Jim Lesurf wrote:

wrote:
On 14 Oct, 00:40, Eeyore wrote:
John Phillips wrote:
Eeyore wrote:
wrote:

An orchestra even in the auditorium can peak at over 120dB.

Do you have a reference for this? I have been looking for credible
sources for peak orchestral SPLs in the auditorium for a long while.

It's a 'well known fact' amongst audio professionals. Google it.

For some reason I have come to be wary of claims thrown around on the basis
of being a "well known fact".

It was actually intentionally slightly tongue in cheek, but remeber I am
referring to PEAK levels not average levels which dB meters read.


That sometimes seems to mean, "Loads of
people have been saying it to one another on the basis that someone else
told them. They've been doing this for so long that no-one can recall who
made it up in the first place." :-)

See above.


In other words completely useless because they haven't the tiniest
clue what they're measuring. Thankfully or even orchestras would have
to be banned from playing for HSE reasons.

However I have only semi-credible figures for places in the
auditorium and they only go up to 109 dB SPL.

IIRC I read an old article by John Crabbe a while ago that reported
measurements. I can't recall details, but if I do I'll report them.

Clearly then, you'll know that having two speakers increases the nominal
sensitivity by 3dB for a central sound, and having them in an average
living room gives you another 3dB or so of reverberant sound, so you can
hit a 120dB peak from 91 db/watt speakers with about 23dB of amp power,
which is 200 watts. Not trivial, but readily obtainable from many modern
amps.

FWIW The effect of room reverb in UK domestic rooms might be somewhat
higher than a 3dB gain. I did some analysis of this a while ago (see Hi Fi
News August 2008). Hard to give a figure as it will probably vary from room
to room, but 3dB may be on the low side as an estimate of what is typical.
IIRC some texts also give details that indicate well above 3dB for this.

3dB relative to WHAT ? Are you familiar with nearfield and farfield
measurements ?


That said (again as discussed in the HFN article) there is a distinction
between the actual instantaneous peak measured power, and the peak level
perceived, due to the way human hearing tends to 'integrate' the effect of
short term delayed reflections into one percieved peak.

Quite. It's not simple.

Graham

In article , Eeyore
wrote:


Jim Lesurf wrote:

wrote:
On 14 Oct, 00:40, Eeyore
wrote:

It's a 'well known fact' amongst audio professionals. Google it.

For some reason I have come to be wary of claims thrown around on the
basis of being a "well known fact".

It was actually intentionally slightly tongue in cheek, but remeber I am
referring to PEAK levels not average levels which dB meters read.

I was aware of that. For all I know, the claim is quite accurate. But the
problem is the one I described.


That sometimes seems to mean, "Loads of people have been saying it to
one another on the basis that someone else told them. They've been
doing this for so long that no-one can recall who made it up in the
first place." :-)

See above.

See above. :-)



Clearly then, you'll know that having two speakers increases the
nominal sensitivity by 3dB for a central sound, and having them in
an average living room gives you another 3dB or so of reverberant
sound, so you can hit a 120dB peak from 91 db/watt speakers with
about 23dB of amp power, which is 200 watts. Not trivial, but
readily obtainable from many modern amps.

FWIW The effect of room reverb in UK domestic rooms might be somewhat
higher than a 3dB gain. I did some analysis of this a while ago (see
Hi Fi News August 2008). Hard to give a figure as it will probably
vary from room to room, but 3dB may be on the low side as an estimate
of what is typical. IIRC some texts also give details that indicate
well above 3dB for this.

3dB relative to WHAT ?

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.


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?


That said (again as discussed in the HFN article) there is a
distinction between the actual instantaneous peak measured power, and
the peak level perceived, due to the way human hearing tends to
'integrate' the effect of short term delayed reflections into one
percieved peak.

Quite. It's not simple.

That was indeed, part of my point. :-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Jim Lesurf wrote:

Eeyore wrote:
Jim Lesurf wrote:

FWIW The effect of room reverb in UK domestic rooms might be somewhat
higher than a 3dB gain. I did some analysis of this a while ago (see
Hi Fi News August 2008). Hard to give a figure as it will probably
vary from room to room, but 3dB may be on the low side as an estimate
of what is typical. IIRC some texts also give details that indicate
well above 3dB for this.

3dB relative to WHAT ?

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 ? They're really odd.

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.


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). 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.


That said (again as discussed in the HFN article) there is a
distinction between the actual instantaneous peak measured power, and
the peak level perceived, due to the way human hearing tends to
'integrate' the effect of short term delayed reflections into one
percieved peak.

Quite. It's not simple.

That was indeed, part of my point. :-)

Ok.

Graham

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

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

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...

What summer was that then?..


Slainte,

Jim


--
Tony Sayer

In article , tony sayer

wrote:
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...

What summer was that then?..

The one we just had that seemed wet enough to keep the geese happy. :-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Thu, 16 Oct 2008 16:17:03 +0100, Jim Lesurf
wrote:

In article , tony sayer

wrote:
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...

What summer was that then?..

The one we just had that seemed wet enough to keep the geese happy. :-)

Slainte,

Jim

I'm still waiting for summer. I won't be putting the clocks back or
celebrating christmas 'till I've had my summer!

Marky P.