A little deeper on amp power please....


If somebody could elaborate on exactly how a higher watt amp will improve the sound of speakers (lower sensitivity speakers that “need” power).  More specifically, I get that when the nature of the recording and the volume setting demand an immediate spike in power, an amp that delivers the spike will perform better than one that does not.  But when I used to have an amp with output meters, it would be in single digits for most normal listening, and I don’t recall what a spike would have been - I want to say 15 or 20 watts.  What I am scratching at is whether there is something more to power, i.e. the notion that the effortless power of, say, a 300 watt amp would somehow be an improvement over an otherwise similar 75 watt amp…even if a spike is just 20 watts.  Hope the question make sense.

mathiasmingus

As a low volume listener with hard to drive speakers, I think total wattage is less important than how the amp handles changes in impedance. It is a good sign if the wattage doubles as the impedance halves. To use the race car analogy, I think of this as having lots of torque even at low RPM’s. 

I forgot to mention, I agree current capability of the amp is more important. --Jerry

Speakers are a much more complicated load than the fixed value resistor used on a test bench to determine the power spec rating for an amp.  First, speakers typically have a resistance curve that varies widely with frequency. An 8 ohm speaker may vary from below that number to way above it. Second, many speakers also present a capacitive load which can be difficult for some amps. And, the amp also has to deal with the signal it gets back from the speaker. Once a speaker starts moving, particularly at lower frequencies, it has inertia, so continues vibrating momentarily after the input signal stops. This turns the voice coil/magnet assembly into a power generator which can return power back to the amp. How the amp reacts to this signal can be an issue.

So, you can see this issue is more complex than just how many amplifier watts are generated. Some amps handle complex loads better than others. The specs alone rarely cover all the bases.

I think the reality is a little complicated, but you are right that most of us never exceed 20 Watts listening.

I think it may best be explained that some speakers are a lot harder to drive than you would think, and an amp that can handle them without sagging tends to be bigger, heavier and higher power.

By sagging I mean both reduced overall output but also changes in frequency response. That is, the ideal amplifier would output the same frequency response regardless of speaker, but as we get further and further from ideal the amplifier’s output tends to start to mirror the speaker impedance, even at low listening volumes.

One of the best sources of information about this are the Stereophile amplifier reviews.  Take a look at the measurements where they test with a simulated speaker load, and pick a few tube amps vs. a few solid state amps and you'll start to see a pattern.

Nothing is ever easy, and I will need to learn more. I get that power, impedence, and damping factor will all play, and then I need to learn more....

What inspired this is that I thought I had my end-game speakers in Harbeth 40.2. But then I got interested in playing around with low powered gear (I know it can be expensive too, but there are definitely interesting economies of design and $$$ in producing, say, 5 high quality watts vs 100). Some people say they have had good experience with low power amps and these speakers, others have said running SS monoblocks is a must-do! With unlimited space and budget, I would love to add a set of high sensitivity speakers for experimentation. (can somebody loan me their La Scalas?)😂