Microphone Elements Explained

For this week’s Harmonica Microphones post we asked Greg Heumann to give us the low-down on the bewildering universe of mic elements. In the first of a double post, he describes two kinds of elements used for amplified blues harp and… well, it gets technical after that.

The Harmonica Microphone Series beginsThere are many kinds of elements in all of microphone-dom, including ribbon mics, condensers, electret, crystal and dynamic. Acoustic players may well use any of these. However, except in the recording studio, amplified players will only be concerned with dynamic and crystal elements.

Fact 1: There is no such thing as a mic element designed for harmonica players.
Every microphone uses an element that was designed for more general purposes. As a rule, the more expensive a mic was when new, relative to other mics of its vintage, the better it performs as a general purpose mic. To engineers, this means it has better frequency response (able to “hear” higher and lower sounds), flatter frequency response (no particular frequencies are made significantly louder or softer), and/or more “headroom” (the ability to tolerate higher sound pressure levels without distorting).

In this case “better” is usually means better for acoustic players. But…

Fact 2: For amplified, bluesy ballsy tone, “better” is worse.
Although low-end frequency response is good, harps simply don’t make any fundamental notes that are way down in the bass range. All the bass is added by the amplifier through harmonic distortion. And too much high frequency response can sound harsh, even hurt people’s ears. The reason vintage bullets are so popular is that their frequency response typically falls off at as low as 3000 Hz – even though some humans can hear as high as 20,000 Hz.

Fact 3: High headroom also works against us.
It prevents us from overdriving the microphone. The Audix Fireball, marketed as a good harp mic, has the most headroom of any mic I’ve played – 140dB according the spec. And it is a good harp mic for playing acoustically, or for avoiding a distorted input signal for other reasons such as playing through an amp modeling pedal. But the difference in tone between cupped and uncupped with this mic is far less than it is with an “older tech” microphone. In the case of amplified tone, older and cheaper is often better.

The venerable Shure Green Bullet and the Astatic JT30 are prized by harp players – because they give us that “old-school” sound. They are, in many cases, what our harmonica heroes used. Do you know why they chose them in the first place? Because they were cheap, even when they were new! The JT30 was the entry-level microphone in Astatic’s line, and came on the market at a price of about $6.

Dynamic and crystal: what’s the difference?
In my next post I’ll be talking more about vintage dynamic elements made by Shure: “Controlled Reluctance” and “Controlled Magnetic” elements (“CR” and “CM”). Both crystals and CRs/CMs have a great tone for amplified blues. It is hard to describe the difference, but to me a good crystal has a slightly nasal “honk” to it that the CR or CM doesn’t have. CR/CM elements have more bottom-end and can sound a little fatter and richer. The only way to know is to try good examples of each.

However, there are some other important factors to consider. Crystals have a lot going against them. The good ones were made 70 years ago and are at the end of their life. Many have died, most are dying, and a single drop can kill a good one. They are also extremely high-impedance elements. This means a low-impedance connection will dramatically reduce their tone. Just as turning on all the electric stuff in your car makes the engine work a little harder to keep turning the alternator, lowering the resistance across the mic’s terminals is like dragging your foot on the brake. Not only does the total output drop, but the frequency response changes too.

For this reason some custom harp amps are made with a 5 megohm input specifically for crystals. An amp with 50K input impedance will suck the tone right out of the best crystal. Anything you add between the mic and the amp, such as a volume control or a long cable, can lower the impedance as well. A good amp and good volume control will still let you get good tone, but you have to be aware that this is an issue and manage it. Finally, if your amp hums when you connect a cable that has no mic at the end, you can expect hum when you connect a crystal-element mic. A dynamic element may well reduce or even mute the hum.

Dynamic elements (including vintage ones) are practically bulletproof. They have lasted well all these years, so they are less expensive and more plentiful. Their impedance is lower so they stand up well to volume controls, pedals, splitters, etc. (Ultimately though, if the input impedance drops too far you will suck tone from any element.) And you can drop them (protected, of course, by a proper gasket inside a microphone shell) and they don’t break!

How do they actually work?
A dynamic element uses the electromagnetic principle to convert sound into electrical energy. A diaphragm is an extremely thin membrane that vibrates in response to sound waves. The diaphragm in a dynamic mic either directly moves a coil around a fixed magnet, or moves a pin which in turn moves inside a coil. Either way, the movement generates an alternating electrical current. A dynamic microphone and a speaker are almost identical in principle. With the speaker, you take electric energy and convert it into sound by sending the current through a coil, which then wants to move relative to a fixed magnet. The speaker cone is attached to the coil. Voila – sound! A microphone is the reverse – you take sound energy and turn it into electrical energy by moving a coil past a magnet. A speaker can actually be used as a microphone, and a dynamic microphone can be used as a speaker (think headphone speaker.) Please don’t experiment with your good harp mic elements to see how well they work as speakers. They don’t work well, and the risk of your damaging them is very high.

Biscuit microphone, courtesy of Harmonica MasterclassA crystal element relies on an entirely different principle called the “piezoelectric” principle – the diaphragm is connected to a crystal of “rochelle salt” or a manmade ceramic with piezoelectric properties. Mechanically deflecting the crystal generates an electric current. The lighter on your gas barbecue uses a crystal too. You press down on a button which mechanically bends and “snaps” a crystal (without breaking it) and with no battery required, a spark is generated. Crystal elements are rarely made these days, although they can be made incredibly cheaply so they still exist for entry level applications and are found in some production microphones. The new ones, unfortunately, don’t have the tone of the older ones – and the older ones are becoming very expensive.

Keep an eye open for the second half of Greg’s post on elements, where he names some of the most sought-after crystal and dynamic elements, and explains how to shop around for one.

Greg Heumann is curating our Harmonica Microphones section. You can find more from him at www.blowsmeaway.com.

10 thoughts on “Microphone Elements Explained

  • September 9, 2010 at 7:52 am
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    I have been playing for about a year now and bought a Hohner Blues Blaster around December. This mic is lo z and really sucks! I later found out that the Diaphram is busted and really ticked about it. I found out that it had the crystal element inside but it really stinks and now I am going to buy the Paul Butterfield mic which is the Shure 545 SD. I have also been researching the Shure SM 57 but I was wondering if you had any knowledge on which to convert to. I know that the Shure 520 is not made like the old one and will probably not go back to the bullet mics made today.

    Another thing is that I am looking for nice crunchy just walked out of the Juke Joint deep Amplifier. Now I have talked to other harp players on this debate even communicated with Adam Gusso and everyone is telling me to go with a 6v6 tube and 12×7 tube amp and that I will not get the swampy overdriven sound out of say the Peavey Delta Blues which I almost had bought but have put on hold. I need advice on buying both the mic and the amp.

    Thanks,
    Austin Hardiman

  • November 21, 2010 at 9:21 pm
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    Hi Austin. There is no simple, definitive answer. Which is why you’ll get different responses or none at all. Folks can only tell you what they believe gives the best crunch combo from the kit they have tried, but there’s always plenty more out there they won’t have tried. For my part, 4 x 10 speakers are a way ahead. The best amps I’ve heard for crunch are the Fender Bassman, Fender Twin Reverb and Sonny Junior amps. I’ve tried JT-30 mics, other bullets, vocal mics and whatnot. I’m starting to come back to the Green Bullet. It just seems to do the trick, although it is damned heavy compared to other mics!

  • May 9, 2011 at 10:56 pm
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    i want to thank sites like this they are so helpful. i have a the shure sm 57 with a custom bullitizer.built by greg.and i love the tone. I found it picks up the cromatic much cleaner than a bullit. i use several mic,s at differrent gigs.am a mic whore. having small hands the bullitizer was made jjust for me . (not) Greg was alwayes cool and knows his gift. mahalo Kona Steve of south oceanside

    i

  • May 26, 2011 at 9:59 am
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    A mic whore! That’s a first! Stephen thanks for your feedback. I’m sure Greg will be thrilled to hear that you endorse his work so strongly. Let us know if you have any top tips about which mic you use for which gig, song etc. Best wishes, Wilf

  • May 29, 2012 at 3:35 pm
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    Blimey Jarrett are you with NASA? Ebay will be a lottery as there is no real way of telling the crystal quality until you get the mic through the post. I think you’d be best to email Greg Heumann direct with this one. Doc

  • November 13, 2012 at 1:42 pm
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    sorry To argue… But there is a crystal elemnent made for Harmonicas .. and when it a Wooden Bullet shell.. it has that ole school Chicago sound

    http://www.youtube.com/watch?v=jYiQ3FX29L0&list=UUiK9snmbUVz58tpvhyhqamQ&index=4&feature=plcp

    I would like to learn how this element is made… this is the same element placed into a gord bullet shell…
    http://www.youtube.com/watch?v=N3DZX5izeyY&feature=player_detailpage

    Would really like to learn how to make a few of these.. he is selling a BUNCH of them on ebay…
    But doesnt answer my mail.. I hope its just because he is to busy..

  • November 17, 2012 at 3:23 am
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    Does anyone know if the mic elements that are in phone receiver are high-z or low-z ? I have been turning wood for years.. And plan on building myself a mid for myself and a few custom mics to sell.. If they are low-z is the a converter that is small enough to set inside the wooden shell to allow it to be conected right to an amp with a guitar chord?
    Ray
    PS. where would I go to find some decent grills for the mics?

  • May 9, 2013 at 4:59 pm
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    I play mostly chromatic harmonicas and use a few different Mics, The Audix Fireball ( made specifically for the harmonica player) and the Shure SM-58, both clean mics. For a more bluesy sound I make my own mics using old telephone mouthpieces, I’ve even made a few with small speakers. Ray, These are high Z mics, like the green bullet. Low Z’s have an XLR plug (like the SM-58 and Fireball. For a grill, I’ll either drill holes in a metal cap or cut out the center of a plastic jar cover and ad some screen for the center.
    Denis

  • September 16, 2013 at 11:28 pm
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    I have been toying with the idea of turning an old Mini Maglite into a mic.
    Drill out the base and install a cable connection, 3.5mm mono maybe so I can scavenge the cable from an old harmsol unit with a belt mounted volume control.
    The one main problem is finding an element 2 cm wide and about 1 cm thick.

    Could be an interesting little project.

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