If you use low-impedance earphones, your first priority should be keeping the amplifier’s output impedance at 2 ohms or below. Connect a 16-ohm load to an amplifier with a 10-ohm output impedance and the damping factor drops to 1.6, which produces a sound pressure deviation of up to 1.9 dB on models whose impedance varies with frequency.
What to prioritize
This article picks up where Do You Need a DAC/Amp? left off. Once you have decided that you need one, the next question is which numbers to check.
The definition of damping factor (DF) is simple: it is the load impedance divided by the amplifier’s output impedance, or DF = Z_load / Z_out. Drive a 32-ohm pair of headphones from an amplifier with a 1-ohm output and the DF is 32; drive the same headphones from a 10-ohm output and it drops to 3.2. As a rule, higher numbers are considered better.
Although this figure is often explained through the image of “controlling the driver,” in the context of headphones a different phrasing is closer to what happens in practice. What is at work here is voltage division. Because the amplifier’s output impedance and the load sit in series, the voltage across the load drops to the ratio Z_load / (Z_load + Z_out). Converting that ratio into decibels gives the attenuation.
What matters here is that headphone impedance is not constant across frequencies. Even when a model is rated at a nominal 32 ohms, it is not unusual for its impedance to rise to 64 ohms at its low-frequency resonance point. When impedance moves, the voltage division ratio moves with it. In other words, driving headphones from an amplifier with high output impedance alters the frequency response itself. At bottom, the damping factor question is about whether the tonal balance changes.
Here is the calculated difference. When a model whose impedance swings between 16 ohms and 32 ohms is driven from different output impedances, the sound pressure deviation works out as follows: 0.13 dB at 0.5 ohms, 0.26 dB at 1 ohm, 0.50 dB at 2 ohms, 1.10 dB at 5 ohms, and 1.86 dB at 10 ohms. By contrast, on a model whose impedance swings between 250 ohms and 600 ohms, driving it from a 10-ohm output keeps the deviation within 0.20 dB.
The gap between those two figures sets the order of priorities. High-impedance headphones are insensitive to output impedance; low-impedance earphones are sensitive to it. Checking how many ohms your load is comes before shopping for a “better amplifier.”
Three patterns calculated backward from the load
All of the figures above are calculated values, not measurements. Because DF, attenuation, and deviation are determined solely by nominal impedance, the same formulas apply regardless of the model. Conversely, anything that does not come out of these formulas (distortion, noise, actual timbre) is not covered here.
Attenuation of 4.2 dB at 16 ohms drops to 0.144 dB at 600 ohms
Attenuation caused by output impedance shrinks as the load increases. With 600-ohm headphones, even a 10-ohm output drops the level by only 0.144 dB. A difference of 0.1 dB is too small to tell apart even in an instant A/B switch.
With that same output impedance, a 16-ohm load drops by 4.217 dB. That is a clearly audible loss in volume. Still, if the only effect were lower volume, turning the volume knob up would settle it. The real problem lies further on.
Because attenuation is a function of load impedance, a model whose impedance varies across frequencies suffers different amounts of attenuation at different frequencies. A 16-ohm point drops by 4.2 dB, while a 32-ohm point drops by 2.4 dB. The 1.86 dB difference between them turns directly into a ripple in the frequency response, and turning the volume up cannot correct it.
It is equally important to be clear about what the calculation does not tell you. Nowhere in the formula does it say what DF value makes the sound “good.” A rule of thumb of 8 or higher is widely used, but that is an operating convention rather than a standard. The table above uses DF 8 as its benchmark simply to match that convention, not because the number 8 has a special physical threshold.
There is one more limitation in nominal impedance itself. Manufacturers usually state the value at 1 kHz and do not publish the full impedance curve across frequencies. The premise of “swinging between 16 ohms and 32 ohms” is therefore an assumed condition we set for calculation; the actual swing of a given unit cannot be known without measuring it.
Quantities derived from nominal specs and quantities that require measurement
Every figure up to this point is determined by nominal impedance alone. Differences caused by output impedance amount to a few decibels at most, and depend on the impedance curve of the specific model. Distortion, noise, and actual tonal color do not come out of the same equation.
A table built strictly from nominal values has one practical advantage: plug in the nominal specs of your own gear, and you can build the exact same table for your setup. For deciding whether you need an amplifier in the first place, see the earlier article linked above.
A high damping factor does not by itself prove driving power
Records to listen to in this setup
Music with sustained bass makes the difference easiest to hear on models with large low-frequency impedance swings. In recordings where the bass holds the same note at length, such as spiritual jazz, the attenuation in that band shapes the impression directly. That is why playing the same record through devices with different output impedances can make the weight of the low end sound different.
If you care about this number on low-impedance earphones, checking the fit first makes a much larger difference. Changes in seal, covered in What Changes When You Swap Ear Tips, move the low end by far more than a few decibels. In order of priority, fit comes first and output impedance comes second.
On recordings with a narrow bandwidth and little low-frequency information, the difference rarely shows up. With 1960s jazz or mono recordings, there is little need to worry about this figure; in many cases the era of the recording matters far more than the electrical conditions of the gear.
DF, attenuation, and deviation are values calculated from nominal impedance, not measurements of actual units. Calculated on August 25, 2026.
Sources and technical standards referenced: International Electrotechnical Commission IEC 60268-7 (Sound system equipment – Part 7: Headphones and earphones) and Sennheiser HD 650 official technical specifications (checked August 25, 2026).