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Dynamic Duos: BlockHead and Grado Amps & Sennheiser and Grado 'Phones
by Max Dudious, with some additional pensées by David W. Robinson


Some folks, arguing the function of the critic, say the most important thing a critic can be is consistent. If the critic makes the same sort of judgments again and again over a range of products, it gives the reader a chance to see if his own judgments match up with this or that critic over time. Take the movie critic: if you have one you rely on, probably he likes the same kind of films you like, for the same reasons. With audio gear, it should be the same. I like music reproduced with high definition detail; with silky highs, liquid mid-range, robust bass; and with enough startle-ability or "zotz" to surprise me with its dynamic range when listening to Haydn's Surprise Symphony. I like that because, to me, it is the closest approximation to acoustic instruments in an acoustic environment (without tizzy highs, too etched mid-range, or boomy bass). I find it more "natural," if you can allow me to use such a vague term, when compared with the more electromagnetic sound that you're apt to hear in a studio mastering disco music. You might say the above is my definition of "natural" or "good" sound. I broke up a great system (Klipsch horns on the bottom, Quad electrostatics on the no-zotz mids, and Fostex ribbon tweeters on the highs) twenty years ago to seek the Holy Grail of great sound from dynamic drivers.

I'm not sure what stimulates me to write more comparisons and contrasts between top-of-the-line Grado headphones and the similarly line-topping Sennheisers; between the simple Grado headphones amplifier and the complex HeadRoom BlockHead amp, but here I am—again. Perhaps it's to learn more about the ins and outs of headphone design and performance, or perhaps it is something about The Emperor's New Clothes, which has always held me in thrall. But before we can answer the question: "Just what do dedicated headphone amplifiers do for listening to music that makes them attractive, yet a little bit tricky to deal with?" we'd have to know our reference headphones (Grado RS-1s and Sennheiser 650s) inside and out. Let me describe some of the differences (to my tired old ears) between these two sets of headphones that can drive otherwise mild-mannered audiophiles to vituperative haranguing, or, on occasion, to fisticuffs. Gentleman, start your head-amps!

For those of you unfamiliar with the joys of headphone listening, the most obvious benefit is to be able to listen at all hours of the day or night without bothering your loved ones or neighbors,—privacy. You can play your favorite music as loud as you can stand it without waking anyone up. Portability is, perhaps, the next best attribute in that you can take damn good sound to the beach, or to a hotel, or to listen with in an automobile ride, or in an airplane trip. A good, small playback system can offer these things. A great system can offer you a facsimile of the recording venue, clarity of tone, availability of detail, outstanding dynamics—all the best performing attributes you'd expect of an A-Class big rig. In other words, a first-class headphone system offers privacy, portability, and performance, all at the highest level.

Years ago, before Positive Feedback became an e-zine, the similarities and differences between the then top-of-the-line Grado and Sennheiser 'phones had me a bit up a tree, and I got into it in some detail mostly as a learning exercise. This time I want to try to bring my thoughts up to date, to see if my personal database has increased, and if I can communicate what new information I've gleaned in my conversations with various audio buddies.

It's a shame that guys are born with the DNA imperative to be number one, to associate with other number ones, and to buy products that proclaim their number one-ness. Headphones are obviously one item, like wristwatches, that make such a statement. That is further complicated by the mistaken notion that if one pair of headphones (amps, speakers) is right, then all others are wrong. Nothing could be farther from the truth.

Following the Eastern model, I'd say we each have a bit of deity within (for lack of a better word—a soul), and the universality of the divine leads us inevitably to realize that the other guy is as entitled to his bit of divinity as we each are entitled to ours. And each of us has individual characteristics that we got from our ancestors, such as height, weight, IQ, genetic pre-disposition to allergies, to high or low blood pressure, and other things too gruesome to mention. This leads us to the tentative conclusion that though we are very much alike, we are also different, and we can't get so attached to the similarities that we overlook the differences. Sounds like pablum, but let me have the benefit of the doubt. We hear differently. Men hear spectacularly differently than women do, and less differently from one another, with age.

There are many things that set us apart as individuals in how we prefer to listen. Some of us like to listen to music in rapt attention, hanging on every musical phrase as we would hang on every phrase of a Shakespeare sonnet, allowing nothing to break our concentration. Some of us like music played loudly enough to approximate the level of a performance venue: others like music played much more softly, so that we might read, or enjoy conversation while we listen. Some folks (including me) like to sit up-front in the hall to catch the details; others (including fellow PFO audio scribe Marshall Nack) prefer way-back to hear the blend, while some others like to sit in the middle sections, which seem to capture a balance of blend and detail. Some of us like to listen for the "inner voices" of symphonic music (woodwinds, violas), while others value the "wall of sound" of a large orchestra (or rock band) in full cry. And where you'll be happy on this near/far continuum will likely help determine which of the two headphones in question will be your favorite, the Grado RS-1s or the Sennheiser 650s.

The 650s are the direct descendants of their parents and grandparents, the Sennheiser 600s and 580s, with a few subtle changes in their physical makeup. On the bar that connects the right and left ear-cups of the 650s they now have a dark gun-metal grey lacquer, replacing the faux marble finish of the 600s. You'd think since it is much less labor-intensive, this change would allow Sennheiser to cut costs on this model, and reduce the price to the consumer. The Sennheiser model 600s can be purchased from HeadRoom for $350 while the 650s are priced on their Website at $400. Grado RS-1s have not changed much to look at (a little deeper foam on the ear-cups), but they are further refined by increased attention to adhesives, driver coatings, and other invisible materials. The RS-1s still cost $695, except when discounts are offered (as by musicdirect where they sell the RS-1s plus the RA-1 amp, usually $1045, for $845). The overall sound of the two manufacturers' headphones has moved gently toward the other, and, like the Spartans and Athenians, they have begun to resemble each other in at least two ways.

Whereas the Grados once had a distinct advantage in bass response and presence, and the Sennheisers had more control over excessive "bloom" or "ringing," now the Sennheisers have boosted their bass a notch or so, and the Grados have reined in their mid-range bloom a tad. The Sennheisers really sound their best with the aftermarket Cardas interconnect designed to optimize the 650s' performance, and the Cardas interconnects are listed at various prices depending on the input plug. With 1/4 inch diameter plug, the price is $150 per 10 ft.: with XLR three-pin plugs (for balanced inputs that isolated the chassis ground from the return leg) the price is $275 per 10 ft. That brings the "audiophile" price of Sennheisers to $550 for 1/4 inch plug, and $675 with the XLR plugs, or nearly the same as the Grados. The Grado RS-1s still cost $695, and can be softened a notch both in physical comfort and in sound quality by substituting the yellow ear replacement pads for the Senn model # 414 headphones, at less than $4.00/ pair when ordered directly from Sennheiser. See

How does this all work? I'm not sure. I can say that the Grado headphones have a nominal impedance of 32 Ohms, while the Sennheisers are rated at 300 Ohms (according to published specs). That's quite a bit of difference, an order of magnitude, like (say) 32 ounces (about two and a half cans) of beer at one sitting, versus 300 ounces (about two cases of 12 oz cans). You get the idea. (If you don't, then you obviously need to have anotherr beer! And for those of you reaching for your keyboards: don't bother. Even audio writers get to be facetious.) We know some things differ in amount from each other though they are the same thing, and the difference in quantity makes such a great deal of difference they take on a new quality and must be given a new name.

For one example, wind. The Beaufort Scale (1858) breaks down winds of differing forces into 12 categories. Winds of less than 1 mph are considered "a calm." Wind of 1-3 mph is considered "light air." Then there are the breezes: wind of 4-7 mph is called a "light breeze," 8-12 mph wind is a "gentle breeze," 13-18 mph wind is "moderate breeze," a 19-24 mph wind is a "fresh breeze," while a 25-31 mph wind is a "strong breeze." Next come the gales: "moderate gale" at 32-38 mph, "fresh gale" at 39-46 mph, "strong gale" 47-54 mph, and "whole gale" at 54-63 mph. The storm stands alone at 64-72 mph. And the hurricane checks in with a range of 73-136 mph. Weren't the Victorians strong on details? Think of what they could have done for audio terminology!

All this to allow me to demonstrate an order of magnitude of rainstorms might be the difference between a 20 mph April "shower" that brings May flowers, and a 200 mph "tornado" that can destroy a whole town in a short time. Same basic phenomenon—rain—differing by a factor of ten in wind speed. (See? My job is to entertain as well as inform.) The difference in the impedance between the Grados and Senns is very nearly an order of magnitude. To make a reasonable comparison, we need to keep this difference in mind. Technically, what we have here is a potential failure to match impedances. (Note that Grado now also offers a model RA-1-HG, or High Gain, for headphones over 100 Ohm impedance.)

A three hundred Ohm impedance headphone driver would have smaller diameter wires on its voice coil, or in addition it might have (in some magical combination with Q, in this case stiffness or floppiness) some stiff mechanical damping that could restrain it from "ringing." A thirty-two Ohm impedance headphone driver would likely have larger diameter wires on its voice coil, and would have to pay attention to damping by various means to restrain it from "ringing." (By "ringing" I mean the continuance of a tone in the driver after the tone burst has stopped in the amplifier. This is given visible representation by tracings of a tone burst on an oscilloscope, comparing what the scope sees as representing the tone "in," and how the transducer reproduces it as tone "out.") There are two commonly used schemes for controlling impedance: raising of the electrical impedance by increasing the number of wraps of thin wire on the voice coil; as opposed to a bulkier, lower electrical impedance voice coil with increased mechanical damping in the suspension of the driver. Neither is perfect, but both do a creditable job. More than that, each of them can sound damn good. (Please note I have omitted electrostatic drivers in this discussion.)

All amplifiers have a damping factor that is usually stated in the spec sheet. Some are higher, and some are lower. Solid state amplifiers sometimes have damping factors in the thousands, often in the hundreds. Tube amplifiers usually have damping factors under one hundred, with some as low as fifteen or twenty. Damping factor is usually viewed as the grip the amp has on the drivers. Some large scale speakers sound better with transistor amps, others with tubes. Most electrostatic loudspeakers sound better through tubed gear because the tubed amplifiers have lower damping, while speakers with regular magnets, cones, and domes seem to perform better with higher damping, transistorized amps. That is an observation that most folks arrive at when comparing such set ups. Comparing the Grado and Sennheiser phones, there is a distinct possibility for mis-matching impedances here.

In fact, the Sennheiser 650s (with the factory interconnect cord) played through the Grado RA-1 (battery-powered) headphone amp sound just out-of-kilter enough to have some of my audio buddies who heard it ask if they were the same headphones that are the rave just now. My own Grado RS-1 'phones, through my original Grado RA-1 amp, got the nod from 100% of my listening panel, my wife, my daughter, my son-in-law, a Baltimore Symphony Orchestra musician, and one old clarinetist friend who listens to Lowthers driven by triodes. I have tested this panel often and found them reliable. That is, they repeatedly make harsh judgments about harsh sound, and off-kilter comments about off-kilter sound, and they delight in disagreeing with me when they have a good case. When I changed the Sennheiser 650s' cord to a dedicated, after-market Cardas cord, the performance of the Sennheiser's 'phones through the Grado amp improved to the point of being not quite the equal of the Grado RS-1 phones plus Grado RA-1 amp, and it caused my daughter to marvel on how important a piece of wire can be. I tentatively concluded that since there was such a positive change, the Cardas cables probably reduced the overall impedance of the Sennheiser phones with their stock cord. This was before I knew about the Grado amp with the High Gain option.

The next step was to play the two headphone sets through Headroom's BlockHead headphone amp. The HeadRoom guys do a lot of testing with fancy gear loaned to them by Sennheiser. You might say the HeadRoom guys and Sennheiser guys have a "special relationship." I think if you scratched Tyll Hertsens, he'd fess up that the BlockHead 'phones amp was designed with the Sennheiser 650s in mind. And there's nothing wrong with that. There are lots of similar symbiotic relationships in audio that benefit the consumer, and the whole industry, and aren't spoken of too often.

How does it sound, this "special" combination of Headroom and Sennheiser? The HeadRoom guys build special XLR plugs with which to terminate the Cardas cables that are plugged into the Sennheiser 650s. The idea behind this is to avoid any hum, RFI, EMI, and crosstalk that might be picked up by unbalanced connectors. To make an A/B comparison with any other headphones in a rigorous test, the HeadRoom guys fixed up one set of RS-1 (top of the line) Grado headphones with shielded and grounded double cables (to reduce impedance) that were terminated with XLR connectors. All this to have the game on a level playing field: alternating listening through a Sony CD Walkman D-E356 fed to the BlockHead, then to each of the headphones by turn.

The big BlockHead is an imposing piece, actually two separate amps with dual mono construction that only come together at the selector switches. The front panel has separate channel toggle switches marked gain (hi-lo-or medium), filter (off, bright, and brighter), phase (normal or reversed), and process (intra-channel cross-feed on or off), and volume (a quality potentiometer). The output XLR sockets are there so you can easily change headphones, as we did. The rear panel has separate IEC connectors for each channel, separate on/off switches, separate ground-floating control, XLR sockets for input and cross-feed. In other words, there are a lot of features. The Grado, by contrast, has an on/off switch, RCA jacks for in and out, and a stereo volume control: that's all. The BlockHead has numerous eletrolytic capacitors in both the power supply and the signal path. The Grado has very few Wima capacitors in the signal path, and none in the power supply, since battery supplies are by their nature DC.

Through the BlockHead, the gap between the two sets of elite headphones closed, and, believe it or not, they started to sound alike. I'd say some sort of impedance match was made that agreed with both the Sennheiser and the Grado 'phones. And here, the Sennheisers did shine their brightest. Some said the differences were merely whether you liked your seat forward, or mid-hall. Others said the over-all image was larger on the Sennheisers. Some preferred the Grado sound. I thought each headphone sounded a bit too much rounded off, not quite in sharp focus, something for which electrolytic capacitors are infamous.

When we went back and played the Grado amp with the two sets of 'phones, both pairs of headphones seemed sharper. We could tentatively offer the hypothesis that all the features, and extraneous parts on the BlockHead made for a kind of "Doris Day filter," if I can make an analogy to photography, where everything in the photo frame is in sharp focus, but the center of the frame—Doris—is soft focused. Something like that was going on in this comparison. Though I fear the whole frame was soft focused through the BlockHead. These findings were not unanimous, but there was significant agreement.

During the '05 HE Show, at the NY Hilton, Tyll Hertsens (chief designer, cook, and bottle washer), and CEO at Headroom, told me the big BlockHead had been discontinued, and that it had been replaced by a new model that he was carrying around with him. I take this as a tacit admission that the guys at HeadRoom thought that the BlockHead could be improved in some significant ways. The new model features a stand-alone power supply in one small box, and the circuitry in another. The two boxes, atop one another in a nylon traveling kit, made for a clarity of sound—minus the Doris Day filter—that I, for one, could really appreciate. This will improve the upcoming HeadRoom piece in terms of portability, one of our dudely qualifications for a good headphone system. I think the size and AC requirement of the BlockHead made it a stay-at-home piece. This is much like the fact that the Sennheiser 650s stationary ear-cups make it not as easy a traveling 'phone as the Grado RS-1s, which can lie flat with their swiveling ear-cups at 90 degrees to their listening position.

This year 2005 experience has taught me that, as a critic, I am consistent in my preference for the Grado headphones and amplifier, a consistency that is sought for. Grado's stuff was my delight in hard copy years ago (Positive Feedback, Vol. 8, No. 3), and still is. But I have to admit that I could very easily live with the Sennheiser 650s, which are much the equal of the Grado RS-1s through carefully selected gear, like the high gain Grado amp. I'm sorry I didn't have a high-gain version of the RA-1 available to me. I am really surprised to report that I heard almost no difference between balanced (XLR sockets) circuits and unbalanced (RCA jacks) circuits. The balanced circuit improvement in clarity so many have touted was inaudible to me. Perhaps that was due to an imperfect setup that had RCA-to-XLR adapters in one spot (custom-made for YOE by Jena Labs, but they seldom err). I am also sorry that I couldn't provide a balanced line all the way through. I was expecting Marantz's new SACD/redbook CD player Model SA-11 (with its XLR outputs) to show up, but I'm told that new model has proven popular with the public and all the stock has been on back-order. So as rigorous as I tried to be, some details got by. But, then again, the awaited improved clarity could have been marred by less than audio-ideal capacitors.

I am gladdened that the big BlockHead has been superseded, because that confirms that other folks may hear the way I hear, even if it is impolitic to insist. So I remain what has been called, "a positive-feedback truth-teller," who doesn't always see the Emperor's New Clothes. I think finding a mate for the Sennheiser 650s is trickier than it seems at first glance, due to its high impedance. And I think too many less than ideal capacitors keep the BlockHead from being as high-resolution as I expected. So, these are the kinds of tips a critic has to be able to make, unfettered by large corporate dictates, and editorial intervention—neither of which we see at Positive-Feedback. And this is how I try to remain a truth-teller.

If you would know more about Grado, see

Similarly, for more about HeadRoom, see

And Sennheiser is at

OK guys. That's about it from my little beach shack on the shores of the Chesapeake where the surf's always up.

Catchya later.


Some thoughts from Ye Olde Editor on the Headroom BlockHead headphone amp, and Sennheiser vs. Grado cans
by David W. Robinson

In which our hero meditates… [Drawing by David W. Robinson]

Headphones. A subset culture within fine audio. Not for everyone, either …some find headphones to be too confining, too "inward," too problematic to get right. Most folks don't care; an iPod or a Discman and whatever comes with it is enough.

For listeners who do give more than a hoot, though, there are headphone systems that allow you to go to extremes to get the most out of a pair of cans. The best that I've heard so far is the Headroom BlockHead headphone amp, a design that makes headphones sound like you really should give a goodly demme or two about them. Though Headroom has recently made the decision to pull the plug on the BlockHead in favor of a new design line, I want to comment on this over-achieving product.

Max is right about the virtues of 'phones: the ability to listen to whatever, whenever, without jarring the significant other, the kids/kats, and the neighbors can be a real treat. (Heck, for some apartment dwellers, it's essential.) Apart from that is the fact that a good set of headphones and a good 'phones amp can deliver some prodigious sound without requiring an enormous investment in a room, room treatments, and arguments with other members of the household.

On the other hand, headphones are exclusive, not inclusive, devices; you won't be building a great deal of audio chumminess through shared musical experiences by using these. Like a Discman or iPod user on a bus, the 'phones are an implicit invitation to "stay away."

Inwardness in action, and all that.

That said, I have to say that I enjoyed the Headroom BlockHead immensely once I found the optimal configuration for me. Max has profiled its layout pretty well; it's a true dual-mono construction with a unified chassis housing separate left and right sections, and wired for that rarity in consumer-grade headphone operation, balanced mode. IEC's for two power cables, left and right pots of superior quality …Nobles, that is (stepped attenuators are an option); switching to allow standard left/right playback, or processed playback for a better "in your head mix" of left/right (you get to avoid the vertigo of the "ping-pong effect" that some recordings will give you with 'phones); switchable filtering for various brightness levels; and switchable gain levels. The rear has an innovative XLR cross-feed to allow cross-feed processing between left and right channels, and a ground-float switch (always a handy thing).

The BlockHead even had phase inversion, a feature that I consider to be extremely important.

I spent quite a while with the BlockHead, experimenting with several combinations of headphones, cables, and power cables. The power cables I ended up using were a pair Kimber PK 10 Palladians, an exceptionally fine match for this product, if a bit bulky to situate. The standard power cables are throwaways, as far as I'm concerned—then again, that's always true in my experience. I used the Headroom-supplied XLR cross-over for the cross-feed processing. Over time, I generally used cross-feed, and kept the filtering set to the middle setting; overly bright headphone playback is not pleasant.

The bigger question was which set of XLR phones would do it for me: the Sennheiser 650s, or the Grado RS-1s. The Grados had integrated XLRs from Headroom, but the Sennheisers have the ability to plug alternative cables via the female jacks in the 'phones. This lead to a further question with the Sennheisers: which pluggable headphone cable would be the better to my ears, the standard Sennheiser XLR, or the Cardas XLR that Headroom had been kind enough to send along?

Headphone selection came first. My long-time headphones have been a pair of Beyer Dynamic BT-990s that I purchased years ago. The Beyers have no bad habits, are comfortable, and impart a certain richness to playback. I've used them for both general listening and for radio production work over the past decade, and I've become used to them. They don't do everything as well as I might like; they can be a bit too rich at times, and don't give me as much spaciousness as would like to have. Personally, my short list of audio virtues includes the articulation of detail, spaciousness, dynamics, top-to-bottom tonal integration, and a reasonable full-range frequency response in audio playback generally (yes, I do have a much longer and much more detailed list of the audio virtues); within the limits that headphones bring to the table, I like the same things.

How to proceed? First of all, I sorted out the cable question on the Sennheisers. After spending a few hours with the Sennheiser standard XLRs, I shifted to the Cardas reference headphone XLR cables.


No contest! Even fresh out of the box, the Cardas headphone cables (10 foot length) definitely provided better extension of higher frequencies, noticeably improved tonal integration, and a delightful air and spaciousness to the sound. My humble opinion: you shouldn't purchase the Sennheiser 650s without Cardas headphone cables. Period—game, set, and match! And that settled the cable question very efficiently. I would spend the bulk of my comparison time listening to this combination versus the Grados.

How did these two sets of cans shape up for me? In short, I found that both headphones did very well in the mids. I felt that the Cardas-equipped Sennheisers had a somewhat more spacious feel to their presentation than did the Grados, with a bit more air, and perhaps a touch more dimensionality. The Grados pointed in a somewhat more substantial bass, and a better sense of dynamic slam, an area where the Sennheisers occasionally sounded perhaps overly refined …maybe just a bit too polite. Just a bit. Maybe.

One area of headphone virtue that the Maxmeister did not emphasize is an important one to me: that of comfort. Having spent time in audio and radio production hither and yon over the years, I can tell you that there's nothing worse than a case of "headphone headache." It generally comes from wearing a set of 'phones that clamps too firmly over your ears, or doesn't hang well on your cranium. Sometimes the design of the headphone cups is not particularly engaging either, which means that large ears stick out or are uncomfortable with the fit. Another problem is to have headphone foam or vinyl that's too hard or is the wrong size, or don't allow your ears to "breathe" correctly. Any of these vices mean that you'll have unpleasant times, and won't enjoy your headphones over time.

The more comfortable set of headphones for me: without a doubt, the Sennheiser 650s.

The BlockHead drove both sets of 'phones wonderfully, and helped me to see the strengths of each one. Robinson's rule here is simple: every audio component or system is a collection of trade-offs, of virtues and vices; nothing is perfect for everyone. (Alas, anyone who disagrees with this audio postulate is probably in the category of "insufferable audio bore." Let's hope that this does not describe you, eh?) With all due respect for my good friend Max's perspicacity on things audio, by the time I finished comparing the Senneheiser 650s with the Grados, I ended up definitely preferring the Sennheiser 650s, but only when equipped with the Cardas headphone cable. Longer term, I preferred the spaciousness and detail of the Sennheiser 650/Cardas; I also found the Sennheisers to be much more comfortable on my head. The Grados were simply not as pleasant to wear for extended stretches of time as the Sennheisers were.

The BlockHead amp itself is a wonder, and is the best headphone amp that I've heard so far. Max has the advantage of me here; I wasn't at HE 2005, and thus didn't get to hear the new Headroom reference model that Tyll Hertzens was apparently carting around as the heir-apparent to the now-discontinued BlockHead. This new Headroom max model is apparently not yet in production; the Headroom web site says that it won't be available until this winter. If so, then headphone aficionados will just have to wait for the next iteration in Headroom land. (Either that, or contact Headroom to see if you can score a discontinued BlockHead!) Max and I will keep our eyes and ears peeled; perhaps we'll be able to update our commentary in 2006, after the new product debuts.

You don't have to wait until then to essay either the Sennheiser 650s or the Grado RS-1s, though. Both of these are worthy headphones, and one or the other should be to your taste. (Remember to get the Cardas headphone cables with the 650s, though …that's very important.)

The proverbial "bottom line": the combination of the Headroom BlockHead, the Sennheiser 650s, and the Cardas XLR headphone cable received my Brutus Award in December of 2004 for the best headphone system.

Enough said….