Analyze the sound from its acoustic structure
Date: 2020-11-23
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How are speakers classified?

Speakers are classified from different angles and standards according to their acoustic structure. There are airtight boxes, invert boxes, passive radiator boxes and transmission line boxes.
Please refer to relevant boxes for their respective characteristics. Inverting box is the mainstream of the current market; From the size and placement of speakers, there are floor boxes and
bookshelf boxes, the former volume is larger, generally directly enlarged on the ground, sometimes also installed under the speakers with shock absorbent foot nails. Due to the large volume
of the box body, and facilitate the use of larger and more bass units, its low frequency is usually better, and the output sound pressure level is higher, the power bearing capacity is strong, so
it is suitable for the occasion of large listening area or more comprehensive requirements. The bookcase is small in volume and usually placed on the foot shelf. It is characterized by flexible
placement and does not take up space. However, limited by the volume of the box and the caliber and quantity of the bass unit, the low frequency is usually lower than the landing box, and the
bearing power and output sound pressure level are also smaller, so it is suitable for use in small listening environment. According to the playback of the bandwidth of the narrow band speakers,
most speakers are designed to cover as wide a band as possible, belonging to the broadband sound box. The most common type of narrowband speaker is the ultra-low sound speaker, which
is interested in home theater and is only used to restore a very narrow band from ultra-low frequency to low-frequency. According to whether there is a built-in power amplifier, can be divided into
passive speakers and active speakers, the former does not have a built-in power amplifier, can be divided into passive speakers and active speakers, the former does not have a built-in power
amplifier and the latter has, at present most household speakers are passive, but ultra-low sound speakers are usually active.


What is the characteristic of airtight box?

The speaker unit of the closed speaker is installed in a completely closed box. In this way, the anti-crosstalk wave radiated back from the diaphragm is completely blocked by the box body
and will not run out of the box to offset the positive crosstalk wave in front of the diaphragm, which solves the problem of "sound short circuit" and enables the bass to radiate effectively.
Compared with other types of speakers, the low-frequency attenuation characteristic of the closed box is flat, which is similar to the attenuation curve of a second-order low-pass filter, which
means that it has the best transient response among all types of speakers. At the same time, the air enclosed in the box forms a strong "air spring", which can effectively restrain the
displacement of the diaphragm at the resonant frequency and reduce the nonlinear distortion. However, the air stiffness also makes the low frequency resonance frequency of the horn unit
rise, so that the overall low frequency lower limit of the speaker than the unit in the free space condition has been increased, compared with the invert box, transmission line loudspeaker such
as the design, the lower limit of the closed box is relatively poor. Furthermore, the radiation from the rear of the diaphragm is not utilized, resulting in a lower efficiency.


Are hoverbox and hermetically-sealed speakers the same thing?

Air cushion sound box is a kind of closed box, its characteristic is to use seibel sex sperker and cabinet design small enough to make the air in the cabinet of the stiffness and much higher than
the unit and the stiffness of vibration system, for the vibration of the unit system, the air in the oven to its role as a strong elastic cushion, the speaker hence the name. Hoverboxes were once
popular for their low distortion and transient performance, but they were generally less sensitive due to their use of highly damaged units.


What are the characteristics of inverting boxes?

Inverting box is the most commonly used sound box at present. Based on the closed box, it adds a load catheter. One end of the catheter is connected to the air inside the box, and the other end
leads to the outside of the box through an opening on the box wall. When the diaphragm of the horn unit moves, on the one hand, it radiates sound waves directly outside, and on the other hand,
it compresses the air inside the chamber. Makes the control of gas from the inverter in the cabinet mouth out, thus, inverting mouth became second diaphragm to conduct air, if the design skillfully,
and inverting the tube - body system can just make the diaphragm to the radiation sound wave inverter after 180 degrees (hence the name) inverter box, so acoustic radiation through opening out
and the radiation of the diaphragm in front of sound waves in phase, and phase for sound energy superposition of radiation, so strengthening and extending the speakers generally low frequency
response. Inverting chamber and airtight make use of the backward radiation energy of diaphragm, so the efficiency is relatively high. However, the invert box is not perfect, except that the design
and debugging is more difficult than the closed box, the air flowing rapidly at the opening is easy to cause airflow noise. In addition, the inverse phase effect is achieved by acoustic resonance in
essence, so the transient response of acoustic wave radiated by the opening is poor.


What are the characteristics of passive radiator speakers?

Passive radiator speaker, also known as empty paper basin speaker, is actually a variant of the inverting box. Its working principle is very similar to the inverting box, except that the inverting tube is
replaced by passive radiator. The structure of the passive radiator is similar to the horn unit, with a folding ring and a diaphragm radiating sound waves, but without a voice coil and magnetic circuit
system, the motion of the diaphragm can be completely affected by the box body to obtain a better low-frequency response, and the efficiency is relatively high. However, it also has the characteristics
different from the inverter box. Since the inverter box treatment overcomes the problem that the inverter mouth is easy to produce airflow noise box, however, the passive radiator speakers have
steeper low frequency attenuation than the inverter box, which means that the transient response is worse than the inverter box. Polk Audio is the most representative manufacturer of passive radiator


What's so special about a transmission line speaker?

The design idea of the transmission line speaker is completely different from that of the closed box or the phase conduction box. It USES the transmission line of 1/4 wavelength to achieve the purpose
of absorbing unit resonance, suppressing diaphragm displacement and expanding the lower limit of low frequency. Transmission line speakers have the following basic features: a long catheter
(transmission line) is connected behind the bass unit. The length of the catheter is 1/4 of the wavelength of the low-frequency resonance frequency (or slightly higher frequency) of the unit. For the sake
of blending, the catheter is usually folded inside the box, looking like a maze. The cross-sectional area of the transmission line connected to the horn unit is at least 25% larger than the radiation area of
the unit, and then gradually decreases until the exit of the transmission line is exactly equal to the radiation area of the unit diaphragm. The transmission line is laid with damping properties such as wool
or glass wool. Transmission line speakers have deeper bass compared with airtight boxes and inverting boxes, etc. However, some people represented by the famous British speaker expert Martin
Colloms think that transmission line speakers are more difficult to avoid sound dyeing caused by transmission line resonance.


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