In article , Eeyore
wrote:


Jim Lesurf wrote:

Eeyore wrote:


If you look at what Stewart wrote (Hi, Stewart! :-) ) that seems to be
comparing the effect of the room reverb with a situation where such
reverb would be absent. At least that is my understanding of his
saying, "...having them in an average living room gives you another
3dB or so of reverberant sound..." If that is wrong, I'm sure he will
correct me, but that was what I then was referring to. Sorry if you
didn't follow what I wrote.

It's certainly true that a domestic room will have a far or ambient
field that is greater than an anechoic chanber. Ever been in one btw ?

Yes. Although 'retired' as an academic I still have my old University
anechoic chamber as a 'lab'. (This translates to my also using its anteroom
as my 'office' when in the physics building. :-) )

They're really odd.

Indeed. :-)

But then again does one listen to one's speakers at 1 metre distance
usually ? so the SPL will have dropped off by X dB anyway by the time it
reaches the sofa.

Indeed. That will tend to happen.


Are you familiar with nearfield and farfield measurements ?

Yes - although you haven't said which particular mechanisms you have
in mind for the factor(s) which affect how they differ, so I don't
know which one(s) you have in mind. Have you read the article I
referred to?

Don't need to. In the near field, SPL will drop off at a rate of 6dB per
doubling of distance (inverse square law).

You haven't noticed that close-in that general assumption may break down?
Consider what happens for example when your distance from the source is
both less than a wavelength and less than a source diameter. Have you seen
the AES papers, etc, that deal with sound levels close in?

There is an analogy here with RF antennas. Near to the antenna the fields
are not simply 'radiated in free space', and the change in level with
nominal distance isn't inverse square. Nor is the wave impedance always the
same as for open space propagation.

So the difficulty here is that 'near field' has more than one defining
meaning. For room acoustics it may mean relative to the boundary between
being dominated by the direct radiation and the reverberant. But there are
other effects.


In the far field it's anyone's guess due to all the factors previously
mentioned. Where the far field begins depends the size of your room and
those other factors.

Indeed. This is one of the reasons the MF 'sliderule' was somewhat
misleading.

BTW I just paused as I heard that Winter is approaching. The geese are
flying over. So loud that I can hear them though the double-glazing. Nice
sound, but sorry to wave farewell to summer...

Slainte,

Jim

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