Many car enthusiasts are faced with a situation where, after upgrading the audio system in the car, they are still working, but no longer needed. component speakers. Itโs a shame to throw away high-quality sound, and itโs not always possible to sell used sets. A logical idea arises - to give them a second life by assembling active or passive acoustics for home use or the garage.
However, direct connection car acoustics to a home receiver or computer often leads to disappointment: the sound becomes quiet, distorted, or the equipment completely overheats. The whole problem lies in the fundamental differences in electrical parameters and acoustic design, which cannot be ignored.
In this article we will analyze in detail the technical aspects of the remodeling, calculate the necessary parameters and understand whether the game is worth the candle. You'll find out why coil resistance 4 ohms is a critical parameter when choosing an amplifier, and how to properly design the speaker in the cabinet to avoid the โsound from the bucketโ effect.
Physical differences between car and home audio
The first thing that catches your eye when comparing is the design of the dynamic head. Car speakers are designed to work in difficult conditions: vibrations, temperature changes and, most importantly, the lack of ready-made acoustic volumes in doors or shelves. Therefore they Thiel-Small parameters Doors are often optimized for use in confined spaces, simulating a closed box.
Home acoustics usually have higher sensitivity and are designed to operate at greater distances from the listener. In a car you are half a meter from the speakers, at home you are a few meters away. An attempt to use a car speaker as a bookshelf speaker without taking this difference into account will lead to the fact that you will have to turn the volume to maximum, driving the amplifier into clipping.
โ ๏ธ Attention: Car speakers often do not have a protective metal mesh on the front, as it is installed in the door card. When using at home, take care of the decorative grille, otherwise the diffuser can be easily damaged by your finger or when cleaning.
In addition, the magnetic โcar audioโ system is often more powerful than a home one with the same dimensions in order to provide sufficient diffuser travel (Xmax) to reproduce low frequencies in conditions of limited volume. This makes them potentially interesting for creating subwoofers or wideband near-field monitors, but requires a competent approach to amplification.
Impedance problem and amplifier matching
The most critical point that beginners forget about is the nominal resistance. Standard for home hi-fi equipment - 8 ohm, while the automobile standard is 4 ohm (less often 2 ohms). If you connect a 4 ohm speaker to an amplifier rated for 8 ohms, you risk overloading the output stage.
When the resistance is halved, the current consumed by the amplifier increases proportionally. A home receiver may simply go into protection or burn out due to overheating of the transistors. However, modern AV receivers and many stereo amplifiers are often labeled 4-16 Ohm, which allows the use of car acoustics.
To check compatibility, review your amplifier's technical documentation. If the minimum supported impedance is specified as 6 ohms, then you can connect 4-ohm speakers only if the volume is low. Otherwise, you will need to add series resistors, which, however, will โeat upโ some of the power.
- ๐ Check the rear panel of the amplifier for an impedance selector switch (4ฮฉ/8ฮฉ).
- ๐ Use a multimeter to measure the actual coil resistance (it will be approximately 20-30% less than the nominal value).
- ๐ Make sure that the amplifier's power supply can withstand the increased current consumption.
If your home amplifier is not compatible with 4 ohms, try connecting two identical car speakers in series. The resistance is summed up (4+4=8 Ohms), and you get a safe load for the equipment.
Selection and assembly of acoustic design
A car speaker without a housing sounds flat and lacks bass. In the car, the role of the body is played by the door, which is sealed with vibration insulation. At home you will have to create this volume artificially. Simply screwing the speaker to the board (screen) will give a very weak result, since the sound waves from the back will cancel out the waves from the front.
The optimal solution to start with would be to design the type closed box (Closed Box). This is the most forgiving type of enclosure: it forgives errors in volume calculations and provides clear, although not the deepest, bass. For calculations you will need the parameters Fs (resonant frequency), Qts (total quality factor) and Vas (equivalent volume).
The best material for the body is plywood with a thickness of 16 mm or MDF (fibreboard). The use of chipboard is undesirable due to its low moisture resistance and loose structure, which can resonate. The walls of the box must be rigid so as not to vibrate along with the diffuser.
| Housing type | Difficulty of manufacturing | Speaker requirements | Sound |
|---|---|---|---|
| Closed box | Low | High Qts (>0.7) | Clean, fast bass |
| Bass reflex | High | Low Qts (<0.4) | Deep, powerful bass |
| Passive radiator | Average | Any (requires a subwoofer) | Soft, voluminous |
How to calculate the volume of a box?
For a closed box, the volume (Vb) is often calculated using the formula Vb = Vas / ((Qtc/Qts)^2 - 1), where Qtc is the desired quality factor of the system (usually 0.7-0.9). To simplify things, you can use online calculators by entering the speaker parameters there.
Circuit design: passive crossovers and filters
If you use component acoustics (midbass + tweeters), you will definitely need a crossover. It is often included in the car, but its parameters are tailored to the car interior, where there are many reflections and resonances. For a home, crossover frequencies may require correction.
Simple first-order crossovers (one capacitor for HF and one coil for LF) are easy to assemble with your own hands. However, for high-quality sound it is better to use second or third order circuits. This will allow you to cut off unnecessary frequencies with a steeper slope and protect the tweeter from overload with low frequencies.
When assembling a crossover, it is important to consider the power of the components. Capacitors must be designed for a voltage of at least 50-100V, and the coils must be wound with wire of sufficient cross-section so as not to introduce parasitic active resistance. A poor-quality crossover can โstrangleโ the dynamics of the music.
โ ๏ธ Attention: The polarity of connecting speakers in a crossover is critical. If you mix up the plus and minus on one of the speakers (for example, on a tweeter), an acoustic short circuit will occur at the crossover frequency, and the bass will disappear completely.
Selection of amplifier and signal source
To power homemade acoustics from car speakers, active computer speakers with a broken case or specialized class D amplifier boards are best suited. Class D has high efficiency, heats up little and easily copes with low resistances.
A popular solution is to use chip-based boards TDA7498, TPA3116 or more modern TAS5805. They are inexpensive, compact, and often have built-in Bluetooth. For garage acoustics, this is an ideal option, allowing you to avoid installing a separate 12-14 Volt power supply.
If you want to use a full-fledged home stereo amplifier, make sure that it operates in bridged mode or has a current reserve. The signal source can be anything: from a smartphone to a TV set-top box. The main thing is the level of the output signal. Car PGs often have an amplified output (4x50W), while home appliances produce 1-2 Volts at the linear output.
- ๐๏ธ Class D boards are often powered by 12-24V, which is convenient for use with laptop power supplies.
- ๐๏ธ Pay attention to the presence of cooling radiators even for โcoldโ amplifier classes.
- ๐๏ธ For stereophony, use shielded interconnect cables to avoid AC hum.
โ๏ธ Check before first use
Operation and common errors
Once you've assembled your system, don't expect studio quality right away. Car speakers, especially budget ones, can have a sharp rise in high frequencies, characteristic of compensating for road and engine noise in the car. This problem is often solved by using a software equalizer or adding an attenuator to the crossover.
A typical mistake is insufficient sealing of the housing. Even small gaps around the speaker or in the corners of the box will result in air whistling and loss of bass. Use automotive sealant or silicone to seal all joints. It is also important to properly secure the speaker itself so that it does not rattle at high volumes.
Don't forget about aesthetics. Bare plywood looks unpresentable. You can use self-adhesive film โcarbon-lookโ or โwood-lookโ, or cover the body with carpet, as is done in car audio. This will not only improve the look, but will also add some cushioning to the walls.
The main secret of success is not in the power of the amplifier, but in the correct acoustic design. A good 4-ohm midbass in a well-designed closed box will outperform an expensive 8-ohm speaker simply thrown on a shelf.
FAQ: Frequently asked questions
Is it possible to connect car speakers directly to a computer?
No, you can't do it directly. The headphone output or built-in sound card does not have enough power. An external amplifier is required because 4 ohms may damage the built-in amplifier of the motherboard or laptop.
Why are car speakers quieter than home speakers at the same power?
This is related to sensitivity (SPL). Home speakers often have a sensitivity of 88-92 dB, while car speakers, especially those with a powerful magnet and long throw, may have a sensitivity of 84-86 dB. To get the same volume, a car speaker needs 2-4 times more power.
Do I need a subwoofer if I make speakers from coaxial speakers?
Depends on the size of the speakers. 10-13 cm (4-5 inches) coaxial cables are physically unable to reproduce deep bass (below 60-70 Hz). For full sound in the room, it is advisable to add a separate subwoofer or use speakers measuring 16 cm (6.5 inches) or larger in a surround cabinet.
Will the speakers burn out if you apply 12 volts to them?
The speakers are powered by alternating current (signal). 12 Volts DC from the car battery is normal to power the amplifier. However, if you apply 12 Volts permanent DC directly to the speaker terminals, the coil will burn out instantly as it acts as a short circuit to DC.