Bass clipping (I think) on HD 595 -- looking for advice - Page 5

Hi,

Sorry for (another!) thread bump, but this is important.

I said that I was going to sell the V-Can, due to a perceived clipping problem. I didn't sell it, because I didn't know how to word the ad. ;^) I simply put it away and stopped using it.

However, I've got it out again.  I can't reproduce the clipping problem any more, and I think I was probably wrong about the V-Can. If I wasn't overdriving anything, then there is one other possibility I can think of. Sometimes, if I sort of twitch my ears a bit, I hear a little "click" sound, which can sound VERY much like a sharp clipping problem. I think it's just the opening of my eustacian tubes clicking. (can anyone else make their ears click like this? I've always been able to do this, and it doesn't feel in any way "wrong")  Further, I have noticed that I do this unwillingly sometimes, when I play a loud chord on the piano. It's kind of a small wince. (recall that I am playing live software pianos through the V-Can)

I was toying with the idea of just saying nothing, but that wouldn't be fair. I absolutely hate the idea that I have misrepresented the V-Can, and I am truly sorry.

So I am finally a happy Musical Fidelity customer.  ;^)

Greg.

And yes - another thread bump.

I was still a bit uncomfortable about this V-Can/K601 clipping issue. As you can see in my previous reply, I had put it down to a clicking sound in my ears (eustacian tubes). There's no doubt that my ears DO make little clicking sounds if I wiggle my ears in a certain way - it feels/sounds like it's just the moist openings of the eustacian tubes. My ears don't make these clicks normally, however as I said, sometimes when I play piano forcefully, I sort of wince, and this thing happens to my ears. (I sort of pull my ears back) If anyone thinks this is abnormal, I'll have it checked out, however it doesn't feel/sound in any way abnormal to me. 

HOWEVER, I decided to do some more testing.

The first thing I did was simply play some music loudly. I can make it clip quite easily. The overall volume is very loud, but not painfully loud. I can turn the V-Can all the way to 100% and still tolerate it.

I then fed a 220Hz sine wave into the V-Can. (I chose a relatively low frequency, because I think that I can tolerate loud low frequencies more than loud high frequencies). Again, I could make it clip. I measured the output of the V-Can at 3.2V RMS at the onset of audible clipping. Looking at the specs for the V-Can, it can generate 250mW into 32 ohms, which is 2.8V RMS, which is in the ballpark of the 3.2V measurement.  This is a sign that I am simply overloading the V-Can.

I then connected the K601 headphones up to the headphone output of my NAD 320BEE integrated amp, and the laptop to the AUX line in. At 3.2V RMS, I could not hear any clipping. I increased the volume further, stopping at about 4.5V RMS - still no clipping.  Conclusion: the clipping I reported appears to be indeed the V-Can reaching it's maximum output level.  It is reaching (if not exceeding, slightly) it's specifications.  My initial hunch was probably correct - the V-Can is not entirely suitable for the K601 headphones, for loud listening.

The K601 headphones have a sensitivity of 101dB/mW. If my maths is correct, 3.2V would be generating about 119dB SPL in my ears, which is very loud. However, recall that I only really complained about a problem when playing solo piano, live. (i.e - actually playing a virtual software piano live, and listening through the V-Can & K601), and even then, only on the attack transients.  The overall sound level I am listening to would probably be MUCH less than 119dB - it's just the occasional excursion in the attacks where it sometimes clips.

For comfortably loud music listening, the V-Can/K601 is fine. For genuinely loud listening, IMHO it is not a suitable combination.

Also, the maximum power rating of the K601 is 200mW, and 3.2V RMS is only 66mW. I am nowhere NEAR overloading the K601 headphones. 

Greg. 

Note that I was ignoring the 5 ohm output impedance of the V-Can in my calculations in my previous reply. When I take this into account (working back from the V-Can's spec of 250mW into 32 ohms), I calculate that the maximum unloaded output voltage is 3.27V RMS, and when loaded by the K601, it drops slightly to 3.14V RMS.  This is now even closer to my measured maximum of 3.2V RMS. 

Looking at the specs for Music Fidelity's M1, I see that it has four times more power than the V-Can.  I'm quite sure this would be good enough for me with my K601 headphones. 

I see that for the V-Can II (same power as the original), they still say: "This means it will drive any headphone available with ease". (I remember the same words for the original V-Can). I'm not sure these words are all that accurate. 

Greg.

I've just discovered that I have probably been using the sensitivity specification for the K601 as the efficiency specification.  ;^)

Here are the specs for the K601: http://www.headphonesolutions.com/akg-k601-wired-headphones.html   Am I correct in saying that these specs only provide the sensitivity, because there is only one figure (101dB), and the asterisk is next to "db/V", meaning 101dB for 1V RMS?  (why do they even mention dB/mW if they don't provide it? Very confusing)

Assuming the above is correct, then the SPL at which the V-Can clips is 20*log[10](3.2/1) + 101 = 10dB + 101dB = 111dB SPL.   However, I see from the frequency response plot that the response is up by about 2dB at my test frequency of 220Hz, so that makes it 113dB SPL.    This is 6dB quieter than my original estimate of 119dB.

Greg.