The first post lists the equipment we will use. I thought I would discuss some of the equipment a little more. All playback and measuring will be done with an HTPC. For output we are using the Steinberg MR816x. It connects to the HTCPC with a firewire cable. You can think of it as an external 8-channel DAC or soundcard. We will use a 5.1 speaker configuration which will use 6 outputs. We can route the subwoofer output to the remaining 2 ouputs for a total of 3 subwoofer outputs.
The measurement microphone is a Behringer ECM8000 that has been calibrated from 5-25,000 Hz by Cross-Spectrum Labs
The microphone require phantom power to operate. The MR816x has 8 microphone inputs with +48V of phantom power so I could use the MR816x as both the output and input device. I connected a cable from Output 1 to Input 1 and measured with REW set to ASIO drivers and using the soundcard calibration. The signal chain starts to roll off at 40 Hz and is -3.5 dB at 10 Hz and -7.7 dB at 5 Hz.
I didn't know if it was the inputs or outputs that were rolling off so I decided to measure my Tascam US-122L. It is what I normally use for measuring with the ECM8000.
The Tascam US-122L measured a little better than the Steinberg MR816x when using a loopback from its output to its input. I then decided to measure the output of the MR816x to the input of the US-122L. This provided the least amount of rolloff. It shows that the output of the MR816x is flatter than the US-122L, but the input of the US-122L is flatter than the MR816x. For all measuring, our signal chain will be output on the MR816x to the ECM8000 connected to the input on the US-122L. In REW one has to have the drivers set to JAVA to have different input and output devices.
Here are the measurements of the signal chain. The blue line represents the soundcard calibration file that will be used. It is down .25 dB at 20 Hz, .8 dB at 10 Hz, and 2.7 dB at 5 Hz. This will allow our testing to have accurate results.