18-inch large speaker

For those who like to sing karaoke, they always feel that their own dual 6.5-inch speakers and dual 8-inch speakers do not have the "momentum" of karaoke hall or square speakers, and those who like to make music also feel that those small home speakers cannot play the "notes" on the left side of the music keyboard. How about a pair of 18-inch speakers?

Recently, I have completed the trial production of a pair of 18-inch large speaker boxes. The results are satisfactory. All components used are domestically made. For amateur speakers, it is not easy to make them well, and it is even more difficult to make them accurately. A more realistic approach is to abandon accurate indicators and those frequency response curves - just to make a pair of "good boxes" that can "howl" and listen to music. Now I will present the production process and ideas, relevant materials and parameters for reference by audiophiles.

The process of making a speaker

Since the speaker I use is an 18-inch domestic professional box. The speaker is new, but the box is damaged and can only be remade. The tweeter is an 8Q aluminum alloy rectangular horn, with a nominal power of 80-120W, a measured DC resistance of 6Ω, a magnet of φ100mmx20mm, and a net weight of about 2kg for each speaker. I used various 4.7μF, 3.3μF, 2.2μF, and 1μF capacitors in series with the amplifier for listening. I feel that the sound is most ideal with the 2.2μF/630V capacitor marked with CBB22. The woofer is an 8Ω18-inch aluminum alloy basin frame cloth-edge paper basin woofer, with a nominal power of 160-400W. The measured DC resistance is 7.5Ω, the magnet is φ220mmx25mm, and the net weight of each speaker is about 13kg. I happened to have a pair of two-way frequency divider printed boards on hand. So it can be completed by just soldering the components. Since φ3.0mm and φ2.5mm enameled wires are used to wind the coils, the original coil holes need to be expanded, and the copper surface around the holes needs to be scraped after expansion to facilitate the welding of thicker inductor coils. The winding method of the inductor coil is: 11 Use φ3.0mm enameled wire to wind 9 turns on the φ20mm skeleton, flatly wind four layers of 36 turns, then demould, and tie them tightly on all sides with nylon wire, and then wrap three layers of insulating tape on the outside. 12 Use φ2.5mm enameled wire to wind 14 turns on the φ20mm skeleton, flatly wind nine layers of 126 turns, then demould, and tie them tightly on all sides with nylon wire, and wrap three layers of insulating tape. The sound box connection box uses pure copper terminals that can be plugged with large banana plugs or thick copper core wires with a cross-section of more than 20mm2. The connecting wire in the box is 6mm2 pure copper wire. The schematic diagram of the divider is shown in Figure 1.

The production of the box is the key, so the material selection, cutting, hole opening and other production are handed over to the furniture store. The box is made of 25mm thick high-density fiberboard, and the inner corners of the box are reinforced with 30mmx30mm wood square white latex and screws. At the same time, the same high-density board as the box is pasted on each large surface of the front, back, left and right, and a vertical board is added between the tweeter and the woofer to do the reinforcement, and it also serves as a bracket for the magnet of the tweeter horn speaker. After completion, a layer of sound-absorbing felt is pasted inside to prevent the box from resonating. The dimensions of the speaker are shown in Figure 2. Each surface of the speaker is veneered with black leather. After the leather is pasted, the crossover, junction box and speaker can be fixed. Since the black round hole steel plate mesh is used in the front, the edges and corners must be wrapped, otherwise the speaker will look ugly. In order to make the box "slimmer", the corners and edges are not the black angle iron and black plastic corners of the general professional box, but chrome-plated corners and stainless steel edges. The corners are commercially available products, and the edges are made of 1.2mm thick brushed stainless steel plates. The dimensions are shown in Figure 3 and Table 2. Because this box is heavy, universal rubber ball wheels are used for the bottom feet. The 80kg large speaker is very easy to move, and the rubber feet themselves can also reduce shock. Compared with the original reference box and most commercially available professional boxes, this box is less stable and more delicate.

Second, the sound test results of the speaker

After the speaker is finished and adjusted, it is time to test the sound. The equipment used for the test is: 1. TC1's TD-F63P DVD player. The RC4558 in the machine has been replaced with 0PA2604. 2. The signal line is a homemade 75P signal line. 3. The power amplifier is a modified WESAudio BU-5000 1000W+1000W power amplifier. 4. The speaker cable is a 500-core oxygen-free copper 4N cable. The cable length is 4 meters. The cable cross-section is 12mm2. 5. During the test, the volume potentiometer is adjusted to the 8 o'clock position on the clock face. 6. The software used for the test: Chinese Guqin music "Guangling San", Yang Yuying's "Telling You Gently", the stage show 2001 spring selection "FashionTV", Huang Hongying's "Russian Trip".

When listening to "Russian Journey", the bass is full of elasticity. When listening to the small box, the bass drum is located deep in the stage, but now it is moved from the deep stage to the front of the stage, and the sound is no longer "distant". In particular, the sound of the cello is soft and dives, and even the sofa behind it trembles. The listening experience is quite comfortable, and both the body and mind are happy. When listening to Yang Yuying's "Tell You Gently", the singer's whisper-like "telling" voice is soft and beautiful, which makes people feel "sweet in the heart". When listening to the ancient qin music "Guangling San", the advantages of this box are perfectly displayed: the friction, kneading, pressing, hooking and playing of the fingers on the strings, such as close listening, especially each note, due to the different frequencies and different techniques, the notes are projected when the strings are hooked, and the notes of the strings are directly shot out. When playing and picking two strings, the two high notes will form a solid entity with a certain length in space, like a javelin. Condensed in the space of about one meter in front of the speaker, it is amazing.

　　Finally, we have to test the "strength" of this pair of speakers. Increase the volume little by little. Listening to the stage show "fashionTV", when the volume potentiometer is adjusted to the 9 o'clock position on the clock face, the drum beats are no longer knocking downwards, but "smashing" straight towards you. At this time, even if you cover your ears, your body will feel that the "sound pressure" is so "strong". It can be said that this pair of speakers cannot be "fully exerted" in a living room of dozens of square meters, and the distortion of the speakers at this volume does not increase, and the box body does not vibrate. It can be said that the speaker production is successful. Although the audition is over, I am still in an excited state. How can the sound "condense" in space? Is it the CD, the disc player, or the power amplifier? Or the speaker? Regardless of whether this pair of speakers is really HI-FI, as long as the ears hear the fax and vividness, and I am satisfied, it is a success.