Of Near and Far, Desktops, Couch and Cars

[Blumlein 88]

This is contra what Everest & Pohlmann write in the Master Handbook of Acoustics. I'm going from memory here, but the near field is defined as the region where sound power decreases by 12dB per doubling of distance. I can't remember the other distinctions at the moment. An anechoic chamber definitely follows the characteristics of the free field and is defined that way without conflation with the term near field. (Near/mid/far field don't map onto that chart Blumlein posted, for example.)

That technical definition, as far as I can see, is used independently of the term "near field" in the colloquial manner of engineers and others. It doesn't mean that you can't come to some meaningful agreement about the general references (smaller monitors, close listening distances), but it should not be used when describing optimized speaker placement or to define speakers by type because it (as do mid/far field) tends to wobble in meaning when you look at it closely.

In field recording specifically, near/mid/far field mic positioning is done on-location and in a variety of conditions (like forests and open fields). The general distinction is the degree of ambience, distance to source and type of microphone (shotgun, figure eight, omni). In this context these are terms of convenience and do not follow the technical acoustical definitions.

That's pretty much all I'm trying to establish. Critical distance, on the other hand, has a very specific acoustical definition and it seems inappropriate to loosely mix it with terms which are used mostly colloquially, especially for purposes of definition. Sitting inside the critical distance won't eliminate the effects of room reflections, for example.

Db SPL and db sound power aren't the same. So it's really saying the same thing.

 

[LTig]

This is contra what Everest & Pohlmann write in the Master Handbook of Acoustics. I'm going from memory here, but the near field is defined as the region where sound power decreases by 12dB per doubling of distance.

Just looked into the book - your memory is correct. The near field region as described by E&P is the short region so close to the speaker that it no longer acts as a point source. But E&P also write: This near field region (not to be confused with "near-field" or "close field" studio monitoring") is of limited interest. So they know that there are other usages of the term near field. And they are not quite correct with this statement: for big planar speakers their near field region cannot be neglected.

I can't remember the other distinctions at the moment. An anechoic chamber definitely follows the characteristics of the free field and is defined that way without conflation with the term near field. (Near/mid/far field don't map onto that chart Blumlein posted, for example.)

My understanding maps the term near field to E&P's term free field, and the term far field to E&P's term reverberant field.

Wikipedia describes it as follows: The sound field very close to a sound source is called the "near-field." By "very close" is meant in the predominantly direct, rather than reflected, sound field. A near-field speaker is a compact studio monitor designed for listening at close distances (3 to 5 feet (0.9 to 1.5 m)), so, in theory, the effects of poor room acoustics are greatly reduced. This is consistent with my mapping.

That technical definition, as far as I can see, is used independently of the term "near field" in the colloquial manner of engineers and others. It doesn't mean that you can't come to some meaningful agreement about the general references (smaller monitors, close listening distances), but it should not be used when describing optimized speaker placement or to define speakers by type because it (as do mid/far field) tends to wobble in meaning when you look at it closely.

I wouldn't be so critical. The terms may not always be used in a strict sense but give a hint what to expect.

In field recording specifically, near/mid/far field mic positioning is done on-location and in a variety of conditions (like forests and open fields). The general distinction is the degree of ambience, distance to source and type of microphone (shotgun, figure eight, omni). In this context these are terms of convenience and do not follow the technical acoustical definitions.

I have no experience with recordings but I assume that depending on the type of microphone the effects of the reflections can be minimzed or maximized, which should have an influence on the criticial distance of the miked instrument.

That's pretty much all I'm trying to establish. Critical distance, on the other hand, has a very specific acoustical definition and it seems inappropriate to loosely mix it with terms which are used mostly colloquially, especially for purposes of definition. Sitting inside the critical distance won't eliminate the effects of room reflections, for example.

It will not eliminate them but can suppress them quite a bit.

 

[andreasmaaan]

Yeh, that exactly right @pozz. "Near-field" and "far-field" as they're used in an everyday sense are not the same as the technical definitions, which would better be described as "within the room's critical distance" (near field) and "diffuse field" (far field).

And anechoic chamber is certainly "free field", not near or far field.

Just to complicate it even further, when it comes to loudspeaker measurements, near field and far field are colloquially used in yet another completely different fashion.

 

[pozz]

@andreasmaaan For measurement, near field would be when the distance between the mic and driver is within a certain fraction of the transducer's diameter, and far field would increase that to a certain multiple. Is that right?

@LTig All that's fair. Also, if you've never looked into field recording it's pretty interesting. It takes layers of takes and some fairly creative mixing to end up with a convincing soundscape. Two releases I really like:

• Chris Watson & BJ Nilsen - Storm (2006)
• Dorninger - Looped Nature & Machines (2008)

 

[andreasmaaan]

@andreasmaaan For measurement, near field would be when the distance between the mic and driver is within a certain fraction of the transducer's diameter, and far field would increase that to a certain multiple. Is that right?

A certain fraction of the baffle’s largest dimension, as it’s off that which the sound waves diffract.

 

[LTig]

@LTig All that's fair. Also, if you've never looked into field recording it's pretty interesting. It takes layers of takes and some fairly creative mixing to end up with a convincing soundscape. Two releases I really like:

• Chris Watson & BJ Nilsen - Storm (2006)
• Dorninger - Looped Nature & Machines (2008)

I listened to a few field recordings (see below) but never really got the knock to make my own ones. I have an Roland R09 field recorder which I mainly used as MP3 player and for recording jam sessions (and a bootleg I have to admit). For real field recordings its noise is too high and the mics too bad.

Anyhow, here is a good story told, and it sounds great both on speakers and on headphones: Annapurna on quietamerican.org (MP3 download)