Do headphones really need a bass boost?

Die somniantes

SRSLY??? R U **NG KDDNG ME?

For God's sake, it seems Goldenears.net has officially implemented a low-frequency boost in their headphone measurement data, +9 dB for earphone, and +6 dB for headphones respectively, caused by the missing 6 dB effect. And they verified the claim with a comprehensive listening test as well. Wait a minute, the effect has been debunked already!

Previously, GE's contradiction on mannequin measurement data has been discussed. While their idea of a high-frequency attenuation is a reasonable method to minimize possible perceived tonal error for reproducing loudspeaker materials, correlating such subjectivism with mannequin data simply does not work, considering how IEC 60268-7 clearly defines the purpose of a mannequin use.

Basically with the claimed target curve, its "ideal" headphone should have a frequency response with a sound pressure attenuating as the frequency arises, as seen above. It is absolutely true that a negatively tilted room response is ideal for a hi-fidelity loudspeaker reproduction. And although headphone manufacturers know it is not a definitive solution to diminish the association principle mismatch between loudspeaker-headphone acoustics, they still tune their headphones in a similar way, so that their headphones do not sound too sharp and dry. According to Dr. Sear Olive's research from 2009:

"A flat in-room target response is clearly not the optimal target curve for room equalization. The preferred room corrections have a target response that has a smooth downward slope with increasing frequency. This tells us that listeners prefer a certain amount of natural room gain." from: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html

And GE's target curve closely matches the above description quite well. Well, there is always a catch:

"If the room is acoustically dead with few reflections and/or the directivity of the loudspeaker is quite high, the in-room response will represent a higher proportion of the direct sound, which should be flat. Using a target curve with large downward tilt will make the loudspeaker sound too dull...The only case where a flat in-room response would be desirable was if the room were the acoustic equivalent of an if anechoic chamber and the listener is hearing just the direct sound."
from: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html

Not to mention even a slight offset of a driver placement on the head causes a night and day difference in the frequency response(extremely directive), considering headphones' transient properties mostly derive from the drivers' own sole mechanical performance, it is only logical to assume the (compensated) frequency response must remain flat on headphones. Should GE's claim verified to be true, typical headphone measurement data must be as complex as in-room loudspeaker measurement data, with various reflective/reverberant characteristics skewing the direct sound. Unfortunately, that is just not the case with headphones; even cogitating a very-reverberant SONY MDR-CD3000's measurement data.


A compensation to no avail

Then how about the listening test? GE say they were able to verify their claim under a reference test condition. As mentioned before, to normal untrained listeners, the low frequency error is still prevalent due to the association principle mismatch. The bottom line is that there is absolutely no way to correctly measure the definitive number for compensation, since it is deriving from an auditory illusional phenomenon after all.

from Olive and Rumsey

One may argue that there is a ~6 dB bass level increment even in IEC 60268-13 conditions, headphones must reflect it as well. According to the above data, this argument seems sound. However, it must not be forgotten that below the Schroeder frequency, at which the room acoustics start to kick-in, there is no absolute 'response target' in regards to 'an ideal bass':

"it is necessary to diminish the importance of the curve at these low frequencies. In fact, we can ignore these effects because they will be merged with, and indeed swamped by, the standing-wave/room resonances active in this frequency region." F. Toole, "Sound Reproduction", Focal Press (2008).

Moreover, there is nothing known about GE's room condition, so it can't be assumed that the sound pressure level difference perceived between speakers and headphones was correctly measured. In other words, even if the frequency responses of both speakers and headphones were well-matched, other factors might have altered the perceived in-room response; there are just too many acoustic variables affecting this frequency region.

"there was evidence of variations in judgments due to irregularities in bass performance. Again, humans seem to be able to adapt to a certain amount of bass misbehavior, but the more extreme the problem, the more difficult it is to completely ignore...there is nothing that can be done in advance of building and setting up a room that has a high degree of certainty of achieving good bass. Probabilities may be improved in some respects of acoustical performance, but not all respects. There is no “magic bullet.” F. Toole, "Sound Reproduction", Focal Press (2008).

Various reference targets do not reflect such hump in the sub-bass region: from B&K, Olive, and Toole.

And how about the discrepancy with earphones? It has been found that the eardrum over-excursion caused by a pressurized ear canal increases the lower frequency response. Since this type of excursion error causes a boost of ~15 dB @ 20 Hz, GE's "test-confirmed" compensation figure of as much as 9 dB can be explained. As the perceived bass of earphones mostly depends on the interpersonal variance of the eardrum's compliance & the amount of air pressure built-up in the ear canal, GE's approach can be interpreted as a case of haste & immature generalization.

Do headphones really need a bass boost?

With all the data I've discussed put into consideration, I would say the answer is definitely 'NO'. A simple amplification in the sound pressure level may reduce the error for normal listeners, but does not solve the source of the problem. Also, it is not simply possible to turn headphones into loudspeakers either, unless an accurate binaural synthesis is implemented.

I think, ironically, headphone enthusiasts' best bet lies in loudspeaker acoustics, by extending the low frequency bandwidth:

"The average bass extension - the low-cutoff frequency - progressively decreases as the fidelity rating increases. The listeners liked low bass - not more bass, in the sense that it is boosted, but bass extended to lower frequencies." F. Toole, "Sound Reproduction", Focal Press (2008).

Then why flogging a dead horse?

I've been wondering, why such objectivism-oriented websites continue to implement rather 'unobjective' test methodologies, when the resulting data can seriously mislead the end-users? Such target curve turns typical headphones' frequency response more favorably to the manufacturers, who simply rely on a pressure level compensation due to the lack of research on their ends. As long as the graph looks good, the product should sell. Since commercial-oriented websites depend on sponsorships, their relationship with headphone manufaturers can be easily understood; They do this for living, in the end. (wait, that is why I can't get a single test sample from any manufacturers! LOL)