[Wayne A. Pflughaupt]

jpv wrote:

Thanks for the reply, I see the traces are at diff volumes then each other and your last graph they are the same. I did not realize the program will seperate the diff traces. It looked like they were just getting louder. How do you turn that feature off or on?

Sorry for the confusion, jpv. On the left side of the REW screen you’ll see the “Trace Adjustments” button. Under it is a function called “Trace Offset.” All I did was separate the traces by 8 dB in the top graph and 12 dB in the second, for the sake of clarity. Otherwise, it would be difficult to precisely see the differences from one trace to the next because they would all be on top of each other.

also how many traces do you do to make a good judgement of the room. Do you take an avg over many days?

Actually, I’ve been using the same EQ settings since September (all those graphs are unequalized baselines), and nothing has changed audibly, despite the differences the measurements show.

What you might do is save your baseline readings and take some additional baselines from time to time to see if anything drastic appears that wasn’t coming through before, and perhaps re-tweak the equalizer if you see it regularly re-occuring. But truth be told, you probably won’t hear a difference one way or the other. IOW, don’t loose any sleep over it.

OvalNut wrote:

Something as simple as a change in barometric pressure and/or temperature can affect sound pressure readings. Also, any furnace/AC fans blowing or not blowing at the time.

...oh, and the curvature of the earth.

You bet.

Here is another graph. I was taking some measurements one morning earlier this month at 2-minute intervals to see what kind of differences I would get between them. It was cold outside and I had the furnace running and a thermometer was measuring 73° inside the house. Just for grins, I wondered what I would happen if the SPL meter was warmer. So I set it on a window sill where there was streaming sunlight. The thermometer showed 86° in the sun. After 30 minutes I took a few more REW sweeps, and the graph below shows the results.

2 rew graphs 73 deg. vs. 86 deg..jpg

The blue trace is a 73° reading, the red after the meter set in the 86° sunlight for half an hour. As you can see, the “hot” trace (no pun intended) registers 1.5 dB higher overall. (The receiver’s volume control was not changed.) I had five readings at 73° and four at 86°; all the 86° traces were 1.5 dB higher. For illustration purposes, the two I picked here were the most closely identical in appearance.

Regards,
Wayne