Headphone isolation box testing

So do you guys remember the Abyss Diana V2 fiasco where ASR crapped on the Diana because of bad measurements, namely the early bass rolloff and corresponding craptastic bass distortion that usually goes along with such rolloff (IME, the Abyss headphones are very dependent upon seal, something easy to bork during measurements - the truth is that the reality is somewhere in between)? I believe Jude at HF did his own Diana V2 measurement to provide another data point while illustrating the effect of varying seal. Data is just data. We are human and we all make mistakes and learn from him. FWIW, I actually think Jude does a very good job with taking measurements. Amir on the other hand seems to rush things and at times appears to have an axe to grind.

Anyway, you guys know how Amir loves to shit on everyone else's methodologies except his own? I recall Amir poking holes into Jude's measurements because Jude puts his torso/head thing in heavy box lined with foam inside. Amir said something to the effect that such a box would wreck measurements because of internal reflections and that any foam lining inside would be of limited effect.

Being a man interested in science (different from religion), I wanted to test Amir's hypothesis that such a box would wreck measurements. Theorycrafting is good and all, but I wanted to know for sure. I mean, I don't exact trust a dude that totally wrecked Microsoft's consumer division. I figured I would start with the most basic ghetto setup: a bare cardbox box. I'd then move toward lining the inside of the box with foam, polyfill, etc. And maybe at the end, I will build a real box with MDF (heavy).

When I was in California, I used my garage (on slab), and would take measurements after everyone went to bed. I don't do this now and as a result have noticed that the distortion measurements are a bit more inconsistent (this is anecdotal). My place in TX still on slab, but I'm not longer in that California isolated garage with exposed insulation and rafters with random stuff over the top for diffraction. I just take measurements in the room next to my desk.

Measurements in the open (TX)


Here is the bare cardboard box.


Let the games begin. I will take several sets of distortion measurements for each of the above. This is just to start comparing the effects the measurement rig out in the open to being inside a bare cardboard box. All measurements will be taken within an hour's time with no attempt to block ambient noises or for noises to quiet down.

 

Headphone measurement rig in open. Will do this five times.

Measurement #1


Measurement #2


Measurement #3


Measurement #4


Measurement #5

 

Headphone measurement rig in ghetto DIY cardboard box with no foam lining inside and tower throw over the front. (I am using this primitive contraption intentionally to see what happens in a worst case). Will do this five times as well.




Measurement #1


Measurement #2


Measurement #3


Measurement #4


Measurement #5

 

The measurements taken inside the unlined box appear to have wiggles from the mids to the highs.

Unlined box measurement


Other than that, the in the unlined box measurements look fairly consistent to each. Of the measurement taken out in the open, #5 is an outlier from the rest in a couple of spots.


Probably not enough samples to say that the in the box measurement is more consistent.

Next step: can we get rid of the wiggles in the FR on the in box setup by lining the inside with absorbent materials?

 

Here are the graphs blended:

Outside of box


Inside unlined box

 

So this is what I did next. I quickly threw some microfiber towels over the two foam panels closest to the headphone channel being measurements. My gut instinct was to go with towels because I found that old towels made better absorbers than foam with DIY panels. Note that the inside top, bottom, and left remained bare.



Inside box lined on two sides with towels over pink foam


Looks like these simple tweaks were good enough to stop the wiggles in the FR. In addition, note that the grouping of the distortion is tighter.

Next up: Will head to Walmart and buy some more towels to line the entire inside of the box. May also glue additional pieces of cardboard for mass loading - theoretically isolating the bass for tighter grouping of the 3rd and 4th harmonics.