RU2707905C2 - Acoustic system with slotted adjustable helmholtz resonator - Google Patents

Abstract

FIELD: acoustics.

SUBSTANCE: invention relates to acoustics and can be used in making high-quality columns for stereo systems, especially for tube amplifiers with low damping ratio, relating to class of Hi-End equipment. Closed-type acoustic column comprises a Helmholtz resonator and is configured to fine-tune the Helmholtz slot resonator built into the closed volume of the housing and to vary the cross-sectional area of the neck and obtain the best AFR for a specific speaker. Column comprises a partition, which consists of two plates, wherein the fixed plate is configured to divide the volume into two chambers and to provide rigidity to the side walls, and the movable plate is configured to control the resonant frequency of the resonator, design of the column is configured to smoothly change the width of the neck and is equipped with a screw, the head of which is located outside on the front wall of the housing, wherein the speaker is made broadband with a common Q-factor Qts ≥ 1.

EFFECT: technical result is improvement of sound quality.

1 cl, 6 dwg

Description

The invention relates to the field of acoustics. The housing design allows the use of high-quality broadband speakers with high full Q factor (Qts≥1) in the acoustic design of a “closed box”. Most of these speakers were designed for open design, which has its drawbacks associated with radiation from the back of the diffuser. The use of such a speaker in a closed case of a reasonable volume (in terms of aesthetics and dimensions of the listening room) leads to negative results - an increase in Fs and an increase in resonance. Attempts by developers of acoustic, electrical and electro-acoustic damping of these unpleasant resonant phenomena lead to certain successes. These include filling the internal volume of the box with various sound-absorbing materials, using an acoustic impedance panel, reducing the output impedance of the amplifier (down to a negative value), etc. The preference for acoustic damping is more pronounced among “lovers of high fidelity” who want to use tube amplifiers with a usually low damping factor in their sound path. The remarkable property of the Helmholtz resonator to absorb the energy of spurious oscillations of the diffuser at the resonance frequency was previously used by the developers of acoustic systems. Well-known speakers from the Symphony radio *, which did not have a “chatter” and a low-frequency rumble characteristic of many modern speakers, but had a “biting and fast” bass. But they did not have the opportunity to individually customize each product as a “unique musical instrument” after assembly. Such a function was not provided for by the design. Apparently this was not particularly necessary in conditions of mass production and the demands of that time. Modern requirements for sound quality have increased. Of interest is the ability to fine-tune the resonator built into the enclosed volume of the casing after the final assembly of the column for a specific speaker (having in practice a significant spread of Qts and Fs), with the possibility of obtaining a smooth and hump-free amplitude-frequency characteristic. Also of interest is the possibility of using a high-quality broadband speaker with Qts≥1 in a closed box type column.

, гдеThe formula for calculating the frequency of natural oscillations of the Helmholtz resonator

where

v is the speed of sound in air, S is the area of the neck, V is the volume of the resonance chamber, L is the length of the neck.

From the formula it follows that by changing the cross-sectional area of the neck of the resonator (S), you can change the natural frequency of the resonator (F). The column design provides for the possibility of smoothly changing the width (b) of the neck (slit) with the back cover closed by means of a screw (1), the head of which is located outside on the front wall of the housing. Structurally, the column is a closed box with a volume of 50 l, divided into two chambers by a partition. The lower chamber (2) - Helmholtz resonator - volume \ / = 15 l. The partition consists of two chipboard plates. The fixed partition (3) serves to divide the volume into two chambers and to give greater rigidity to the side walls. A movable partition (4), 16 mm thick (L-neck length), serves to control the frequency of the resonance of the resonator.

The gap formed between the movable plate (partition) and the rear wall is the mouth of the resonator (5). To reduce the quality factor of the resonator, which turned out to be very high in practice, the neck of the resonator is filled with a loose syntepon roller. The amount of syntepon was determined experimentally by measuring the frequency response and giving it the most smooth and "humpback" shape. The dimensions of the resonator were calculated and adjusted experimentally.

To increase the rigidity of the casing walls, “sandwiches” are glued from two 16 mm thick chipboard plates. To eliminate standing waves inside the case, opposite walls (upper and lower, front and rear) are located at an angle relative to each other.

A brief description of the drawings.

Fig. 1. The design of the speaker system with a tunable Helmholtz resonator.

Fig. 2. Front view. Under the decorative “nameplate” (6) is the head of the adjustment screw

Fig. 3. Movable partition (4). Adjusting screw (1). Sintepon in the neck of the resonator (7).

Fig. 4. The dependence of the speaker impedance on the neck area of the slot resonator. From completely closed to open. Setting the resonator frequency slightly higher than the resonance frequency of the speaker in the box allows you to achieve a rise in frequency response below the Fs of the speaker.

Fig. 5. The effect of syntepon on the impedance of the speaker.

Fig. 6. Frequency response of the speaker (RF emitter-off). Broadband speaker Boston-HQ48414P (Fs = 100.9Hz, Qts = 1.225 (!)).

*IN AND. Deryabin, V.G. Ponimansky. High-end stereo radio tubes. TRZ issue 82. M., Communication, 1975.

Claims (1)

A closed box type acoustic column containing a Helmholtz resonator, configured to fine tune the Helmholtz slot resonator built into the closed volume of the enclosure and to change the neck cross-sectional area and obtain the best frequency response for a particular speaker, characterized in that the column contains a partition that consists of two plates, while the fixed plate is made with the possibility of dividing the volume into two chambers and stiffening the side walls, and the movable plate is made with the ability to control the frequency of the resonator’s own resonance, the column design is made to smoothly change the neck width and is equipped with a screw, the head of which is located outside on the front wall of the housing, while the speaker is made broadband with a total Q factor of Qts≥1.

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