Dipole (speaker)
A dipole loudspeaker is a sound transducer that radiates the sound energy evenly both forwards and backwards ( radiation characteristic "eight") - the equivalent of the directional characteristic of microphones . It is implemented in its simplest form by installing a single (conical) loudspeaker chassis in an open (open-baffle principle) baffle. Large electrostatic, magnetostatic or ribbon loudspeaker systems usually also follow the dipole principle. Some dipole speakers have symmetrically arranged speaker cones on the front and back. These must then be connected with the wrong polarity.
Compared to direct radiating loudspeakers, the much higher proportion of indirect sound that reaches the listener a little later (especially that reflected from the rear wall) leads to a more spacious, airy sound from a dipole loudspeaker compared to a conventional, exclusively direct radiating loudspeaker .
Dipole bass speaker (subwoofer)
Since around 1996, dipole speakers have also increasingly appeared as subwoofers . The volume requirement of open dipole constructions is considerably less than that of closed, bass reflex or bandpass constructions. The open dipole system as a whole also has, almost without exception, a more precise impulse behavior than other, not completely open principles, since the Q-factor of the overall system is practically identical to the Q-factor of the loudspeaker chassis, which is usually below 0.5. A re-oscillation of the membrane is effectively avoided in the absence of an opposing spring force. Impulse-compensated versions with two loudspeaker membranes have the advantage of dipole subwoofers that hardly any vibrations are transmitted to the open housing (Linkwitz (1996) or Ridtahler principle (2002)). The resonance frequency of the overall system is then also lower than that of the individual chassis, so that a particularly deep bass reproduction is possible. The sound of dipole subwoofers is usually described as drier, faster, more precise and immediate than with conventional subwoofers. In contrast to the midrange, this effect in bass loudspeakers should not so much affect the inclusion of the room (creates additional space), but rather the electrical parameters of the overall system, which works "more freely" than in conventional constructions, and the effect of the musical instruments (including the eardrum a kick drum works as a dipole). The only but often decisive disadvantage of open dipole subwoofers is their poor electrical efficiency, since a lot of sound power is lost due to the partial "acoustic short circuit" caused by the lack of a largely closed housing. In the home cinema area, where extreme levels at the lowest frequencies are more decisive than a pure decay spectrum, dipole subwoofers have therefore not yet been able to establish themselves.
Home theater
In the home cinema sector, dipoles are often used to generate a diffuse sound image as rear surround sound speakers. Home theater dipole speakers should be mounted at least 0.15 meters from a wall at a height of approximately 1.40 to 2.10 meters to reproduce typical atmospheric cinema sound. With THX -certified speaker systems, dipole speakers are the rule as rear speakers. Dipole loudspeakers do not necessarily improve the sound because they are also used in the THX standard. This standard considers sound technology and room acoustics together.
Conclusion
Dipoles particularly include the room acoustics in the sound. Is the room acoustics rather poor because the walls reflect the sound very strongly, or is there sufficient distance from the wall for stereophonic playback (here it should be at least 1 to 1.5 meters so that the ear can distinguish the room reflections from the direct sound and not the indirect sound as "smearing") is not possible, then it may make more sense to use a normal loudspeaker because it emits the sound without ultimately signal-changing reflections. Even with a normal loudspeaker, the walls will reflect the sound, but not as strongly because they are not stimulated directly.
literature
- Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9