Reverberation

A Hall device is an electro - acoustic or electronic system for generating artificial reverberation.

Electromechanical reverbs

Spring reverb ( " Reverb " )

One or more metal coil springs are clamped loosely in a frame. The type of restraint allows both the longitudinal, lateral and torsional vibrations of the spring. Near the suspensions are each electromechanical transducer mounted (magnetic and current-carrying coil ). The magnets are connected to the spring, the coils are fixedly attached to the frame. The transmitter coil is injected through an amplifier, a current. The amplifier is controlled by said electrical signal to be applied to artificial reverberation.

On one side the mounting of the magnet is rotated by the current in the transmitter coil to vibrate. The vibration propagates on the spring and comes with a small delay at the other end of the spring on. There does, the second transducer coil ( slave coil) to the oscillation and converts it into an electrical signal which is coupled via a second amplifier.

Also the vibration is reflected and travels on a time of the spring back and forth after the input vibration is decayed. The result is a reverberation effect. Practically can delay of several 10 ms and reverberation times of a few seconds to achieve.

Properties Besides the advantage of simple and thus inexpensive construction, the electro- mechanical spring system has more than two undesirable properties:

• The transmission behavior is resonant, more or less depending on the design. It comes to color the sound. By combining multiple springs with different characteristics, the transmission characteristics can ( the sound ) can be influenced. The input and output amplifier can filter out by a particular interpretation of resonances to a limited extent.
• The delay on the spring is constant, which makes it sound more or less unnatural the Hall. There are therefore suspended two or three springs with different delay in parallel.
• Improved systems with longer delay time can reach spring lengths of over a meter. To save space, the spring is clamped in practice (for example in the form of a "Z" ) is also folded.
• May signal pulses, the spring system due to its inertia does not follow, so that a characteristic rattling noise.
• Hall spirals Vibration, airborne noise and structure-borne noise sensitive. To minimize unwanted noise, the springs are suspended in an auxiliary frame, which is in turn suspended in swinging a main frame ( decoupling). The overall system is often installed in a sound- insulated housing.
• There are no parameters that can be varied. Only the addition of reverb to the original signal can be adjusted in a mixer ( "Reverb " adjuster on many guitar amplifiers).
• The electromagnetic transducer are prone to interference from electric and magnetic fields, which manifest themselves as noise.

Hall plate

→ Main article: Hall plate ( acoustic )

A Plate reverb works on a similar principle as a spring reverb, but is as oscillating mechanical system, a steel plate used. In contrast to the spring reverb several parameters can be influenced. With the Hall plate an almost natural sounding reverberation can be generated due to the required dimensions and the high price of this technique, however, was reserved largely professional studios.

Band Hall device

→ Main article: Band Hall device

A tape reverb unit works with an endless magnetic tape. On read and write heads, the audio information is recorded on the tape and read from the tape. About the speed of the magnetic tape and the volume settings of the delay and the reverb depth can be adjusted.

Electronic Hall

Today, most of artificial reverberation electronically in digital signal processors ( DSP) is generated. This method has none of the disadvantages of mechanical systems, but a lot of computing power is required when the Hall effect is to be simulated realistically.

→ see also: convolution reverb

Application

Mechanical Hall devices are technically obsolete. They were used regularly until the 1970s in the recording studio next echo chambers for generating reverberation.

Today, however, still often spring reverb systems ( Reverb ) are used in guitar amplifiers for electric guitars, in modular synthesizers and the Hammond organ. The characteristic sound is reminiscent of the pop music of the 1960s. They especially like and overdosed it is still used today in the surfing music. The really unwanted rattling and gurgling dynamic peaks is used here deliberately for the sound color.

Since the 1980s, artificial reverberation is usually generated by electronic devices. The realization is so inexpensive that even simple mixers for amateur musicians are often equipped with it.

Trivia

• Hall feathers were originally used by telephone companies for echo cancellation. Here, the property of the delay was applied, the reverberation was undesirable.
• In the 1960s, spring reverb units were available as accessories for hi-fi systems. Thus, a Hall - controller was installed among other things, stereo tube equipment of the Grundig brand in general. The reverb unit itself was connected externally and based on the " reverb " by Hammond.
• In vehicles the U.S. Imperial brand car radios were installed, the rear speakers was controlled by a spring reverb. For example, to avoid interference from vibrations while driving, probably a considerable engineering effort had to be driven.
• From the 1960s to 1970s, it was with some rock bands common to end the concert (not only) to destroy their amplifiers (Example: The Who ). The resulting sounds were mainly caused by the rattling Hall feathers.
• In a currently (2005) sold children's toys in the form of a hand microphone, a spring reverb mounted that is stimulated by sound to mechanical vibrations and creates an artificial reverberation swinging out.
• Hall springs can be mechanically manipulated from outside ( for example with the hands ). The resulting noise is dramatically used, eg, in plays and in electronic music.