Microphones 101 B: Pickup Patterns

Directional Properties

Every microphone has a property known as directionality. This describes the microphone's sensitivity to sound from various directions. Some microphones pick up sound equally from all directions; others pick up sound only from one direction or a particular combination of directions. The types of directionality are divided into three main categories:

  1. Omnidirectional
    Picks up sound evenly from all directions (omni means "all" or "every").
  2. Unidirectional
    Picks up sound predominantly from one direction. This includes cardioid and supercardioid microphones (see below).
  3. Bi-directional or figure-of-eight
    Picks up sound from two opposite directions.

***The following graphs are called polar patterns.

Omnidirectional

Uses: Capturing ambient sound; Situations where sound is coming from many directions; Situations where the mic position must remain fixed while the sound source is moving.
Notes:

  • Although omnidirectional mics are very useful in the right situation, picking up sound from every direction is not always desired. Omni sound is very general and unfocused - if you are trying to capture sound from a particular subject or area it is likely to be cluttered by other sources.
  • Omnidirectional microphones have no proximity effect*.

Right-click here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture from the Internet. Omnidirectioal

Cardioid

Cardioid means "heart-shaped", which is the type of pick-up pattern these mics have. Sound is picked up mostly from the front, to a lesser extent the sides, and minimally from the rear.
Uses: Emphasizing sound from the direction the mic is pointed while leaving some latitude for mic movement and ambient noise. Controlling feedback.
Notes:

  • The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioids.
  • Cardioid mics have proximity effect.

Right-click here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture from the Internet. Cardioid

Supercardioid

This is the cardioid or "heart shaped" pattern that picks up less from the sides at the expense of some sensitivity to the rear.
Uses: When more directionality than the cardioid is desired. Can be more effective against feedback.
Notes:

  • Supercardioids have more proximity effect than cardioids.

Right-click here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture from the Internet. Hypercardioid

Figure-of-Eight

Picks up sound equally from two opposite directions.
Uses: Figure-of-eight microphones have uses in various stereo and ambient techniques. They also work well when capturing two people facing each other (like across a table). The very-low side sensitivity can be helpful controlling feedback and leakage. The pronounced proximity effect is often used when more “fattening” is desired (guitar amps and vocals).

Notes:
Figure-of-eights have more proximity effect than supercardioids.

Right-click here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture from the Internet. Bidirectional

Variable Pattern
Some mics allows you to adjust the polar pattern continuously from omnidirectional to figure-of-eight by turning a knob on the front of the microphone.


© Copyright CAD Professional Microphones · 6573 Cochran Rd. Bldg. I · Solon, Ohio 44139
Phone: 800-762-9266 Ext. 211 · Fax: 440-248-4902 · E-mail: sales@cadmics.com
Used by permission. All Rights Reserved.

Microphones 101 A: Types of microphones

Dynamic Microphones
There are two basic types of dynamic microphones. These are moving-coil dynamic microphones and moving-ribbon dynamic microphones.

Moving-coil Dynamic Microphones

Moving-coil dynamic microphones are versatile and ideal for general-purpose use. They use a simple design with few moving parts. They are relatively sturdy and resilient to rough handling.

They are robust, relatively inexpensive and resistant to moisture, and for these reasons they are widely used on-stage. They are usually better suited to handling high sound pressure, such as from close-up vocals, certain musical instruments, and amplifiers. They generally have no internal amplifier and do not require batteries or external power.

How Moving-coil Dynamic Microphones Work

When wire is moved within a magnetic field a current is generated in the wire. Using this induction principle, the dynamic microphone uses a wire coil, magnet, and a thin diaphragm to capture the audio signal.

The diaphragm is attached to the coil. When the diaphragm vibrates in response to incoming sound waves, the coil moves backwards and forwards past the magnet. This creates an electrical current in the coil, which is channeled from the microphone along wires.

Moving-ribbon Dynamic Microphones
CAD Mics: Trion 7000

Moving ribbon dynamic microphones are generally more fragile than their moving-coil cousins and usually spend more time in the studio than on stage. (However, many Trion 7000s have been seen on several high-profile tours.) Ribbon microphones have a mellow sound of their own and work well on brass instruments, guitar cabinets, and other aggressive sources.

How Moving-ribbon Dynamic Microphones Work
Like the moving-coil dynamic microphone, the moving-ribbon dynamic microphone utilizes induction. However, instead of a coil of wire, a thin corrugated aluminum ribbon is suspended in the magnetic field. As this ribbon vibrates sympathetically to impinging sound an electrical current is generated in the ribbon.

Condenser Microphones

CAD Mics:Trion 6000, Trion 8000, C195, GXL2200, GXL1200, GXL2400, M179, M177, M9, e60, e70, e100-2, e300-2, ICM417, CM100, ST100, MG115, MG120

Condenser is a legacy term meaning capacitor, a device that stores energy in the form of an electrostatic field. Although the term is obsolete in engineering it is still used to describe microphones that use a capacitor to sense acoustical energy.

Condenser microphones tend to be more sensitive and responsive than dynamic microphones, making them useful for capturing subtle nuances and intricate detail. They are not always ideal for high sound pressure work as their high sensitivity can cause overload distortion in some mixers and preamps.

How Condenser Microphones Work

A capacitor consists of two conductive plates near each other. In the condenser mic, one of these plates is made of a very thin, light, flexible material and acts as the diaphragm. The diaphragm vibrates in the presence of sound waves, varying the distance between the plates, which varies the capacitance.

A bias voltage is required across the capacitor to sense this change in capacitance. This voltage can be supplied internally by a fixed electrostatic charge or externally.

As the capacitance changes so does the voltage across the capacitor. This voltage can be sensed by a vacuum tube or a field-effect transistor. In either case, power is needed to run the circuit. This power can be provided by internal batteries, an external power supply, or in the case of some CAD equitek microphones, both.

Phantom Power

Phantom power (labeled as +48 V or P48 on some audio equipment) is a method that sends DC power through microphone cables. It is called "phantom" powering because the supply voltage is effectively invisible to balanced microphones which do not require it, e.g. most dynamic microphones.

It is best known as a common power source for condenser microphones, though many active DI boxes also use it. Stand-alone phantom power supplies are available, but usually they are conveniently integrated into mixers, microphone preamplifiers and similar equipment.


© Copyright CAD Professional Microphones · 6573 Cochran Rd. Bldg. I · Solon, Ohio 44139
Phone: 800-762-9266 Ext. 211 · Fax: 440-248-4902 · E-mail: sales@cadmics.com
Used by permission. All Rights Reserved.

Lectrosonics: "The Sky is NOT Falling"

There are currently two issues of concern regarding changes to allocation of RF spectrum in the UHF range.

They are:

  1. Auctioning of the “700MHz band” (698-806MHz). As of February 17 2009, this portion of RF spectrum will be available to be used by the companies that won the auctions, and will no longer be available to Part 74 users (i.e. wireless microphones).
    • At the same time, analog TV stations will shut down and only DTV stations will be in operation. Because the 700MHz band will no longer be available to TV broadcasters, the few that are left will have to move to a lower range.
    • Thus, our blocks 27, 28 & 29 will have new (as of yet unknown) transmissions operating, while our blocks 21-26 may have a few new DTV channels when compared to today, depending on the local market.
  2. The FCC has approved the development of unlicensed consumer products that will use the “white spaces” (remaining unused spectrum between existing TV transmissions). Here’s what that means
    • These new devices will be required by the FCC to employ “Spectrum Sensing” technology that will determine what, if any, other users may be present in the RF spectrum, including TV transmissions and wireless microphone systems, among others.
    • These devices will also use a geo-location system (GPS) along with a database f known signal sources, such as TV broadcasts and high-profile wireless mic users to avoid interference.
    For a summary of the recent FCC rulings, download this PDF

What This Means

  1. Starting in February of 2009, there will be fewer TV stations in operation overall. This is because today, many stations are running redundant NTSC (analog) and DTV broadcasts. After February, 2009, they will only run their DTV broadcasts. Not only this, but DTV allows for multiple program channels to be embedded within a single DTV broadcast carrier. There is little financial incentive to add transmission channels at this time.
    • Please note the tables in the sidebar at right showing some examples of major metro markets and the available white space spectrum now and after February, 2009
  2. Lectrosonics makes high-powered systems, from 50mW to 250mW, with the standard units at 100mW. Thus, we already have a major advantage over systems with low-powered transmitters. Also, all of our transmitters have isolated outputs, thus using higher power, as we do, is not the problem (intermodulation products) as it is with competitor’s units that are not isolated. Bottom line: our systems will operate very well even with a fair amount of broad-band noise.

However, it will not be legal for us (or any manufacturer) to make and sell transmitters above 698MHz following February 17, 2009. In November of 2007, we announced to our dealers that we would cease stocking any transmitters in blocks 27, 28 and 29. However, these blocks will be available only on a special-order, non-returnable basis through the end of 2008. In addition, we have added three blocks at the low end of the spectrum (blocks 470, 19 and 20) so that spectrum lost at the high range can be compensated for on the low end. In addition, we will be adding products in the 944-952MHz range, including Venue, IFB, SM Series, UCR401 and SR.

Keep in mind that the first 68 frequencies available in block 27 will continue to be legal. If you are using block 27 systems, you may NOT need to do anything.

For those customers who would like to convert their block 27, 28 or 29 systems to lower blocks, please consult this PDF price table. This applies only to current products and to those products purchased new within the last 5 years from an authorized dealer.

Conclusions

  1. The sky is not falling (remember Y2K?). Wireless mics in the UHF band will not be rendered useless within the next few years. Existing and foreseeable-future wireless mics, particularly those made by Lectrosonics, will be fully operational for years to come. Yes – there may be some challenges but mostly it will be about learning and adapting to the new RF spectrum.
  2. Although the FCC requires the 700MHz band to be "vacated' as of February 2009, it is unrealistic to expect that all users of low-powered devices (wireless mics) will stop using their current systems. It is very likely that most wireless mic users in this range will continue to operate illegally for some time. Licensed, legal, part 74 users such as broadcast stations will have to cease operation in the 700 MHz band. Manufacturers of part 74 devices will have to cease manufacturing, importing, or even shipping units that operate in the 700 MHz band. Commercial development of this band will begin in the large metro areras first, then work its way out to the further reaches of the country, the same way that cellular coverage did in the 1990s.
  3. Lectrosonics, will, as required by the FCC, cease manufacturing and selling blocks 27, 28 and 29 for the US market at the end of 2008. To convert your systems in these blocks to lower blocks, consult this PDF pricing table.
  4. No one currently knows what will happen in the 470 to 700 MHz range. If and when the consumer "white space devices" hit the market (probably starting at the end of 2009 or later), the UHF band will be similar in terms of congestion to the way the 2.4 GHz band already is today. In other words, it will be workable with proper planning, good system components and good system design.

Lectrosonics is very concerned about these issues, and we hope to do everything possible to make you aware of what is happening and help you with the transition. If you have any questions, please don’t hesitate to contact us.