Active box

Comparison of a passive and an active box with an active crossover. The latter is not a (compulsory) part of active boxes. Hybrid solutions are often found in 3-way systems.

Active box or active speaker (English powered speaker ) refers to an integrated unit of speaker and amplifier in one housing (box); the opposite is a passive box that does not contain an amplifier.

Term etymology

In the original sense, active speakers were used to describe loudspeaker systems that are equipped with active loudspeaker crossovers , several external or internal amplifiers and loudspeaker boxes . An amplifier integrated in the speakers is not necessary in this original sense, but corresponds to the current standard.

With the increasing spread of broadband systems with built-in amplifiers, the term was also extended to those systems that do not use an active crossover, but which are instead characterized by an integrated amplifier. In this sense, these boxes actively amplify the input signal.

history

The FA is the inventor of the active boxes. Sennheiser . Some of the first active speakers were monitor speakers from JBL . In 1964 JBL introduced the speaker amplifier SE401 Stereo Energizer . By installing it, any pair of monitor speakers could be converted into a pair of an active speaker and a passive speaker operated by it.

An early example of a studio monitor loudspeaker with bi-amping and active crossover is the Altec 9846B from 1971. This combined the passive Altec 9846-8A loudspeaker box with the 771B bi-amp amplifier, which generates 60 watts for the woofer and 30 watts for the Tweeter provided.

Internal structure

The integrated amplifier requires its own power supply, which is why active speakers always with power supply or batteries (or battery operated). An external power amplifier is not required.

In the case of multi- way active boxes, the necessary frequency distribution can take place both in front of and behind the power amplifier. In simpler systems - only one amplifier is required - a passive crossover is usually used between the power amplifier and the chassis . (The phrase "passive" here only refers to the internal structure of the crossover itself and otherwise has little to do with the active or passive operation of loudspeaker boxes.) In more complex or professional systems, however, each loudspeaker is supplied by its own power amplifier; the signal processing - frequency filtering etc. - then takes place before the respective final amplification. Various combinations of these systems are also possible.

Advantages and disadvantages

Inexpensive active loudspeakers, as they are usually operated on a PC.

Active 3-way bass reflex floorstanding speaker (the chair shown is used for size comparison). By using class D amplifiers , heat sinks can be dispensed with in this box, despite the high power available.

The relevance of the advantages and disadvantages depends in part on the intended use.

advantages

Precise adaptation of the amplifier to the loudspeakers used and thus avoidance of damage to the amplifier or loudspeaker due to incorrectly adapted or overloaded components. In passive speakers, overloaded tweeters due to strong distortion in bass signals are typical.
possibly lower costs than with the combination of passive speaker and amplifier, since the passive crossover in the power range can be saved. High quality crossover components are expensive, while amplifiers and power supplies are becoming cheaper.
Frequency response deviations of the loudspeaker can easily be corrected at line level using appropriate filters. Compared to passive concepts, even narrow-band frequency response drops in the loudspeaker chassis can be linearized to catch up (amplify) and run times corrected using digital technology.
Feedback circuits can be used to monitor the actual behavior of the loudspeaker and counteract deviations (example: motional feedback )

The particularly short cable connection between loudspeaker and amplifier (output stage) enables a high attenuation factor. This can result in a higher sound quality.

There is no need for expensive loudspeaker cables. Wireless ( WLAN , Bluetooth, etc.) audio connections are increasingly used.

disadvantage

Structure-borne noise from the loudspeakers can have a direct disruptive effect on the electronics.
Less flexibility; If one part (loudspeaker or amplifier) fails, the entire unit must be replaced
Higher costs, since each box has its own power supply unit and more circuit boards and heat sinks are required.
An additional power cord is required. With protective earthing combined with an unbalanced connection , interfering noises are possible that do not occur with active speakers with input circuitry for symmetrical signal transmission .

Area of use

Active boxes are most commonly used for the following purposes:

In professional recording studios and broadcasting

Monitor loudspeakers , studio loudspeakers as high-quality single loudspeakers

The very highest sound quality is possible thanks to the precise coordination between the active crossover, amplifier and loudspeaker as well as additional control options such as motional feedback .
PC and similar speaker systems: The simple handling and the low price due to the mostly very simple chip amplifiers with a few watts are the main advantages. The amplifier is often integrated in one of the loudspeaker boxes, the other (s) are connected as simple passive boxes.
Mobile public address systems: The greatest advantage here is that no additional devices such as external amplifiers or crossovers have to be set up and adjusted. In addition, the risk of damage from overloads is reduced.

Additional active subwoofer in the recording studio as well as in the home

With many stereo devices, the use of an additional subwoofer in the bass / deep bass range is not intended for construction. In addition to the amplifier for the increased performance requirements in the low frequency range, further signal adjustments can be made:

Crossover to extract the bass frequency range
Level adjustment for connection to the loudspeaker outputs of an amplifier without a suitable subwoofer output
Merging of stereo signals into a mono signal
Phase / level setting for adaptation to the other loudspeakers

These are therefore available as a function in many active subwoofers.

Home cinema equipment usually has a suitable connection for a subwoofer; The only requirement here is the additional amplifier.

literature

Ekkehard Scholz: Self-built active loudspeakers. 3rd edition, Franzis Verlag GmbH, Munich, 1991, ISBN 3-7723-2073-2

Web links

Commons : Active speakers - collection of pictures, videos and audio files

Individual evidence

[1] Audio.de active speaker test

[2] ubert.de active box A300