Usable amplifier power

[TankTop5]

Just trying to wrap my brain around amplifier power and understand it in a meaningful way for myself. I have been in the auto industry for half my life, a 200 horsepower car will only spend 1% of its life at 200hp and a 400hp car will only spend 1% of its life at 400hp but a 400hp car can easily access 200hp any time it wants. Would it be reasonable to think amplifiers are similar? If I have a 50 watt amplifier actually getting 50 watts is a bit optimistic but a 200 watt amplifier can easily jump between 1 watt and 50 watts easily and quickly and it can control 50 watts easily, I think that’s called headroom? Is this a good analogy?


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[lovinthehd]

Try these various articles on amp power and requirements here at AH. https://duckduckgo.com/?q=understanding+amplifier+power+requirements+site:audioholics.com&t=ffnt&atb=v136-1&ia=web

Might play with this spl calculator to see the relationship between speaker spl (sound pressure level), sensitivity, amp power and distance from the speakers http://myhometheater.homestead.com/splcalculator.html

Don't think generally car analogies work for audio....

 

[TankTop5]

Don't think generally car analogies work for audio....

Power, heat, potential etc are universal, home theater amplifiers aren’t any different.

The brakes on your car turn mechanical energy into thermal energy and the disks dissipate that thermal energy.

Speakers turn electrical energy into mechanical energy which in turn pressurizes a volume of air. How quickly a transducer can move a specific volume of air is directly related to how efficient the transducer is and how quickly the amplifier can change between 5 and 50 watts, which I believe is called current. On a car the ability of an engine to change from 50hp and 200hp is called torque.

My question is, will a 500 watt amplifier switch between 5 and 50 watts faster than a 100 watt amplifier? The description of energy may be different but the effect is the same. What specs in an amplifier am I looking for in its ability to quickly and efficiently dramatically change the output wattage?



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[lovinthehd]

It's not a mechanical engine, tho. I still don't like the car analogy. Consider it takes a doubling of power to merely gain 3dB spl, to handle a 20dB peak requires 20x the power and complicated by the constantly varying electrical demands of a speaker by frequency. The amp responds to the demands of the spl for the speakers you're using, and does it at the speed of electricity; I wouldn't worry about how "fast" the amp responds at all but rather worry about clipping/distortion at the limits of the amp.

ps as pointed out 20dB requires 100x power not 20x....d'oh!

 

[mtrycrafts]

Just trying to wrap my brain around amplifier power and understand it in a meaningful way for myself. I have been in the auto industry for half my life, a 200 horsepower car will only spend 1% of its life at 200hp and a 400hp car will only spend 1% of its life at 400hp but a 400hp car can easily access 200hp any time it wants. Would it be reasonable to think amplifiers are similar? If I have a 50 watt amplifier actually getting 50 watts is a bit optimistic but a 200 watt amplifier can easily jump between 1 watt and 50 watts easily and quickly and it can control 50 watts easily, I think that’s called headroom? Is this a good analogy?

Car analogies and amps rarely work out.
No, if that 50 watt amp is properly rated, then it is a 50 watt amp, continuously, not optimistically. Both amps will reach 50 watts in the same amount of time.
There is no mechanical comparison of an electrical amp and a mechanical engine.

 

[highfigh]

Power, heat, potential etc are universal, home theater amplifiers aren’t any different.

The brakes on your car turn mechanical energy into thermal energy and the disks dissipate that thermal energy.

My question is, will a 500 watt amplifier switch between 5 and 50 watts faster than a 100 watt amplifier? The description of energy may be different but the effect is the same. What specs in an amplifier am I looking for in its ability to quickly and efficiently dramatically change the output wattage?

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The ability of an amplifier to go from a low voltage to a higher voltage is called 'Slew Rate' and has a specific range because it has been found usable for a wide variety of amplifier circuits, expressed in Volts/millisecond. If the number is high, it's a good indicator that the amp will handle dynamics well, but it doesn't say anything about handling dynamics at all frequencies- that comes from having a very wide frequency range (if it can reproduce extremely high frequencies, it really won't have a problem at frequencies in the audible range).

" How quickly a transducer can move a specific volume of air is directly related to how efficient the transducer is and how quickly the amplifier can change between 5 and 50 watts, which I believe is called current."

No, current is electron flow. Period. It's expressed as Amperes, defined as One Coulomb per second and the number associated with One Coulomb (rounded down) is 6.24x10^18 electrons.

"On a car the ability of an engine to change from 50hp and 200hp is called torque."

With what load and RPM? That's not torque but I think you mean that an engine that can increase its RPM when under load produces more torque than one that bogs or remains at the same RPM when the pedal is pressed (or mashed to the floor). Torque is expressed in Foot-Pounds- HP is different and it's possible to have a high HP/low torque engine or a low HP/high torque engine.

 

[highfigh]

It's not a mechanical engine, tho. I still don't like the car analogy. Consider it takes a doubling of power to merely gain 3dB spl, to handle a 20dB peak requires 20x the power and complicated by the constantly varying electrical demands of a speaker by frequency. The amp responds to the demands of the spl for the speakers you're using, and does it at the speed of electricity; I wouldn't worry about how "fast" the amp responds at all but rather worry about clipping/distortion at the limits of the amp.

A 20dB increase requires 100x the power, peak or continuous.

 

[PENG]

Power, heat, potential etc are universal, home theater amplifiers aren’t any different.

The brakes on your car turn mechanical energy into thermal energy and the disks dissipate that thermal energy.

Speakers turn electrical energy into mechanical energy which in turn pressurizes a volume of air. How quickly a transducer can move a specific volume of air is directly related to how efficient the transducer is and how quickly the amplifier can change between 5 and 50 watts, which I believe is called current. On a car the ability of an engine to change from 50hp and 200hp is called torque.

My question is, will a 500 watt amplifier switch between 5 and 50 watts faster than a 100 watt amplifier? The description of energy may be different but the effect is the same. What specs in an amplifier am I looking for in its ability to quickly and efficiently dramatically change the output wattage?



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Same principles and theories perhaps, but different characteristics for sure. Consider this on the electrical side:

Current = Voltage/Impedance
Power = Voltage X Current X Cosine of the angle between voltage and current
Energy = Power X Time (duration)

For your question, energy does not apply and only voltage need to be considered, given a fixed impedance at a given moment/instant.

Unlike in cars where there are many mechanical and physical things involved, so it takes seconds for it to go from 0 to 100 kph, whereas the effects of "torque" produced by current change is virtually instantaneous.

Current changes virtually instantaneously as voltage change, so I would say the specs you are looking for is the "slew rate". Audio amplifiers generally have slew rate fast enough for the audible (by human) band, though many audiophiles still insist on seeing near perfect square waves at the output.

 

[ski2xblack]

If I have a 50 watt amplifier actually getting 50 watts is a bit optimistic but a 200 watt amplifier can easily jump between 1 watt and 50 watts easily and quickly and it can control 50 watts easily, I think that’s called headroom?

[Highfigh and Peng beat me to it] I think what you're describing could be analogous to the term "slew rate", or "rise time", which concerns bandwidth. If, using your example, one of the amps couldn't jump between 1 w and 50w as fast as the other, regardless if it was the more powerful or less powerful amp, it would have less bandwidth than the other amp.

Headroom, in terms of specifications from manufacturers, refers to the amount of power the amp can deliver above and beyond it's rated power (which most amps typically can do, for at least a few cycles, excluding those with fully regulated supplies), or more generically, it can be referring to however much clean power is available above average power usage (e.g. "If my average power is 3 watts, do I have enough headroom to reproduce this +20db peak in the program material?").

 

[lovinthehd]

A 20dB increase requires 100x the power, peak or continuous.

Aargh...I know that....

 

[markw]

I look at watts like this. Like horsepower, money and oxygen, it's better to have too much and not need it and need it and not have it.

Several facts have already been made clear: 2X the normal listening level (10 b requires 10 x the power., 4X that level (20 db) requires 100 x the power.

Keep in mind that these are generally worst case instantaneous peak levels,

Considering that a normal, comfortable listening level in normal sized rooms is attained with about 2 watts (with a majority of speakers),you should be able to determine about what you will need.

Also, keep in mind that most power is needed for deep bass, With today's powerd sub-woofers providing most of the oomph here, the strain on the receiver is greatly minimized.

But, before you pull your hair out in angst, keep in mind that big stereo's in the 60's saw power ratings of maybe 30 - 50 watts and they still played loud and sounded pretty durn good. Been there, done that, sold them, had them.

 

[Verdinut]

A 10dB is considered as the increase in SPL necessary to perceive a sound with double the loudness. To my knowledge, it has never been scientifically proven that this is the exact factor.
Personally, I would be inclined to think that 9dB, which represents 8 times the power factor is the closest to the real answer. I could be wrong but this is only my opinion.

 

[TankTop5]

The main reason for my question is I’m really enjoying watching movies and 2.1 stereo but sometimes I feel my older 40 W per channel NAD is trying a little too hard. I’ve heard people say that when they got a more powerful amp their speakers really “woke up”. I’m watching a NAD 216, may try to make a lowball offer and see if I get it. There’s also a NAD 902 with similar specs to my NAD 705 but I e read people feel the 902’s specs are more than conservative. I can buy the 902 for $72.50


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[markw]

What speakers do you have* and how large is your listening room? That could have a serious impact on your needs.

* or at least their rated sensitivity?

 

[highfigh]

Aargh...I know that....

I do that more than I'd like to admit, so I won't.

 

[highfigh]

A 10dB is considered as the increase in SPL necessary to perceive a sound with double the loudness. To my knowledge, it has never been scientifically proven that this is the exact factor.
Personally, I would be inclined to think that 9dB, which represents 8 times the power factor is the closest to the real answer. But this is only my opinion.

It's the accepted increment, but not in a reverberant field- it would require less power to achieve double the loudness than in an absorptive space.

 

[highfigh]

I look at watts like this. Like horsepower, money and oxygen, it's better to have too much and not need it and need it and not have it.

But, before you pull your hair out in angst, keep in mind that big stereo's in the 60's saw power ratings of maybe 30 - 50 watts and they still played loud and sounded pretty durn good. Been there, done that, sold them, had them.

Watts is like "It's easier to ask for forgiveness than permission".

The speakers from that era had bigger woofers and bass makes everything sound louder, so they were self-contained systems, rather than weak sounding little POS speaker cubes and a sub that's crossed over at about 250Hz (as I found that the Bose Lifestyle 48 system is set, just two weeks ago).

Dinky speakers can't move enough air to sound loud in any kind of full-range setup- I replaced the Bose system in a boat and left the speakers in place because I couldn't find anything small enough to be inconspicuous on such short notice, so I played the system and moved my phone close to one of them while using my Dynaudio RTA app- I saw a definite notch at about 250 Hz so, before connecting the sub, I listened to the system without bass. Just installing the Marantz AVR, it sounded better- not as screechy and annoying. Before I fired up the sub, I set the LP crossover to Max and in the Marantz, I set the Speakers to Small and dialed the crossovers to 240Hz. It obviously had subdued mids, but with a bit of manual EQ, it actually sounded decent for a lot of music and it takes a lot of self control for me to admit that without diving off of my porch.

 

[davidscott]

I look at watts like this. Like horsepower, money and oxygen, it's better to have too much and not need it and need it and not have it.

Several facts have already been made clear: 2X the normal listening level (10 b requires 10 x the power., 4X that level (20 db) requires 100 x the power.

Keep in mind that these are generally worst case instantaneous peak levels,

Considering that a normal, comfortable listening level in normal sized rooms is attained with about 2 watts (with a majority of speakers),you should be able to determine about what you will need.

Also, keep in mind that most power is needed for deep bass, With today's powerd sub-woofers providing most of the oomph here, the strain on the receiver is greatly minimized.

But, before you pull your hair out in angst, keep in mind that big stereo's in the 60's saw power ratings of maybe 30 - 50 watts and they still played loud and sounded pretty durn good. Been there, done that, sold them, had them.

Yeah I remember in the mid 70s my friend had a Pioneer 50wpc receiver that I considered the holy grail as I could only afford a 25wpc Nikko. It was plenty loud with my speakers in my small apt but boy did I want 50wpc. Like you said been there done that but never sold them.

 

[TankTop5]

What speakers do you have* and how large is your listening room? That could have a serious impact on your needs.

* or at least their rated sensitivity?

Focal 706s

DESCRIPTION
Description:
2-way bass reflex bookshelf wall mounted
Speakers: 6-1/2" Polyglass mid-bass, 1" TNC inverted dome tweeter
Frequency response (+/- 3dB): 55Hz-28kHz
Sensitivity (2,8V/1 m): 90dB
Nominal impedance: 8 ohms
Crossover frequencies: 2400Hz
Maximal power handling with musical program: 80W


The room is small to medium size but has an adjoining dining room, kitchen, stairwell going down and a hallway. The stairway is behind the couch and behind there listening area. The couch is approximately 10 feet from the speakers, standard height ceiling



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[markw]

They are nice speakers but you'll get a certain level of loudness before straining them. With a max rating of 80 watts, that NAD 216 will more than satisfy theit needs, with power to spare.

But, I doubt you'll be able to attain a satisfying bass response without a powered sub in the mix. My spidey sense tells me that depending on how loud you listen, that strain you feel may be your speaker complaining about trying to fill that space more than the amp.

Try getting a powered sub first and see how that works for ya.