Amplifier Power Specs

[Martin]

Why do headphone amplifier makers publish power specs at different loads?

Some examples using balanced input/balanced output figures:

• Topping A90: 2000mW (32Ω) / 320mW (300Ω)
• Benchmark HPA4: 6W (16Ω)
• Geshelli Erish: 1W (32Ω)
• Monolith THX 887: 8800mw (16Ω) / 6000mW (32Ω) / 700mW (300Ω) / 350mW (600Ω)

etc.

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

Thanks,
Martin

 

[RayDunzl]

Ohm's Law is the starting point.

http://www.sengpielaudio.com/calculator-ohm.htm

And there's a related headphone guesstimator:

http://www.digizoid.com/headphones-power.html

 

[RayDunzl]

I have a pair of LCD-3 that are rated to handle 5W at 110Ω.

5W @ 110Ω would require the amplifier to output 23.45Vrms and 213 milliamps.

Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

The power that can be drawn from an amplifier by some specific load could be limited by the voltage it can output, or by the amount of current it can supply.

Plug in numbers and see what happens.

 

[Doodski]

Why do headphone amplifier makers publish power specs at different loads?

Some examples using balanced input/balanced output figures:

• Topping A90: 2000mW (32Ω) / 320mW (300Ω)
• Benchmark HPA4: 6W (16Ω)
• Geshelli Erish: 1W (32Ω)
• Monolith THX 887: 8800mw (16Ω) / 6000mW (32Ω) / 700mW (300Ω) / 350mW (600Ω)

etc.

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

Thanks,
Martin

The amplifier output power versus the load-headphone resistance is not linear. If it was linear then each time the headphone resistance halves then the power will double. That is according to Ohms Law. As you have seen the power rating into various headphone resistances does not seem to have any sense to the numbers and that is because the amplifier cannot maintain linearity into the lower load resistance. The lower the load-headphone resistance is then the more difficult it is for the amplifier to drive the headphones and the linearity suffers. In the case of a non-linear amplifier there is no formula and the only way to know is to measure the amplifier output at various headphone resistance values.

 

[amirm]

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

As a guestimate, you can assume 2 to 3 times more power than 300 ohm rating. Current capability starts to become a factor there which it is not at 300 ohm, hence the range.

 

[RayDunzl]

I have a pair of LCD-3 that are rated to handle 5W at 110Ω.

While that is informative, it may relate to the limit the headphone can be expected withstand, say, by accident, and not how it would be used while cradling your auricles.

A more useful LCD-3 specification notes:

Sensitivity
101 dB/1mW (at Drum Reference Point)

If true, let's extrapolate toward the 5W measure:

111dB at 10mw (already more than loud enough)
121dB @ 100mw
131dB @ 1W

And the specification also notes:

Maximum SPL >130dB

 

[Martin]

Thanks for the responses everyone...

While that is informative, it may relate to the limit the headphone can be expected withstand, say, by accident, and not how it would be used while cradling your auricles.

A more useful LCD-3 specification notes:

Sensitivity
101 dB/1mW (at Drum Reference Point)

If true, let's extrapolate toward the 5W measure:

111dB at 10mw (already more than loud enough)
121dB @ 100mw
131dB @ 1W

And the specification also notes:

Maximum SPL >130dB

OUCH!

Martin

 

[JustAnandaDourEyedDude]

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

Here's a guesstimator using the same info as provided by the previous posters. You are considering a pair of headphones rated at a nominal resistance of Rh ohms (per earpiece), with a sensitivity of Ef dB/mW. A headphone amp mfr lists full scale (max vol knob setting) power P in watts into resistance (load) R in ohms (per channel) for one or more load conditions k=1, 2, ... as (R1, P1), (R2, P2), ... You want to know what max (vol knob setting) power Ph this amp will deliver per channel into the above headphones. In the mfr's list, find the load Rk nearest in magnitude to Rh. Then Ph can be estimated as Ph = Pk x Rk / Rh watts. From this, the max sound pressure level Ps in dB is estimated as Ps = 1000 x Ph x Ef. If all the electrical powers are used in milliwatts, then the preceding all stays the same, except Ps = Ph x Ef now.

The above guesstimate will break down if Rh is very low and the amp mfr has not provided a data point for a nearby value of R. Also, you can get fancier than the previous para if the mfr has provided more than one load data point by interpolating the voltage V (which is V = Sqrt[P x R]) of the two loads between which Rh lies to find Vh, and then calculating the corresponding power as Ph = Vh^2 / Rh.

 

[bahamot]

Why do headphone amplifier makers publish power specs at different loads?

Some examples using balanced input/balanced output figures:

• Topping A90: 2000mW (32Ω) / 320mW (300Ω)
• Benchmark HPA4: 6W (16Ω)
• Geshelli Erish: 1W (32Ω)
• Monolith THX 887: 8800mw (16Ω) / 6000mW (32Ω) / 700mW (300Ω) / 350mW (600Ω)

etc.

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

Thanks,
Martin

What you quoted for Topping A90 output figures are wrong.

 

[Martin]

Why do headphone amplifier makers publish power specs at different loads?

Some examples using balanced input/balanced output figures:

• Topping A90: 2000mW (32Ω) / 320mW (300Ω)
• Benchmark HPA4: 6W (16Ω)
• Geshelli Erish: 1W (32Ω)
• Monolith THX 887: 8800mw (16Ω) / 6000mW (32Ω) / 700mW (300Ω) / 350mW (600Ω)

etc.

I have a pair of LCD-3 that are rated to handle 5W at 110Ω. Is there some formula I can use to determine how much power a headphone amplifier will put out at 110Ω?

Thanks,
Martin

What you quoted for Topping A90 output figures are wrong.
View attachment 69302

Oops! My mistake...

Should have been:

• Topping A90: 7600mW (16Ω) / 6400mW (32Ω) / 250mW (300Ω) / 125mW (600Ω)

Martin