Small and convenient bookshelf speaker production schematic

High frequency probe high frequency line can be customized other specifications

Photocoupler

Speaking of speakers, people can easily think of large-scale floor-standing speakers. As for small speakers, people generally do not expect that the sound quality will exceed that of large-scale floor-standing speakers.

So the sound quality of the small speakers is really not good?

I have a pair of "silver flute" YD131-727X 5-inch low-range speakers and a pair of "silver flute" YDQG4-2 tweeters, which can make a pair of small speakers.

The production process is as follows:

(1) First, make sure to make a closed or inverted speaker. I feel that although the bass is deeper in the inverted phase, the closed bass is better, so I decided to choose a closed speaker.

(2) Determine the volume of the speaker. Use the following formula

V=355a ⁴ /αf _o ² m _o (1)

V = effective internal volume of the speaker (L); a = effective vibration radius of the speaker (cm); α = stiffness ratio; m _o = equivalent mass of the woofer vibration system (g); f _o = low frequency resonant frequency of the speaker.

There are two ways to use the sub-form to find the volume. One is to first determine Qoc; the other is to first determine foc (the lowest resonant frequency of the closed speaker).

The first method: first determine Qoc (set to the ideal value Qoc = 0.7) and substitute the specific value into the formula 1

Where α=(Qoc/Qo) ² -1=(0.7/0.5) ² -1=0.96

The result is: V = 355 × 4.8 ^{4 /} 0.96 × 65 ² × 6.6 ≈ 6.5 (L)

The second method: first determine foc. As a closed speaker in general

Foc=fo×(1.2～2.0)

In this case foc=fo×1.4=90Hz, the specific value is substituted into the formula 1

Where α=(foc/fo) ² -1=(90/65) ² -1=0.96

The result is: V = 355 × 4.8 ^{4 /} 0.96 × 65 ⁴ × 6.6 ≈ 6.5 (L)

From the results calculated by the two methods, the calculated volume of both methods is about 6.5 liters. And the same values ​​as recommended by the manufacturer. Such a coincidence shows that the closed speaker has a minimum resonance frequency of 90 Hz which is a very suitable value. Therefore, the volume of the speaker is determined to be 6.5 liters.

(3) Determine the proportion of the shape of the speaker. In order to prevent the generation of standing waves, the ratio of length, width and thickness must not be proportional. Also consider whether you can put the speakers into the cabinet and whether the shape is harmonious. After considering the above, the ratio of length, width and thickness is finally selected to be 1.6:1.0:1.1. Then calculate the length of each edge of the speaker using the following formula:

Take N as a constant. Then length = 1.6N; width 1.0N; thickness = 1.1N.

1.6N×1.0N×1.1N=6500cm=6.5(L)

1.96N2=6500; N3=6500/1.96; N=14.5

Length = 1.6N = 1.6 × 14.5 ≈ 23.5cm;

Width = 1.0N ≈ 1.0 × 14.5 = 14 5cm;

Thickness = 1.1N × 14.5 ≈ 18.5cm

At this point, the shape of the speaker is determined. see picture 1).

(4) Design of the frequency divider. From the range of playback frequencies of the two speakers. The woofer is as high as 15k and the tweeter is as low as 3k, so the crossover frequency can be chosen to be around 5K. If you compare Table 1 and Schedule 2, you will find that the sensitivity of both speakers is 88dB, but the nominal impedance of the woofer is 6Ω, while the nominal impedance of the tweeter is 8Ω. In this way, the woofer output sound pressure level will be higher, which just complements the low efficiency of the woofer and eliminates the high-pitched attenuation network. The circuit diagram is shown in Figure 2. The high cut-off point of the woofer is designed in 6dB/oct, and the low cut-off point of the tweeter is designed in 12dB/oct. The values ​​of the inductor and capacitor are not taken as calculated values ​​but empirically, but such deviations are small. There will be no problems in the actual application.

Schedule 1 "Silver Flute" YD131-727X Subwoofer Parameter Table

Schedule 2 "Silver Flute" YDQG4-2 Tweeter Parameter Table

(5) Assembly of the cabinet. Because the pair of speakers is small, so. Solid wood panels can be used. Refer to Figure 1 for cutting.

When assembling, the cut sheets should be glued together, and then all the joints should be tightened with wood screws. After the glue has dried out, pour a layer of asphalt into the inner wall of the box. After the asphalt is solidified, it can be bonded to a 5 cm thick acrylic fiber as a sound absorbing material. Finally, the speakers and crossovers can be loaded into the cabinet. The box is assembled.

(6) The decoration of the cabinet. After the assembled box is flattened with woodwork putty. Then use sandpaper to smooth the entire box and paint it. I sprayed it three times with "self-painting". In addition, a pair of speaker protection nets are needed, and the mesh surface can be stretched on the wooden frame by the stockings. At this point, the production of the pair of speakers is done.

The next step is the audition. First, use the "Audio Test CD" to test the subjective feeling that the 90Hz ~ 18kHz is basically flat. The actual listening is also true, but the dynamic is a bit lacking. However, it is very good to listen to popular songs and light music. As for listening to the big dynamic symphony, there is a little power. My power amplifier is the tube (6N2+6P14), and this pair of small speakers is perfectly matched. Listening to country music and saxophone, the sound quality is really impeccable.

It can be said that the big speakers have the advantage of large speakers. The small speaker has the characteristics of a small speaker. It can be fixed on the bookshelf or the corner with mosquito nails at will. It is convenient to install and disassemble, and the sound quality is good, and it feels the wonderful music it brings.