How important is RMS for selecting an Amplifier?

I would look at power ratings largely in relation to the room size, speakers driven, and the headroom needed for the kind of music played and volumes one listens to.

Its sometimes like choosing a large 8 cylinder engine in your car against a more efficient 6 or buy car with 4.
Sometimes there is need for power and sometimes not.

What advantage does a yammy 100 watter have or the 60 watt marantz ? Not much of you are looking for a certain quality.
And the yammy would play a bit louder than the marantz in the overall scheme of things. Will it play cleaner is anybody's guess.

I am a believer in low/medium power amps for the music I listen to, partucularly in average indian homes.

Manek

to complicate the matter, not all ratings are similar. there are certain lower RMS rated amps which feel like they have more grunt than other higher RMS rated amps.

case in point...my rotel 60 or 70 (can't remember exactly) wpc rated RA 971 MkII sounds much more powerful than my 95 wpc Marantz PM 7200. (The marantz sounds much better though due to other factors, but thats not the point)

you need to see factors like :
Does the amp have enough headroom ?
Can the amp run difficult speaker loads ? Or does it run out of steam ?
Is it stable at 3 or 4 ohms ?

Whats the sensitivity of the speaker you intend to mate with the amp ?
Speaker sensitivity is also a factor which influences the perceived power of an amp is which speaker you are pairing it up with. An amp which normally drives a speaker with a sensitivity of say 88db will sound twice as loud when its driving speakers with a sensitivity of 91 db.

Above are some of the criteria that are probably equally or more important than just the RMS rating in isolation.

Look up "high current ampifiers". Basically how much of current the amplifer can swing when needed.

Also when i need to match speakers with the amp is it a must that the RMS of speakers which I choose should always be more than what I have in the AMP.Is this correct?

by and large you can ignore the "wattage" rating of the loudspeakers.

The basic rule is : the amplifier must have sufficient power to drive the speakers. an amplifier that struggles to drive a given speaker is not good news for either the amplifier or the speaker.

How do you determine if a speaker is a heavy load or a relatively easy load ?

1. Sensitivity
A speaker with a sensitivity of 91 db is easier to drive than a speaker with 88 db. Every 3 db represents a DOUBLING of levels.
On the other hand some speakers have sensitivity values such as 84 or 85 db. Such speakers will require amplifiers with real grunt if you want to play them loud.
Whereas some speakers such as those of Klipsch are very sensitive and are quite an easy load for an amplifier to drive. This is the reason why you will see tube amps generally very carefully mated to speakers with higher sensitivity.

2. Speaker impedence
The higher the resistance the easier it is for the amp.
The lower the resistance, the more grunt the amp needs to have. i.e. 4 ohm speaker will place higher demands on the amplifier than a 8 ohm speaker.

if it helps think of it this way. since there is less resistance (4 ohm) , the easier it is for the current to flow, and so the amp must keep that amount of current flowing. if there is higher resistance (8 ohm) current does not flow that easily and it does not require the amp to keep as much current flowing. the above is a very very simplistic explanation, and most probably not entirely technically accurate, but will suffice for an explanation.

additionally, the resistance of a speaker is not a constant value. a speaker with a nominal resistance of 8 ohms will not have the same value through its operation. depending on the continuosly varying musical frequencies, the resistance value will constantly keep changing. A speaker could have a nominal impendence of 8 ohms but could drop to minimum of 3 ohms. these dips to 3ohms put tremendous demands on the amplifier.

So check for the nominal and minimum impedence of the speakers as well.

Hi,
Whose RMS should be higher when I match - the pair of speakers or the amplifier?

Two schools if thought here :

1) The speakers rms rating to be equal or slightly higher to amp so that the amp doesn't overdrive the speakers

2) The speaker rating does not matter if the speakers are not driven to distortion or amps are not made to clip.

Do remember an amp driven to clipping or audibly distorting at high volumes can damage speakers. So if you treat your system well, you would have no problems either way.

If you redline your car too often or too long you are bound to damage the engine, same goes here too.

Manek

Dear Jayashree,
Forget all these. Just pick up the amplifier here and a decent speaker which is a reasonably good load and you will be happy for a long time.
http://www.hifi-foru...um_id=120&thread=301