ampere vs wattage

loud

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Which is more relevant?

Let say we have 2 amplifiers with rating:
Amplifier A
80watt8ohm 120watt4ohm

Amplifier B
50watt8ohm 100watt4ohm 200watt2ohm

How to know which of the 2 is more power capable?

Some people suggest that the rating of watts isn't very accurate for the amplifier's true power and i was also told about amplifier that doubles its wattage when its resistance loads is halves will have more current and power.

Looking forward to understand more about this issue so any opinion is welcome.

Thanks!
 
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One should do an apple to apple comparision.
Usually good floor standers are 8 ohm.
So an amplifier that can produce the maximum wattage for speakers of 8 ohm is the best load driving amp.
If one has 4 ohm speakers then wattage when driving 4 ohm loads should be compared.
The amp with more wattage per load drives more current into the load I.e speakers.
The more the current into the speakers, the better they sing.
 
One should do an apple to apple comparision.
Usually good floor standers are 8 ohm.
So an amplifier that can produce the maximum wattage for speakers of 8 ohm is the best load driving amp.
If one has 4 ohm speakers then wattage when driving 4 ohm loads should be compared.
The amp with more wattage per load drives more current into the load I.e speakers.
The more the current into the speakers, the better they sing.

but most speakers tend to drop their impedence upto even 2 ohms. No speaker will stay at 8 ohms through out the 20hz to 20khz frequency.
 
You will have to compare Continuous output power at 8 ? or whatever your speakers are rated. Ensure that the rating is specified for the same THD usually <0.009 % (ref. 20 Hz - 20 kHz). The THD (Total Harmonic Distortion) is important as the same Amp can get rated significantly higher for a higher THD.

The specs are only half the story and the better Amps will have a better Dynamic response. This means that the Amp delivers very high outputs momentarily - this is dependent on the circuitry and also significantly on the transformers used. Remember reading somewhere that a good thumb rule comparison is to compare the weight of the Amp.

Also many FMs vouch that a lower rated Tube Amp will beat a higher rated Solid State Amp
 
The amp with more wattage per load drives more current into the load I.e speakers.
The more the current into the speakers, the better they sing.

Watts are over-rated. The best upgrade I ever did was from an 120W amplifer to a 50W amplifier. The tube people will tell you what sweet sounds they get with even smaller numbers. I would not worry about power output in absolute numbers (which are probably produced as much by the marketing dept as by the engineers) unless I had unusually insensitive speakers or a very large space to fill. I would absolutely never rate one amplifier over another on the basis of those numbers. Watts may, with a given speaker, have a mathematical relationship to loudness, but not to quality.
 
My understanding, if you take jsut speakers+ amps, is that this is a lot more complex that it sounds like and is an example of Wrong measurements/specs
The amps capability of supplying enough current so that the voice coil can produce enough of magnetic field is the crux of the woofer moving is what defines a good synergy between speaker/amp
watts are just a representation of this ability but often abused by manufacturers as unless you know what the max current is and also How quickly it can supply it (Slew rate) aacross the audible frequency range and at different loads, specs cannot be used of matchng. even if the increase in current is microseconds late due to the inability of the amp, the moment is lost and music sounds duller/out of sync.

Thats the reason people prefer higher rated amp, as it will always supply the needed current (but could lose out on subtlety).. But a Well designed lower powered amp will still manage the above..thats why a sugden 25W amp will drive speakers better than a Nad/Rotel 50-75 w amp.


The current delivered depends on the power/voltage of the output and the impedance of the speaker+ cable
the problem is that the RLC of the cable + speaker varies with frequency and hence the demand at each frequency is different
At any instant a music signal carries a Complex signal (including harmonics/ subharmonics ) which all see a different impedance.


Hence choose a good amp and always try to have more power than recommended.
 
Yet another query from a noob ....

Some amp specs states output of 100W at 8 0hms and 200W at 4 ohms, while other amps state 100W at 8 ohms and 120 to 160W (in that band) at 4 ohms! Does this have any bearing on the amp performance / overall sound quality, IF mated to a 'fixed' speaker of say, 8 Ohms??

Just wish to clear a long lingering doubt .... Thanks.
 
Yet another query from a noob ....

Some amp specs states output of 100W at 8 0hms and 200W at 4 ohms, while other amps state 100W at 8 ohms and 120 to 160W (in that band) at 4 ohms! Does this have any bearing on the amp performance / overall sound quality, IF mated to a 'fixed' speaker of say, 8 Ohms??

Just wish to clear a long lingering doubt .... Thanks.
Since a speakers impedance is never fixed..what is important to figure out the Min impedance of the speaker. if it is nominal and 8 drops to 4 ohms then the amp should have the capability to output at that load thats all.

else all of the above specs dont mean much..
 
@ arj ... not so convinced here. I guess, the latter combination should start distorting at higher volume levels much earlier. Impedance levels in any speaker (depending on the track played) can fall to as low as 2 ohms (let alone 4 ohms) for very brief periods too.

Does the earlier combination relate to 'higher current' design by any chance?
 
@ arj ... not so convinced here. I guess, the latter combination should start distorting at higher volume levels much earlier. Impedance levels in any speaker (depending on the track played) can fall to as low as 2 ohms (let alone 4 ohms) for very brief periods too.

Does the earlier combination relate to 'higher current' design by any chance?

unless you have really demanding speakers and really large room..you will never consume 100W ;) except for some instant peaks..that too rarely
mostly your RMS would be around 20-30 W or less. most 90dB speakers may only need single digit watts or even less for most of the duration/content of music

also..if an amp is Linear . then 100W into 8 ohms rating would also mean 200W i at 4...and so on (look at the rating of any good amp from brands like Pass, krell. Accuphase etc.. they will go down to 800w into 1 ohm in the same way and some speakers like apogee scintillas do go down to 1 ohm.)
 
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Some amp specs states output of 100W at 8 0hms and 200W at 4 ohms, while other amps state 100W at 8 ohms and 120 to 160W (in that band) at 4 ohms!

I am really not very good at these numbers, although I try to understand --- but, when you look at reviews that include measurements, you will see graphs with lines that are nothing at all like straight.
the latter combination should start distorting at higher volume levels much earlier
If you are able to drive your system to distortion levels, you are either deaf (or soon will be) or one or more parts of your system are very bad. [or you are running a PA system at a wedding/function ;) ].
 
.. 'you are either deaf (or soon will be)' .. this is more likely :):D

Have noted this linear characteristic (eg. 100W at 8 O or 200W at 4 O) in some of the very high end amps, but not all ... A few of the very good ones did not possess this. Was wondering what significance it had from a practical point of view, than anything else to carry this linear feature.
 
Which is more relevant?

Let say we have 2 amplifiers with rating:
Amplifier A
80watt8ohm 120watt4ohm

Amplifier B
50watt8ohm 100watt4ohm 200watt2ohm

How to know which of the 2 is more power capable?

Some people suggest that the rating of watts isn't very accurate for the amplifier's true power and i was also told about amplifier that doubles its wattage when its resistance loads is halves will have more current and power.

Looking forward to understand more about this issue so any opinion is welcome.

Thanks!

Amplifier B would be better.

.. 'you are either deaf (or soon will be)' .. this is more likely :):D

Have noted this linear characteristic (eg. 100W at 8 O or 200W at 4 O) in some of the very high end amps, but not all ... A few of the very good ones did not possess this. Was wondering what significance it had from a practical point of view, than anything else to carry this linear feature.

In technical perspective it tells us the fact that the power supply of such amplifiers is quite stiff and has high current draw sustainability. Same way it also tells us that the output stage of such amplifier is stable to lower impedance loads as well. This gives better cone control and tight bass.

The amplifiers in which the power doesn't doubles with halving of impedance simply states that the power supply sags during high current draw.
 
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Which is more relevant?

Let say we have 2 amplifiers with rating:
Amplifier A
80watt8ohm 120watt4ohm

Amplifier B
50watt8ohm 100watt4ohm 200watt2ohm

How to know which of the 2 is more power capable?

Some people suggest that the rating of watts isn't very accurate for the amplifier's true power and i was also told about amplifier that doubles its wattage when its resistance loads is halves will have more current and power.

Looking forward to understand more about this issue so any opinion is welcome.

Thanks!

With a simplistic model, assume the amplifier has to develop a constant voltage and once the resistance is known, the current is fixed (Ohm's law). So sqaure root of (power * resistance) is voltage.
Your 80 watt amplifier at 8 ohms develops sqrt(640) volts. The same amp at 120 watts 4 ohms develops sqrt(480), much lower than the 8 ohm load. Your 50 watt 8 ohm / 100 watt 4 ohm / 200 watt 2 ohm always develops the same voltage. Technically, there is no doubt that the second amplifer is easy to drive the varying impedance of a speaker whereas the first will struggle.
Of course, the voltage is not DC but AC in a real life amplifier and the speaker impedance will depend not on just one frequency but a range of frequencies it is reproducing and accordingly will be the current demand.
However, the basic principle always holds good and the second amplifier is better designed than the first.

Hope this helps.

murali
 
The current delivered depends on the power/voltage of the output and the impedance of the speaker+ cable
the problem is that the RLC of the cable + speaker varies with frequency and hence the demand at each frequency is different
At any instant a music signal carries a Complex signal (including harmonics/ subharmonics ) which all see a different impedance.
.

Effects of RLC of speaker cable is negligible when compared to drastic effects of passive crossover sitting in between amplifier and the driver. The amount of reactive current drawn by passive crossover is much more difficult to handle for an amplifier than the current required to drive the voice coil.

For example: If you take a typical 8 Ohm driver and have a look at its impedance curve it will never dip to even 50% of its rated value because RDC[voice coil DC resistance] is always present there as the minimum possible dip.

Now same way do the analysis of a 8 ohm speaker system with a passive XO inbuilt in it. The impedance curve at some point can even touch lower to 2ohms also, just due to the LCR components present in it. The reactive load need a reactive current draw to quench the thirst of passive XO, remainder is left for voice coil to do the actual bit.


Active systems/Active speakers which are devoid of passive XOs are much easier to drive and give out much better response.
 
Effects of RLC of speaker cable is negligible when compared to drastic effects of passive crossover sitting in between amplifier and the driver. The amount of reactive current drawn by passive crossover is much more difficult to handle for an amplifier than the current required to drive the voice coil.

For example: If you take a typical 8 Ohm driver and have a look at its impedance curve it will never dip to even 50% of its rated value because RDC[voice coil DC resistance] is always present there as the minimum possible dip.

Now same way do the analysis of a 8 ohm speaker system with a passive XO inbuilt in it. The impedance curve at some point can even touch lower to 2ohms also, just due to the LCR components present in it. The reactive load need a reactive current draw to quench the thirst of passive XO, remainder is left for voice coil to do the actual bit.


Active systems/Active speakers which are devoid of passive XOs are much easier to drive and give out much better response.

you are the boss :). thanks for the above info in bold..never made that connection earlier

i would agree that the speaker cable RLC is relatively smaller..negligible impact or not is something i will not comment due to obvious reasons ;)

my
 
you are the boss :). thanks for the above info in bold..never made that connection earlier

i would agree that the speaker cable RLC is relatively smaller..negligible impact or not is something i will not comment due to obvious reasons ;)

my

Negligible effect when

1. Compared to effects of passive XO

2. If the system is active, no passive XO

But yes RLC of speaker cable does have interaction and its effects but only because of presence of passive XO, they get magnified and are easily detectable.
 
I understand the amp section needs to be stable (without or with minimal power sag) when the impedance touches the lower range. I guess this is what many call it as the Dynamic power - the ability to supply a short burst of power with minimal fuss/THD. I used to hear from people on how some of the best amplifiers, with conservative power rating, could drive big speakers without any problem. So my understanding is that the dynamic power is one of the important parameters in SQ.

Having said about the amp section's ability to be stable across the varying speaker impedance range, I would like to the know the role of the input power supply section of the amplifier. People say that the weight of an amplifier is also one of the good indicators of how it can supply huge current/power to the speakers. As far as what I know, the input power supply section of the amplifier constitutes the major portion of the amplifier weight. I have seen in few amplifiers/receivers that it's weight is more at one side where the transformer(s) are located. So , is it true or a myth about the weight of the amplifier being one of the indicators of the amplifier's ability to supply heavy current ? I am not saying that it is the only parameter.
In what way a good input power supply section of an amp influence the overall sound quality ?

Some amplifiers/receivers seem to have in-uilt isolation transformer at the input stage of the power supply. Few others have SMPS based input power supply system. I was told by a AV service engineer that SMPS based systems tend to weigh less when compared to the systems having isolation transformer. So do these different power supply systems have any role in the SQ ?

I am not sure if the above questions sound illogical or novice in the eyes of experts, but I would very much appreciate if one teaches me on the above stuff. Thanks in advance !!!
 
let me give you my simple way of understanding this.which i am sure other experts will add on and/or correct

any amplifier works on the principle of the control signal which shapes the output signal and the input power which is the "raw material"

hence the input electricity comes into the amplifier gets converted to DC and becomes this raw material, the quality of which is defined by the power supply (quantity & quality being important)

the control signal comes in from the preamp and the amplifier duplicates the control signal into the High powered output signal

in simple words, the Input signal is the photograph(s), the amplifier the sculptor, the power supply the Quarry to excavate the marble and the rectified power the Blank marble..and you get a sculpture :)

the quality of the sculpture depends on the skill of the sculptor, the quality of the marble and the completeness of the photograph in all respects to give a 3d ;)

more the marble and better its quality, the more lifelike the sculpture
 
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So , is it true or a myth about the weight of the amplifier being one of the indicators of the amplifier's ability to supply heavy current ?
In what way a good input power supply section of an amp influence the overall sound quality ? I was told by a AV service engineer that SMPS based systems tend to weigh less when compared to the systems having isolation transformer. So do these different power supply systems have any role in the SQ ?

If the power supply is Linear, means toroidal core or EI core transformer based then yes, weight plays important role.

If its SMPS based then the weight no longer has any influence provided the SMPS is designed to handle the peak current demand of amplifier itself. :)

A beefy and clean power supply unit is always good for sonics, it helps in preserving the perfect transient attack of the music signal and clean background which gives you high signal to noise ratio for listening to the micordetails hidden in the music passages.



Arj has given a nice analogy in simple terms, best for layman to understand it in easy manner.
 
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