Low-frequency resonance in the maze: the benefits and harms of increasing sound power by 200 times
This year in the Journal of the American Acoustical Society, scientists Jiajun Zhao, Likun Zhang and Ying Wu published an article about their invention, which increases the sound power of the low-frequency waves through resonances. Judging by the report of the researchers, a plastic case with a diameter of 10 cm, which was invented by them and made on a 3D printer, can increase the sound power of the subwoofer by 200 times.
Traditionally, to increase the volume (sound pressure) use an increase in signal power, and in the case of low frequencies and a large area of radiation. These classic methods have obvious drawbacks - large overall dimensions and high power consumption. In this regard, the increase in sound pressure due to acoustic design has become a popular practical problem. Developers are driven by the desire to maximize power and keep a small amount. With traditional speakers, this effect was achieved thanks to a phase inverter. Now it's the turn of the portable audio. Under the cut a few words about innovation and the likely prospects for its development, as well as a fly in the ointment of bright prospects.
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The implementation of a rather bold idea is dictated by necessity. The abundance of portable technology requires solutions in which the acoustic design with a large volume can not be applied, while the consumer wants a lot of bottom. Thus, the solution proposed by scientists is likely to be in demand for smartphones, portable portable speakers, docking stations.
It is known that developments of this kind were conducted from the end of the 19th century (Helmholtz experiments) until the 20s of the last century, that is, until the time when passive means of increasing sound pressure could compete with electroacoustic ones. So there was a horn acoustic design.
The authors of the article “Emission Enhancement of Sound Emitters using an Acoustic Metamaterial Cavity”, which formed the basis of the described invention, wrote about historical continuity. It can be argued that once in a situation where electrical equipment had exhausted the efficiency resource, the developers remembered the time when the horn design of the loudspeakers was the leading trend.
The idea was to significantly increase the amplitude of the sound waves emitted by the low-frequency speaker, while abandoning the traditional increase in amplifier power and increasing the size of the radiator. An additional goal was to preserve the radiation pattern, since the classic shout changes it. To implement the idea, scientists took advantage of resonant modes that were formed using a libyrinthous acoustic design.
Simply put, the developers have applied the principle, which can be observed by placing the sound source (for example, a smartphone) in a mug. The sound is enhanced as the mug becomes a resonant chamber.
Here the principle is close, but instead of a single cavity, specially calculated labyrinths are used, which allow to selectively enhance the low-frequency range.
In an interview, developer Ying Wu described the principle of operation as follows:
As can be seen in the figure, labyrinth passages depart from the center of the round case of a ten-centimeter device, where the speaker is located, which provide for the emergence of resonant modes and, accordingly, passively increase the sound power of certain frequencies. It is important to note that the dB scale is logarithmic ; accordingly, a 200-fold increase in power will result in an increase in sound pressure of approximately 20 dB. One of the authors who wrote on this subject, compared 20 dB with eight divisions on the iPhone volume scale.
As a result of comparative and control measurements, it turned out that the use of the design really allows to increase the sound power in the low frequency range by 200 times. The design also makes it possible not to significantly change the radiation pattern, which would be impossible when using classical horn systems. More information about the results of the experiment can be in an article that is published in the public domain .
It is obvious that the result obtained (in the event of a successful development of events for this innovation, which is discussed in the next section) can be used to create portable wireless speakers, mobile gadgets, headphones.
The article theoretically proves the possibility of a resonant increase in power by 200 times, provides formulas and comparative measurements, but, as in the old joke, there is a nuance ...
Bass enhancement due to resonances has a number of features that make it difficult to use this method when creating high fidelity hardware. Many people are well aware of the detrimental effect of this method on the sound quality of the phase inverter acoustic design of the speakers. When using a phase inverter, the low gain is also achieved due to the resonance, the only difference is that with this form factor, the phase inverter is less effective than the labyrinth.
The ambiguity of using resonances to increase the bass power is described in detail in the article “The Great Low Frequency Hype” published by Show Master magazine, courtesy of www.sound-consulting.net .
Probably, many noticed that the study carried out comparative measurements of sound power in the low frequency range and estimated changes in the directivity pattern, paid attention to the properties of the materials used. At the same time, standard measurements of the harmonic distortion, linear frequency response, and the occurrence of spurious overtones and other sound distorting phenomena were not carried out.
As written in the above-mentioned article, the resonant system can not start and stop instantly, and accordingly, there are delays. Given the number of reflections in the presented labyrinth resonant system, it can be assumed that these delays will be higher than in a similar one with a phase inverter or a classic closed box.
Thus, using resonant amplification, we can get much more bottom, while impulse response deteriorates. In addition, it is not known whether such a system introduces distortions, noises, etc. (the study does not contain a comparison of the distortions before and after using a new acoustic design).
With the exclusion of all hypothetically probable problems, innovation can change a lot. Preservation of properties while reducing the size will allow the use of such acoustic design in smartphones, which will significantly increase the volume. Use with portable wireless speakers will reduce power consumption, and therefore increase the duration of the portable devices.
I sincerely hope for a lively and productive discussion about the prospects of the labyrinth. For my own conclusions about the fate of the invention, I lack information. Traditionally, I propose to take part in a survey and express my opinion on the invention.
Jeans
In our catalog is presented A wide range of high fidelity speaker systems .
Traditionally, to increase the volume (sound pressure) use an increase in signal power, and in the case of low frequencies and a large area of radiation. These classic methods have obvious drawbacks - large overall dimensions and high power consumption. In this regard, the increase in sound pressure due to acoustic design has become a popular practical problem. Developers are driven by the desire to maximize power and keep a small amount. With traditional speakers, this effect was achieved thanks to a phase inverter. Now it's the turn of the portable audio. Under the cut a few words about innovation and the likely prospects for its development, as well as a fly in the ointment of bright prospects.
')
Fresh look or well forgotten old
The implementation of a rather bold idea is dictated by necessity. The abundance of portable technology requires solutions in which the acoustic design with a large volume can not be applied, while the consumer wants a lot of bottom. Thus, the solution proposed by scientists is likely to be in demand for smartphones, portable portable speakers, docking stations.
It is known that developments of this kind were conducted from the end of the 19th century (Helmholtz experiments) until the 20s of the last century, that is, until the time when passive means of increasing sound pressure could compete with electroacoustic ones. So there was a horn acoustic design.
The authors of the article “Emission Enhancement of Sound Emitters using an Acoustic Metamaterial Cavity”, which formed the basis of the described invention, wrote about historical continuity. It can be argued that once in a situation where electrical equipment had exhausted the efficiency resource, the developers remembered the time when the horn design of the loudspeakers was the leading trend.
Idea and result
The idea was to significantly increase the amplitude of the sound waves emitted by the low-frequency speaker, while abandoning the traditional increase in amplifier power and increasing the size of the radiator. An additional goal was to preserve the radiation pattern, since the classic shout changes it. To implement the idea, scientists took advantage of resonant modes that were formed using a libyrinthous acoustic design.
Simply put, the developers have applied the principle, which can be observed by placing the sound source (for example, a smartphone) in a mug. The sound is enhanced as the mug becomes a resonant chamber.
Here the principle is close, but instead of a single cavity, specially calculated labyrinths are used, which allow to selectively enhance the low-frequency range.
In an interview, developer Ying Wu described the principle of operation as follows:
“It’s a little bit more than that.”
“Resonance of air in the channels allows to get more sound power than without them (channels - approx. Avt.) With equal power consumption”
Emission enhancement
a) The structure is made of rigid materials (gray part), where spiral channels filled with air extend the sound path (red line) to reduce its equivalent speed in the radial direction along the rigid walls of the channels (azimuthal anisotropy ρθ → ∞ρθ → ∞).
b) Phase distribution of sound fields emitted from the monopole source, simulating at three resonant frequencies (see Fig. 2 (c)).
c) Same as b), but for a dipole source. (d, e) Comparison of the far-field directivity with and without a shell, simulated for the lowest resonance in b) and c), respectively.
As can be seen in the figure, labyrinth passages depart from the center of the round case of a ten-centimeter device, where the speaker is located, which provide for the emergence of resonant modes and, accordingly, passively increase the sound power of certain frequencies. It is important to note that the dB scale is logarithmic ; accordingly, a 200-fold increase in power will result in an increase in sound pressure of approximately 20 dB. One of the authors who wrote on this subject, compared 20 dB with eight divisions on the iPhone volume scale.
As a result of comparative and control measurements, it turned out that the use of the design really allows to increase the sound power in the low frequency range by 200 times. The design also makes it possible not to significantly change the radiation pattern, which would be impossible when using classical horn systems. More information about the results of the experiment can be in an article that is published in the public domain .
It is obvious that the result obtained (in the event of a successful development of events for this innovation, which is discussed in the next section) can be used to create portable wireless speakers, mobile gadgets, headphones.
The article theoretically proves the possibility of a resonant increase in power by 200 times, provides formulas and comparative measurements, but, as in the old joke, there is a nuance ...
Resonance as a bosom enemy
Bass enhancement due to resonances has a number of features that make it difficult to use this method when creating high fidelity hardware. Many people are well aware of the detrimental effect of this method on the sound quality of the phase inverter acoustic design of the speakers. When using a phase inverter, the low gain is also achieved due to the resonance, the only difference is that with this form factor, the phase inverter is less effective than the labyrinth.
The ambiguity of using resonances to increase the bass power is described in detail in the article “The Great Low Frequency Hype” published by Show Master magazine, courtesy of www.sound-consulting.net .
Probably, many noticed that the study carried out comparative measurements of sound power in the low frequency range and estimated changes in the directivity pattern, paid attention to the properties of the materials used. At the same time, standard measurements of the harmonic distortion, linear frequency response, and the occurrence of spurious overtones and other sound distorting phenomena were not carried out.
As written in the above-mentioned article, the resonant system can not start and stop instantly, and accordingly, there are delays. Given the number of reflections in the presented labyrinth resonant system, it can be assumed that these delays will be higher than in a similar one with a phase inverter or a classic closed box.
Thus, using resonant amplification, we can get much more bottom, while impulse response deteriorates. In addition, it is not known whether such a system introduces distortions, noises, etc. (the study does not contain a comparison of the distortions before and after using a new acoustic design).
Application prospects
With the exclusion of all hypothetically probable problems, innovation can change a lot. Preservation of properties while reducing the size will allow the use of such acoustic design in smartphones, which will significantly increase the volume. Use with portable wireless speakers will reduce power consumption, and therefore increase the duration of the portable devices.
Total
I sincerely hope for a lively and productive discussion about the prospects of the labyrinth. For my own conclusions about the fate of the invention, I lack information. Traditionally, I propose to take part in a survey and express my opinion on the invention.
Jeans
In our catalog is presented A wide range of high fidelity speaker systems .
Source: https://habr.com/ru/post/374137/
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