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Scaling port response to speaker nearfield
Scaling port response to speaker nearfield
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Old 24th March 2020, 06:28 PM   #1
mecedo is offline mecedo
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Default Scaling port response to speaker nearfield

If I have flared port like on the attached picture and need to scale his response to speaker nearfield which dimension should I use in scaling formula? E or D?
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Old 24th March 2020, 08:18 PM   #2
PeteMcK is offline PeteMcK
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use D, the important thing is the volume of air in the port, and D, being the average diameter, should give the closest result to calculating that.
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Old 24th March 2020, 09:31 PM   #3
mecedo is offline mecedo
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Thanks. It seems to be logical��
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Old 25th March 2020, 02:34 PM   #4
mecedo is offline mecedo
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An what I found interesting about mic position:

"Mic in the center of vent at baffle surface if vent is not rounded. If vent has rounding, penetrate few millimetres inside, where tube with constant diameter begins. Not too deep."
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Old 25th March 2020, 03:49 PM   #5
celef is offline celef
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no need to calc, just align the low end responses for port to woofer

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Old 25th March 2020, 07:30 PM   #6
eriksquires is offline eriksquires  United States
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I have to say, I've never had very good luck with the formulas. It could very well be my own lack of experience, and the like, so I end up using far-field to validate my calculations.
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Old 26th March 2020, 08:51 AM   #7
mecedo is offline mecedo
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Quote:
Originally Posted by celef View Post
no need to calc, just align the low end responses for port to woofer
It's not so simply. What in this situation?
https://www.diyaudio.com/forums/atta...1&d=1585212152
There are three options:
https://www.diyaudio.com/forums/atta...1&d=1585212628
https://www.diyaudio.com/forums/atta...1&d=1585212628
https://www.diyaudio.com/forums/atta...1&d=1585212628


Which is correct?
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Old 26th March 2020, 09:01 AM   #8
silverprout is offline silverprout  France
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The air turbulence noises should be audible in the nerfield, you should look a more adapted one, like those that JBL have putted in the K2 S9800.
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Old 26th March 2020, 09:10 AM   #9
mbrennwa is offline mbrennwa  Switzerland
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Scaling port response to speaker nearfield
Quote:
Originally Posted by mecedo View Post
If I have flared port like on the attached picture and need to scale his response to speaker nearfield which dimension should I use in scaling formula? E or D?
I guess your goal is to scale the sound output (SPL) from the port in order to merge it with the woofer output, correct? If so, the scaling depends on the sound emitting surfaces. For the woofer, this is the effective cone (piston) area, Sd. For the port, it's the effective cross-sectional area at the end of the port. With your flared port I'd say you should use E or C, which is the "effective diameter" at the end of the port (not D, which is the diameter somewhere along the inside of the port). But then again it's not so clear what the effective diameter at the end of a flared port really is.

As an alternative, I'd recommend the "microphone in box" technique to determine the bass response of a bass-reflex system. This technique provides a direct measurement of the total (summed) output of the woofer and the port, so there is no need to measure the woofer and port separately and then merge the two.

The Microphone-in-Box technique is described here (you need to scroll down a bit): Measuring Loudspeaker Low-Frequency Response | audioXpress

The original publication with more details (and absolute SPL scaling) is: R H Small. Simplified loudspeaker measurements at low frequencies. Journal of Audio Engineering Society (JAES), 20:28–33, 1972
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Last edited by mbrennwa; 26th March 2020 at 09:13 AM.
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Old 26th March 2020, 09:16 AM   #10
mbrennwa is offline mbrennwa  Switzerland
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Scaling port response to speaker nearfield
Quote:
Originally Posted by eriksquires View Post
I have to say, I've never had very good luck with the formulas. It could very well be my own lack of experience, and the like, so I end up using far-field to validate my calculations.
Low-frequency measurements in the far field require an anechoic room or a very large tower to move the speaker and the microphone away from any walls or other reflective surfaces. Not easy.
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