Audiophile car audio
Over the weekend I undertook the nasty task of installing a stereo into my car. Audiophiles such as myself have a dislike for car audi0. For some strange reason all principles of audio engineering do not seem to apply to car audio. Instead of trying to achieve balanced hi fidelity sound its all about shoehorning another subwoofer into the boots. Car audio does not appear to use any form of real measurement as I discovered and seem to pull arbitrary specifications out of thin air.
Choosing The Equipment
I went to my local automotive accessories supplier to find a reasonable collection of speakers. The shop assistant looked like he had more experience removing car stereos from Bankstown carparks than installing them. He showed me some Sony speakers which he seemed to think where the best things going, which sounded very nasty.
One of my major issues with car audio is the location of the speaker, its going to be near imposable to achieve any sort of reasonable stereo imaging with two speakers just above the floor of the car. Our hearing is very directional at higher frequencies so I took this into consideration when shopping and opted for a two way design. This has two woofers and two tweeters that mount on the dashboard of the car. Separating the tweeter from the woofer is another issue in its self, and creates a huge range of problems of its own, most notably the sound from the tweeters reach your ears before the sound from the woofer. I decided that this was going to be about the only way I was going to get any reasonable sort of stereo imaging, it’s a trade of but everything in car audio is.
After listing to a selection of speakers I settled on a 6.5” two way design by an audio company called Alpine, the speakers did not sound good by a long shot but sounded allot cleaner in the midrange than everything else. The tweeters sounded horrible and beamy.
Fitting The Speakers
The next problem I had was the car door of my company car had 4.5” speakers and the speakers I liked where 6.5” I got on the phone to a few friends who had experience with car audio installations and the general consensus was to cut some of the door out and fit a spacer to the door. I used a nibbler tool and made a cutout to fit these speakers. 
Once I cut the hole I used some spaces to get the speaker spacer to sit flat on the door. I used gaffer tape to make sure I had an airtight seal around the spacer. 
Measurements
Once I had everything installed I turned it up, it did not go particularly loud before clipping. I was surprised as the Pioneer head unit I had installed had a rating of 50W per channel. I connected up my oscilloscope to the output and calculated the output at an amazing 7W RMS into my 8Ohm dummy load. Needles to say even into a 4Ohm load the power output was laughably low compared to the specs. The frequency response on the side of the box showed the frequency response between 50hz-22K on a graph with the smallest unit on the vertical of the graph being 20dB! Needless to say at a glance the speakers appeared to have an amazingly flat response. Quite frankly every single specification the manufacturer gave on these speakers where not worth the paper they were printed on.
I don’t know what it is with all these car audio systems, from time to time in home theater we get some amplifiers boasting more than optimistic power output but nothing quite this ridicules. For some odd reason most things in car audio seem to be measured in peak power output which is a completely meaningless value directly proportional to the size of the power supply capacitors.
Once I got the speakers in I measured the frequency response, there was a big peak around 8k and another at around 190hz, the response was very ordinary with peaks and troughs all over the place, (nothing like that nice flat response boosted on the side of the box!)
I spent some time with the EQ getting the response as flat as possible. The speakers rolled off at around 120hz so if I am to achieve any bottom end I will need to look at installing a subwoofer.
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