Why are there so few headphones that can cover the full audio range well?

High end Etymotics should cover the spectrum without any audible volume differences between the frequencies. Texture wise the bass could use some help as it's fairly one note.

Other than that, I'm not sure that's what any manufacturer us after. Personally, I'm shocked that nobody has been able to tune and electrostatic or 8-element IEM to be flat as a rail and incredibly defined in every range.

When I briefly listened to the LCD2, I didn't notice the bass excelling over the treble. It seemed indistinguishable from reality to me during the 10 minutes I listened.

Other than that, perhaps it's all relative. If treble is bright, then the bass isn't going to sound as deep unless it's a V-shaped curve, and if they bring up the midrange, it will be back to a neutral 'bland' Etymotic like sound.

My understanding, and this is based on "bigger" speakers, is that it isn't fundamentally possible to produce a single driver that can reproduce a true flat full-range signal (or to put it another way, to produce a driver that can perfectly reproduce the input signal - this isn't 20-20k, this is 0-inf). With speakers you get around this by using multiple drivers and a crossover, but the crossover will introduce problems of it's own (phase distortion). Multi-driver headphones (I don't mean IEMs) do exist, but most of them have their own host of problems (the only modern production multi-driver headphone I can think of is the Klipsch M40; they don't sound bad per se, but they're a very unique listening experience to say the least).

You also have to remember that most headphone designers (just like most speaker designers) don't target an arbitrary "ruler flat" reference, they target something more tangible, like a given compensation curve, or a specific house sound (look at AKG 240DF and Grado RS-1 as examples - neither is designed from day 1 to be "ruler flat," they both aim at different references).

Basically with any speaker design (and I assume with headphone designs as well), you always have to make a compromise at some point. Sometimes related to cost, sometimes related to more direct limits - like physics (in other words, that 0-inf driver can't exist, so there's a compromise), or what can actually fit on a human head, or if your Super-Special Ultra-Mega-Swanky 5000XL can be mass produced (so sure you can build the ultimate headphone as a one-off and spend 300 hours on it, but can you translate that to an assembly line that turns out a few thousand of them?). You also have to remember that just because it can shoot "ruler flat" in an anechoic environment, doesn't mean it will sound that way to the listener. With a headphone, a "ruler flat" response would sound fairly bright, for example.

Finally I think customer preference plays a role - not to quote Guttenberg too heavily here, but how many people in general really want a ruler-flat headphone or speaker outside of the audio engineering/production world? Most people I know, and most threads I see, tend to want some form of colored response or another. So even if all of the above is a non-issue (say it is for the sake of argument), would it be worth the investment on the part of whatever company to produce Super-Special Ultra-Mega-Swanky 5000XL? Or are they going to be better off producing Bass-Boomer Deluxe, Ultra-Detail Master Mark VI, and Generic Celebrity Endorsed Swagerphone instead? This is probably the least critical reason that, overall, the above doesn't exist (because I'm sure someone, somewhere, would do it, even if the market is small), but it probably explains why companies with huge budgets (like Monster, Sony, etc) don't spend their time on such a problem.
Edited by obobskivich - 10/14/12 at 9:55pm

 

As a matter of fact, I agree on this point. At one point, the market is highly favoring Beats. Nobody's gonna give up profit for the sake of "true" audio quality. Everyone wants a share of the new trend.

Both LCDs and HEs do cover the hearing range, but maybe not in a way you define as 'well'. The problem is that there are limits to mechanical equalization. Maybe with a lot of R&D you could construct a headphone and a driver that has a frequency response nearly exactly as you want it, but that amount of R&D only happens with high-end headphones and even then there's probably way more listening than measuring resulting in a sound the engineers like. What these people like can be very far away from "covering the full audio range well" or flat. And headphone measurements are far from perfect as well.

 

Sources? I'm not so sure sources struggle covering the full audio range.

Edited by xnor - 10/15/12 at 12:10pm

Also remember that human hearing is variable, and we are more sensitive to some frequency ranges than others. So a headphone with "recessed mids" may not affect the audible effect to the listener, since they can hear mids better than lower frequencies anyway. 

 

There is a lot at play. And for me, performance in the sub 30hz to over 15khz range is mostly a non-issue. 

There are lots of design compromises with headphones.

- Most headphones are closed which is inherently bad for acoustics (standing waves form, resulting in certain frequencies being louder than others), but needed for isolation.

- Headphones usually only use a single driver for all frequencies (opposed to separate tweeter and woofer with a crossover). I'm sure manufacturers do this for a reason.

- The small size makes it difficult to design a flat response.

 

You can get into timing and image placement problems with multiple drivers that close to the ear. Some manufacturers have managed that by having the tweeter nested inside the larger woofer. 

Crossovers can cause other issues (peaks/valleys) and take up space to add the capacitors and inductors needed. The general rule is that the best crossover is no crossover. 

Even if you do achieve a ruler flat response, I reckon you won't be able to 'hear' the whole spectrum, depending on the frequency components of your music. A 0dB tone at 10KHz will 'mask' out other tones at lower frequencies. You may get to hear them if your headphones aren't really neutral.

So there's no one way to enjoy music. The good thing about such a headphone would be that it can be EQ'd and used to create the desired response.

Edited by proton007 - 10/15/12 at 6:34pm

With planar magnetic drivers/orthos, from what I've read, there more that can be improve on the drivers. One is making the diaphragm even lighter with newer materials. Another is pleating the drivers like the ribbon drivers. This would increase the driver area and therefore can move more air.

That isn't correct. The masking effect causes higher frequencies to be cancelled out, not lower ones. And if your response is flat, you won't have a problem with it. Masking is an issue if you have spikes in the upper mids. (More like 2-3kHz than 10kHz) The spike masks the octave above, wreaking havoc with first level harmonics. A flat response has no masking, making the high end sound dull. That's why you want a flat response.

 

The reason most headphones aren't flat is because most people judge sound quality by accentuated bass and treble. They listen to electronic music where there really is no baseline response. Goosed bass and treble really isn't better sound, but that's how a lot of people think.

 

Better headphones, like certain models of Sennheisers are pretty doggone flat... flatter than any speakers. They sound MUCH better with acoustic music (jazz and classical) than colored cans.

Edited by bigshot - 10/15/12 at 10:45pm

 

Hey I didn't make it up, but thanks for the additional info. Masking can happen both in higher and lower frequency regions.

I'm curious about the context of that... where did that chart come from? I've never heard of masking down range, only up. Also, that chart shows a 20dB difference. When the effect was demonstrated to me, it was only a spike of a few dB around 3kHz that caused the treble to become clearly dull. 20dB seems like a lot. I'm interested to hear how masking is used in practice. I'm guessing that chart is illustrating something other than frequency response in music.

 

sure crossovers have their problems, but full range speakers still cannot compete with a tweeter+woofer+crossover design... the peaks/valleys are much worse when you try to use a single driver for all frequencies