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On Mon, 03 Jan 2005 18:40:27 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Mon, 3 Jan 2005 15:16:08 +0200, "Iain M Churches"
wrote:

Please get a copy of IEC/EN/BS EN 60268-5 and read it carefully for
yourself. As has been stated many times, there is no 8 Ohms standard.
What we are concerned with is deviation from a nominal impedance.

If you do a full vector measurement of a speaker in the complex plane,
you will see that the main part of the range from the upper bass
resonance to the point where the tweeter inductance starts running away
is a pretty good circle. The centre of that circle is typically the
"nominal" impedance of the speaker, even though the actual impedance is
nowhere near it at any point. You can't see this on a normal rectangular
plot, so without the full vector data it doesn't seem to make much sense.

That's an interesting point. Maybe LS impedances and amp o/p impedance
should routinely be plotted on Smith charts in the reviews... :-)

The last Smith chart I can recall offhand in HFN is - I think - in one of
the Radford articles on his power amp kit back circa 1960-ish. Must check
to see if my memory is playing tricks on me!

Slainte,

Jim

An interesting idea to plot amp output impedances on a Smith chart. A
potentially embarrassing one for a few manufacturers, though, as it
would show up instantly those duffers that are unstable into some
loads. An S22 curve running outside the graph is always a tricky one
to explain for an amplifier.

d

Pearce Consulting
http://www.pearce.uk.com

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In article , Jim Lesurf
wrote:


I have also known of cases where there has been 'unhealthy'
relationships between some reviewers and some writers/magazines.

Sorry, typo - brain out to lunch. I meant the above to say:

...between some manufacturers/dealers and some writers/magazines.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

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"Jim Lesurf" wrote in message
...
In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...

But there is an "AES 8 Ohm spec" when I am using that phrase to mean a
speaker which would accord with the spec you mention with a nominal quoted
value of 8 Ohms. I was however trying to keep my sentence short. :-)

Agreed, understood and accepted:-)


Agreed. The snag being that in many cases no-one bothers to mention any
value at all. Hence leaving the (prospective/actual) buyer in ignorance of
the actual impedance properties of the speakers in question.

It would be interesting to see what would happen, if after such a poorly
presented review, 75% of the readership would complain to HiFi News or
whichever magazine, by telephone, fax and e-mail.
I am sure heads would roll. But as my Svenska
journalist friend says, a magazine rarely makes an effort to surpass the
minimum standard demanded by its readership.

[snip my comments on the consumer audio mags]

Alas, what they publish rarely considers what data might aid clear and
reliable comparisons from one review to another. Their methods, and what
they report, varies from one review to another. I'm afraid that a lot of
what appears is almost 'content free' in technical terms, and consists of
someone saying how they liked a given item.

Especially after the manufacturer has allowed them to buy it for a nominal
sum, (usually a tenner) as a shop soiled/damaged unit:-)

Andre Jute told me once that he wrote a an equipment review, and after this
was published, he phoned to the magazine to ask about the return of the
review unit. They were greatly surprised:-)

One prime example was a set of 'reviews' in HFW which discussed the
'sound'
of various cables, but said nothing about the music used, the equipment
used, the room, etc. Hence even accepting that the perceived differences
were not imaginary we have no idea if anyone else would have come to the
same conclusions using their own ears, choice of music, etc, etc. These
reviews stuck in my mind as they didn't even give the name of the
reviewer.
Hence you couldn't even try to guess on the basis of any prior experience
of how your own views of past comments by the writer agreed (or not) with
your own.

Hmm! No by-line on a review? That's worthless, IMO. But that's why I
read Studio Sound. There are regular reviewers who have regular columns
with their name, and also photograph at the top, so you know who do look
for when you do a drive-by in your S-Class Mercedes with an Anschutz rifle.

And if you want to know what sometimes passes for 'technical' reports in
the magazines, have a look at the 'Current dependent phase effects in
cables' example I have analysed in the 'analog and audio' section of the
'Scots Guide'. This was a set of articles reporting a startling new
'discovery' that would have revolutionised our understanding of cables.

Or it would have done it it hadn't been nonsense based on incorrectly
carried out and wildly misinterpreted measurements. :-)

But why do the British audio public put up with this drivel?

I've encountered similar technobabble in the mags on many occasions. e.g.
more cable nonsense, this time by Hawksford in HFN many years ago. I long
ago lost track of how often this happens - and in Electronics World as
well, which you might hope was better. :-/

Is the man I know? Professor Malcolm Hawksford. BSc PhD Aston,
CEng FIEE FAES FIOA. Professor at the University of Essex.
I am surprised that he would get involved in anything like that.
He is a highly respected scholar, closely involved with the UK's only
Tonmeister course, at the University of Essex.

Iain, I'd recommend you buy a few copies of mags like Hi Fi News and Hi Fi
World. You will find some useful info in them, but I fear you will be
puzzled/surprised by quite a lot of what you see! Not for the
faint-hearted, though... :-/

Audio equipment reviews are not close to my heart. though I do like to read
recorded music reviews, especially of projects in which I have been
involved, to see if the reviewer has really picked out the relevant
points:-)

So maybe I will just stick to Studio Sound, JAES and Cranial Surgery for
Beginners.

Iain

(Oh, I have just realised that Studio Sound
abbreviates to SS - I must cancel my subscription immediately:-))

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On Mon, 03 Jan 2005 18:40:27 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Mon, 3 Jan 2005 15:16:08 +0200, "Iain M Churches"
wrote:

Please get a copy of IEC/EN/BS EN 60268-5 and read it carefully for
yourself. As has been stated many times, there is no 8 Ohms standard.
What we are concerned with is deviation from a nominal impedance.

If you do a full vector measurement of a speaker in the complex plane,
you will see that the main part of the range from the upper bass
resonance to the point where the tweeter inductance starts running away
is a pretty good circle. The centre of that circle is typically the
"nominal" impedance of the speaker, even though the actual impedance is
nowhere near it at any point. You can't see this on a normal rectangular
plot, so without the full vector data it doesn't seem to make much sense.

That's an interesting point. Maybe LS impedances and amp o/p impedance
should routinely be plotted on Smith charts in the reviews... :-)

The last Smith chart I can recall offhand in HFN is - I think - in one of
the Radford articles on his power amp kit back circa 1960-ish. Must check
to see if my memory is playing tricks on me!

Slainte,

Jim

Jim - here's a plot - rectangular and complex for one of my speakers.
It shows what I mean.

http://www.donepearce.plus.com/odds/speaker.pdf

d

Pearce Consulting
http://www.pearce.uk.com

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"Don Pearce" wrote in message
...
Jim - here's a plot - rectangular and complex for one of my speakers.
It shows what I mean.

http://www.donepearce.plus.com/odds/speaker.pdf

d

Don - how is the data for the Smith chart collected?

Iain

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On Tue, 4 Jan 2005 12:15:36 +0200, "Iain M Churches"
wrote:


"Don Pearce" wrote in message
...
Jim - here's a plot - rectangular and complex for one of my speakers.
It shows what I mean.

http://www.donepearce.plus.com/odds/speaker.pdf

d

Don - how is the data for the Smith chart collected?

Iain


You can do it manually measuring magnitude and phase at each frequency
point (using a tiny resistor to sniff the current) then convert that
to real and imaginary components of impedance, or do what I did, which
was to build a network analyser with directional couplers and do the
measurements automatically. Not a job for the faint hearted, though,
and I could really only do it because I have a background in the
design of measurement systems.

d

Pearce Consulting
http://www.pearce.uk.com

Tube amplifiers
 

In article , Iain M Churches
wrote:

"Jim Lesurf" wrote in message
...



Agreed. The snag being that in many cases no-one bothers to mention
any value at all. Hence leaving the (prospective/actual) buyer in
ignorance of the actual impedance properties of the speakers in
question.

It would be interesting to see what would happen, if after such a poorly
presented review, 75% of the readership would complain to HiFi News or
whichever magazine, by telephone, fax and e-mail. I am sure heads would
roll. But as my Svenska journalist friend says, a magazine rarely makes
an effort to surpass the minimum standard demanded by its readership.

This is to some extent a matter of 'Darwinian selection' in that the
magazine either finds an audience or it does not. This ends up meaning that
we get the government we deserve, :-)


Andre Jute told me once that he wrote a an equipment review, and after
this was published, he phoned to the magazine to ask about the return of
the review unit. They were greatly surprised:-)

I really must take up one magazine's offer of lending me an SACD player...
8-]



And if you want to know what sometimes passes for 'technical' reports
in the magazines, have a look at the 'Current dependent phase effects
in cables' example I have analysed in the 'analog and audio' section
of the 'Scots Guide'. This was a set of articles reporting a startling
new 'discovery' that would have revolutionised our understanding of
cables.

Or it would have done it it hadn't been nonsense based on incorrectly
carried out and wildly misinterpreted measurements. :-)

But why do the British audio public put up with this drivel?

I will now put on my 'ex-academic' hat...

IMHO for the same reason that the numbers of UK students taking exams in
topics like physics and maths is declining, and the number of Universties
offerring physics courses is declining, and the number of UK undergrads in
such topics is falling.

The problem with such topics is that they are perceived as poorly paid,
poorly regarded, and 'hard' to learn/do.

Hence in a country where the number of undegraduates is rising, the number
who can do 'hard sums' or have learned physics, etc, is falling.

If you read the UK consumer mags you will see some technical content. But a
lot of the content is 'information free' and consists simply of writer
opinions on subjective matters. Also, if you pay peanuts, you get monkeys.
:-)

To write in a UK mag you either need to write a lot, or do so simply out of
enthusiasm as a 'hobby', or have some stand-out talent that draws a higher
rate of pay.

To be able to carry out a decent set of measurements requires a fair bit of
kit, kept in good calibration, and the time to make the measurements. Also
the skill to understand them. This all costs money.

There are some good 'technical' writers. But many do not seem either to
understand, or feel it matters.

I've encountered similar technobabble in the mags on many occasions.
e.g. more cable nonsense, this time by Hawksford in HFN many years
ago. I long ago lost track of how often this happens - and in
Electronics World as well, which you might hope was better. :-/

Is the man I know? Professor Malcolm Hawksford. BSc PhD Aston, CEng
FIEE FAES FIOA. Professor at the University of Essex. I am surprised
that he would get involved in anything like that. He is a highly
respected scholar, closely involved with the UK's only Tonmeister
course, at the University of Essex.

Yes. He has done a lot of good work. But he has also produced at least one
series of articles that showed quite neatly that being a good engineer and
mathematician does not prevent someone from misunderstanding the relevant
physics. :-)

In fairness, though, we *all* suffer at times from making errors. I
certainly make them. The problem, though, is getting these identified and
corrected in the 'popular press'. FWIW for the item I have in mind I
exchanged letters with him many years ago and he accepted that his
'evidence' was not actually correctly interpreted, and that his theories
had a problem. But none of this ever appeared in print so far as I know.

Also, the matter in question was quite a subtle and complex one, and is
widely misunderstood. So my complaint here is not really with him, but with
the way such matters tend to be treated by the magazines over the years.
Again, though, the editor does not necessarily know one way or the other.
Quite understandably, he wants to produce a successful magazine, not an
academic journal.


(Oh, I have just realised that Studio Sound abbreviates to SS - I must
cancel my subscription immediately:-))

LOL. Perhaps I should subscribe. You can send me your copies if you wish.
;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Tube amplifiers
 

In article , Don Pearce
wrote:

Jim - here's a plot - rectangular and complex for one of my speakers. It
shows what I mean.

http://www.donepearce.plus.com/odds/speaker.pdf

Thanks for doing the above plots. The results do look very interesting
plotted in that manner. I can't recall that being done for loudspeakers
before and it now looks like an 'obvious' method for showing up the speaker
behaviour. :-)

It occurred to me that it would be even better if the line had 'blobs' at
uniform log frequency intervals so we could see how much of the audio
interval was represented by given sections of the plotted line. Once that
was done it would show very neatly the speaker impedance properties. Make
assessment much clearer. Then put another plot on the graph showing the amp
o/p impedance locus... (Ideally, a point at the origin!)

Alas, I wonder what chance we have of getting consumer mags to adopt such a
display. They might like it as it looks 'impressive', though... :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

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"Iain M Churches" wrote in message
...

(Oh, I have just realised that Studio Sound
abbreviates to SS - I must cancel my subscription immediately:-))



And send out (for) an SOS immediately ;-)

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On Tue, 4 Jan 2005 11:34:39 +0200, "Iain M Churches"
wrote:

"Jim Lesurf" wrote in message
...

And if you want to know what sometimes passes for 'technical' reports in
the magazines, have a look at the 'Current dependent phase effects in
cables' example I have analysed in the 'analog and audio' section of the
'Scots Guide'. This was a set of articles reporting a startling new
'discovery' that would have revolutionised our understanding of cables.

Or it would have done it it hadn't been nonsense based on incorrectly
carried out and wildly misinterpreted measurements. :-)

But why do the British audio public put up with this drivel?

I've encountered similar technobabble in the mags on many occasions. e.g.
more cable nonsense, this time by Hawksford in HFN many years ago. I long
ago lost track of how often this happens - and in Electronics World as
well, which you might hope was better. :-/

Is the man I know? Professor Malcolm Hawksford. BSc PhD Aston,
CEng FIEE FAES FIOA. Professor at the University of Essex.
I am surprised that he would get involved in anything like that.
He is a highly respected scholar, closely involved with the UK's only
Tonmeister course, at the University of Essex.

That's him - read the HFN articles and prepare to be startled! As with
Tim de Paravicini, he may know his stuff in some respects, but in
others, he is *seriously* out to lunch! Mad professor, indeedy......

They're all around, James Boyk is another, across the pond.

Iain, I'd recommend you buy a few copies of mags like Hi Fi News and Hi Fi
World. You will find some useful info in them, but I fear you will be
puzzled/surprised by quite a lot of what you see! Not for the
faint-hearted, though... :-/

Audio equipment reviews are not close to my heart. though I do like to read
recorded music reviews, especially of projects in which I have been
involved, to see if the reviewer has really picked out the relevant
points:-)

So maybe I will just stick to Studio Sound, JAES and Cranial Surgery for
Beginners.

Iain

(Oh, I have just realised that Studio Sound
abbreviates to SS - I must cancel my subscription immediately:-))

You could just think of it as 'Jaguar', that seemed to do the trick
for Swallow Sidecars when a similarly unfortunate connotation occurred
in the '40s....... :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering