Relationship of Power and Sound

[BlueWizard]

Well, I got in trouble for duplicate posts, so I've substantially reduced the post in the Amps Forum, and am now reposting the information that was originally found in the 'On the Nature of Sound and Power' thread which was deleted.

Though, I really can't blame the Moderators for doing their jobs.

However, the threads are no longer even remotely the same, and therefore are in no way duplicates.

I know both this posts and the one to follow are long winded and probably boring to most, but hopefully the information can be of some help to some, both in understanding and in using their Stereo equipment.

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In recent discussions here in this forum, we touched on the nature of power as it applies to both Amps and Speakers, and how that power relates to volume or perceived loudness.

So, I decide to do a little experiment. I wondered just what was the average power at 50% turn of the volume control on my amp? I have reasonably efficient speakers so 50%, or 5 on a marked scale of 10, is pretty loud.

Even when I was throwing big drunken parties I rare to never turned the volume up more that about 6 to 6.5 on a scale of 10 with 10 being a full, to the limit, turn of the Volume control. Well, here is the part that will amaze you, at 50% turn of the Volume Control, my volt meter was averaging between 1 volt and 2 volts with occasional peaks to 3 volts. Trust me that was loud.

So, let's work out the power -

P = Power measured in WATTS
E = Electricity measured in VOLT
R = Resistance or impedance in OHMS
I = Current measured in AMPS

So, we know Voltage and Resistance, and we can calculate Power using this formula -

P = (E^2)/R

where (E^2) is Voltage Squared.

example: 2 volts
P = (2^2)/8 P = (4)/8 P = 0.5 watts

Residual average signal of 1 volt = 0.125 watts
Average low level surges of 2 volts = 0.50 watts
Peak average surges of 3 volts = 1.125 watts

Most of the time, it stayed between 1 and 2 volts

Now, I turned the Volume up to 60% that was about as loud as I could stand. Were as before, the signal was averaging between 1 and 2 volts, it was now more like between 2 and 3 volts with peaks up to 4 volts.

2 v into 8 ohms = 0.50 watts
3 v into 8 ohms = 1.125 watts
4 v into 8 ohms = 2 watts

I made a couple of videos of the experiment, I will provide you with links to them. The videos are in Quicktime .MOV format and are about 11Mb each.

The first video you can see the Analog Voltmeter along side my Oscilloscope. The average signals observed on the Scope are consistent with the reading on the Volt Meter Dial.

Warning on these Videos, turn the video player volume control to half or less, or it is going to be obnoxiously loud.

In the first video,
- the volume is set to 5 on a marked scale of 10, which is with the volume indicator pointing straight up.
- the Scope is set to 1 volt per division of the dial, the division can be clearly seen.
- Music = CREAM - Disraeli Gears - "Tales of Brave Ulysses" (Lots of nice surges.)
- The Volt Meter is on the 10 volt scale which is near the bottom just above the red arc. It is marked off in even number increments, so the scale looks like this -

0.....2.....4.....6.....8.....10

http://www.homestead.com/BlueMoonMar...iv_5of10-1.mov

Full scale on the Scope at 1v/div is 4 volts (center = 0, top = 4v). Notice that peaks and surges do jump off the Scope. Even if we double or triple full scale, we are still only at 8 to 12 volts, or respectively, 8 watts and 18 watts.

The second Video,
- the volume is set to 6 on a scale of 10.
- the Scope is set to 2v/div or 8 volts full scale (center to top)
- the volt meter is still set to the 10 volt scale.
- Music = CREAM - Disraeli Gears - "Tales of Brave Ulysses"

http://http://www.homestead.com/Blue...iv_6of10-3.mov

With the Scope set to 2v/div, we can see the peaks a lot better. We do occasionally get off-the-scale or 'over- the-top' readings. If we do as we did before and assume 2 to 3 times viewed full scale peaks, we have peak in the range of 16 to 24 volts.

Converted to power, that is -

16 volts into 8 ohms = 32 watts
24 volts into 8 ohms = 72 watts ( which is unlikely since I only have a 50 watt Amp, meaning a 20 volt max.)

So why do we need all this power, if we are only cruising along at 0.125 watts to 2 watts????

Power isn't there to make your stereo loud. One Watt is enough to make your speakers, if not painfully loud, then annoyingly loud. It is there to make it clear and clean, and to make sure you don't run out of 'head room'.

In this example, with my ceiling of only 20 volts, it is likely there was some clipping of the signal. That is, the music wanted to jump to a 24 volt surge, but my amp is limited to 20 volts. But keep in mind that volume was at 60 percent.

What we ideally want in an amp is unlimited headroom. We want the sharp high peaks in the signal to never reach the ceiling; to be able to reach out into infinity and beyond. But sadly, electronics do have limits.

Here is a range of power supply voltages and the power they are capable of producing.

20 volts = 50 watts
30 volts = 112.5 watts
40 volts = 200 watts
50 volts = 312.5 watts

At high volume, very narrow but high power peaks can easily reach any of these voltage levels; the thump of a bass or the snap of a snare. These power peaks are of such short duration, that you are very unlikely to consciously notice any distortion in them. They come and go so quickly, and the music is running ever onward, that we simply don't notice. But unconsciously, or subconsciously, this distortion, this constant bumping up against an invisible ceiling, does reduce our listening enjoyment.

One last point before I leave you to ponder this information, if I can get my hands on a Sound Pressure Level meter, I'll take some readings and well see just how loud 50% and 60% volume are.

Thought? Ideas? Question?

Steve/BlueWizard

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PS: There is a slim chance my brother might be able to get me an SPL Meter so I can test my speakers at the Volume settings used in this test. Regardless of the measured numbers, trust me, it was loud.

[BlueWizard]

Short version for metropolis -

At 60% turn of the volume control, my amp is averaging 1 to 2 watts of power to achieve a VERY substantial Volume.


Regarding Speaker Efficiency or Sensitivity -

As penumbra points out, a speaker with a sensitivity of 90 db puts out twice the acoustical power of a speaker with 87 db sensitivity. But, that doesn't necessarily mean it is twice as loud. Power and volume are not linear, they don't track each other equally or proportionally. The 90 db speaker is going to be slightly louder than the 87 db speaker.

In my example, you will notice that 20 volts will give you 50 watts, but 40 volts give you 200 watts. Double the Voltage equals FOUR TIMES the Power. Again, this is just to illustrate that signal strength, which we perceive as loudness, is not the same as power.

Speaker sensitivity is given so that you can match speakers. For example, if you have speakers that are 93 db sensitivity in the BACK, and roughly equal sized speakers that are 87 db sensitivity in the FRONT, you have mismatched speakers. The back speakers are louder than the front speakers.

To best match the speaker in a front/rear or surround sound system, you want the back speakers equal to or slightly less in sensitivity than the front. You want to hear the music and sound in the front speaker, with the back speaker re-enforcing the front sound.

As another example, look at some of the mid-prices 5.1 surround sound systems out there. They have nice big tower speakers in front, and compact bookshelf in back. Again the principle is that you want the apparent source of the sound you hear to come from the front channels with the rear channel simply re-enforcing. If you check the sensitivity on such systems, you will also see that the rear channel speakers are equal to or less than the front.

So, in short, we use sensitivity to match speakers and get a general sense of their relative efficiency. Personally, I like efficient speakers. A good set of 3-way bass reflex (ported) speakers are going to appeal to me on general principles far more than a tight closed cabinet.

Plus, I'm what you would call 'old school'. The modern tower and mini-bookshelf speakers of today don't impress me. My current speakers are 17.5"w x 13"d x 26"h, and weight 50 pounds each; 12" bass, 3x9"; mid horn, 3x3" high horn...old school.

Keep in mind that I'm only using a 50 watt amp, so I need all the efficiency I can get. If I had a 100 watt amp, I wouldn't be so concerned about it.

Also, efficiency and sensitivity are not a mark of the quality of the sound you will hear. Many sealed cabinet speakers sound great, you just need to pump a little more power into them. But that doesn't matter unless you are comparing them side-by-side. Normally, you just crank it up until it sounds the way you like it, and you are good to go.


Resistance and Impedance -

This is very tricky, and I will try to avoid the technicalities. Resistance is just that pure resistance. Impedance comes into play whenever, inductance (coils) or capacitors are in the circuit. When coils (as in voice coil) or capacitors are in a circuit, the voltage and current are slightly out of phase. To you, the typical user, that means nothing. To a technical person, it just means you have to do a few extra calculations to determine the power at any given point in time.

For most of us, even though it is not technically true, we can just assume speaker impedance acts like pure resistance.

Now, it is true as penumbra says, that a speakers impedance varies with frequency, but for a vast majority of speakers, we don't need to consider this. Normally, a speaker's rated impedance is it's minimum impedance. In fact, with a vast majority of speakers, if you put an ohm meter on them, you will find that the DC resistance is the rated impedance. Again, the rated impedance usually represent the lowest a speaker can possible go because that rating is the internal resistance of the wire making up the voice coil.

Now with a very few speakers, it might be possible for the impedance to technically go below the rated impedance, but that will be at frequencies that are outside the range that they are likely to encounter. So, while it may be technically possible, it is unlikely in a practical sense.

Now, the above applies mostly to raw speakers. This gets even more complicated when you have multi-frequency speaker systems (bass, midrange, high freq) with complex crossover networks. Crossover networks are nothing but a big collection of coils and capacitors with a few small resistors thrown in. Now, to some extent, all bets are off. This collection of components can cause substantial shifts in a built-cabinet speaker's impedance. But, on general principle, I still stand by what I said earlier.

Here is a link to a relatively straight forward 3-way bass reflex speaker design. Click on the link marked "Crossover Design", then on the next screen, click on the drawing of the 'Crossover Schematic';. The things marked 'uF' are capacitors, 'mH' are coils, and items marked with the Greek Omega symbol are resistors.

http://www.partsexpress.com/projects...blue/index.htm

All these components, plus the various frequency range speakers fading in an out, could cause some odd impedance fluctuations, but over all, it is unlikely to fall below its rated impedance.

To see a complete list of tested projects by this designer, look here -

http://www.partsexpress.com/projects.../homeaudio.cfm

Many of the speaker designs at this website have frequency response and impedance-across-frequency graphs that can help you get an idea of how impedance can shift and fluctuate. Note that even though the impedance is all over the place, frequency response remains relatively flat.

I know I rambled quite a bit, but hopefully you can pick out some useful bit and pieces there. Plus, I'm willing to be contradicted.

Steve/BlueWizard

[Badger0-0]

That's all well and good mate, I understand the theory because of my ham days
I agree with all you say

But I have to wonder what the point of the post is

I'm not being nasty, just confused as to what you're getting at.

[BlueWizard]

Well, I'll try and keep this short. (HA! Like that's ever happened before.)

I realize I can get a bit long winded, and that probably bores a lot of people who want quick concise answers, but this post is really a combination of curiosity and information.

People are always writing to this group and asking 'I've got this amp what speakers will match it?' or 'I've got these speakers, what amp should I get?'. And, of course, the answer is, get any amp or speakers you like in a compatible power range and a comfortable price range.

Though I admit certain combinations of Amps, Speakers, Rooms, and personal preference appeal to some people more than others. That is, while on general principle, any amp will do, some people do have, and are able to hear, combinations that sound pleasing to them.

But, in the course of discussing which Amp, which speakers, the subject of overpowering the amp relative to the speakers or underpowering it invariably comes up. Example; 100 watt speakers on a 50 watt amp, on a 100 watt amp, or on a 200 watt amp; which is safe, which is dangerous?

Next, this invariably brings up the subject of whether or not Underpowered Amps are more dangerous to your speakers than overpowered amps. The answer is 'sort of', and my little experiment demonstrates both how underpowered amps are dangerous and how they are not dangerous.

I'm perfectly happy with my 50 watt amp and have never blown a speaker.

So, I wondered, exactly what is the average, and therefore sustained, an therefore most dangerous, power of an amp at high volume? So, I decided to test it. Believe it or not, and you can watch the videos, the range of average power is only 0.5 watts to a rare 2 watts. I assumed people would find that amazingly and unbelievably small. Trust me, my stereo at 50% and 60% was loud.

So, really this is just an accumulation of curiosity arising from a variety of subjects that have come up in a variety of posts.

But, I think, not only did it satisfy my curiousity, it pointed out several factor that I assumed people were not aware of. Like, -

Why do I want a lot of Power?

What do I lose with low power if the loudness is the same?

What is speaker efficiency and sensitivity all about?

We all see sensitivity specs but do we know how to regard them? Do we know how to apply them? Do we know what they mean?

Impedance, as you know from being Ham operator, is very complex, too complex for the average user, but it is still important. I see people slapping speakers on to amplifiers right and left with no regard for the combined impedance. If your amp and speakers survive, fine, but I though it would be nice for people to have a basic working knowledge of this, and maybe a few formulas to help them.

Next, what is the relationship between Loudness and Power? It's not what a basic user might think.

So, from my curiosity, and from my little test, comes a whole lot of relevant information for any one working with stereo equipment. To some users this is all boring old-hat, to others it is completely over their head, but it touches on a variety of subjects that come up here often. Knowledge is power, and hopefully everyone got some small piece of knowledge out of it.

So, in the short view -

"At 60% turn of the volume control, my amp is averaging 1 to 2 watts of power to achieve a VERY substantial Volume."

In the long view -

"Knowledge is power." ...and power is nice.

So... ...the point... ...a blend of satisfied curiosity and a lot of information; hopefully, helpful information.

Steve/BlueWizard

[Dr Force]

Blue

That is over my head fella but kinda makes sense even though I now have a headache

[Badger0-0]

Originally Posted by BlueWizard

Well, I'll try and keep this short. (HA! Like that's ever happened before.)

I realize I can get a bit long winded, and that probably bores a lot of people who want quick concise answers, but this post is really a combination of curiosity and information.

People are always writing to this group and asking 'I've got this amp what speakers will match it?' or 'I've got these speakers, what amp should I get?'. And, of course, the answer is, get any amp or speakers you like in a compatible power range and a comfortable price range.

Though I admit certain combinations of Amps, Speakers, Rooms, and personal preference appeal to some people more than others. That is, while on general principle, any amp will do, some people do have, and are able to hear, combinations that sound pleasing to them.

But, in the course of discussing which Amp, which speakers, the subject of overpowering the amp relative to the speakers or underpowering it invariably comes up. Example; 100 watt speakers on a 50 watt amp, on a 100 watt amp, or on a 200 watt amp; which is safe, which is dangerous?

Next, this invariably brings up the subject of whether or not Underpowered Amps are more dangerous to your speakers than overpowered amps. The answer is 'sort of', and my little experiment demonstrates both how underpowered amps are dangerous and how they are not dangerous.

I'm perfectly happy with my 50 watt amp and have never blown a speaker.

So, I wondered, exactly what is the average, and therefore sustained, an therefore most dangerous, power of an amp at high volume? So, I decided to test it. Believe it or not, and you can watch the videos, the range of average power is only 0.5 watts to a rare 2 watts. I assumed people would find that amazingly and unbelievably small. Trust me, my stereo at 50% and 60% was loud.

So, really this is just an accumulation of curiosity arising from a variety of subjects that have come up in a variety of posts.

But, I think, not only did it satisfy my curiousity, it pointed out several factor that I assumed people were not aware of. Like, -

Why do I want a lot of Power?

What do I lose with low power if the loudness is the same?

What is speaker efficiency and sensitivity all about?

We all see sensitivity specs but do we know how to regard them? Do we know how to apply them? Do we know what they mean?

Impedance, as you know from being Ham operator, is very complex, too complex for the average user, but it is still important. I see people slapping speakers on to amplifiers right and left with no regard for the combined impedance. If your amp and speakers survive, fine, but I though it would be nice for people to have a basic working knowledge of this, and maybe a few formulas to help them.

Next, what is the relationship between Loudness and Power? It's not what a basic user might think.

So, from my curiosity, and from my little test, comes a whole lot of relevant information for any one working with stereo equipment. To some users this is all boring old-hat, to others it is completely over their head, but it touches on a variety of subjects that come up here often. Knowledge is power, and hopefully everyone got some small piece of knowledge out of it.

So, in the short view -

"At 60% turn of the volume control, my amp is averaging 1 to 2 watts of power to achieve a VERY substantial Volume."

In the long view -

"Knowledge is power." ...and power is nice.

So... ...the point... ...a blend of satisfied curiosity and a lot of information; hopefully, helpful information.

Steve/BlueWizard

I see

Well, whilst I agree with your findings, I have to say you have a long winded way of saying it

Seeing as speakers give around 85+ dB with one watt at a metre, it should be obvious, but it's not.

It makes you wonder why you need 100W per channel, but you summed it up with the transients thing

I only have one suggestion mate.

Severely condense your posts.

Whilst this is a fairly technical site, it's not that technical and plain speaking rules.

You have good stuff to say, just not the right way of saying it, IMO.

No offence meant

[Helicon]

Originally Posted by BlueWizard

People are always writing to this group and asking 'I've got this amp what speakers will match it?' or 'I've got these speakers, what amp should I get?'. And, of course, the answer is, get any amp or speakers you like in a compatible power range and a comfortable price range.

The problem with this statement is that there are amps out there like the Sugden A21. At 22 wpc, most would instantly dismiss it claiming lack of power, but in reality, this fantastic sounding amp will sound just as loud and powerful as most other 50-100wpc amps from other manufacturers, and it'll control speakers in the £1,000/2,000 price point where an equivalently powerful Pioneer or something wouldn't stand a cat in hells chance. Power isn't the be all and end all as there are exceptions to the rules, like the Sugden.

Though I admit certain combinations of Amps, Speakers, Rooms, and personal preference appeal to some people more than others. That is, while on general principle, any amp will do, some people do have, and are able to hear, combinations that sound pleasing to them.[/quote]Whilst i agree, it comes back to previously discussed threads about whether amplifier make any difference at all. The 'technical' people will say all amps sound the same, but during demonstration, they're obviously not. "Any amp" won't do, and there are way too many people using amplification that just isn't getting the best from their speakers, resulting in a lacklustre, dull sound. But to most, that sounds good - inoffensive and easy on the ear. And when they do go to listen to some real hi-fi, they dismiss what they hear complaining that it's too bright/forward/lacks bass etc.

This is particularly true of users of AV amps/receivers. Compare them to an equivalently priced hi-fi amp, and the AV amp will be blown away. Even to a hi-fi amp half the price, the AV amp doesn't stand much of a chance. Some of these amps may quote 100/200wpc, but they just haven't got the real balls and control needed to drive a £1,000/2,000 hi-fi speaker, regardless of the AV amps cost.

[BlueWizard]

Helicon, believe it or not, I agree with just about everything you said; like 98.5%.

As far as 'any amp will do', that's not quite what I said -

"...get any amp or speakers you like in a compatible power range and a comfortable price range.

Infinite money and good sense, will get you near infinite quality. Sadly very few of us have infinite money, so we settle for less. But to match an amplifier and speaker 'any amp will do', for the most part; that is in a compatible power range and a comfortable price range. With the exception of a few amps, any reputable amp in a consistent price range with your speakers is going to be fine.

By that I mean, ridiculous extremes are just that - ridiculous. You don't put $100 speakers on a $5,000 amp, and you don't put a $100 amp on $5,000 speakers. A common sense balance plus personal appeal are really all the average user needs.

I do agree with your comments about AV Amps; something just doesn't ring true. I posted a question in the Amps forum, asking if perhaps AV amps multiplexed the output. That is, you only have two real amp, the other channels are just the same two amps with redirect input and output creating the appearance of 5 or 7 channels. Well, several people shot that idea down and said the manufacturer's denied that possibility.

But still... Recently, my trusty tried-and-true Pioneer SA-7500 II (45 watts per channel RMS, two channels) grew weak in one channel and I decided look for a replacement. Stereo amps and multi-channel surround sound amps were roughly the same price, that doesn't quite seem to add up. How can I get 5 or 7 100-watt channels for roughly the same prices as two 50 watt channels? There has to be a sacrifice somewhere.

So, I purchased an Onkyo TX-8011 Stereo AM/FM Reciever with 50 watts per channel AND a phono input. Most of my music is in vinyl so I needed a phono input. I'm still using the 3-way bass reflex speakers that I built in 1986. They still sound good.

So, to my original statement any reasonable amp really will do for the typical, even typical high end user. I think most people look for a respectable brand name, a balance of cost and desirable features, temper it all with personal rather than technical preferences, and finally choose what they choose. I think it is only the exceptional and very experienced user who can tell the difference between $500 Amp-A and $500 Amp-B when played with $500 speakers-C.

Oddly, there is a certain weird psychological factor that will actually make us choose bad equipment over good on a quick casual listen. For example, many speaker manufacturers, usually well below the quality we see discussed here, will intentionally build a bass resonance into their speakers. By 'bass resonance I mean the heavy droning one-note bass you find in cheap speakers. On a quick listen, people are impressed by the bass and think these must be some 'kicking' speakers.

Also, harmonic distortion, within reason, can make the music sound louder and more full. Again, psychologically, this appeals to us; or to some people. However, in both cases, if you are a discerning listener, these 'distortions' become very annoying very quickly. What sounded loud, heavy, and full in the store, is like fingernails scraping on a blackboard after a few hours at home.

Another psychological factor, is simply loudness. If you are testing two speakers side-by-side, and you are not able to overrule your psychological impulses, you will probably pick the louder speaker as the better one, regardless of any other factors.

Buying stereo equipment has a lot more to do with general human, as well as personal, psychology than the average person understands. Very discerning and very experienced users, can, as I said, to a limited extent, fight back false psychological impulses, and make a truly informed decision. But for far more of us, "THE Best Choice" is really OUR best choice; we don't necessarily choose what is right, we choose what pleases us, and as long as we choose quality reputable equipment, everything is OK. And, why shouldn't we please ourselves. I don't have the greatest stereo equipment in the world, but what I do have generally pleases me, so I'm satisfied, and really, in the end, that is the ultimate test.

Here I am, rambling on too long again. On general principle, I do agree with everything you said.

Steve/BlueWizard