Semi Random Q&A #2 - Shure CM/CR elements
Happy New Year, everyone!
Today I wanted to answer another very common question (which nobody here asked....) What is the difference between CM and CR elements?
First - "CM" means "Controlled Magnetic" and "CR" means "Controlled Reluctance" and the difference in terminology was simple a marketing decision Shure made.
It turns out there were many evolutions of the element Shure put in its bullet style microphones. Chronologically, it went like this, from mid-forties to today:
Late 40's------->Early 50's-------> Late 50's------------->Early 60's----------->Mid 80's----------> Present
Black label CR --> White label CR --> Single impedance CM -->Dual Impedance CM -->Dynamic
With each successive generation, the elements got a little cleaner, gained a little more high frequency response, and a little more headroom (ability to withstand high sound pressure levels without distortion.) Of course since what we crave is the "right" kind of distortion, we often prefer the older elements.
Let me try to describe the difference this way:
1 - dual impedance CM (99S556)
2 - single impedance CM
3 - premium CM
4 - white label CR
5 - black label CR
The difference between a 1 and a 5? Almost anyone can hear it. The 5 is warmer, fatter and grittier. Between a 2 and a 4? Most good players can hear it. Between any two adjacent numbers? A really good player can hear it - but the variation from one element to the next of the SAME category is as big or bigger a difference. In other words, moving from a 4 to a 5 improves your odds, but may or may not result in an appreciably better element. The price is driven by both tone AND scarcity which is why the prices begin to get really steep as we go back in time. I put #2 elements in my wood mics by default and they are very, very good elements. (In fact, the difference between 1 and 2 is a good deal greater than any other interval.)
ALL of these elements are better than the element in the current 520DX, and WAY WAY better (for warm/brown/fat/dirty blues) than the elements that come in the other currently available commercial bullet mics like the Blues Blaster, Peavey, Bushman, etc. ALL of these more modern elements have much more high frequency response which can cause a harshness in your tone, especially if your cupping technique isn't very developed.
Here's a little more info.
CR's (99A86, 99B86, 99G86 and 99H86)..... A really good black label CR is, to my taste, the best element I've ever used. However "the best" is one out of every 10 or 15 elements. Shure switched the labels to white before they stopped making CR elements, and these are very, very close to the black labels for a little less money. The diaphragm in a CR element is affixed to the "pin" (which transfers the acoustic energy down into the coil to create electric energy) in a different manner than the later CM elements, which are glued. Those of us "in the know" (more accurately "in the informed guess") believe this is the primary reason for the difference in sound. There were also subtle changes in the way the coils were made and wound over the years.
The Single Impedance CM (99A86, 99B86 most common) was in the original Model 520 Green Bullet. This is still available on the collector market and is a very, very good "tone for $$" element. This is the element I collect and install in my wood mics by default. The first CM's used a different glue to affix the center pin to the diaphragm. It is opaque in appearance and either pinkish or beige in color. The later CM's used a more transparent brown glue. Once again, it is likely that the rigidity of this glue has an impact on the freedom of the diaphragm to vibrate (just like the "hat" on the CR's") and therefore impacts tone. I call the early "opaque" glue elements "Premium" CM's because they do sound just a tiny bit better than the later CM's.
The dual impedance CM, 99S556, is what came in a 520D. Still a large, aluminum diaphragm CM element, it has good tone but is a little harsher/brighter than its predecessors. These are the most plentiful CM elements still available and trade at lower prices like
The element in the model 520DX Green Bullet (the one with the volume control) is NOT a CR or CM - it is a more modern design dynamic element with a mylar diaphragm. The diaphragm's considerably lighter mass increases the high frequency response and headroom without distortion - not what we want. And, as a side note - the 520DX shell is even bigger and heavier than its predecessors - great for use as a weapon but it can really tire your hands!
Note that as your cupping technique improves, your cup will naturally mute the higher frequency components of your sound. But as a beginner, there will be a lot of high frequency content, and a mic that has more high frequency response will sound considerably harsher than one where the frequency response tapers off at a much lower frequency. A good player can get good tone out of most mics - but a beginner needs all the help he or she can get!
Hi, Eddy
It is a reasonable question. Why doesn't someone just tool up to make elements like they used to? The answer is that the market is simply too small to justify the investment in tooling required. There has never been an element specifically designed for harmonica players. Harp players have always used what was available (usually cheaply) at the time. The old elements were mfg'd in the hundreds of thousands - and in Shure's case maybe millions - to suit the general purpose market. The vast majority of THAT market wants:
1) CHEAPER
2) Higher frequency response
3) More headroom
Those happen to correspond nicely to what most engineers strive to accomplish. Shure has been making the 520DX (and the bullets that came before it) for years and years and years. They never intended it as a harp mic. Now, the harmonica market is about all that's left for the Green Bullet, but the investment was made a long time ago and has been recovered. Shure is simply milking the current product for all its worth. And because of the Green Bullet's reputation (which came from the early models) as a great harp mic, many beginners STILL buy them.
Without exception, all of the factory produced bullet harp mics (The 520DX, the Hohner Roadhouse JT30, Blues Blaster, Peavey Cherry Bomb, Bushman Torpedo, etc, etc )- ALL use elements that are mass produced for next to nothing. You can buy the elements that come in these mics from electronics supply houses for a few bucks. That doesn't mean there aren't good values out there in current mics - the Hohner Roadhouse JT30 is a damn good mic FOR THE MONEY - but don't expect anyone to reproduce old elements anew, let alone bullet mics made with them. They would cost significantly more to produce and have a tiny market.
Greg, sometime in the next few months you and I are going to choose a CM or CR element for the Shure brown bullet you're working on with me. Got a couple of questions that could help me communicate better and maybe help us all understand Shure elements better.
1) Will the inherent gain level of either a CM or CR element vary from sample to sample or are CR's always higher in gain than CM's? Note that all other things being equal I'm inclined to go with higher gain.
2) If gain is not an issue when comparing CM's to CR's does that just leave tone as the distinguishing factor?
3) Are there any subjective terms you could use to describe the tonal variations between a CM and a CR? Particularly interested in things like bottom end, dirt, 50's Chicago and harshness.
4) If a modern day 520 rates at 50% and your favourite black CR is 100% where would you put a typical CM and a typical white label CR?
Hoping this info can help others as well. Thanks!
Hi, Smoke
Good questions.
First, let's not confuse gain with output. Gain is more commonly associated with amplifiers, and expresses the slope of the curve of input to output. With a mic, gain should be linear - i.e., an increase of 10x in sound pressure level should result in an increase of 10X in the mic's output - while with an amp, an increase in input level of 10X might produce 100 or 1000x increase in output.
Here's the best way I can describe gain - and it is important in understanding why too much gain is really the enemy of us harp players. Imagine if you have a 2000 pound sports car with a 500 HP motor, but the gas pedal only moves 1⁄4 inch between idle and full throttle. It doesn't have any more power than the same car with a “normal” gas pedal. It would just have a hair trigger and be very hard to drive smoothly. That's what playing with too much gain is like. Reducing the gain is like increasing the travel of the gas pedal. Idle is idle, full throttle is full throttle, but with 6 inches of pedal travel it is a lot easier to drive smoothly.
On average, there is VERY LITTLE DIFFERENCE in output (or gain) between CM's and CR's. There IS difference in output from element to element, whether CM or CR. The hotter element will drive an amp's preamp circuit harder - but may also be more prone to feedback.
The key difference between a CM and a CR is tone. Shure's engineers "improved" their product over time by increasing its frequency response and reducing its distortion. Of course, that might be the exact opposite of what you want in an element. One of most significant changes they made was in the manner in which they connected the center pin to the diaphragm. On CR elements this was done with a small metal "hat" that was crimped onto the pin in addition to a small drop of glue. With the CM's they stopped using the hat and used glue only. They went through a variety of glue formulations, beginning with a stiff, opaque epoxy type glue and evolving to a translucent and more flexible type. It is my belief that the mass and flexibility of this system affects the vibrations of the diaphragm and explains the principle reason that CR's have more limited high frequency response, AND more "color" to the nature of their breakup when pushed.
Bottom end comes more from cupping technique than anything else.
As for the differences - trying to define it in writing is impossible - here's the best I can do:
1 - dual impedance CM (99S556)
2 - single impedance CM
3 - premium CM
4 - white label CR
5 - black label CR
The difference between a 1 and a 5? Anyone can hear it. The 5 is warmer, fatter and grittier. Between a 2 and a 4? Most good players can hear it. Between any two adjacent numbers? A really good player can hear it - but the variation from one element to the next of the SAME category is as big or bigger a difference. In other words, moving from a 4 to a 5 improves your odds, but may or may not result in an appreciably better element. The price IS driven by both tone AND scarcity which is why the price begins to get really steep. I put #2 elements in my wood mics by default and they are very, very good elements. (In fact, the difference between 1 and 2 is a good deal greater than any other interval.)
Thanks for helping me out. Couple of more points to clarify. Interesting subject! For the uninitiated it's a bit tricky to formulate questions that make sense but your answers help a great deal.
1) Do you test and measure output as part of your evaluation of an element or is functioning normally the only criteria needed given the minimal differences normally found?
2) Given the presence of a volume control on the mic should the mic's output level be a non issue regarding feedback? It would seem to me that more output would be preferred when using different amps so long as the mic has a volume control to keep things in check when necessary.
3) Is there an element you might tend to recommend to someone who considers themselves more of a rock player than a blues player?
1) Do you test and measure output as part of your evaluation of an element or is functioning normally the only criteria needed given the minimal differences normally found?
I do not measure the resistance of elements or the output -except with my ears.
2) Given the presence of a volume control on the mic should the mic's output level be a non issue regarding feedback? It would seem to me that more output would be preferred when using different amps so long as the mic has a volume control to keep things in check when necessary.
I agree with you - hotter is USUALLY better for most players and a volume control definitely helps manage things.
3) Is there an element you might tend to recommend to someone who considers themselves more of a rock player than a blues player?
Rock players often want a more biting sound with less distortion. That's easier to find - an Ultimate 57 for example makes a great rock mic. Also the Shure dual impedance CM (99S556) is the least expensive of the CM's BECAUSE it is a little harsher with more high frequency response - but that can be an advantage for the rock player.
Hi Greg,
Unless something goes wrong, when you build something, you try to make it better and better. I don't understand why Shure doesn't do it. If everybody is OK to say that the 520 DX doesn't suit, why do they carry on building this microphone supposedly appropriate for harmonica playing.
All the best for 2013,
Eddy