Hey all,
Sorry if this has been asked before, but as I read some posts and literature the term "acoustically small" and "acoustically large" seem to pop up quite a bit. Is this a reference to the point when the wavelength exceeds or becomes smaller then the diameter of the woofer? How does that affect speaker design?
Sorry if this has been asked before, but as I read some posts and literature the term "acoustically small" and "acoustically large" seem to pop up quite a bit. Is this a reference to the point when the wavelength exceeds or becomes smaller then the diameter of the woofer? How does that affect speaker design?
That sounds like a good definition.
As to the affect on loudspeaker design, there are many aspects of speaker design that require one to pay attention the the wavelength vrs a physical feature.
Probably one of the biggest is the nature of diffratiuon as the box transitions from "acoustically small" to "acoustically large”. Edge diffraction and reradiation when the wavelength is acoustically small when it reaches the edge of the enclosure, and called baffle step when the wavelength is acoustically large compared to the box.
And a favourite thing i like to do is keep drivers withion a quarter wavelength at the XO point.
dave
As to the affect on loudspeaker design, there are many aspects of speaker design that require one to pay attention the the wavelength vrs a physical feature.
Probably one of the biggest is the nature of diffratiuon as the box transitions from "acoustically small" to "acoustically large”. Edge diffraction and reradiation when the wavelength is acoustically small when it reaches the edge of the enclosure, and called baffle step when the wavelength is acoustically large compared to the box.
And a favourite thing i like to do is keep drivers withion a quarter wavelength at the XO point.
dave
Most well-designed multi-way loudspeakers are designed so that the polar coverage angles of each way (driver) matches the polar coverage of the crossing "way" (driver or drivers) at the crossover center frequency. This is because the human hearing system is sensitive to directivity of loudspeakers--the consistency of polar coverage angles vs. frequency.
In fact, in Dr. Sean Olive's (Harman/JBL) subjective/objective factors for loudspeaker preferences, it actually turns out that directivity consistency is the most important overall factor for subjective loudspeaker preference ratings:
As the wavelength of sound being produced becomes shorter than the diameter of the driver's diaphragm, the polar coverage angle of the driver's effective acoustic output begins to collapse.
Chris
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From Acoustics by Beranek: "For the special case of a very small source, whose radius is small compared with one-sixth wavelength (that is, ka<<1)"
https://acousticfrontiers.com/blogs...is-response-theory-and-measurement-techniques
"Off axis cancellation effects are often illustrated through polar response graphs which show the dB level at various angles from 0 to 90 degrees. In the diagram the dimensionless number ka refers to circumference* divided by wavelength. *circumference can be easily calculated as pi or 3.141 multiplied by the diameter.
. . . . Above ka = 1 the piston starts to become directional. Relatively smooth off axis response is maintained to ka = 2 (500Hz for the 15″ piston) but by ka = 5 (1250Hz for the 15″) the piston is beaming with notable response lobing."
https://acousticfrontiers.com/blogs...is-response-theory-and-measurement-techniques
"Off axis cancellation effects are often illustrated through polar response graphs which show the dB level at various angles from 0 to 90 degrees. In the diagram the dimensionless number ka refers to circumference* divided by wavelength. *circumference can be easily calculated as pi or 3.141 multiplied by the diameter.
. . . . Above ka = 1 the piston starts to become directional. Relatively smooth off axis response is maintained to ka = 2 (500Hz for the 15″ piston) but by ka = 5 (1250Hz for the 15″) the piston is beaming with notable response lobing."