Amplification 102

Mics, Pickups, Amps, and PA Systems

Amplification technology has made great improvements in the past 30 years.  When close-mic amplification first began in the 1980’s, the only two amplification options were (electric) guitar amplifiers, or PA systems (multi-component, bulky, and complex).  Today, there are a variety of guitar amps are now available, and multiple vendors sell high quality PA systems smaller and lighter than the average guitar inside a flight case. While this wide range of options is a great asset to getting the best possible amplified sound, there can also be confusion about what type of amplification equipment is designed for what type of pickup or microphone, including the2Mic™.

In the 1930’s, when amplification first began to be used with live performance, there was not a significant amount of difference between the magnetic pickups used for guitars, and the microphones used for vocalists.  Early pickups and microphones both produced a mono line level signal that connected with an amplifier very similar to traditional guitar amps. The concept of a multi component PA system did not really come into existence until the 1950’s.

To a large degree, the fundamental technology of magnetic pickups has not evolved significantly since the 1950’s.  A mono line level signal remains the standard for most pickups. And the piezo pickup that came to be used with acoustic guitars, copied the same mono, high impedance, line level signal format.   But microphone and PA technology has made significant improvements and continues to do so in the present day.

The biggest improvement in Microphone technology came with the development of the “balanced low impedance signal”.  A 3d wire, often designated as “B+” was added that stabilizes the signal, and protects the signal from outside invasion (radios, fluorescent light ballasts, wireless signals, etc.).  This more stable signal is also able to travel greater distances without any deterioration of the signal quality (line loss). Mono high impedance signals generally cannot travel more than 30 feet (9 m) without a drop in output strength or an increase in hiss or noise.  

Low impedance signals allowed microphones to achieve a much higher tone quality.  The more nasal and “tinny” sound of early high impedance microphones was replaced in the 1950’s and 60’s with much higher quality low impedance microphones.  At the same time, PA systems became more sophisticated, and capable of reproducing high quality sound for increasingly larger audiences.

Low impedance signals also brought a uniformity to the strength of the signal produced in the range of 500 – 1000 ohm.  Whereas high impedance signals can vary from 4000 – 12,000 (4k-12K) ohms in strength. This variance in signal strength for high impedance signals can create problems with an “impedance mismatch”, so that a pickup (or 2Mic) having a low range high impedance signal of 4K ohm, will perform poorly when plugged into an input expecting to receive a 10K ohm signal. Using pre-amps can help pickups convert to a high impedance signal, but there is threshold for impedance with microphones where increased impedance leads to lower overall tone quality. (This threshold is approx. 4-5K ohm by our testing.)

Microphone design further improved with higher quality mics being produced in smaller and smaller enclosures.  Eventually these “lavalier mics”, or “button mics”, came to be equal in quality to some to the better hand held or studio microphones.  And these high-quality miniature microphones led to the first applications of close-mic technology in the 1980’s.

Early PA systems used a powered mixer or mixer & power amp to send a powered mono signal to passive speakers.  But in the late 90’s powered PA speakers began to appear where the amplifier was located in the speaker itself and a non-powered mixer sent a balanced low impedance signal to the powered speakers.  This created both improved sound quality, and a reduction in weight & size for the speakers.

A decade later, powered speakers appeared with an EQ mixer located in the speaker itself, so that a single Powered PA speaker with an on-board mixer could function, with the2Mic™ in a manner very similar to how a pickup works with a guitar amp.  Part of the improvement comes from these speakers always having a speaker stand cup so the speakers can be easily elevated. The full frequency response of microphones is best reproduced using elevated speakers so the sound can disperse evenly across an audience.  The common practice to place guitar amps on the floor behind the performer is not a good choice with any microphone, including the2Mic™, as this makes for poor sound dispersion.

In conclusion, the emergence of powered PA speakers has proven to be an important technology advance for amplification of classical and flamenco guitars using the2Mic™.  These powered PA speakers offer many of the “plug and play” conveniences formerly found only with guitar amps, but with a capacity to reproduce the full frequency spectrum of a classical or flamenco guitar amplified by the2Mic™, and without problems of feedback or sound distortion.