Why You Don't Need a Lot of Power for Your Car Stereo System
I get a lot of emails from people that are planning mega-watt systems for their vehicles and I usually try to talk them down from the mega power ledge. I'm not against big systems in any way but most seem to be jumping in without knowing what they're getting in to. There are a lot of hidden costs involved in these giant systems and usually they're not necessary to get the sound you want. Here's why.
Car Stereos are Loud
If you've ever checked the sensitivity rating on a speaker you will usually find that it is in the 90 decibel range. This means that at a distance of one meter the speaker will put out 90 decibels of sound with only one watt of power. You may not realize it but that is pretty loud. You're not going to set any records but it's still fairly loud. OSHA, the government agency that regulates work place safety in the US, states that 90 decibels is the maximum level an employee can be exposed to over an 8 hour day (constant level). For a non-occupational setting that same level is the maximum you can listen to safely for one hour (in a 24 hour day). If you have an older home stereo system with a power meter you may have noticed that the power doesn't exceed 3 watts for most comfortable listening. Combine that with the additive effect of multiple speakers and you easily reach the 100 decibel level in an automobile.
How Loud for How Long
The next question you have to ask is how loud do you want it. If you're trying to set an SPL record then you're going to need lots of power and probably lots of woofers. But if you just want your system to pound out the bass notes then you probably don't need a system bigger than 500 watts. Acoustic power operates on a logarithmic scale. This means that past a certain point you're only going to get a small increase in the sound level even though you're increasing the power input enormously. As an example, with 100 watts of power you will increase the sound pressure level by 20 decibels. Add this 100 watts to a speaker with a 90 decibel sensitivity and you'll be at the 110 decibel level. But if you add another 100 watts (200 watts total) you'll only increase the sound level by 23 decibels (a 3 decibel increase over 100 watts). Each time you double the power you'll increase the sound level by 3 decibels and that ain't a lot. So with 400 watts of power (assuming your speaker will handle it effectively) you'll get a 116 decibel output. Not a big increase in sound level but it is a big increase in amplifier price and in current draw from your electrical system.The bottom line is you'll probably only use those 400 watts for a brief period of time because you'll risk hearing loss if you listen for extended periods at those levels.
The Additive Effect of Multiple Speakers
Every time you add an identical speaker with the same amount of power you add 6 decibels to the total SPL. If you add an identical speaker but split the original power between the two speakers you will add 3 decibels.
Example: A speaker with 100 watts driving it and a sensitivity of 90dB will have an output of 110dB. Adding a second identical speaker with 100 watts driving it will raise the total SPL to 116dB. If you add that second identical speaker but only drive each speaker with half the power (50 watts each) the total SPL will be 113dB.
Summary:
- Doubling the speakers and the total power adds 6dB
- Doubling the speakers while keeping total power the same adds 3dB
- Keeping the same number of speakers but doubling the power adds 3dB
Electrical System Upgrades
Another big factor to consider is the cost of electrical system upgrades you'll need if you do have a mega-watt system. The current draw can easily reach in the 150+ amp range which will almost certainly require an alternator upgrade. These are expensive both in equipment and installation cost. Custom alternators can run $500 though you may be able to use a high output alternator from another model that your car's manufacturer makes (contact a qualified mechanic about the possibility of fitting and interfacing a larger OEM alternator). Then you'll need to use the larger 0/1 gauge wiring which is about $6/ft as compared to 4 gauge wiring which is closer to $2/ft. With large current draws everything is going to need to be bigger, not just your amps. The law of diminishing returns starts to kick in and your mega-watt system may cost you four times as much while only delivering 6 decibels more output as compared to a more modest system.
How Much Power Do You Need
So the question really becomes how much power do you need. For most listeners that want a clear top end and a solid bottom end you'll do well with a 500 watt or less system. That should probably be split 40/60 with the lion's share of the power going to the subwoofer system (200 watts for the highs and 300 watts for the lows). This will keep the current draw from your alternator at a more reasonable level while still providing punch and clarity to your system. The cost will also be much less overall and your pocket book (and your ears) will thank you.
The Car Audio Help DVD catalog includes five different videos covering many areas of car audio installation and custom fabrication. Topics range from basic system installation (head units, CD changers, amps, speakers, etc.) and mobile security (car alarms and remote start) to subwoofer box design and fiberglass fabrication. If you're interested in custom fabrication and car audio installation be sure to check out what we have to offer.
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