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What is frequency response (And why it doesn't matter)

In a recent Facebook post, discussing the merits of the Beyerdynamic DT990, the topic of their frequency response came up. For the DT990 in particular, it has an insanely wide frequency response range. 5hz to 35khz. 

Source: Beyerdynamic Website

So, does that 5 hz to 35khz mean the DT990 is good?

Nope! The DT990 IS a good pair of headphones, but that number has nothing to do with it. There are multiple reasons why these numbers are... well, to be taken lightly.

The Problems

Problem 1: Human Hearing -

Humans hear roughly between 20hz and 20khz. While this varies based on sex, age, individual, and source you use, the widest cited research I can find puts it between 15hz and 20khz. As we age we really lose our ability to hear high frequencies as well. According Chris D'Ambrose's page, by middle age we only hear up to about 15khz.

Source: Hypertextbook

In short, anything below 15hz or above 20khz is kind of meaningless to nearly everyone, though probably of great importance if you're making dog headphones!

Problem 2: Quality - 

The numbers given by headphones and, yes, microphone manufacturers is simply based on one thing: Can the device produce or receive that frequency. 

It has absolutely nothing to do with the question "Can it do it well?" or "Accurately?" or "Does it sound good?"

Source: DIY Audio Heaven

Take the graph above, which is called a frequency response graph, that shows how loud a sound is at different frequencies. You can see on the left is 10hz, which means in theory the DT990 is still producing graph results 5 more hz to the left, but given how quickly the volume is dropping off, even if your human ears could hear it, it would be entirely masked by the much louder 10-50hz range.

And here's the real kick in the teeth: Even this graph doesn't tell you if the sounds are being reproduced accurately. Often times these graphs are bandied about as proof of something. Sadly, a frequency response graph also has to be taken with a grain of salt because it is majorly influenced by several factors:

  • How well the headphones fit on the test device (or your head).
  • What device(s) are being used for playback, such as amps.
  • Or even just what mathematical formula you are using to draw the lines!

There's simply no industry standard for measurement, so two people testing the same headphones can come up with fairly different graphs. 

For instance: 


Source: GoldenEars.net

If you compare the two graphs above you'll notice that while they look similar, they are in no way the same. The bass hump peaks at 100hz on GoldenEars and at 150hz on Audio Heaven. You'll also see Audio Heaven has a massive spike at about 15khz (right at the edge of our hearing) that is far more muted in Golden Ears. I suspect this is because of the difference in calculation, Golden is using smoothing and Audio isn't. Which is right? Both? Neither? There's just no method that is agreed upon for doing this stuff.

The Counter Arguments:

Counter #1: +/- dB -

Very rarely you'll see a frequency response that looks like this

20hz - 20khz +/-3dB
This is actually a very different number than the ones above. This is a measure of flatness. It's saying that in the range between 20hz to 20khz the signal never moves more than 3dB up or down. This tells you a lot about what range of sound is produced in a loud way, but there's still no standard of testing that everyone is using, so this figure is prone to manipulation by the manufacturer. Still, it's better than nothing.

Counter #2: Felt Vibrations -

While we can't HEAR below 15hz, we can FEEL vibrations below this. That's the real value of a subwoofer. So if the driver is large enough and the headphones produce these low frequency waves strong enough (meaning their volume isn't dropping like a rock) maybe our ears can still pick up the feeling of the bass.

"Maybe" is the operational word here. In researching this I found a great thread on head-fi.org. SIX forum pages of people discussing, arguing, and questioning this idea. 

The short version is...maybe? Nobody seems to draw any grand conclusions. Some people say they can feel it, others say it's just psychological. Some people test multiple headphones using test-tones. Mostly people seem to agree that headphones drivers are too small and not powered enough to move the air in a way that sends any meaningful "infrasound" (the technical name of this low frequency sound).

The Conclusion:

So why does everyone still use these apparently arbitrary numbers? 

Marketing!

People really do look at these numbers. They influence people, that is why it came up in conversation. As a result, even though they're kind of pointless we can't just leave it out. People would notice and maybe even think something was being hidden.

Plus it does mean something. You certainly don't want headphones with a frequency response range worse than 20hz to 20khz, so if the headphones are telling you they top out at 10khz you have a real POS on your hands. It's like an assurance that yes, they make all the sounds you can hear.

This whole article has been about headphones for the record. This has nothing to do with what your voice can produce in sound, which varies far more widely based on individual, but by and large is far less than the 20hz to 20khz range.

Because a mic is likely not a clean source like the audio track of you listen to, and most of us are not trained opera singers, most microphones operate in a more limited scope, approximately 100hz - 15khz range, though there's plenty of wiggle-room, even among our own products, for higher and lower. Something around that figure tends to be the happy medium between quality voice pickup and rejecting unwanted room noise.

Just keep in mind that the frequency response range and the associated graphs, while important, are not likely to be what determines if a headphone sounds good to you. No matter the differences or the overblown frequency response range, both websites above, and we here at Antlion, agree the DT990 is an excellent pair of headphones with strong bass and treble.

And yes, they are a perfect addition for a ModMic


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