Small-sized speakers for high-quality sound reproduction


Created on 08.05.2008 01:05.

Updated 01.24.2021 15:52.

Author: Doctor of Science I. Vozhenin.

One of the main problems of sound reproduction is sound quality, efficient operation of sound sources. In this technique, contradictions have accumulated between the ability to record and reproduce electrical signals of the audio range with high fidelity, on the one hand, and the low quality of converting electrical signals into audio signals, on the other hand.

With the advent of digital recording of electrical signals, almost all questions regarding the quality of recording and reproduction have been removed, however, the significant use of these achievements is difficult due to the insoluble problems that occur when reproducing low frequencies and parasitic harmonics, caused primarily by the pneumatic response of the volume of sound speakers. especially in inexpensive and small-sized ones.

Suffice it to say that when reproducing low frequencies, even in 100-liter speakers, the diffuser of the low-frequency head experiences loads due to the pneumatic effect up to 3: 4 kg.f. This pneumatic force limits the range of oscillations of the diffuser, and also causes its spontaneous deformation and numerous resonances, both in the diffuser itself and in the volume of the speaker. The limitation of the oscillation swing causes a drop in the amplitude-frequency characteristic at low frequencies, and parasitic resonances – the harmonic distortion of the reproduced signals.

The drop in frequency response in 100-liter speakers starts from about 60 Hz; to provide high-quality sound from 30 Hz, the volume of the speakers is already 400 liters.

As you can see, even in very expensive speakers with a volume of up to 400 liters, a whole octave is reproduced unsatisfactorily – 16:32 Hz, and harmonic distortions are 20 times higher than the permissible values. In the columns of average cost, with a volume of 60: 100 liters, the second octave is reproduced unsatisfactorily – 32:64 Hz and the first one is practically absent, while harmonic distortions exceed the permissible limit by 50: 100 times.

The final word in solving this problem is the active subwoofer – a separate loudspeaker designed to reproduce the extremely low frequency region of the sound spectrum. The dimensions of such subwoofers range from 70:40 liters, the frequency range is usually 30: 150 Hz, but the “sweet-voiced” speakers for it do not exceed 10-12 liters.

The rise of low frequencies in subwoofers is provided due to the forced amplification modes, the amplifier built into it, which inevitably generates an increase in harmonic distortion.

To match a subwoofer with a pair of standard speakers, a special digital filter is required – all taken together leads to a price of about 500 US dollars.

As you can see, improving the acoustic characteristics of small-sized speakers with the help of sound absorption inside the box remains attractive. The proposed new original technical solution for the formation of a sound-absorbing environment can significantly simplify the situation. A decrease in the sound pressure in such a medium by up to 50 times has been obtained experimentally.

In addition, the sound-absorbing medium, in comparison with air, has a significantly higher viscosity; this quality, combined with the ability to reduce the sound pressure, has the most favorable effect on the suppression of numerous resonances in the box, i.e. leads to smoothing (straightening) of the amplitude-frequency characteristic and a decrease in harmonic distortion.

There are no restrictions on the dimensions and shape of the absorbing medium, on the magnitude of the sound pressure. A modern acoustic system contains, as a rule, 3 electro-acoustic transducers: high-frequency, mid-frequency and low-frequency (woofer). The first 2 transducers do not require large volumes for high-quality sound reproduction, therefore, they are supplied already packaged, and the woofer requires large volumes, therefore its case is the speaker case.

The new technical solution will make it possible to reduce the physical dimensions of the woofer cabinet to the size of the woofer itself and open up the possibility of supplying it also in a package, then the special requirements for the speaker cabinet disappear.

For example, encapsulating a 10 ” woofer with a sound absorbing medium in a volume of 6 liters provides the following characteristics:

  • Frequency range (with unevenness of ~ 0.5 dB and a fall of 31.5 Hz – 6 dB): 31.5 … 1250 Hz.
  • Maximum acoustic pressure: 110 dB.
  • Harmonic distortion at 90 dB: 0.5%

Compared to a modern subwoofer, the reproduction of low frequencies using the proposed solution is half an octave deeper, even with a closed-type acoustic design, the diffuser experiences a pneumatic load no more than in free space, the medium is viscous, as evidenced by the disappearance of the self-resonance of the speaker system – all this ensures extremely low harmonic distortion.

If we take into account that the new technical solution provides an order of magnitude less dimensions, does not need an amplifier and an expensive digital filter, and provides a price several times lower, then you involuntarily begin to solidify with those who believe that modern subwoofers are a “step aside” : “A gesture of despair” born of the awareness of severe limitations in achieving the deepest bass when using classic speakers. “

The real way to solve the problem of deep bass is opened by Russian patent No. 2107949 for the invention “A device for high-quality sound reproduction”.

Rice. 1. A device for high quality sound reproduction… The device contains sound-reflecting surfaces that delimit a closed volume, forming a sealed housing 1, which houses a sound source 2 and a sound pressure control unit in the housing, including a heat accumulator 3, the surface of which is covered with condensing vapor, an evaporating liquid 4, saturated vapor with gas 5. Unit sound pressure control is separated by a gas-tight sound-transparent membrane 6 from the sound source 2.

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