Some headphone models won’t get loud because their sensitivity is low relative to the limited power (especially voltage) your phone, laptop, or controller can deliver. When the source hits its output limit, turning the volume up further can’t add more real signal—so loudness plateaus.
Headphone sensitivity is the “how much sound you get from a little electricity” number. It’s usually written as dB SPL per milliwatt (dB/mW) or dB SPL per volt (dB/V), and that difference matters because most everyday devices are voltage-limited, not “infinite power” sources.
Sensitivity is loudness per input—so the unit decides what it predicts
Two sensitivity specs can describe the same headphone very differently:
- dB SPL/mW: how loud the headphone gets from 1 milliwatt of power.
- dB SPL/V: how loud it gets from 1 volt (RMS).
If your source is a phone dongle, a laptop jack, or a game controller, it typically has a maximum voltage swing it can provide before distortion or clipping. That means dB/V often predicts real-world loudness more directly than dB/mW—unless you also factor in impedance.
Impedance decides how much power you get from a given voltage
Impedance (ohms, Ω) is often treated like “high ohms = hard to drive,” but the practical rule is more specific:
- Your device can only provide so much voltage.
- The headphone’s impedance determines how much power that voltage turns into.
The key relationship (you don’t need to memorize it, just use the direction):
- Power increases when impedance is lower, if voltage stays the same.
- Power decreases when impedance is higher, if voltage stays the same.
So if two headphones have the same sensitivity in dB/mW, the higher-impedance one will generally end up quieter on a voltage-limited source, because it receives fewer milliwatts at the same volume setting.
A quick way to sanity-check “will this be loud enough?”
You can do a rough loudness estimate using simple decibel steps. The idea:
- Sensitivity tells you the SPL at a reference input (1 mW or 1 V).
- More input raises SPL logarithmically.
Useful rules of thumb:
- 10× power ≈ +10 dB
- 2× power ≈ +3 dB
Example with dB/mW
Suppose a headphone is rated 90 dB SPL/mW. Many people want peaks well above that (not recommended for long listening, but it happens). If you wanted roughly 110 dB SPL peaks, that’s +20 dB over 90 dB.
+20 dB requires about 100× the power (because +10 dB is 10×, so +20 dB is 10×10×).
So you’d need about 100 mW to hit those peaks.
Plenty of phones and laptops can’t provide anything close to 100 mW into many real headphone loads—especially not cleanly—so the headphone tops out.
Why this can mislead you without impedance
If that same headphone is, say, 300 Ω, your source needs a lot more voltage to deliver 100 mW than it would into 32 Ω. Many small devices simply cannot swing that voltage. Result: you might get only a fraction of the required milliwatts, and the headphone stays quiet.
dB/V is often the “tell” for quiet headphones on phones
If a headphone’s sensitivity is listed as dB SPL/V, you can interpret it more directly for typical consumer devices.
- If it’s high (for example, well above ~100 dB/V), it will usually get loud on almost anything.
- If it’s low, you’re more likely to run into “max volume, still not loud” scenarios.
The catch: manufacturers don’t always publish dB/V, and when they do, you still need to watch measurement conditions. But as a practical buying/diagnosis tool, low dB/V is one of the clearest warning signs for underwhelming loudness from small sources.
Why two “similar” headphones can behave totally differently
People often compare two models and assume they should reach similar volume because they both say “32 Ω” or both say “100 dB.” The problem is that those numbers might not be comparable.
Common mismatch situations:
- One sensitivity spec is dB/mW, the other is dB/V. They will not match unless you convert.
- Impedance varies by frequency. The “nominal” impedance on the box is simplified; real loads are more complex, which changes how much power the source can deliver at different parts of music.
- Different seal and fit change perceived loudness. Especially with closed-backs and in-ears, a better seal can raise bass and overall perceived level without the electrical signal changing.
- Some devices limit output for protection or compliance. Certain phones, dongles, and OS settings can cap maximum level, making any headphone seem “harder to drive.”
The real bottleneck is usually the source, not the headphone
When headphones won’t get loud, the limiting factor is typically one of these:
1) The device runs out of voltage
High-impedance headphones and many “audiophile” designs need more voltage to reach the same SPL. A dedicated headphone amp or a stronger output (some desktop interfaces, some DAPs) can provide that headroom.
2) The device runs out of current
Very low-impedance headphones can demand more current at higher volumes. Some small outputs handle voltage fine but sag or distort when current demand rises. That can sound like “it won’t get louder” or “it gets harsher instead of louder.”
3) The device is intentionally conservative
Battery-powered gear often trades maximum clean output for battery life, heat control, and reliability. Some controllers and laptops simply have weak analog stages.
How to diagnose the problem in 2 minutes
You don’t need lab gear to narrow it down.
- Try the same headphones on a stronger source (desktop interface, dedicated amp, AV receiver headphone out, or a reputable dongle known for higher output).
- If volume becomes normal, your original device was the limiter.
- Try easier-to-drive headphones on the same quiet device.
- If those get loud easily, the original headphones are likely low-sensitivity and/or need more voltage.
- Check whether sensitivity is specified in dB/mW or dB/V.
- Low dB/mW plus higher impedance is a common “quiet on phones” combination.
- Confirm nothing is software-limiting you.
- OS volume limits, “reduce loud sounds,” app-specific volume, Bluetooth absolute volume behavior, and communication modes can all cap output.
What actually fixes it (without chasing specs forever)
If the headphone is fundamentally low-sensitivity for your source, the solutions are straightforward:
- Use a source with more available output (often a better dongle DAC/amp, audio interface, or dedicated headphone amp).
- Choose headphones with higher sensitivity (especially dB/V when available) if you want guaranteed loudness from phones and laptops.
- Avoid assuming impedance alone predicts loudness. It’s the sensitivity-plus-source-limit combo that decides.
A final practical note: if you find yourself consistently needing “almost max volume,” you’re operating near the source’s ceiling. Even if it gets “just loud enough,” you’ll have less headroom for quiet recordings and may hit distortion sooner.
Why does this matter
When a headphone won’t get loud, it’s usually not defective—it’s a predictable mismatch between sensitivity, impedance, and the device’s output limits. Understanding that mismatch saves money (buying the right source or the right headphone once) and reduces the temptation to push unsafe listening levels just to compensate.
Sources
- https://benchmarkmedia.com/blogs/application_notes/14017381-headphone-impedance-and-sensitivity
- https://service.shure.com/s/article/understanding-earphone-headphone-specifications
- https://blog-en.beyerdynamic.com/what-impedance-should-i-choose-for-my-headphones/
