Home Audio vs. Car Audio Power Ratings


Bronze Member
Username: 3k_fx

Iowa United State...

Post Number: 16
Registered: Sep-05
Currently, I am confused over the drastic difference in power output between home audio equipment, and car audio equipment. Why is there such a large difference?

For instance, I have two Pioneer TS-W306-C subs (borrowed from a friend). I've been looking for a cheap amp to power them to use as a subwoofer (until I have money to build my own). However, seeing as how the speakers RMS at 400 watts and peak at 1000 watts, it appears as though they need quite a bit of power. I was unable to find any cheep amps (<$50) to buy just to hold me over for the time being.

However, I can power them off of the extra channels on my Pioneer VSX-515-K. Sending them full range audio isn't the best case in the world, but it works. My amp will only supply them with 110 watts max, but they seem to reach a very loud volume and also the excursion seems to get very high as though they are getting a lot more power than they really are.

Seeing as how they're built to max out at 1000 watts, I don't see any reason why they should be driving so loud on only 1/10 that power. Is there some difference in how much "power" is being driven to the speakers depending on whether the amp is home or car auido?

Then I ask, why is there such a difference in power ratings for home and car audio. I can pick up a very cheep $40 dollar car amp at Walmart that will supposedly drive 800 watts (I know this doesn't mean it's clean power, but bear with me). Now, to find a home audio amp that will drive a similar 800 watts to two channels, you have to look online at power amplifiers and spend over $300. Why is there such a big difference in power usage in home audio and car audio? Shouldn't the larger volumes in home theatres and such require more power/higher SPL to fill the room with sound than a small car cabin?

I would think that a in a vehicle wear power is draw is a concern in high power systems, it would be of top priority to make as lower powered systems as possible to make sure there are no power draw issues. Then in homes, where the outlet can supply you with a much more continuous supply of high power output, wouldn't it be more reasonable to have the high power systems?

Don't the two fields seem reversed?

Silver Member
Username: Eramsey

South carolina United States

Post Number: 356
Registered: Feb-05
Logan: Car amplifiers typically are able to produce more true power (W) than home systems. This is due to the fact that car systems of course use DC as the input voltage. With DC more wattage can be produced than single phase AC for several reasons. I'll try to explain without getting too technical but that may be rather difficult. First and foremost, with DC in an automobile there is very little variation in voltage,usually between 12-13.5V and this amount is a constant at a high current. Whereas with single phase AC the voltage in one full cycle is constantly changing, from 0V at 0deg, to about 108-110V RMS at 90deg then back down to 0V at 180deg then -110V at 270deg then back up to 0v at 360deg. There is also one less step for power conversion in a car amp that is already DC and has to be changed to AC for just the speaker output. Now you may ask well if the voltage is higher for home components why can't higher amounts of power be produced equating to higher SPL's? Since the voltage component of home components is much higher, much less current input is required and to insure safety no amp or receiver can have a input current consumption greater than 15A which will trip the circuit breaker the AC receptacle is connected to and or blow fuses. This is primarily for safety reasons. With about 110V available you do not need much current for this to be powerful. Some of the most powerful home amps,which are few in number, can exceed 15A so with these a 20A outlet will be required. But the point is with a home amp no more than 20A at 110V(North America) will be supplied to the input of the amplifier. In the case of Europe and other countries, the voltage will be nearly doubled but the current will be less than half of the up to 20A by North A. A car amp on the other hand will have a much lower voltage but the current factor will be very much higher on the order of up to several hundred amps for very powerful car systems. This is because a car amp runs straight off the battery, and a car battery cells are large and provide a huge surface area where current flows. Open the case of a powerful car amp and you will see many large high current transistors and many large DC capacitors. This is also the case with large home amps but as I said the the available current to the power supply of a home component is much less so additional needed current must be produced through induction, i.e. "transformer". Higher SPL's can be produced in a car because because of the smaller area. This is merely a matter of physics. If you clap your hand a few inches from your ear it will be slightly louder than 2 feet away. This is because the sound has less distance and less air to travel through. This is basically what is going on in the interior of an automobile which is basically a sealed chamber. In the home enviroment there is more space-air for the sound to travel through so less SPL can be produced than in the closer confines of a car. It should be noted that while car stereos can produce deadly SPL's >160dBl, this amount of power has major drawbacks. While a powerful car amp may produce 1KW rms it will operate at much higher levels of distortion often as high as 10%or even more,which is terrible, with peak near clipping volume levels. Your average home system consisting of at least a seperate receiver or amp will have levels of THD a hundred times less which is a much truer presentation of material and thus more enjoyable. Also the amount of noise that can effect a car system is considerably higher. There are many types, road noise, interior noise,electrical and mechanical from the engine, just to name a few. Sorry to be longwinded but I hope this helps.


Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 6701
Registered: May-04

Not having had anything to do with car stereo for well over ten years, I cannot count myself as an expert in the area as it currently exists. However, I never saw "large DC capacitors" in any of the car stereos I came across. Not in relation to the size of the power supply caps in home audio where high end amplifiers often have several capacitors the size of family-style soup cans.

Whether large caps exist in car stereos or not is somewhat irrelevant since car stereos do not generally have large reserves of power. When asked to produce wattage on demand, a car amplifier will glad pull from the battery (hopefully) until the job is completed. In home audio of decent quality that approach is frowned upon since it depletes the supply reserves and leaves the amplifier less able to deal with the quietest pasages which might follow. As ER has pointed out, quiet passages are not the forte of car systems due to the higher ambient noise levels in the vehicle.

Also, As ER suggested, the home and car amplifiers run in a different "class of operation". Most home amps seldom leave class AB1 which has minimal notch distortion. Almost all home amps will actually run in class A without notch distortion for a small percentage of their power bandwidth. This is beneficial in a situation where the home listener is at "average" levels of less than ten watts. Most car amps run in the far more efficient, but far less clean, class C or G operation. The notch distortion is high and the hope is the listener either won't notice or the distortion will be lost in the ambient noise. With this type of operation, an amplifier can produce much higher wattage on paper while trading subtlety for brute force.


Silver Member
Username: Eramsey

South carolina United States

Post Number: 357
Registered: Feb-05
Jan to further add to what you and I both said, I'll level with and say I'm not a fan of neighborhood shaking car stereos and neither is the city in which I live which has a noise ordinance against such. In one of my vehicles I have a factory cd player with four speakers. It probably puts out about 10W max RMS but it is clear and I can hear little distortion from it. Since I spend only about 30 min. a day in my car this is quite sufficient for my needs. I don't know much about car audio either nor do I care to for that matter but I will say that the Lightning brand car audio caps at 1 Farad are about the largest caps that can be purchased for consumer audio use. I have seen many home amps with a large supply capacitance, with multiple 10KuF caps together exceeding 100KuF total or more but this is only 1/10 of the capacitance of the Lightning cap. I saw one receiver with a large torridal and 2 37KuF caps for supply,which were about the size of V8 juice cans, very beefy and decent especially for a receiver. A power supply this large will produce a total field voltage, technically refered to as input to output isolation voltage in eccess of 1KV. This is why it is very dangerous for someone who doesn't know what they are doing to go poking around near this. I have never seen a capacitor as large a soup can as this would be gargantuan and must say I am quite curious what home equipment would have such a large capacitor. I once did some programming and maintanence on an ABB robot which is 3phase 480V and it had 3 main AC caps at 30KuF each. If you in fact open any decent quality high power car amps,like Alpine or Fosgate or Kenwood you will find several large supply caps often at least 10KuF each which is on par with many receivers and home amps.
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