Shure | 520DX | all about harmonica microphones

 All about harmonica microphones… And then some Greg Heumann BlowsMeAway Productions HTTP://WWW.BLOWSMEAWAY.COM Copyright © 2010-­2014 latest revised 3/14
All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com All About Harmonica microphones, and then some….. Table of Contents Introduction ..............................................................................................................................................3 Acoustic vs Amplified...............................................................................................................................3 Acoustic tone ............................................................................................................................................4 Where does “amplified tone” come from?....................................................................................4 Amplifiers -­ Tubes vs. Transistors?........................................................................................................... 5 Cupping: ............................................................................................................................................................. 5 Why are some mics more responsive to cupping? ....................................................................................... 5 Factor 1: Mic shape and size:........................................................................................................................................ 5 Factor 2: Headroom ......................................................................................................................................................... 6 Microphone shapes ........................................................................................................................................ 6 Microphone Elements..........................................................................................................................8 Headroom .......................................................................................................................................................... 8 Which are the most desirable Dynamic elements?.............................................................................. 9 Which are the most desirable Crystal elements? ................................................................................. 9 Dynamic and crystal: what’s the difference? ...................................................................................... 10 Side note: How do they actually work? .............................................................................................................. 11 How do I get one? ......................................................................................................................................... 11 Does the “ohm reading” matter?............................................................................................................. 12 What's Impedance? .............................................................................................................................. 12 Feedback -­ are some mics better than others? ........................................................................ 14 What can be done about feedback?............................................................................................................. 14 Reducing feedback by reducing gain -­ amplifier tube substitution ............................................ 15 How to be heard ................................................................................................................................. 17 Mic it ................................................................................................................................................................. 17 Line Out ........................................................................................................................................................... 17 Maybe you simply need a bigger amp! The dB defined................................................................... 17 Other feedback management tips:............................................................................................................... 18 Volume controls............................................................................................................................................... 19 What about Wireless?....................................................................................................................... 19 Choosing a mic builder..................................................................................................................... 21 Conclusion ............................................................................................................................................ 21 Page
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com All About Harmonica Microphones, and then some….. Introduction If you're a harmonica player, sooner or later you're going to want to play through a microphone,
to be better heard, to change your tone, to record.... or some combination thereof. I'm a semipro harp player, and through my business, BlowsMeAway Productions, I have had the chance to
play through, repair, modify and build a wide range of microphones. Over the years, I've learned
a few things. These are my thoughts about what you should know in order to choose the mic
(and other components of an amplified system) that's right for you, and how to get good tone
through it. I'll define terms as they come up - I think this is better than presenting a glossary of
boring terms up front. But let's just agree on the obvious - a "microphone" is a device that
converts acoustic energy (sound waves, changes in air pressure) to electrical energy, which in turn
allows for electronic amplification. This conversion is the job of the microphone's "element". In
practice, when we talk about mics we tend to care not only about the element, but also the
physical housing, or "shell" for the element.
The most common housing styles are commonly referred to as "Stick mics" or "Bullets". Stick
mics tend to have smaller heads and long handles. The most popular among stick mics today can
be found on just about any stage in the world - the Shure SM57 and SM58. Bullet mics are
larger housings, shorter and bigger around. Many taper to a point in the rear so they have a
"bullet" shape. So - when we talk about mics, we're talking about both the housing and the
element, and both are important.
Acoustic vs. Amplified In choosing a microphone, the most important question of all is “what do you want to sound
like?” There are two classes of sound, with infinite variety in each class. If you’re a classical
musician, you’ll probably stand in front of a stand-mounted microphone and you want the
amplified sound to cleanly reflect the tone of your playing – giving the closest representation of
what it would be like to be in the same room with you, with no microphone or amplifier at all.
We call this kind of sound “acoustic” even though it may in fact be picked up with a microphone
and amplified.
When I talk about acoustic playing, I do not mean “not amplified”. I do mean, however, that the
microphone is in free air – that is, on a rack or a stand, and not in your hands.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com If you’re a blues musician, you might want the fatter, more distorted sound that is so prevalent in
the genre. We call this style “amplified” style as opposed to “acoustic” tone. (Hey, I didn’t write
the rules – sorry if it is confusing!) In this case the microphone is almost always hand-held. Jazz,
Country, Bluegrass and other styles often find themselves between these two extremes.
Acoustic tone Acoustic amplification is straightforward and can be effectively done with modern, relatively
inexpensive gear. A standard vocal mic like Shure’s venerable SM58, plugged straight into the
PA, is a safe bet and usually sufficient. Lapel mics, which are usually of the “electret condenser”
type, can also be used, although most harp players prefer a dynamic or ribbon mic for acoustic
playing. The PA is a very clean-sounding amplifier designed to accommodate multiple
microphones, each with their own volume and tone controls. Most PA's have simple effects like
reverb that can be added to each microphone channel, and deliver sound to the “house” speakers
(for the audience to hear) and to “monitor” speakers which are on stage (to help musicians hear
themselves and each other).
Good acoustic tone is largely a function of the player’s tone in the first place. So for now I’m not
going to talk about acoustic microphones specifically. I will talk about them when they come up
in conversation. However one essential piece of wisdom is that your distance from the
microphone makes a huge difference in volume. It is, unfortunately, rather easy to hurt people’s
ears when you walk up to an acoustic mic set up for someone to sing through at a distance of 6
inches, and you play loud harp right up against it, or worse, pick it up and cup it. The secret to
good acoustic tone through a microphone is to learn to play quietly! If you sing and play through
the same mic, a volume control on the microphone is a very useful tool.
Where does “amplified tone” come from? To understand the amplified sound, we need to talk about the interaction between the player, the
amp and the mic. Where does that big fat gritty sound come from? It comes from a combination
of your technique, the microphone, and an amplifier’s tendency to add distortion in the form of
manufactured notes (related to, but not the note or notes you’re playing). These notes are called
“harmonics.” This distortion can occur simply because the amplifier itself is operating beyond its
“clean” volume range, but as players we have control over the degree to which it occurs by our
own technique and microphone choice. We can overdrive the microphone, through our own
playing volume and more importantly a technique called “cupping”, so that it sends a distorted
signal to the amplifier. The amplifier responds by amplifying that distortion and more readily
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com adding its own. Of course, amplifiers vary a great deal in the degree to which they add
harmonics, and in the quality of that sound. So let me just say a word about amps.
Amplifiers -­‐ Tubes vs. Transistors? An important characteristic of tube amplifiers is that they produce “even ordered harmonics”
and “analog clipping” when they distort. These are felt to be pleasing to the ear. Solid state
amplifiers tend to produce “odd ordered” harmonics and “square wave” clipping when they
distort. These can sound very harsh. As a rule, either kind of amp played cleanly/acoustically will
sound fine. But overdriving a solid state amp, such as any modern PA, or some modern guitar
amplifiers, usually results in harsh sound. A very important advantage of the tube amplifier is our
ability to manage feedback through tube substitution to lower the amp’s gain. More on that later.
Cupping: Good amplified tone starts with the player's tone, and is accentuated by microphone technique.
Cupping is an art; a learned skill that is neither obvious nor easy in practice. Properly done at its
extreme, no air you suck or blow can escape "the seal". If you can do this perfectly, no sound can
come out of the harp at all! So we always allow a slight leak, but until you can cup so tightly that
you literally can’t get a sound from the harp, you haven’t perfect this technique. In reality it is
very hard to do this, and it is hard to even come close at first. Note that to accomplish such a
seal, you must not only create an airtight seal between the rear of your harp and the microphone,
you must also seal off the open holes on the front of the harp - otherwise the air you blow/suck is
free to travel under the cover plates, through all the open reeds and out/in the other open holes
on the harp. You can learn the technique acoustically before ever attempting it amplified.
When the seal with a microphone is very good, the air pressure changes are effectively "coupled"
to the microphone's diaphragm in a way that is very, very different from the normal "free air"
mode in which mics were designed to operate. The result is a very distorted signal sent to the
amp, that has more low frequency components and fewer high frequency ones.
To choose a good harp mic, you must understand what cupping is - as different microphones will
respond in dramatically different ways to the technique.
Why are some mics more responsive to cupping? Factor 1: Mic shape and size: When a mic's physical shape or size makes it hard to achieve a good seal, the effect of cupping
will be less.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Factor 2: Headroom When a mic has a lot of "headroom", which is the amount of sound pressure it can tolerate
before it distorts, it will obviously distort less. A perfect example of this is the Audix Fireball,
which has something like 140dB of headroom. A brilliant feat of engineering, but it makes almost
no difference to your tone whether it is cupped or not.
Microphone shapes There are literally hundreds, if not thousands of different kinds of microphones to choose from.
Mics vary in cost, size, purpose, tone, and shape - all of which affect us. For amplified tone, one
of the most important variables is the mic's shape. There is little about the shape that affects the
mic's tone in free air. However everything about its shape affects your ability to cup it easily and
effectively. People's hands and muscles differ, so one size most definitely does not fit all.
Some mics have holes all over the place and are virtually impossible to cup effectively. A stick
mic with a ball end like the SM58 can also be difficult for smaller hands. The smallest diameter
stick mics, like Shure's SM57, are easy for some to cup, yet cause hand cramps for others.
And their length gives the weight of the cable leverage to pull down on the end of the mic –
another fatigue factor. (The weight and length of Shure stick mics was one of problems I set out
to solve when I developed the Ultimate Series Microphones.) The following photograph
illustrates this:
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com The largest diameter bullet in popular use is the current model of Shure's Green Bullet, called the
520DX. It is hard for people to cup well unless they have fairly large hands. It is also one of the
heaviest mics available - and when you perform a three or four hour show, hand fatigue is a real
factor worthy of your consideration. Finally, some mics like the popular JT30 or Hohner Blues
Blaster have bumps around the circumference that make tight cupping very uncomfortable.
Among vintage bullet mics, there are many shells that are a little smaller. The Electro-Voice 630
and M23/43, the Astatic T3, the Shure 707 are all excellent shell choices and are popular among
“do it yourselfers” as mic project starting points. And of course BlowsMeAway’s wood mics are
among the most comfortable to play thanks to their reasonable diameter and light weight.
Another variable is where the mic’s shell places the element relative your harp. Some shapes will
hold the element further forward, others further back. Further forward reduces the size of the air
cavity between harp and element, reducing the tonal changes from cupping. This effect is slight
but real.
A mic's shape makes a real difference! You'll have to experiment to find what works best for you.
The other important variable, of course, is the element.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Microphone Elements There 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, with the
exception of the recording studio, amplified players will only be concerned with dynamic and
crystals elements.
There is no such thing as a microphone element that was designed for use by
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 indeed usually is better for acoustic players. Beyond that, choosing an
acoustic microphone requires a very critical ear and a lot of listening to hear any difference
between mics. Among modern instrument and vocal mics, the differences lie in sensitivity, and
subtle changes in frequency response. Some mics tend to accentuate certain frequencies that can
work for us or against us.
But here’s a shocker: for amplified, bluesy ballsy tone, better is worse. 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 5000 Hz – even though
some humans can hear as high as 20,000 Hz.
Headroom 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 wanting to
avoid 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/cheaper is often better. The
venerable Shure Green Bullet and the original 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
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com were new! The JT30 was the entry level microphone in Astatic’s line, and came on the market at
a price around $6.
Which are the most desirable Dynamic elements? The most desirable dynamic elements among amplified players are the vintage Shure
“Controlled Magnetic” and “Controlled Reluctance” elements (“CM” and “CR”.) Yes, CR’s
and CM’s are dynamic elements – but because they are special ones we usually refer to them by
their marketing names instead of just lumping them in with all the other “plain old” dynamic
elements. These elements came in the Shure 520 and 520D microphones, among others. The
current 520DX has a more modern dynamic element that is less desirable tone-wise. It is brighter
and has less bottom end.
Much has been written about Shure’s Bullet elements; Dave Kott’s excellent site
http://www.greenbulletmics.com/ has more information than you’ll ever need so I won’t repeat
it here. Suffice it to say that these are great elements, and because of their “magnet and coil”
construction, they have tended to last much better than crystals. Many players are still using the
dynamic elements from vintage Electro-Voice microphones as well.
Dynamic elements are the most common among modern microphones as well. They are used in
the majority of mics marketed to amplified harp players (Shure 520DX, Peavey Cherry Bomb,
Bushman Torpedo, etc.) as well as the most popular instrument and vocal mics like the Shure
SM57 and SM58. There is a huge range of dynamic elements. The newer they are, the more
likely they are to appeal to acoustic players and the less they will to amplified players. This is
because they have extended high frequency response that can be harsh and they don’t tend to
“break up” as easily, making it harder to induce distortion at the amp. However there are
exceptions. The Shure SM57, for example, actually breaks up very nicely and makes an excellent
harp mic.
Which are the most desirable Crystal elements? The most desirable crystal elements craved by harp players were those made by Brush, Turner,
and Shure. Shure and Astatic both manufactured their elements under license from The Brush
Development Company, who had several patents on the technology at the time. Unfortunately
those elements are all but extinct. The MC-151 element was made for a much longer period of
time, but has still been out of production for many years. They are available (I still collect them
for my customers) but their prices are going through the roof. Over time, any crystal absorbs
moisture and softens until it literally falls apart. (If you buy an “untested” crystal on eBay, it is
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com practically guaranteed not to work. Often, if you shake them they rattle. This is what is left of the
crystal bouncing around inside the element.) Along the way, they become more and more
susceptible to damage from drops, temperature extremes, or even very aggressive playing. (I once
ruined a crystal, which undoubtedly was getting ready to go anyway, by drawing really hard with
a tight cup. The vacuum pulled too hard on the diaphragm, and broke the connection to the
crystal.)
Crystal elements are still manufactured, but with the goal of extremely low cost. They differ
significantly in design, with much smaller diaphragms, and in tone. The last Hohner Blues
Blasters contain modern crystal element, as does the Hohner Roadhouse JT30. These are very
good value-for-money and can produce decent tone in the hands of a good player. But they
simply don’t have that characteristic “crystal honk” that the old ones had.
Dynamic and crystal: what’s the difference? Both crystals (and their close cousins, “ceramics”) and CRs/CMs have a great tone for amplified
blues-style playing. It is very hard to find words 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/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 useful life. Many have
died, most are dying, and a single drop can kill a good one. They are also extremely highimpedance 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 mics' 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
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com 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!
Side note: 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
that 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 chance of your damaging them is very large.
A 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 that 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. If you’re an engineer or a scientist and want to read some really deep theory
(and interesting history, engineer or not) on the entire subject – check out
http://mysite.du.edu/~jcalvert/tech/microph.htm
How do I get one? Ah, the million dollar question. If you like to gamble, you buy them on eBay. If you don’t, buy
them only from a reputable dealer who knows harp and knows elements. eBay is filled with
deception and ignorance. If you see a crystal element available (usually in a mic shell) with a
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com description that says “I have no way to test it” you should assume it is dead. Of course this isn’t
always the case, but it is generally true. Crystals don’t always fail all the way at once. Their
output can simply get lower and lower. Or they will respond unequally in response to positive vs.
negative sound pressure (blow vs. draw.) So even one that “works” may not work well at all. The
only way to know is to try an element by hooking it to an amp. And the only way to know then
whether it is in truly great shape is to know how loud they’re supposed to be. I buy crystal
elements to provide to my customers. I charge a high price for them. Why? Because I’ve had to
eat the cost of a lot of lousy elements I will not resell. If you buy from me, you get a good
element, or your money back!
Does the “ohm reading” matter? You’ll often see eBay vendors showing you the resistance measured across an element. Rule
number 1: never hook an ohmmeter to a crystal - you can damage the crystal this way. But
across a dynamic element, the fact that the resistance is neither 0 ohms (a short) or infinite (open)
tells you that the coil in the element is still working. The value will also tell you something about
the element’s impedance. 50-100 ohms indicates a low impedance element, somewhere around
1000 ohms indicates a high impedance element, and somewhere in between can indicate a
medium impedance element. These are rare, but should be avoided, as it is difficult to find a
proper impedance matching transformer for them. More on impedance-matching transformers
later.
The ohmmeter’s reading, however, will not tell you much about the tone of a particular element.
Do not believe that 1.1K ohms is better than 1.2K ohms, or vice versa – it simply isn’t true. This
isn’t to say that there isn’t a physical meaning to these numbers, only that other factors are much
more important when resistance readings are within a few hundred ohms of each other. A valid
ohms reading is also not proof that the element is good. An element that’s corroded or squashed
may not work or will work poorly, even if the coil is OK.
What's Impedance? The microphones we are talking about are referred to as “high impedance” or “low impedance.”
In general, a vintage bullet mic is a high impedance device and a modern vocal mic is a low
impedance one. This is not always the case. You need to know what you have and how to use it.
By definition, impedance is "resistance to an AC signal" – AC means alternating current – in this
case the signal from your mic, which is an electrical picture of the sound going into it. Power in
electrical terms is all that matters, but you can have the same amount of power with low voltage
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com and high current, or high voltage and low current. But you don't need to know that. All you need
to know is this:
1) Microphones and amplifiers work best with certain load or drive levels, respectively. For this
reason, it is desirable to "match" the impedance of the microphone to the impedance of the
device it is connected to – an amp, a foot pedal, a wireless transmitter, or....
2) Impedance matching transformers are simple devices that can "match" a low impedance mic
to a high impedance load, or vice versa.
3) Low impedance systems came later than high impedance ones, and were developed to enable
much longer cable runs and better reject noise (like hum) that gets injected via the cable.
4) There is no inherent difference in tone or feedback rejection between low and high.
5) Low impedance systems are almost always wired with "XLR" jacks and plugs. This is a
worldwide industry standard.
6) Many different kinds of connectors are used for high impedance devices, including XLR.
However when XLR is used, the cable-to-pin wiring is not the same as it is for low
impedance XLR. Mixing low- and high-impedance cables and mics just because
you can physically connect them together can lead to poor performance. When
you see a mono 1/4" jack or plug (like guitar players use) it’s a safe bet that you're looking at
a high impedance device. The same is true for the "screw-on" connector that was made by
Switchcraft and Amphenol, was found on many vintage mics and is still produced today.
7) There's nothing wrong with connecting a high impedance mic with an XLR connector to a
high impedance load (like an amp) with a cable that has XLR at one end and a 1/4"
connector at the other. There is something wrong, however, with using that same cable to
connect a low impedance mic to the amp. First, there is an impedance mismatch and neither
the amp nor the mic will perform as well as they could. More importantly, high impedance
XLR and low impedance XLR cables are wired differently. When you use an XLR!1/4”
cable with a low impedance mic, you will get less than half of the mic’s output! The
proper way to connect a low impedance mic to a high impedance amp is to use a low
impedance cable (XLR to XLR) together with an impedance matching transformer.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Feedback -­‐ are some mics better than others? Feedback is that awful loud screeching, humming or whistling sound a system makes when a
microphone picks up the sound from the amplifier's speaker and sends it back to the amplifier for
further amplification. Every system (i.e. microphone plus amplifier) has a feedback threshold.
Turn the volume up loud enough and feedback occurs. Keep the volume below that point and it
doesn't. The most common cause of feedback is needing more volume than your system can
produce without encountering it! An amp that sounds extremely loud in your living room may be
completely inaudible on stage. So you turn it up. And it feeds back. It is a law of nature. You
can’t bring a knife to a gun fight – whatever your mic/amp combo are – they WILL feedback if
turned up too far!
Unfortunately we often need to have our volume very close to the feedback threshold in order to
be loud enough, and feedback can come and go as conditions change. But some systems are less
prone to feedback than others. And some microphones are less prone than others. Factors
influencing feedback are:
1) Volume required exceeds pre-­‐feedback power available 2) Gain of the amplifier 3) Sensitivity of the microphone 4) Distance of microphone from speaker (amplifier or PA, house or monitors) 5) Tone settings 6) Player technique 7) Directionality of microphone What can be done about feedback? Believe it or not, microphone choice is not as important as you might think. Many players believe
one microphone feeds back more than another, only because that microphone is
louder/hotter/more sensitive than the other. The only "fair" way to judge one mic vs. another is
to adjust the amplifier's volume so that the sound out of the speakers is equally loud from mic A
to mic B. If mic B is louder to begin with, it will appear to feed back sooner if this isn't done.
With all that said, extremely sensitive mics will indeed be more feedback prone, but I have found
these to be fairly rare among mics I’ve seen. Every once in a while I encounter a bullet mic that
just seems to feed back very quickly compared to others of the same brand and model.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Sometimes this can be attributed to holes in the mic, but often the only solution is … don’t use
that mic!
Vocal mics and instrument mics are designed to be "directional" – to pick up more sound from
the front than from the sides or the rear, specifically to help avoid feedback on stage. So a welldesigned microphone can help with a feedback problem – but only when it is in free air – in
a rack or on a stand, and not in your hands. Once you pick up a microphone and cup it,
all bets are off. If you hand hold a mic, feedback will be more of an issue because the mic is
moving around and facing different directions. When you move your "cup" away from your
face, your other hand can act like a satellite dish and can catch and reflect more sound to the mic
than if it was in truly free air. Many players learn to manage this by pressing the face of the mic
against their chest while not playing. Ideally, you should be set up just a little further from "the
hairy edge" of feedback so it isn't too difficult to manage.
When you play acoustically, you can help to control feedback by ensuring that little to none of
your sound is coming through your monitors. Depending on the frequency of the feedback,
equalization (tone control) can help as well.
When you're playing amplified, all of the above applies. A microphone is designed specifically to
pick up sound waves from the air, so it is a much more sensitive and troublesome feedback device
than a guitar string. Consequently guitar amplifiers (and most harp amps start out as guitar
amps) are set up with much more gain than we need. This allows the guitar player to get
Hendrix-like feedback when he or she wants it, but it can be a nightmare for a harp player.
Gain is the most important variable in taming an amp’s tendency to feed back.
Remember, an amp is only so loud. No 5 watt, 8” speaker amp will cut through at a jam unless it
is mic’d. The best weapon of all is a more powerful amp with more speaker area. Read on for
more on this topic. But a typical guitar amp can be made much more harp friendly by reducing
its gain, so let’s talk about that for a moment.
Reducing feedback by reducing gain -­‐ amplifier tube substitution First, let’s define gain. Gain is not the same as volume. Gain is the slope of the line mapping input
volume to output volume. Here's an analogy. Imagine you have a light weight sports car with a
500HP V8 up front. Now imagine the gas pedal only moves 1/2". Idle is idle, full throttle is full
throttle - but the engine is so hard to manage in between, you have to drive even slower to be
safe. Now let's use the same engine but give the throttle pedal 5" of travel. Idle is still idle, full
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com throttle is still full throttle, but in between it is much easier to sneak up on that power smoothly.
You will get around the racetrack much faster with this setup.
This is completely analogous to how gain affects an amp. Reducing the gain is like adding
throttle pedal travel. It doesn’t increase power, but it does change the nature of feedback.
Instead of leaping out of the amp at the slightest touch, it comes on more gently and
progressively, allowing you to control it with your technique and volume control. For that reason
you can actually use more of the amp's available power without feedback.
Unfortunately you can't easily adjust the gain of most solid state amplifiers. For those, a more
expensive solution in the form of an anti-feedback pedal such as the Kinder Anti-Feedback +
(http://www.kinder-instruments.com/afb+.htm) or the “Squeal Killer”
(http://thesquealkiller.com) can be very effective.
However with tube amps we can simply substitute lower gain tubes for higher gain ones in the
amp's preamp section – and this can instantly make an amp more harp friendly. The
most popular preamp tubes are the 12A# series. A typical Fender guitar amp has three tubes in
the pre-amp section, and all are 12AX7's as the amp comes from the factory, set up for electric
guitar.
Here are the gain factors of the 12AX7 and its compatible cousins:
GAIN FACTOR 100: 12AX7 -­‐ aka ECC83, 7025, ECC803, E83CC, 6681 GAIN FACTOR 70: 5751 GAIN FACTOR 60: 12AT7 -­‐ aka ECC81, 6201, 6679 GAIN FACTOR 45: 12AY7 -­‐ aka 6072 GAIN FACTOR 41: 12AV7 -­‐ aka 5965 GAIN FACTOR 19: 12AU7 -­‐ aka ECC82, 5963, 5814, 6189 As you can see, three 12AX7's creates a huge amount of gain. On an amp like this, you will likely
not get the "normal" channel volume past 2 before feedback. If your amp has an "overdrive"
channel it will be completely unusable. There are way too many combinations and permutations
to describe here, but here is one recipe for success: On a Fender Bassman type amp with three
preamp tubes, replace the two 12AX7's closer to the amp’s center with 12AU7's. This should
make a significant difference. If it isn't enough, replace the outer one with a 12AT7 or 5751. You
should now be right in the ballpark and grasp the concept - continue to experiment and pick
what you like.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com How to be heard Although reducing the gain of your amp makes it more manageable, it will not perform miracles.
A Blues Jr sounds ear-splittingly loud in your living room. Yet you get on stage at a jam and
wonder why it can't be heard. So you turn it up until it is feeding back and conclude that you
have a feedback problem. But you don't. You have an amplifier problem. Said another way, just
because your amp doesn’t feed back easily doesn’t mean it is loud.
Mic it One solution is to mic the amp or use its line out feature (if it has one) to connect the amp to the
PA system in use. This is effective and allows much more volume in the audience. Small amps
can have outstanding tone – and they’re less expensive. There is no free lunch, however. The
volume “out front” may be sufficient but if you can’t hear yourself, or the band can’t hear you, it
is very difficult to play well. And small amps can easily be drowned out when stage volumes are
high. The “normal” solution to helping people hear themselves on stage is to add some of what
the audience is hearing through the PA into the “monitors” – those speakers on the floor at the
front of the stage, facing the musicians. Unfortunately you’ll find that having much of the
harmonica sound in the monitors is a feedback nightmare. It is best to be able to hear your amp
itself.
If you’re playing at jams, you may not have the option to mic your amp at all.
Line Out Some amps have a “line out” circuit – a jack that provides the amp’s audio at an appropriate
level to plug into another amp or the PA. The idea is the same as mic’ing an amp – just without
the mic. It has the advantage of being easier to connect to an amp on stage, and eliminates the
common problem of someone kicking a floor mic out of position. Good line out circuits are
driven from the amp’s speaker circuit and as such can have a very good representation of the
amp’s tone.
Maybe you simply need a bigger amp! The dB defined. Without getting too technical, the decibel, or “dB” is the unit of measure for “sound pressure
level” or SPL. Because it is expressed on a logarithmic scale, it can be a little bit confusing. As an
example, a doubling of volume is not equal to twice the number of dB. Studies have shown that
most humans cannot detect a difference of volume of less than 3dB. Yet it takes twice the power
for a 3dB increase in SPL. Now here’s the thing. To double the volume (an increase of 10dB), we
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com need ten times the power! Hypothetically, your 5W amp might make 93db – which is
freakishly loud in your living room. But to hear on stage with a typical live band you need about
103dB– that’s an increase of 10dB. Therefore – going from a 5W amp to a 15W amp isn’t going
to do the job. You need 50W. (Yes, everyone should play more quietly – there’s no reason to
play that loud, etc. etc. If you have your own band you have some control. If you don’t, you
don’t. I have a sound pressure level meter and I have used it in live settings. The above numbers
are indeed very realistic.) More Speaker, too
As power goes up, so should speaker surface area. Trying to push 50 W through a single 12 inch
speaker usually results in harshness of tone and less air movement. More speakers, given
sufficient power, increase volume because they move more air. Doubling the number of speakers
produces about a 2dB increase in SPL for the same power. Compare both power and the surface
area of the speakers on different amps. A Fender Blues Jr, is a 15 watt amp with a single 12”
speaker – if you do your “Pi r2” you’ll know it has 113 sq. in. of speaker surface area. My Sonny
Jr. Cruncher is about 35 watts, and has a 12” and two 8” speakers. That’s 213.5 sq. in of speaker
surface area – more than twice as much power and almost twice as much speaker area. I can get
the volume on that amp to 9 with no feedback because it is built to be harp friendly. But even
that isn't loud enough at some of the jams I go to. If I want to be heard at a jam, I bring out the
big guns. My Sonny Junior “Avenger” amp has about 50 watts, and has a 12” speaker, a 10 inch
speakers and 2 8” speakers. A little more power, but another big jump in speaker surface area 292 sq. inches to be exact. The difference is huge. Room filling volume, and again, completely
manageable feedback!
Other feedback management tips: Avoid "overdrive" amplifier channels or pedals: generally speaking these work by adding lots of
gain and will be feedback nightmares. If you're using a PA system and your amplifier is mic'd, tell
the sound guy to take you out of the monitors completely. If you can't hear yourself on stage, and
getting closer to (or further from) your amp doesn't help, have him sneak a tiny bit back in.
Change where you stand. Turn the treble or midrange down. Use an “anti-feedback” pedal. If
none of that cures your feedback problem, you are simply asking more of your amp than it can
deliver. The bigger the amp and the more speakers it has, the more likely it is that you can get
good volume before feedback, regardless of which mic you choose!
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Volume controls And finally, get a volume control! There is nothing worse than getting everything all set during
sound check, and then encountering feedback during your performance. But this happens all the
time, because room conditions change for a variety of reasons (the sound man included.) You
certainly don't want to have to dive for your amp to adjust it, knowing the feedback problem will
be worse when you get closer. A volume control at the mic is the perfect solution to this problem.
You can instantly kill feedback from where you stand just by lowering the volume a bit. When
you perform, you often can't be sure where the feedback is coming from. IF you hear feedback
on stage (everyone else will too) – lower your volume control immediately. If the feedback
persists, you get to throw your hands up with that “Hey - it isn’t me!” expression.
Volume controls are useful tools even if feedback isn't an issue. Although any good player has
good dynamic control over his instrument, there can still be a wider dynamic range in your
playing and with the band than you can accommodate merely by playing softer. Being able to
back the volume off right at the mic is really nice when you're comping behind a quiet passage in
the music. You can also use a volume control to explore the tonal range of your amp, when
otherwise you'd be firmly in feedback territory. An amp turned up to 10, with the mic's volume
controlled by you to remain below the feedback threshold, will sound different than the same
amp at 6 with the volume control on the mic all the way up.
Some players pooh-pooh volume controls. They’re usually players who have simply never tried a
good one! Practically every pro player I have seen uses a volume control. Charlie Musselwhite,
Kim Wilson, Rick Estrin, Rod Piazza, Jason Ricci, Rob Paparozzi, Billy Branch, Curtis Salgado,
Mark Hummel... the list just keeps on going. All of them use volume controls. And it isn’t
because they don’t have excellent dynamic control.
What about Wireless? Many players want to go wireless – fun, because you can go out in the audience and play, dance
up on the bar, or merely be free of that cumbersome cable. A wireless system always consists of
two parts. The transmitter stays with you, connects to your microphone and sends the signal out
into the air using radio waves. The receiver is located near and connected to your amp. There
are many types of wireless systems available to us. None of them are totally transparent – they all
tend to “compress” the sound to some degree, which you may or may not like. As a rule, you
usually get what you pay for. But there are some practical considerations.
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Some wireless transmitters are small and physically connect to your mic, making a single selfcontained unit. Others need a cable that connects to a "belt pack." The belt pack systems are
often of very good quality and fairly economical, but they have a drawback in that you cannot
simply put your mic down and move away. Because I double on saxophone in my band, I need
to switch instruments quickly and so I have to be able to just lay the mic down. With a belt-pack
system I would still be tethered to the mic. Some belt-pack users will simply shove the mic in their
pocket – if this is okay with you don't rule out belt pack systems.
Of the self-contained systems, there are two flavors. The "guitar bug" is a device designed for
(guess what) an electric guitar. It has a 1/4" plug on it – and can be used with a high impedance
mic with a 1/4" jack. An example of this is the Samson Airline 77 system with the AF1
transmitter.
The other flavor is designed to plug into the end of a vocal mic. It therefore has an XLR
connector and is barrel shaped. A good example of this kind of system is the Samson CR77 with
AX1 transmitter. Although the XLR connector might suggest this transmitter would only work
with low impedance microphones, it turns out this transmitter is perfectly happy working with a
high impedance microphone, provided that the microphone’s XLR connector is wired “Pin 2
Hot.” BlowsMeAway Productions sells adapters for microphones with screw on connectors, with
and without built-in volume control, that provide exactly this connection so that these mics can
be used with this system.
Regardless of the wireless system you choose, it is important to know that they must be properly
set up if your goal is a “cable-equivalent” sound. Set up improperly they will be very different.
Set up correctly, they can come very close to a cabled sound. BlowsMeAway provides wireless
systems specifically for harp players, and will set your system up for your microphone and
amplifier. See the http://www.blowsmeaway.com/wireless.html page for more information.
Important to users in the United States: Under an FCC rule anyone who uses a wireless
microphone that operates in the 700 MHz Band, and that means almost every wireless system
sold prior to late 2009, is supposed to have stopped using it no later than June 12, 2010. This
action helps complete an important component of the DTV Transition by clearing the 700 MHz
band to enable the rollout of communications services for public safety and the deployment of
next generation 4G wireless devices for consumers.
For further information, please visit the website at http://www.fcc.gov/cgb/wirelessmicrophones
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All About Harmonica Microphones © 2010-­‐2013 Greg Heumann, BlowsMeAway Productions http://www.BlowsMeAway.com Choosing a mic builder I have worked on many mics that others have worked on before me and I can tell you that mic
builders are NOT all created equal! There are a few very, very good ones out there. And there
are some guys who rave about their mics but do really poor quality work. I urge you to consider
the following:
1. Choose a builder who is easy to communicate with! If you can’t get your emails or phone
calls answered in a day or two you’re dealing with the wrong guy.
2. Check the builder’s reputation. Google him. Ask online. If someone has had a bad
experience they may not choose to air their laundry in public, but they’ll send you a
private email. I have gone so far as to conduct a web-based customer satisfaction survey
and have posted the results on my web site.
3. See who the builder’s customers are. If pros are willing to associate their name with the
builder, that’s a strong recommendation.
4. Can they play? I mean really play? A mic builder doesn’t have to be Charlie, Kim or
Rod, but if he can’t at least produce great tone and demonstrate good microphone
technique then he probably doesn’t “get it.” If he doesn’t perform, he may not
understand what’s important, not just about tone, but about compatibility, reliability,
feedback control, etc. – experience that comes from the performance environment. And
if he can play, I guarantee there are videos and/or sound files on the web and/or CD’s to
prove it.
Conclusion This has been a rollicking stream-of-consciousness core dump on my part. I hope it has been
helpful. There are many subjects left untouched. In the end only one thing matters, and that is
your personal satisfaction. You can’t know enough when you buy your first mic. Only when you
buy your second can you understand how it differs from the first. The more you try, the better
your technique becomes, the more situations you play in – the wiser you will become and the
better you will be able to hear the differences. Still, you can avoid wasting a lot of money by
choosing your sources wisely, and then trusting their advice.
Feel free to contact me at BlowsMeAway Productions by email – greg@blowsmeaway.com - any
time if you have a question. That’s what I’m here for!
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