List Price: $2,149
Dr. John Richardson
I really like pro audio gear (made for commercial recording studios and such), but I’ve never cared much for headphones.
Now how’s that for the opening line of an audio review? You’re hooked, right?
Before you write me off as a total kook, let me give you a bit of personal history concerning my audio habit/sickness that might lend some meaning to the above statement. Like most audio enthusiasts, I have a day job to keep the bread rolling in to support my stereo habit (and my family). That often leaves only the night hours for critical and recreational listening. My main audio system is in my attic man cave, which is unfortunately situated right above the room where my wife and I sleep. When I listen to music, even at reasonable volumes, my early-to-bed wife is forced to be an unwilling participant. I finally had to take the hint that someone was getting a bit grumpy when she presented me last Christmas with a pair of nice open-backed Audio Technica ATH-AD900 headphones. Yes, I’ve used headphones before, primarily as a tool for monitoring the digital archiving and noise reduction on my vinyl records. While useful in this context, I can’t say that I ever really enjoyed the experience to the point that I would rather listen with ‘phones over my normal speaker-based setup.
That is, until now.
While my new Audio Technica ‘phones sounded just dandy driven by the headphone output on my Metric Halo ULN-2 DAC, I was intrigued enough to wonder what might be possible if I could get my hands on a really good dedicated headphone amplifier. During my research on the topic I ran into a thread on a popular audio chat site that was dedicated to this somewhat retro looking amp, the Phonitor, made by a German pro audio company called SPL (Sound Performance Labs). I had always thought that headphone amps were dinky little things; I mean, how much power do you really need to get the best out of a pair of ‘phones? Well, let me tell you that the Phonitor looked bad-ass. I really can’t come up with a better descriptor for it. Not only was this thing big, it looked like it meant business, such that it could easily kick the wimpy butt of any other headphone amp in the neighborhood that might care to challenge it. In addition, headphone fans were reporting that the Phonitor offered unmatched transparency, resolution, and neutrality coupled with a sense of effortless power. And it reportedly had some highly sophisticated analog audio processing features that served to make the headphone listening experience that much more natural and enjoyable.
On a lark, I decided one afternoon to drop an email to Marty Druckman, head honcho over at SPL-USA. SPL stands for "Sound Performance Lab", not "sound pressure level", by the way. Within ten minutes I had a reply in which Marty said he’d love a review in the audiophile press, as SPL had lately been selling a lot of Phonitors to audiophile types. He just happened to have a sample, but it wouldn’t be available until after a couple of audio shows, and I’d be next in line. I couldn’t wait... This was one review I really excited about, mainly because of all of the unknowns that lay in my path.
When the Phonitor finally arrived, I was still surprised by how big it was, even after viewing plenty of photos of it in the context of various audio systems. It’s also a hefty bugger, which is always a good sign from a quality perspective. The thing that really struck me, however, even before I turned it on for the first time, is how incredibly cool the made-in-Germany Phonitor looks. It’s something I would almost expect the mythical Most Interesting Man In The World from the beer commercials to have on his desk. My sample was black all around, with various knobs and switches on the faceplate, which is punctuated by a pair of analog VU meters backlit in a sexy yellowish orange glow. Just admiring the appearance of the Phonitor, I knew this thing could be my siren, my Lorelei, calling me to my eventual doom. It’s utterly cool in a beautifully geeky old-school sort of way, somehow reminding me of those analog oscilloscopes from my graduate school days studying chemical instrumentation.
Before getting into details of how the Phonitor sounds, a bit of background is in order. Since SPL is a pro audio company manufacturing gear for recording and mastering studios, the Phonitor was not designed for the casual, or even audiophile, listener. However, like products from other pro audio manufacturers such as Benchmark, Lavry, and Metric Halo that I have owned or reviewed, there has been crossover to the audio enthusiast population. Many of us who desire a very high level of performance and sonic truthfulness at a fair price often look to well regarded pro audio manufacturers for some of the best values in the audiophile world. But don’t tell anyone.... Let’s keep it our secret lest the manufacturers start to charge double the price so audiophiles will take their products seriously.
That said, the SPL Phonitor was originally designed as a means for studio mastering engineers to mix down their recordings using headphones instead of monitor speakers. In other words, SPL wanted to simulate the sound one gets from a pair of nearfield speakers using headphones, including soundstage width and depth cues normally only associated with speakers.
SPL says, "As many already know, there are clear advantages to monitoring and mixing with headphones, but there are also a couple of disadvantages. The main one being that it is very difficult (if not impossible) to accurately judge room ambience. Therefore, several years ago SPL began planning the development of a compact, professional headphone amplifier design based on its 120 volt technology. The inspiration came from project manager Hermann Gier‘s desire to eliminate major disadvantages in working with headphones. It therefore meant transferring the essential ambient parameters of loudspeaker monitoring to headphone monitoring. After several years of development and painstaking optimization, SPL have now introduced the Phonitor, whose name is a derivative of 'Headphone' and 'Monitor'."
As I got to thinking about this, I realized that maybe SPL was onto something that might speak to audio enthusiasts as well. Maybe the reason I never really warmed up to casual headphone listening was because of the somewhat weird and unnatural sense of having the music trapped solely between my ears! The Phonitor’s lineage also explains the presence of features not normally found on a consumer level headphone amp, such as the ability to isolate left and right channels, independently reverse phase of each channel, and sum both channels to mono.
They go on to say, "Traditional headphone reproduction produces 180-degree stereo width in the middle of the head, and it is exactly this which creates the very problematic-to-impossible headphone mixing environment. An essential reason for such unnatural ambiance is the complete separation of the channels, which does not exist either in natural hearing or in stereo loudspeaker reproduction. This makes it nearly impossible to judge tonal balance, a stereo image and the phantom centre level. Panorama adjustments as well as related EQ settings that one attempts with headphones, typically just do not function on loudspeakers.
Moreover, what is often called the “super stereo effect” with headphones usually creates a great deal of ear fatigue in the long run. Over loudspeakers the sound stage is felt in front, while in contrast, when monitoring through headphones, the stage is present on the left and on the right – but frontal and rear information is lost."
All of this brings me back to those analog processing features I mentioned a bit earlier, which may well be the main reason you would want to consider buying a Phonitor. On the front panel, to the bottom left of the volume attenuator, are two smaller knobs labelled “crossfeed” and “speaker angle.” Crossfeed is well known to many headphone listeners, with several amplifier manufacturers also offering it as an option. Here, the concept is simple: we want to bleed some of the left channel signal to the right channel, and vise versa. The reasoning is that when we listen in a natural acoustic environment, there is no true “left” or “right”; what gets to our ears is really a conglomeration of information from both channels (in a stereo situation) due to room reflections and the like. Conversely, when listening with headphones, we get an unnatural “super stereo” effect since the drivers are enclosed around each ear, which to me translates to an aural “doughnut” in which sound is concentrated at the outer edges of my skull with an occasional sense of nothingness in the middle (yes, I also sometimes feel like that when I wake up in the morning). Our brains then have to work overtime to try to process this less natural presentation into something more familiar, which in turn leads to listening fatigue. What’s cool about the Phonitor’s approach to this problem is that the amount of crossfeed is incrementally controlled by the listener.
The other part of the equation is the adjustable speaker angle adjustment. Here, the idea is to match the listening event with headphones to what one would hear from a pair of speakers situated at a given angle in front of the listener. On the Phonitor, the speaker angle adjustment is variable between 15 and 75 degrees.
One final processing adjustment is available, and it’s found to the right of the volume knob: the center level adjustment. When crossfeed and speaker angle are used together, one result can be overemphasis of the center image in the stereo soundstage. The center level adjustment is used to incrementally attenuate this center image if needed to give a more natural and balanced stereo presentation.
For the mastering engineer, the idea is to listen to monitor speakers set up in a favored configuration, then plug into the Phonitor and incrementally dial in the combination of crossfeed, speaker angle, and center level attenuation needed to match the soundstage provided by the speakers. The manual suggests starting with an initial set of parameters and then working out from there.
After some casual listening with all of the processing modules turned off, I couldn’t help myself. I just had to turn them on and play around a bit. I’ll be blunt here: don’t expect to be initially blown away by the effects, as they are really quite subtle. I also found that they were more audible on some types of recordings, but made very little difference on others. Keep in mind that I had listened for some time with the modules off first in order to get a feel for how the amplifier behaved on its own. To initially evaluate the processing, I started by dialing in a crossfeed of 3, as instructed by the manual. I then switched the speaker angle setting to 15 degrees, and initiated the processing (yes, the processing can be switched in and out with a single toggle switch for comparison purposes). What I heard was an audible narrowing of the soundstage, with the image pushed out toward the front of my head, somewhere up near the forehead. As I dialed in larger values of speaker angle, the soundstage broadened out and seemed to move further back toward the center of my head, actually extending in width beyond my ears. More importantly, however, I noticed a more stable and coherent center image. For example, when listening to unprocessed solo voice or piano in the center of the soundstage, I sometimes sensed a disjointedness in the center image such that there were right and left channel contributions, but they just didn’t seem to want to meet in the middle. With the crossfeed and speaker angle options working together, the center image just sounded more stable, present and natural. Overall, I found the center level control to have the least overall effect on the music, and I often left it off.
While all of this analog processing business is certainly interesting and potentially useful, does it make the Phonitor a one trick pony, or are there other outstanding aspects to the device? Luckily, there are. Through the Phonitor, I get something I have lacked when using other means of headphone amplification: a sense of scale and slam. Before, one of my complaints has been that headphones lack that sense of impact that one gets from a good pair of speakers. It only makes sense, as the drivers in a pair of ‘phones can only be made so large. Analogously, I view headphones sort of like good minimonitors in that they do detail and resolution really well, but don’t offer the same sense of scale and dynamics that a larger pair of speakers can. As my friend Mike Peshkin, who also doesn’t much like headphones said, “try playing your favorite organ recording through your headphones and then get back to me.” Point taken; we can’t re-write the laws of physics. Even so, the Phonitor has a way of making music sound bigger, punchier, and more dynamic than I have heard before using headphones. Maybe not as big and punchy as I get with my full-range speaker system, but very good nonetheless.
Looking a bit deeper, we find (right on the Phonitor’s face plate) a description that refers to something called a “120 V audio rail.” What we have here, according to SPL, is a special type of operational amplifier that runs on a +/- 60 V rail voltage. Now this is news indeed, as all commercial op amps that I’m familiar with run on rail voltages on the order of 12 or 15 V. One job of an op amp is to amplify voltage. This is fine and dandy, as long as the voltage at the output doesn’t try to exceed the rail voltage. If it does, the output signal gets clipped right at the rail voltage value. The audible results of such a mishap are self-explanatory. Since these custom amplifiers are used exclusively in the gain stages of the Phonitor, the device has the capability to provide huge voltage swings to the headphone drivers when needed, and without clipping. Maybe this revelation helps explain why the Phonitor sounded so punchy and dynamic to me.
Alright, more about the sound. All of my listening was done using my Mac Mini as a source, with Pure Music as the associated playback engine. The digital signal was sent via Firewire to a Metric Halo ULN-2, which in turn tossed the bits to either a Rein Audio X-Dac or Lavry DA10 DAC (both reviewed here at Stereomojo), from which the analog signal was passed on to the Phonitor. Headphones used were my Audio Technica ATH-AD900 and Sennheiser HD 650 lent to me by fellow reviewer and listening buddy John Fritz.
First, as expected, some ‘phones will sound better with the Phonitor than others. This is just a matter of careful component matching, much like you would take the time to do when mating a power amplifier to a favorite pair of speakers. As with other amplification components, impedance matching plays an important role. SPL suggests that the Phonitor be used with higher impedance ‘phones, as it is optimized to drive loads on the order of 600 ohms. This was potentially bad news for my Audio Technica ATH-AD900 ‘phones, as they have a relatively low impedance of 35 ohms. On this argument alone, the Sennheisers should be a better match with their impedance of 350 ohms. Potential buyers should also be aware that the analog inputs to the Phonitor are of the balanced XLR variety. If you run single-ended RCAs out from your DAC or preamp, you’ll need a pair of RCA to XLR adaptors. I ended up using the Rein Audio and Lavry DACs because both offer balanced outputs.
After much listening with both sets of ‘phones, I’ve concluded that I think the Phonitor highlighted the important sonic properties of each. Through the Phonitor, each had its own characteristic sound, and it really came down to personal preference for me. I’ll cut right to the chase here: I preferred the Sennheisers over the Audio Technicas. While the ATH-900 sounded light, fast, and airy in the treble, I just didn’t feel that it fleshed out the lower midrange and bass to my satisfaction. Here, the Audio Technicas reminded me of the pair of Triangle speakers I owned for a long time. As much as I tried, I just couldn’t quite warm up to them. They were fleet of foot and sparkly in the highs, but they never demonstrated the midrange “meat” and bass impact I really needed to stay involved in the music. Again, this is a matter of taste, but I know what I need to really get into a musical performance. Maybe with warmer sounding amplification, I’d like the ATH-900 better; I suspect a vacuum tube-based amplifier would sound wonderful with them. In contrast, the Sennheisers are known for being a bit darker sounding, and I therefore found them to be a very nice match to the ultra neutral Phonitor.
Tonally speaking, the Phonitor was definitely neutral, as it didn’t seem to add anything color-wise one way or the other to a recording. If the recording was a bit on the warm and bloated side, the Phonitor conveyed that; if it were a bit cooler, then that came across as well. Even so, I never found it unpleasant to listen to, as it never crossed the line to the over-analytical or excessively chilly side. If anything, I sensed a slight halo of warmth with the Phonitor when driving the Sennheisers, which was probably attributable to the ‘phones themselves.
A fine example of a nice warm sounding recording I have been enjoying lately is Freddie Hubbard’s “The Hub of Hubbard” which I digitally transcribed from the MPS/BASF lp that I found in a thrift for a buck. The band is exceptionally tight on this 1969 German studio recording, and Freddie’s trumpet sounds exquisitely burnished, as if surrounded by an evanescent halo of golden-yellow aural light. Most of the music is standard hard bop, with plenty of improvising and soloing. Take for instance the cut “Blues for Duane,” which was written for Freddie’s son. A bit down-tempo, the piece has great interplay between Hubbard and his band, all of which is showcased nicely by the Phonitor. Each instrument has its location in space, yet all work together toward a common goal. The Phonitor also offers plenty of punch and attack, adding to the sense of energy that must have been present at the recording session. I especially enjoyed listening to the snap and pop of Richard Davis’ string bass improvisation, which was rendered with harmonic and spatial precision via the Phonitor. I also can’t fault the Phonitor’s capability, via the Sennheiser ‘phones, to let me hear into the recording by resolving the tiniest details and presenting them in three dimensional space, all inside and around my head! Of course, all of this is with the crossfeed/speaker angle processing engaged. Without the processing, I heard a slightly wider soundstage, with a shift of certain instruments a bit away from center, but with no discernible change in timbre or harmonics. In this case, I can say that I could be equally happy listening with our without the signal processing.
Perhaps the effects of the signal processing were best demonstrated to me using large scale orchestral recordings with a lot of complex soundstage information. A recording I’ve enjoyed hearing through the Phonitor has been an older cd highlighting several well-known (and not so well-known) modern trumpet concertos, which is entitled simply“Trumpet Concertos” (Australian Broadcasting Corporation). This disc sports plenty of brass and orchestral fireworks across the four flamboyantly colorful concertos written by Lovelock, Tomasi, Mills, and Arutyunyan. The Phonitor never disappointed, providing a gutsy and robust rendering of these works showcasing the virtuoso trumpet work of Geoffrey Payne. As I fiddled with the different processor settings, especially the speaker angle, I could easily control the presentation and soundstage of the performance. Keeping the crossfeed at a setting of 3 or 4, I could muster a rear balcony setting in a typical shoebox hall by adjusting the speaker angle to 15 degrees. Changing the setting of 30 or 40 degrees, I was placed more up-front and center, with the orchestra arrayed almost around me. Interestingly, with the latter settings, toggling the processor on and off yielded very little difference in presentation: perhaps I felt a bit more soundstage solidity with the processing on, whereas with the processing off, I sensed a slight emphasis in the area of the drivers near the sides of my head.
I can only conclude that my time with the SPL Phonitor has been revelatory. I never had any idea that I could have so much fun with headphones or enjoy such a meaningful audio experience with them. I now consider myself at least somewhat educated in this regard. Is the Phonitor for all audiophiles and music lovers? Well, probably not. THere are probably lots of guys that would like to listen to their music collections more privately, at different times and volume levels, than they conveniently can, but have had unsatisfying experiences with headphones, especially the "music between your ears" effect. While this is still different than sitting in front of speakers, it's a much better pleasure than listening via your amp's headphone jack.
At $2,149 It’s expensive, though it can be found at discounts to around $1,900, so Cheap Bastards need another paddle with which to row. Also, all of the processing options could be a blessing or a curse, as those who can’t leave well enough alone could drive themselves to distraction (or worse) messing with the knobs while becoming hypnotized by the dancing VUE meter needles.
For those who would be interested in utilizing SPL’s “120 Volt Rail” technology, but who don’t want all of the processing options, SPL also makes an amplifier called the Auditor; it’s essentially the Phonitor without the bells, whistles, and VUE meters. It also costs half of what the Phonitor does, so it could well be a real bargain in the headphone community.
Ultimately, the Phonitor is one of those components that could easily have you assessing critically the quality of associated components; you may well end up on the inevitable upgrade path when it comes to source components and headphones! Proceed therefore at your own risk...
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