View Full Version : Dumb Question: Car vs. Home- Wattage


haromaster87
03-09-2010, 01:40 PM
Okay guys,

So my nephew is all into ridiculous, terrible sounding, thumping car stereo's. No offense if anyone likes those style systems, just not my style. Anyway, I've looked at a lot of components they use and I see them using 1000w amps and things of the sort. Then he ask about my Hi-Fi rig and I tell him it makes about 27 watts per channel. Yet my little Pioneer CS-77's make A LOT of noise and great bass response, etc. I guess my question is, why do they use so much more power? I mean, I know they have home receivers that made, 300+wpc, but those were known as monster receivers and powered large speakers, I presume. Is there some technical difference between everything, or is the wattage rating more of a bragging medium, or what? I know this is a dumb question that ignores a lot of specifics, but I think someone will get what I mean. Btw, if there's any car audio guys, I'm not trying to offend anyone, just curious.

donberry
03-09-2010, 01:45 PM
most car amps you see are rated a whole lot different then that receiver you have. Yours is rated at continuous power, and if vintage, continuous for 1 hour and still had to stay in spec.
Most car amps, at some point, at some frequency, it may see the stated power for a couple of nanoseconds.
Sure it is a 200 watt amp, at 1kz for 4 nanoseconds it hits 200 watts......
tis with all matters audio, usually no such thing as a free lunch and there really is a huge difference between that $100.00 500 watt car amp and the $600.00 200 watt car amp.

willyrover
03-09-2010, 02:13 PM
Most car amps are also rated into 4 ohms or less. While that doesn't excuse rediculous claims, it does make the wattage appear higher than their 8 ohm rated home amplifier brothers.

1000watts into 2 ohms really isn't all that impressive when you do the math.

CallMeJoe
03-09-2010, 05:42 PM
most car amps you see are rated a whole lot different then that receiver you have...
:thmbsp: :thmbsp:
IIRC, mobile amplifiers are not subject to the same FTC regulation as home electronics.
This allows rating for "instantaneous peak power" at absurdly low load impedance and equally high distortion levels, all in the interest of inflated power figures.

meandog
03-09-2010, 06:10 PM
Well said. I always wondered about this too. Thank You.

cademan
03-09-2010, 06:30 PM
I think it has a lot to do with specs also. Watts are watts, car or home, but a 500watt car amplifers specs may say (I say may) 500 WPS with rated specs of 10% THD and will usually push a very inefficient speaker. My nephew is the same way, he has the ridiculous 1000 watt power with very inefficient speakers.

It sounds ok but I have shown him that I could blow his system away with just a couple of hundred watts and he asks, what do you have, a couple of thousand watts? I reply, nope, just a couple of hundred watts and he is totally blown away.

I couldn't even push one of his 500 watt rated inefficient speaker (well, maybe with my Phase Linear 700 watt amp) as those cones and surrounds are way too tight. They are something like 85db, 1 watt or lower, but he doesn't care. Ahh, youth! LOL

Wheras, he may blow one of my very efficient speakers with his 1000 watt amplifier.

Some of us older people here may remember those cheap swap meet car booster/equalizers that were rated at 200 watts but the specs were terrible. A friend of mine had one once and we connected it to a scope and watt meter. Oh sure, it put out 200 watts but all of it was distorted and that thing heated up so much you could fry an egg on it. I think something like 5 or 8 watts was actually usable.

Check this out: Click on, "Learn the Truth" tab.
http://outrageousaudio.com/

Jdubya
03-09-2010, 06:43 PM
Funny you should ask that as I was just wondering the same thing earlier today. I kind of figured that it wasn't an apples to apples comparison (i.e. ohms, RMS, etc...).
An old customer of mine had a car audio shop and he had an S-10 pickup with a fiberglass shell on the back. He cut the back of the cab out to pass through to the box where he had 20 12" subs back there. He "only" ran 250 watts, but managed 156 db with it setting a record at the time (early 90's) for that class. The top edge of the windshield would move at least an inch back and forth when at full throttle. It was ridiculous.

stereofanboy
03-09-2010, 07:17 PM
It's been many years since I had a serious setup in my car. It's funny to see how some of the mighty have fallen and how some of the shit companies are still in business and still selling shit.

Dave C
03-09-2010, 07:20 PM
Yup a big watt amp and a one note sub, that's all you need to drive down the street.

Markw
03-09-2010, 07:27 PM
And power is generally the limiting actor in amp power.

Batteries can supply virtually unlimited power for a limited time period. That's why they are rated in amp/hours.

They can supply so many amps or so many hours.

They can supply 2x those amps for 1/2 the time.

They can supply 4x those amps for 1/4 the time. ...and on and so on and so on ad infinitum.

A home power supply is limited by the power it can supply by the transformer, the line voltage and many other factors.

whoaru99
03-09-2010, 08:03 PM
Most car amps are also rated into 4 ohms or less. While that doesn't excuse rediculous claims, it does make the wattage appear higher than their 8 ohm rated home amplifier brothers.

1000watts into 2 ohms really isn't all that impressive when you do the math.

Yes, that's true, but most car speakers are 4 ohms and many these days are 2 ohms so it's all relative. 1 ohm setups are not terribly uncommon, and I've seen some 0.5 ohms setups too.

Lower impedance in car audio is advantageous because it facilitates making power using more current instead of more voltage.

Reputable car stereo gear provide CEA-2006 ratings for their amps...

On May 28, 2003, the Consumer Electronics Association published standard CEA-2006, "Testing & Measurement Methods for Mobile Audio Amplifiers." This "voluntary" standard advocates a uniform method for determining an amplifier's RMS power and signal-to-noise ratio. Using 14.4 volts, RMS watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers.

cademan
03-09-2010, 08:55 PM
Batteries can supply virtually unlimited power for a limited time period. That's why they are rated in amp/hours.

Also remember that you can purchase some pretty spendy voltage inverters that will do a fine job, as long as the vehicle is running. It has to do with the sine wave it reproduces.

Motor homes use these along with onboard generators.

Another fascinating aspect of voltage inverters is the old 50's tube car radios that used what's called a vibrator and step up transformer to obtain the tubes B+ voltage. Most newer ones contained 12volt tubes (12V6, 12SQ7, 12AV6 etc.) so the filaments could run directly from the battery supply.

zenith2134
03-09-2010, 09:10 PM
It is interesting to note that of course Watts = Volts * Amperes, so most car systems derive say, 100W from mostly current as opposed to mostly voltage which is often the case in a home system. This is of course all relative and as always there are exceptions to the rule.

haromaster87
03-09-2010, 09:14 PM
Wow. Glad I'm not the only one who wondered about this. Thanks for all the info guys, it was mega helpful. And it came as good news to me as I now know that I wasn't crazy in thinking most of their power numbers were kind of ridiculous. haha Well now I'll know what to tell my nephew when he ask why my stereo makes a louder, cleaner sound then his system, and it does it with apparently less then 10% of the power his does. Now I know that if I ever wanna make a nice system for my car, I'll wanna try modifying home stereo stuff. :P

whoaru99
03-09-2010, 09:23 PM
.... And it came as good news to me as I now know that I wasn't crazy in thinking most of their power numbers were kind of ridiculous. haha Well now I'll know what to tell my nephew when he ask why my stereo makes a louder, cleaner sound then his system, and it does it with apparently less then 10% of the power his does. Now I know that if I ever wanna make a nice system for my car, I'll wanna try modifying home stereo stuff. :P

Just be careful of the blanket assumptions and statements. There is good and bad in all gear, and more factors are involved than just the watts and distortion.

TNRabbit
03-09-2010, 09:39 PM
This is a TERRIBLE quality video, but I'm running 1000 REAL watts into the two subs & 265 wpc into the Klipsch KB 3.1 speakers. In reality, it sounds INCREDIBLY CLEAR & distortion-free:

http://i251.photobucket.com/albums/gg286/TNRabbit/th_MOV01984.jpg (http://s251.photobucket.com/albums/gg286/TNRabbit/?action=view&current=MOV01984.flv)

Renzor213
03-10-2010, 12:19 AM
As already mentioned, most of the better car install's are rated in real deal low distortion RMS watt's. Speaker impeadence doesn't figure in when thing's are rated in watt's, as low impeadence car speaker's is just a way to keep amplifier rail voltages low, but current draw increases appropriately. Car speaker installs are very inefficient, fighting an evironment purposely designed to quell acoustic energy. Home speaker's are many time's more efficient, and the room usually act's as further amplification. Since you need ten time's the amplifier power for 10db gain(twice as loud) and home install's about 20db advantive from the get go, it's easy to see the difference in power need's.

DR_Simpkins
03-12-2010, 01:38 AM
My nephew lives with me and he installed in his S/10 a 300 wpc amp and a sub behind his seat and some 300 watt max tweeters up near his sun visor and wired it up using the stock dash speakers for midrange. I was expecting to hear some great sound and was surprised that it sounded like shit! All he really cared for was that it had a loud bass note! He blew the dash speakers the first few days and it sounded worse! Besides Rap , he likes 60's and 70's soul and you couldn't really enjoy that music because the voices that should've come through the midrange speakers was coming through the sub mostly. I said , Dude that sounds horrible! I took his CD and stuck it in my garage system and just filled the garage with beautiful soul music. I explained that my Pioneer SX-450 was only 15 wpc powering two large efficient Wharfedale Airedales and two fairly large but efficient offbrand speakers that had horn mids and looked sort of like Mach 1's. My bass was much better and he just couldn't believe it was only 15 wpc driving my system. I finally talked him into finding some decent coaxials and we mounted them and dialed down his sub to where you could enjoy the music a little but it seems the kids nowdays want heavy bass in music that wasn't even intended to emphasize the bass in the songs!

SaSi
03-12-2010, 04:34 AM
My Blaupunkt car stereo brings out a modest 4x20W and drives 4 speakers plus tweeters. I've never cranked up more than 45/100 and the volume level is pretty damn loud.

hypertone
03-12-2010, 12:31 PM
I remember the Rockford Fosgate Punch 45 amp from my high school days. That little amp and a pair of old school subs would rock a whole block. 22.5 REAL Watts per channel....

Nikko75
03-12-2010, 12:45 PM
Many individuals that are into loud car audio place great pride in power ratings. What they fail to understand is the problem with most of those systems is they didn't have enough gain to ever actually reach maximum output, so they keep moving to bigger amps.

pete_mac
03-12-2010, 02:54 PM
I remember the Rockford Fosgate Punch 45 amp from my high school days. That little amp and a pair of old school subs would rock a whole block. 22.5 REAL Watts per channel....

Sure would! Old-school high current amps like that would double their power as you halved the impedance. This resulted in FAR greater output in real world conditions when connected to multiple woofers, often of the dual voice coil variety to provide further flexibility regarding impedance matching.

I agree with one of the previous posters regarding cars being a much more hostile environment for audio. Road and wind noise coupled with poor/limited speaker placement means you're working harder to get acceptable volume levels. I think some of the comments regarding car amp output levels are a bit misguided. It's not uncommon for high-end home audio amps to have several hundreds of watts, so why not car audio too? The subwoofers in a car audio application are typically the speakers that are amplified by the bigger amps, much like in a domestic home theater setup. Whilst 50wrms for the main speakers and 150-200wrms for a single sub will give great results in most cars, like home audio enthusiasts, many desire the the extra output and dynamic headroom afforded by higher powered amps.

I've heard some brilliant car audio setups with 1500wrms on tap that would shame many, many high-end home setups. I've also heard terrible setups that concentrate on huge bass with little regard for the overall balance of sound. Parallels can be drawn with domestic audio in this regard too. Like anything in audio, there's the good and the bad.

MunkeyQ
03-13-2010, 12:38 PM
I had a very cute little Blaupunkt car amp from a mid 90's Lexus. Rated at 30wpc and by god did this thing sound good. Machined steel case, big power MOSFETs and general amazing build quality. I used it as a computer amp hooked up to some pretty damn inefficient Kefs...sounded better than most small silver recievers (Pioneers etc)

Never seen anything like it elsewhere nowadays though...all seems to be shiny chrome and inflated ratings.

electronjohn
03-13-2010, 02:40 PM
One of the nicest-sounding car stereos I recall is an install I did for a friend in his '73 Lotus Europa. Car came with no radio & a nice chunk of English walnut to fill the hole. I carefully cut a rectangle in the walnut plate and mounted a tiny, tiny Pioneer cassette player. No holes could be cut anywhere in the car, space was at a premium (if you've ever seen a Europa, you'll see why), so I mounted a pair of walnut cube speakers from Team (about 7X7X7) w/5" drivers up under the dash & against the wheel wells. 10WPC never sounded so good!