The bass reflex system (also known as ported , vented box or reflex port ) is a type of cage loudspeaker that uses ports (holes) or ventilation holes into the cabinet and parts of pipes or pipes attached to ports. This port allows the sound from the back side of the diaphragm to increase the efficiency of the system at low frequencies compared to the sealed-box loudspeaker or unlimited baffle installation.
The reflex port is a hallmark of this popular enclosure type. The design approach improves the lowest frequency reproduction generated by the woofer or subwoofer. The port usually consists of one or more tubes or pipe mounted in front (baffle) or back of the enclosures. Depending on the exact relationship between the driver parameters, the volume of the enclosure (and the filling if applicable), and the tubular cross section and length, the efficiency can be substantially enhanced over the performance of the same enclosure.
The DO bass reflex cabinet has a poor temporary response, causing "fouling" or resonance longer than the bass tone. Although the sound coming out of the port may have the same phase from the front surface, but it can never be at the same time, thus, the extended bass energy is actually a noise disguised as a signal. This disguise only works when the sound is a continuous tone (one of the reasons why some people prefer certain types of music for the audio system), but reveals itself most clearly in reproducing percussion sounds. For the same reason, the Linkwitz-Riley crossover has the same problem.
Video Bass reflex
Description
Unlike closed-box loudspeakers, which are almost airtight, the bass reflex system has openings called cut-out ports that are cut into the cabinet, generally consisting of pipes or channels (usually circular or rectangular cross section). The air mass at this opening resonates with the air's "flexibility" in the enclosure in exactly the same way as the air in the bottle is echoed when the air current is directed to the entire opening. Another frequently used metaphor is thinking of air like a spring or a rubber band. The frequency at which the resonating/boxing port system, known as Helmholtz resonance, depends on the effective length and width of the channel cross section, the internal volume of the enclosure, and the speed of sound in the air. In the early years of ported speakers, the speaker designer had to conduct extensive experiments to determine the ideal diameter of the port and the length of the tube or port pipe; However, recently, there are countless computer tables and programs that count, for the size of a particular cabinet, how large the port should be and how long the tube should be. Even with these programs, however, some experiments with prototypes are still needed to determine whether the enclosures sound good.
If the airflow/air box contains resonance so it is chosen to be at a lower frequency than the natural resonant frequency of the bass rider, an interesting phenomenon occurs: the reverse wave of the bass driver sound is reversed in the polarity for the frequency range between the two resonances. Since the backwaves are already at the poles opposite the front waves, this inversion carries two emissions in phase (although the emissions of the ventricles are lagging by one wave period) and therefore they reinforce each other. It has a useful purpose for generating higher output (for every given driver trip as opposed to a closed box) or, conversely, the same output with smaller trips (which means less driver distortion). The fines generated for this reinforcement are the time of greasing: basically the resonance vent adds to the main driver output by imposing a "resonant tail" on it. For frequencies above the driver's natural resonance, the reflex equations have no effect. For frequencies below the ventilator resonance, the inversion polarity is not reached, and the backwave cancellation occurs. Furthermore, the driver behaves as if faltered in the free air, because the air box flight is absent.
When speakers are designed for home use or for high volume live performance settings (for example, with amplifier amplifier speakers and PA system speakers and subwoofers, manufacturers often consider the benefits of porting (improved bass response, lower bass response, increased efficiency) rather than loss (port noise, resonance problem). This design is popular among consumers and producers (speaker cabinets can be smaller and lighter, for more or less equivalent performance) but increased bass output requires close matching of drivers, enclosures, and ports: Design inappropriate reflexes may have unfavorable characteristics or weaknesses, making them unsuitable for settings that require high accuracy and neutrality of sound, such as studio monitor speakers for use by audio engineers in monitoring facilities, recording studios, etc.
Maps Bass reflex
Comparison with passive radiator
Passive radiators are a "bass reflex system" similar in operation to porting ", and both methods are used for the same reason: to"... extend the system's low frequency response [speaker cabinet]. " "So far, ports are the most common means of extended bass response in cabinets.The second most common bass extender for loudspeakers is called passive radiators." A passive radiator is the use of one or more additional cones (diaphragms) in a non-port cabinet. This passive diaphragm has no magnet or voice coil and is not connected to power amplifier. Passive radiators are also called "cone drones".
History
The effects of various speaker parameters, cage size and port dimensions (and ducts) on the performance of the bass reflex system were not well understood until the early 1960s. At that time, a pioneering analysis by A.N. Thiele and Richard H. Small are linked to these factors in a series of "alignments" (sets of relevant speaker parameters) that generate useful and predictable responses. This allows speaker manufacturers to design speakers to fit a variety of enclosure sizes, and to match attachments with supplied speakers with great predictability. All of this is limited by the laws of physics, which are discussed in detail in Thiele and Small's work. It is impossible to have small speakers in a small enclosure that produces an extended bass response at high efficiency (ie, requiring only a low-powered amplifier). It is possible to have these two attributes, but not all; this has been called the Iron Law of Hofmann after J. Anton Hofmann of the KLH summary (with Henry Kloss) of Edgar Villchur worked many years earlier. The resulting sound pressure depends on the efficiency of the loudspeakers, the mechanical or thermal power handling of the driver, the input power and the size of the driver.
Benefits
Such resonance systems add to the driver's bass response and, if properly designed, can extend the driver/enclosure combination frequency response to below the range that the driver will reproduce in a sealed box of the same size. The resonance of the enclosure has a secondary advantage because it limits the movement of the cone in the frequency band centered around the tuning frequency, reducing the distortion within that frequency range. Portable cabinet system is cheaper than passive radiator speakers with the same performance; while a passive radiator system requires one or two "drone cone" speakers, the porting system requires only a hole or port and a length or a tube.
Limitations
Low frequency drivers in resonating enclosure systems such as portable cabinets or passive radiator cabinets can not start and stop instantly as can be done in closed cabinets. To achieve their bass output, ported speakers enclosure staggered two resonances. One from the driver and the air box and one from the air and the box port. This is a more complicated case than an equivalent closed box. This leads to an increase in delay time (increased group delay imposed by twin resonances), both in initiating the bass output and in termination. Therefore, a flat steady-state bass response does not occur at the same time as the rest of the sonic output. Instead, it begins later (left behind) and accumulates over time as a long "resonance" tail. Because of the complicated and dependent loading of these frequencies, the ported sheath generally produces a worse transient response at lower frequencies than a well-designed closed-box system. Another problem is that large cabinets will require long port tubes to be tuned properly, meaning that the reflex bass cabinets may be larger than passive radiator radiators with the same performance.
Another trade-off for this augmentation is that, at frequencies below 'tuning', the port disassembles the cone and allows it to move as much as the speaker is not in the cage at all. This means the loudspeakers can be pushed over safe mechanical limits at frequencies below the tuning frequency with much less power than in a sealed sphere of equal size. For this reason, high power systems using the bass reflex design are often protected by filters that remove signals below a certain frequency. Unfortunately, power filtering adds further frequency-dependent group delay. Even if the filtering can be customized to not remove music content, it can interfere with sonic information that is connected to the size and mood of the recording, information that is often present in the low bass spectrum.
Whether these effects in a well-designed system can be heard remains a matter of debate. Improperly designed bass reflex systems, generally set too high or too loose, can ring at tuning frequencies and create booming notes of quality to bass frequencies. As a result, this is due to port resonances that impose its characteristics on the notes being played, and is greatly aggravated if the resonance port coincides with one of the resonance modes of the room, an unusual occurrence. In general, the lower the frequency of a port set, the more inappropriate these problems may occur.
Ports are often placed in the front baffle, and thus can transmit undesirable midrange frequencies reflected from the box. If sized, the port can also produce "wind sound" or "chuffing", due to turbulence around the port openings at high airspeed. The enclosure with the rear-facing port covers this effect to some extent, but can not be placed directly on the wall without causing audible problems. They need some empty space around the harbor so they can do as intended. Some manufacturers incorporate ports facing the floor in the base or speaker base, offering predictable and repeatable port performance within design boundaries.
Port compaction
Port compression is a reduction in port effectiveness due to increased sound pressure level. Because porting systems play harder, port efficiency decreases, and distortions emitted by ports increase. This can be reduced by port design, but not completely eliminated. Asymmetrical loading of the driver cone during high-level usage can be reduced by placing the baffle at the inside end of the port tube. This baffle can also serve as a stiffening structural element on the cover.
Apps
The subwoofer cabinets used in home theaters and sound reinforcement systems are often equipped with ports or vents. Amplifier amplifier cabinets and keyboard amp speaker cabinets, which must reproduce low-frequency sounds to 41 Hz or below, are often built with ports or vents, which are usually on the front of the cabinet (although they are also placed on the back). Even some expensive hi-fi speakers have carefully designed ports.
See also
- loudspeaker case
- Passive radiator
References
Source of the article : Wikipedia
0 Comments