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Thread: Ground Plane Measurement VS Anechoic

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    Ground Plane Measurement VS Anechoic

    I was looking for a study showing the difference between ground plane measurement and (VS) anechoic measurement but I was not able to find anything. Obviously I know that the GP measurement will indicate higher SPL compared to the anechoic that will have lower sensitivity. I am referring to the shape of the response curve. How is that affected? I will also assume that the high frequencies will be affected less than (compared to) the low frequencies.

    Let me give an example of what I am hopping to find;
    For sake of discussion lets assume that we have a 3 cu ft tower speaker (in the upright position) that measured (ground plane) flat 20Hz to 20Khz. Then suspend the same speaker 50ft in the air, take another measurement and compare the two curves to get a picture of how the shape of the curve is affected. I am hoping to find a compatible type of study.

    Any thoughts / suggestions appreciated

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    Quote Originally Posted by Steve C 2020 View Post
    I was looking for a study showing the difference between ground plane measurement and (VS) anechoic measurement but I was not able to find anything. Obviously I know that the GP measurement will indicate higher SPL compared to the anechoic that will have lower sensitivity. I am referring to the shape of the response curve. How is that affected? I will also assume that the high frequencies will be affected less than (compared to) the low frequencies.

    Let me give an example of what I am hopping to find;
    For sake of discussion lets assume that we have a 3 cu ft tower speaker (in the upright position) that measured (ground plane) flat 20Hz to 20Khz. Then suspend the same speaker 50ft in the air, take another measurement and compare the two curves to get a picture of how the shape of the curve is affected. I am hoping to find a compatible type of study.

    Any thoughts / suggestions appreciated
    Any frequency at which a transducer radiates in an omnidirectional pattern will be reinforced or reduced depending on the wavelength, the size or the enclosure and distance from the ground plane. Up in the air it's mostly the cabinet dimension that effect which frequencies reach the measuring mic and which partly radiate into free space. As enclosure dimensions are usually small compared to LF wavelengths the low frequency response will be less in the air, but most likely less ragged than measured on the ground. Ground plane measurement probably give a better idea of LF output in a room, but not necessarily how smooth the response will be.

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    Quote Originally Posted by Epplerd View Post
    Any frequency at which a transducer radiates in an omnidirectional pattern will be reinforced or reduced depending on the wavelength, the size or the enclosure and distance from the ground plane. Up in the air it's mostly the cabinet dimension that effect which frequencies reach the measuring mic and which partly radiate into free space. As enclosure dimensions are usually small compared to LF wavelengths the low frequency response will be less in the air, but most likely less ragged than measured on the ground. Ground plane measurement probably give a better idea of LF output in a room, but not necessarily how smooth the response will be.
    Yes that is true. The size and shape of the front baffle of the speaker affects the frequency response of the speaker. I believe that is referred to as BD (baffle diffraction). Keep in mind that if in the speaker measures flat on a GP measurement, then the issues of BD have already been compensated for (for the most part) when the speaker is moved into an anechoic environment. For this reason, the GP measurement and anechoic measurement should both measure relatively flat.

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