Before we get into the question of What is Sensitivity in Headphones, grab a snack, sit back and relax because..
You’ve come to the right place!!
What I will bring you in this review
What is Sensitivity in Headphones?
SPL and Loudness
Amps and Impedance
Now without further ado, let’s get rolling!!
I previously never gave the word Sensitivity much attention. For the longest time, it was just an obscure term that you could find in the Specifications area of most audiophile headphones. It was just a number and didn’t mean a whole lot.
In reality, it’s pretty important! What’s unfortunate is that a lot of companies don’t specify it very well, and it’s becoming harder and harder to pin point a number a lot of the time.
Many times in my research, I will sift through countless pages in Google before I find a number. This should never be, as Sensitivity is crucial in determining if your headphones will need Amplification or not.
What is Sensitivity in Headphones?
Sensitivityis simply a measure of how efficient a headphone driver is at using the power it receives. What is a Headphone Driver? This power is used to deliver to us the sound we hear (free of distortion).
Sensitivity also refers to the amount of current that a headphone requires. Put another way, if there’s no current flowing through the voice coil of the driver, then there’s no magnetic field. If there’s no magnetic field, there’s no interaction with the magnet. If there’s no interaction with the magnet, there’s no movement of the diaphragm. No movement of the diaphragm = No sound. You can see how important Sensitivity is becoming!
If you have a headphone with a higher Sensitivity, it requiresless power (from the amp) to reach optimal listening levels. Hence, it’s more efficient.
If you have a headphone with a lower Sensitivity, it requires more power (from the amp) to reach optimal listening levels. Hence, it’s less efficient.
This is why it’s essentially useless to buy a powerful headphone amp for a headphone that has high Sensitivity. It just doesn’t have any use for all that power.
So in a nutshell:
Low Sensitivity = Lots of power required.
High Sensitivity = Less power required.
SPL and Loudness
General standards for loudness are around 110dB. If you prefer it louder than that, 115. If you prefer it quieter, 105.
Generally speaking, 97dB is about the middle ground, and is right on the cusp of what I would consider “low.”
A headphone like the HD600 has 97dB of Sensitivity and a 300 Ohm Impedance. This basically means that it requires around 20mW of power to reach this ceiling of 110dB that we talked about.
A great example of this is the relationship between the Audeze LCD4 and the Focal Utopia. On October 10th, 2018 I got a chance to attend the Music Matters Convention at Audio Advice here in Raleigh, NC.
There were a plethora of companies and reps present, including guys from both Audeze and Focal. I have already demoed the Utopia’s on many occasions and to this day they are still the best headphones I’ve ever heard. I wanted to do an A/B comparison with the LCD4 to see if I liked those better.
I was using the fantastic NAIM DAC-V1, and first started with the LCD4. It took quite a bit of knob turning to get the music to an optimal listening level. Why? Because it’s not very efficient. It’s Sensitivity is 97dB.
Once I finally got it high enough (around 100+ on the NAIM) I really liked the sound but thought it lacked a certain energy. It’s a very dark headphone in general, keeping in line with the theme of most Audeze headphones.
Here’s the kicker, and something I knew, but forgot about mid-demo with all the excitement going on, 24bit/96kHz files, Tom Petty’s “Don’t do me like that”. Oh God it sounded sublime.
Anyway, before I get too excited like Solid Snake when Meryl show’s him the gun she snagged for him..
The Utopia’s Sensitivity is 104dB/mW, so it needs less power to reach optimal levels. You can guess what happened. I forgot to turn the volume back down and plugged in the Focal’s. Pressed play and OMG MY EARS!!! I’m dying! Lol. What is SPL?
Mellow out man!
Lol. This is a simple way of describing the concept. Not the video. Haha.
So with a headphone that has a 105dB of Sensitivity, only 2.5mW of power are required to reach optimal loudness (110dB SPL). Easy right?
/Chart Coming Soon!/
Sensitivity is measured in either dB/mV (decibels per millivolt), while efficiency is measured in dB/mW or dB/W (decibels per milliwatt/watt).
Amps and Impedance
Essentially, a headphones Impedance, Sensitivity and resulting Efficiency will help you determine if it requires an amp to reach a listenable level. Listenable simply means loud enough. Peak loudness. It doesn’t just mean “I can hear the music.” If you were to plug an HD600 into your phone without an amp you’d wonder what all the fuss was about. It doesn’t sound good at all, and is much too quiet to actually enjoy.
Higher Impedance headphones need more power from the amp.
Lower Impedance headphones need less power from the amp.
We discussed briefly the power requirements of the HD600. Again, all you really need to know before buying an amp is the Impedance and Sensitivity of the headphones. Both are very important.
The HD600 absolutely needs an amp because it has both a low Sensitivity and high Impedance.
Something like the Samson SR850 doesn’t need an amp because it has both a High Sensitivity and Low Impedance. This basically means that it can achieve a loud sound with hardly any power.
A lot of Planar Magnetic offerings such as my beloved HE400i have a very low Sensitivity (93dB) but also a low impedance. So it needs quite a bit of current, but also a lot of power from the Amp to reach an acceptable level; somewhere between 39-79 mW. Learn more: HIFIMAN HE400i Review!
Even some really cheap open backs like the venerable AKG K240 have extremely low Sensitivity (91dB) and must be paired with an amp. Learn more:AKG K240 Review!
That said, it’s also important to take a gander at the spec sheet of the Amp/DAC in question as well!
For instance, my Oppo HA2 provides 30mW of power into 300 Ohm. It just makes the cut for my HD600’s. Anything over 300 Ohm is not recommended.
An amp like the Magni 3 provides 430mW into 300 Ohms. This is why it works so well with a variety of headphones. It becomes an all purpose tool. The Objective 2 from JDS Labs is similar. It pumps out an insane amount of power for all impedance levels and does fantastic with every headphone I’ve tried with it. Clean and neutral!
One of the best tools at your disposal is a simple spec sheet from the manufacturer when looking at amps. If it doesn’t clearly indicate power outputs at various Impedance loads, you should probably next it. Lol.
A good example of a company I trust is JDS Labs. They always provide concrete numbers so there’s no confusion, their amps are some of the best around, and they’re extremely affordable. I’ve tried their cMoy, Objective 2, and Element. They’re all top notch and provide an insane amount of power into any Impedance rating.
Let’s take a look:
The Objective 2
Max Output (33 Ohms): 613 mW
Max Output (150 Ohms): 355 mW
Max Output (600 Ohms): 88 mW.
Max Continuous Output, 600Ω140 mW (9.4VRMS)
Max Continuous Output, 150Ω505 mW
Max Continuous Output, 32Ω1.1 W
Peak Output Power, 32Ω1.5W
The Element is definitely more powerful than the Objective 2, but both amps sound fantastic. I did a neat comparison on the two if you were interested: JDS Labs Element vs. Objective 2! Check it out if you fancy 🙂
With that, let’s wrap this thing up!
Sensitivity in headphones is a tricky subject, but shouldn’t have to be all that complicated. Generally, a headphone with around 97dB or below isn’t that efficient. Most headphones below this threshold tend to be planar magetics like HIFIMAN, Audeze, etc. Some like the K240 are also extremely low and that’s why it’s important to know these things before you buy!
A headphone that’s around 100dB and greater is very efficient, and usually doesn’t need any sort of amplification to sound good. The internal amp in your mobile device should suffice in most cases, but it’s never set in stone.
My top option for a headphone around the threshold of 97dB is of course my beloved HD600. Interested in learning more about the Gold Standard?
My top option for a higher Sensitivity headphone that doesn’t need a lot of power is most certainly the Sony MDR V6 @ 106dB. It’s been a quintessential studio headphone for decades, and I don’t see it leaving my studio anytime soon!
Stu is determined to provide the truth about all things audio, and strives to deliver excellent content to you the reader! In his spare time, he likes to fish, paint, play guitar, attend church, take photos, record videos, graphic design, and more. His attention to detail and perfectionist attitude are what allow him to excel, but it can be both a blessing and a hindrance at times.