AKG K701 Premium Reference-Class Open-Back Studio Headphones - Professional-Grade Audio for Music Production, Mixing & Critical Listening - Perfect for Home Studios, Audiophiles & Sound Engineers

By way of background, I'm a retired sound engineer/recording studio owner who was looking for a new set of high fidelity reference headphones for home use. While the product field is rather large, few headphones have or come close to providing the flat frequency response curve that's the mark of true reference headphones.I narrowed my prospects to the AKG K701s, AKG K702s and AKG K712s; the Beyerdynamic DT-880 Pro Headphones (250 ohm), and the Focal Spirit Professional headphones. Of that short list, the K712s and the Focal Spirit Professional headphones cost more than I cared to spend, and the frequency response curve of and DT-880s were not as tight as the AKG K701s and K702s. Both have a flat frequency response over the majority of the musical spectrum, great reviews, and a very reasonable price for that level of audio quality.The K701/K702 is aimed not at the iPod generation but at AKG's studio market (found on AKG's "Professional Audio Solutions" web site, "The K702's are reference, open, over-ear studio headphones for precision listening, mixing and mastering."). The K701/K702, being flat and neutral analytical reference headphones (i.e. 30Hz-10kHz +/- 3dB), only reproduce the content of the source, for better or worse. If you have the K701/702 cans powered adequately and the music source you are listening to using AKG K701/K702 cans sounds to you to be strident or muddy, or has a thin bass, or whatever, it's the musical source, not AKG K701/K702 headphones; being neutral and flat, they can only reproduce the true content of the source music. That is the purpose of studio analytic/reference grade headphones. Non-linear headphones are useless for the accurate monitoring/mixing/mastering necessary to create the highest quality artistic decisions about the musical performance.If analytical/uncolored listening is not your goal, then these headphones aren't for you. Seek out a non-linear product that will give you a rewarding listening experience.I chose the "Made in Austria" AKG K701 over the "Product of China" AKG K702 because through sad experience I've lost faith in the long-term reliability of anything made in China ((here's a 2012 example of the Chinese assembly quality of an AKG K242hd headphone: youtube.com/watch?v=Z_fGEK9rokw. Who knows what the interior may look like). At the time of my purchase (January 2014) I was still able to obtain the Austrian made AKG K701 headphones. In March 2014 AKG informed me that *all* AKG headphones are now being designed in Austria and assembled in China. The AKG "Professional Headphones" web page identifies only the K712 and K812 as still "Made in Austria". So it appears the AKG K701s "Made in Austria" will gradually disappear as the remaining stock gets depleted.Using my own original studio masters (covering many genres from rock to classical) as my sound source, I found the reproduction through the K701s to be as precise as I've ever heard those recordings: extremely accurate balance across the audio spectrum, tight bass, superb imaging, neutral coloring, full natural dynamic range, no distortion. And that's straight out of the box, with no burn-in. Enjoy them right out of the box. Playing music or pink noise through them continuously for several hundred hours before using them is silly. They do not require a "substantial break-in period", and any changes that might happen over time, if any, are subtle (see my general comments below on "break-in"). That said, after about 250 hours of use, they did sound a just a tad bit smoother - most likely the result of my ears simply re-calibrating slightly from my vintage Sony MDR-V6 to the AKG K701 headphones.While indeed very similar across the audio spectrum to the venerable and reliable Sony MDR-V6, there's a world of difference in the K701's audio performance. Although sonically almost identical in the reproduction of my masters, the MDR-V6s now feel compact, lacking the refined spatial depth and definition of the K701s. In Beethovan's Symphony No. 5 for example, it's the subtle difference between hearing the timpani rumble (the MDR-V6s) vs. hearing the individual strikes on the drum head as the timpani rumble, just as you would in the concert hall. The K701s are that good.Physically: The leather headband is real, not imitation. They are big - almost 8 inches across and almost 8 inches tall. The cans are oversized and enclose the ear completely. Each ear piece is about 5 inches in diameter. They are comfortable to wear, but a bit snug. By design they are open to the surrounding environment and are not noise canceling. The cable is ten feet long, straight (not coiled) and terminates with a 1/4" (6.3mm) stereo phone plug. A 1/4" stereo female to 1/8" (3.5mm) stereo male plug is included. They weigh 8.3 ounces exclusive of the cable. The full audio bandwith is 10Hz to 39.8kHz. The frequency response +/- 3dB is 30Hz-10kHz. SPL is 105 dB at 1 volt into 62 Ohms. The impedance (SPL sensitivity ) of the K701/K702 headphones is rated in relation to 1 Volt, as are most studio grade cans. The impedance of most consumer grade headphones is usually rated at 1mW. For comparison of the K701/K702 to the consumer headphone reference level, the AKG K701/K702s' 105 db SPL at 1 V into 62 Ohms translates to about 93 dB SPL at 1 mW into 62 Ohms.While my AKG K701s work with my Samsung Galaxy S4's volume set about half way, I get much better results when using the headphone circuit of my 1980s era Harman/Kardon integrated amplifier (80 Watts RMS per channel; frequency response 4Hz to 140kHz +/- 0dB). I don't think that smartphones, Ipods, MP3 players and computers can produce enough output power into a K701/K702 62ohm headphone load to drive the headphones to their full potential. The K701/K702 will benefit from suitable (not esoteric) amplification to achieve their full potential.I would buy these AKG K701s again in a heart beat. They are a music lover's nirvana at an affordable price. If still in doubt as to the intended purpose and audio quality of the AKG K701/K702 headphones, independent reviews at audiophile sites such as KenRockwell, innerfidelity, headphone, and audiophile magazine will affirm the numerous 4 and 5 star ratings of the K701/702 found here.A word of caution, though: If your only exposure to music has been the hypercompressed, loud, bass-heavy thumping of FM radio and such, and you like that, then you probably won't be happy at all with these exquisite headphonesHere's some general background information others have found informative."Break-in" PeriodThe jury is out on this. The only formal study of which I'm aware was inconclusive and can be found on the innerfidelity web site by searching on "On the Measurement and Audibility of Headphone Break-in".I don't know of any professional audio people who give "burn-in" any credence. The subjective perception of "burn-in" is, in my opinion, the user's hearing being re-trained and adjusted to the frequency response curve of the headphone. Thus a listener coming from a headphone whose response curve boosts the lows and dips the mids (as most consumer cans do) will hear a headphone with a flat and neutral response curve (like the AKG 701/702) as having a shallow bass and a strident upper mid range. As the listener's hearing adapts over time to the uncolored accuracy of the neutral/flat headphones, the headphones miraculously "improve" after having been "burned-in", when in fact it's the listener's hearing being "burned-in" by the headphones.Headphone Impedance:Headphones with lower impedance ratings offer higher volumes at the same level of input, but they need heavier drivers to compensate for the low impedance or risk sounding muddy and distorted. The lower mass of the drivers of a higher-impedance headphone can deliver unparalleled clarity and response, but it takes more power to achieve the same loudness.How We Hear-Consumer Headphones v. Analytical/Reference Headphones:At low listening levels the human ear is most sensitive to the mid range (200Hz -2kHz), gradually loosing sensitivity below and above those points. If you picture the ear's frequency reception at low levels it would look roughly like a frown. At higher listening levels, the lows and highs become more pronounced less out of balance with the mid range.The frequency response of consumer grade headphones typically looks like a smile. At higher listening levels the result is unnatural sound (lows and highs artificially boosted by the headphone's particular design). This makes most consumer grade headphones unsuitable for critical/analytical listening because the amount of boost incorporated by the individual manufacturers can be difficult to assess. Most, if not all, boost the low end significantly (+5dB or more), dip the upper mids by -5dB or more, and sometimes also boost the high frequencies. A few start rolling off the upper mids and just keep going downhill. In very broad terms, consumer grade headphones intentionally alter the audio spectrum in the low, mid, and high frequencies. Also, if headphones are underpowered, you won't hear the low and high ends accurately because of the human ear/low volume factor. Underpowered headphones don't get enough power from the source to allow the ear to hear the lows and highs at a level comparable to the midrange.From a performer/producer/sound engineer's perspective (AKG's target market for the K701/K702), it is the non-linear consumer grade headphones that are lacking. Non-linear headphones are only used by the pros to listen to (not create) the rough mix so they can judge what the typical consumer might hear v. the artistic goal for which the musicians and producer are striving, so that they can tweak the mix without seriously compromising the artistic goal.A sound engineer's job is to faithfully capture the sound of the music produced by the musicians. The ONLY way to do that is to monitor using amplification, speakers and/or headphones that are neutral (i.e. have a flat frequency response) over the entire audio spectrum (we'll ignore physical sound treatment of the control room for the moment). I have never met a professional who wanted to produce a mix geared to the lowest common denominator, nor geared to sound good only on the highest end audio equipment. Recording studios spend hundreds of thousands of dollars to achieve the highest degree of audio accuracy so musicians, producers, and sound engineers can make informed decisions about the mix. If the goal is a bass-heavy musical product, the flat, neutral, uncolored monitor speakers/headphones will tell the producer when the mix achieves that goal.The working mix is also played over typical consumer equipment, in car stereo systems, MP3 devices, etc. to see if it works on what the average consumer will be using. Those with high-end and esoteric stereo systems will derive the full benefit of the musicians', producer's and sound engineer's artistic efforts. Those without will still get an enjoyable product. Studio grade analytic/reference headphones provide that flat frequency response required for artistic accuracy.