OK, I got it fine. And it looks like the data is valid.
So here's the rough analysis:
First, the overall full-spectrum frequency response is not too bad:
josephwit--fr-20-20k--1..48.jpg
You are within +/- 12.5 dB, which is sort of almost acceptable for a basic home studio. The minimum goal is +/-10 dB. A top home studio might be around +/- 6 dB. The spec for pro studios are +/- 3dB.
But that's pure frequency domain. Now for the time-domain (how the levels decay over time, sometimes also called the "RT-60" graph, which isn't strictly correct):
josephwit--rt-20-20k.jpg
That shows how each 1/3 octave frequency band decays over time.
Not so good. Specs call for the decay rate to be roughly the same for adjacent bands, but yours are all over the place. The overall decay rate is too low for that room, and skewed towards the lows. You can see that in the high end it's close 150 ms, while at the low end it's more like 400 ms. That means there's too much absorption in the room for high frequencies, and not enough for the lows.
Next up, the waterfall plot, and concentrating on the part that matters most: below 500 Hz...
josephwit--wf--17-500.jpg
That shows the decay rates in a much more detailed manner. In that graph, the z-axis is time (coming out of the screen, towards you), so you can see how the sound intensity drops over time for each frequency. Clearly visible there are the modal issues in the room, which are the spiky peaks that stay up for a long time. 28 Hz, 41 Hz, 80 Hz, 90 Hz, etc. Those are all modal.
You can also see the "holes" which are likely due to SBIR: 65 Hz, 95 hz, 160 Hz, etc. Those are related to room boundaries. And you can see the overall unevenness.
I'm not at all convinced that the very low end is your speakers at all: they don't really go that low. It might be something external that is getting into your room.
The Spectrogram shows you something similar, but from a different point of view. It shows how the sound pressure levels change, but color coded, with time on the Y-axis.
josephwit--sp--17-500.jpg
You can more clearly see where the modes and SBIR issues are there. Once again, it focuses on just the low frequencies, below 500 Hz.
To go along with that one is the close-up view of the frequency response for the same low-end part of the spectrum:
josephwit--fr--17-500.jpg
And finally, what is perhaps one of the most important graphs of all, but also not so easy to interpret: the Impulse Response graph:
josephwit--ir-150ms.jpg
This is purely time and intensity. It shows how the room responds to a sudden extremely short pulse of acoustic energy, and is the most revealing of all.
You can basically think of it as showing a bunch of other impulses that are the reflections of the original pulse, coming back from different parts of the room. (Well... sort of... kind of...)
So the tall spike you see at time=0, that hits 0 dB, is the actual impulse, followed by a train of reflections of that impulse. The time difference after the original impulse tells you how far away that reflection came from, and the height tells you how intense it is.
What you SHOULD see on that graph, is nothing at all above -20 dB. All of the echos should be at least 20 dB down. At the very least, they should be below -20 dB for the first 20 ms, and then they could rise up a bit, to give you a low level ambient or reverberant sound field.
That's not what your graph is showing.
The reason is simple: any "copies" of the original direct signal that reach your ears inside of 20 ms, and higher than -20 dB, mess up the way your brain interprets what your ears are hearing. It skews your perception of frequency response, and it messes up directionality. In other words, your brain thinks the
real frequencies that it heard were actually
different frequencies coming from different directions.
You can see that there in your room there are several very strong echos coming back very soon after the initial impulse. Here's a close-up of just the first 25 ms:
josephwit--ir-25ms.jpg
The first two big spikes are just a couple of dB below the direct sound, and that's a big problem. Those are very strong reflections coming off some hard, solid surface in the room, perhaps the ceiling, the floor, a wall, or the desk. The time difference there shows that there's a difference in path length of 1.4 feet for the first reflection, and 2.4 feet for the second one. There's also about a dozen other reflections within the critical first 20 ms.
That's not so good at all.
So, what I'd suggest for your room is to add some serious bass trapping that does not harm high frequencies, remove or modify whatever it is in there that is sucking out the high end, and treat those first reflection points that are killing your clarity and directionality.
I think that if you do those three things, you'll notice a pretty significant improvement in imaging, clarity, bass tightness, and overall warmth.
- Stuart -