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How many watts??

If I have a 80 watt stereo amp and I normally listen at quarter volume and never play at levels higher than this. Do I really need 80 watts could I use a 15 watt amp at half volume?

My next question if I have speakers that my mfg states needs min 50 watts to really make them sound good with my current amp rated at 80 watts but played at qtr volume does that mean I am not really getting the best from these speakers. If I play at half volume this is too loud, do I need a bigger room. Sorry if I did not explain clearly enough.


ecpninja
ajcrocker1
31 posts
 
Your volume control is most likely logarithmic so you cannot use that as an indicator.  Go to Home Depot, Lowe’s or Amazon.  Order a volt meter.  Set the meter to AC voltage and measure the voltage across the speaker terminals while playing.  This will tell you how many volts you are using.  Amps or current drive is volts divide by speaker nominal resistance.  Power is amps time volts.  Most modern music is fairly compressed so 6dBs or a gain of 2 and 9dB or a gain of 2.8 will do.  A gain of 10 is 20dB which is way more than you will need.
russbutton's avatar
russbutton
420 posts
 
The volume knob is just a gain attenuator in the preamp section of your amp and has NOTHING to do with understanding how much power your amp is actually putting out.   You can't think that it's 1/4 turned, so you're using 20 watts.    Your amp would have to have metering to show you how much power is being used, which is why many amps back in the 70s and 80s had them.

It sounds like you've already got a good match between the power in your amp, the demands of your loudspeakers and how loud you care to listen.  Relax.  You're already set.
limomangus's avatar
limomangus
1,292 posts
 
Back in the late 60s ,100 watts a channel was unheard of then the 70s hit and the wattage started to increase...by 1975....if your reciever didn't put out 100 wpc...you received sucked...then it was 100-150-200 you were told you need more power 300 wpc ....now its 800 wpc to 1,000 Please stop the crap....tubes were always like 8 wpc to 15.....now you see 100wpc tube amps....Stop it ...its nuts and crazy......I gave polk lsim707 they say you need 300 wpc to achieve the sound you need ,I  SAY baloney....I'm running them with a caryin 55 it puts out 30 wpc and it sounds great..
.I can't knock the walls down but I live in a condo village....and it plays loud enough for me....
ghdprentice
6,821 posts
 
It’s a balance between speaker efficiency (less efficient, easier to make accurate) and power requirements. More power generally allows faster rise to transients. The right balance depends on you personal tastes and listening habits. I have 140 watt per channel tube amp and my speaker sensitivity is 90db. I listen at ~70 db… I believe Audio Research is working on a REF 250, I’ll likely buy one. It will increase the dynamics of the system at all levels of play.
liquidsound's avatar
Ag insider logo xs@2x
liquidsound
152 posts
 
Here's a decent guideline that I've used when calculating power needed/used.  See the information below...  Pay attention to the fact that most speakers rate their db-output at 1-meter and your listening position may be 3X that.  You have to consider the drop in db from that measured position as well as how much amplifier head-room you need for your personal listening experiences.  I also use a db-meter at my listening position and add 7db to the reading to get a good idea as to how much power I'm really using.  For example, my speakers are 9-ft from the listening position.  At 94db at 1-meter (assuming my speakers' rating is correct) I lose ~10db at the listening position.  Adding 3db then since there are 2-speakers in the room I end up with -7db at the listening position.  So, starting at ~ 87db (94db - 7db) at the listening position, at 1-watt of power, I need 16-watts of power for 99db sound at the listening position.  I have a 10WPC solid-state amp and an 18WPC SET amp and most of my listening is in the 87db - 93db range at my listening position.  So I have ~ 3db head-room with the 10WPC amp and about 6db head-room with the 18WPC amp.  My 10-watt amp has only 1 output device/channel and is the most detailed and articulate solid-state amp I've ever heard on my system.  The more output devices, the greater chance the subtle differences between them may cause subtle but audible differences in the music.  High-end/high-quality mfg.'s (with correspondingly high $$$ cost) painstakingly match their output components to reduce this, however it's not perfect.  This is one reason I've chosen efficient speakers and lower-powered amplifiers.  

I hope this information is helpful to you.  

Good Luck in making whatever corrections you need to !  

Technical background to our dynamic range/power claims.

This section is slightly technical and may take you a few minutes to read. We would like to take you through to the basic technical elements that make up a hi-fi system and explain how they go together.

Loudspeaker sensitivity

Loudspeaker sensitivity is a measure of how much sound a loudspeaker will give for 1 watt at 1 metre. It is critical to note that the basic measure of sensitivity is at 1 metre and not at a typical listening distance of about 10 feet or 3½ metres.

Sound attenuates (reduces) over distance at the rate of 6dB with each doubling of the distance. At 2 metres distance from the loudspeaker its perceived sensitivity is reduced by 6dB. At a normal listening distance of about 10 or 11 feet from the loudspeaker its perceived sensitivity will be reduced by approximately 10dB.

This is the factual basis for our claims about how much power a system would need for a decent hi-fi dynamic range. We reiterate that this is not made up or marketing hype, it is scientific fact.

Loudspeaker sensitivity – is it real?

Regrettably, most loudspeaker sensitivity ratings are not particularly accurate and are regularly overstated by 2 or 3dB. We have seen several examples of respected manufacturers’ products specifications overstating their sensitivity by 5dB or more.

This does not sound like a big deal, but it has tremendous implications for the power required by the loudspeaker to deliver proper dynamic range.

Amplifier power – confusion reigns.

This is the source of much misunderstanding. Amplifier power is specified in watts, which are a measure of heating power. They have no apparent relationship to what we hear, as they are a linear measure. Loudspeakers (and our ears) perceive things in dB (decibel) steps. These are based on a logarithmic relationship.

This is the fundamental mismatch between what your ears perceive and how amplifiers are specified. The solution to the problem is to recalibrate watts into dB steps. 

As you can see, as soon as you calibrate amplifier power in dB watts, you get a dramatically different view of what amplifier power really means.

First off, you can see that what looks like a large increase in amplifier power, for example from 50 watts to 100 watts, only gives an increase of 3dB.

Things get really interesting as when you get to higher powers. You start needing vast amounts of power for each dB step. For example, only 1dB (remember 1dB is the smallest change in sound pressure level that the human ear can perceive UNDER IDEAL LISTENING CONDITIONS) is the difference between 400 watts and 500 watts. If you really wanted to hear a difference above 400 watts you’d probably need to go to 800 watts (3dB) which should be audible.

You can see why amplifier manufacturers want to sweep these figures under the nearest carpet; they make most of their claims look ridiculous as they predict that most loudspeaker/amplifier combinations will have only limited dynamic range.

How much dynamic range do I need?

Some years ago John Atkinson (current editor of the Stereophile) made some measurements of live music using accurate equipment. He recorded 109dB peaks (brass and percussion) and the quietest was 63dB (solo violin) a variation of 46dB from the quietest to the loudest moments – a huge dynamic range.

The question is what sort of dynamic range a really good hi-fi system should have.

In our opinion, an ability to produce unclipped peaks of 105dB is the minimum starting point for a really good hi-fi system. You are welcome to debate different figures, but that is our basic position.

If you listen to small scale chamber music or usually listen at quiet levels, you will not need the peak capacity we deem necessary. But if you are trying to recreate the listening experience at reasonable levels, 105dB peak is not overly generous.

How do you put all this together.

Assuming that you have accepted the scientific facts this is how you determine what your system can produce.

1.       Take your loudspeaker sensitivity (better yet check back to a technical review to find out what its sensitivity really is). Deduct around 10dB for the SPL (sound pressure level) attenuation over distance. And then add back 3dB because there are two loudspeakers in the room.

Now you have arrived at the practical, real world, in-room sensitivity of your loudspeaker system.

2.       Decide what peak level you want to achieve. We think 105dB is about right. Some people think 110dB is more appropriate. It’s up to you.

3.       Deduct the result of 1 above from your decision about 2. This is how much amplifier power you require in dB watts

General overview.

None of this is intended as criticism of amplifier or loudspeaker manufacturers. You could regard it as a criticism of magazines and shops for not bringing it to your attention. We have been banging on about this for about ten years and many people have reacted adversely because they believed it was just marketing hype. This is not marketing hype, this is scientific fact. Many people do not like the result of a scientific analysis of their equipment but that does not alter the scientific facts.

People have objected to our position claiming that their system sounds great. It might. However, you can’t escape the fact that, if they have a low powered amplifier and relatively insensitive loudspeakers, the system must be clipping, distorting and limiting regularly, which must dominate the listening experience. Maybe the listeners like distortion clipping. Well, each to his own and good luck to them. If you want your hi-fi system to produce as close an approximation to the real live performance as you can get, then you must ensure, for a start, that your amplifier is not clipping.


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