These terms have become almost interchangeable, and there is definitely a gray area between the two. The difference can be in the woofer itself, or how the woofer is being used. A raw speaker or "driver" that we call a subwoofer generally has a limited frequency response range, often not extending above about 400 Hz. A standard "woofer" can have frequency response easily reaching 2500 Hz or higher. This upper limit is a function of electrical and mechanical characteristics; often the large voice coil inductances on high-excursion subwoofers limit their high-frequency capabilities. It is a matter of compromise in the design of the woofer: trying to achieve good high frequency performance generally will cause poor low frequency and power handling abilities, while producing a powerful subwoofer with ultra-low frequency abilities and high power handling will not be able to play well at higher frequencies. However, if a wider-range woofer is used only below 80 Hz or so it could be called a subwoofer due to how it is being implemented.
What's the difference between a woofer and a subwoofer?
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