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Discussion Starter #1
Dear All,
I am using REW 5.1 on Mac El Capitan with a Scarlett 2nd gen 2i4 sound card and a Dayton Mic, both of them with a cal file.
I am measuring RT60 on an empty room that is about 58K2 cubic feet. ( 1650 m3 ). I used two speakers and one sub to generate the sweep. I tried sweep ranges from 256 to 1M on REW. I used different mic positions and different speakers positions and pointing. All the frequency responses and all the RT60 graphs on REW are very similar among them, and all of them have a big peak of about 2s. on 100Hz and 2KHz. but only near 1s. from 200Hz to 1KHz. My manual calculations are near 1s. for the space. Materials on the walls are glass and concrete. The ceiling has a perforated acoustic cover. Floor is concrete also. Has chairs and tables. All of those materials have no big absorption variations on frequency, so I guess RT60 should be very similar over all frequencies. Question is, is it RT60 valid at 100Hz and 2KHz? is this real or is some kind of mistake or issue? May I trust the whole curve from 60Hz to 8KHz with this huge peaks or should I just believe on the 200Hz-1KHz range?
Thanks in advance for your feedback.
My best regards,
Gerardo Ruiz.

REW RT60 strange graph.jpg
 

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You should believe these readings. But, to get an accurate RT60, you should average a number of plots fro various positions. It’s likely that the absorptive material in the ceiling mostly impacts mid to upper frequencies. Also, room resonances will cause funky results, which is why averaging a variety of positions is the best way to determine an RT60.
 

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Discussion Starter #3
Thanks Dave for your inputs. Actually I just put one point since all the 14 different places all over the room showed the same values with just slight differences.
 
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