????Question????

[Low Rider]

i was just wondering if anyone could tell me how car manufactuers measure the power of there car sterio systems.

for example: in my grandfathers Ford LTD it says on the headunit PREMIUM 250WATT SOUND SYSTEM.

when they say 250 watt is that all up when u add up all the speakers or what

and how do i measure my car sterio.
i have a 4x50wat channel headunit
a 300watt 4 channel amp that runs my 6x9's (230watt) and my 6inch fronts (200watt) the subbys are coming later!

cheers

[NOCKY]

Most quoted power figures are "Max" whereas the important figure is "RMS".

Head units always quote "Max", speakers usually "Max" and amps can vary, but usually the cheaper amps quote "Max" and the better ones "RMS".

Basically "Max" is the maximum a speaker/amp should handle, and "RMS" is what it can handle for long periods. (A very simplistic explanation)

I assume that car manufacturers add the "Max" values of all the speakers to come up with a total value.

The wattage of your system is not actually rated on the speakers, but on the total "RMS" output of your amp(s) and head unit.

For example in my VN Calais I run a 5 amp setup rated at 1100WRMS.

There is a figure you can use as a guide to roughly convert "Max" to "RMS", but it varies a lot between manufacturers and models. (And I can't remember what it is, but "RMS" usually varies between 50-75% of "MAX")

Also remember that some amps can be bridged down to lower ohms and thus incease their power output!!

Confused yet?

The only time you need to accurately work out your power output is for power/earth lead sizing, battery selection, and comps, other than that it's not how much power you have, but how it sounds (ie clarity, imaging, staging, frequency response, etc) that counts.

[Low Rider]

yeah i understand what your saying with rms and all but i only just purchased my first sterio for my first car and im pretty picky with the way music sounds weahter its coming from a hi fi system or a car sterio and beleive that most standard systems in cars sound pretty awfull, and just wanted to know what mine should be like compared to say my pas in his LTD coz thats the best standard issue unit i have ever heard but i still hope its much better.

coz i havnt installed my system yet.

cheers

[tandy ass]

Nocky - Not quite

The maximum figure does have a mathematical method to work it out but virtually NO manufacturers adhere to this because if they were truthfull then their maximum output would be less than the competitor's who are clearly lying.

Even RMS figures can be very misleading at times.

Maximum is 1.414 times the RMS figure. If your amplifier makes 100 watts RMS then the maximum power is 141.1 watts.

There are hundreds of bullshit techniques used to measure power, I think PMPO is the greatest of all the BS methods. Look at a stereo system that says 1000W PMPO and its weaker than the stereo that does 15W RMS.

They also can mislead you on the RMS figure, many manufacturers will quote an RMS figure at 10% THD (Total Harmonic Distortion). This, naturally, will sound like shit coming from a transistor (BJT or FET) based amplifier. Valve amplifiers have a lot of THD but they distort in a different manner and actually sound pleasant, of which the technicalities I wont go into now.

The honest guys will clearly print the maximum RMS power at what distortion level, generally anything under 0.1% at max RMS is trustworthy.

That's the basics of it, there is a lot more to it than that but put simply, if no RMS figure exists then the figure is most likely completely useless for any comparasin.

[tandy ass]

Originally posted by Low Rider

i have a 4x50wat channel headunit
a 300watt 4 channel amp that runs my 6x9's (230watt) and my 6inch fronts (200watt) the subbys are coming later!

cheers

Basically, you do not have a 4x 50 watt head unit unless it has its own integrated switchmode DC-DC power supply (the inverter), big heatsinks and a fan inside the case to keep it cool.

200 watts is a lot of power - from a 12 volt supply that would draw almost 17 amps. (edit) - Thats without taking into account that a class AB amplifier is between 30-40% efficient so total power from the 12v input would be in the order of 35-40 amps.

Amplifiers have approximaty 2 volt drop across the output stage when at maximum output. Most newer car amplifiers use the push-pull bridged arangement inside the amplifier IC to extract more power. Maximum RMS power per channel into a 4 ohm load is about 25 watts RMS per channel. Unlike house amplifiers, these do not have a peak output because of the extremely low impedance power supply (the car's 12v rail). Remember this is only with a pure sine wave, so any other waveform (virtually all music) is not a pure sine wave and therefore the power will drop. Even with this figure of 25W RMS you get 35 watts peak. There is no other way to acheive more power. Again some manufacturers make unrealistic situations to make a genuine maximum power output, I've seen one car deck specify maximum power of 55 watts RMS* per channel but in very small writing at the bottom it specified an input voltage of 17 volts. Yeah you're going to get that in a car, pig's ass.

Again saying a 6" speaker could handle 200 watts is a joke. Even 200 watts peak is a joke. I have a 300W RMS amplifier here and most 15" woofers have trouble coping with the amount of power it can deliver. Speaker peak ratings vary quite a bit, if you're pushing techno into a woofer that's rated for 50W RMS then the bass beat could very well be over 100W peak and the speaker will happily cope without damage. If you like grunge/alternative with heavy guitar and strings then you just need to go a poofteenth over 50W peak and the thing will blow. It very much depends on the music content as well....

Watt ratings have become the great lie of the 21st century

[commodore22]

Hi mate, i'm looking at buying an amp for a system very simular to yours. Can u tell me some more info about it, and if it;s worth the money or not.:D :D :D :D :D :D :D :D :D :D :D :D

[Au2low]

Originally posted by Bozz

Watt ratings have become the great lie of the 21st century

True!