Our blog has not yet raised the topic of an arch-rare, exotic type of speaker system - known as a counter-aperture. Speaking frankly, I vaguely imagined what it is, why it is needed and what it is “eaten” with. Therefore I had to google pretty much. Among the sources were a couple of forums, two scientific articles and one patent. Meanwhile, I have a desire to cover all existing types of speakers in this cycle, and therefore I decided not to sidestep this undoubtedly interesting topic.
In Wikipedia and other sources, konperperture speakers are presented as an example of economically and serially unreasonable decisions for the notorious High End. Adherents of kontraperturnyh speakers consider them unfairly forgotten evolutionary branch of sound-reproducing devices, allowing to receive omnidirectional radiation and a lot of other remarkable effects impossible using a different architecture. Under the cut in detail about kontraperturnoy acoustics.
How does it work?
The term “contraception” itself is more often used in optics, where it denotes coaxially arranged light-emitting holes. In acoustics, the meaning changes a little, and instead of holes one should understand loudspeakers.
Acoustic design in such speakers assumes the placement of two identical speakers (and here the values that can be neglected become very small) strictly opposite each other and their common-mode switching. It is important that the emitters do not have phase delays and frequency differences (this significantly increases the cost of the component). When these conditions are met, the waves from the oppositely directed dynamic heads of the antispection speaker emit a resultant wave with a spherical front (that is, in fact, they represent an omnidirectional radiator).
These principles of contraperture radiation were described in the work of L.V. Golovkina “Creation speakers in all sides direction in acoustics”. It was noted that it is possible to determine the optimal distance between coaxially arranged speakers for the appearance of the effect of omnidirectional radiation.
“This distance is determined by the angle of aperture of the radiation pattern of the head and the total sound pressure generated at a certain distance from the head when summing up a certain power.“ (Golovkin)Contraperture and semi-aperture speakers
1, 2 - housing for broadband heads (3), a reflective plate - 4.
Also known so-called. semi-aperture speakers, where a special plate is used instead of the second radiator. The principle remains close, with the only difference being that the effect is achieved using reflected waves.
Experts point out minor differences in the resulting waves when using konperperturny and semi-aperture radiation.
Results of measurement of the frequency response of a full kontraperturny radiator
(solid line - 1) and semi-aperture (dotted line - 2)
Dependence of averaged sound pressure level of emitters on distance
1 - two kontraperturny emitters; 2 - two conventional systems (stereo pair); 3 -
one common speaker system; 4 - one semi-aperture radiator; five -
two semi-aperture emitters; 6 - one kontraperturny radiator.
The similarity was confirmed in the work of Golovkina L.V., Umyarova R.Ya. “Research of kontraperturny emitters in acoustics”, which were conducted at the Kharkov National University of Radio Electronics.
Why and how to use it?
Unlike many irrational, meaningless, commercially speculative decisions in the High End, the use of counter-radiation radiation has both a physical and psychoacoustic rationale. Describes the effects on fidelity playback.Directional pattern
In the interaction of waves coaxially arranged speakers sound pressure is created in the air "column" between them. There is a so-called. “Pressure monopole” or omnidirectional point. In this way, the vertical and horizontal radiation patterns are extended.
It is logical that when using omnidirectional radiation, the zone of comfortable listening increases. Accordingly, there is no need to search for the “apex of the triangle” to create the correct stereo panorama and correct location of the CID (apparent sound sources). The problem of the “far zone” is solved in the same way, in which listening becomes more comfortable.
The forums have met the arguments of the series:
“Thus, the number of reflections will increase, the sound will become porridge and the radiation pattern will not be needed!”
I want to note that the reflections will undoubtedly be, as with the use of speakers with classical architecture. Accordingly, it will be impossible to do without acoustic treatment of the room. At the same time, the classical speakers have no less reflections, they are just uneven and just as well require corresponding solutions in the decoration of walls, etc.
Little about doppler intermodulation
Practically everyone who is allowed to write about konperperturnoy acoustics, mention the Doppler intermodulation. On the website “Fundamentals of Acoustics”
this term is given the following definition: “Phase and frequency shifts or oscillations of a sound wave due to the movement of a sound source”.
If simplistic, the cause of these distortions is the change in distance from the membrane of the loudspeaker to the listener. Any driver with the electromechanical principle of radiation (speaker, iso (ortho) speaker, electrostat, etc.) is not immune from this disadvantage in the classical system architecture.
It is believed that the high sensitivity of hearing to the Doppler intermodulation is due to neuropsychologically. It is based on a mechanism for determining the distance to certain objects using hearing. This ability of hearing has evolved evolutionarily as an indicator of probable danger (of a moving object). For this reason, even slight changes in the distance from the speaker membrane to the ear can be perceived by ear, creating the effect of a natural flanger (approaching / departing train).
In the case of kontraperturny emitters, the radiation source (“pressure monopole”) is static, and does not move, respectively, and the flanger effect of Doppler intermodulation does not occur.The hypothesis of psychoacoustic comfort
A number of authors have noted “high naturalness” and “subjective psychological comfort” from music reproduced through counterpertural acoustics. It is argued that the reason for these effects is the absence of the distance change described above.
In other words, an object constantly moving back and forth is perceived by the brain as more dangerous (at the level of basic reflex reactions), and a fixed one as less dangerous. Such judgments remain hypothetical and have not yet found experimental confirmation, but are popular both among music lovers and among psychoacoustics researchers.
Dry residue: advantages and disadvantages
So, the advantages:
- Omni-directionality of radiation.
- Circular horizontal and wide vertical radiation patterns.
- Lack of Doppler intermodulation.
- Hypothetical reflex comfort (not confirmed).
Specific drawbacks of the kontraperturnyh speakers consider:
- Difficulties with accurate coaxial placement of the speakers.
- The lack of experimental data on the basic characteristics of multi-band counteroptic speakers.
- The complexity of the design of the AU, especially in the case of using a multiband circuit and, accordingly, a decrease in processability.
- Selection of pairs of loudspeakers with strictly identical frequency characteristics.
- Reducing the permissible technological error when installing emitters and reflectors.
- Increased cost (the need to use additional loudspeakers and reflectors).
And as a result of all of the above - the astronomical price.
These flaws made the capping acoustics, perhaps the most unpopular speaker type for a mass producer. In addition, as with any other speaker system, such common problems as contour resonances, frequency response, THD, IMD, problematic filters that “twist the phase”, etc.
The most noticeable and most valuable effect of contraste speakers is the expansion of the “comfort zone” when listening, due to the circular pattern. Doppler intermodulation and hypothetical psychoacoustic comfort are very beautiful, but little convincing arguments in favor of such speakers.
It seems to me - this is one of the least noticeable problems that may exist in acoustic systems. In my experience, the flanger effect becomes truly significant at distances from a few meters (approaching train), which is hardly comparable to vibrations of a dynamic loudspeaker membrane. And the hypothetical danger of moving objects, I believe, is a controversial theoretical argument.
In fairness, I want to note that quite a few people do not share my point of view and argue that the Doppler intermodulation seriously spoils the sound. Blind tests, due to the rarity of such acoustics, and did not have to observe and observe. If readers have information about the visibility of these effects and the “unique comfort” when listening to kontraperturnyh columns - I would be grateful for the comments.
With all the initial attractiveness of the idea, everything spoils the final cost of the product, which also increases due to the fact that the product itself is an exotic rarity. In today's audio market, I know 2 serial manufacturers.Jeans
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