Automotive subwoofers manufactured by the industry do not differ in particular aesthetics. A large square box not only spoils the look, but also takes up a lot of space in the trunk, reducing usable volume. What if the refined ear of a music lover requires a full range of sound frequencies of a musical composition, and practicality does not allow sacrificing boot space? Making a stealth subwoofer “DIY” will help to rectify the situation.
Why do I need a subwoofer?
Some motorists ask themselves the question: do I need a subwoofer in the car? They believe that the full sound of music can be obtained from full-size speakers with a diameter of 16.5 cm. Indeed, manufacturers of audio equipment write that speakers of this size can reproduce frequencies whose lower threshold is 20 Hz. This is the minimum frequency that the human ear is capable of perceiving.
However, if you delve into this issue in more detail, it turns out that the volume at this frequency is much lower than at a frequency of, say, 1000 Hz. In this case, the sound of such instruments as double bass, bass, percussion instruments will suffer. Everything that sets the rhythmic pattern of the musical composition will have a faint sound.
This is where the subwoofer comes to the rescue.
Its very name suggests that it is a woofer. They are divided according to size into 3 categories: 25 cm, 30 cm, 38 cm. The larger the diameter, the higher its volume and the greater the acoustic pressure it creates.
Why stealth?
Car subs are open and closed. Open ones are installed in the rear shelves or mounted in the back seat, which is not a very good option, since the passenger will feel the full power of musical vibrations.
Closed subs are made in a wooden or plastic case and are installed in the same trunk. Well, to solve the problem of aesthetics and rational use of space will help subwoofers such as "Stealth".
The name "Stealth" belongs to the American fighter-bomber F - 117. This is the first aircraft to incorporate invisibility technology for ground-based radars. As for the Stealth subwoofers, they are made in such a way as to be invisible in the trunk of the car. When examining an open trunk, they are not striking. Also a kind of invisibility.
How to calculate the volume of a subwoofer
Making a Stealth subwoofer with your own hands is creating a box for a large speaker that pumps air through oscillatory movements. In order for it to function normally, it needs a certain volume inside the case in which it is installed. For each size there are recommendations for choosing the volume of the box.
Speaker size in cm | 25 | thirty | 38 | 46 |
Volume in liters | 15-23 | 24-37 | 38-57 | 58-80 |
These volumes cannot be neglected. Otherwise, the sound will be flat, and the service life of the subwoofer will be significantly reduced due to excessive air resistance to the speaker membrane.
As a rule, the subwoofer is installed in a niche formed by the rear wheel arch and the rear wing of the car. Therefore, there are not so many options for choosing the size of the speaker. Before making a box for the Stealth subwoofer, you need to calculate the volume of this niche to get an idea of the size of the speaker. It should correspond to the recommended for a given volume or be smaller in diameter.
Depending on the shape, the nishir of the calculation volume will be different. Since the shape is complex, then formulas are suitable for calculating such figures as a box, a triangular prism. It is possible that the niche space will have to be conditionally divided into several simple geometric figures, and the volume should be calculated as their total amount.
How to fit a subwoofer organically into a car interior?
As mentioned above, the sub must be invisible in the trunk of the car. To achieve this, the Stealth enclosure for the subwoofer must meet the following requirements:
- Its shape should be thought out in such a way as not to “eat up” the useful amount of luggage.
- The appearance and texture of the surface should be similar to the factory floor luggage compartment. For these purposes, Carpet of different colors is used.
- The subwoofer must not interfere with the removal of the spare wheel and car tools.
You never need to place the "Stealth" in the spare wheel niche. Although its volume may be suitable for these purposes, an expensive speaker can be easily damaged in this case.
Materials required for manufacturing
To make a Stealth subwoofer with your own hands, you will need tools, materials, and most importantly free time. Since the “Stealth” shape is curved, the body will be made of fiberglass using epoxy. The gluing process itself takes several days, because before applying each new layer, the polymerization of the previous one is necessary.
To work, you will need:
- Fiberglass T 13. It is a non-combustible structural material of high strength. It is able to withstand aggressive environments and is used to create high-strength fiberglass. It is actively used in car and boat tuning.
- Epoxy adhesive. The price of it depends on the volume of packaging and the manufacturer. Since the volume of work remains to be large, it will take from 1 to 3 kg to work.
- Plywood or MDF. This material is required for the manufacture of the outer part of the housing into which the speaker will be embedded. Thickness should be from 0.8 cm and above. The thicker the better.
- Masking tape 50mmx50m, one or two rolls.
- Carpet. This material will make the case in the same style with the trunk.
- Glue “Liquid nails” for gluing the carpet.
- Primer for wood. So that the plywood does not absorb moisture and does not exfoliate, it will need to be processed.
- Filling on wood. This material will eliminate surface roughness before gluing with carpet.
In addition, you will need a milling cutter or a jigsaw to cut the landing rings for the speaker.
Body shaping
Production of a Stealth subwoofer begins with gluing a niche. A body will be created inside it. To do this, masking tape 50mmx50m is cut into strips that are glued to plastic sheathing or carpet inside a niche. The resulting paper layer will serve as the basis for applying the first layer of fiberglass.
Fiberglass T 13 is located in rolls with a width of 90 to 100 cm. This width is enough to completely cover the niche both in width and in height.
Before the formation of the first layer, it is necessary to isolate the paper base from contact with epoxy. To do this, the paper can be coated with paraffin, stearin, parquet polish.
Then you need to mix the epoxy resin with the hardener in accordance with the instructions and apply it on a paper matrix. After the first layer has hardened, it is necessary to apply another one on which fiberglass will be laid.
The fiberglass flap is taken with a small margin, which after the formation of the body will need to be cut off. After applying the first layer, the fiberglass is rolled with a roller and a rough brush. It is important that the material is completely saturated with epoxy glue. The price of poor-quality work is the separation of the body after polymerization.
Then the procedure is repeated. Fiberglass thickness 0.3 mm. To give the necessary strength, you need to lay out from three to five layers. To make it more convenient to work, after the first layer has hardened, the housing can be removed from the trunk and continue to work by gluing fiberglass on the outside, not inside. The process is not fast. It takes several days to make a Stealth subwoofer with your own hands.
Depending on the air temperature and the amount of hardener, drying of the epoxy takes from 30 minutes to several hours. Hardener must not be abused. Firstly, the case will turn out to be fragile, and secondly, you may not have time to apply fiberglass as the resin hardens.
Making the outer cover
The lid is cut out with a jigsaw to the size of the outer side of the resulting case. The inner hole is made slightly smaller than the diameter of the speaker. Then two rings are made, the inner diameter of which must coincide with the diameter of the hole for the speaker. These rings should become the podium.
After the cover is made, it needs to be aligned. For this, a polyester putty is taken and applied to the surface with a thin layer using a spatula. After it dries, it must be sanded with sandpaper. If any irregularities remain, then repeat the procedure.
Then, using a primer, you need to protect the surface of plywood or MDF from moisture. After the soil has dried, the seat rings for the speaker stick to the surface of the cover. For this, carpentry glue or the same epoxy is used.
Carpet pasting
In order to stick the carpet on the outer cover of the Stealth, you need to cut off a piece of fabric whose dimensions will exceed the size of the cover of the subwoofer by 10 cm. This stock is needed in order to hide the edges of the carpet on the back side.
The use of Liquid Nails glue gives a good result, and the use of 888 Ultra aerosol glue is the best option. The spray allows you to apply evenly the adhesive base.
Glue is sprayed on plywood and on carpet. Then an interval of 60 seconds is maintained, after which the fabric is laid on plywood and spreads from the center to the edges so that there are no wrinkles. Each section of the carpet must be carefully pressed to the surface for better fixation. Bonding occurs instantly and depends on the pressure. Full solidification occurs in a day.
Final installation
The final step in the manufacture of a Stealth subwoofer with your own hands is the installation of a speaker. To do this, a hole for the wire is drilled in the back of the box. The speaker is screwed to the podium using self-tapping screws and is closed by a decorative grille from above.
After that, the entire structure is inserted into the niche between the wing and the rear wheel arch and is fixed with screws.
The last thing to do is to connect the sub to the amplifier and enjoy the music.