November 2009

Sennheiser HD 650 Headphones
The Crown Prince of quality.
Review By A. Colin Flood
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  When is a headphone review like a loudspeaker review? When the cans in question are a $499, top of the line model from a renown and respected manufacturer, which won dozens of rave reviews and yet something, somehow, is not quite right...

Since 1992, HeadRoom is an Internet purveyor of portable pleasures, specializing in ear cans and head amplifiers (Micro DAC and amplifier review). They represent every classic name brand headphone I can think of, except Stax electrostatics. So after PR maven Ivy Burford of HeadRoom said Sennheiser  650s were some of HeadRoom’s all time favorite headphones, I wanted hear a pair for myself (critics are such skeptics)! In fact, HeadRoom says  650s are “gleaming world-class,” with “articulate laid-back sound.” Therefore, she rushed me a pair to compare to the only other full size cans in residence, my Audio-Technica ATH-A700 headphones.

Located near Hannover, Germany, 60-year old Sennheiser designs some of the best sounding headphones. Their products include the renown Neumann studio microphones. The 650s are the crown prince of the Sennheiser line. The 650s are often highly recommended components, supplanted only recently by their new 800s. The new 800s are twice the price. It will be interesting to see if they are twice the sound quality. The 650s appear decidedly conventional:

The plastic frame is charcoal gray

Open back, back mesh covered ovals surround the ear

Soft black cloth covers the head and ear pads

The 10' plastic cord has a standard 0.25-inch jack. It is Y shaped, from below the knot of your tie to the ear pieces. The cord detaches.

Fit And Feel
The 650s do not look or feel like cans that are four times the price of my goofy looking ATH-A700 wings. The ovals fit onto the head snugly. The construction is traditional: a simple strap across your dome. The frame appears sturdy, built well enough to last a long time, but not as solid and beefy as the Koss Pros I coveted as teenager. The 650s are open-back design, meaning that sound escapes, making them less than perfect for the gray rabbit warren of cubicles where I most often toil in silence. The 650s’ weight is similar to my Audio-Technica wings. They are comfortable for a time, yes, but after a movie, your ears feel relieved just to be free of their snug embrace.

Yes, I did experience the dreaded "Sennheiser jiggle," where the Y connection cord becomes just loose enough at the earpiece to lose sound in one channel. The first time led to a frustrating equipment check to find the cause. It never happened again because I constantly checked to make sure the Y-cord was tight against the earpieces. HeadRoom makes a balanced XLR (multi-pin) cord available with the 650s for another $150 more.

The left and right side of the cans are marked with an “L” and an “R.” Better yet, the left side has three Braille bumps where the yoke meets the headband to indicate proper direction. Reversing the L and R sides does not dramatically alter the soundstage, though the 650s fit better when worn properly.

Long Bass Hump
HeadRoom also said that two of the biggest indicators of whether or not you need a headphone amplifier are the impedance and sensitivity of the headphones. Many headphones have a medium nominal impedance of 30–60 ohms. They typically display quite a wide variation of impedance versus frequency. The 650s not only have 300-ohm impedance, but also 102-db sensitivity. So you might think they could be driven by a portable CD player. Yet, Burford says “there is NO doubt the 650's require an amp... just do the listening test yourself, it's very obvious!”

Headroom’s site has a wonderful Build a Graph feature, where you can compare frequency response, harmonic distortion, impedance, isolation and square wave response for up to four different headphones! According to the graphs, the 650 frequency response should sound smoother, with less of a treble peak, than my ATH-A700 wings. Even with the high-end roll-off, the 650s frequency response is within a respectable 10-dB.

According to HeadRoom’s graphs, the 650s should sound similar to the new king of the line 800s. The 800s have been called a “must-hear musical revelation.” Though the 800s are nothing like the 650 construction, with the treble of the 800s looking sweeter and brighter, the rest of the frequency response appears similar.

Todd Warnke reviewed Sennheiser’s previous heir to the throne, the 600s, back in 2002. Comparing the graph of the older brother, the 650s should be quieter, not as sweet in the mid and upper ranges, with less distortion, easier impedance curve and better mid-range definition.

Tyll (pronounced “Tile”) Hertsens, HeadRoom’s founder, runs around audio shows with his portable Micro stack. He is the kind of tweaking audiophile who makes his own headphone amplifier. Hertsens likes the 50 Hz square wave graph because it is a “particularly tough test.” Although he said, “no headphone really can hold the bass well enough to get” the wave perfectly square, a flatter top on the wave indicates “how coherent and integrated the resulting sound” will be.

“Better bass response,” he says, “usually has more to do with the headphone's acoustic design and earpiece seal around the ear.” My A700 cans, he says, “tend to have a hard time sealing at the top of the ear pad, and might account for the loss of bass.” Hertsens had to point out “that if you skim through a lot of the headphones and their FR measurements, you'll find that it's very common to have a long hump between 20Hz and around 800Hz. This is mostly due to the fact that the driver is fairly small, and it has to pressurize an ear cup that is fairly lossy.

“In ear monitors do a bit better job getting a linear bass response because they seal the ear canal tightly and can compress the volume better without losses. Some cans do it well, too, the Denons in particular. The Sennheiser HD800, “he says, ”is a great can, but the Denons really do manage to get a punchy, impactful and controlled bass like few other cans.”

Hertsens says impedance on headphones is a “little different than speakers, but not too much. Mostly headphones are so easy to drive (relative to speakers) that once the amp has an output impedance of a couple of ohms or less, and maybe 150mW or more power, interaction between headphones and amp are pretty minimal.

“In other words,” Hertsens says, “what you hear mostly on headphones is the sound of the headphones themselves (mostly due to their acoustic design), and the sound of the amp. You are less likely to be hearing the combination of the two.

“Of course, this is just a generalization, and there is some interaction, but not nearly the kind of thing you get with speakers. He said, “as long as the amp has the voltage to swing linearly, a 300 ohm headphone will have a better damping factor than a 100 ohm headphone.”

Oppo Lotta Difference
Yet that was not where I had a problem with 650s. I reviewed them with a cheap Magnavox CD/DVD and my Oppo DV-981HD player. The Oppo of course was much better in terms of texture, details, smoothness and balance. It showed that the closer the sound is to your ears, the more important the quality of your source becomes. It this case, the Oppo made a huge difference. Talk to an engineer, but Windows Media Player and the Magnavox did not let me enjoy the music the way that the 650s on the Oppo did. Initially, I thought the 650s were hard to drive; none of the tube amplifiers sounded really good with them. Slide the Oppo into the mix however and everything sounded better with them.

In general, the 650s are crisp, clear and can get loud. They are not as dynamic at the ATH-700s. The mid-range is very well balanced. Extending to a very high 35 kHz, the highs are extremely good, without seeming bright or harsh. However, they don’t sparkle like they do on my ancient but beloved Stax SR-40 Electret headphones. The Stax are quick and light like electrostatic speakers, especially when driven by tube amplifiers, so everything has this sparkling quality.

Certainly more accurate than my ATH-700s, the 650s are more analytical than euphonic. They let you to hear the source or recording for what it is.

There is no comparison to my Sony ear buds. The 650s sound like a full size family sedan. The buds are light Mopeds. The HD650s do cut outside noise better than ear buds, but not dramatically so.

So when is a headphone review like a loudspeaker review?

Trend’s PA-10s
Burford was right. There is no doubt the 650's require a headphone amplifier. It is “very obvious.” Without one, my PC clone just didn’t have the oomph to make these cans go. In fact, neither did half the headphone amplifiers I collected for review! Neither the standard Chinese nor the special Russian tube version of the low cost Trend hybrid amplifier could adequately power these cans. The less expensive Chinese mashed the crescendos together horribly.

ASL’s HB1

On The Soloist, with Robert Downey Jr., the 650s need ¾ of the HB1 dial to make Jamie Foxx’s cello sound smooth, gentle, soulful and compassionate. Yet even then, the bass lacks the punch and treble lacks the tingle of my ATH cans. The overall accuracy and detail throughout the mid- range makes the 650s trustworthy. Horns don’t have the sometimes raspy, sometimes annoying bleeding edge.

HeadRoom’s Micro Combo

On Supertramp’s Some Things Never Change (BMG, 1997), the Micro DAC & amplifier combo hardened the bass and treble compared to the tube amplifiers. With three Gain settings, the combo easily had enough power to bring the bass out from hiding. Noon on the dial was too much.

Yet here is the missing punch. Here are the startling attacks. Here is the blare of horns. Here are drums shaking the ears. Here are dynamics conveying the emotion of music.

In my Micro DAC review, I said this combination was a soft point in the pricing curve; the spot where highest sonic qualities meet lowest price. Using the Micro DAC combo with 650s only confirms this view. This is a very enjoyable set-up. Now I see why the 650s are one of HeadRoom’s all time favorite headphones. Without tubes, the mid-range is not lushly warm and the treble is not softly sparkling, and slow drawing notes do not have a growling texture. Yet the 650s with the Micro DAC combo are indeed “gleaming world-class.” While I agree they are “articulate,” when properly powered, I would not describe the 650s as “laid-back.” Accurate and even frequency response is a better description.

I did not notice Hertsens’ “long hump between 20Hz and around 800Hz.” In fact, the bass seems fairly flat, level and correct. It was not thick or boomy.

Benchmark’s DAC1USB

I connected my Oppo 981HD player to the DAC1USB amplifier to through the TOSlink optical cable, yet did not get sufficient volume to blast hard rock. Noon on the dial is subdued. Full volume is almost loud – but nothing a teenager would like. This configuration did not seem right. Probably something I did wrong, but what? Otherwise listening to the 650s confirmed what my DAC1USB review said: super car performance at Corvette prices.

Blue Note Scores
The Sennheiser HD 650 design and sound are quite solid. No wonder they were king of the line for so long. For tweaking audiophiles looking for conventional, full size, open ear headphones, Sennheiser's crown prince has modest styling and a design comfortable enough for a few hours of listening. Properly powered, the 650s are accurate, extraordinary smooth with wide frequency response. Large and solid, they are ill suited for pocket size media players. Inside the house however, the 650s have a king size sound.

The quality and street price of the 650s is in line with such superb headphone amplifiers as the Benchmark DAC1USB or HeadRoom’s Micro stack. Though a grand or two seems like a lot to spend, even for a top-of-the-line headphone and amplifier combination, it is nothing compared to the cost of other hobbies, like racecars or fishing boats.

This is the sixth in my series of headphone and headphone amplifier reviews. Those who read my previous reviews know that I am the harshest grader in the schoolhouse. Only where the review equipment is "very good" – performing above average, do I confer four Blue Notes for Enjoy the Music.com categories.

The 650s are exceptionally capable performers, with few significant sonic weaknesses. In the categories of mid-bass, mid-range and high-frequencies, the 650s are above average. In my own personal category, Enjoyment, they also score four Blue Notes. If the 650s weren’t four times the price of my goofy looking ATH-A700 wings and more comfortable for extended wear, I would award them more Blue Notes in the Value For The Money category.

Specifications
Type: Full size, open back
Driver: Domed, duo-foil design
Frequency Response: 10 Hz to 39.5 kHz (-10dB) 
Nominal Impedance: 300 Ohms
Sensitivity: 102dB
Power: 200 mW
Contact Pressure: approx. 3.4N ( ±0.3N) 
Ear Coupling: Circumaural 
Distortion: less or equal to 0.05% 
Connector: 6.3mm (1/4") stereo jack with 3.5mm (1/8") adapter 
Weight: 260 grams
Price: $499 ($350 street)

Company Information
Sennheiser Electronic Corporation
1 Enterprise Drive
Old Lyme, CT 06371

Voice: (860) 434-9190
Fax: (860) 434-1759
Website: www.sennheiserusa.com