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How close is “near field”

November 15th, 2020, 8:59 pm

In getting a frequency response from a diver where dose the measuring mic go.

Re: How close is “near field”

November 15th, 2020, 9:11 pm

Usually nearfield is good at 1/4" from dust cap. Might need to be a bit farther if a sub with long excursion driver.

Normally only used from about 300Hz down in frequency.

If you measure a port, using a position at the port opening works well.

Re: How close is “near field”

November 15th, 2020, 10:04 pm

Depends on the configuration. On my CBT arrays they are several meters from the speakers. The way the wavefront diverges determines if you are in the near field or not. In an anechoic chamber the far field is where the pressure falls off as 1/(R*R) where R is the distance to the speaker.

Re: How close is “near field”

November 15th, 2020, 11:01 pm

Pelliott321 wrote:In getting a frequency response from a diver where dose the measuring mic go.

You really need an an-echoic chamber or room. Lacking that -- you have the next best thing -- your back yard.

Re: How close is “near field”

November 16th, 2020, 9:15 am

Testing software such as ARTA provides a "quasi anechoic" measurement down to around 200 to 300 Hz depending on your room with the mike 1M from the drivers.

Re: How close is “near field”

November 16th, 2020, 10:01 am

Attached is the paper on near field measurements.
Attachments
Keele (1974-04 AES Published) - Nearfield Paper.pdf
(1.43 MiB) Downloaded 32 times

Re: How close is “near field”

November 16th, 2020, 11:50 am

thanks the article is over my head but the pictures tell me what I need to know.
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