Katz's Corner: Episode One

This story originally appeared at InnerFidelity.com

Editor's Note: Famed recordist Bob Katz is a headphone enthusiast...who knew?

Bob recently offered to write a series of articles for InnerFidelity readers on his recent adventures with headphones. I just couldn't turn down an opportunity for a peek at our favorite head-worn audio device through his venerable ears.

Please help me welcome Bob during his stay here at InnerFidelity in the comments below!

(For more info on Bob check out his website.)

Bob Katz's Corner: Episode One

Single or plural?

Should we say, "The Sennheiser", or "the Sennheisers"? "My headphone", or "my headphones"? One headphone or a pair? I'm sure Tyll has the language all straight in his head, but I'm still struggling with subject and verb matching. Let's just have some fun and enjoy the grammatical flukes.

The Great Headphone Shootout: Part 1
I became a headphone enthusiast at the same time I turned professional recording engineer. 44 years ago, I built a custom audio mixer in a suitcase and for reference monitors, took around my precious set of Stax SRD-3 phones powered by a souped-up Stax SRA-12S preamplifier. Although these phones require the standard bias voltage, I dared to exceed that voltage and got about 3 dB more headphone sensitivity and effective headroom from the amplifier. I turned the voltage up until just below the point where the electrostatic field made the hairs on my arms stand up—which brings new meaning to the expression "those speakers give me goosebumps!" But I never lost a set of cans (or any humans) that way; clearly Stax has conservatively rated their headphones. Plus, there's a high value resistor in series with the bias voltage on Stax phones which protects the user in case of a frayed wire or a short. The stator impedance and the diaphragm impedance are so high that you can parallel multiple Stax phones on the same amplifier without loading or losing level.


Here's a photo of me at a 70s recording session.

Later on I upgraded these to SRD-5 capsules. I owned three SRD-5 phones with a Stax splitter so three people can audition a recording at once with Stax fidelity, but in recent years I sold off two of those cans along with some passive energizers so I could afford to move up to pro models. In 2010 I purchased a set of new phones with gold-edition SRD-5 shells which someone had equipped with pro capsules, cables and connectors. We use these in the Studio B mix room as a secondary reference to the Genelecs, with a little bit of useful bass boost added in a preamplifier to assist the Stax's low frequency response. Even the well-cared-for forty-year old Stax phones sound and look like new, electrostatic cans don't seem to wear out as fast as dynamics. The high end just sweetens a bit with age as the coating slowly comes off the diaphragm. Just replace the earpads when they get hard.

I have dreamed of owning Stax Omegas ever since I heard my first pair while visiting fellow recording engineer Todd Garfinkle, and in 2010 purchased a custom-built KGSS amplifier from HeadAmp along with a new pair of Stax SR-007s, aka the "Omega Mark II". So the dream goes on: Stax has been my secondary monitor reference and listening pleasure center for over 40 years. I've also modified these Omegas by plugging up the port to tighten the bass as per Spritzer's recommendations at Head-Fi. I built a custom 1 dB/step attenuator for this amp as well.

My love for headphones parallels a love for good speakers. Studio A, the mastering room, has a state-of-the-art loudspeaker system whose response measures flat (within 2 dB) to below 20 Hz, including a target rolloff above 1 kHz. Even though the system sounds terrific without any aid, it sounds even better using Acourate Convolver, which is the only digital room and loudspeaker correction system that I have found that sounds completely transparent and improves sound with no compromise.


Above is a before/after graph of the fantastic frequency response improvement with Acourate convolver. This is the left front speaker measured using Acourate's psychoacoustic weighting. You can see that the high frequency rolloff is well controlled to a target I set by ear that has a little bit less high end than the native high frequency response of my Revel Ultra Gems. This high frequency curve results in a group of about 50 of my best reference recordings having a good-sounding high end that is neither too bright nor too dull.

Note how a formerly ragged response has been smoothed out to near-sonic perfection. And it sounds as good as it looks. As you can imagine, listening in this room is a pleasure, which I do for hours each day. The system is accurate, musical, impacting, mesmerizing, captivating...I expect the same performance from headphones, which I always compare with the sound of live music and to that of my reference loudspeakers.

I never liked the sound of the Stax models with rectangular diaphragms, like the Lambdas, they always seem to color the sound with a boxlike resonance that I think is due to the parallel surfaces. The large (circumaural), round Omegas throw a luscious, slightly u-shaped soundstage—you can actually get some imaging towards the front of the head, in contrast to smaller headphones which inevitably image at the sides or towards the rear.

Fellow headphone fans know that the state of the art in headphones has taken a tremendous leap with the proliferation of Planar Magnetic technology. Probably the best-known player is Audeze. I was intrigued to read initial reviews showing the large physical size of the Audeze diaphragm and praising its sonics, so I decided I should look into this new headphone. My friend, producer and musician Charlie Bertini (Applejazz Records) needed a new headphone, and was going to purchase the Sennheiser 650, but I convinced him he should go for the Audeze LCD-2, even though it exceeded his budget. Charlie is thrilled with his phones; when I checked them out at his home, they turned my head, even powered by his bargain Schiit Magni amp, which I also recommended. So I decided that I too should become an Audeze user. I would perform a shootout of the three main Audeze models and purchase the best one for myself, as a complement to my Stax, while performing a friendly contest to see which phone is the winner, the Stax or one of the Planar-Magnetic Audeze.

Getting Ready for Headphone Slutz!
It's very difficult for anyone to assemble the world's best headphones and enough amps to drive them for a shootout, but I set out to do it. The Cable Company has a wonderful deal. You can get a loaner of any headphone, cable, or amplifier for about 10 days and make your decision. The rental rate is 5% of the sale price, which is fully applied towards any purchase, so it's a win-win scenario if you're buying. You then send back the loaner and get a completely new piece. I rented the LCD-3 and LCD-X and borrowed Charlie's own LCD-2, which I planned to shoot out against my venerable Stax Omegas. In addition, I assembled a bunch of dynamic headphone amplifiers and a couple of premium DACs so that nearly all of us could audition at once. Seven of my friends and colleagues joined in the fun, all audio industry professionals—musicians, producers, recording, mixing and mastering engineers, acousticians and speaker designers. I call this group "The Headphone Slutz", and this series is about our great headphone shootout adventure.

Science or Art?
Our ears are wired for "louder". It's part of the way the ear/brain works. Since the louder of two devices almost always sounds better on an instant A/B comparison, it's a common sales gimmick to make the DAC or amplifier you are trying to sell be just a little bit louder than its competitor. Some DAC manufacturers join in the fray by setting the levels of their DACs a bit higher than the 2 volt standard established long ago by Sony/Philips. So, caveat emptor! Even 0.1 dB level difference can influence our perception of an amplifier or DAC. I always match the levels of every amplifier or DAC before listening.

The same issue applies with loudspeakers and headphones. Wouldn't it make sense to match headphones to the same sound pressure level (SPL) with a test rig before comparing them? Or would it? The fact is that when two transducers differ in frequency response (as most headphone models do), it is technically impossible to match their perceived loudness by any meter. Because SPL is not loudness! Let me repeat: SPL is not loudness. SPL is an objective measurement of sound pressure, but it does not indicate how the ear/brain interprets that pressure. When some frequency ranges in one headphone model are emphasized and some reduced in the other, as is always the case, all we can do is use our ears to match them as closely as possible.

The conundrum can easily be shown by this test: subjectively match the loudness of one headphone model to another using a single piece of music. Then change the music. You will discover that on the next selection, headphone A may be a bit louder than B, but on a third piece of music, B sounds a bit louder than A. This is simply because different frequencies are emphasized in different pieces of music, which may favor one headphone over another. So it is actually unscientific to match two headphone models by SPL and the only practical thing to do is try to get them audibly as close as possible to one another and do minor tweaks by ear during the testing. Then listen to a wide variety of musical selections and arrive at your conclusions over time.

In my next column I'll tell you about the objective (scientific) equipment testing I performed on the headphone amplifiers and then invite you to our listening party.