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Topics - gwarder

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Electroacoustics Toolbox / Room Analyzer - best practice?
« on: February 06, 2014, 10:34:27 AM »
I am having a great deal of difficulty getting any real results. So I'd like to start by ruling out "user error" as I am fairly new to this.

My goal is to measure a church where I have recorded a choir/organ ensemble. The end result is for a Masters paper I'm writing.

To measure the room, I have placed an AKG C414 XLIIS in omni mode about 10' up and slightly behind the conductor's position (same place I set the mic array). The mic went into a Millennia mic pre, then to an Apollo 16 interface, finally into a Mac laptop. The Apollo interface also fed a monitor speaker placed in the centre of the choir. This was for the excitation signal.

On launching Electroacoustics Toolbox, I opened Device I/O and selected (and started) the Apollo 16 interface.

Next created a Dual FFT Analyzer. In the bottom drawer I set the source to the appropriate Apollo 16 input. Under the "Excitation" tab, I Selected the appropriate output channel...sine sweep...Logarithmic. I left all other settings at default.

Next I selected Control->Start All Tools. I confirmed that I could hear the repeating excitation signal in the room and that the mic was picking it up. While the excitation signal was in progress, I selected Control->Capture all Data. Then I stopped all tools.

Next I created a Room Analyzer and selected the captured measurement. There are LOTS of n/a boxes in the analysis. Nothing captured in C80, nothing for 4 areas of C50, NO T60 measurements, several bands empty in T20 and T30. Nothing for D80 and 4 blanks for D50. The T measurements that I did get are quite different from a sweep done with "FuzzMeasure" and all seem extremely short.

This is a sanctuary that has a fairly low noise floor (lights, fans and organ turned off during measurement), and a "starter pistol" excitation produces a decay that lasts roughly 4-5 seconds to the naked ear.

I'm wondering what is wrong in my setup. Mic position? Polar pattern? Something in the excitation?

Thanks!

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