amplifier DB meters

I guess I need to clarify "logarithmic." Basically, this means that our ears require multiplicative power consumption to hear louder sound - not additive. Not to mention that the same goes for different frequencies. Bass notes require more power than treble notes. If you are listening to a violin solo, you only need a couple Watts. If you are listening to a concert, you will need hundreds more Watts to get the dynamic range right. You can use less power but when the tympani hits, you will get distortion. If you can live with that, then you don't need much power. :) When I had my MC7200 playing classical, the meter needles could bounce between 0.1W and 150W every couple seconds without ever touching the volume knob.

Also, I already said that to measure real power, you need voltage AND current. Some meters base it only on voltage which is correct if the impedance is constant but as we all know, speaker impedance is all over the map.

The McIntosh meters from the 1980s up to the most recent amplifiers are true power meters and are accurate if their calibration isn't out of whack. They may be off a few Watts but that isn't a big deal. However, the recent integrateds like the 6500 and 6300 have volt meters and not power meters. This was probably done to lower costs and will not be very accurate unless your speakers are a relatively flat 4 ohm load.

You really need to watch an amp with meters one day. You would find it very instructive - I sure did and often I wish I still had a McIntosh with big blue meters.

Arthur

Someone years ago posted pictures of a custom Bottlehead Foreplay preamp they had built with voltmeters, walnut case (with jacks on the back) and a kind of burnished copper top plate. I just tried digging through the archives but no luck. I thought it looked sooooo cool.

Arthur, nice answer.
To expand on that, when listening at 2 watts, if you want to double your perceived volume, you need to increase volume by approximately 10db. Each 3db required a doubling of power. That translates into about 18-20 watts continuous to just double from "mellow" to more. That's why we need 100/200/300 watt amps just to handle the dynamic peaks which can be much louder...

Helio, When my system is playing and I only ever see 4 watts on the meter with the loudest peak, I can figure that the amp is using more watts, than the meter is reading, but how much more? Assuming that the meter is correct - a big assumption I gather - I know I would need a more powerful amp than 4 watts.
I know that this is one of those impossible to answer questions when you figure in the variables ; probably impedances, speaker type etc. I can be pretty well assured though a 400 watt amp can handle the peaks, but what about 100 watt or 40 watt? Any ideas of how much headroom is needed?
Bob

Hi Bob, VU meters usually have averaged response and don't show the peaks. LED-style units exist that do show the peaks; having watched a lot of these it appears that your typical peak is 3-6 db above the reading on an averaging meter, IMMV (definitely not cast in concrete)

6 db is 4x amplifier power, in your case 16 watts, to be safe in this case I would allow for at least double that.

Since our ears operate logarithmically, that's not a huge increase and is the root of the term 'gold plated decibels'. This is why speaker efficiency is such a big deal.