Amp power and SQ for those of us that are SQ oriented

Post by **smgreen20** » Tue Jun 29, 2010 6:41 am

While engaged in a conversation on the Hybrid Audio forum one thing led to another and I came across this.

"How do I choose the right amplifier power for my speaker system?

* Ideally you should pick an amplifier that can deliver power equal to twice the speaker's continuous IEC power rating. This means that a speaker with a "nominal impedance" of 8 ohms and a continuous IEC power rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.
* A quality professional loudspeaker can handle transient peaks in excess of its rated power if the amplifier can deliver those peaks without distortion. Using an amp with some extra "headroom" will help assure that only clean, undistorted power gets to your speakers. Some professional amplifiers are designed so they have additional headroom. These amps can cleanly reproduce transient peaks that exceed the amplifier's rated power. In this case select a model with an output power rating equal to the continuous IEC power rating of the speaker. Consult the amplifier manufacturer or owner's manual to learn more.
* In some applications, such as critical listening in a studio environment, it is important to maintain peak transient capability. For these applications, use an amplifier that can deliver 6db (or four times as much) more power than the continuous IEC power rating.
* If budget restraints or legacy equipment force you to use an amplifier with less power, extreme care should be taken to see that the amplifier is not driven into clipping. It may surprise you to learn that low power can result in damage to your speaker or system. Download our Danger: Low Power tech note for more information."

From:

http://www.jblpro.com/pages/general_faq ... ression%22?

shawn k · Post by **shawn k** » Tue Jun 29, 2010 8:03 pm

Hmmm.. Some interesting thoughts. I think there's a lot of generalization going on there though. I do believe in the "you can never have too much power" way of thinking, but I don't believe it's always necessary. A lot of it depends on personal preference. For instance: If you are one that doesn't ever really "hammer" on your system, and you simply enjoy music at reasonable levels then huge amounts of power probably is not necessary (and any decent amplifer will still have good headroom). Many people don't realize that when we listen to music at "room level" it's typical for the amplifier to be producing only in the vicinity of 1-2watts rms

so headroom isn't much of a concern untill we are talking about significant output levels

Some of it depends on the amplifier as well.... There's a difference between RMS power and Continuous RMS power. The most accurate spec would be "continuous RMS output" which is what an amplifier is capable of 24/7 at full badwidth and is measured so. "RMS output" is derived from a mathmatical formula that determines the theoretical output usually short bandwidth and not necessarily measured and/or "continuous"

Furthermore, how efficient are the drivers? And by efficient I mean how much electrical energy is transduced into acoustical energy. On average most drivers are somewhere between 1-2% efficient others more, others less. Very efficient drivers, or even enclosure designs like horn loading, will all have a factor with how well the power is being used.

What kind of enviornment will the listener have to contend with? Nice quiet living room? Noisy car? Football stadium?

I understand where they are comming from in terms of having headroom, but I can't necessarily agree with their numbers completely. Mainly because the info seems a little too general

winno · Post by **winno** » Thu Jul 01, 2010 4:16 am

The trouble I have with some of those generalisations is that power requirments are going to be driven by a driver's efficiency, among other things, and NOT its power handling.
In fact, when choosing amplifiers, I'd go so far as to say that the speaker's power handling is the last thing you should consider. A power handling figure is just that; how much power it can handle before reaching its thermal/mechanical limits and melting, etc. It's most certainly NOT a measure of what power it needs or works 'best' with.

My rule: buy as much power as you can afford (within limits - no point wasting money on kW's that you will simply not use) in an amp that gives you any other features you may want, and that sounds decent.