Following Don's very helpful reply, I redid the RT60 measurements in my room
using his method with filtered white noise and Audicy (Cool Edit).

The results are now much more what my ears tell me:- RT60 at 125Hz 0.6 sec,
RT60 at 4kHz 0.2-0.3 secs. (difficult to tell exactly)

IEC standard is 0.3-0.65 secs at LF.

I've looked into what went wrong earlier using the unfamiliar software. I
made the measurements at 85dBC, and my room in daytime is only just 60dB
below that, measured wideband, so I may not have got to 60dB down,
especially when adding mic amp noise on top from the mic amp built into the
Sound Level Meter. I think the software just gave me a 2.5 seconds
indication which didn't change with frequency as it couldn't make a proper
measurement. Anyway, using Don's filtered noise method, I can measure down
to -60dB.

These figures were taken at the listening position, I recorded measurements
at several other points in the room, and I'll check if there's any great
difference elsewhere.

Nice to know there's not a lot wrong with the RT anyway, as the room sounds
pretty good since treating the walls etc.

S.

On Fri, 16 Mar 2007 18:48:45 -0000, "Serge Auckland"
wrote:

Following Don's very helpful reply, I redid the RT60 measurements in my room
using his method with filtered white noise and Audicy (Cool Edit).

The results are now much more what my ears tell me:- RT60 at 125Hz 0.6 sec,
RT60 at 4kHz 0.2-0.3 secs. (difficult to tell exactly)

IEC standard is 0.3-0.65 secs at LF.

I've looked into what went wrong earlier using the unfamiliar software. I
made the measurements at 85dBC, and my room in daytime is only just 60dB
below that, measured wideband, so I may not have got to 60dB down,
especially when adding mic amp noise on top from the mic amp built into the
Sound Level Meter. I think the software just gave me a 2.5 seconds
indication which didn't change with frequency as it couldn't make a proper
measurement. Anyway, using Don's filtered noise method, I can measure down
to -60dB.

These figures were taken at the listening position, I recorded measurements
at several other points in the room, and I'll check if there's any great
difference elsewhere.

Nice to know there's not a lot wrong with the RT anyway, as the room sounds
pretty good since treating the walls etc.

S.



That sounds much more likely. I'm always wary of measurements when I
don't understand how they arrived at the answer. They may be right,
but then again they may not. What you have now measured sounds far
more reasonable for a decent listening room. Just a case now of making
sure the modes are nicely busted up, so you have no dead spots.

As was suggested (by Arnie, I think?) if you are struggling to measure
down to -60dB reliably, measure to -30 and double the time.

d

--
Pearce Consulting
http://www.pearce.uk.com