Live Vocal Microphones

A live vocal microphone needs to have a good sound quality, be rugged enough to get knocked around on stage, survive episodes of feedback and perform consistently in any environment.

Dynamic microphones are a relatively simple design of microphone and fit this description perfectly. They are relatively inexpensive and are the most widely used microphone for live vocals.

Studio Vocal Microphones

A studio microphone needs to have excellent sound quality, but doesn’t need to be rugged in the same way that a live microphone does. Condenser microphones are much more sensitive than dynamic microphones; however the relatively safe studio environment suits them perfectly.

Of course there are occasions where dynamic microphones can be used in the studio and where condenser microphones can be used on stage, however for the reasons outlined above; there are good reasons why most people use them in their more typical environments.

In conclusion

Ultimately, when choosing your vocal microphone, follow the rules above, but try out as many different varieties of each microphone as you can to find one that suits you. Think about microphones like musical instruments, each model has a slightly different characteristic, which will make some microphones suited to your vocal more than others.

Gemma King is a professional singer, songwriter and vocal coach. You can find more of her articles on her website becomeasinger.net

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How microphones work – in a nut shell.

A microphone captures sound waves with a thin and flexible piece of metal known as a diaphragm. Sound waves are introduced into the microphone, vibrating the diaphragm. The vibrations are then converted by various methods into an electrical signal that is an analog of the original sound.

There are various types of microphones, today we’ll be discussing laser, lavalier, contact, and parabolic microphones.

1. Laser Microphones

A laser microphone utilizes, well, laser technology to capture vibration and convert it into sound. The laser will be reflected off of glass or another flat and rigid surface that vibrates with the sound nearby. The laser measures the distance (very accurately) between itself and the surface it is reflecting off of, and measures the fluctuations of that surface when the sound waves from nearby vibrate said surface. This form of mic is portrayed in movies as spy equipment. But contrary to it’s portrayal, the device is very new, expensive, and not very portable.

2. Lavalier Microphones

This type of microphone is commonly used for hands-free operation, usually clipped to a person’s lapel. They usually have their own power source and can run directly into the mixer, or may be wireless, making it ideal for television.

3. Contact Microphones

In the world of microphones, contact mics are a little different than the rest. They are designed to pick up sound vibrations from solid objects, instead of vibrations carried through the air. This is mainly used to record low level sounds that you would not be able to pick up with a regular mic. These mics consist of a moving coil transducer, a contact plate and pin. The contact plate is placed on the object which you would like to record, the vibration is passed through the plate to the pin which passes it to the transducer. The experimental electronic music group Matmos used this on their album “A Chance to Cut is a Chance to Cure”, to record the neural activity of a crayfish.

4. Parabolic Microphones

Parabolic microphones use a parabolic reflector to pick up and focus sound waves for a microphone receiver. It is similar in function to a satellite dish in the way that it pick up radio waves. These mics are commonly used for law enforcement surveillance. But they are not very well suited for regular recording, as their low frequency response is very poor.

So this wraps up our Microphones 101 series of articles. I hope you all learned as much from these articles as I have from researching and writing them!

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Frequency Response

Frequency response measures how a microphone reacts to different sound frequencies. An ideal “flat” response (equal sensitivity) microphone would respond equally to all frequencies within the audible spectrum. This results in a more accurate reproduction of sound and produces the purest audio. The truth is that even microphones which are advertised as having a “flat response” can deviate somewhat at certain frequencies. Typically spec sheets will list frequency response as a range like “20Hz to 20kHz”, meaning that the microphone can reproduce sounds that fall within that range. What this does not explain is how accurately the various individual frequencies will be reproduced. Some microphones are purposely designed to respond differently to certain frequencies. For example, instrument microphones for bass drums are generally engineered to be more responsive to lower frequencies while vocal microphones would be more responsive to the frequency of a human voice.

As a general rule of thumb, condenser microphones have flatter frequency responses than dynamic. This means that a condenser would tend to be the better choice if accuracy of audio reproduction is the main goal.

Sensitivity

Microphone sensitivity measures how much electrical output (measured in “millivolts” mV) is generated for a given sound pressure input. Typically when measuring microphone sensitivity the mic is placed in a reference sound field where a sound pressure level (SPL) of 94 dB (1 Pascal) at 1000 Hz is maintained at the microphone. (Some vendors like Shure use 74 dB 0.1 Pascal). The distinction is that 94 dB SPL is the typical sound intensity of someone speaking twelve inches away while 74dB SPL would be the same speaker one inch away. A typical condenser microphone might have a value listed either like “7mV/Pa” or -43dBV in the technical specification. These two values mean the same thing – they’re just expressed differently.

If two microphones are subject to the same SPL and one generates a higher output voltage, that microphone is said to have a higher sensitivity rating. Although knowing how to read/compare microphone sensitivity (output) is important, the actual sensitivity rating usually is not a major consideration in mic selection. Typically the design of a microphone for a particular application plays a role when manufacturers determine the appropriate output level. For example, dynamic microphones are typically less sensitive than condenser mics as they’re generally used fairly close to the sound source. Listed below are the typical specifications for three different microphone transducer types:

Condenser: 5.6mV/Pa (high sensitivity)

Dynamic: 1.8mV/Pa (medium sensitivity)

Ribbon: 1.1mV/Pa (low sensitivity)

Impedance

Impedance is how much a device resists the flow of an AC current (such as audio signal) and is measured in ohms. Typically when referring to microphones, “low impedance” is considered anything under 600 ohms. “Medium impedance” would be 600 ohms to 10,000 ohms and “high impedance” would be greater than 10,000 ohms. All microphones have a specification regarding their impedance – sometimes the value is written on the mic somewhere, other times you might need to consult the technical manual or manufacturers’ website to determine the number. Generally speaking, low impedance microphones are better than high impedance, and quite often you can use impedance as a rough gauge when determining overall quality. The advantage of low impedance microphones is that they can be used with very long cable runs and negligible signal loss. Mics with hardwired cables and a 1/4″ jacks are high impedance, while mics that require a balanced audio cable and xlr connector are low impedance.

When connecting your microphone it’s important to know the corresponding ohm level of the sound mixer or amplifier. A low impedance microphone should always be connected to an input with a higher impedance value, otherwise signal loss will result. Typically “low impedance” audio mixers have inputs with impedance levels between 1000 and 2000 ohms, and are designed to work with the lower level microphone impedance levels.

Self Noise Level

Self noise is the electrical hiss that a microphone produces. Typically the self noise spec is “A weighted”, meaning that the lowest and highest frequencies are flattened in the response curve, to better simulate the signal response of the human ear. (We tend to perceive mid range sound frequencies as louder.) As a general guideline, an A Weighted self noise spec of 18dB SPL or less is excellent (very quiet), 28dB SPL is good, while anything over 35db SPL is not well suited for quality audio recordings.

Because dynamic microphones do not have active electronics (no phantom power requirements) they have very low self noise when compared to condenser microphones. Most spec sheets for dynamic microphones do not include self noise measurements.

Signal to Noise Ratio

The signal to noise ratio (S/N) is the difference in dB between a microphone’s sensitivity and self noise. A higher S/N means that the signal is cleaner (less noise) and that the microphone has more “reach”. Reach can be defined as the accurate pickup of quiet/distant sounds due to high S/N. Typically reach is not listed as a metric on a tech sheet as any microphone can pick up a distant sound if the source is loud enough. For example, even a very inexpensive mic can pick up a thunderclap from far away.

As a general rule when evaluating S/N ratios, given 94dB SPL, anything over 74dB is excellent, a S/N spec of 64dB is considered good.

Summary

Hopefully these definitions have helped to provide some understanding about typical microphone specifications. The truth is that there is no “ideal” microphone that is perfect for every situation. Manufacturers design their microphones with specific audio applications in mind – such as live performances or studio reproduction, and as a result have tailored the specifications so that the mic sounds the best that it can with a given hardware configuration. Generally speaking, more expensive microphones are engineered with better hardware, which results in better specifications and performance.

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