New mod, need help

[BuSy_keniff]

This mod is kinda PC related and kinda not... I need to figure out how many amps a car stereo amp pulls. I'm looking for the amperage on a 500-600 watt RMS amp. I'm hoping it will be less than 6. Any ideas? I noticed that most amp kits come with somewhere like a 20 amp fuse.

[Wampa]

Well, I am teaching myself electronics, so I'd wait for an 'official' reply from Dave (Brown) on this, as he is the resident electronics guru. If I remember, watts is power, and the formula is P=VI (P=power, watts; V=volts; I=current, Amps). Assuming that the speaker runs off the car's 12v, at 500 watts it would be consuming 42A. That is rearranging the forumula so it reads P/V=I. I have not really done any electronics work with stereos, or much calculating with watts for that matter, so don't take my estimate as an official word.

[BuSy_keniff]

that sounded like a fair assessment wampazulu! I can think of a cheap way of doing 12v 10amp car battery charger, but I'm not sure if that will be enough...hmmm My test PSU says...12v 15a.

[insulglass]

BK, Wampa is correct and yet not correct. Here's why...

Most audio equipment is rated in RMS, which stands for ROOT MEAN SQUARE. I won't get too lengthy here, but basically it is the average power. Actual power may different significantly than average power over a time window. Add in the decibel factor, and rated versus actual is often deceiving.

For example, pick an average sound at 85dB, which is relatively equivalent to speech and normal stuff you might hear. An addition of 3dB is required to double the sound, which would be at 88dB. Say the following...

82dB - whisper
85dB - speech
88dB - fairly loud music
91dB - loud music
94dB - painfully loud music
97dB - large engine noise

And so forth, these are just examples. However, DOUBLING the sound requires a square of the input power. Therefore, TWICE as loud will require FOUR times as much power. THREE times as loud will require NINE times as much power. FOUR ==> SIXTEEN. As you can see, the power requirements can jump in a hurry.

Keep in mind that most music actually requires only a fraction (or less) than a watt of input. That's why most home receivers rated at 25-50 watts of output can sound almost as loud as a 100 watt receiver. A full watt thorugh a pair of headphones would be deafening. Literally.

Where lots of watts DOES provide a huge advantage is on the low end of the audio spectrum. Think about it, a bass woofer physically can move up to an inch or more, and the resulting air volume with it. Physical movement requires a lot of power to operate. Oppositely, your tweeter moves only a fraction of an inch to produce sound in it's frequency range. THAT's why you need lots of watts for bass punch, and 10 watts will provide brilliant sound at the high range. The quick bass notes create a fast transient where power is required but the need curve dies quickly.

Now, applying this back to your original question... your amp may be capable of producing 500 watts. However, in actual use, less than a few watts ON AVERAGE is delivered. Large power requirements are only needed for a fraction of a second whenever a bass note is to be produced. Therefore, your amp is CAPABLE of large wattage but only USES a small amount of watts on average. Therefore, the input power is not an actual 12v x 42A = 504 watts, but rather more like 12v x 15A = 180 watts on a continual basis. The amp can draw the extra power from your car's electrical system to provide short surges to make up the power - but not for long before it would get hot and blow the fuse. In fact, many audio systems have large capacitors for energy storage to meet surge demands.

If you ran a continuous bass note, your amp would quickly overheat and blow your fuse protection. Finally, your amp should have a nameplate rating for input power.

Hope this helps -

Dave
_________________
Blah, blah, yada, yada.

[BuSy_keniff]

The idea here is to use car stereo equipment to create a home stereo subwoofer! I need a PSU that can cut the mustard. I wanna run a 15 or 18" woofer. I have been installing car stereos since I was 15, so I gots da knowhow. I've just never attempted to run it off of AC voltage. I was thinking of running a cap with the setup. I have a friend that runs a stereo shop and a cuz that werks at BestBuy.

[Wampa]

Sounds interesting. Thanks for the lesson, Dave; I knew that there were more complicated electronics involved in audio setups, but at least I have a decent grasp of the basic formulas

Good luck on the project!

[BuSy_keniff]

If I can get past the Power Supply, the project will be easy! Thanks Dave. I suddenly feel...inferior..hehehe

[KingJames]

180 dB - whale

http://www.surtass-lfa-eis.com/Terms/

[insulglass]

[BuSy_keniff]

sooooo insulglass...you looking to adopt a kid? hehehehe I'm potty trained...I wipe my own butt...I don't eat much...
You guys are TOO much help. I'll definitely get back to you on that!