Friday, July 30, 2010

DIY car audio using home audio components

Car audio is the only way for me to listen to music with standard loudspeakers. Although a listening space in the car is far from ideal because of various noises and limited installation/listening space, etc., it's the only space that is isolated from the outside, enabling to use loudspeakers without complaint by anyone else. Here I show my approach to car audio, using home audio components.

There were some reasons why I chose home audio components but not car audio components. My primary motivation was a difficulty to replace a audio deck of my car, 2nd Gen Mazda Demio (Mazda 2) DY-3W, that I purchased recently. Its front panel of the audio deck was unified with a controller of air conditioner, and Mazda and and any 3rd parties did not provide alternative panel for standard DIN-size audio decks. This meant that I had to use home or mobile audio components for the audio player.

Since I have all music albums in my iPod classic 6th gen with Apple Lossless format, I chose it as a juke box and transporter of the digital data -- but not the analog source. The key component for it was a digital data converter, Onkyo ND-S1.
ND-S1 converts the digital data from iPod to standard S/PDIF outputs. It was installed beneath the passenger seat.

A step-down DC/DC converter was used to supply 5V power for ND-S1.
The iPod classic was connected to ND-S1 through a dock extender cable.
Its optical output was connected to a digital amplifier, Rasteme RSDA302P.


RSDA302P is a low-cost high-quality digital amplifier that amplifies digital data using STmicro STA328 without conventional D/A conversion. Its compact size and low-power consumption are very suitable for car audio.


A step-up DC/DC converter, which was originally designed for laptops, supplies 24V to RSDA302P. Well, perhaps you can make it better by yourself... but I was lazy.

A speaker output of the default CD player and AM/FM radio tuner deck was input to a high-low converter manufactured by Audio Technica, and then input to the analog in of RSDA302P.


It was not necessary to use home audio loudspeakers, but I chose them instead of car speakers that could be installed easily. The reason was that I preferred full range speakers rather than coaxial units or multi-speaker units which are usually adopted for car audio. Since high-quality full range speakers for car audio are rare, I chose full range speakers from home audio components. After investigation, I purchased Markaudio Alpair 10.

To install Alpair 10, I designed a speaker baffle using a free 2D CAD software.


This CAD file was sent to a wood processing pro, which offers the service inexpensively.
The baffle was delivered after 3 weeks from the order.

Before installing the speakers, it was necessary to strengthen the damping of the doors -- so-called deadening.

This photo is the door panel before the installation.

The door panel was removed. You can see the default paper cone speaker. The service hole was covered with a plastic, which seemed to contribute to weight saving and deadening.

The default speaker was removed, and damping sheets made of asphalt were attached behind the speaker hole and on a part of the plastic. I purchased the sheets from Tokyu Hands.
On the damping sheet behind the speaker, I attached acoustic absorption sheet.

The Alpair 10 was installed.

At this step, once the door panel was attached and the sound was checked. Unfortunately, I found large acoustic resonance from the plastic plate. To reduce the resonance amplitude and to move the center resonance frequency around a few hundred Hz to a few ten Hz, I pasted lead sheets, Tokyo Bouon TA-1000.

I pasted 1.5 sheets, which have approximately 3 kg, for each door.


The damping sheet was pasted on the lead sheet to reduce the resonance further.

Since the speaker conflicted with the door panel, its inner plastic was grinded by a grinder. This photo shows the door panel before grinding.

Using a grinder, the plastic was grinded.

Using a metal brush attached on an electric screwdriver and air brush connected to a compressor, grinded dust was cleaned up.


After the grinding and cleaning.

The acoustic absorption sheets were sticked inside the door panel.

At last, the door panel was attached on the door.



The system sounds smoothly and mellifluously, and best suits jazz music. The RSDA302P drives the Alpair 10 nicely. It's not powerful, but easy to listen, which would be rather preferable for BGM when driving. This simple, low-cost, high-quality, full digital, full range car audio system using home audio components can be recommended to anybody who wants to listen to music in a car. I'd welcome any questions and comments.