Several people have emailed to ask for the uncompressed audio files to the above soundcloud file. The sound file is from the Scottish oil storage tank that holds the World record for the ‘longest echo’. There were 6 impulses measured that can be downloaded as WAV files from freesound.
Details of the measurement
The storage tank measured used to contain 5.6 million gallons of shipping oil. You can find out more about the oil tanks and their acoustics (and why the World record is incorrectly called an echo) in my new book.
The measurements were carried out according to ISO 3382-2 2009 “Acoustics – Measurement of room acoustic parameters Part 2: Reverberation time in ordinary rooms”. The impulse response measurement method was used using a starting pistol firing 9mm revolver blanks. Two ½” inch laboratory quality omnidirectional microphones were used (Bruel and Kjaer 4165 condenser microphone connected to Bruel and Kjaer 2669 preamp). These were connected to a Norsonics 336 Front End power supply and pre-amplifier. The outputs from the Norsonics 336s were recorded on a Roland R44 sound recorder at a sampling frequency of 44.1 kHz with a 24 bit precision uncompressed.
Six source-microphone combinations were measured. The two microphones were placed roughly a third of the way from the rear wall of the room, approximately 5 m apart, roughly 2 m and 3 m from the centre line running along the length of the room. One was approximately 1.5 m above the ground the other approximately 2 m above the ground. Three source positions were measured, starting roughly a third of the way from the entrance and ending about half way into the room. Source positions were away from the centre line of the room. In feeesound the impulses are labelled 1-6. 1&2 were measured at the same time (similar for 3&4 and 5&6).
If you want to EQ the effect of the gunshot, you’ll need to download this anechoic measurement of the starting pistol from freesound. The anechoic measurement was measured on the stereo microphone pair of a Edirol R-09.
If you end up using the sound files, please let me know about it.
Prof, regarding the six source positions which is 2 microphone positions and 3 source positions I still don’t understand how to average the measured reverberation time based on the results obtained from the two microphones simultaneously. Can you explain how you average the reverberation time?
You’d normally calculate the reverberation time for each of the 6 microphone positions. You would then average those numbers.
The simulataneous measurement using two microphones was just a convenient way of getting more measurement positions quickly.
So prof means that the results of the six impulse responses obtained from the storage tank were from six different positions of microphone and the final result based on the averaged by six?
2 mic positions and 3 source positions meaning there were 6 unique source-receiver pairs
Now I understand. Thank you prof. There are a lot of things I have learned from your articles. Really looking forward for your next post 🙂
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I don’t know about the “longest echo” but this is one of the most beautiful – https://www.youtube.com/watch?v=mCdJfa4sxQo&spfreload=10
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