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How much audible change has taken place in relation to treatment applied?

The key is how much treatment. In a "normal" size room you'll get a meaningful improvement from just four 2x4 foot bass traps plus two 2x4 HF absorbers at the side-wall reflection points. The effect is cumulative, so the more you have, the better it gets more or less. Though I'd call it logarithmic - four bass traps is good, four more is much better, but you need to double again to 16 to get the next "much better" step up.

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Is the change an improvement?

It can be if you know what you're doing or buy from someone who knows what they're doing. Versus what I often see where someone buys a bunch of too-thin foam, slaps it all over the place, then complains the room is too dead yet still has bass problems.

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Is it therefore possible through calculation to predict improvement based upon measured data?

Of course! For large spaces you can use Sabin's formula which takes as input the size of the space and current decay time, and spits out sabins needed to achieve a result decay time. For smaller rooms you can just load up with bass traps, hit the reflection points, and call it a day.

--Ethan

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I'm just probing here to see if I'm missing something.

Yes, there is a better method. For most domestic size rooms you can assume a few things:

You'll never get the LF response perfectly flat with no ringing, so the more bass traps you have the better. Note I say bass traps, not necessarily broadband absorbers. Next is early reflections which can be absorbed or diffused. Good diffusion costs a lot more than good absorption, so many people opt for absorption. This does not have to make the room too dead! You just need to put it in the right places. For all the treatment in my 25 by 16 foot living room (48 panels so far), the room is definitely not too dead. If you're willing to spring for diffusion you can get even better results and stay even that much farther away from too dead.

--Ethan

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We hear more like a spectrum analyzer and this explains why we do not hear comb filtering as drastically as it looks with a mic.

Yes, but with one clarification. The classic report I saw (R. Bucklein, AES Journal, 1981, Vol. 29, #3) that attempted to assess the audibility of nulls versus peaks did not align the nulls with the music being played. If you have a deep null at 110 Hz and play music in the key of A, I promise you'll hear that null no matter how narrow it is.

Nulls are also less noticeable than they appear on a graph because a null present in one ear is not likely present in the other. So at least one ear is getting the information. However, if you cover one ear you'll hear that characteristic hollow sound more clearly.

--Ethan

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Nulls are also less noticeable than they appear on a graph because a null present in one ear is not likely present in the other. So at least one ear is getting the information. However, if you cover one ear you'll hear that characteristic hollow sound more clearly.

That should be easily proved or disproved by simply moving one's head 12", which is more than the width of one's head. If true, moving one's head should create a clear difference in sound.

Take care.

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BTW - I do not agree with the premis of this thread: "Double blind test are inherently flawed."

In general neither do I. Depends on the component under test and how the test is performed.

Hi Scott,

I think it would be interesting to see how the tally compares after 3 ABs (back and forths) per AB test (several tests to get 21 AB total) vs 1 test of 21 straight ABs.

I think it would be quite interesting. My bet would be that habituation to stimuli and cochlea fatigue skew the results in the single test of 21 straight ABs, indicating typical tests are not as nearly as sensitive as the multiple AB test would be. Of course other factors are at play such as tonal balance, time factor, spl level etc which would affect the results.

Take care.