This page covers some of the details on how I determined which factors affect frequency response and how. Here is the rig I built:
The testing was done with a flat plate and microphone, rather than a replica human ear. Thus it is a little flawed, but I believe it is still very valuable for showing the general effects of design/build variables.
The test equipment is:
- Microphone: MiniDSP UMIK-1
- Software: REW (Room Equalisation Wizard)
One of the most important requirements of this testing is repeatability. If the way the headphone was placed on the rig caused significant variation in the results, it would be impossible to tell the impact of the variables being examined. Therefore I made only one ‘ear’ and put some bolts on the headphone and corresponding holes in the rig that would ensure the position and alignment on the rig was exactly the same each time. The ear piece was held in place with clamps.
Before doing any proper testing I removed the headphone, disassembled it, then tested it a few times. The results were all very consistent. Furthermore, during testing I frequently went back to ‘baseline’ configuration to make sure nothing in the rig or headphone had fundamentally changed.
The graph below shows all the tests that were run. Variations from ‘baseline’ configuration are light blue and baselines are black.
The following conclusions can be drawn from this graph:
- The repeatability is good,
- The rig did not ‘drift’ or change in its performance throughout all the changes of configuration, and
- The effect of changes in configuration are much greater than ‘normal variation’ in the test method/equipment.