[Invinsible]

Originally Posted by karankapoor

but most of the amps are overrated and underrated,aren't they.

and this dosen't mean that if they are rated as 900 x 1 they will give 1200 or will give 500rms

how one can calculate the power,when you buy some product first thing you see is the specs & features of the product.

No one is saying that if they are 900x1 they would give 500rms. It's just that the company says 900 but it would give the power between 700 - 800Rms roughly under continous use. Where some are underrated when they 900rms they landup delivering somewhere around the same or 10-15% higher also depends on electricals.

Incase of the kenwoodKAC-9104D it is highly overrated amp. Delivering just around 650RMS of their claimed 900 at 2ohms.
Here's a detailed tech info on it. Please have a read.

Kenwood KAC-9104D - Car Audio & Electronics

[abhibh]

Guys on Test bench most of the amps will fail to produce the amount of power they specify.

And talking about caraudiomag they are inclined towards US products.

[navin]

Originally Posted by abhibh

Guys on Test bench most of the amps will fail to produce the amount of power they specify.

And talking about caraudiomag they are inclined towards US products.

on the contrary...on a test bench, under the conditions specificed by the manufcturer most amps will outperform their published specs. It is in the real world (less than 14.4V DC, full frequency range, reactive speaker loads, etc..) that most amps fail to live up to their published specs.

[panky12345]

Originally Posted by abhibh

Guys on Test bench most of the amps will fail to produce the amount of power they specify.

I disgaree completely! I've seen couple of bench tests in the US.. and sadly, near 95% of the amps like MTX (old school), JL, Alpine put up more than the specified RMS ratings.

Edit: Just saw Navin's reply.. complete agree here!

[low_bass_makker]

Originally Posted by karankapoor

but most of the amps are overrated and underrated,aren't they.

how one can calculate the power,when you buy some product first thing you see is the specs & features of the product.

Good reputable brand which make amp can be considered as underrated but normal mainstream amp are always overrated.

For calculating the power capability I would simply checkout the fuse rating on the amp or if not on board would check the manual of the same. And would reverse calculate the same. Like if a company says a amp is 1200 x 1 at less than 1 % THD at 14.4 volts. Then there are two variable here also. First at 1% THD the amp is overrated, a good amp is always rated at .1 % THD so in this case the output would have to be less if you need cleaner sound. Now comes the voltage this is the major factor which make the HYPE. Firstly there will never be 14.4 volts in your car the real fiqure will be approx 13 volts. So again the output will be lowered.

Now comes the value of the fuses on the amp. In the above example the fuses on board are 120 amps. So if we reverse calculate it would be like the following...

120 amps so at 13 volts it would consume (120 x 13 = 1560 watts) since the above amp is a AB class it would be 50 % efficient then the real watts it will be giving will be 780 watts.

( Note :- this is the continuous load if we play a sine wave. In music the load will not be continuous.)

So do check all the specs before buying.

[abhinav.gupta88]

I'll leave that part for you.
What would a JBL amp (14001).
1200 watt at 4 ohms at 0.04%. give out effectively?

[low_bass_makker]

Originally Posted by abhinav.gupta88

I'll leave that part for you.
What would a JBL amp (14001).
1200 watt at 4 ohms at 0.04%. give out effectively?

Abhinav your amp has 40 amps x 4 fuses on board it means 160 amps...if we reverse calculate it would be 160 amps x 13 volts = 2080 watts. Since yours is a D-Class I would take 75-80 % efficiency so it would be....approx 1560 watts which is quite accurate as mentioned by the manufacturer.

[abhibh]

Originally Posted by abhibh

Guys on Test bench most of the amps will fail to produce the amount of power they specify.

And talking about caraudiomag they are inclined towards US products.

Originally Posted by panky12345

I disgaree completely! I've seen couple of bench tests in the US.. and sadly, near 95% of the amps like MTX (old school), JL, Alpine put up more than the specified RMS ratings.

Edit: Just saw Navin's reply.. complete agree here!

Arey even i disagree with my above statement. I did a typo there, forgot to add NOT

[abhinav.gupta88]

Originally Posted by low_bass_makker

Abhinav your amp has 40 amps x 4 fuses on board it means 160 amps...if we reverse calculate it would be 160 amps x 13 volts = 2080 watts. Since yours is a D-Class I would take 75-80 % efficiency so it would be....approx 1560 watts which is quite accurate as mentioned by the manufacturer.

But that is at 2 ohms
What about at 4 ohms.

[navin]

Originally Posted by low_bass_makker

So do check all the specs before buying.

the spec should read as follows:

Power at 12V:
XX watts 20Hz to 20kHz, all channels driven @ 4ohms, THD at rated power < 0.1%, IM at rated power < 0.05%.

even then other factors like the input level at which the amp overloads, the damping factor, and even the weight of the amp can help establish the amp's build quality.

[karankapoor]

i think this is more easier way to check how efficient a amp is
as lbm said the total of fuse say 120 amp multiply it by 6 for class AB and by 10 for class D you will get your ans.

[low_bass_makker]

Originally Posted by navin

the spec should read as follows:

Power at 12V:
XX watts 20Hz to 20kHz, all channels driven @ 4ohms, THD at rated power < 0.1%, IM at rated power < 0.05%.

even then other factors like the input level at which the amp overloads, the damping factor, and even the weight of the amp can help establish the amp's build quality.

Very true Navin Ji very few mention all this. And some good amp manufacture also mention the Temperature at which they are measured.

Originally Posted by karankapoor

i think this is more easier way to check how efficient a amp is
as lbm said the total of fuse say 120 amp multiply it by 6 for class AB and by 10 for class D you will get your ans.

I would take 6.5 for the AB class and 9.5 for the D Class.

Originally Posted by abhinav.gupta88

But that is at 2 ohms
What about at 4 ohms.

By the fuse method we can calculate the max output of the amp at which it can play.

[panky12345]

That means my JBL 1201.1 can churn out 1404 W RMS (at the peak in continous play) as against 1114W RMS? Then what is meant by Dynamic Power?

Interesting observation though.. Lets compare some more..

[abhinav.gupta88]

Originally Posted by low_bass_makker

By the fuse method we can calculate the max output of the amp at which it can play.

Is there a method by which i can find out how much does it churn out at 4 ohms when the one at 2 ohms churns out 1500.

Originally Posted by panky12345

That means my JBL 1201.1 can churn out 1404 W RMS (at the peak in continous play) as against 1114W RMS? Then what is meant by Dynamic Power?

Interesting observation though.. Lets compare some more..

What is the fuse rating on your 1201.1?

[abhinav.gupta88]

Also i dont think it should make a difference but , is it better to get 2 amps of 1200 watt rms powering the subs at 4 ohm or 1 amp of 2400-2500w rms powering the sub at 2 ohm?