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roadcykler
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Moving coil vs. Moving magnet

It seems mc cartridges are the vast majority of cartridges reviewed/recommended these days but it wasn't always so. I suspect the cost difference has a big part to do with it (the usually true axiom, you get what you pay for), but is there any objective information as to the differences in why one would be better than the other? Better frequency response and that kind of thing.

ethanwiner
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Re: Moving coil vs. Moving magnet

I'm not an expert with this, but it's my understanding that a tiny coil weighs less than a tiny magnet, so the coil has a better high frequency response because it can move more quickly.

--Ethan

Jan Vigne
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Re: Moving coil vs. Moving magnet

Less effective mass, better transfer function, generally higher quality of materials comensurate with higher cost. Everything has a trade off, mc's are no different in this regard.

absolutepitch
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Re: Moving coil vs. Moving magnet

Both Ethan and Jan are correct from what I know about cartridges as an audiophile, but not as a cartridge builder.

A moving magnet (MM) has more mass than a moving coil (MC), all other things being equal, such as cantilever length and diameter, magnet or coil location on the other side of the pivot, and so forth. On can analyze the system as a vibration problem where the theory is well-known. Whether the MM has too much inertia depends upon the actual mass and the frequency range it needs to respond to. Sure a MC has less mass in comparison, but the MC also needs more amplification before it gets to the phone pre-amp input. That means that the "pre-pre-amp" for the MC must be very good quality.

Unfortunately what I have written here this is all 'talk' in generalities. Specific designs could differ. A very narrow, longer cantilever has more leverage on a magnet than a shorter cantilever, which might offset the advantage of a shorter MC cantilever and lower mass coil. However, a longer narrow cantilever will flex more. It just depends on the tradeoffs made in the design.

Most of the time you won't have a chance to compare the designs in detail anyway. So I do the usual, such as read reviews and then listen to it. How does it sound? Then I buy what I like up to the point I can afford.

Jan Vigne
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Re: Moving coil vs. Moving magnet

The most improtant thing to consider here is not mass alone but "effective mass" (http://search.yahoo.com/search?ei=utf-8&fr=slv8-hptb5&p=effective%20mass...). Effective mass has to do with amount of energy required to set an object into motion, moment of inertia and how much energy is required to get an object in motion stopped.

In a tonearm effective mass is affected by the position of the counterweight at the back end of the tonearm. While hardly the only thing that affects the effective mass and inertia of the arm this can easily be understood as the effective mass of the arm is altered when the postition of the counterweight is changed. As the mass of the weight is moved closer to the bearing center (pivot point) the effective mass is reduced and conversely the effective mass increases as the weight is moved further away from the pivot point of the bearing.

If the position of the counterweight remains the same relative to the pivot point but the actual mass of the weight is increased or decreased the effective mass also changes. If both are changed, the mass and the position, you can go a long way to changing the effective mass of a tonearm. This is the idea behind the "heavy weight" counterweights sold for many tonearms. They, of course, can alter the original designer's goals for the arm and make the system one that no longer operates as intended, so be careful when choosing your trade offs in arm design.

Now take that idea down to the smaller dimensions of the cantilever attached to either a chunk of magnet or a coil of wire. The pivot point remains constant while the mass and therefore the effective mass of the system changes with what is attached to the end of the cantilever. Obviously, the coil of wire has less mass than the chunk of magnet so when it is postioned at the end of the cantilever the effective mass in the system has been lowered. At the stylus end of the cantilever this means a more faithful replication of the extremely small traces of information within the groove wall.

Think of effective mass in this sense; how much more accurately can you sign your name if you hold the pen in your hand vs. if the pen is attached to the opposite end of a baseball bat that you must weild. Less effective mass in a cartridge means it is easier for the stylus to follow the groove modulations since it has less mass to drag along with it at the other end of the cantilever.

There have been numerous trade offs in the design of mc's vs. mm's one being a generally higher tracking force and lower compliance required to control the accurate movement of the stylus when incorporated into a mc system. This has not been a problem of real dimensions if you do not thnk the lightest tracking force and the highest compliance make for the best cartridge - in general once again, the lighter the tracking force, the more groove damage might occur if the arm/cartidge combination is not well matched. Most cartridges and tonearms of any variety have moved away from the lowest effective mass and highest compliance in order to deal with the real world conditions of modern day pressings.

Output voltage has also been a traditional trade off between cartridge types. In order to minimize the effective mass of the system in a mc cartridge, the coils have fewer windings than in a mm design which results in less voltage being generated by the movement of the coils within the magnetic field of the (now) fixed magnets. Therefore a traditional trade would be the lowest effective mass in a mc would result from a motor with with the fewest coil windings (minimal wire mass) which would then provide the lowest output voltage but supposedly the "best" sound quality.

To bring this extremely low output voltage up to a workable level requires more voltage gain in the phono pre amp or "pre" pre amp (a step up device placed before the phono pre amp). Various methods have been designed to raise the voltage of the very lowest output mc's but each has its own trade off. An active pre pre amp will add more noise and distortion to the signal along with the other issues common to all active electronic circuits. An active pre pre amp however is the most flexible of the options.

In the past few decades more powerful magnets and finer control over the winding process involved in constructing a mc cartridge have resulted in higher output voltages for H.O. mc's. Today you can find many mid priced mc's that can work directly into a mm phono stage without extra circuitry.

Ethan's suggestion of "better" high frequenct response has traditionally been coupled with a rising high frequency response in many mc's which has made sound quality a bit of a dicey trade for many of us. The inability of the mc designer to fully damp the resonance of the moving coils in order to minimize this ringing has long been a traditional trade against the more "even" response of the better mm's. Some listeners will say this extra bit of "zing" they hear from a mc gives a sense of airiness and openess while others say it is just distortion. Still others feel there is a solidity to the presentational style of most mm's that is absent in most lower to mid priced mc's.

In all of audio the phono system is the one most like the bumblebee that shouldn't be able to fly but does. The trade offs are obvious no matter which way you look. There are also other types of phono cartridge motors available such as induced, variable reluctance, strain guage and moving iron systems. Each of these try to overcome the basic problems associated with mm's and mc's. In each case you must look at the various trade offs each system introduces and decide which might best suit your taste and system. There is no one best way to achieve high quality music reproduction, just a series of trade offs that work best for you when each component plays to the strengths of the others and minimizes the flaws of the rest.

http://search.yahoo.com/search?ei=utf-8&...ridge&type=

KBK
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Re: Moving coil vs. Moving magnet

To add:

INDUCTANCE.

Lower mass coils moving nearby a big magnet induces a signal into the coil.

Now, a small magnet needs a BIG COIL..and we end up with LOTS of inductance in this coil. Some go as far to say that the transients in MM systems are all 'hashy' sounding as they are slurred in time and are actually distortion, not transients.

A MC system can and generally does have big magnets and tiny (short wire, low number of turns) coils.

It is my understanding that the motional mass or moving mass of a Moving magnet system is notably LIGHTER than that of a Moving COIL.

Moving coils (MC)are traditionally and in most cases heavier by a goodly margin than the moving portions of a MM cartridge. this is part and parcel of the requisite high tracking mass for proper function of most MC cartridges. 2 grams, on average, where most MM's top out in the 1.5gram range.

It tends to be that the coil inductance of the MM system limits high frequencies.

This is the reason behind the ridiculous HF numbers for some MC cartridges, as in some of the Denon units and the like. Spec'ed out to about 65kHz to 80kHz. Which is impossible in daily practice in most situations, as no groove on any record at the common 33-1/3 rpm is capable of carrying such information.

There are variations (higher, lower, worse, better, etc) of this (in either MM or MC land), but that is the general lay of the land.

I am a -HUGE- fan of low output MC cartridges, I find them to have the lowest distortion of all, in the specific areas where any given distortions that can and are generally associated with each given type (MM or MC) would bother me.

I'm talking about 0.2mV output or less, with coils measuring in the 10-20 ohms - or less.

Mid to high output MC cartridges get right back to the flaws of MM systems so I will not and have never bothered with them..after trying to tolerate about 10 of them, I've given them up as a bad job.

Jan Vigne
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Re: Moving coil vs. Moving magnet

While I admire the very low (O.2 mV) output mc's ability to extract information and not suffer from the excessive high frequency garbage that too often accompanies the music with higher output mc's, I have to admire the solidity of the soundstage acquired through a good mm design. Despite a lasting desire for a Koetsu after hearing the line twenty years ago I've stayed with an alternative I find most appealing.

I've found my particular balance in either induced or moving iron designs. IMO they strike a well thought out balance of magnet and coil size without the flaws of many mm's and without the need to resort to the excessive gain stages of the very low output mc's. With the one exception of an early H.O. mc many years ago I have been using moving iron designs for a long, long time without the need for step up devices or silly 3/4 gram tacking forces.

http://www.soundfountain.com/amb/ortodeccatan.html

absolutepitch
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Re: Moving coil vs. Moving magnet


Quote:
The most improtant thing to consider here is not mass alone but "effective mass"

Yes, Jan. That's what I refer to as Moment of Inertia, but used only the term inertia, which is adequate, if not precise, if all else is equal. The effective mass is really referring the real distributed mass of an object to an equivalent point mass at a given distance from a rotational point, which is more conveniently expressed as moment of inertia.


Quote:
Think of effective mass in this sense; how much more accurately can you sign your name if you hold the pen in your hand vs. if the pen is attached to the opposite end of a baseball bat that you must weild. Less effective mass in a cartridge means it is easier for the stylus to follow the groove modulations since it has less mass to drag along with it at the other end of the cantilever.

Your analogy is correct in the case of writing with a pen. May I add that there's a difference in a stylus on an LP, playing music than in dragging the tonearm around.

In your pen analogy, the pen operates at very low freqencies. The cartridge stylus operates throughout the range from basically near DC to it's upper response limits, probably above 20 KHz. The tonearm and cartridge/stylus has a system resonance that's often designed to be in the 8-12 Hz range, if I recall correctly. Moving a tonearm from the outside of the record to the inner grooves requires the stylus to push the arm. The rate at which it pushes is fairly slow and nearly constant velocity, and is effectively a static mechanical condition, operating at nearly zero Hz. I would surmise that most of the force required is applied at the lead-in grooves where more acceleration of the arm is needed from the stylus to push the arm than while playing the music where there is nearly constant groove advance rates (constant velocity = no force).

When music is playing, the frequency range is much above the resonant frequency of the tonearm-cartridge-stylus system. The stylus follows the modulations in the groove while the arm remains virtually motionless. If the arm was wagging while the stylus is wiggling, you would get gross distortions of what is recorded on the LP sent to the pre-amp. If the arm must remain virually motionless, effective mass does not matter for groove modulations.

The tonearm mass and cartridge mass in concert with the stylus compliance must place the system resonant frequency in about that 8-12 Hz range. That's how the stylus can drag the arm across the record, while the stylus can also follow modulations in the groove without vibrating the arm. The tonearm mass, hence effective mass, is designed to match most cartridges expected to be used with that arm.

Jan Vigne
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Re: Moving coil vs. Moving magnet


Quote:
Moving a tonearm from the outside of the record to the inner grooves requires the stylus to push the arm. The rate at which it pushes is fairly slow and nearly constant velocity, and is effectively a static mechanical condition, operating at nearly zero Hz. I would surmise that most of the force required is applied at the lead-in grooves where more acceleration of the arm is needed from the stylus to push the arm than while playing the music where there is nearly constant groove advance rates (constant velocity = no force).

How many grooves are there on one LP?

absolutepitch
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Re: Moving coil vs. Moving magnet

It depends on how the LP is cut.

Typically there are one (if only one side is recorded) or two (one on each side) continuous grooves spiraling inward. There can be more than two if the record is cut with multiple independent starting and ending grooves on the same or both sides of the LP (I think it's called a 'locked groove' where you need to physically lift the arm to move it to the next cut). The only time I have encountered the locked groove is on a LP test record.

plynn
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Monty Python and the Extra Groove


Quote:
It depends on how the LP is cut.

Typically there are one (if only one side is recorded) or two (one on each side) continuous grooves spiraling inward. There can be more than two if the record is cut with multiple independent starting and ending grooves on the same or both sides of the LP (I think it's called a 'locked groove' where you need to physically lift the arm to move it to the next cut). The only time I have encountered the locked groove is on a LP test record.

Monty Python's Matching Tie and Hankerchief had two grooves on one side, as a joke. Their lead-ins were not equally spaced. This gag worked perfectly on my family. We had listened to the record, and our favorite bit was the first part on one of the grooves on the side with two. So when my father came home, we insisted "listen to this," put the record on, and were flabbergasted by hearing a "side" of the record that hadn't been there before.

absolutepitch
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Re: Monty Python and the Extra Groove

Peter,
That's interesting. I'm now curious what other LPs were cut like that and why.

dbowker
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Re: Moving coil vs. Moving magnet

Lee Renaldo, of Sonic Youth, had an album of ambient tracks years ago and each track ended in some sort of continuous loop. It was cool, if you like that kind of thing, which I did back in the day. And just to f*** with you a little MORE, the album was pressed on clear vinyl, making it a real challenge to even find the next lead in! I still have it... maybe I need to go give it a spin again...

absolutepitch
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Re: Moving coil vs. Moving magnet


Quote:
... And just to f*** with you a little MORE, the album was pressed on clear vinyl, making it a real challenge to even find the next lead in! ...

One of the record companies gave a talk at an audio store many years ago. It was described that the record vinyl is translucent or clear material and becomes black when they add some stuff, which my memory seems to point call up "carbon". I guess the black color give it the right reflection to see the lead-in and transition grooves.

tom collins
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Re: Moving coil vs. Moving magnet

this is amazing, an actual 14 entry exchange without any insults and very interesting to boot. keep it up guys.

roadcykler
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Re: Moving coil vs. Moving magnet


Quote:
I have been using moving iron designs for a long, long time without the need for step up devices or silly 3/4 gram tacking forces.

http://www.soundfountain.com/amb/ortodeccatan.html

By "step up devices" are you referring to a phono pre-amp or something else? I'm not up to speed on what some of these terms mean or if they are interchangeable.

tom collins
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Re: Moving coil vs. Moving magnet

roadcyc: yes, i believe that is what he is referring to. a phonopre is a transformer or step-up device that takes the small electical output from a cartridge and magnifies it or steps it up to a higher level so that it is understandable to the preamp or integrated amp. but these are available from around $100 up to maga-thousands of dollars. some people say that not having another device in the chain is better. that may or may not be, but it certainly is less expensive if your preamp or integrated has a phono input built in. many do not these days, so you will be adding another transformer whichever type of cartridge you choose. so, if your pre or integrated already has this feature, you can try vinyl with just a table, moving magnet or moving iron or even high output moving coil cartridge fairly easily and inexpensively (relatively speaking).

Jan Vigne
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Re: Moving coil vs. Moving magnet

You can step up the output of a low output mc by using either an active "pre" pre amp or by using a passive step up transformer. Each will have their own advantages and disadvantages and you should decide which would best suit your system should you decide a low output mc best suits your system needs. Should you choose a high output mc or a moving magnet or moving iron cartridge, no step up devices would be required and would actual work against your system.

http://www.stereophile.com/reference/50/index.html

Look through the archives of AD's column, he did a very good piece on step up transformers not too long ago; http://www.stereophile.com/artdudleylistening/

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