Sep 29, 2017 at 12:51 PM
- Dec 12, 2011
- Reaction score
- Dec 12, 2011
Leakage in the chamber facing the eardrum. Free airflow out of the chamber at lower frequencies limits the bass response unless the driver is compliant enough that its excursion would increase in a leaky chamber to sustain low frequency pressure. If the stiffness of the driver is far greater than the cavity, the excursion does not significantly change and a large loss of bass can be observed.What exactly do you mean by leakage in the headphone leading to limited bass extension? The iSines are open back and doesn't require a tight seal from the tip, but the bass is well extended.
Opening the back alone does not. The ear cavity leak is the very reason for difficulties in pressurizing below the fundamental. This is deliberate in typical open backed headphone design. This may illustrate the point more clearly.1. In an open headphone? Wouldn't the open back make any intentional leakage moot? I know that the trend lately is for closed designs to have intentional leakage built in so as to decrease reliance on a tight seal, but I was of the understanding that dynamic drivers have poor bass extension in open enclosures because they have trouble producing output below their resonant frequency.
2. Above about 10 kHz, this is certainly true for every headphone, and it's also outside the guaranteed area for measurements so it's probably safe to ignore what happens here unless the average output is markedly deviant from the norm. Below that, though, there are headphones that measure reasonably smoothly and ones that don't. Maybe the average trend line is the most important thing, but there's certainly better and worse performance here.
3. The source of measurements doesn't matter, as long as the measurements are internally consistent. Tyll's raw measurements universally show the peak at ~3.5 kHz in headphones, and at ~2.5 kHz in IEMs. For that matter, all the raw measurements I've seen elsewhere also have the peak at around 3.5 kHz in headphones, so if it's actually supposed to be 2.7 kHz, then all these measuring rigs have the same error. And even if they do, this is irrelevant because the IEM measurements are still offset by about 1 kHz from the headphone ones, and it's this offset--not the actual numbers--that's important. Significantly, Tyll's dummy head stuck in a room with speakers measured the peak around 3.5 kHz, implying that where it places this peak for headphones corresponds to what a listener actually hears with speakers or with live music. The IEMs are the odd one out here.
3.5. The 1 kHz bump in electrostats and planars is in comparison to other headphones, which generally don't have this feature. The compensation shouldn't matter, as the difference exists regardless of the compensation used. One may of course argue that this level of energy around 1 kHz is actually correct, and that headphones that don't have it are less accurate in this area. Tyll's new compensation curve incorporates this very assumption, in fact. However, that of course is debatable and it nonetheless doesn't obviate the existence of the 1 kHz lift as a distinct feature shared by electrostats and planars and rarely seen elsewhere.
4. Indeed, this is the difficulty in getting an IEM to sound correct. Unfortunately, because of the physics involved with shortening and stopping up the ear canal, they struggle. Additionally, an individual listener might prefer a deeper or shallower insertion depth or different tips from the ones the IEM was designed and tuned for, and the depth and fit might vary significantly each time the IEM is used. These factors will create variations in performance from user to user and from session to session. It's a difficult set of problems to overcome, and it's kind of amazing that any IEM manages to sound good.
5. I'll defer to the consensus of the thread here, since this is a topic I could stand to learn more about. I'll submit some points for discussion, though. In my understanding, treble spikes generally produce ringing, but at least in the case of the DT880, this doesn't seem to be the case. It has significant spikes at ~6 kHz and ~8.5 kHz, but I've seen CSD charts (elsewhere, in places unmentionable) that show it having a smooth, even decay across its entire frequency range. Additionally, its square wave measurements have only a small section of clear ringing at the beginning, which resolves to a flat line relatively quickly. Its measurements here mimic those of the HD 6x0 family, which does not have any significant treble spikes. Is there perhaps something going on here that has nothing to do with the treble, that's similar between the two headphones and which produces such similar square waves? Why don't the DT880's spikes ring the way they do on many other headphones? And, probably the most important question, how much of this can we actually hear?
The ear imposes its directional transfer function on the input sound. This is generally preserved in headphones, save some loading of the ear by closing it off with a headphone. If the canals are shorter than the average, the ear resonance is shifted upward when tested by a far off loudspeaker and when subjected to a headphone. The IEM must reconstruct the subject's open ear resonances that are not present.
Time and frequency compose a conjugate variable pair, and their response functions are related one-to-one to the other by Fourier and inverse Fourier transform. While we tend to ignore the phase component in practice and only consider the magnitude, headphones operate in mostly minimum phase.
A key property of conjugate variables is described by Heisenberg's uncertainty principle. A resonance that is sharply focused around around a particular frequency cannot be localized sharply in time, and vice versa.