This was one of the first mods I made to this car, as I am a audio fanatic. When I purchased the car, the the door speakers and one tweeter were blown, causing sound distortion. The rear speakers were replaced by the previous owner with Kicker speakers, but as they are small 3 1/2 inch speakers driven by the stock radio, they were insuffucuent to power the car. In this page, I will rundown the design process, the parts I used and the installation.
My requirements for the sound system was to have:
The first step was to determine all the speaker positions and sizes. I found a forum which stated that the front door speakers were 5 1/4 inch but could fit some 6 1/2 inch speakers and the rear speakers were 3 1/2 inch. The doors also have tweeters mounted on close to the side-view mirrors.
I decided to purchase Infinity Reference 5030CX speakers for the door speakers. These are produced by Harmon Kardon which have a good reputation for car speakers. These are component speakers, meaning that they have the door woofer speakers that come with separate tweeters. This kit also come with crossovers which contain high pass filters for the tweeters and mid-to-low pass filters for the woofers. These in combination with the amp, produced crisp and clear sound.
As brilliant as these speakers were, they lacked sub-bass. To fix this, I needed a subwoofer. I wanted a subwoofer that woud produce clear and clean bass rather than powerful for a balanced sound system. I was also limited by the small interior of the MR2 with little space behind and under the seats. Note that this is a two door mid-engined car. This also meant that the trunk is behind the engine, so I can't place it there either. Doing some research for inspiration, I decided to have one behind the seat as that's where I had the most space. For optimal sound, subwoofers need an enclosure that is proportional to the diameter. With larger diameter subs being more capable at delivering lower frequencies, bigger is better. There are also sealed or ported enclosures. Ported had more benefits for audio quality but took more space. There are also powered subs which have an inbuilt amplifier, but I had found a great amp great for the door speakers and sub. Luckily, I found another solution. Kicker produces subwoofers in professionally tuned encosures that are quite slim. After measuring, I found that the 8-inch model fit perfectly behind the car seat. Although this is a small diameter, this sub also features a passive radiator, which is just the diaphragm. This is basically another speaker without a motor driver. It simpy reacts to the changes in air pressure in the encosure to improve the bass response. I managed to also get a 4-ohm model for better quality (less volume).
Next was to research ampifiers. There are two common types of car audio amplifiers. Class D and Class A/B. Class A/B amplifiers are an older design which can produce very high quality amplification. However, modern Class D amplifiers can do the same much more efficiently coming in much smaller sizes and producing less heat than a Class A/B of equal power rating. Another consideration to be made was that I would be using low power inputs from my phone AUX or the stock 26 year old head unit. Thus my options were purchasing a pre-amp unit or an amp with speaker-level input. I decided to choose speaker-level input, which just take the old output to speaker cables as input. This was a much more affordable for me as a Uni student, though I might switch to a phone pre-amp in the future.
To drive the speakers, I had to first consider the number of channels. The door speakers plus tweeters, take two channels (left and right), the rear speakers also take two channels (left and right) and I decuded to bridge two channels for the subwoofer, as speakers for lower frequencies draw more power. This is because the lower frequencies move less volume of air in the same time. Thus, they require larger diameter speaker diaphragms to move a greater volume of air. This requires a larger motor driver which draws more power. Thus I decided to get one 4-channel amp for the door speakers and the sub, and a lower power 2-channel amp for the small rear speakers. I found a class-D 1200W Pioneer amplifier as these were capable of supplying slightly more RMS power and peak power to the door speakers than they are rated, to maximise the use of them. They also were capable of bridging 2-channels for the sub-woofer and also came with a bass-level adjuster knob. It also had the option to switch to a low-pass filter. I found a tiny motorbike amp for the rear speakers which was also class D. Both amps were capable of speaker-level input.
Speakers
Audio Switch