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SPL Phonitor Headphone Monitoring Amplifier

For accurate headphone monitoring for remote recordings or “after hours” mixing, Phonitor may be just the ticket.

Have you ever needed to mix on headphones? If so, then you’ve likely experienced that moment of surprise when you realize the “headphone mix” doesn’t sound the same on speakers. If you could be assured that everyone would listen to your mix on headphones or earbuds (an increasingly prevalent proposition these days) then you’d be set, but a lot of music is still listened to on speakers in cars and homes and stages.

So is there a way to help you figure out how your headphone mix will sound when listening on the stereo? There is now. The SPL Phonitor is a headphone amp that offers several unique features to make your headphones resemble the sound of speakers.


Using SPL’s standard 120V power supply rails, discrete components and Class- A circuitry, the unit is first and foremost a formidable headphone amp. Featuring stereo VU meters that also offer a PPM (Peak Programme Meter) setting, its elegant front panel is dominated by a large non-stepped volume knob that offers markings from -90 to +10 for recalling settings. Other monitoring options include Solo (L, Off, R), Polarity Reverse (L, Off, R) and Mono (Off, On). The meters are switchable between 0 or +6 and the volume can be “dimmed” by 20 dB, to yield greater range. On the back panel are XLR in and outputs (paralleled) and a ground lift and power switch. There are also ingenious folding front feet to angle the unit for desktop use.

To understand what the Phonitor does, we should start with a little background on how our ears interact with stereo speakers. Everybody knows that listening on speakers introduces reflections from the listening room that can greatly impact our perception of the sound. But even in the best control room there are issues that impact the sound — phantom center, HRTF, speaker angle.

Phantom center is the artificial “ghost” center image that is created when the same signal comes out of two equidistant stereo speakers at the same level. It’s how we make the vocalist “appear” in the center of the mix without a center speaker. I don’t have space here to teach a class on HRTF (Head-Related Transfer Function), but oversimplified it is a description of the effect of having our ears (our sonic receptors) positioned separately on either side of a solid mass (our head). One effect this has when we listen on speakers is a reduction of apparent level (at certain frequencies) of the phantom center due to crosstalk between the speakers and each ear. When our ears get discrete information like when wearing headphones, left channel to the left ear only and the same with the right, then that reduction doesn’t happen, but then we have to deal with the extra-wide soundstage because of the discrete delivery. Then there’s the width/angle of the speaker positions that also have an effect. The Phonitor offers unique options to deal with these.

The Phonitor’s monitoring options (Control Elements) are comprised of three knobs labeled Crossfeed, Speaker Angle, and Center Level with two switches to defeat them. Crossfeed, in six steps from Min(imum) to Max, interacts with Speaker Angle and simulates the frequency-dependent crosstalk between the Left speaker/Right ear and the Right speaker/Left ear. The Speaker Angle control offers six positions with angles from 15-75 degrees. These can be switched in and out together. The Center Level control offers phantom center reduction in six steps from -0.3 to -2 dB.

In Use

I spent hours with the Phonitor listening to dozens of familiar CDs played from my sole-surviving CD player, a Masterlink ML- 9600, using four different headphones (Audio-Technica ATHM50, Ultrasone 550, AKG K271, Samson CH700), utilizing the DACs in the Masterlink and a Crane Song HEDD 192 and the speakers were ADAM A-7s. Ultimately, I relied on the ATH-M50s and the Crane Song for my reference playback. As a headphone amp, the Phonitor is very nice with lots of clean power. The Solo, Polarity, and Mono switches are a welcome addition for analyzing mixes, though it would be nice to go from L to R without the audible disruption of going through the center switch position. The VU meters are nice, if dimly lit by LEDs, and the PPM setting may reflect peak values but they seem slower in attack and release than any PPMs I’ve used, likely not an issue since many are not familiar with PPM meters.

Next, I compared the sound in the headphones to the sound of speakers in the room. While I was skeptical, even after hours of auditioning the Control Elements, I was very surprised at how closely the Phonitor could match the sound of the speakers when I did direct A/B comparisons. I ended up with settings of Max Crossfeed, 40 degrees and -2 dB Center Level, and the balances were very close when putting on and taking off the phones. Since the Phonitor adjusts left and right channel interaction, I was particularly interested in how it would sound with hard-panned source material. When comparing the timeless classic “Stairway to Heaven” by Led Zeppelin, the hard-panned acoustic guitar (L) and whistles (R) on the intro seemed natural on the speakers but were disturbingly wide in headphones until I switched on the Phonitor’s options. Then the balance in the phones seemed just like the speakers. The same was true of the lead-vocal level on all the CDs I auditioned. On headphones, the vocal level was always louder than on speakers, when mixing this would make the vocal too soft, until I switched on the Center Level reduction, which brought the two back in agreement.

The acid test was comparing a mix done on headphones to one on speakers. One of the typical problems I have with mixing on headphones is the relative level of reverb. Picking reverb sounds and settings is not nearly as problematic as accurately determining how much to use. For this test, I pulled up a very accurate remake of Taylor Swift’s hit, Fast Facts “Love Song.” I compared the mix in the phones with no Phonitor options, and it felt too wide and too swimmy — too much reverb. But before I changed anything in the mix, I dialed in these settings: Crossfeed 4, Spkr. Angle 40 degrees and Center Level -1.6. This was the sonic equivalent of what I heard on the speakers, and the reverb seemed just right again. Those elements that were hard-panned didn’t make me flinch or want to change the mix. It now sounded in the phones like the mix I had done on the speakers. Very good.


So could you mix using just the Phonitor and not be surprised when you listen on your main speakers? Based on my experience, I think so. In conclusion, will the Phonitor save you money compared to spending $2,000+ on speakers? Likely not. But if you are forced to rely on accurate headphone monitoring for remote recordings or “after hours” mixing while the wife or kids are asleep, then it may be just the ticket. It certainly will allow you to better translate headphone mixes to the real world.

Lynn Fuston is the technical editor for PAR and owner of 3D Audio.