The thing that immediately strikes you about the 325 is the clarity and smoothness of the midrange. For those not raised from birth on audiophile Kool-Aid, I should be clear that this observation carries more weight than might be readily apparent. The fundamental tones of most instruments are in the mid-range. Get the mid-range right, and you’re 80% of the way home. As easy as the sentence is to write, I should also be clear that it isn’t that easy to do. Check out my Sennheiser HD800 review for a discussion of a high-end headphone that struggles just slightly in this area. And, yes, I am saying you can validly compare and cross shop the SR325is and the HD800 (assuming your goal is musical accuracy).
The mid-range clarity of the SR325is shows up in its’ natural portrayal of the tonality and timbres of individual instruments. When we think of tonal balance in an audio product, we sometimes mean that overall bass/midrange/treble evenness that allows a band or orchestra to sound right. But it is also very important for audio products to render the distinctive, “signature” voices of individual instruments well. This latter idea is a critical test of smooth and balanced midrange, because that’s where most instruments produce sound.
Take the voice of an acoustic guitar as an example. Fundamentals on acoustic guitars range from about 80hz to 3khz, and most of what we hear, including overtones is in the 200Hz-4kHz range. This is a midrange instrument (so are voice, cello, clarinet etc). I listened to track after track of acoustic guitar recordings on the 325s, and was impressed with how natural the sound was, particularly the way the body sound and overtones were clearly defined and in balance.
That’s good and all, but we also want a headphone to be able to play large-scale material, not just solo or ensemble stuff. Fortunately, handling more complex music is another strength of the SR325is. My listening notes are full of references to the excellent sense of instrumental separation the headphones give. In other words, when you’re listening to a band, you not only hear the overall mix, but can also pick out the contributions of each individual performer, just as you can when listening to a good live performance. In short, the 325s deliver both smooth response and low distortion throughout the midrange.
When it comes to overall frequency balance, I found the 325s to be somewhat chameleon-like. The Grados sometimes seemed slightly forward in the midrange, and on the light side in the bass and upper treble. No sooner did I make this note than I’d play something with powerful bass and be surprised at how solid the low frequencies of the 325 could be. After going over lots of recordings, my conclusion is that the bass, mid-range and treble are very well balanced, but that the 325s sound as if they have a slightly “n”-shaped response curve (in other words, the levels of low 40Hz frequencies fall slightly below 1kHz mid-band frequencies, as do high 10khz frequencies). This would contrast with, say, the Denon AH-D5000s, which have a definite “u” shaped response curve (where the levels of 1kHz frequencies fall below those of sound in the 40Hz or 10kHz range). At the very highest and lowest frequency extremes (20Hz and 20kHz, respectively) the 325’s frequency response continues to show a slight degree of rolloff. But let me emphasize that these broad response shapings don’t consistently come across as “light bass” or “mellow treble” in the case of the 325, since in truth they are not dramatically far off from the ideal of “flat” or dead-neutral response. Instead, these shapings tend to make you feel that the 325s sound more “clear” and “natural,” rather than “rich” or “extended.”
Given this discussion of tonal balance, I want to comment on treble performance. Every headphone I have tried has some issues in the treble range. The issue with the 325 is that it can occasionally sound a little splashy or sibilant. This can make the 325s sound a tad brighter than my comments above might indicate. I felt this was a smaller issue with the 325s than it is with most headphones, but it is there. At times this may simply be a matter of the 325s revealing quite well what is on the recording, but sometimes there is a slight peakiness to the sound. Still the 325s sound both better balanced and less uneven that the Sennheiser HD 650s or the Denon AH-D5000s, both very good headphones that sell for nearly twice the Grado’s price.