Patent Application
20070064964
1. Field of the Invention
This invention relates to speakers, and more particularly, but not exclusively, to flat panel speakers used in public address systems.
2. Background
Audio speakers come in different configurations. Generally, an audio speaker is a device which takes an electrical signal and translates it into physical vibrations, which create sound energy.
A typical speaker configuration uses a driver or exciter that produces sound energy by rapidly pushing and pulling in a piston-like action, a light weight diaphragm, typically fashioned into a “cone” shape. The cone shaped diaphragm is usually made of paper, plastic or metal, and is attached to a suspension module. The cone shaped geometry is used to create a rigid mechanical structure that can be kept light weight. The cone shape provides rigidity, which is important to ensure that the diaphragm can be effectively driven by the driver.
The suspension module is a rim of flexible material or a specially contoured shape of the same cone material that allows the cone to move. The suspension module is attached to the driver's metal frame, called the basket, and controls the cone diaphragm's maximum amplitude.
The narrow end of the cone is connected to a voice coil. The voice coil is attached to the basket by a suspension spring of the voice coil, also known as a spider. The spider holds the coil in position within a magnetic gap, but allows the coil to move freely back and forth.
Unfortunately, the cone type speaker assembly can be hard to install in an aircraft interior, since the loudspeaker assembly height can be high, such as between 2 to 3 inches. The speaker assembly may also be heavy and require a speaker grill. In addition, a cone diaphragm speaker has narrow angle sound projection and is therefore, directional, which does not provide adequate coverage in an aircraft interior.
For public address (PA) speaker applications, flat panel speakers have many advantages over cone type speakers. For example, flat panel speakers provide dispersion of over 120 de- grees versus a cone speaker, which has a dispersion of about 80 degrees. The flat panel speaker also has no on-axis beaming problem and can be made to blend into specific architecture and thus be virtually “invisible”.
However, when efficiency is a concern (for example, in an airplane PA application it is desirable to that the speaker have low power consumption to minimize the impact keep on emergency battery package weight), the typical flat panel speaker is less efficient than conventional cone speakers due to the difference of the “moving mass” between the two speaker designs.
Conventional cone speakers have the strength advantage provided by the geometry of the light weight paper cone diaphragm. Flat panel speakers have a flat diaphragm, which provides no specific geometrical advantage to help strengthen the diaphragm. The soft flat diaphragm creates self canceling, which does not provide good and effective audio performance. To reinforce the flat diaphragm structure, more solid and thicker materials must be used, such as a sandwich lay-up (i.e. honey comb, foam, flute structure, or even solid acrylic board etc). However, these flat diaphragm reinforcing materials add 20 to 100 times the weight relative to paper cone speakers, which lowers the speaker's efficiency.
Unfortunately, it has been shown that even using the lightest available flat panel diaphragm materials available, such as polyester foam board, the flat speaker diaphragm is still at least 10 times heavier than conventional cone speaker diaphragms, which causes a 6 to 12 dB decrease audio level performance than the highest efficiency cone speaker. In addition, the flat panel speakers have poor high frequency response, which starts to roll off as early as from 800 Hz, due to an inappropriate material flexibility coefficient.
Therefore, there is a need for a speaker assembly, which overcomes the restrictive nature of cone type speaker assemblies and the inefficiencies associated with conventional flat panel speakers, provides optimum sound quality, is cost effective and is easy to install/maintain.
The present invention provides an isobaric flat panel speaker assembly which solves the inefficiencies of conventional flat panel speakers.
In the present invention, the flat panel speaker assembly captures otherwise unused audio energy, which generally escapes from the back side of conventional flat panel speaker configurations. The present invention converts the escaping audio energy to right phase and tunes it to a preferred frequency range. For example, in a PA application in an aircraft interior, the mid frequency range of between 300 Hz and 1 KHz is desired. The escaping audio energy is tuned to this audio frequency range and then redirected towards the front side of the speaker providing a higher output performance.
In one aspect of the invention a speaker assembly is provided which includes a first diaphragm, a second diaphragm, and a driver operationally positioned in an enclosure formed by the first diaphragm and the second diaphragm. The second diaphragm is made of a material composition which allows it to block sound energy, and reflect sound energy back to the first diaphragm.
In another aspect of the invention, an aircraft is provided which includes an audio system. The audio system includes an input device, an amplifier; and a speaker assembly. The speaker assembly includes a first diaphragm and a second diaphragm, where the second diaphragm has a material composition which allows it to block sound energy and reflect sound energy to said first diaphragm.
In tests, an isobaric flat panel speaker assembly of the present invention was shown to boost the audio output performance by about 4 to 8 dB. With this boost in audio output, the flat panel speaker of the present invention is capable of the same average level of performance efficiency as high efficiency cone speakers.
The flat panel speaker assembly of the present invention can be plugged into a mating panel structure formed into an aircraft bulkhead during the bulkhead assembly process. Once the aircraft interior is completed, there is no visual impact on the appearance of the interior bulkheads. Moreover, because of the modular nature of the speaker assembly, repair and maintenance of the flat panel speaker can be accomplished with minimal impact to the aircraft bulkhead.
Additional advantages, objects, and features of the invention will be set forth in part in the detailed description which follows. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide further understanding of the invention, illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures:
To facilitate an understanding of the present invention, the general architecture and operation of an audio system (for example, a PA system) will be described. The specific architecture and operation of the present invention will then be described with reference to the general architecture.
It is noteworthy that although
Driver 106 is safely secured and strategically positioned in speaker assembly 100 to assure secure coupling conditions between driver 106 and main diaphragm 102, and to ensure optimum performance conditions. Structure 106A supports and/or locates the driver assembly 106 in the proper position. In accordance with an embodiment of the present invention, secondary diaphragm 104 is free from physical contact with driver 106. Driver 106 is offset from second diaphragm 104 by gap 110. In one embodiment, the distance between diaphragms 102 and 104, and thus the height of speaker assembly 100, is about 1 to 2 inches.
Speaker assembly 100 can be installed, for example, by inserting the entire speaker assembly 100 into a pre-cut hole on a ceiling panel 112 during a lay up process (i.e. during bulkhead fabrication). Speaker assembly 100 may be glued or similarly mounted into panel 112 using conventional speaker mounting means. A covering 114, such as a laminate covering, may be used to cover speaker assembly 100, making speaker assembly 100 virtually invisible to the interior of the aircraft.
In one embodiment, main diaphragm 102 and laminate covering 114 are designed to operate together in audio terms to produce any desired PA quality performance. In this embodiment, the weight, stiffness, rigidity and thickness of laminate covering 114 may be modified to provide optimum sound quality. For example, the thickness of the laminate covering may be determined by a progressive thinning process where the thickness is decreased and each thinning step is followed by an audio test to verify optimum sound quality results. It is noteworthy that the present invention is not limited to any particular material or thickness. The thickness depends on the density of laminate covering 114 and also on the overall diameter of speaker assembly 100.
In operation, a typical flat panel speaker emits audio energy equally on both sides of its respective flat diaphragm. In accordance with an embodiment of the present invention, speaker assembly 100 operates to redirect the “rear directed” or “back firing” audio energy to benefit the “front directed” or “front firing” audio energy, thus, increasing the overall dB level output of speaker assembly 100.
Speaker assembly 100 is not a coherent speaker that works by pumping air in and out in a coherent manner, thus, the function of redirecting audio energy is not accomplished by phase tuning or speaker cabin air pressure modification (unlike a cone speaker assembly). Rather, the redirection of the audio energy is accomplished by means of resonant and reflection tuning, controlled primarily by the function of secondary diaphragm 104, and its distance from main diaphragm 102. Details of the redirection of audio energy in accordance with the present invention are described below.
As described above, speaker assembly 100 has dual diaphragms—main or active diaphragm 102 and secondary or passive diaphragm 104. Unlike some consumer sub-woofers that use a passive radiator to utilize woofer energy more effectively, passive diaphragm 104 of speaker assembly 100 is not intended to emit or radiate sound outward (i.e. to the rear of the speaker).
Referring again to
For ease of understanding, below is a detailed description of a particular embodiment of the present invention, which is not intended to limit the invention in any manner.
Accordingly in this exemplary embodiment, speaker assembly 100 can include active diaphragm 102, which is made of one ply of 120 glass and one ply of glass fly Screen on separate sides of a Nomax honeycomb core having a thickness of about 0.12 inches. The size and material composition of active diaphragm 102 in this embodiment is a result of a timely research and testing—matching (installed) with the audio attributes of a 0.375 (⅜″) thick ceiling laminate 114.
In this embodiment, the use of active diaphragm 102 alone performs in audio quality tests at about 8 dB less efficiency than production airplane PA speakers. Using diaphragm 102 provides higher efficiency and dynamic performance than conventional flat panel speakers.
In accordance with the present invention, the addition of passive diaphragm 104 to speaker assembly 100 increases the output efficiency. It is noteworthy that the composition of passive diaphragm 104 is significant to the successful implementation of the present invention. Improper material uses may actually reduce the efficiency of active diaphragm 102.
In this embodiment, passive diaphragm 104 can be made of one ply of 120 glass and one ply of 181 glass on separate sides of a Nomax honeycomb core. Lab tests have verified that the combination of dissimilar composition diaphragms 102 and 104 boosted the audio output by an additional 4-8 dB of speaker output at a range of about 500 Hz to 11 kHz.
In this embodiment, passive diaphragm 104 is about 30% to 75% stiffer than active diaphragm 102. Being stiffer, the mass of diaphragm 104 is not necessary so much heavier than active diaphragm 102. In one aspect, the mass is about 10% heavier.
Given the structure described in
In addition to blocking sound energy, passive diaphragm 104 reflects sound energy back to active diaphragm 102. At the same time, the material composition of passive diaphragm 104 creates a range of desired resonance in reaction to the performing audio frequencies and level. The resonance, along with the reflection of sound energy, and the tailored distance between both diaphragms 102 and 104, can assure additional frequency output of between about 500 Hz -11 kHz of speaker assembly 100.
Test data confirms the significant improvement of the dB output of speaker assembly 100.
Table 1 summarizes the results of an on-axis test performed using this embodiment of speaker assembly 100. On-axis measurements were made at varying frequencies of a speaker assembly having active diaphragm 102 only and a speaker assembly 100 having an active diaphragm 102 and a passive diaphragm 104 positioned in enclosure 108 with a predetermined gap 104 in accordance with an embodiment of the present invention.
The on-axis data in Table 1 shows an increase, for example, of 4.4 dB at 1 kHz with passive diaphragm 104.
Some test were conducted which compared speaker assembly 100 with a typical cone speaker, at 60 degrees off-axis at a two meter distance. Speaker assembly 100 measured more dB output than the cone speaker due to the weak dispersion nature (less than 90 degrees) of cone speakers, and the wider dispersion (over 120 degrees) capability of speaker assembly 100. The wider angle coverage capability of speaker assembly 100 is particularly beneficial for covering seats in the interior of an aircraft that are located away from the center aisle (i.e. window seats). Conventional cone speaker would have to be driven much louder in order to cover wider area, at a cost of greater amplifier power, and may become unbearable for passengers sitting along the axis of the speaker.
As will by now be evident to persons of ordinary skill in the art, many modifications, substitutions and variations can be made in and to the materials used for the reliable, low-cost, speaker assembly 100 of the present invention without departing from its spirit and scope. It is understood, that the speaker system of the present invention may find use in vehicles or general domestic and commercial applications other than airplanes. All such uses are within the scope of the present invention.
Accordingly, the scope of the present invention should not be limited to the particular embodiments illustrated and described herein, as they are merely exemplary in nature, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents. What is claimed is:
