1. Technical Field
This invention relates generally to loud speakers used in audio systems. More particularly, this invention relates to a speaker port with a contour that reduces boundary layer separation.
2. Related Art
There are many types of speaker enclosures. Each enclosure type can affect how sound is produced by the speaker. Typically, a driver is mounted flushed within the speaker enclosure. The driver usually has a vibrating diaphragm for emitting sound waves in front of a cone. As the diaphragm moves back and forth, rear waves are created behind the cone as well. Different enclosures types have different ways of handling these “rear” waves.
Many speakers take advantage of these rear waves to supplement forward sound waves produced by the cone.
In many speaker enclosures, sound waves passing through the port generate noise due to boundary layer separation. A sudden expansion or discontinuity in the cross-sectional area of the port can cause boundary layer separation of the sound waves from the port. Boundary layer separation occurs when there is excessive expansion along the longitudinal axis of the port. The fluid expansion causes excessive momentum loss near the wall or contour of the port such that the flow breaks off or separates from the wall of the port.
To minimize boundary layer separation, many port designs use flares in the shape of a nozzle at opposing ends of the port to provide smooth transitions. Often, different flares are tried until the “best” one is found. In many flare designs, the performance of the port may be poor because boundary layer separation will occur at the point along the longitudinal axis of the port where the adverse pressure gradient is largest. The pressure gradient or change in pressure may become great enough that the momentum of the sound wave or fluid is greater than the pressure holding the sound wave to the wall or contour. In this case, the sound wave separates from the wall, thus generating noise and losses. The point where the maximum pressure gradient occurs along the port limits the flow velocity from the port before separation occurs. Once the sound wave or flow separates from the port contour or wall at the point of maximum pressure gradient, flow losses increase dramatically and result in poor performance of the port.
This invention provides a speaker port having a substantially constant pressure gradient that reduces or minimizes boundary layer separation. With a substantially constant pressure gradient, there essentially is no point in the speaker port where a higher pressure gradient occurs to limit the velocity of the sound waves.
The speaker port comprises a flare having a substantially constant pressure gradient. In a method to reduce boundary layer separation in a speaker port, the inner wall of a flare is configured to have a substantially constant pressure gradient.
Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims.
The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.
The flares 204 and 206 each have an inner wall 210 that reduces or minimizes boundary layer separation so that fluids, such as air or sound waves, may flow through the flare at a higher velocity without boundary layer separation. The inner wall 210 is contoured so that the pressure gradient or change in pressure along the longitudinal axis of the flare from its inlet duct 212 to outlet duct 214 is substantially constant. The pressure gradient is substantially similar along the longitudinal axis of the flare. If the momentum or velocity of the fluid overcomes the pressure forces holding the flow to the wall, boundary layer separation can occur along the entire length of the flare. The performance of the flare improves because there is essentially no point along the longitudinal axis of the flare in which a higher pressure gradient occurs to limit velocity of the fluid. The point where a maximum or highest pressure gradient occurs has been changed so that performance is improved or optimized. With an essentially constant pressure gradient over the entire length of the flare, there is no peak or maximum pressure gradient at any point along the flare that limits the flow velocity of the fluid or sound wave.
In one aspect, the cylinder 202 is the interior portion of port 200 that has an essentially constant diameter. In this aspect, the flares 204 and 206 are the exterior portions of port 200 that have variable diameters. Generally, the cylinder 202 may be a separate or integral component of the flares 204 and 206. There may be no cylinder 202, when flare 204 transitions directly into flare 206. There may be only one flare or other multiples of flares. Flare 204 is essentially the same as flare 206. However, flare 204 may have different dimensions and/or a different configuration from flare 206.
A substantially constant pressure gradient along the length of the flare 304 minimizes or reduces the adverse affect of the pressure gradient on any point and allows for a higher or maximum velocity of air flow to occur without boundary layer separation. A flare without a constant pressure gradient has one or more points from the inlet duct 312 to the outlet duct 314 with higher pressure gradients. Boundary layer separation can occur at high pressure gradient points along the flare with air velocities that are comparatively lower than if there was a constant pressure gradient.
The pressure at points along the length of the flare 304, P0(x) through P6(x), changes with respect the widening of the flare. If the change in pressure with respect to the change in distance is too high, an excessive adverse pressure gradient occurs. The pressure along the boundary of the walls 310 will not be enough to overcome the momentum of the sound wave or air flow U(x). An essentially constant pressure gradient allows a higher or maximum air flow velocity without flow separation because the constant pressure gradient causes the flow to expand uniformly along the points of the flare length as the sound wave or flow progresses through the flare 304.
The shape or contour of the inner wall 310 provides a substantially constant pressure gradient along the length of a circular flare and is defined or determined as follows:
The contour of a flare is calculated using Equation (14) with an initial velocity Uin, an initial flare area Ain that specifies the initial radius rin such as Ain=πrin2, a desired pressure gradient Δ=dp/dx, the fluid density ρ, and the integration constant c. Equation 14 may vary depending upon the initial cross-section area and other cross-sectional areas of the flare, especially when the flare is non-circular.
In another aspect, the shape or contour of the inner wall 310 provides a substantially constant pressure gradient along the length of a circular flare and is defined or determined as follows:
The contour of a flare is calculated using Equation (20) with an initial velocity Uin, an initial flare area Ain (which specifies the initial radius rin such as Ain=πrin2), a desired pressure gradient Δ=dp/dx, and the fluid density ρ. Equation 20 may vary depending upon the initial cross-section area and other cross-section areas of the flare, especially when the flare is non-circular.
With either Equations (14) or (20), the inner wall 310 of the flare 304 may be shaped or configured to provide a substantially similar pressure gradient over the length of the flare 304 between the inlet and outlet ducts 312 and 314. With either Equation, the length of flare 304 between the inlet and outlet ducts 312 and 314 may be used to increase the velocity of the fluid or sound wave through the flare 304 while avoiding boundary layer separation. The inner wall of the flare 304 is thus shaped so that the pressure gradient along the flare 304 is substantially similar or constant, thus minimizing or reducing boundary layer separation.
The same port performance can be achieved using non-circular sections, non-symmetrical sections, or a combination. Equations 14 and 20 are adjusted by substituting the appropriate area relationship for the configuration of the port. In addition, the port may not be rotationally symmetrical. One side could be flat while the other side is varied to maintain the desired area expansion.
Other pressure and/or fluid equations may be used to shape or configure the inner wall to provide a substantially constant pressure gradient. Various computer programs may be used to perform the calculations of this invention including Matlab™ and Mathematica.™ These programs may be used to plot the contour of a flare while keeping the pressure gradient constant.
While various embodiments of the application have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.
This application is based on U.S. Provisional Patent Application No. 60/300,640 entitled “Flare Design for Minimizing Boundary Layer Separation” and filed on Jun. 25, 2001. The benefit of the filing date of the Provisional Application is claimed for this application.
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Number | Date | Country |
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2001-501426 (T) | Jan 2001 | JP |
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Number | Date | Country | |
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20030076975 A1 | Apr 2003 | US |
Number | Date | Country | |
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60300640 | Jun 2001 | US |