Chris Hornbeck <(E-Mail Removed)> wrote:

> On Thu, 26 Feb 2009 20:19:28 GMT, (E-Mail Removed) (Don Pearce) wrote:
>
> >On Thu, 26 Feb 2009 20:11:09 +0000,
> >(E-Mail Removed) (Adrian Tuddenham) wrote:
>
> >>For long circuits, a mic and a pre-amp both matched to a standard of 120
> >>ohms would give the best results
>
> >We were at cross purposes - yes to all the above.
>
> And I still disagree. Although there are good solid reasons,
> especially for RF-reared folk, to wish to terminate mic
> lines in their characteristic impedance, this model is
> just not applicable at less-than-a-country-mile to audio
> mic lines with typical mic's and typical uses.

We were discussing atypical uses - such as trying to get the lowest
possible noise and the theoretically optimum arrangements of mic and
pre-amp. it was a theoretical exercise to work out what we should be
aiming for.

On the purely practical side, I am sure I have read in a well-known mic
manufacturer's specsheet that the cable should not exceed a certain
length or there will be HF loss. I presume they would not have included
that information if the problem had not arisen for at least a
significant number of their customers.

The manufacturer should have pointed out that such a limitation only
applies to incorrectly terminated lines and anyone contemplating using
long lines should invest in a correctly-terminating pre-amp. Throw the
problem back where it belongs.

>
> Yes, an unterminated line is reactive. But it don't matter as
> much as several other important things, for this gig. "Best results"
> must include existing infrastructure - like that.

It is perfectly possible to get good results with all sorts of kit if
you know what you are doing, but if you are setting up a flexible
collection of professional gear, to save hassle in the future you should
try to aim for as few compromises as you can at the outset. Then when
you find you have to work with existing infrastructure, at least you
will only have one set of problems, not two.

Designing a pre-amp that matches the mic is (or used to be) such a basic
requirement, it is a mystery to me why so many manufacturers seem to be
designing pre-amps that don't.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Don Pearce <(E-Mail Removed)> wrote:

> On Fri, 27 Feb 2009 11:13:39 +0000,
> (E-Mail Removed)lid (Adrian Tuddenham) wrote:
>
> >Don Pearce <(E-Mail Removed)> wrote:
> >
> >> On Fri, 27 Feb 2009 06:20:32 GMT, "Paul Stamler" <(E-Mail Removed)>
> >> wrote:
> >>
> >> >"Adrian Tuddenham" <(E-Mail Removed)> wrote in message
> >> >news:1ivrfhb.ile3cf1c4ajq6N%(E-Mail Removed) nvalid.invalid...
> >> >> I think we have got at cross-purposes here. I assumed you were talking
> >> >> about being unable to generate a 30-ohm input impedance at the pre-amp
> >> >> in order to terminate older 30-ohm mics. There is no problem designing
> >> >> a pre-amp to do that, at least three different conventional solutions
> >> >> exist. As far as I know, none of the older 30 ohm mics had an internal
> >> >> capacitor unsuited to 30-ohm termination.
> >> >>
> >> >> If you are saying that terminating a modern higher impedance mic with a
> >> >> low impedance pre-amp is a bad idea, I agree - but I wasn't advocating
> >> >> that.
> >> >>
> >> >> If you are saying that some manufacturers of higher impedance mics have
> >> >> skimped on capacitors so that they cannot be terminated with their
> >> >> nominal rated impedance, they deserve to be named and go out of
> >> >> business.
> >> >
> >> >No, I wasn't saying any of those things. I was saying that issues relating
> >> >to coupling capacitors only arise when dealing with condenser mics.
>>>>>Dynamic
> >> >mics don't have issues with coupling capacitors, because they don't
> >> >(usually) have any.
> >> >
> >> >Peace,
> >> >Paul
> >> >
> >>
> >> Dynamic mics have the inverse of the problem - their leakage
> >> inductance - which will cause a loss of top if they are fed into too
> >> small an impedance.
> >
> >Are you referring to the leakage inductance of an in-built matching
> >transformer? I can't see any mechanism for leakage inductance in the
> >moving coil unit itself, unless the magnetic field is shorter than the
> >coil. (Good grief !! What a design error that would be.)
>
> There will be plenty of leakage inductance in the voice coil. In fact
> it will be almost entirely leakage inductance (I'm not talking about
> stray magnetic fields leaking into the air, you understand).

It is certainly a significnantly inductive impedance, which would give
the HF losses you described . I was confused by the use of 'leakage' in
that context because I assumed that all the turns would be doing equally
useful work and that the inductance of those turns would therefore not
count as 'leakage'. (It was just a matter of conventions)


It is normally up to the mic manufacturer to specify the terminating
impedance which give the flattest response; and that would take into
account any inductive effects. If a user then intentionally
mis-terminates it, the resulting problems are of his own creation.

Beginners in this field have my sympathy. Not only is it difficult to
find anywhere that teaches the fundamentals; but when you have learned
them and try to apply them, you will be hard put to find the
information you need - and you will be bombarded with mis-information
from salesmen and others.


~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Don Pearce <(E-Mail Removed)> wrote:

> On Fri, 27 Feb 2009 14:15:37 +0000,
> (E-Mail Removed)lid (Adrian Tuddenham) wrote:
>
> >> There will be plenty of leakage inductance in the voice coil.
[...]
> I was using the term in the transformer sense,...

Understood.

[...]

> >Beginners in this field have my sympathy. Not only is it difficult to
> >find anywhere that teaches the fundamentals; but when you have learned
> >them and try to apply them, you will be hard put to find the
> >information you need - and you will be bombarded with mis-information
> >from salesmen and others.
>
> Beginners are pretty fortunate these days. You buy a mic, you buy a
> mixer and plug them together. The result in 99.9% of cases is that the
> system works pretty much as desired.

That's fine if you want to always be a beginner. If you want to learn
the job properly, it's more difficult now than it was a couple of
generations ago because the fundamentals are rarely taught properly.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Adrian Tuddenham <(E-Mail Removed)> wrote:

> Don Pearce <(E-Mail Removed)> wrote:
>
> > On Fri, 27 Feb 2009 14:15:37 +0000,
> > (E-Mail Removed)lid (Adrian Tuddenham) wrote:
> >
> > >> There will be plenty of leakage inductance in the voice coil.
> [...]
> > I was using the term in the transformer sense,...
>
> Understood.
>
> [...]
>
> > >Beginners in this field have my sympathy. Not only is it difficult to
> > >find anywhere that teaches the fundamentals; but when you have learned
> > >them and try to apply them, you will be hard put to find the
> > >information you need - and you will be bombarded with mis-information
> > >from salesmen and others.
> >
> > Beginners are pretty fortunate these days. You buy a mic, you buy a
> > mixer and plug them together. The result in 99.9% of cases is that the
> > system works pretty much as desired.
>
> That's fine if you want to always be a beginner. If you want to learn
> the job properly, it's more difficult now than it was a couple of
> generations ago because the fundamentals are rarely taught properly.

A composer/producer/engineer friend of mine in Austin was recently
lamenting the loss of any real mentoring in the chain that leads to
recordists these days. Your comments are extremely cogent here.

--
ha
shut up and play your guitar

hank alrich <(E-Mail Removed)> wrote:

> Adrian Tuddenham <(E-Mail Removed)> wrote:
>
> > Don Pearce <(E-Mail Removed)> wrote:
> >
> > > On Fri, 27 Feb 2009 14:15:37 +0000,
> > > (E-Mail Removed)lid (Adrian Tuddenham) wrote:
> > >
> > > >> There will be plenty of leakage inductance in the voice coil.
> > [...]
> > > I was using the term in the transformer sense,...
> >
> > Understood.
> >
> > [...]
> >
> > > >Beginners in this field have my sympathy. Not only is it difficult to
> > > >find anywhere that teaches the fundamentals; but when you have learned
> > > >them and try to apply them, you will be hard put to find the
> > > >information you need - and you will be bombarded with mis-information
> > > >from salesmen and others.
> > >
> > > Beginners are pretty fortunate these days. You buy a mic, you buy a
> > > mixer and plug them together. The result in 99.9% of cases is that the
> > > system works pretty much as desired.
> >
> > That's fine if you want to always be a beginner. If you want to learn
> > the job properly, it's more difficult now than it was a couple of
> > generations ago because the fundamentals are rarely taught properly.
>
> A composer/producer/engineer friend of mine in Austin was recently
> lamenting the loss of any real mentoring in the chain that leads to
> recordists these days. Your comments are extremely cogent here.

That was brought home to me quite forcibly recently by two incidents:

A friend's son at 'media college', ostensibly learning music recording,
made a complete hash of the effects to accompany a simple speech sound
track. I explained, via. his mother, what was wrong with simply taking
a track off an effects CD and slapping it into the mix and suggested he
should ask one of his lecturers for a bit of help in the art of making
your own spot effects.

It transpired that none of the lecturers knew enough to help - and none
of the students had ever been shown how to use a microphone!


On another occasion I was interviewed by someone who had worked for a
large and relatively well-funded community radio station. He began by
dumping the mic at an odd angle on a wooden table top. I asked what the
pickup pattern was, because I couldn't see how any of the conventional
mic types could work properly in the way he was pointing it.

After a lot of prevaricating, it turned out that he had no idea which
way to point the mic or how to estimate its pickup pattern, so I
finished up testing it for him and setting it up correctly. He looked
pained and mystified.

As the interview progressed, he started fiddling with a pen and
absent-mindedly clicking it near the mic. Each time he did this, I
stopped and back-tracked a few words, until it became so regular that I
had to stop altogether. Again. when I explained it to him, he looked
pained and mystified.

A few weeks later I discovered from one of his colleagues that he used
to train the interviewers for the station.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk