how good are class D amplifiers?
 

"Serge Auckland" wrote in
message
"Jim Lesurf" wrote in message
...
In article , Serge
Auckland wrote:

You put everything into the 'sig' of the posting so I
had to fiddle about the rescue it for the following:


Ak! I can't have that I'm afraid. I think I understand
what you're saying, but what I'm saying is that
loudspeakers are non-linear loads and something


Loudspeakers are *not* in any way non-linear loads.

Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and
magnet) speakers have distinct nonlinearities. e.g. the
inductance of the coil is affected by its surroundings
and the interaction varies with displacement. I have a
feeling there are JAES papers on this stemming from
ideas about changing from voltage drive to current
drive. IIRC There is also a similar effect in terms of the back EMF
varying with the changing field
coupling. I think this can be measured as current
waveform effects.

This is measureable, but generally slight.

However that does not change the basis of using the
voltage input to the speaker for setting levels when
doing an amp comparison as any speaker nonlinearity will
be 'common mode'. If you are using the same speaker to
compare two amps, either they are (un)affected by the
above in the (audibly) same way, or not.

Agreed. When we did ABX tests of amplifiers, we set voltage levels measured
across the speaker's input terminals. We *never* noticed any effects due to
speaker nonlinearity. However, our measurements were within 0.1 dB which is
about 1%. That means that there might have been nonlinear effects below 1%
that we did not measure. However, if there were audible effects, they would
have been heard in our ABX tests.

Jim, as befits an academic, is of course correct in
saying that there are non-linearities, but as far as I
know these are secondary if not tertiary effects which
are swamped by the mechanical non-linearities of a
loudspeaker.

That can be true from the acoustical side. These sorts of things are most
important at low frequencies. In the middle range, they tend to be far
smaller. At low frequencies they tend to be masked by the natural acoustical
nonlinearity of the speaker.

The variation in load impedance with
displacement is of such a low level that, in engineering
terms if not in academic terms, can be safely ignored.
Jim, if you have some figures that are at odds with this
view, I would be interested to know them.

It's usually a second or third order effect under normal listening
conditions.

how good are class D amplifiers?
 

"Rob" wrote in message


The *real* point I'd like to explore would be the notion
that conventional measurements are not a reliable guide to
sound experienced.

Investigations of this kind ahve been made by people with far better
resources than you seem to have available to you.

Of course (again) such a statement comes across to some
as something between witchcraft, homoeopathy and
astrology, but I set it out here just so you can categorise my comments
properly.

There's nothing wrong with wondering whether or not a full set of
conventional measurements are a reliable guide to sound quality in normal
listening. It is a question that has been answered again and again,
affirming the idea that a full set of conventional measurements are a
reliable guide to sound quality.

how good are class D amplifiers?
 

In article , Serge Auckland
wrote:


"Jim Lesurf" wrote in message
...
In article , Serge Auckland
wrote:



Loudspeakers are *not* in any way non-linear loads.

Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet)
speakers have distinct nonlinearities. e.g. the inductance of the coil
is affected by its surroundings and the interaction varies with
displacement. I have a feeling there are JAES papers on this stemming
from ideas about changing from voltage drive to current drive. IIRC
There is also a similar effect in terms of the back EMF varying with
the changing field coupling. I think this can be measured as current
waveform effects.

However that does not change the basis of using the voltage input to
the speaker for setting levels when doing an amp comparison as any
speaker nonlinearity will be 'common mode'. If you are using the same
speaker to compare two amps, either they are (un)affected by the above
in the (audibly) same way, or not.

Jim, as befits an academic, is of course correct in saying that there
are non-linearities, but as far as I know these are secondary if not
tertiary effects which are swamped by the mechanical non-linearities of
a loudspeaker.

I'm not sure of the 'secondary'/'tertiary' point. However I'd agree that
the transducer nonlinearities seem to be dominant.

The variation in load impedance with displacement is of
such a low level that, in engineering terms if not in academic terms,
can be safely ignored.

Yes. It is certainly the case that people tend to ignore the impedance
nonlinearities for quite sensible practical reasons. One being as you give.
Another reason IIRC is because the general expectation is that the amp will
have a low output impedance and the speaker works on the basis of
translating the asserted voltage patterns into sound pressure ones. That
implies that the load nonlinearity only matters to the poor amp maker who
has to ensure the appropiate current is delivered 'on demand' by the load.
:-)

Jim, if you have some figures that are at odds with this view, I would
be interested to know them.

I don't have any figures in mind, and agree with what you say. IIRC there
is at least one AES paper that looked at this and decided the effects were
(on the above basis) not worth too much concern, but I can't recall
details. I think the area cropped up due to muddles about the claimed
effects of 'bi wiring' wrt speaker distortion, but I'd need to check that.
These areas have been riddled with confused claims and attempts by others
to sort the reality from the nonsense.

However I have more recently become curious about combinations of speaker
load nonlinearity and amplifiers which have relatively high output
impedances which may also vary with frequency and signal level. Where the
assumptions that seem reasonable and sensible to most audio engineers may
not hold. One of the topics on my 'to do' list to look at sometime... :-)

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

how good are class D amplifiers?
 

In article , Arny
Krueger
wrote:


There's nothing wrong with wondering whether or not a full set of
conventional measurements are a reliable guide to sound quality in
normal listening. It is a question that has been answered again and
again, affirming the idea that a full set of conventional measurements
are a reliable guide to sound quality.

Alas, the problem seems to be that many 'reviews' not only fail to make
appropriate measurements. They also fail to give any explanation of their
meanings and what can be drawn from them. Instead the 'review' has purple
prose extolling the writer's impressions about a system and room the
readers will never use.

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

how good are class D amplifiers?
 

"Arny Krueger" wrote


There's nothing wrong with wondering whether or not a full set of
conventional measurements are a reliable guide to sound quality in
normal listening. It is a question that has been answered again and
again, affirming the idea that a full set of conventional measurements
are a reliable guide to sound quality.




So simple, isn't it? When you are selecting kit, you just buy a heap of
stuff where the figures (or, at least, the figures 'as claimed') tell
you it'll work and Bob's your uncle! Yet the (hifi) world is full of
people who have done just that and who are not happy with the result -
time and time again, some of 'em!

You'd think it would be impossible to get it wrong, wouldn't you??

how good are class D amplifiers?
 

"Jim Lesurf" wrote


e.g. Despite Sony being a regarded name I recently tried a DVD
recorder
from them. It had a cooling fan that was so loud that it was
distracting
when listening to dialogue on items recorded. This is absurd and
needless,
yet when I asked a local Sony center their reaction was 'they all do
it'.
They seemed not to think it was a problem, and clearly had no idea
that
quiet fans can be bought. Perhaps they think everyone is too busy
looking
at the pictures to notice the sound of a helicopter accompanying it.
;-


Given your supersensitivity to noise ('rifle shots' on vinyl for
example) I can see it would be a problem, but the harsh reality is that
even SS/digital creates heat and noise - the computer I am using right
now is really very noisy but it doesn't stop me using it for audio. The
trick is to 'tune it out', 'drown it out' or just stop noticing it!

I guess DVD players/recorders are not designed to be too close in use
(more 'over by the telly' ?) - perhaps you got a bad 'un or you have
sited the device badly where it runs hotter than necessary? I think it's
more usual that the fans don't kick in too often unless they get very
hot - FWIW, I have a Panasonic DVDR which I can't say I ever notice is
'noisy', but then I don't use it very often and I don't suffer from
'vinyl noise' except on extreme examples...??



The above is nothing to do with amps per se. But it shows that some
companies end up being run by suits, and have development engineers
who
just produce what they are told by the suits and go home with their
paychecks. The spec says nothing about the fan not making a loud
noise, so
this cheap one is fine...


A development engineer who can't deliver the spec. required by his
employers is looking at a career change, at the very least...


I've also repeatedly witnessed companies who bring out 'new' products
distinctly worse than the ones they'd made a year or two before.
Different
suits and a different R&D team. No internal communications. No clue.
The relevant suits and engineers are often isolated from the public
and getting contact with them is almost impossible in practice.


I think that one can be safely put down to 'market forces at work in the
context of the new, cheap Digital Era' - witness the recent decline in
quality and ultimate disappearance of the Technics brand...

how good are class D amplifiers?
 

"Keith G" wrote in message
...

"Arny Krueger" wrote


There's nothing wrong with wondering whether or not a full set of
conventional measurements are a reliable guide to sound quality in normal
listening. It is a question that has been answered again and again,
affirming the idea that a full set of conventional measurements are a
reliable guide to sound quality.




So simple, isn't it? When you are selecting kit, you just buy a heap of
stuff where the figures (or, at least, the figures 'as claimed') tell you
it'll work and Bob's your uncle! Yet the (hifi) world is full of people
who have done just that and who are not happy with the result - time and
time again, some of 'em!

You'd think it would be impossible to get it wrong, wouldn't you??

I think that with electronics, it is pretty much impossible to get it wrong
if you buy on the figures, *provided* that you understand what the figures
are telling you *and* that the published figures are reliable. Sadly, specs
are rarely comprehensive, seldom if ever give you the methodology under
which they were derived, and even with reputable manufacturers, are not
always met.

When choosing electronics myself, I've chosen on facilities, price and looks
from products who's specs are acceptable, and from manufacturers who's
reputation is sound. So far, they only problems I've had are with things
that are not part of the specification, like Jim's DVD recorder with a loud
fan. In my case it was a Sony DVD/VCR combi player who's remote control was
incompatible with Sony's own learning remote system. I bought the Sony
DVD/VCR unit only because I assumed being Sony, it would be compatible with
Sony's remote. Silly me!

The only equipment I would listen to before buying would be loudspeakers,
and then only in my own room. Having said that, I bought my current Meridian
D5000s sight-unseen, being familiar with Meridian's previous loudspeakers,
and I wasn't in any way disappointed.

S.


--
http://audiopages.googlepages.com

how good are class D amplifiers?
 

"Keith G" wrote in message


"Arny Krueger" wrote

(in the context of amplifiers)

There's nothing wrong with wondering whether or not a
full set of conventional measurements are a reliable
guide to sound quality in normal listening. It is a
question that has been answered again and again,
affirming the idea that a full set of conventional
measurements are a reliable guide to sound quality.

So simple, isn't it?

Not at all. It is almost impossible to find a set of manufacturer's specs
for a consumer amplifier, that includes anything like a full set of
conventional measurements.

When you are selecting kit, you just
buy a heap of stuff where the figures (or, at least, the
figures 'as claimed') tell you it'll work and Bob's your
uncle!

Typical of your stupid straw-men, Keith. The topic is amplfiiers, and now
you're ranting and raving like a loon about "kit" which as I understand your
vernacular, means any kind of audio gear.

Yet the (hifi) world is full of people who have
done just that and who are not happy with the result -
time and time again, some of 'em!

That's because they made the same stupid assumptions that you have embodied
here, Keith.

You'd think it would be impossible to get it wrong,
wouldn't you??

Keith, with loons like you misreading everything that's posted, I'm not the
least bit surprised.

how good are class D amplifiers?
 

"Serge Auckland" wrote in message
...

"Keith G" wrote in message
...

"Arny Krueger" wrote


There's nothing wrong with wondering whether or not a full set of
conventional measurements are a reliable guide to sound quality in
normal listening. It is a question that has been answered again and
again, affirming the idea that a full set of conventional
measurements are a reliable guide to sound quality.




So simple, isn't it? When you are selecting kit, you just buy a heap
of stuff where the figures (or, at least, the figures 'as claimed')
tell you it'll work and Bob's your uncle! Yet the (hifi) world is
full of people who have done just that and who are not happy with the
result - time and time again, some of 'em!

You'd think it would be impossible to get it wrong, wouldn't you??

I think that with electronics, it is pretty much impossible to get it
wrong if you buy on the figures, *provided* that you understand what
the figures are telling you *and* that the published figures are
reliable. Sadly, specs are rarely comprehensive, seldom if ever give
you the methodology under which they were derived, and even with
reputable manufacturers, are not always met.

When choosing electronics myself, I've chosen on facilities, price and
looks from products who's specs are acceptable, and from manufacturers
who's reputation is sound. So far, they only problems I've had are
with things that are not part of the specification, like Jim's DVD
recorder with a loud fan. In my case it was a Sony DVD/VCR combi
player who's remote control was incompatible with Sony's own learning
remote system. I bought the Sony DVD/VCR unit only because I assumed
being Sony, it would be compatible with Sony's remote. Silly me!

The only equipment I would listen to before buying would be
loudspeakers, and then only in my own room. Having said that, I bought
my current Meridian D5000s sight-unseen, being familiar with
Meridian's previous loudspeakers, and I wasn't in any way
disappointed.


Frankly, I don't see what else you can do if you don't have the budget
(or inclination) to put yourself into the hands of a 'hifi specialist
who promises to do it all for you. Also, there's a lot of highly
impractical advice from a 'certain quarter' here that advises
auditioning all sorts of kit kit like the dealers have actually *seen*
some/most/all of the Desired Items - let alone stock them and will let
you home demo them!! (The only way - what good is a 'shop demo'?) All
very good in theory, difficult to do in the real world...

For me, half the fun is trying to wring a decent sound out of
cheap/secondhand crap and/or homebrew and there are those who would say
I've had my successes. It's hardly a question of economics I might add -
if I had trusted a 'specialist' to throw a system together a few years
ago it would have almost certainly saved me a lot of time and money!! My
methodology is to buy stuff on spec (yes, the figures matter here - what
else is there to go on?), heap it up, sort through it at my leisure and
run comparisons over weeks/months - latest candidate is a nice little
valve pre that hasn't distinguished itself yet (other than on my
Dynacos). It was the right price, looks the business and has definitely
got posh innards - my money's on it dropping in somewhere reet nicely at
some point...

Now, having mentioned that - a 'tubie question': if the afore-mentioned
pre has 6SN7GTBs fitted, can I substitute 6SN7GTs as a straight drop-in?
Duncan says 'different rating or performance' but the 'Application Data'
figures appear identical for both valves??

how good are class D amplifiers?
 

"Serge Auckland" wrote in
message

I think that with electronics, it is pretty much
impossible to get it wrong if you buy on the figures,
*provided* that you understand what the figures are
telling you *and* that the published figures are
reliable.

Right - that's the same think we've been trying to explain to Keith and his
fellow loons for a dog's age.

Sadly, specs are rarely comprehensive, seldom
if ever give you the methodology under which they were
derived, and even with reputable manufacturers, are not
always met.

Totally agreed. Particularly true of consumer electronics.

When choosing electronics myself, I've chosen on
facilities, price and looks from products who's specs are
acceptable, and from manufacturers who's reputation is
sound.

Been there, done that and it also worked.

So far, they only problems I've had are with
things that are not part of the specification, like Jim's
DVD recorder with a loud fan. In my case it was a Sony
DVD/VCR combi player who's remote control was
incompatible with Sony's own learning remote system. I
bought the Sony DVD/VCR unit only because I assumed being
Sony, it would be compatible with Sony's remote. Silly
me!

Sony does some of the weirdest things, especially lately.

The only equipment I would listen to before buying would
be loudspeakers, and then only in my own room. Having
said that, I bought my current Meridian D5000s
sight-unseen, being familiar with Meridian's previous
loudspeakers, and I wasn't in any way disappointed.

I bought my last 4 sets of speakers either unheard, or heard and thought
they sounded pretty poor in the demo room.