The impulse response of the Optimus Pro 7 speaker was measured in the anechoic chamber using a Neumann KMi 84 microphone at a distance of 1.4 meters. The measurement technique was exactly the same as the HRTF measurements. The speaker impulse response can be used to create an inverse filter to equalize the HRTF measurements, as will be discussed later.
In addition to measuring the speaker response, we also measured a variety of headphones placed on the KEMAR. The headphones measured are listed in Table 2.
Table 2: Description of headphones measured
It is possible the HRTF data will be used to create a spatial auditory display, in which case the frequency response of the headphones used to render the display is important. The above headphone responses may be useful to create appropriate inverse filters. We did not gather data on the repeatablitity of such measurements (i.e. how much variation in the frequency response is expected each time the headphones are placed on the head).