Isobaric speakers

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The Isobaric or isobarik loudspeaker construction technique was originally introduced by Harry Olson in the early 1950's. It is derived from the term Isobaric, which is of Greek origin: "Iso" meaning "constant" and "Baric" meaning "pressure". It defines the operational characteristics of the use of at least two woofers (bass drivers) in a loudspeaker unit.

The use of isobaric loading in a loudspeaker in practical terms is to lower bass frequency response.

1 Design principles
2 Examples
3 References
4 External links

[edit] Design principles

Isobarik loudspeaker in a cone-to-magnet (in-phase) arrangement. The image above shows a sealed enclosure; vented enclosures may also use the isobarik scheme.

The two bass drivers are coupled to work together as one bass unit: they are mounted one behind the other in a casing to define a chamber of air of constant pressure in between. The two drivers are placed either "cone to magnet" and wired in phase with one another or "cone to cone" or "magnet to magnet" and wired out of phase with one another so that cones move together when driven with an audio signal, keeping the pressure of air in the chamber substantially constant. The loudspeaker which is mounted on the front wall of the cabinet thus operates under substantially "ideal" conditions.

Any changes in sound pressure within the chamber which may rise represents distortion components, and are absorbed by absorbent material inside the chamber^[1].

The result is that the coupled driver pair (iso-group) can now produce the same frequency response in half the box volume that a single driver of the same type would require. For example, if a speaker is optimized for performance in a 40 litre enclosure, one iso-group of the same speakers can achieve the same low frequency extension and overall response characteristics in a 20 litre enclosure.