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Old 30th December 2005, 08:01 PM   #1
2litre is offline 2litre  United States
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Default Near field / far field?

Hi All,

Could someone expain or describe, in simple terms, what the terms near field and far field mean?

In the past I've been lucky enough to own fairly good systems (never liked Bose or mini-systems) and I've just recently jumped into DIY speakers. I'm almost done with my first project, a pair of speakers based on the Visaton NoBox design. The dimensions are almost spot on but I've used different drivers.

It seems that they may be to big for my rooms. My house is very old and it's biggest room, besides the unfinished basement, is 11'x16'. My listening room is almost 10'x13'.

The speakers when tested in my 21'x21' garage construction area sound real nice, but when I get them inside the house they seem to lack bass and the mids and treble are more pronounced.

Have I built speakers that are better suited for much larger rooms?

R/ Jim
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Old 30th December 2005, 09:00 PM   #2
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Jim,

Here are the definitions from Parts Express:

Near-Field: The near-field can be defined as any distance relative to a speaker at which driver integration is not fully complete. Typically the near-field of a speaker is distances less than 1 meter. Near-field measurements are useful because they can measure the response of a driver without the effects of the room. Near-field measurements are only good up to several hundred Hz however, since interactions with cabinet edges and across the driver itself are not taken into account. In studio monitoring situations, near-field and far-field listening techniques are used to evaluate a mix.

Far-Field: The far-field can be defined as any distance from a loudspeaker at which inter-driver integration is complete. Typically set at 1m. Far-field measurements are useful because they usually take baffle step and driver-to-driver spacing into account. In studio monitoring situations, near-field and far-field listening techniques are used to evaluate a mix.


It's hard to say but I would think you are having a problem with speaker placement. Try moving them around a bit and see if you can get that bass back up. If not, are you against using an EQ to tame the dragon?

EDIT: What speakers did you build?
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Old 30th December 2005, 10:07 PM   #3
2litre is offline 2litre  United States
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Cal,

Thanks for the explainatin and where you got it. At 1m far field really isn't really far at all, is it?

I'm finishing off (staining this weekend after final installation of the front baffle) a budget verision of Visaton's NoBox open back speakers. They're 48hx21wx14d with the front baffle laid back 5deg, like the original. The drivers though are a 12", an 8" w/ whizzer and a 3.5" w/ whizzer. The 12" is centered 10.5" off the floor and the 8" is at 31.5" off the floor. The 3.5" is close in above the 8". I wonder if some of my issue comes from the 21" of main driver seperation?

I don't know if most first timers make this mistake but I didn't quite grasp just how much real estate they would consume in a 9.5'x13' room. As such I don't really have much manuvering room, maybe a foot or so each way 'round to keep them seperated by 6' or so. I'll try positioning them a bit more.

One other thing. I haven't adheared any sound deading material to the cabinet backs yet. Maybe that will help a bit. I've just used some heavy terry cloth towels suspended behind the 12" so far.

R/
Jim
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Old 31st December 2005, 03:40 AM   #4
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The near/far field transition is typically defined at a distance of d²/l, where d is the effective diameter of the driver, and l is the wavelength of sound. Note that means that as you either increase the diameter OR play a higher frequency, the near/far field transition occurs at a further distance.

In the far field, the driver obeys the expected drop in SPL with range (either 1/R or 1/R², depending upon the type of speaker). For all intents and purposes, the response is continuous and linear.

In the near field, the response is, for lack of a better term, chaotic. The SPL can increase AND decrease as you move closer to the driver. The response is not continuous, and not linear. A shift of just a few inches can yield frequency response changes at some frequencies of 5 dB or more.

I believe what Parts Express was talking about wasn't near and far field, but close and and far mic positions. Those are completely different terms.

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Old 2nd January 2006, 09:44 AM   #5
Rudolf is offline Rudolf  Germany
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Jim,
to give still another (valid?) definition of near/far field:
Near field could be defined as the distance where direct sound from the loudspeaker is stronger than the reverberant sound from the room. Border line between near field and far field is the reverberation distance. For a definition you may look here:
http://www.linkwitzlab.com/rooms.htm

Regarding the lack of bass response in house:
Did you give the dipoles sufficient distance to the back and side walls? Please remember that bass response of dipoles is best far from walls, just opposite to the response of boxed sppeakers.
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