amplifier DB meters

Bob,

Music is dynamic. An amplifier meter is only indicative of clipping/power. Power is a function of load (resistance/reactance) and load is a function of frequency. More expensive amplifiers will have a high speed soft clipping circuit to protect speakers (often with a clipping warning light) - this is all that is really necessary to assure good sound. A clipping meter is only a ball park device.

If an amplifier does not have meters can you hook one up or use a test meter to find out how many watts you are using?

You can - but measuring power is quite complex - very few test meters can measure this correctly. A device to measure power accurately would probably cost more than the amplifiers. Yokogawa Power Meters

Most power meters (common in the 70's) are just estimates of power - they measure voltage (easy to do) assume an RMS conversion (using a a fixed load factor and sinusoid waveform type) such as 8 Ohms....all very inaccurate and only indicative). You need to measure current very accurately as well as voltage to get power.

They are so inaccurate as to be useless. Some do look cool though!

Hi, So most of the meters are inaccurate? Though they give a reasonable indication of power, is that correct? As I originally stated I use mine for tuning my system, I can see more or less power being used when setting crossover, EQ or listening level. Yes I can hear the changes but seeing them is also a good confirmation and it is repeatable as I freq write notes. Also I guess it is kind of fun to watch them, I will admit to that!
If most of us "only listen at 1 or 2 watts" why such big amps? I know that is true with myself, but how do you know you are only using 1 or 2 watts when you really dont know that without a meter? Arthur says that you need peak power which is understandable but how much more power do you need if you are only using those 1 to 2 watts.? The reason I ask is my subwoofer amps at the most use less the 4 watts or so on the loudest bass I have seen and indeed 90 percent of the time much less than 1 watt as indicated on the meters, with my 200 watt per channel amp, can I use a much less powerful amp?
Bob

We set the meters on our amps for full power full scale and 1 watt full scale. However they are calibrated for an 8 ohm non-inductive load. Any variance in the load will throw the reading off, sometimes quite a bit. They are handy for relative power though.

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