The Most Excellent Sennheiser Amperior and HD 25-1 II Page 2
Stretch a rubberband between your forefinger and thumb; with your other hand pull the rubberband like it was a slingshot; then let go. Sproing! It vibrates like a guitar string for a bit, and eventually stops. When you pulled the rubberband back, you were storing energy in it; when you let it go, it released the energy with a bunch of vibration before going back to its stable state.
In a headphone, the diaphragm makes acoustic energy, which radiates off the front of the diaphragm for you to hear. But the rear of the diaphragm also radiates energy and, in a sealed headphone especially, this acoustic energy pushes and pulls on the rear of the housing, which stores a bit of the energy depending on how elastic/stiff it is.
Now imagine you have headphones on, and you play the sound of a single hand clap. (No, not one hand clapping, one single hand clap ... an impulse.) You'll hear the sound at your ear, but the sound will also go off the rear of the diaphragm, smack the back of the housing, and have some of its energy stored. In the very next moment, it will release that energy and you'll have a little extra sound in the headphones that you may hear from the vibrations of the housing ... just a little ... but it's there.
In the image to the right, at the top you'll see again the inside of the HD 25-1 II. The small walls radiating from the center are there to stiffen the rear wall of the housing so it doesn't absorb and re-radiate acoustic energy ... but plastic is pliant, so it does store a bit. Below it, you'll see the Amperior's aluminum capsule housing. It doesn't have these stiffening walls, but because it's aluminum it's dramatically stiffer than the plastic housing. It will not store nearly the same amount of energy as the plastic housing, and therefore releases less energy after the fact to muddy up the sound.
This phenomenon is readily apparent in the measurements of these two headphones. In the 300Hz square wave responses to the right, you can see that both waveforms are quite similar in general, showing that these two headphones are nearly identical. But it's also obvious that the HD 25-1 II response is noisier. I think this indicates the capsule housing releasing the stored energy from the intense transient of the leading edge of the square wave. There is obviously less of this noise in the Amperior square wave.
Similarly, you can see in the impulse response of these two headphones that the HD 25-1 II "rings" more, and creates a longer trail of noise after the impulse.
Again, for my full take on the general nature of the sound quality of these cans you can read my review on the Sennheiser Adidas Original, which is exactly the same as the HD 25-1 II. All these headphones sound very good, indeed: clear, articulate, well-balanced, and punchy.
The big surprise for me, however, was the subjective difference between the plastic versions of this headphones and the aluminum Amperior. The effect of the small amount of extraneous noise in the less stiff housings of the plastic headphones was quite obvious. While the HD 25-1 II is a good sounding headphone, I would characterize its performance as "very good mid-fi," while my experience with the Amperior reached what I would consider "entry-level audiophile" performance. The Amperiors are the best sounding supra-aural sealed cans I've heard to date, handily besting the DT1350, V-Moda M-80, and, of course, the HD 25-1 II. I love these headphones.
Previously, I've felt the HD 25-1 II had a bit of an edge to them, in the case of the Amperior the highs are simply clear and articulate; there may be the slightest edge to the sound, but it's not bothersome in the least. Sure, they don't manage to pull off the airy, spacious highs of reference quality cans; and neither do they deliver the liquid coherence and transparency that a full-size, open headphone can. But for this type of headphone (small, sealed, portable) they are remarkable.
My One Gripe
Both these headphones did drive me crazy, though. The 1/8" stereo mini-plug at the end of the cable was TOO DAMN LARGE TO REACH THE JACK OF MY iPAD OR iPHONE THROUGH MY OTTERBOX DEFENDER CASE!!!! Jumpin' Geebus, Sennheiser, look around at the cables out there! Everybody is making slender plugs these days. What's up with that?
Sennheiser will be shipping the Amperiors with a three-button phone adaptor, but I don't know if it's going to have a small plug. The good news is that the cables are relatively easily replaceable, and if Sennheiser figures out that they've blown it on the connector and make a new cable, you'll be able to replace it.
Is it worth nearly twice the price of the HD 25-1 II for the Amperior? Yes! Sure there's always a diminishing returns curve for all things audio, but hogging out (machining), finishing, and anodizing aluminum capsules ain't cheap. The improvement isn't just cosmetic either; the increase in capsule stiffness nets a very real improved listening experience. Both are very high performers in this type of headphone at their respective price points, however.
Beyond the great sound quality performance, the incredible durability, excellent isolation, and extremely secure fit on the head, make both these headphones outstanding performers. The lower impedance and higher voltage efficiency of the Amperior make it an excellent portable headphone EXCEPT THE PLUG IS TOO DAMNED BIG!!!
Both these headphones are going on the Wall of Fame. The Sennheiser HD 25-1 II is an extremely cost-efficient headphone for audio pros needing a small sealed headphone for DJ, ENG, location recording, and musicians' studio purposes. The Sennheiser Amperior is simply an outstanding portable headphone for audio enthusiasts and pros wanting a headphone that will also be accurate and articulate enough for mixing and mastering applications. Both highly, highly recommended.
Video and Resources after the measurements.
Raw frequency response measurements show these headphones seal fairly well and reliably. Bass is somewhat rounded and emphasized to 200Hz, then fairly flat to 2kHz. I like this curve for these cans, it gives them a solid bass response even when they aren't quite sealing, and mids that are fully present throughout. The subsequent roll-off to 6kHz is typical and likely heard as fairly flat. The peak at 8kHz is also somewhat typical of headphones generally; I hear this peak in listening as slightly too bright in this area. Highs remain fairly strong after 8kHz, and are about the right level. This frequency response curve is a good result.
30Hz square wave shows a slight bowing as indicated by the bow in frequency response from 10Hz to 300Hz.
300Hz square wave shows slightly more overshoot than I'd like to see; the upward slope thereafter shows a strong upper mids response, which tends to deliver a punchy sound. Both 300Hz square wave and impulse response show this headphone to be fairly free of ringing due to the machined aluminum cups and extra damping.
THD+noise measurements indicate good power handling and tight bass response. The distortion peak at 5kHz is a bit disturbing and again may explain a slightly grainy sound at times.
Broadband isolation at -13dBspl is good, and with 24 Ohm impedance and 24mVrms to reach 90dBspl loudness, these will play fairly loud on portables. The high performance of these cans would benefit from a good portable headphone amplifier, if you so choose.
Current measurement .pdf and updated measurement notes for the HD 25-1 II on this page.
1989 Manual for original HD 25 and newer HD 25-1 II and HD-25 SP II.
Cool U.K. custom paint jobs on DJ headphones.
A review from the DJ perspective at Scratchworx.
Head-Fi threads for the HD 25-1 II here, here, here, here, here, and here.