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Old 22nd May 2007, 06:32 PM   #1
Audist is offline Audist  United States
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Default Near field vs Far field

Hello,

I build my loudspeakers but I have some problem.
When I test my loudspeakers in near field measurement (tweeter and woofer separately in the real cabinet) and use with phase and combine, the frequency range is beautiful and very flat.
But when I measure at Far field method, the graph look with problem at 1500Hz to 2800Hz. maybe is my room. maybe not.. I'm dont know.
I use with very high resolution - 24bit/96Khz.

I can to rely on near field measurement or is not say nothing?

Thank you
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Old 22nd May 2007, 07:23 PM   #2
ente is offline ente  Germany
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... here you will find some information regarding your question

http://www.fesb.hr/~mateljan/arta/Ap...d-Rev03eng.pdf

Heinrich
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Old 22nd May 2007, 09:42 PM   #3
Svante is offline Svante  Sweden
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Default Re: Near field vs Far field

Quote:
Originally posted by Audist
Hello,

I build my loudspeakers but I have some problem.
When I test my loudspeakers in near field measurement (tweeter and woofer separately in the real cabinet) and use with phase and combine, the frequency range is beautiful and very flat.
But when I measure at Far field method, the graph look with problem at 1500Hz to 2800Hz. maybe is my room. maybe not.. I'm dont know.
I use with very high resolution - 24bit/96Khz.

I can to rely on near field measurement or is not say nothing?

Thank you
I think that what you see in the far field measurements is the baffle step. The baffle step is supressed in close field measurements due to that the distance to the baffle edges is larger than the distance to the driver.

Below is an example on how the baffle step varies when the microphone is moved between 3 metres (green) and 5 cm (red).
Click the image to open in full size.
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Old 23rd May 2007, 12:35 AM   #4
claudio is offline claudio  Italy
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Default Re: Near field vs Far field

Quote:
Originally posted by Audist
Hello,

I build my loudspeakers but I have some problem.
When I test my loudspeakers in near field measurement (tweeter and woofer separately in the real cabinet) and use with phase and combine, the frequency range is beautiful and very flat.
But when I measure at Far field method, the graph look with problem at 1500Hz to 2800Hz. maybe is my room. maybe not.. I'm dont know.
I use with very high resolution - 24bit/96Khz.

I can to rely on near field measurement or is not say nothing?

Thank you
Hi Audist,
the NF measurement is made with the mic very close to the woofer dustcap, and it's valid till a frequency=10950/D where D is the driver diameter in centimeter. Said this, measuring a tweeter in NF is useless.
The NF technique is used for the low frequency spectrum.

The far field measurement you performed is gated or not?
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Old 23rd May 2007, 10:19 AM   #5
Audist is offline Audist  United States
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Default Re: Re: Near field vs Far field

Quote:
Originally posted by claudio


Hi Audist,
the NF measurement is made with the mic very close to the woofer dustcap, and it's valid till a frequency=10950/D where D is the driver diameter in centimeter. Said this, measuring a tweeter in NF is useless.
The NF technique is used for the low frequency spectrum.

The far field measurement you performed is gated or not?

Hi claudio.
Thank you very much and yes, in NF measurement I see the problem in 10000 Hz to 10950 Hz. on the woofer and on the tweeter.

What the best technique to test the woofer and the tweeter in problematic (live) room?
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Old 23rd May 2007, 12:35 PM   #6
claudio is offline claudio  Italy
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Hi Audist,
let's assume your woofer has a diameter D=15 cm so Fmax = 730 Hz that means that we can use the near-field response till this frequency. However this is valid for a driver mounted on infinite baffle, while lowers for a driver mounted on a panel, cause of the baffle effects.
You say your woofer problem are in the 10000 Hz region: what kind of woofer are you using? Sounds a little too high frequency for a woofer. Isn't that you are measuring with both drivers (woofer+tweeter) working?

For a tweeter let's say it has a diameter of 2 cm: Fmax=5475 Hz, but you are already in the FAR FIELD range, so it's not necessary to make a NF for a tweeter.

Far Field: you didn't say if it is a gated or not measurement, the one you performed.
Looks you did room response, that is an ungated Far Field, with both drivers playing.
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Old 23rd May 2007, 05:21 PM   #7
Svante is offline Svante  Sweden
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Default Re: Re: Near field vs Far field

Quote:
Originally posted by claudio


Hi Audist,
the NF measurement is made with the mic very close to the woofer dustcap, and it's valid till a frequency=10950/D where D is the driver diameter in centimeter. Said this, measuring a tweeter in NF is useless.
The NF technique is used for the low frequency spectrum.

The far field measurement you performed is gated or not?
You have to weigh in the baffle size as well into that equation too. I am convinced that the fluctuations in the far field comes from the baffle step. Also, 10950 sounds terribly accurate, of course there is a transition zone where the measurements gets gradually better/worse.
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Old 23rd May 2007, 05:30 PM   #8
Svante is offline Svante  Sweden
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Audist: Could you post the dimensions of the driver and baffle, and the placement of the driver on the baffle. In that way I could simulate the baffle contribution for you. Or you could do it yourself with The Edge in my signature.
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Old 23rd May 2007, 06:27 PM   #9
claudio is offline claudio  Italy
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Default Re: Re: Re: Near field vs Far field

Quote:
Originally posted by Svante


You have to weigh in the baffle size as well into that equation too.
Hi Svante,
I think I did in post #6 when I said: ". However this is valid for a driver mounted on infinite baffle, while lowers for a driver mounted on a panel, cause of the baffle effects."
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Old 23rd May 2007, 08:38 PM   #10
Svante is offline Svante  Sweden
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Default Re: Re: Re: Re: Near field vs Far field

Quote:
Originally posted by claudio


Hi Svante,
I think I did in post #6 when I said: ". However this is valid for a driver mounted on infinite baffle, while lowers for a driver mounted on a panel, cause of the baffle effects."
Ah, yes, sorry.

Anyway, I'm curious about the dimensions of the baffle, and also about the measurements. I would hope to see them?
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