Auralex kits...??

[AVare]

With all the writing reverb room negative values, am I only one who remembers BBC RD 1991-7 and the increase in reverb time at certain frequencies when carpet was added to room?

Remembering,
Andre

[Ethan Winer]

If you mean Figure 1 showing more reverb after adding ceiling tiles, isn't that likely due to the same run-to-run variation we're talking about here?

[AVare]

If you mean Figure 1 showing more reverb after adding ceiling tiles, isn't that likely due to the same run-to-run variation we're talking about here?

It is discussed in slightly more detail in section 6.2.3. The discussion in this thread is about low end effects. In the RD Report the increase is in the high end around 1.6 kHz and up.

If it was lack of repeatability, I am certain that Fletcher would have determined that and not reported what he did.

Andre

[lovecow]

André,

If it was lack of repeatability, I am certain that Fletcher would have determined that and not reported what he did.

I don't think it had anything to do with repeatability. When you add absorption to the ceiling and floor of a room, the reverberation times (T60s) tend to look wonderful on paper, but test very poorly. This is because of the pronounced artifacts that you get - mostly of the flutter echo variety. My guess - and it's only a guess - would be that the test mic(s) in the room picked up increased T60s from flutter anomalies. These would have otherwise been "buried in the noise" for the test without carpet. When a flutter echo, which tends to have a higher decay time than that of suitably diffuse reverberant field, is detected, suddenly the T60s would appear to increase. But what's being measured is no longer a T60 in the technical sense.

I have measured this myself in admittedly larger rooms. The T60s will look fine until the mic is setting right in the path of a flutter echo, whereupon everything goes to hell in a handbasket. It was through studying this that I believe I coined the phrase "misappropriation of absorption." (™ ) Architects throw absorption at the ceiling and the floor thinking that T60 is the only thing they have to consider. The don't fully understand or appreciate that there's more to a good-sounding space than just getting enough absorption in the room...

Further, the BBC room was relatively small and was probably rapidly approaching a non-diffuse state - even at high frequencies - when so much absorption was added. The reliability (and applicability) of T60 equations decreases as absorption increases.

Non-diffuse + possible flutter echoes could very well = unexpected increases in T60.

My $0.02.

[AVare]

Thanks Jeff:

You added to my belief that one metric by itself says nothing.

Humbled by one,
Andre