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

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?)😂

One of the things I learned along the way is that there is a really big difference between tubed amplification and solid state. For solid state, more power… of the same quality make most speakers sound better at most volume… even at nearly a whisper. This is also what is “said” in audiophile circles and it is typically very obvious unless you have very efficient speakers… then it can be a liability. Why? I have not really found investigating why results in a means of determining if speakers match amps other than at the most general way… like don’t pair a 2wpc amp with 82db efficient speakers.

Most speakers are much less sensitive to the overall power from tube amps… quality is more of primary concern… so I used to use a 350wpc SS amp to power my 90db speakers and dropping to 250 wpc would make a difference. I replaced it with a 140 wpc tube amp and they sound very different (the tube amp sounds way better… and different). I can operate my tube amp at 140wpc or 70wpc in triode mode and there is virtuallly no difference in volume or punch, but the 70wpc sounds better and more musical. Why? I have not really found investigating why results in a means of determining if speakers match amps other than at the most general way… like don’t pair a 350wpc amp with 100db efficient speakers.

So after fifty years of passionately pursuing high end audio what is my conclusion? If you are trying to come up with a set of specs that will lead you to the right choice of amp forget it. You must try them. However, if you are simply interested for the sake of learning… carry on… good luck. But still make sure you audition amps first… especially if you have a big spread in the sensitivity / amp power.

 

Also, one of the most amazing / interesting systems I have heard was a huge panel electrostatic powered by a 4 wpc Viva tube amp. Which was the most ridiculous pairing that would never be something that theory would have led you to put together.