Hi Mark. Good to see our resident experts here
.Agree and I think I noted that there is little reason to run waterfalls and stare at them
. I personally would make the correction in frequency response and not worry about what the time domain is doing. Agree that the standard amplitude response is easier on the eye with respect to the decay. I ran the waterfall because that also addressed what Ethan had done on his web site.
. I am speculating because I am not seeing amplitude reduction. So the noise response would be good to see.
(...) Agree and I think I noted that there is little reason to run waterfalls and stare at them
No, I am not questioning REW. What it does is governed by the underlying restrictions of time vs frequency resolution so it is not possible to do better (there is an advanced point regarding windowing of the edges which I won't go into). What I meant is that if you accept that time domain ringing similarly improves with pulling down the peaks, other than satisfying one's curiosity, then there is no reason to look at time domain response. Simply run the standard frequency response ("SPL" graph in REW lingo) which you can then run at the highest resolution with no smoothing. Once there, focus on pulling the peaks down there. That's all I did and as I said, the subjective improvement was really high. It took me just a few hours to do all of this. Same if you are using acoustic products. If there is no improvement in frequency response, then it is not doing its job as our ears are very sensitive to the anomalies there. Ringing is secondary to that.
In this context it literally means how long the note lasts. So if you like you can call it decay.
Hi Mark. Good to see our resident experts here
Agree and I think I noted that there is little reason to run waterfalls and stare at them
.
Hi Micro. I have seen that brochure. You may know this already but what they show is not the result of a single unit but many. They don't say how many
. We can tell there is a lot of absorption from the much reduced levels in bass. The overall level in "before" is -10 db while the after, is -25 or so for a total reduction of 15 db (scales are different in each graph). If you simply lowered the signal by 15 db, you would also get a fair bit of reduction in ringing! A bunch of the tail would wind up in the noise.
Hi Micro. I have seen that brochure. You may know this already but what they show is not the result of a single unit but many. They don't say how many
Anyway, what is different about their case is that they show both frequency response change, and massively so, and time domain. Here is the SPL graph:
You could by just looking at this one display know that you have done good in smoothing out those peaks, putting aside the loss of total energy in that region. One advantage of electronic control of those peaks is that you have better control of how far you pull down those peaks. You can listen quickly before and after and adjust.
.
As the thesis of my original set out to show, there is no question that waterfall displays are subject to misleading information. The math simply cannot be escaped. (...)
Does this run counter to a ton of reporting and analysis out there? Sure. But the fact that so many people do things doesn't make it right. I am about to put up my WSR article on first reflections and the issues around that. 99% of the what is talked about online runs counter to that research. But the research is incredibly strong and convincing if one digs in. The fact that so many people are not exposed to it or are but look the other way doesn't remove its weight and convincing conclusions it creates for us
Darn itWe are done?
Nope, not completely.
.It is not as much that it was Audyssey but the fact that he didn't pay attention to the fact that the EQ did not do what it was supposed to: pulling down the peaks. Further, he mixed up auto-eq with EQ.
As Mark indicated, there are room conditions that are non-minimum phase. In this context though, which is application of EQ to pulling down the peaks, experience and research shows that they are minimum phase phenomena. Here is Dr. Toole:
This is where multiple seats and SFM come to help us. Here is a four sub configuration at quarter points in the room (with ceiling the realistic implementation):
Look to the right in the first image. That is showing an impulse that goes way "instantly" yet the room keeps playing that note at lower and lower levels until it gets down to noise. Application of EQ, the solid line, shows that flattening the peak in frequency response, likewise lowered the amplitude of ringing and hence, the amount of time it lasts audibly in time. I did not show the graph for the second research but I can. It is very similar to Dr. Toole's.Hopefully my quoting will isolate the right graphs!
TBH, I don't really see anything that is definitively 'reduction in ringing' other than your say so based on others interpretation of these graphs. For starters, what would be a definition of ringing we can all agree upon?
The room acts like a pendulum at certain frequencies. If we measure the pendulum effect, and inverse how much energy we put into the pendulum, we can nullify its effect. This is no different than if you had an amp with a 2 db peak and I put a -2 db eq in front of it. By definition, minimum phase systems are reversible so they work the same way. But sure, you can also change the room. Question is what is easier and more convenient. I think better placement and number of subs and EQ are far easier than using acoustic products to tame low frequencies.
Darn it
Look to the right in the first image. That is showing an impulse that goes way "instantly" yet the room keeps playing that note at lower and lower levels until it gets down to noise. Application of EQ, the solid line, shows that flattening the peak in frequency response, likewise lowered the amplitude of ringing and hence, the amount of time it lasts audibly in time. I did not show the graph for the second research but I can. It is very similar to Dr. Toole's.
No, I have just been busy getting my next article out. I will be posting that shortly on first reflection. It is a long article with a good number of pictures which makes web publishing difficult.Ahh, flushed you out!
Yes, that is SFM. It is the science of driving multiple subs differently and with it, solve a key problem which is the fact that rooms are not symmetrical.
The graph is generated using computer modelling. The line you see is the average response for a 16 seat location in the center of the room so easily encompasses the typical listening position. Before you worry about the average vs a single point
, these optimized sub locations work their magic by cancelling room modes. As such, the seat to seat variation within that central area is sharply reduced. Actual simulation shows next to no variations between seats in the sub frequencies. The variations start to show about 75 to 80 Hz but even there is very small. That's all you need to see
. If the room mode is eliminated, then there is no reason to wonder about time domain. The resonance is gone and gone with it are time domain ringing. I think you are reading the graph caption wrong. Most of the magic came from using 4 subs. What the subs do is that they eliminate nasty nulls. But they also at times create more energy at certain frequencies. The EQ they talk about is applied to that peak and bringing that down to the level of the rest of the graph. So it is not one magic filter that gave you flat response.
That's correct.
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