# How does a low ohm headset consume less power? How is this related to the amp?

#### DoDo

##### Member
Beyerdynamic dt 770 pro 32, 80, 250 ohm all versions need 100 mW power. In this case, how is it easier to drive 32 ohm headphones than 80 or 250?
if the audio interface audio output has a constant voltage ; 32 ohm dt 770 pro, uses much more amperage ( 'i' ) than 80ohm or 250 ohm dt 770 pros. Same output but not same power. This is okay.

İf the voltage can vary :
These examples: 1) Audient id 4 MK2 headphone output : 30 ohm - 2.59VPeak, 1.827V RMS, 223mW ----- 62 ohm - 4,18 Vpeak, 2,95 V RMS, 280mW ! Voltage can vary. !

2)
''1.37 second. '' For example : Motu m2.
How 16 ohm into power more less than 32 ohm into?

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Few things:

1. The language of this forum is English, so I took the liberty of running your post through google translate. This may not be quite accurate.
The design of the Beyerdynamic dt 770 pro 32, 80, 250 ohm headphones needs 100 mW. So how is it easier to use 32 ohms than 80ohm or 250ohm? if the audio interface output voltage is stable; 32 ohm dt 770 pro, using much more amps' and also using the same voltage. In this case I can feed the same amp output power 32 ohm dt 770 pro. And you cannot feed 250 ohms to the same amplifiers. All right. If the voltage can vary: These examples are 1) Audient id 4 MK2 'wristband output prices: 30 ohms - 2.59V Peak, 1.827V RMS, 223mW ----- 62 ohms - 4.18 V Peak, 2.95 V RMS, 280mW! Voltage is changing. 2nd) For example: Motu m2. How to input 16 ohm power less than 32 ohm ???

2. This has to do with Ohm's law. Power = Current * Voltage. Power = (voltage^2)/resistance (impedance) and power = (current^2)*resistance. Higher impedance loads need more voltage swing but less current to generate the same power, and vice versa for lower impedance loads.

3. Power drops below a certain impedance (usually ~32R) because of current supply limitations. It drops higher up because of voltage supply limitations.

Thank u for answering. İ dont know english too.
İ think i know Ohm's law.
When asked how much amperage the amp can deliver, shouldn't we look at the ohms of the amp's output? Motu m2 has 0.06 output impedance. So Motu m2 must be can generate amperage to support up to 0.06 ohms ? So 32 ohm so much bigger than 0.06 ohm. ?

For example: scarlet 2i2 3.gen headphone output +7dBU this is = 1.735 Voltage. And scarlet output can support bigger than 1 ohm headphones. İn this case : 1.735V^2 / 1 ohm = 3.010 Watt max. with 1 ohm headphone.
So scarlet with 32 ohm headphones : 3.010 / 32 ohm = 0.094 watt = 94 miliwatt. ''''' Okay but these true if voltage is constant ! '''''

As seen in the id4 mk2 example, the voltage is not stable. Voltage is vary.

Thank u for answering. İ dont know english too.
İ think i know Ohm's law.
When asked how much amperage the amp can deliver, shouldn't we look at the ohms of the amp's output? Motu m2 has 0.06 output impedance. So Motu m2 must be can generate amperage to support up to 0.06 ohms ? So 32 ohm so much bigger than 0.06 ohm. ?

For example: scarlet 2i2 3.gen headphone output +7dBU this is = 1.735 Voltage. And scarlet output can support bigger than 1 ohm headphones. İn this case : 1.735V^2 / 1 ohm = 3.010 Watt max. with 1 ohm headphone.
So scarlet with 32 ohm headphones : 3.010 / 32 ohm = 0.094 watt = 94 miliwatt. ''''' Okay but these true if voltage is constant ! '''''

As seen in the id4 mk2 example, the voltage is not stable. Voltage is vary.
Think of the amp like a light socket with a dimmer instead. A high impedance headphone is like a night light bulb that doesn't draw much current because of its high resistance and a low impedance headphone is like a low resistance 60w bulb, drawing more current at the same voltage. To match the current, heat, light, you need to turn the output way down for the 60w rated bulb. In practice, this is more like a tube amp, but still, perhaps the analogy is helpful in considering how the headphone draws current from the amp based on its impedance.

Think of the amp like a light socket with a dimmer instead. A high impedance headphone is like a night light bulb that doesn't draw much current because of its high resistance and a low impedance headphone is like a low resistance 60w bulb, drawing more current at the same voltage. To match the current, heat, light, you need to turn the output way down for the 60w rated bulb. In practice, this is more like a tube amp, but still, perhaps the analogy is helpful in considering how the headphone draws current from the amp based on its impedance.
Thanks for answering. İ can understan resistance and current relation.
As seen in the id4 mk2 example, the voltage is not stable. ( 30 ohm - 2.59VPeak, 1.827V RMS, 223mW ----- 62 ohm - 4,18 Vpeak, 2,95 V RMS, 280mW ) Voltage can vary. What is the voltage and current limit range of the headphone output of the audio interface ? What determines the current it can give the most? What determines the voltage it can give the most ?

Thanks for answering. İ can understan resistance and current relation.
As seen in the id4 mk2 example, the voltage is not stable. ( 30 ohm - 2.59VPeak, 1.827V RMS, 223mW ----- 62 ohm - 4,18 Vpeak, 2,95 V RMS, 280mW ) Voltage can vary. What is the voltage and current limit range of the headphone output of the audio interface ? What determines the current it can give the most? What determines the voltage it can give the most ?
Yes. The answers to these questions vary a lot depending on your amp and headphone. That is why good headphone amps have power in spades. If the voltage was constant then low impedance headphones would draw too much current and fry stuff, more akin to shorting your light socket with a fork.

Yes. The answers to these questions vary a lot depending on your amp and headphone. That is why good headphone amps have power in spades. If the voltage was constant then low impedance headphones would draw too much current and fry stuff, more akin to shorting your light socket with a fork.
Thanks for anwers. But i cant understand. What is the voltage and current limit range of the headphone output of the audio interface ? ))) İf u want you can explain with an example with these:
Any amp's watt or voltage, and amp's ohm / two different ohm headphones. Like dt 770 pro 80 ohm, 250 ohm (these two need 100 mW power for 116 dB)

Thanks for anwers. But i cant understand. What is the voltage and current limit range of the headphone output of the audio interface ?
Both are defined by the power supply. You can calculate them by the power measurements under load.

For example, the MOTU M2:

We can see that at 300 ohms, it does 22 milliwatts. If we plug that into our power formulas, we get the maximum clean output we can do is about 2.5 volts and about 8.5 milliamps. The low current draw means voltage can swing more.

And, at 33 ohms, it has similar power output... Which means 871 millivolts, but about 26.5 milliamps. The extra current draw limits the voltage swing available.

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Beyerdynamic dt 770 pro 32, 80, 250 ohm all versions need 100 mW power. In this case, how is it easier to drive 32 ohm headphones than 80 or 250?
if the audio interface audio output has a constant voltage ; 32 ohm dt 770 pro, uses much more amperage ( 'i' ) than 80ohm or 250 ohm dt 770 pros. Same output but not same power. This is okay.

They all are equally 'easy to drive'.
All versions require an equal amount of power to reach the same SPL level.

32 Ohm just requires less voltage (and more current) to reach the same SPL as 80 Ohm version. The 250 Ohm version requires more voltage and thus less current.

For 100mW rating:
32 Ohm requires 1.8V and 56mA This can be achieved with a low supply voltage of around 5.5V, 80mA peak is required
80 Ohm requires 2.8V and 35mA This can be achieved with a medium supply voltage of around 8V, 50mA peak is required
250 Ohm requires 5V and 20mA This can be achieved with a higher supply voltage of around 15V, 30mA peak is required

It is equally easy to design amps that meet the above requirements.
15V and 80mA peak can drive all these versions.
However, in most cases a limited power supply voltage is available in the design which imposes a practical limit.

All* amplifiers are voltage sources. These voltage sources have a limited output voltage AND a current limit by design.
In general the output resistance is not the current limiting factor but with higher output resistances the output resistance is the current limiting factor.
Depends on the design...
Amplifier A might be able to deliver a higher voltage but may be limited in current = suited for high impedance headphones.
Amplifier B might be able to deliver a lower voltage but higher current = suited for low impedance headphones.
amplifier C might only deliver a low voltages and low current = can't drive headphones loud.
Amplifier D might be able to deliver a high voltage and a high current = can drive all headphones.

The design of an amplifier (incl. its power supply) thus determines what headphones it is suitable for (can drive).

It's just ohms law and about voltage limits, current limits, efficiency and impedance.

What is the voltage and current limit range of the headphone output of the audio interface ? What determines the current it can give the most? What determines the voltage it can give the most ?

Voltage limits are determined by the design and internal power supply rail voltages.
Current limits are determined by design mostly but also by output resistance and with some designs determined by DCDC converter power limits.
So again ... determined by design and available power supply voltage(s).

The output voltages of an amplifier thus can vary depending on the current limit of the design and the applied impedance.

* Almost all amps, some very rare amps (Bakoon and some OTL tube amps) act more like voltage limited current-alike sources.

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[QUOTE = "dfuller, post: 657109, üye: 15274"] Her ikisi de güç kaynağı tarafından tanımlanır. Bunları yük altındaki güç ölçümleriyle hesaplayabilirsiniz.

Örneğin, MOTU M2:
View attachment 109715

300 ohm'da 22 miliwatt olduğunu görebiliriz. Bunu güç formülümüze bağlarsak, yapabileceğimiz maksimum temiz çıktıyı yaklaşık 2,5 volt ve yaklaşık 8,5 miliamper elde ederiz. Düşük akım çekişi, voltajın daha fazla salınabileceği anlamına gelir.

Ve 33 ohm'da, benzer güç çıkışına sahip ... Bu da 871 milivolt, ancak yaklaşık 26,5 miliamper anlamına geliyor. Ekstra akım çekişi, mevcut voltaj dalgalanmasını sınırlar.
View attachment 109716[/ALINTI]
Thank u but i know ohm law. This is not my questions answer.

They all are equally 'easy to drive'.
All versions require an equal amount of power to reach the same SPL level.

32 Ohm just requires less voltage (and more current) to reach the same SPL as 80 Ohm version. The 250 Ohm version requires more voltage and thus less current.

For 100mW rating:
32 Ohm requires 1.8V and 56mA This can be achieved with a low supply voltage of around 5.5V, 80mA peak is required
80 Ohm requires 2.8V and 35mA This can be achieved with a medium supply voltage of around 8V, 50mA peak is required
250 Ohm requires 5V and 20mA This can be achieved with a higher supply voltage of around 15V, 30mA peak is required

It is equally easy to design amps that meet the above requirements.
15V and 80mA peak can drive all these versions.
However, in most cases a limited power supply voltage is available in the design which imposes a practical limit.

All* amplifiers are voltage sources. These voltage sources have a limited output voltage AND a current limit by design.
In general the output resistance is not the current limiting factor but with higher output resistances the output resistance is the current limiting factor.
Depends on the design...
Amplifier A might be able to deliver a higher voltage but may be limited in current = suited for high impedance headphones.
Amplifier B might be able to deliver a lower voltage but higher current = suited for low impedance headphones.
amplifier C might only deliver a low voltages and low current = can't drive headphones loud.
Amplifier D might be able to deliver a high voltage and a high current = can drive all headphones.

The design of an amplifier (incl. its power supply) thus determines what headphones it is suitable for (can drive).

It's just ohms law and about voltage limits, current limits, efficiency and impedance.

Voltage limits are determined by the design and internal power supply rail voltages.
Current limits are determined by design mostly but also by output resistance and with some designs determined by DCDC converter power limits.
So again ... determined by design and available power supply voltage(s).

* Almost all amps, some very rare amps (Bakoon and some OTL tube amps) act more like voltage limited current-alike sources.
Thank u so much. I understand now, actually, in summary, it's about design. Since we are not the people who produce the audio interfaces, we cannot know exactly which numerical values we will reach unless we measure on the devices.

Correct.
The calculations can be made from the plots @dfuller linked to.

You can calculate the voltage limit from 300Ohm load power levels and current limit from 16 Ohm (or lower) power limits.
When these low impedances aren't measured 32 Ohm power rating plots could give a clue of the current limit.

Correct.
The calculations can be made from the plots @dfuller linked to.

You can calculate the voltage limit from 300Ohm load power levels and current limit from 16 Ohm (or lower) power limits.
When these low impedances aren't measured 32 Ohm power rating plots could give a clue of the current limit.
i have one question more
Is the 8x rule correct ? For example i have audent evo 4. Audient evo 4 has 22 ohm headphone output resistance. So 22*8=176 ohm
Can't I use the Dt 770 80 ohm with this audio interface? Does the frequency response of the audio interface deteriorate ?
For example there is m50x (38ohm) using with Evo 4 together
Or id4 mk1 has 22 ohm headphone output resistance.

i have one question more
Is the 8x rule correct ?

Rules are there to be broken.

The reality is some headphones do not have a substantially varying impedance, some do.
Low impedance headphones that do have a substantially varying impedance are best connected to low output R amps.
Low impedance headphones that do not have a substantially varying impedance do not vary much in tonality on higher output resistance amplifiers but do sound a lot softer in loudness on them.

For this reason the '1/8th rule' was invented... why not 1/10th beats me, would be easier to remember and is 'even better'.
Anyway.. when you do adhere to this rule your will always be on the 'safe' side of things when it comes to tonal balance changes.

Problem is that not all manufacturers specify the output resistance.

So while there is a 'rule' it is kind of arbitrary and does not apply in all cases.
Lets just say that in general it is best to have a headphone amplifier with a low output resistance.
I would consider amps with an output R below 5 Ohm to fit this description.
It really does not matter if it is 0.01 Ohm or 1 Ohm. This is inconsequential but gives very different 'damping factor' numbers but not audible effects.

Rules are there to be broken.

The reality is some headphones do not have a substantially varying impedance, some do.
Low impedance headphones that do have a substantially varying impedance are best connected to low output R amps.
Low impedance headphones that do not have a substantially varying impedance do not vary much in tonality on higher output resistance amplifiers but do sound a lot softer in loudness on them.

For this reason the '1/8th rule' was invented... why not 1/10th beats me, would be easier to remember and is 'even better'.
Anyway.. when you do adhere to this rule your will always be on the 'safe' side of things when it comes to tonal balance changes.

Problem is that not all manufacturers specify the output resistance.

So while there is a 'rule' it is kind of arbitrary and does not apply in all cases.
Lets just say that in general it is best to have a headphone amplifier with a low output resistance.
I would consider amps with an output R below 5 Ohm to fit this description.
It really does not matter if it is 0.01 Ohm or 1 Ohm. This is inconsequential but gives very different 'damping factor' numbers but not audible effects.
'' The reality is some headphones do not have a substantially varying impedance, some do. '' The impedance of the headphones is not stable? How ?

By design.
It also has nothing to do with stability but how well mechanically/acoustically well damped the driver resonance frequency is,
Only impedance measurements will show the extend of the impedance swings. It is never noted in specifications.

By design.
It also has nothing to do with stability but how well mechanically/acoustically well damped the driver resonance frequency is,
Only impedance measurements will show the extend of the impedance swings. It is never noted in specifications.
Thank u so much I want to buy id4 MK 2 and i will use 80 ohm dt770 pro and 250 ohm dt990 pro. What is your opinion for this topic ? Thank all answers.

should be no problem.
180mW in 80 Ohm, 120mW in 250 Ohm

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