Where do the other watts go? Need basic understanding please

[YesChickenNuggets]

Also, is there a musical example of when all this 1.21 jigawatts is "utilized."

What music track would you guys use to test, POWER, sustained or otherwise ?

 

[Koeitje]

Here's an example: Magnepan 3.6/R which produce 86 dB @ 500 Hz @ 2.83 V. At 500 Hz they have 4.2 ohm impedance so 1.9 W makes 86 dB. If you want to achieve the THX standard (85 dB plus 20 dB headroom = 105 dB) you need to go 19 dB louder, which requires 160 watts.

PS: at the opposite extreme, if you have very efficient speakers, especially in a small room, then 25 watts might be more than you need.

And this an example of speakers that don't even have really low sensitivity. Sensitivity that is 4db lower than this is not uncommon, that would require much more power. Usually you run into speaker limits before you hit the THX standard. With 2 82dB loudspeakers at 4 meters near a wall you need almost 850W to hit 105dB.

Also, is there a musical example of when all this 1.21 jigawatts is "utilized."

What music track would you guys use to test, POWER, sustained or otherwise ?

None, because that wouldn't be music anymore. But if you want to test dynamic power just get an Overture 1812 recording where they use real cannons (Telarc has one). But don't come complaining to me if you smoke your woofers.

 

[YesChickenNuggets]

Did tchikovsky ever specify which cannons to be used in his music? I'd imagine different cannons had different sound signature.

 

[Koeitje]

Did tchikovsky ever specify which cannons to be used in his music? I'd imagine different cannons had different sound signature.

I don't know if you are baiting, but I doubt he cared. This is what he said about it:

Meanwhile, Tchaikovsky complained to his patron Nadezhda von Meck that he was "... not a conductor of festival pieces," and that the Overture would be "... very loud and noisy, but [without] artistic merit, because I wrote it without warmth and without love." He put it together in six weeks. It is this work that would make the Tchaikovsky estate exceptionally wealthy, as it is one of the most performed and recorded works from his catalog.

 

[multichannel_guy]

Why worry about amps.. the real burners are your speakers:

96dB is just above 2% efficient. The rest is converted to heat.

As it was explained to me by an amp designer, it is apparently difficult to design an amp that works well with a very high sensitivity speaker (98+ db) as such a speaker only uses fractions of a watt at most normal listening levels, linearity issues at fractions of a watt and so on.

 

[DVDdoug]

It is apparently difficult to design an amp that works well with a very high sensitivity speaker (98+ db) as such a speaker only uses fractions of a watt at most normal listening levels, linearity issues at fractions of a watt and so on.

Like a headphone amplifier? It's actually easier (and cheaper) to build a headphone amp than a power amp, but you do need lower noise.

 

[Deleted member 48726]

Like a headphone amplifier? It's actually easier (and cheaper) to build a headphone amp than a power amp, but you do need lower noise.

I think he meant like a headphone amp capable of both clean 5 mW and 100 Watt

 

[multichannel_guy]

Like a headphone amplifier? It's actually easier (and cheaper) to build a headphone amp than a power amp, but you do need lower noise.

Not a headphone amp, a power amp for very high sensitivity speakers that only end up using fractions of a watt.

 

[wwenze]

I don't like to call it efficiency as the majority of the "unused" energy is not converted... But I get the idea. Just call it sensitivity.

Amps and speakers designs follow each other. If the industry had lots of 98dB sensitivity speakers, there would be more 1W amps. A powerful headphone amp can probably drive that.

Yup, most speaker amps are noisy because big amp circuits are noisy no surprises here. Noise at -80dB relative to a watt would be inaudible with a speaker of 80dB sensitivity at a watt. Linearity at low voltages is generally not a problem with analogue amps, beyond the usual 0.1 to 0.01%. Actually most amps might even enjoy not moving too much on the transfer function curve. Unless you encounter crossover distortion that is, but even that can be avoided by keeping your voltage swing even lower.

 

[Hayabusa]

I have 93 db speakers. So at 1 watt I get 93db of SPL/DB sound.

So 2 watts = 96 db etc etc

My current amp is SPL S1200. Specs state 300 wpc. If I only need to get 2 to 4 watts to the speaker where do all the other watts on the amp go?
Why are they needed vs 15 watt amp?

Thank you. I love learning

jh

It also about the peak to average ration (crest factor). This can vary wildly from 6 to 20dB.
But lets take 6 and 12 as an example:
if you play at an average level of 93 dB your amp will see peaks of 99dB (+6) and 105dB (+12) and needs to do this without clipping.
So in this case: 99dB = 4 watts but in the 105dB case you need already 64 watts.

 

[DonH56]

Not a headphone amp, a power amp for very high sensitivity speakers that only end up using fractions of a watt.

Years ago low-level linearity (e.g. crossover distortion) was sometimes an issue for certain amps. Whilst it is still possible, I think the biggest issue today is that high-power amps generally have higher gain and higher noise floor, leading to hiss driving highly-sensitive speakers.

IMO - Don

 

[multichannel_guy]

Years ago low-level linearity (e.g. crossover distortion) was sometimes an issue for certain amps. Whilst it is still possible, I think the biggest issue today is that high-power amps generally have higher gain and higher noise floor, leading to hiss driving highly-sensitive speakers.

IMO - Don

That's good to know. I wish the low noise floor amps, e.g., Benchmark were a bit more affordable. I've been eyeing it for a while now.

 

[MaxwellsEq]

That's good to know. I wish the low noise floor amps, e.g., Benchmark were a bit more affordable. I've been eyeing it for a while now.

Low noise floor is often a function of gain.if you get a popular Class D amplifier which has variable gain settings and you use the lowest gain, your noise floor will be similar to the Benchmark which has low gain.

 

[johnah5]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

 

[Deleted member 48726]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

Crossovers waste power-->

And voicecoils-->

 

[Hayabusa]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

read my post about the crest factor..

 

[mhardy6647]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

Yes, the passive components in the crossover dissipate heat -- sometimes with spectacular results.

 

[mhardy6647]

Crossovers waste power-->
View attachment 347511

And voicecoils-->
View attachment 347512

You beat me to it, by seconds!
This is why - ahem - some of us use much greener loudspeakers -- and waste much less electricity in the process of soundscaping our domiciles.
These, e.g., have sensitivity of about 104 dB/watt at 1 meter -- nearly 100-fold more sensitive than the hypothetical 85 dB loudspeaker referenced in recent posts.

They're also more electrically efficient (I'd have to figure the nominal increase in efficiency out -- I can get back to you on that!).

 

[DonH56]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

What do you mean by "extra watts"? (I am trying to understand exactly your question; I am pretty dense, so without a better explanation of what you are asking, the question is sort of like "How high is up?")

Eight feet away, a pair of 85 dB/W/m speakers will produce about 85 dB SPL driven by 3.5 W each.

The power from the amplifier creates acoustic power (sound) by converting the electrical energy into acoustic energy through a mechanical device, the speaker drivers. It is not a terribly efficient process. The coupling from electrical input to acoustic output is fairly "weak" so acoustic power output is considerably lower than the electrical power input (my grad instructor said 1 acoustic watt would blow your ears off). It's a conversion process and energy is always lost in a conversion. In addition are all the other causes mentioned by others, such as loss in the crossover (wasted heat in the components), heating in the voice coil (where electrical energy is converted into mechanical energy to create sound), and so forth. Bottom line is power (energy) is lost as wasted heat in the crossover and drivers, and due to the loose coupling from electrical signals to acoustic signals (a speaker is not a good power matching system).

There are many other examples of power lost during a conversion process, such solar cells that convert sunlight into electricity, transmissions that convert raw engine power into power at the wheels, electrical power into light bulbs to create visible light, and on and on. In most if not all cases the "extra" energy is converted to (lost as) heat someplace in the chain. For speakers that is primarily the crossover and voice coils.

 

[MaxwellsEq]

This is all great info but I am trying to understand where the extra watts go? So if you have 85db efficient speakers does the crossover in the speaker eat some power? Do other things eat power so that a 3.5 watt amp like I have, is not able to produce more than enough power to drive 85db speakers?

If you listen to music for a long time and at high sound levels, then quickly dismantle the loudspeakers, you will find the crossover and the drivers are really quite hot. One studio monitor I worked on had a big heatsink on the midrange units! This is where some of the Watts go.

The rest of the Watts get eaten by the mechanism of vibrating air in your listening room. This is hard work, partially because the air resists this happening. Smaller drivers find this task tougher than large drivers. Horn-shaped speakers act like "air transformers" matching the driver behaviour to the air in a better manner.