Installing a high-quality sound system in a car is not just replacing the factory tweeters with louder devices, but a complex process that requires an understanding of the physical principles of sound propagation and the technical features of a particular body. When the question arises of which speakers to put in the rear doors of a car, many car enthusiasts make the mistake of choosing components solely based on maximum power, forgetting about coordination with the head unit and the features of the interior acoustic design.
The rear row of speakers has a specific function: they provide background fill to the stage and add dimension to the sound, but rarely act as the main source of high frequencies for the driver. The wrong choice of components can result in the rear shouting over the front, ruining the stage presence and making listening to music tiresome. In this article, we will analyze in detail the selection criteria, technical nuances and installation stages so that you can get clear and powerful sound without extra costs.
Before going to the store, it is necessary to conduct an audit of regular places. Often the geometry of the door seats does not correspond to the standard dimensions of aftermarket acoustics, which requires the manufacture of spacer rings or trimming of door card elements. Ignoring this step may result in failure of installation or damage to the door trim when closing.
We determine the size range and technical limitations
The first and most critical parameter is the diameter of the speaker. Car audio standards dictate their own rules, and most modern cars use 13 cm (5.25 inches) or 16 cm (6.5 inches) formats. An attempt to push a larger speaker into a standard place without seriously altering the door will result in the diffuser resting against the metal of the outer door skin, which will cause wheezing and mechanical damage.
It is important to consider not only the diameter, but also the planting depth. Magnetic system Modern speakers can be quite massive, and if there is a window lift mechanism or amplifier behind the door panel, there will be a space conflict. In such cases, you have to use remote baskets or choose models with a recessed magnet.
You should also pay attention to the coil resistance. Standard head units are usually designed to operate with a 4 ohm load. If you decide to install speakers with a resistance of 2 ohms, this may cause the radio amplifier to overheat and enter protection mode. On the contrary, using 8-ohm speakers with a factory head will result in a loss of volume and dynamics.
- 📏 Measure the diameter of the standard speaker and the depth of the free space behind it.
- 🔌 Check the type of connection connector (chips may differ from standard ones).
- 🔊 Check the maximum power that your radio can produce without distortion.
Coaxial or component acoustics: which is better for the rear?
When choosing the type of acoustics for rear doors, the choice most often arises between coaxial and component systems. Coaxial acoustics is a design where the high-frequency speaker (tweeter) is mounted directly on the low-frequency axis. This solution is ideal for the rear, as it allows you to get a full frequency range from one installation point without the need to drill racks or dashboards for individual tweeters.
Component acoustics, consisting of free-standing midbass and tweeters, are usually used on the front stage to build proper stereo. Installing a component system in the rear only makes sense if you are building a complex multi-way system with an active crossover and audio processor. Otherwise, you'll just end up wasting money on complex components that won't reach their full potential in the background.
However, there is a nuance with the diffuser materials. For rear doors, where high-quality sound insulation is often lacking, it is better to choose speakers with diffusers made of polypropylene or composite materials. They are less sensitive to changes in humidity and temperature than paper counterparts, and provide a more even frequency response in conditions of a “walking” door.
⚠️ Attention: When installing coaxial speakers, make sure that the tweeter is not pointed straight up or down, if possible. The optimal direction is towards the interior, so that high frequencies are not absorbed by the door trim or plastic.
What is the difference between 2 and 3 way coaxial speakers?
The 3-way system adds a midrange driver, which theoretically improves midrange detail. However, in a tailgate environment where volume is limited, the third speaker often creates interference, making the sound "mushy". For the rear, 2-way coaxial often sounds cleaner and more natural.
Power and sensitivity: looking for balance
Many beginners mistakenly believe that the more watts indicated on the box, the louder the music will play. In fact, the parameter rated power (RMS) it only tells you what kind of thermal load the speaker can withstand without destruction. If your stereo outputs 20W RMS per channel, and you install speakers at 100W RMS, they will play quietly and without bass, since the amplifier does not have enough current to drive them.
Much more important is the sensitivity parameter, measured in dB (dB/W/m). A speaker with 92 dB sensitivity will sound significantly louder and lighter than a model with 88 dB sensitivity at the same power input. For rear doors powered by a built-in radio amplifier, high sensitivity is priority number one.
It is also worth considering the margin of safety. The speakers in the rear doors often work in “boost” mode when you need to block out road noise or add volume. Therefore, it is wise to choose a model with a power reserve of approximately 1.5–2 times the output power of the head unit. This will ensure there is no compression or wheezing at high volumes.
For a standard radio, choose speakers with a sensitivity of at least 90-92 dB and a power 1.5 times greater than the power of the head amplifier.
Preparation of the door card and sound insulation
The sound quality depends 50% on the correct preparation of the installation site. A standard car door is a sieve with many technological holes through which low-frequency pressure escapes. Without proper preparation, even the most expensive speaker will sound flat and lack bass.
The first stage is vibration isolation of the metal part of the door. It is necessary to seal the inside of the outer metal wall with vibration material, especially in the area of the speaker. This will reduce metal resonances and turn the door into a closed volume. Then you should close the technological holes in the inner wall of the door (the one to which the plastic is attached) with a layer of sound insulation or plywood, leaving a cutout only for the speaker.
To install speakers of non-standard size, you will need to make spacer rings. It is best to use moisture-resistant plywood with a thickness of 10-15 mm or composite materials. The plastic spacers that come with the kit are often too thin and resonate. The ring should be pressed tightly against the metal of the door, and the speaker should be pressed tightly against the ring, without any gaps.
☑️ Door preparation checklist
Connection diagram and crossovers
Connecting the rear speakers is usually not difficult if you use standard wiring. However, if you change the type of acoustics (for example, install a component system instead of a coaxial one), you will need to resolder the wires. In a coaxial cable, the tweeter is connected in parallel through a built-in crossover (capacitor), while in a component, the signal to the tweeter goes separately.
If you are installing a component system at the rear, the crossover must be connected correctly. The low-frequency head (midbass) is connected to the LF/MF output, and the tweeter is connected to the HF output. Mixing up the outputs can lead to instant burnout of the high-frequency speaker, since it will receive the full spectrum of the signal with powerful low frequencies.
For advanced users, setting frequency cuts is important. If the system has an amplifier or processor, the rear channel must be fed a signal with a high-pass filter (HPF), cutting off everything below 60-80 Hz. This will protect the speakers from being overloaded with unnecessary bass and free up the cone stroke for reproducing mid frequencies.
| Parameter | Standard acoustics | Budget aftermarket | Middle class |
|---|---|---|---|
| Diffuser material | Paper/Pressboard | Polypropylene | Fiberglass/Kevlar |
| Magnet | Ferrite (small) | Ferrite (medium) | Neodymium |
| Sensitivity | 86-88 dB | 89-91 dB | 92+ dB |
| Crossover | Simple capacitor | 1st order | 2-3 order, RF protection |
⚠️ Warning: Never connect component tweeters directly to the wires where the coax used to be without checking the circuit. In coaxial the signal is already filtered, and direct connection of the full signal will kill the tweeter.
Setting up and balancing the system
After physical installation, the configuration stage begins. The main task is to ensure that the rear speakers do not draw attention to themselves. The sound should be balanced: the front stage (main vocals and instruments) should dominate, and the rear should only slightly feed the sound, creating the effect of presence.
Use the balance and fader on the head unit. Move the fader forward a little so that the bulk of the sound comes from the front doors. The rear speakers should be barely audible when you're sitting alone in the car. If you clearly hear the singer's voice behind you, the balance is off.
Also check the phasing. If the bass has disappeared completely and the sound has become flat, the speakers may be connected out of phase (plus to minus). You can check this by turning on a track with pronounced bass and temporarily changing the polarity on one of the channels: if the bass “shot”, it means that the phase was initially incorrect.
When you first adjust the volume, turn down the bass on the EQ to avoid sudden cone surges that could damage the new speaker during the bedding-in period.
Typical installation errors
One of the most common mistakes is using thin wires to connect powerful speakers. Standard wiring often has a cross-section that is insufficient to transmit the current necessary for high-quality operation of new acoustics. This results in power loss and poor bass damping.
Another mistake is the lack of sealing. The car door is a high humidity area. If you do not treat the ends of the spacer rings and the cut areas with varnish or sealant, the plywood will quickly absorb moisture, swell and lose its acoustic properties, and the metal will rust.
Don't forget about the fastening. The speaker must be screwed tightly. Any rattling of fasteners at high frequencies will irritate the ear and create extraneous sounds that cannot be removed by equalizer settings. Use wide head screws and lock washers.
Is it possible to put ovals (13x18, 10x15) in the rear doors if there was a circle there?
Technically it is possible using transition frames, but this often requires cutting the plastic of the door or card. Oval speakers reproduce low frequencies better due to their larger cone area, but they are more difficult to correctly orient along the sound axis. If you have no experience, it is better to stay in the 16 cm round format.
Do I need a separate amplifier for the rear speakers?
For background audio, the power of the standard radio is sufficient (if it produces an honest 18-22 W RMS). A separate amplifier is only needed if you are building an SPL (for volume) system or want to get high-quality, detailed sound with a dynamic margin that a built-in head amplifier cannot provide.
How to grind in new speakers?
For the first 10-15 hours of operation, you should not turn on the music at full volume and set a lot of bass. The speaker suspension needs to be developed. During this period, it is better to listen to music in the middle volume range, gradually increasing the signal level.
Why do speakers wheeze at high volumes?
There can be three reasons: lack of amplifier power (signal clipping), mechanical limitation of the diffuser stroke (rests against a magnet or basket) or resonance of the door card. Check whether the diffuser does not touch the protective mesh or door elements at maximum travel.