The Effect of Glasses on Headphone Frequency Response
Not long ago a reader asked me if I would experiment with how glasses effects headphone measurements. Having measured a lot of headphone and knowing how important the seal is I kind of knew how this would turn out: very varied. Some headphones are very sensitive to seal, and some aren't. Generally speaking, the more leaky or open the acoustics in the chamber between the driver and the ear, the less sensitive they are to a seal.
The problem is that the amount of seal in the ear cup is not typically apparent in the measurements I do. I would say the only time it is, is when you can see the headphone sometimes sealing and sometimes not in the measurements. For example, in these Master&Dynamic MH40 and KRK KNS8400 measurements.
Both headphones were having troubles getting a good seal in the measurement, and when the seal was broken the measurement would be dramatically different. So, while I can tell how tightly a headphone seals and how sensitive it is to a seal breaking, I will often times be able to adjust the headphones carefully so that it's not actually apparent in the final raw data. Only when I'm having problems getting the seal will I intentionally allow the measurements to wander, as that reflects a real trouble with the headphones.
What I'm driving at is I see a wide variety of sensitivities to seal in the headphones I measure and as I try to get a good series of measurement on a headphone it will make that sensitivity to seal less and less apparent. But I can tell how sensitive to seal they are when I do the measurements. Bottom line: I can show you the typical variety of responses of wearing glasses with headphones by doing the experiment, but I can't tell you how to predict when a headphone will be sensitive to glasses based on the measurements. Sorry.
It was pretty simple really, I picked five headphones that I knew would have a representative variety of responses to the seal being broken by the glasses. I used the: Philips Fidelio X2; Audeze LCD-2F; Focal Spirit Pro; Audio Technica ATH-M50x; and Master&Dynamic MH40. I measured the raw response of the headphones on the head without glasses, and then with two different glasses I have hereone with thick arms and one thin.
I then averaged the left and right channels together for each measurement and created a plot comparing the measurements with and without glasses.
Results, as expected, varied quite a bit. Let's start with the open headphones...
The Philips Fidelio X2 above is an open headphone and ear pad seal shouldn't have too much effect on response, and indeed it didn't.
The Audeze LCD-2F is an open headphone, but the seal between the driver and ear is actually pretty tight. Still, the glasses didn't seem to have as much effect as I thought they might. Just a slight roll-off below the pad resonance.
The Focal Spirit Pro is a sealed headphone, but the glasses didn't seem to have much effect. Perhaps it's because these pads are a bit small and they may be sealing partly on the ear as well as around the ear.
I would guess the effect of glasses on the Audio Technica ATH-M50x is probably close to average. Here there's a clear loss of bass energy, and just breaking the seal is enough to do the jobthe thick and thin frames had similar effect.
I knew the very tight seal of the Master&Dynamic MH40 would show up strongly on this test. Often times with a headphone having this strong a seal, I will put a piece of felt between the ear pad and the side of the head. This mimics hair and will provide a controlled leak that is often more representative of how the headphone normally sounds. (I was taught this trick by a professional headphone engineer.)
I'm sorry I can't tell you how to predict the sensitivity of a particular pair of headphone by looking at the measurements. But I know this subject has come up before and simply showing you the measurements will satisfy some of the curiosity out there.
Thanks for reading!