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Originally Posted by Tomcat
As I said, if what I hear pleases me, I'm glad. I tend to look like this:
Actually, I believe the gravest mistake any audiophile can make is disregarding listening pleasure.
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Of course I don't disregard it, as little as I want to establish guidelines for other people's listening philosophies. Just my own thoughts on the matter from an objectivized view. The motto: «if it sounds good, it is good» is a bit naive, at least it doesn't take into account how much the sound can be manipulated until it sounds pleasing. I'm definitely not a lover of euphony, not just from an ideologic standpoint, but at least as much from how I'm touched by the music. I don't like a sugarcoated sound.
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| But about your point of fidelity. What about speaker cabinets? Are they merely effects devices, altering the inherent performance of a driver in an undesirable fashion? That's hardly the case. |
The dimensions are quite different, therefore the resulting effects are as well (--> wavelength!). But the effects from a closed cabinet are undeniably audible and predominantly not of a pleasing kind to my ears. Actually you can't sufficiently dampen the sound waves radiated into the cabinet, so they will be reflected back to the driver membrane and through the latter, mixed to the direct signal, meanwhile full of dirt (resonances, distortion...).
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| A properly designed enclosure will change the driver's resonance frequency... |
...yes: in an unwanted direction: to higher frequencies...
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| ...it will improve the acoustic impedance... |
...no, at least not in a favorable way, as the acoustic impedance becomes highly uneven and frequency-dependent, making for a higher Q factor, which means in fact lower dampening of membrane movement than in the free field, so you can virtually speak of a lowered acoustic impedance...
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| ...it will increase efficiency and dynamic behaviour at lower frequencies and it will increase bass extension. |
Efficiency is only increased around the bass resonance, in fact by making the resonance more resonant -- an unwanted, but unevitable effect for achieving reasonable bass extension at all. Which indeed needs the enclosure to avoid cancellation from the opposite-phase rear sound waves, but that doesn't mean the enclosure has a favorable effect, it's just for allowing decent bass reproduction in a living room. You'd get better -- lower, cleaner and more accurate -- bass without the enclosure, e.g. by using an infinite baffle (i.e. a wall) for preventing phase cancellation instead. Or you can use a finite baffle (dipole principle) which allows -- in cooperation with equalization -- for lower frequencies down to and even below 20 Hz without drop-off and is the only way to renounce any system resonance in the audio band (usually the bass resonance is the only directly audible driver resonance, because the ones of squawkers and tweeters are cut off by the crossover network). Moreover it drastically reduces the excitement of standing waves in the listening room (because of its directionality). You see: the speaker cabinet is rather a necessary evil than a blessing. You can look at it this way: Every interface and every hollow space is acoustically harmful, because it inevitably changes acoustic impedance in a frequency-dependent way and makes it uneven, generally speaking does a lot of harm in the time domain which isn't (fully) corrigible anymore. Hollow-space effects, (near-field) reverberations and resonances are three of the worst evils in audio. But they can absolutely have pleasing effects at times, to some ears.
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| I perceive similar effects from closed headphones. By balancing the volume the driver has to work into and the volume the driver works out of, the diaphragms movement becomes more piston-like. Less break-up at higher excursion and SPL levels, which, again, is especially relevant for the dynamic reproduction of lower frequencies. To my ears, a good enclosure improves bass response, slam and, before all, it improves harmonic cohesion in the crucial fundamentals range. Instruments have greater palpability and a more natural body with closed headphones. More music, less hi-fi. |
The latter point may indeed be true, but I'm not sure what you're trying to say with your technical description. The more piston-like membrane movement actually isn't a quality criterion with headphone membranes, since they're designed to act as partial vibrators and therefore have very soft membranes. Also I can't see how a closed design could improve this behavior. But if you're speaking of the closed pressure chamber between driver and ear in the case of a closed design, you're right that it offers the advantage of lower membrane movement in that it can make full use of the radiated sound waves, at least with lower frequencies, and that's a fundamental difference to fully open designs such as the HD 650, MDR-F1 or K 1000. BTW, also open designs with sealed baffle offer this feature, so it isn't reserved to headphones with closed back. And that's why the closed back on the HD 650 makes no sense at all, because it doesn't make a closed headphone out of it, since its baffle is completely open -- so the described positive effect from the closed design (actually the sealed baffle) doesn't apply here. In turn the closed back doesn't offer the least advantage when it comes to signal accuracy: it can only make it less accurate by introducing resonances and reflections. In terms of prevention of phase cancellation the speaker analogy doesn't apply here anyway, so from this perspective the closed cabinet doesn't make sense at all.
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| It's not all that easy to overcome the inherent problems of an open headphone design. You are aware that the world's very first open headphone was invented by Sennheiser in 1968: the HD 414? You know, up to that point, all headphones were designed as they ought to be: closed. |
In fact it's the other way round: It's not easy to overcome the problems of the closed design -- as today's headphone designers probably will confirm unisono. The HD 414 was a fully open design and as such revolutionary, but the most revolutionary component was the supraaural design -- which I'm sure caused some problems for achieving a proper frequency response at the beginning, as it was a fundamental change of the acoustic precondition (maybe including the not airtight seal from the foam cushions). The open rear should have caused minor problems, if at all just because of the deviation from the norm when it comes to sonic balance.
I don't deny the sonic merits of closed headphones, but as I see it they are mainly the result of pleasing effects rather than of signal accuracy. Maybe in a way like impressing thumping bass can be perceived as «thight» and controlled, although it's in fact highly resonant (like typical disco bass).
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