Here's the AutoSpeed special feature that'll point you in the right direction in selecting the audio system for your car.
Decking your car out with a high-performance stereo system is just like enhancing any other aspect of a car. If you think long and hard before you make any changes, chances are you'll end up with a highly effective system. But it's all too easy to go along to a car audio specialist and walk out having spent 2-3 times what you were initially prepared to pay. Have you ever stood around listening while the consultant rattles off a list of mega-dollar components that just seems to get his or her rocks off more than anything else? "Oh yeah, you'll need this, that and the next thing..." And the whole time, it's your bank account that's taking an all-mighty hammering.
So here's a guide to what basics are needed as prerequisites for quality car sound. Paying more than this means you'll be paying heaps for a lot of other flash gear that certainly abides with the law-of-diminishing returns theory.
How you want the system to sound will depend on your personal tastes. But, remember, it has to be that - a complete system. There shouldn't be any holes in the frequency response from your chosen list of speakers - bass, mid and treble should all be well balanced. For the majority of people, they're after strong bass, clear treble and plenty of punchy well defined mid frequency in between.
So let's jump in to how to get it!
Head Units
It's the head unit from which all sound signals originate. If this is of a poor quality, no matter how good your amps, speakers and cable are it'll still sound crap. This means you'll need the sound quality of a good CD unit to reach all the low and high frequencies present in music. These can come as a single CD/tuner unit, a multi-disc remote stacker, or even a 3-disc/tuner head unit with an additional multi-disc stacker to boot. The better ones come with high quality RCA outputs that are easily connected directly to an external amplifier and most also come with some form of security measure such as a detachable faceplate.
Amplifiers
The bigger the amplifier you have the better. While you might not want to listen to music at a continuous 300 Watts, the sound coming from an amplifier that is barely raising a sweat will be far better than one that's nearing its peak performance. An over-worked amplifier can also be driven into "clipping". This is when a harsh sound is introduced to the music, and it's usually just a matter of seconds before the amp will shut itself down at this listening level. The advertised power rating of amps can be a little confusing though. There are three different ways of expressing amplifier power output: Watts RMS, Watts PMPO, and Watts PIMPO. It's watts RMS
(Root Mean Square) that is the relevant one, as this is a continuos output not just a split second peak burst. The difference between
these ratings is huge, as a 10W RMS amp might have the same continuos output as a "massive" 200W PMPO unit... So don't be fooled! If you're doubtful of an amplifier's advertised output, compare the capacity of the amplifier's input fuse to other units - higher amperage fuses indicate a higher potential output power.
The number of "channels" an amp has refers to its number of speaker output lines. For example a 2-channel has 2 speaker outputs, a 4-channel has 4 speaker outputs etc. But it can be possible to "bridge" output lines as well. So a 4-channel amp might be able to have its four outputs merged into two - giving the total of the amps power into only two speakers.
Equalisers
Equalisers are used to manipulate the frequency response of the speaker system over the entire spectrum. They usually have up to twelve bands (frequencies) at which adjustments can be made, ranging from ±
12 decibels. This all sounds like good stuff, but for every component wired in between the head unit and the speaker, there is an accompanying loss of sound quality.
Nonetheless, if you like listening to different types of music at different frequency settings, a good quality EQ could be just the thing you're after to reach the balance you're after.
Speakers
A speaker's sensitivity will greatly affect the peak sound pressure level (volume) reached. Its sensitivity is the amount a speaker responds to a given amount of input power. And the difference between just a few dB marked on the box is huge - every 3dB increase requires half the amp power to get the same SPL! So a speaker with a sensitivity of 94dB at one W/1m being fed with 50W will produce just as much SPL as one with a 91dB rating consuming 100W.
The frequency response of a speaker is also of utmost importance. This measure helps you to determine which speaker will be best under certain operating conditions. For example, a mid range speaker that has a minus 3dB drop-off over around 8kHz won't be suitable to run up to the tweeters you have working from 10kHz upward.
Sub Woofers
More often than not, it is technically correct to refer to these speakers as "woofers" not "subwoofers" as they are always labeled - but we'll let that small beef slide for now. The key to achieving the bass response you're after lies in putting the correct speaker in the correct enclosure. Without a properly designed enclosure to suit the speaker, it's easy to be disappointed with bass performance.
Okay, so we need the speaker and enclosure together as a package - but how many speakers are needed, and what size is best?
The "how many" question depends on space limitations and cost, but when it comes to making serious bass - the more the better! A smaller diameter speaker usually has a cleaner and punchier sound than a big 'un, so single or twin 10 or 12-inch subs should take care of the bass department. Yes 15 and 18 inchers are available, but these tend to take up huge volumes of interior space and don't deliver a very precise sound unless you spend up big on a pro-series speaker.
The listed power rating of a sub-woofer can be very important if you are going to drive it hard. It's a good idea to have a fair amount of headroom (at least 30%) between the amplifier's output power and the speaker's power handling capacity.
Mid Range
Mid range speakers fill the frequency gap left between the bass-only subwoofer and the treble-only tweeters. They usually have a frequency range spanning from around 120Hz to 10kHz, so they do represent the majority of the audible sound spectrum. It's for this reason that good quality mid range speakers is preferable.
Presently, it is common to install 4 to 6½ inch mid range speakers in the front doors or the front kick panel area. This gives good sound imaging because the sound is coming from the same end of the vehicle, and it also means you can save money as you've only invested in 2 speakers.
So-called front "splits" are also very popular. They are a properly matched set of mid-range/tweeters sold as a package (complete with cross-overs). This has the advantage of a precisely balanced sound distribution and a visual similarity between the two speakers.
Tweeters
No, you can't just staple a live canary to the dashboard of your car for good treble response. These cute little speakers give you the clear sounds of the high-hats and the upper limits of Maria Carey's vocal chords. They are often mounted in the front sail area at the leading bottom edge of the front side windows, or perhaps slightly lower in the door trim. Three types of tweeters are available: piezo, cone and dome. Generally, piezo tweeters are aimed at the budget end of the market, while the dome tweeter is regarded as the ultimate variety of tweeter. It is important to aim tweeters directly at the vehicle occupants, as the carpet and furniture inside the car easily absorb treble. It is also widely suggested that the closer to ear level they are mounted the better they will sound.
Multi-Axial Speakers
This is the most commonly type of speaker fitted in today's cars. They consist of a main woofer along with one or two tweeters or mid speakers mounted under the same grille cover.
Available from 4-inch diameter right up to big 7x10-inch oval speakers, they offer excellent coverage of the sound spectrum for the dollar (from around 27-26,000Hz at best) - but they generally sound inferior to a split system having separate subs/mids/tweeters. Still, if you're after bang-for-the-dollar a good set of 6x9s on the rear deck of a car is hard to beat.
High and Low Pass Cross-Overs
These are electronic components that reduce the operation of a speaker either above or below the selected frequency. There are "high pass" and "low pass" cross-overs available for any type of speaker. For example, a "high pass" cross-over at 10kHz is just the thing for tweeters - as you don't want bass signals going in, reducing sound quality and possibly damaging the speaker. On the other hand, a low pass filter at 120Hz is what you need to prevent mid range frequencies effecting a subwoofer.
Wire/Cabling
Power and speaker cabling is very important in realising the peak performance of a car sound system. For the best sound, make sure the correctly rated cable is used, the head unit and amp is wired directly to the battery, all wire joins are soldered (or any terminals are very securely fixed), and all Earth lugs lead to a common ground point. Gold plated battery terminals aren't a prerequisite for good sound, although they do look impressive. Their main advantage is resistance to corrosion on the battery posts. And for safety's sake, ensure all fuses are located close to the battery to prevent shorting downstream, and always use high-rated cable to prevent possible electrical fires.
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