max power for full volume?

[bob_v5]

Hi.
Not really sure where to post this, so ill say it here....
To drive speakers at there full rated power without destroying them you need an amp rated at more than the power of the speakers to avoid clipping.
The max power output of the amp will also destroy the speakers.
Generaly I play my music at a sensible volume, but when I'm playing it at a stupid volume, how do I know how high I can turn it before I damage something? (I dont mean my ears! I know the risks and thats why I normaly keep it sensible!)
As a side note the amp I'm using at the moment runs out of steam way before the speakers, even though the power meter on the front says smoke should be coming from my speakers.... bringing back the cliping problem, even though the amp is rated for 80w into 8ohms. That means 40w into 16ohms right? the speakers are only 20w

[soongsc]

Well, if you really want to calculate it:
1. determine signal source maximum output level (normally in the manual)
2. determine preamp gain and volume position versus gain curve. This varies depending on volume control design topology. But can be measured.
3. determine power amp gain and sensitivity and full power input voltage (normally in the manual).
4. now the maximum output voltage of the system can be calculated. also for various volume control positions.

5. based on speaker impedance and output voltage, calculate the power going through the speaker.

[adason]

forget all those calculations
they will not lead to anything reasonable
you have to understand the nature of the music
its very dynamic, so will be power
there is huge difference between rms and peak
20 watts rated speaker you say?
is it rms of music program? is it constant or 10 ms?
if it is 20 watts contant, it can handle 100 watts music most likely
the same applies for amplifier
80 watts amplifier can be clipping while it is only giving 5 watts on average, if the music is so dynamic
forget all the calculations and use common sense
listen, if it is too distorted, turn the volume down
(still its ok to blow something from time to time)
ed

[fpara]

If the tone controls are flat, most amps should hold up to very near the knob's maximum.

[AndrewT]

This is best but simple to understand explanation I have seen.
http://www.prosoundweb.com/studyhall....php?pdf=watts

There are numerous other study hall articles that are worth reading.

[adason]

If the tone controls are flat, most amps should hold up to very near the knob's maximum.

I have slightly different experience, fpara. Number of amplifiers I used over the years with onboard indicators reached clipping level usualy around 1/3 to 1/2 the volume pot, with tone control bypassed. I think it all depends on the input signal. In good old days the line level signal was anywhere between 300-800 mVolts. These days 1-2 Volts on the cd player output is normal. Therefore lower volume setting will lead to clipping.

Thats a nice and simple article, AndrewT.

ed

[AndrewT]

If CD is properly recorded then the average level will be around 10db to 20db below 0dbfs (=2Vac to 2.3Vac)
This equates to 200mVac to 700mVac.
But much of the CD rubbish that is inflicted on us is only 3db to 6db below clipping (0dbfs).

The signals coming from analogue and digital are effectively the same when done correctly.

[BlueWizard]

I think it is, at the same time, easier and more complex than you are making it out to be. Keep in mind if you are putting a single pure sinewave tone to it, it is easy to make the determination you want to make, but that's not a very realistic situation. In reality, musical peaks are constantly trying to jump to infinity and are not reaching it due to limitations on the amp.

As a general rule, I would say that you are wasting your time, your speakers, and your amp if you ever go above about 60% turn of the volume control. That would be about the 1 or 2 o'clock position on the volume control. Any more than that, and you are sorely lacking in head room and good sense.

Also consider that power relative to perceived volume is not linear. Every time you tweak the volume up just a small but noticeable amount, you are doubling the power consumed. So, let's work this out. Let's say we are cruising along at 1 watt and tweak the volume control up one small nudge, now we are at 2 watts, then 4 watts, then 8 watts, 16, 32, 64, 128, 256 watts...etc....

As a side note, I tested my amp and speakers at 60% turn of the volume control, which was painfully loud. At that level, the average power was only 2 to 3 watts, yet transients peaks were way beyond the voltage limit of the amp.

As an example, let's say we are pushing the limits by cruising along at 128 watts with our 100 watt speakers, and we nudge the volume control up one more tiny amount...BOOM!...256 watts and fried speakers. Power is a dangerous thing because it sneaks up on you.

If you put an oscilloscope on your speaker's output and play at a range of realistic but loud levels, you will find that your amp is almost always clipping the very high transient peaks. Generally this passes by unnoticed and with no damage. It is when you push it higher and higher until the average power reaches outrageous levels, and in the process create a very much unwanted DC offset voltage that problems occur.

For what it's worth.

Steve/bluewizard