Headphones and Earphones
- Written by Chris Groppi
- Published on 23 April 2009
- Denon AH-D7000 Headphones and Headroom Ultra Desktop Headphone Amplifier
- Page 2: Design of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 3: Setup of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 4: The Sound of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 5: Measurements for the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 6: Conclusions about the Denon AH-D7000 Headphones and Headroom Amplifier
- All Pages
My first “high end” system consisted of Sennheiser HD-580 headphones, an original HeadRoom headphone amplifier, an Audio Alchemy DAC in the Box, and a Sony Discman with an optical digital out. I was a college student at the time, and there was no way of having a real, properly set up hifi system in my dorm room. It was clear to me at the time, listening to both my system and uber high end Hifi in shops, that my little headphone setup blew away many high dollar loudspeaker based systems. A headphone-based system is by far the least expensive way to experience truly great sound. Many of us can’t afford a hifi system costing tens of thousands of dollars. While the Denon AH-D7000 and the HeadRoom Ultra Desktop amp are not cheap ($2600 total MSRP), this complete system (just add disc player or computer) will absolutely KILL any normal hifi system I’ve heard costing less than $30,000. Sure, you give up the physical slam of bass, and the large soundstage, but the frequency response, tonal accuracy, speed and agility and even imaging and soundstaging (in their own way) are truly spectacular.
- Denon AH-D7000 Headphones
- Design: Over-the-Ears Headset; Sealed Enclosure
- Driver: Dynamic
- Isolation: -8 dB
- Impedance @ 1 kHz: 25 Ohms
- Connector Type: 1/4"
- Cord Length: 9.5 Feet
- MSRP: $999 USA
- HeadRoom Ultra Desktop Headphone Amplifier
- MFR: 10 Hz - 50 kHz ± 3 dB
- THD+N: 0.002% at 1 Volt Output
- Input Impedance: 70 kPhms
- Dimensions: 3.3" H x 6" W x 6" D
- Weight: 1.8 Pounds
- MSRP: $1599 USA with Astrodyne Switching Power Supply
I’ve been looking to upgrade my office listening environment. I have a HeadRoom Total Bithead amp with Etymotic ER-4S headphones that I use mainly for travel on the airplane. At my desk, the isolation of the Etymotics is so good I can’t hear my phone ring when the music is on. People can sneak up on me. On the other hand, my Sennheiser HD-595s I use at home for late night listening have no isolation, allowing office noise to intrude on the music. The Denon D7000s are the perfect compromise. They are sealed headphones with some isolation, which knocks down my computer fan and other background noise, but I can still hear my phone ring and people can get my attention.
I first heard the AH-D7000’s in HeadRoom’s room at the Rocky Mountain Audio Festival in 2008, and decided that I just HAD to review a pair. They were, by no small margin, the best sounding headphones in the HeadRoom display. There, they were paired with the Ultra Desktop Amp, which has HeadRoom’s premium amplifier modules, and their premium DAC. I was able to set up a review of this same system, and have lived with it on my office desk for a few months. To make a long story short, it is not going to leave.
The Denon AH-D7000 is the latest in Denon’s new sealed headphone lineup, and is meant to be the flagship model. At $1000 MSRP, it is a very expensive pair of headphones. Your $1000 does get you a very impressive amount of craftsmanship. The headphones are delivered in a very nice presentation box with a calfskin leather front and silk lining (or at least they seem like calfskin and silk; they may be synthetic). The sealed backs of the headphones are made of beautifully finished certified-sustainable rosewood, with Denon logos under the gloss lacquer. The adjustment mechanisms are made from machined magnesium for light weight, and have been engineered with the precision of a camera mechanism. The feel of simply adjusting the headband screams “high end.” The Earpads and head band are made from the same calfskin or calfskin like material used on the box cover. A Y-shaped headphone cord with fabric cladding is employed, and is made of 7N oxygen free copper wire with a ¼” stereo plug termination. 2” diameter microfiber drivers are used, with frequency response from below 20 Hz to 45 kHz.
The HeadRoom Ultra Desktop amplifier is a perfect match to these headphones. Any high performance headphone requires proper amplification. Just as you would not drive a pair of $180,000 Focal Grand Utopias with a $500 receiver, you wouldn’t want to drive a pair of D7000s with an iPod. The large driver requires power and control to achieve maximum performance. While the flat 25 Ohm performance may seem an easy load to drive, you will not get your $1000 worth without a proper amplifier. The 6”x6”x3” unit contains a stereo headphone power amplifier based on the Burr Brown OPA627 Op amp, one of the highest performance op amps available. We use these same op-amps in a preamplifier circuit for milivolt level signals in the radio astronomy instrumentation I build for my day job. They cost over $20 a piece in small quantities. These op amps are in HeadRoom’s “Max” amplifier modules, which drive both stereo channels. In addition to the Max amplifier modules, the Ultra Desktop also includes the Max DAC module, based on the AD1896 asynchronous sample rate converter and the Cirrus Logic CS4398 DAC. The SRC upsamples and pads all incoming digital data to 24-bit 196 kHz. Toslink optical and coaxial digital inputs accept signals at sample rates up to 24-bit, 192 kHz. The USB input accepts only 16 bit inputs up to 48 kHz. A super high quality ALPS volume pot controls the level, with switchable rear panel RCA outputs available for use as a preamp. Two pairs of RCA analog inputs are also available. The power supply for the Ultra Desktop amp is external. Included is the third-party Astrodyne switch-mode power supply, which can supply up to 42 W of DC power, and autoswitches for 110-220V and 50 or 60 Hz. As a $499 upgrade, HeadRoom offers their own bespoke, linear power supply. My test unit included the Astrodyne power supply.
Setup (or an aside into computer audio)
I deployed the HeadRoom/Denon pair on my desk at work, fed by my computer workstation, a AMD Athlon X2 based machine running Windows XP SP3. Little did I know the effort I would need to go through to supply a high quality digital feed to the Ultra Desktop. I would have preferred to use the USB input and iTunes as the player, but both these methods offered some serious limitations. The Ultra Desktop’s USB input can only accept a 16 bit 44.1 kHz input. As I do have some high resolution digital audio in FLAC and Apple Lossless format, I wanted to be able to feed the Ultra Desktop with a 24 bit 96 kHz signal. Most low cost soundcards do horrifying things to the digital signal, not limited to internal processing at 16 bit 48 kHz regardless of the input signal or desired output signal. I installed a M-Audio Audiophile 2496 soundcard in the PC. This is one of the least expensive soundcards that offer a fully controllable 24 bit 96 kHz digital output. It is available for less than $100. This card also is compatible with ASIO (Audio Stream Input/Output) drivers. Typically, all audio on Windows machines is processed by kmixer, the underlying audio engine in the Windows OS. While it is possible to get good performance with kmixer, it is almost impossible to tell what kmixer is doing. It may or may not perform all manner of sample rate and bit depth conversion on an audio stream without your knowledge. ASIO bypasses kmixer and sends the digital audio data directly to the audio device without any intervention. Use of ASIO requires a soundcard with an ASIO driver, which was provided with the M-Audio Audiophile 2496. For some other common soundcards, including the USB sound CODEC, a free ASIO driver called ASIO4ALL is available on the web for free download (but only supports 16 bit word size and maximum 48 kHz sample rate for USB). The audio player also needs to support ASIO output. The “industry standard” player iTunes, does not support ASIO output. I used another free player, Foobar2000, configured with several plugins to approximate iTunes functionality. While it is not as easy to use or as pleasant to the eye, it does offer ASIO output and offers the user complete control over audio output.
When used on a Macintosh computer running OS X, iTunes does not have to deal with kmixer, and does output a file’s native bit depth and sample rate in a “bit perfect” manner, as long as the digital interface can handle the data. Unfortunately, I am forced to use a Windows box at work to be able to run Windows specific software without the performance penalty of a virtual machine environment like Parallels of VMware.
With the M-Audio soundcard and Foobar2000 configured to feed the Ultra Desktop native bit depth and sample rate data through the coaxial digital input, I was able to get the performance I wanted and was confident that the system was doing what I expected.
I recently ripped all my CDs and DVD-Audio discs to Apple Lossless format and/or FLAC (Free Lossless Audio Codec). Both are capable of encoding high-resolution audio (up to 24 bit 192 kHz) in a lossless manner, i.e. the decoded data is bit identical to the source data from the disc. Lossy formats like MP3 and Ogg do not encode the data such that the decoded data is identical to the source therefore information is lost. The Apple Lossless decoder in Foobar2000 does not decode high-resolution files, only 16 bit 44.1 kHz. I therefore converted all my high-res files to FLAC. At home, I use a Mac for audio so I retained the ALC files for that use. iTunes currently does not support FLAC.
All this is proof that computer audio is not as transparent as it should be for audiophiles. This stuff should Just Work, even across platforms. It does not. It takes a bit of investment in time to learn the details to get your computer working as a high quality digital transport for your situation. When this is done, however, the results can be very good. At home I feed my main system with an Apple Airport Express wirelessly connected to my Mac. It feeds a Bel Canto DAC-1.1 with a Toslink connection. The Bel Canto does a good job of rejecting jitter from the Airport, resulting in sound that is actually superior to my Oppo DV-983H when used as a CD transport for 16 bit 44.1 kHz files. The Airport Express does not support high resolution digital files (Grrr!).
For break-in, I played my playlist from the beginning at moderate volume over a weekend while I was not in the office. These 48 hours or so of constant music did a reasonable job at breaking in the drivers. The HeadRoom amplifier was an already used show demo unit, so it required no burn in.
Links for computer audio software and information:
- Foobar 2000 audio player for windows 2000/XP/Vista
- ASIO4ALL free ASIO driver for USB audio and many common soundcards
- Make Foobar2000 Look Like iTunes
- FLAC: The Free Lossless Audio Codec
- Apple Lossless Codec
If there is one phrase to describe the sound quality of the Denon/HeadRoom combo, it is “jaw-dropping.” One of the main drawbacks of headphone-based audio is a lack of low bass. Most headphones are simply not capable of producing large amounts of low bass due to the small size of their drivers and the small volume of air moving. Any serious bass below 40 Hz is hard to achieve, and any sense of power and weight in the bass region as a whole normally comes with excessive bloat and boom. Most good headphones end up sounding light in the bass, although still quick and agile. The AH-D7000s, with proper amplification, turn this paradigm on its head. I knew the bass was good, so one of the first tracks I listened to was Daft Punk’s “Human After All.” At moderately high volume level, I though the bass was going to implode my skull. Not that there was more bass than there should be, by the way. This particular track has a huge amount of very powerful low bass. The subterranean frequency extension and sheer power delivered by the AH-D7000s put my home system to shame, 500W monoblocks, subwoofer amplifier and dual voice coil woofers and all. Any loudspeaker that could deliver bass like this would cost many tens of thousands of dollars. The bass was also stupendously fast, agile and tonally accurate. Since there are no room effects between the driver and your ear, none of the normal acoustic effects that plague loudspeakers in a normal listening room are present. Over the course of a couple of months as the drivers broke in, the bass became even more tonally accurate and tight than when I first listened to them.
Midrange and treble tonal accuracy and presentation of timbre were also first rate, a trick for a sealed headphone. Most high performance headphones are open baffle designs. Sealed loading of the driver usually results in a closed in and tonally muffled midrange, but the Denons have been carefully engineered to avoid this fate. Tonal accuracy is at least as good or better as the Sennheiser offerings I have had the pleasure to listen to (HD 580, HD 595 and HD 600). High frequency smoothness and extension were also essentially perfect. Transient response and speed matched or exceeded any headphones I have ever heard.
Headphone soundstaging is somewhat different than normal loudspeaker soundstaging. Typically the soundfield seems to be inside and around the head. For me, the center of the soundstage is between my ears, inside the head. As sounds move “farther back” in the soundstage, they seem to sound to come from above my head. Similarly, the left and right of the soundstage seem to be inside my head near the left and right ears, and extend out beyond my head to the left and right. This results in a soundstage plane that is vertical, not horizontal. With the AH-D7000, the soundstage ranged from inside my head to 1 to 1.5 feet outside my head. This is the largest perceived soundstage I have heard with headphones. This was facilitated by the HeadRoom amplifier’s crossfeed circuit, which mixes some of the right channel into the left (and vice versa), through a time delay and amplitude filter. This simulates the effect of sound waves from the left and right stereo channels in free space (i.e. from a loudspeaker), which eventually get to both ears but at different times and at different volumes. The crossfeed can be defeated, but this results in the soundstage collapsing to three “blobs” of sound, left center and right.
When compared to my pair of Sennheiser HD-595s, the Denons were superior in every way. The soundstage was larger and more airy, transient response and speed were superior, treble extension and smoothness were better. Midrange smoothness and tonal accuracy was also greatly improved with the Denons. The bass was no contest, although there is no headphone I have ever heard that can compete with the Denon’s bass, period. The sealed design of the Denons was also preferred to the Sennheisers when any background noise was present. Compared to my pair of Etymotic ER-4S, the Denons were also superior in every way. The Etymotics have a bass shy balance anyway, and since they are in the ear headphones there is no air movement around the ear to reinforce the weight of the bass. The Etymotics do offer vastly superior sound isolation (23 dB vs 8 dB for the D7000s), allowing for fantastic detail retrieval in the face of background noise. Of course, you won’t be able to hear your phone ring either.
I also used my battery powered HeadRoom Total Bithead to power the AH-D7000s. This portable amp is also a headphone amp with a built in DAC. The DAC is USB input only, and does not offer sample rate conversion or as high a quality DAC. The headroom amplifier module is of a similar design and uses upgraded parts as compared to the standard module. It does not use the super high quality OPA627 op amps, and is powered by 3 AAA batteries rather than a beefy power supply. Every area of performance, while still listenable and WAY better than an iPod, was significantly degraded. The AH-D7000s want a lot of power to deliver their bass punch, and midrange and treble agility and speed. The total bithead made an effort, but could not keep up. The DAC was also a bit grainy and dynamically flat by comparison. While a full-up Ultra Desktop is not strictly speaking necessary to enjoy the AH-D7000s, the headphones will benefit from every bit of improvement you can provide in the source and amplification electronics.
The data provided below were measured by HeadRoom using an artificial head microphone system. This model head has microphones imbedded in replica human ears, so it listens just as we do. This does make for frequency response plots that are different than we’re used to looking at for loudspeakers. The folds and ridges of the ear cause the high frequency response of a microphone imbedded in a model ear canal to have various peaks and dips caused by in and out of phase interference of sound travelling around the ear. The human brain equalizes this response. We never see these peaks and dips with loudspeaker measurements because they are measured with bare microphones. All headphones will show these high frequency peaks and dips. At lower frequencies, where the wavelength of sound is significantly longer than the size of the ear, there is no effect.
Most headphone manufacturers aim for a couple of dB more bass than flat to add a bit of bass weight and impact that is lost due to the fact that sound waves do not hit the whole body of the listener. Also, note the y-axis scale. Most loudspeakers, when measured in-room, have response variations of over 10 dB from flat due to room effects. Good headphones rarely deviate by more than a few dB from flat since there are no room effects for them.
These measurements, plus measurements for all headphones HeadRoom sells, can be found on their “Build a Graph” page:
Frequency response of the AH-D7000s extends all the way to below 20 Hz. The -3 dB point is about 17 Hz. There is a broad response bump in the bass peaking at about +5 dB at 40 Hz, typical, although lower in frequency compared to most headphones. High frequency response is rather flat until a suckout comes in at about 15 kHz. This suckout is likely due to cancellation in the folds of the simulated ear on the HeadRoom measurement system, as discussed before. It is paradoxically different in the left and right channels, which could have been caused by the drivers sitting on the artifical head differently on the left and right.
Distortion of a 500 Hz sine wave is spectacularly low, with the highest harmonic product just over – 80 dB. This would be good for a preamp, much less a loudspeaker!
Isolation begins to kick in at about 800 Hz, and is an impressive 15 dB or so from about 1 kHz up. Low frequency isolation is basically non-existant. Only in the ear headphones like the Etymotic ER-4S can provide good low frequency isolation. Compared to open back headphones, the Denons have isolation from 800 Hz up, as compared to 5 kHz and up as with my Sennheiser HD-595s.
Listening to headphones is a different experience that listening to loudspeakers, for sure. If you are looking for the best possible sound quality (i.e. frequency response, clarity, tonal accuracy, retrieval of detail, imaging, soundstaging, etc), at the lowest possible cost, headphones are unbeatable. The Denon AH-D7000s, when powered by the HeadRoom Ultra Desktop amplifier and DAC, offer world beating performance at something like 1/10 or 1/20 the price of admission for an equivalent loudspeaker based system. I covet the AH-D7000s and the HeadRoom Ultra Desktop amp. They make working at my desk a much more pleasant and relaxing experience. I will not be letting them leave.