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Old 6th May 2016, 06:35 PM   #1
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Default Baffle compensation for nearfield measurement

I'm trying to do a near-field measurement using ARTA (for the bass driver). Following the tutorial on their manual and I stumbled upon something I don't understand.

After the measurement is complete, they are suggesting to make some sort of baffle compensation, before we scale the curve to far-field. There is an option called " LF box diffraction" where you enter the dimensions of the baffle. As an effect, the low frequencies are lowered by few db.

I understand that the near-field measurement ignores baffle gains, room gains etc. In a far-field measurement all of these would be present. But I am also aware that baffle gains only apply to high frequencies.

If there are no gains for low frequencies, what am I compensating ? And if there were partial gains, shouldn't the low frequencies go up, to compensate for the lack of baffle gain ?
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Old 6th May 2016, 07:18 PM   #2
bwaslo is offline bwaslo  United States
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When you measure nearfield, the mic doesn't see the effect of LF flowing toward the back, it sees the response as if all the propagation is coming only forward from an infinite baffle. To correct for that, the LF part of the curve needs to be reduced, to simulate the LF pressure loss that actually exists around the box when seen from a more practical listening distance.
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Old 6th May 2016, 08:03 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Compared to near field a driver in farfield only has baffle loss.
There is no baffle gain, as nearfield is equivalent to an infinite baffle.

For higher frequencies there is no loss as the speaker front is
big enough to be similar to half space, infinite baffle response.

When the speakers transitions to full space lower down there
is an eventual 6dB loss in output compared to half space.

rgds, sreten.

Last edited by sreten; 6th May 2016 at 08:06 PM.
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Old 6th May 2016, 08:08 PM   #4
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Now I get it!

Since near-field "sees" the speaker on an infinite baffle, all frequencies gain 6 db.

In reality it is a finite baffle and only the high frequencies get the boost. So I need to decrease the LF to match reality.

Thanks guys !
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Old 6th May 2016, 09:33 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Except all drive sensitivities are specified into half space.
(Think about it, it is the only sensible engineering option).
There is no 6dB gain, only loss compared to half space.

rgds, sreten.

Last edited by sreten; 6th May 2016 at 09:35 PM.
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