REW measurement makes an SPL graph and an IR. If I apply the IR to a 1 cycle tone or a long tone, the SPL is different. What gives?

[neRok]

As per title. When I export REW's measure in-room IR and convolve it with tones of the same frequency (Edit: Frequencies about a room mode in particular) but different length, the SPL increases. So my question is - is REW's SPL graph based upon either a "dirac impulse" or 1 cycle tone, OR the maximum SPL of maximal tones?

Attached is an example of a measured IR applied to different length "tones" (maybe not the legit terminology) of the same frequency. I have done this "simulation" in Audacity. The Amplitude window shows that the 1 cycle tone is 1.65dB less than the example long tone.
Edit: I see that I labelled the 2nd track wrong, and it was just the convolution of the 1 cycle tone.

 

[neRok]

To add more data, my room has an unsual shape and thus a "double mode" at ~82Hz.

Here it is amp'd equal to above (notice that it clips, which confirms increasing SPL);


Here's the same but the amplification is "normalised";


Here's another users much larger room, with the length mode at ~33Hz;

 

[STC]

Try to add delay in millisecond increment to the IR.

 

[neRok]

Try to add delay in millisecond increment to the IR.

Why? AFAIK the IR has captured hundreds of milliseconds of the effect of millisecond#1. Isn't millisecond #n is just the same, it's just applied over the previous milliseconds?

Edit: I delayed my 82Hz demo by 1/4 cycle. It's effectively the same result. There maybe minor differences at the start, but long term it "settles in". Actually I think I need even more than 10 cycles to see where my room "settles in".

 

[STC]

I am just guessing by looking at the sinewaves there could be attenuation due to phase difference. Anyway, I use SIRTOOL engine so I was just guessing.

 

[JohnPM]

is REW's SPL graph based upon either a "dirac impulse" or 1 cycle tone, OR the maximum SPL of maximal tones?

No. A sweep measurement measures the system's transfer function. That can be presented as an impulse response or magnitude and phase, they are equivalent. The REW primer has an explanation. To better understand the different results of convolving your various tone bursts it may help to look at the spectra of the tone bursts, then you can see what it is you are passing through the system (it isn't a single frequency).