General Discussion General discussion about all things car audio, from pioneer, orion, alpine and eclipse.

rms and max power

Old 12-28-2007, 05:38 PM
  #1  
0 Watt CAFz'r
Thread Starter
 
kgrideout's Avatar
 
Join Date: Dec 2007
Posts: 4
rms and max power

Lately i have noticed that there are several brands on the market that advertise amps to have lets say a 300w rms, but the max power rating is 3x more then this rateing at 900w. I thought that the rms rating was generally half of the max power, so why is the products being advertised in such a way ?
kgrideout is offline  
Old 12-28-2007, 05:48 PM
  #2  
500 Watt CAFz'r
iTrader: (3)
 
LOWTONEZ's Avatar
 
Join Date: Apr 2007
Posts: 872
A good rule of thumb to use when looking at an amp, is its fuse rating. If an amp says it is 500 rms and it has 20 amps of fusing, multiply the fusing by 12 volts. 20 amps x 12 volts = 240 watts. So this amp wouldnt push what it they say it can. But if it had 50 amps of fusing. 50 amps x 12 volts = 600 watts, so this amp would be a much better buy. But generally an amp will do 1.5-2 times max power what its continous rated power is.
LOWTONEZ is offline  
Old 12-28-2007, 05:57 PM
  #3  
0 Watt CAFz'r
Thread Starter
 
kgrideout's Avatar
 
Join Date: Dec 2007
Posts: 4
hey thanks for all the in site, i did not know that a amps power rating could be figured out from its fuse rating. Now i know it would never be a very good idea, but lets say if i was to replace a 20A fuse with a 25A fuse, would that mean i would increase the power rating on my amp?
kgrideout is offline  
Old 12-28-2007, 06:02 PM
  #4  
Level 3 Supporter
iTrader: (17)
 
Father Yuli's Avatar
 
Join Date: Oct 2000
Posts: 11,606
lol that would work if power came from the fuse lol. no man that wont increase the power rating. fuses tell you how much current the amp should draw.
Father Yuli is offline  
Old 12-28-2007, 07:04 PM
  #5  
4000 Watt CAFz'r
iTrader: (3)
 
Haunz's Avatar
 
Join Date: Jun 2002
Posts: 4,218
Consider that for a sine wave the peak instantaneous power is 2x the average power. (or so called RMS power)

Now as far as 'maximum' power, in my experience this generally refers to burst power output where the amp is cycled on and off... most amps will produce more 'maximum' power then they can continuously; and this may better represent the amount of power the amplifier can produce on a musical transient...

Of course a manufacturer could call maximum power whatever they want and it may be a rating with the amp seeing 18V, a reduced load, or any other test conditions they choose.....



It sounds to me like MTX is advertising maximum instananeous power on their aformentioned heatsinks under who knows what test conditions......
Haunz is offline  
Old 12-28-2007, 07:15 PM
  #6  
Yankee
 
JohnVroom's Avatar
 
Join Date: Oct 2003
Posts: 3,599
Originally Posted by kgrideout View Post
hey thanks for all the in site, i did not know that a amps power rating could be figured out from its fuse rating. Now i know it would never be a very good idea, but lets say if i was to replace a 20A fuse with a 25A fuse, would that mean i would increase the power rating on my amp?
fusing is there to protect the amp in case of a fault, a larger fuse size would allow more fault current probably damaging the amp.

And would putting in a larger fuse allow it to make more power... my knee jerk response is NO NO NO ... but if it is a true input fuse and not a stage (multiple fuses may protect different stages of the amplification) fuse the you could put out more power as it slowly destroys itself.
bottom line- you put a larger fuse in the amp than the manufacturer put there you are asking for trouble. Yuli and Haunz has a good point, increasing fuse size does not give you more transistor output devices, it will also not help you sink more heat... therefore it shouldn't necessisarily increase your power, and if it does happen to allow more power through... you wont enjoy it long

Last edited by JohnVroom; 12-28-2007 at 07:20 PM.
JohnVroom is offline  
Old 01-10-2008, 10:24 AM
  #7  
50 Watt CAFz'r
 
M.C. Ryan's Avatar
 
Join Date: May 2004
Posts: 467
Originally Posted by kgrideout View Post
Lately i have noticed that there are several brands on the market that advertise amps to have lets say a 300w rms, but the max power rating is 3x more then this rateing at 900w. I thought that the rms rating was generally half of the max power, so why is the products being advertised in such a way ?
I just did a little Goggle'ing and found this on JBL's website... http://www.jbl.com/car/product_support/AUTOMEDIA_CEA2006.pdf

This might help explain how some manufacturers rate their amplifiers.
M.C. Ryan is offline  
Old 01-10-2008, 11:34 AM
  #8  
500 Watt CAFz'r
iTrader: (1)
 
loudtdi's Avatar
 
Join Date: Dec 2004
Posts: 628
Originally Posted by r1d1n5p1nn3r5 View Post
A good rule of thumb to use when looking at an amp, is its fuse rating. If an amp says it is 500 rms and it has 20 amps of fusing, multiply the fusing by 12 volts. 20 amps x 12 volts = 240 watts. So this amp wouldnt push what it they say it can. But if it had 50 amps of fusing. 50 amps x 12 volts = 600 watts, so this amp would be a much better buy. But generally an amp will do 1.5-2 times max power what its continous rated power is.


When doing this simple calculation, do not forget to factor in the amplifiers efficiency.

From the sample above, 50 amps X 12 volts equals 600 watts. Just remember that the 600 watts is a combination of the wattage the amplifier is capable as well as the heat output of the amplifier.

Since most class D amplifers are approx 80% efficient we can estimate that the amp above would produce about 480 watts. A class AB amp with approx 50% effieiency would give us an amplifier that would produce approx 300 watts.
loudtdi is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
TragicMagic
Car Audio Technical Discussions
2
10-16-2008 08:35 PM
DaVibe
Car Audio Wanted (WTB)
0
03-26-2008 06:14 PM
splescort
Car Audio Wanted (WTB)
0
02-15-2008 02:22 PM
zzzzzzz
Install related
14
03-29-2006 07:14 PM
Hardcore Rock Superstar
General Discussion
2
08-12-2004 12:40 PM


Thread Tools
Search this Thread
Quick Reply: rms and max power


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.