Background noise or room acoustics?

[ElectroKinetic]

I took my Sony SS-u3030 studio monitor and placed it on my futon along with my meter. I ran two tests and calibrated the SPL before each one. The first test was with both the speaker and the meter sitting on the mattress. The second was with a fluffy comforter over them to deaden erratic sound waves in the room. the meter was roughly 1 foot away from the speaker. REW only needed 3db of headroom for the second test as opposed to 6db for the first. The graphs are very close together. Am I seeing more background noise or room acoustics?

Red - normal
Blue - Blanket deadening sound

[robbo266317]

Here's what I did to check background noise (Coal Loader & railway about 2 km away - lots of ELF energy)
I set REW up and did the standard 75dB test then unplugged the input to the amp and ran the test again. REW will complain the level is too low, however, continue as normal and the graph will be your noise floor.

[ElectroKinetic]

I thought the headroom measurement was basically the noise floor?

[brucek]

The second was with a fluffy comforter over them to deaden erratic sound waves in the room

This is not the way to remove the room. It renders the results quite inaccurate.
Place the speaker and mic away from any surfaces and set the mic at 12". After the measurement gate the impulse response to 6msec to remove any reflections from surfaces greater than 1 meter away.. This will limit your bottom end to about 166 Hz, but it's fine if you're trying to measure the upper response of your monitor.

brucek

[Wayne A. Pflughaupt]

What brucek said. Basically, what you're doing is taking a super-fast reading before the signal has a chance to bounce around the room.

Regards,
Wayne