically communicates the temporal code, the acoustic roughness, and an excitation frequency, such as <NUM> for example, to the sound driver <NUM>. The sound driver <NUM>, powered by the drive current from the power control <NUM>, uses this information to supply power to the piezoelectric sounder <NUM>, and more specifically to the piezoelectric diaphragm <NUM>, to generate a desired acoustic pattern and frequency, illustrated schematically at <NUM>. In the illustrated, non-limiting embodiment, the piezoelectric sounder <NUM> is shown including an electro-acoustic transducer <NUM> and an acoustics Helmholtz resonator <NUM>. However, it should be understood that a piezoelectric sounder <NUM> having another suitable configuration is also within the teaching of the disclosure.

With reference to <FIG>, a maximum sound pressure level is achieved by the sounder <NUM> when the resonance frequency of the sounder <NUM> and the excitation frequency generated by the excitation frequency generator <NUM> match. In an embodiment, the sounder <NUM> is typically designed such that the resonance frequency and the excitation frequencies match when the sounder <NUM> is at a nominal temperature of about <NUM> or room temperature. It can be seen from the graph that the sound pressure level output from a piezoelectric sounder <NUM> at a fixed excitation frequency varies in response to the temperature of the sounder <NUM>. Accordingly, the resonant frequency of the resonant chamber <NUM> of the sounder <NUM> varies with temperature. As shown, the sound pressure level output from the sounder <NUM> gradually reduces as the temperature of the sounder <NUM> deviates from this nominal temperature due to an increasing discrepancy or mismatch between the resonance frequency and the excitation frequency.

Accordingly, the sound pressure level output by the sounder <NUM> may be enhanced by determining the temperature of the sounder <NUM> and compensating for the difference between the identified temperature and the nominal temperature of the sounder <NUM>. With reference again to <FIG>, the sound engine <NUM> of the notification horn circuit <NUM> additionally includes module <NUM> for determining the temperature of the sounder <NUM>. In an embodiment, the module <NUM> includes a sensor for monitoring the ambient temperature surrounding the sounder <NUM>. However, any suitable mechanism for detecting the temperature of the sounder <NUM> itself (or one or more of its components), or the environment surrounding the sounder <NUM> is contemplated herein. Alternatively, the module <NUM> may estimate or infer the temperature of the sounder <NUM> from other available data, such as from power consumption of the sounder <NUM> for example.

The sound engine <NUM> additionally includes a resonant frequency compensation module, illustrated schematically at <NUM>, configured to identify the resonant frequency associated with the sensed temperature. In an embodiment, the resonant frequency compensation module <NUM> includes or is able to access a stored database or table identifying a resonant frequency of the sounder <NUM> associated with various temperatures within a temperature range. Alternatively, or in addition, the module <NUM> may be able to determine, such as via an algorithm or other calculation for example, the resonant frequency of the sounder <NUM> using the temperature identified by the temperature determination module <NUM>.

The resonant frequency identified by the resonant frequency compensation module <NUM> indicates the ideal frequency provided by the excitation frequency generator so that the resonant frequency of the sounder <NUM> at the identified temperature and the excitation frequency generally match. Accordingly, the excitation frequency is adjusted to reduce or eliminate the difference between the resonant frequency and the excitation frequency at a given temperature. The resonant frequency identified by the module <NUM> is communicated to the excitation frequency generator <NUM>. The excitation frequency generator <NUM> will identify the closest possible excitation frequency available and communicate that to the sound driver <NUM> for implementation during operation of the piezoelectric diaphragm <NUM>. Although the compensation system and method is illustrated and described herein with respect to a sounder, it should be understood that the system and method may be adapted for use with any sound generation mechanism where the sound output therefrom may vary significantly depending on temperature.

Claim 1:
A method of operating a sound generation mechanism that includes a piezoelectric sounder (<NUM>), comprising:
determining, via a temperature sensor, a temperature of the sound generation mechanism, optionally wherein determining the temperature of the sound generation mechanism includes sensing a temperature of an environment surrounding the sound generation mechanism;
identifying a resonant frequency of the sound generation mechanism associated with the determined temperature, wherein identifying the resonant frequency of the sound generation mechanism associated with the sensed temperature includes selecting a stored value of the resonant frequency from a database;
selecting an excitation frequency, wherein the excitation frequency is selected to minimize a difference between the identified resonant frequency associated with the determined temperature and the excitation frequency;
communicating the excitation frequency to the sound generation mechanism; and
operating the sound generation mechanism to produce one or more sounds.