A Look at the Torque t402v Bass Adjustable Headphone
This is not a review of the headphone, but rather just a good opportunity to learn about a bit of headphone acousticsand let my curiosity run amok. I wanted to see what the measurements of the Torque t402v looked like. With two pads having four filter settings each it took me all day to acquire the data and make the comparison worksheet. It didn't quite turn out as I expected.
The photo above show a close-up of the on-ear pads and headphone capsule of the Torque t402v bass adjustable headphone ($399). If you look at the driver capsule in the middle of the image above, you'll see a port at the top (circled in red) that vents the space behind the driver into the space between your ear and the headphone.
In the crude illustration to the right, you'll see how the sound from the front of the driver (green arrow) goes directly to the ear, and the sound from behind the driver (red arrow) goes through the vent and then to the ear. At low frequencieswhere the wavelength is much longer than the path length of the red arrowthe signal from behind the driver is out of polarity with the signal in front. This will cause the signal near the ear to be somewhat cancelled out by the interfering acoustic signals. Basically, the bigger the vent, the more out-of-phase rear signal gets to the ear chamber, causing more cancellation and a lower level in the low frequencies.
The pads of the t402v are perfectly square and can be rotated and installed in four positions. Each position has its own ventseen as the variously colored plastic inserts in the photo aboveeach of which will align with the capsule vent when in the upper position.
The yellow vent has the smallest holes, giving less sound from the rear of the driver therefore yielding the most bass. The blue vent is slightly larger and should reduce bass some. Likewise the red is larger still, and the black hole should have the most air passage theoretically yielding the least bass.
And there's where things start going pear shaped. Here's the plot of the over-ear pads.
As you can see, the yellow filter does indeed have the most bass; the blue is next. But when we get to the red and black settings things seem swapped. Damn. I triple checked this and these numbers are correct. Also odd is that the black plot seems to be oddly different in a number of other places. At 7kHz, for instance, the black plot is at the top when the order of traces would cause one to assume it would be at the bottom.
Care to make a stab as to what's going on in the comments?
My guess is that the fully open hole of the black vent has an air turbulence structure different than the filters with 8 holes making it behave a bit differently. Who knows.
Worse yet, when I switched to the on-ear pads...
...I got very little bass adjustment at all, but for the yellow filter which has some. This may be due to a poor seal not creating a good enough chamber for the front and rear acoustic waves to cancel effectively...or not. It may be just how the graphs are aligned because it does look like the treble hump at 3kHz is being adjusted, and in the right order. When I listened to the on-ear pads, I do think I heard a distinct difference in bass response with the various pads.
I did make a little .pdf booklet of all the measurements. I found it interesting to note that bass distortion on the open ear pads increased, and/or got more erratic, as the hole got bigger. It's also fun to watch the low-Q impedance hump at 80Hz grow with vent size.
I should mention I didn't think these headphones sounded particularly good. I suspect that you may also get effects from the vent at other frequencies, which would roughen up the frequency response. I've heard four or five acoustically bass adjustable headphones and only the AKG K267 Tiesto sounded any good to me at all. Here's its compensated plots as opposed to the Torque's raw plots above.
Anyway, curious if you've got any ideas on the data...
...but don't spend too much effort on it, there's turkey and stuffing in need of attention!