CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => Headphone Measurements => Topic started by: ultrabike on March 30, 2014, 05:21:02 AM
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So these are noise cancellers. If turned on, there is some noise rejection and an increase in volume (about 8 dB). I think I've heard better noise rejection from the Bose's though. Still, I preferred the sound w the noise cancelling circuit on. It seems the circuit performs some equalization to these cans and brings out IMO better balance. The internal amp noise floor is audible.
The biggest problem I had with this cans was distortion. I think it's audible with some of the songs I used in the form of glare and resolution loss. These are not bright though.
Here are some measurements w the NC circuit off:
Frequency Response
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=5999;image)
CSD right
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6001;image)
CSD left
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6003;image)
Distortion right
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6005;image)
Distortion left
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6007;image)
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Here are some measurements w the noise canceller circuit on...
Frequency Response
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6009;image)
CSD right
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6011;image)
CSD left
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6013;image)
Distortion right
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6015;image)
Distortion left
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6017;image)
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NC = Bass boost, heh.
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Yeah. Regardless of what the plots say, I did find the cans more engaging (and loud) when powered on, than not. Noise cancellation was not that great IMO. I'll post some FR overlays later.
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I'd be curious to see if there's any relation/correlation between distortion and isolation for noise cancelling cans (or between the different "modes" they seem to have).
The only noise cancelling can I've tried that didn't create some weird pressure effect on my ears was an Audio Technica ANC7b. The worst I ever felt was something by Able Planet that actually made me feel nauseous after a few seconds.
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In this case it does seem like the NC circuit increases distortion and noise floor, but dunno about other NC cans.
The measurements above and in overlays below where done @ 90 dB with pink noise for both NC off and NC on. However, for the overlays I aligned the plot of the NC off so the treble area would match.
Yellow = NC off, Blue = NC on
(http://www.changstar.com/index.php?action=dlattach;topic=1528.0;attach=6019;image)
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NC = Bass boost, heh.
These effects are inherently 'coupled'.
The noise cancelling works by comparing sounds on the outside of the cup to those within the cup.
It thus has 2 microphones (which is what makes the NC so noisy in most cases).
The headphone also has to know which signal should be in the cups and that is the audio signal.
Because of this the NC also compares the signal the driver reproduces against that from the mic inside the cups.
If the driver/earpad combo is rolled off the mic inside will try to compensate the bass levels 'flat'.
This is why with NC on you generally see a better LF extension/flatness.
The difference between 2 mics only works for lower frequencies because of acoustic wavelength/delay which needs to be much bigger than the relative sizes inside the cups.
For this reason the BW in which NC works is limited to the upper mids at best so you don't see/hear much effects in the highs, although it might appear that way due to the masking by the increased lower frequencies.
The increase in 'distortion' with NC on is most likely caused by noise (mic pre-amps) and things the microphones pick up rather than THD of the amplifier section in the headphone itself.
Think of the 'bass correction' as Philips Motional FeedBack, although that was done inside the woofer with a X'tal 'pickup' instead of a mic insde the cabinet.