Grado SR325i and Sennheiser HD 600: Professional Headphones Reviewed

In this review, we are going to discuss two headphones models from the top sector of the mass market: Grado SR325i and Sennheiser HD 600. It is interesting to compare these models with inexpensive products (we took a Grado SR80 for that) and also with each other since they represent two different approaches to design.

by Sergey Romanov , Oleg Artamonov
12/27/2007 | 12:31 PM

Among various categories of appliances we buy and use it is only with audio equipment that we have a broad price range but no simple and comprehensible criteria to base the price on. Amplifiers, speakers, headphones, audio cards – all of this can cost you from a few to a few thousand and even tens of thousands dollars while the formal parameters such as frequency range, frequency response and distortions do not always indicate what the particular device is going to sound like and if you personally are going to enjoy it. Besides that, there are quite a lot of firms that use the customer’s lack of knowledge to their advantage and offer solutions that have a fantastically high sound quality only on paper but come at a high price.


There is only one way to deal with this situation: listen and compare. In this review, we are going to discuss two headphones models from the top sector of the mass market: Grado SR325i and Sennheiser HD 600. It is interesting to compare these models with inexpensive products (we took a Grado SR80 for that) and also with each other since they represent two different approaches to design. Grado Labs reassures you that the ascetic design will only emphasize the uncompromising sound quality whereas Sennheiser tries to combine high-quality sound, ergonomics and modern appearance in a single product. Let’s see if they succeeded.

Grado SR325i: Design and Ergonomics

Most of us are perfectly aware that the contents is more important than the form, yet we are so used to seeing both match each other that we regard suspiciously each product that breaks this rule.

We guess that after looking at the photos users who are not familiar with the Grado brand may wonder how this could cost as much as $300.

The SR325i headphones leave an odd impression. On one hand, this model has a simple, even primitive, design: a flat head-band, round foam-rubber ear-pads (not even trimmed with fabric). The height adjustment is implemented with simple steel rods that move up and down in the plastic casing. The association provoked by this design is that of a radio operator from the times of World War 2. But on the other hand, the quality of manufacturing cannot be unnoticed: the head-band is trimmed with natural leather (as opposed to the Grado SR80 with its plastic imitation). The casings are milled out of aluminum and anodized to a golden color. So, this design is only a stylization implemented on the modern level.

Alas, these interesting and intriguing headphones provoke problems at everyday use due to the special design.

The headphones’ cups are rotating freely by 360 degrees. There are no stoppers to limit this rotation – one cup is turned around in the photo above, for example. So when you take the headphones from a table, you should make sure the cups do not rotate under the weight of the cable or you’ll soon find that the cable has twisted into a spiral. Besides the lack of stoppers in the cups, the thick and heavy cable itself is a problem – once twisted, it tends to twist again all the time.

The head-band is made from a flexible steel plate trimmed with leather. Despite the simplicity of design and lack of any additional pads, this seems to be the only element of the SR325i that we can find no fault with: it is soft and steady on the head.

The ear-pads are a different story. They are nothing else but foam-rubber circles, rather stiff and not trimmed with fabric. They are rather small and do not cover the whole ear but press against it. As a result, it may become uncomfortable for the ears to wear these headphones for too long. The good thing is that the ear-pads can be taken off easily for cleaning.

Although the housing of the dynamic capsule is a plastic cylinder, it has an aluminum casing anodized to a gold color. This is one of the differences of the SR325i from low-end headphone series which have a plastic exterior casing. It’s hard to tell if the use of aluminum has any effect on the sound quality, but it is no good for ergonomics. The headphones are heavy and can just drop off if you make a sudden movement with your head.

The fastening of the steel rod in the cup case is a potential problem, too. An author of this review knows of its unreliability from his own experience: after a year of using a Grado SR80, which have a similar design, one cup slipped off the rod and could only be fastened back in place with a drop of good glue. Users have reported the same problem at forums, too.

The height is adjusted by means of the mentioned steel rods that can move freely, with little friction, within the plastic casings fastened in the head-band. They keep the set height quite firmly and do not relax with use. On the other hand, the discrete regulation of height employed by many other manufacturers, especially when you need to apply an effort to switch from one position into the next one, is handier than smooth adjustment.

As we wrote above, the headphones are equipped with a thick, stiff and heavy cable that is not handy for everyday use, but also unlikely to be torn accidentally or frayed with use.

The connector is 6.35 millimeters, so you will need an adapter for the more widespread size of 3.5 millimeters to connect to most devices. Anyway, as we found out in our tests, the Grado SR325i should be used with an appropriate amplifier to reveal their full potential.

Sennheiser HD 600: Design and Ergonomics

Grado Labs is a manufacturer of a relatively small series of top-class headphones for home and, perhaps, studio use whereas Sennheiser is known in many fields. It turns out open and closed headphones, musical and monitor headphones, headsets for air traffic controllers and earphones for pocket mp3-players. The company is present on the market of high-end headphones as well. The Sennheiser HD 600 model enjoys no less recognition from lovers of high-quality sound as the Grado SR325i.

The design concept of the HD 600 is the opposite of the Grado model. It’s got large soft ear-pads and a glossy plastic case. The manufacturer saw to every detail in this appealing design.

Like the SR325i, the HD 600 is open-type headphones. You can see the dynamic head and the diaphragm through the protective grid above the exterior of the case. Well, this is a de-facto standard for high-class model as it ensures a higher sound quality. Closed headphones are meant for concert, to isolate the musician or sound technician from all ambient sounds, or for use in public transport and other noisy places. The closed design is also employed in inexpensive products because it results in a louder (bit not any more accurate) bass.

The head-band is rigid by itself. It is made from plastic with a stiff steel band inside and has soft pads at the bottom. It does rest snugly on the head.

The height is regulated by extracting the steel band the cups are fastened on from the central part of the head-band. The adjustment is discrete, and each step is accompanied with a click and requires some effort – the headphones won’t change the position spontaneously. That’s a small advantage over the SR325i in terms of ergonomics. The height adjustment range is quite sufficient.

The velvet ear-pads are large and encompass the ear. They press against the head rather than against your ears, without straining the latter even if you are listening to music for hours. Being lighter and steadier on the head than the SR325i, the HD 600 do not slip off when you are moving your head.

The HD 600 are equipped with a thin, soft and light cable that won’t twist or burden you. We didn’t spot that problem, but some users reported that the contacts of the connector the cable is attached to the cups with often fail.

The headphones’ native connector is an ordinary 3.5mm stereo plug. An adapter is included into the kit for 6.5mm devices.


Good headphones call for a good amplifier! We learned this at once as soon as we tried to listen to something in the tested headphones. The Grado’s impedance of 32 Ohms is too much for most operation amplifiers that are installed in the outputs of audio cards and some home appliances. At such a high load the amplifier’s THC increases greatly while the inter-modulation distortion often exceeds 1%. The headphones’ own distortions are much lower, so it is impossible to adequately evaluate their sound quality – the sound acquires noise and loudness that can be easily mistaken for an irregular frequency response. In fact, the Grado SR325i indicate the need for a serious amplifier with their 6.35mm connector and lack of any adapters in the kit. The Sennheiser HD 600 are equipped with a 3.5” connector and come with an adapter for 6.35mm connectors. The impedance of their dynamic heads is 300 Ohms but our measurements proved that it is an improper load for the ordinary line output, too. There appears a hump at the speaker’s resonance frequency, below which the bass is too low. The frequency response is too high at high frequencies as well.

After reading through various reports about headphone amplifiers, we took the HD53R-80 model from the Japanese firm C.E.C. Besides impressive specs, it features two stereo class-A amplifiers with independent volume regulation, which simplifies the test process. The headphones you want to compare are attached to the two inputs of the amplifier, and you only have to put them on one after another.

The amplifier proved to be up to our expectations, working well with every headphones model we had and delivering a very transparent sound. We measured the amplifier’s nonlinear distortion coefficient at an output voltage of 2V (this is the measurement limit for most non-professional audio cards) without load and found it to be 0.02% - the signal spectrum was limited with the third harmonic. When we attached the Grado ST325i, only the third harmonic rose up, and the total nonlinear distortion coefficient grew to 0.028%. Measured for a -1dB level, the amplifier’s frequency range was 30Hz to 30kHz. Thus, the C.E.C. HD53R amplifier suits perfectly for a correct test of top-class headphones.


The sound source was an Auzentech X-Fi Prelude audio card that proved its worth in comparative tests with other audio cards. The sound quality was evaluated using a number of selected recordings of different genres.

Besides, we were also interested to compare the two top-end headphone models with a cheaper product to see what you lose saving some money. We took the Grado SR80 for this test. Designed alike to the SR325i (except for an all-plastic case without anodized aluminum), this model has worse dynamic capsules. Although the difference between the specified parameters of the SR80 and SR325i seems to be small, their prices differ 2.5 times.

Strangely enough, the Grado SR325i at first proved to be inferior to the much cheaper SR80 in terms of sound scene, frequency balance and reproduction of details. It turned out that this was caused by the cups pressing to hard to the ear. The default ear-pads do not provide enough space between the diaphragm and the ear conch while it is highly necessary for the Grado SR325i. The similarly designed SR80 is free from that problem. There are two ways to correct it. You can remove the ear-pads from the cups, squeeze them slightly and put them back on one side only (on the top of each cup, for example). This will move the speaker away from your ear. You can also buy additional ear-pads from other headphones or use them together with the default ones. After these simple procedures the sound of the SR325i changes dramatically. The bass does not muffle the medium frequencies, in which every detail becomes audible, while high frequencies become much smoother. As a result, the SR80 was out of competition instantly, losing to the SR325i in every parameter: it has a less detailed bass, a flat but lifeless middle, and serrated high frequencies. Although the sound of the SR80 is energetic, light and not tiresome, it does not create a full music picture. It is too sketchy – here is a beat of the drum, here is the cymbals, and here is the singer. The Sennheiser HD 600 and Grado SR325i carry much more information, so it took us more time to learn their peculiarities.

The fundamental difference between these two headphones is about the bass and the reproduction of space. They form the audio scene differently. The Sennheiser moves the virtual sound sources away from you and wide from each other, which results in an unpleasant feeling of vacuum in your head with some specifically mixed recordings, but it is superb at reproducing live unprocessed recordings. The SR325i places the sound sources closer to each other and merges them into a single whole, but in some recordings you get a feeling of a musical instrument pressed right to your ear.

It is hard to tell what is better when it comes to reproducing space, but the Grado SR325i is obviously better in reproducing bass. It is not about its quantity (there is enough of bass in the Sennheiser, too) but in the level of detail: it is deep and energetic, variegated and superbly controlled. Sometimes there is even too much of it. The Sennheiser HD 600’s bass is not very solid and seems vibrant in its top part. This adds more charm to the contrabass but is no good for drums or tomtoms. The high frequencies are not quite natural with both models. The Grado SR325i has an increased middle of the high-frequency range and some jingles just deafen you while the ambient noise is hissing irritatingly. The Sennheiser HD 600 emphasizes the top of the sound range, which is sometimes discomforting.

The sound of medium frequencies is similar between the three headphone models, but the Grado SR80 cannot match the other two in the liveliness of reproduction. The Grado SR325i is superb at reproducing string and wind instruments, the piano sounding lush and energetic. The specific acoustic enclosure of the speakers adds some reverbs to all medium-frequency sounds, enlivening them. Male vocals are natural and energetic with pleasant bass tones but the emphasis on the bottom middle is not good for female vocals. It seems that the singer is forced to sing one register lower. It’s all otherwise with the Sennheiser HD 600: male vocals lose the bass tone but female vocals are just splendid. The HD 600 also has a minor advantage when it comes to the sound of the fiddle, reproducing the resonance of the instrument’s case better. A special feature of the Sennheiser headphones is that they show all insignificant sounds such as the touch of the lips and the tongue, the rustle of clothes, the touch of the strings and case with the fiddlestick, etc. All these sounds are audible in the Grado SR325i, too, but they do not distract you from the music proper. The emphasized detailedness allows the Sennheiser to reproduce the harp perfectly, but the vibrating top bass makes the sound of trumpets and saxophone rather unpleasant. The electric guitar sometimes lacks the drive you want from it, the bass guitar lacks strength, and the acoustic guitar has an emphasized high-frequency jingle of the strings. The HD 600 is especially unconvincing when reproducing symphonic recordings where the Grado SR325i sounds superbly. The relaxed sound of the Sennheiser proved to be optimal for compositions of The Doors, Mylene Farmer, Madonna, and many calm live recordings, though.

While listening to music with the Sennheiser HD 600 we had an impression that they needed a different amplifier, with a smooth decline in the high frequencies, which would be able to enliven this product, excellent in many respects. Unfortunately, we didn’t have a proper amplifier to check this out in practice, but this supposition is confirmed by users’ reports.


Besides sharing our subjective impressions with you, we want to give you some objective data. We measured the frequency response and sound pressure of the headphones by means of an audio analyzer Euraudio PRO600S with the default calibrated third-octave microphone. The measurements were performed on pink noise at a maximum volume of the headphones outputs of the semiprofessional audio interface E-MU 1820. The microphone was wrapped into a thick layer of foam rubber and pressed against the headphones’ ear-pad.

Grado SR80

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So you can note a very deep and flat bass smoothly connecting to the bottom middle. There is a reduced section at the joining point of medium and high frequencies, and a sudden rise at a range of 5-8kHz, which is noticeable to the ear. Anyway, the frequency range and sensitivity of these headphones is very good.

Grado SR325i

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Here, we can see an undulating diagram with a stress on middle bass and the middle of the high-frequency range. This must be a feature of all Grado products. The minor rise in the top middle adds a slight coloring to female vocals and to the sound of many musical instruments while the slump at 4kHz explains the rather narrow scene created by these headphones and, probably, the lack of stress on vocalists’ smacking sounds. These headphones are over 3dB inferior to the junior model in terms of sensitivity, yet it is more than enough for any application.

Sennheiser HD 600

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The frequency response of the Sennheiser HD 600 is a treat to the eye even though it differs from the curve you can see at the manufacturer’s website.

A separate diagram with the difference in frequency response between the Grado SR325i and Sennheiser HD 600 helps avoid the irregularity of the measuring equipment and show the difference between the two models. The diagram is constructed with a step of 1dB. Blue marks the advantage of Sennheiser, red marks the advantage of Grado.

The increased middle, the more emphatic bass and the specific high frequencies of the Grado headphones become apparent. Note that the frequency response of the two headphone models almost coincides in the medium-frequency range except for its top octave.


The Sennheiser HD 600 should be commended for its ergonomics. These headphones sit firmly and comfortably on the head, providing some sound insulation. Their sound doesn’t change much when the cups change the position slightly relative to your ears.

The design of the Grado SR325i isn’t that handy. They are heavier and less tolerant to head movements. This design is also not optimal in terms of acoustics. The Grado headphones just call for larger ear-pads but the manufacturer offers no alternative and the audiophile will have to make ones with his own hands. But after this modification, you can drop out of the real world for a long time, listening to album after album and even enjoying compositions you have never liked before.

Unfortunately, no model in this review is universal although the Grado SR325i is close to that status. At the same time, it is hard not to notice a number of objective drawbacks of its design, including the stiff and rather short cable. So, if you’ve got a high-quality amplifier capable of providing a low distortion coefficient at a load of 32 Ohms, if you can sit at a distance of no more than 1.5 meters from it, if you are listening to music motionless and in full silence, and if you are ready to tamper with the ear-pads all the time, you can really enjoy these headphones. But don’t forget that the people around you will be listening to your music as well, but won’t get as much pleasure from that.

The Sennheiser HD 600 needs an amplifier, too. Not all home appliances are capable of providing a sufficient volume and smooth frequency response for high-resistance headphones without an amplifier’s help. If you are planning to buy this model, make sure the device you are going to connect it to will work normally with it. Otherwise, you have to buy an additional amplifier.

Do you need such expensive headphones anyway? Yes, they differ from simpler models when reproducing almost all music genres, so the difference in price between the Grado SR80 and SR325i is justifiable. The question is if this difference matters for you personally, but you are the only person who can produce the answer after comparing different headphones. We hope this review has made you interested in such an exciting subject as high-quality audio.