Installing 20 cm speakers in the front doors: car audio guide

Standard acoustics in modern cars often leave much to be desired, especially for those who value high-quality sound on the road. Many car owners decide to replace the standard 16-centimeter speakers with more powerful models with a diameter 20 cm (8 inches). This solution produces deep, rich bass and significantly improves the cabin scene, but requires careful preparation and technical knowledge. Installing speakers this size is not just a bolt-on replacement, but a serious audio upgrade project.

Before you begin dismantling the door cards, you need to understand that 20cm midbass requires more space than the standard landing site. You will have to face the need to modify the door space or make spacer rings. Ignoring this step may result in the speaker simply not going into place or touching the trim elements. In addition, the increased power will require checking the wiring and possibly installing an additional amplifier.

In this article we will analyze in detail all stages of installation: from selecting components to final configuration. You will learn how to correctly measure the diffuser stroke depth, why it is important door panel resonance and how to avoid common installation mistakes. A competent approach will allow you to turn the front doors of your car into a full-fledged acoustic screen.

Selection of components: why 20 cm?

Upgrading to 20cm speakers is justified if you want a full-fledged midbass without using a subwoofer. Smaller speakers physically cannot produce the same sound pressure and go as deep into the low frequencies. However, the choice should be based not only on the diameter, but also on the parameters Thiele/Small, which determine the behavior of the speaker in a specific volume.

Pay attention to the diffuser stroke (Xmax). To obtain high-quality bass in a limited door volume, a speaker with a large linear excursion is required. If you take a model with a small Xmax, at high volume the sound will become “mushy” and distortion will appear. Power also plays a role, but more important is the sensitivity and ability of the head to work in a confined space.

Thiel-Small parameters

what to look for?: Key parameters to choose: Fs (resonant frequency) - the lower, the better the bass; Qts (quality factor) - for a door, optimally 0.4-0.6; Vas (equivalent volume) - affects the choice of design.

When choosing acoustics, you should consider well-known brands specializing in car audio, such as Morel, Hertz, Audison or Ground Zero. Their products often have parameters adapted for installation in doors. You should not chase the maximum rated power if your standard wiring or head unit is not capable of producing the corresponding signal.

Doorway diagnostics and measurements

The start of work should always be accompanied by careful measurements. Standard places in doors are rarely suitable for installing 20 cm speakers without modifications. You need to measure the available depth from the mounting location to any obstructions on the inside of the door (window regulator, door reinforcement, lock). Planting depth is a critical parameter that cannot be ignored.

Use a caliper or ruler to determine the diameter of the hole in the metal. Often a 20 cm speaker requires widening the hole or shifting the mounting axis. It is also important to evaluate the condition of the metal around the regular place: if it is thin, when the bass is played loudly, rattling will begin, which will ruin the entire sound.

Pay special attention to the trajectory of the glass. When lowering, the glass should not touch the magnetic system or speaker basket. In some cases, it is necessary to lower the speaker lower or move it inside the door, which entails the manufacture of complex podiums. Incorrect calculation will result in broken glass or damaged speaker.

Manufacturing of podiums and spacer rings

To install 20 cm speakers, in 90% of cases you will need to make spacer rings or full-fledged podiums. The simplest option is to use MDF or high-density plywood. Wood dampens vibrations well and does not resonate as much as metal or plastic. The thickness of the material must be at least 15-20 mm to ensure structural rigidity.

The manufacturing process begins with the creation of a template. Cut a cardboard shape that perfectly follows the contours of the door and allows you to place the speaker. Then transfer the outline onto the MDF and cut out the ring with a jigsaw. It is important to make bevels (chamfers) on the ring to direct the sound into the interior and not into the door trim. This will improve stage and sound detail.

⚠️ Attention: When attaching spacer rings, use only stainless steel bolts and nuts. Ordinary black metal will quickly rust from moisture condensing inside the door, and the fastening may fail.

Finished rings must be treated with a moisture-proofing compound, for example, polyurethane varnish or epoxy resin. A door is an aggressive environment with changes in temperature and humidity. If you don't protect the wood, it will swell and the speaker will warp. After drying, the rings can be covered with carpet or painted in the interior color.

Vibration and sound insulation of doors

Installation of powerful 20 cm speakers is impossible without high-quality vibration isolation. When a large diffuser operates, the thin metal of the door turns into a membrane, creating extraneous sounds. The first layer is applied vibration-absorbing material (bitumen-polymer mastic layer with aluminum foil). should be at least 70-80% of the area of ​​the external metal door card.

The second layer is a sound insulator or sound absorber (for example, splen or felt-based materials). It is applied on top of the vibration insulation or on the internal door card. This helps cut out external noise and improve the acoustic design of the speaker, creating the effect of a closed volume. For midbass, this is critical to getting clean bass.

Material	Function	Place of application
Vibroplast / Bimast	Metal vibration damping	External door card
Splen / Accent	Heat and sound insulation	Inner Card/Skin
Vibton/Girlin	Anti-creak	Joints of plastic parts

Don't forget to glue the ends of the plastic door trim anti-creaking (madeline or foam tape). When the woofer is actively working, the plastic can make unpleasant sounds of friction against metal. High-quality noise will not only improve the sound, but will also make the door heavier and more solid to the touch, which will also have a positive effect on the sound.

Connectivity and crossovers

After the physical installation comes the electrical connection stage. For 20 cm speakers, the car's standard wiring is often not enough. Thin wires have high resistance, which leads to loss of power and damping. It is recommended to lay a separate copper wire with a cross-section of at least 2.5 mm² or 4 mm² from the amplifier or radio directly to the speakers.

If you are installing component speakers, the signal must pass through the crossovers. Crossover is a device that divides frequencies, sending lows to the midbass and highs to the tweeter. It is important to set the cutoff frequency correctly. For a 20 cm in-door speaker, a typical low-pass filter (LPF) cutoff is about 80-100 Hz to remove the middle and give it to the midrange or leave it to the midbass if the system is two-way.

Recommended slice settings (example):
Low Pass: 80 Hz (12 dB/oct)
HPF (High Pass): 60-80 Hz (to protect the speaker)

The polarity of the connection must be strictly observed. If you mix up the plus and minus on one of the speakers, a phase shift will occur and the bass will “fail,” making it quiet and flat. You can check the phasing using a battery (the diffuser should extend when positive is applied) or a test track.

System setup and common errors

The final stage is setup. Even perfectly installed 20cm speakers will sound bad without the correct head unit or processor setup. The main task is to coordinate the work of the midbass with the subwoofer (if there is one) or with the midrange speakers. Use test tracks with pink noise or sine to look for resonances.

One of the common mistakes is trying to squeeze maximum volume out of speakers without taking into account their capabilities. Clipping (signal overload) kills speakers faster than mechanical stress. Adjust the Gain (input level) on the amplifier so that there is no distortion at maximum volume.

It is also worth checking the operation of the window regulators after installation. Sometimes even a millimeter shift of the podium prevents the glass from lowering all the way. In this case, it may be necessary to modify the window lift mechanism or the shape of the podium. Don't ignore small details as they can cause problems in the future.

⚠️ Attention: Do not use standard plastic clips to secure the trim after installing the podiums. They may not be able to withstand the weight and vibration. Replace them with reinforced ones or add additional fixation points.

Frequently asked questions (FAQ)

Is it possible to install 20 cm speakers without an amplifier?

Technically it is possible if the radio produces sufficient power (usually from 50 W RMS per channel). However, 20-centimeter speakers often have low sensitivity and require a lot of travel, which standard radio amplifiers cope with poorly. The sound will be quiet and lacking dynamics. To unlock your potential 20 cm midbass amplifier is required.

Do you need a subwoofer if the doors are 20 cm apart?

Good 20 cm speakers can play bass down to 40-50 Hz, which covers the needs of most music lovers. A separate subwoofer may not be needed if the goal is simply a high-quality front. However, for genres like hip-hop or electronica, where infra-low bass (20-30 Hz) and high sound pressure are needed, a subwoofer will still be useful.

How to protect speakers from moisture in the door?

Use plastic protective nets or special acoustic screens. It is also important that the podium is varnished and that the speaker itself is protected from moisture (for example, a polypropylene diffuser or treated paper). The gasket between the speaker and the podium must also be moisture resistant.

Which is better: coaxial or 20 cm component acoustics?

For the front doors, where the stage is being built, component acoustics are definitely better. In it, the tweeter (tweeter) is taken out separately and installed in a stand or corner of the door, which allows you to properly set up the stage. Coaxial (where the tweeter is built into the midbass) is usually installed at the back or where there is no room for separate installation.