Audio, hi-fi and car audio - Why moving coil

Audio Banter (https://www.audiobanter.co.uk/forum.php)

- uk.rec.audio (General Audio and Hi-Fi) (https://www.audiobanter.co.uk/uk-rec-audio-general-audio/)

- - Why moving coil (https://www.audiobanter.co.uk/uk-rec-audio-general-audio/3811-why-moving-coil.html)

AZ Nomad wrote:

On Thu, 16 Mar 2006 21:21:59 +0000, Ian Bell

I am surprised there has been so little development of cartridges beyond
the two basic magnetic types and good old ceramic. What about an optical
cartridge for example?

Are you talking about bouncing a laser off the record groove? It was a
failu it was too expensive and worked worse than traditional methods as
it was best at reading the crud in the groove instead of just pushing it
aside.

No I was thinking more of a small low mass pair of mirrors in place of the
MM for example with perhaps fibre optics to carry the data - no hum issues
for a start.

Ian

On Thu, 16 Mar 2006 23:23:34 -0000, "Serge Auckland"
wrote:

"Bill Taylor" wrote in message
...
On Thu, 16 Mar 2006 19:08:27 -0000, "Serge Auckland"
wrote:

Similarly, frequency response plots of moving magnets and moving coils
don't
show any particular benefit to the MC, nor does stereo separation or
harmonic and intermodulation distortion. So why *are* MC cartridges
throught
to be better?

If anyone knows of any good engineering reasons why this should be so, I
would be most interested to hear.

The only vaguely convincing explanation that I've heard is that MCs
can use less damping of the stylus assembly. Theoretically this
should allow better trackability at mid frequencies. I also have vague
recollections that the cantilever can more easily be made shorter,
which would help in keeping the effective tip mass down, which should
give better HF trackability. (Compliance only needs to be more than
about 10-12c.u. to track all records)

Not being a member of the MC owners club, I don't know if these
theories have any validity.

Bill

Interesting theories. Can you tell me a bit more as to why a compliance of
10-12cu is sufficient for all records? Interesting that in vinyl's heyday,
some cartridges were providing 30-40 cu. It could be a marketing exercise
rather than having a sound engineering reason for it, but it would be useful
to know why such high compliances are not necessary.

According to J Walton in "Pickups - The Key to Hi Fi" (published 1968,
but the physics haven't changed): the maximum excursion on an LP is
about .005cm, "if compliance were the only factor involved a
compliance of 2 c.u. is quite sufficient to track the largest stereo
amplitude of .005 cm at 3 gm tracking weight". It's possible that a
small number of modern LPs have slightly higher excursions, and
tracking weights are a bit lower, so a slightly higher compliance is
needed, but not that much higher.

The very high compliances of the 70s were very much a marketing
excercise. The other important factor with compliance is the LF
resonance with the cartridge/arm mass. The ideal resonant frequency is
about 10-15 Hz, any lower than that and the cartridge system is liable
to become unstable and skip grooves with the slightest disturbance,
and the oscillations caused by these disturbances produce very audible
wow and tracking force variations. Some of the high compliance
cartridges needed a negative mass arm in order to get the LF resonance
up to a reasonable frequency.

I recently changed my turntable. The only reasonably priced one that I
felt that I could trust was the Technics DJ turntable (basically a
1970s HiFi turntable with a speed control). The supplied arm has
quite a high effective mass and with the Shure V15-V that I had to buy
as well the LF resonance is plainly much to low, this cartridge has a
more reasonable compliance of about 23c.u., but it is still too high.
Forunately the Shure damper more or less controls the resonance.

There is another advantage of MCs that was certainly true in the 60s
and 70s. It is much easier to create a large magnetic field with a big
static magnet in the body of the cartridge than it is with a small
magnet on the end of the cantilever, so in the days of less effective
magnets it would probably be possible to keep the effective tip mass
lower with MC rather than MM cartridges.

Bill

In article , Trevor
Wilson wrote:

Similarly, frequency response plots of moving magnets and moving coils
don't show any particular benefit to the MC, nor does stereo
separation or harmonic and intermodulation distortion. So why *are*
MC cartridges throught to be better?

**Er, not quite. The FR plots of MC carts, in some cases, CAN be shown
to be superior. The reason, of course, is blindingly simple. It's all
about inductance. The inductance of (LOW OUTPUT) MC carts is very low,
indeed. This enables them to produce a very flat, very wide (up to
around 60kHz) frequency response, with a correspondingly superior rise
time.

The problem with this is that the mechanical resonances will still exist.
:-)

Also bear in mind that with a decent MM cartridge you can arrange the
loading to give quite a flat response if that is your concern. I've not
personally had any worries on that score with my own Shure V15/III...

Alas, magazines and makers now tend to avoid giving any useful data on
cartridges. Hence we usually can't now assess the level of compliance, tip
mass, etc, etc. Nor, indeed the levels of distortion.

My recollection was that MC's became 'flavour of the year' with some
subjective reviewers precisely because the ones in question did *not* have
a flat response, and they liked the changes, but then ascribed this to
'magic'... :-)

The real benefit of such a system is that LC resonance effects
are often well outside the audible range. This means that a low output
MC cart may exhibit a very flat phase response within the audio band.
This may not be the case with high output MC carts nor with some MM
carts.

For the record: Many, well designed, MM carts do not exhibit any
resonance problems without the audio band.

Indeed. Thus this isn't really a reason for arguing that MCs as a class of
object are 'better' to MMs as a class. :-)

The reality is that there will be 'good' and 'bad' examples in each class,
and a 'good' one in either may deliver excellent results.

FWIW I don't know of any MCs that can provide the same levels of tracking,
etc, of something like a Shure V15. But this may be because no-one for
years can be bothered to even consider such things in 'reviews'. sic

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

In article 441a6e41.0@entanet, Ian Bell wrote:
AZ Nomad wrote:

On Thu, 16 Mar 2006 21:21:59 +0000, Ian Bell

I am surprised there has been so little development of cartridges
beyond the two basic magnetic types and good old ceramic. What about
an optical cartridge for example?

Are you talking about bouncing a laser off the record groove? It was
a failu it was too expensive and worked worse than traditional
methods as it was best at reading the crud in the groove instead of
just pushing it aside.

No I was thinking more of a small low mass pair of mirrors in place of
the MM for example with perhaps fibre optics to carry the data - no hum
issues for a start.

IIRC Denon did this about 25 years ago, but the result was not a commercial
success.

People have tried various 'exotic' methods, but for whatever reasons, they
did not catch on. Bear in mind that audio is largely a 'fashion' industry
and people tend to consider what is recommened or repeatedly mentioned in
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

In article , Bill Taylor
wrote:
On Thu, 16 Mar 2006 23:23:34 -0000, "Serge Auckland"
wrote:

"Bill Taylor" wrote in message
...

(Compliance only needs to be more than about 10-12c.u. to track all
records)

Interesting theories. Can you tell me a bit more as to why a compliance
of 10-12cu is sufficient for all records? Interesting that in vinyl's
heyday, some cartridges were providing 30-40 cu. It could be a
marketing exercise rather than having a sound engineering reason for
it, but it would be useful to know why such high compliances are not
necessary.

According to J Walton in "Pickups - The Key to Hi Fi" (published 1968,
but the physics haven't changed): the maximum excursion on an LP is
about .005cm, "if compliance were the only factor involved a compliance
of 2 c.u. is quite sufficient to track the largest stereo amplitude of
.005 cm at 3 gm tracking weight". It's possible that a small number of
modern LPs have slightly higher excursions, and tracking weights are a
bit lower, so a slightly higher compliance is needed, but not that much
higher.

Afraid I don't have a copy of Walton. However I suspect the above may
either be an over-simplification on his part, or is out of context.

I may need to re-read some of the articles by Stan Kelley, but the above
looks to me as if is simply dealing with static compliance at LF. Thus the
physics may not have "changed", but may also not be as simple as the above
implies...

I also note that it quotes a playing 'weight' of 3g, which is high. A
small-radius tip could be expected to risk vinyl deformation even with an
unmodulated groove at such weights. Was he assuming a mono stylus which
would probably have been larger than a stereo one, and spherical?

If I look at Goddard's article in the 1963 "hi fi yearbook" he gives
a graph of the minimum acceptable compliance as a function of weight.

Simply to ensure contact this rises from 8 cu at 3g up to 20 cu at
1g playing weight. This ignores tip mass which will also contribute,
s you'd want a lower value to ensure avoiding mistracking. Also,
due to the finite compliance of the vinyl - which is more significant
with small contact profiles - you'd want a low compliance to minimise
vinyl deformation - and hence reduce distortion and wear.

The very high compliances of the 70s were very much a marketing
excercise.

They became so, but my recollection was that they grew for very good
reasons. Namely that unless the compliance was high and the mass was low,
the result was mistracking, high distortion, etc. (Also increased record
wear.) Personally, I'd regard a complaince as low as 10 cu would be too
low for comfort. I'd much prefer well over 20 cu.

A value as low as 2 cu would strike me as being unusuable for a modern
stylus profile - although the magazines rarely give any useful data
on this any more, so for all I know the profiles may be poor to
lower the pressure on the groove walls...

An advantage of high compliance and low tip mass is that you can have
a smaller contact area to improve the response and lower the distortion
level as well as keep down the wear on the LP.

I can't comment on modern MCs. But my experience with some of the early
ones that were enthusiastically welcomed by 'reviewers' was that they
mistracked to an audible extent on many LPs, and this was the main
difference I noted when comparing them with something like a Shure V15.

I suspect the reviewers liked the way the mistracking and groove
deformation alterted transient peaks. It was noticable at the time
that the reviewers who liked the early MCs (e.g the Asak) also liked
'pop and rock' music, not classical music, and may have perhaps
liked the 'enhancement' on the transients of electric guitars and
drums... :-)

Above said, I see no real reason why either an MM or an MC can't
deliver good results provided it is well designed, etc. Thus I
personally regard the magazine preference for MC as being mainly
a 'fad' prompted by lack of knowledge by the relevant reviewers
in the past...

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

"Bill Taylor" wrote in message
...
On Thu, 16 Mar 2006 23:23:34 -0000, "Serge Auckland"
wrote:

"Bill Taylor" wrote in message
...
On Thu, 16 Mar 2006 19:08:27 -0000, "Serge Auckland"
wrote:

The only vaguely convincing explanation that I've heard is that MCs
can use less damping of the stylus assembly. Theoretically this
should allow better trackability at mid frequencies. I also have vague
recollections that the cantilever can more easily be made shorter,
which would help in keeping the effective tip mass down, which should
give better HF trackability. (Compliance only needs to be more than
about 10-12c.u. to track all records)

Bill

Interesting theories. Can you tell me a bit more as to why a compliance of
10-12cu is sufficient for all records? Interesting that in vinyl's heyday,
some cartridges were providing 30-40 cu. It could be a marketing exercise
rather than having a sound engineering reason for it, but it would be
useful
to know why such high compliances are not necessary.

According to J Walton in "Pickups - The Key to Hi Fi" (published 1968,
but the physics haven't changed): the maximum excursion on an LP is
about .005cm, "if compliance were the only factor involved a
compliance of 2 c.u. is quite sufficient to track the largest stereo
amplitude of .005 cm at 3 gm tracking weight". It's possible that a
small number of modern LPs have slightly higher excursions, and
tracking weights are a bit lower, so a slightly higher compliance is
needed, but not that much higher.

Thanks for the reference. I'll try and find one if possible.

The very high compliances of the 70s were very much a marketing
excercise. The other important factor with compliance is the LF
resonance with the cartridge/arm mass. The ideal resonant frequency is
about 10-15 Hz, any lower than that and the cartridge system is liable
to become unstable and skip grooves with the slightest disturbance,
and the oscillations caused by these disturbances produce very audible
wow and tracking force variations. Some of the high compliance
cartridges needed a negative mass arm in order to get the LF resonance
up to a reasonable frequency.

Yes, remember the ADC25? Compliance 50 units, cartridge mass 8.3 gm. Needed
a 0 mass arm!

"Serge Auckland" wrote in
message

My question is why Moving Coils should be thought to be
better than moving magnets. I can think of several
reasons why they should be worse, lower compliance and
higher mass, but not why they should be better.

Good question.

Trackability should be better on a MM, as should record
wear due to lower tracking weights.
The quality of the stylus may be better on an expensive
cartridge, but in my own case, I have a Goldring 1042 and
a Shure V15IIIMR. The stylus in the Goldring is the Gyger
S, I understand similar to the VdH, the Shure MR is a
Namiki profile, so they are as good as anything available
on a moving coil.

Similarly, frequency response plots of moving magnets and
moving coils don't show any particular benefit to the MC,
nor does stereo separation or harmonic and
intermodulation distortion. So why *are* MC cartridges
throught to be better?

MC cartridges seem to be harder to make, so they can be priced higher and
provide more profits for their makers and sellers.

They also are more critical of the electronics that they are used with -
more opportunities for snob appeal and more profits.

If anyone knows of any good engineering reasons why this
should be so, I would be most interested to hear.

Don't hold your breath for anything believable.

"Nick Gorham" wrote in message

Bret Ludwig wrote:

The moving coils are lighter but put out less energy
than the moiving magnets.

Voltage, maybe, but if you look at the source resistance
of a MC, I am not sure its less "energy".

The stylus on a MC does I suspect have less mass to move.

Nope.

"Fleetie" wrote in message

The stylus on a MC does I suspect have less mass to move.

--
Nick

I always kind of assumed that was the reason. But I
don't know enough about such things to be sure.

Why not ask Ortofon or one of the still-extant cartrige
manufacturers?

AFAIK Ortofon primarily sells MM cartridges.

Compare

http://www.ortofon.com/html/body_mag...nical_data.asp

to

http://www.ortofon.com/html/body_mov...nical_data.asp

Even Ortofon's own technical data favors their MM cartridges