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Originally Posted by
jim19611961 /t/1449924/simplified-rew-setup-and...nd-how-to-interpret-graphs/3060#post_23365031
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Originally Posted by AustinJerry /t/1449924/simplified-rew-setup-and...how-to-interpret-graphs/3050_50#post_23364960
I don't think this would be out of bounds at all. However, I also think that as a starting point, we should establish and agree upon some basic standards. I have read Nyal's "Acoustics Measurement Standards", and while I think this is a wonderful and useful document, I think some of the standards are unrealistic for those of us who have a mixed-use listening room. For example, I am currently working on reducing early reflections. All of my reflections are -15dB or better in the 20ms time frame (except for that damn ceiling fan), and all are -20dB or better after 20ms. However, I think I have heard that all reflections should be -20dB, regardless of the time frame. An attainable standard for the purposes of this thread would be useful.
I believe we have already agreed upon a modal decay standard--all resonances below the 40dB noise floor by 450ms in the 40Hz-300Hz range. This is somewhat less aggressive than Nyal's standard.
So, I'm not sure I will ever adopt a "model" per se, but I am very interested in understanding the various theories. I am especially interested in some topics we have not explored in detail, e.g. diffusion (when and where to use it), and how to re-direct reflections so they add spaciousness to the listening room, i.e. more good reflections, less bad reflections (and a clear understanding of what this means).
So much to learn, and so much fun on the journey!
There are a lot of threads that discuss different room models, both here and at GS. Thats not to say we couldnt start a new one though.
I would advise a bit of hesitancy on working too hard in any direction on your room until you have a model in mind. How each deals with reflections differs considerably. Putting a lot of effort into minimizing early reflections (depending on how you define early) could lead to having to redo everything later. While most models work with the early (10ms, especially >20ms is all over the place.
What is a
BAD reflection or a
GOOD one depends in part on how the chosen model works. If you are not emulating any model, then its a crap shoot to whether reducing some given reflection will be beneficial or not.
But there is more to reflection analysis that just magnitude and timing. Bandwidth and directionality can be crucial as well.
This is SO TRUE!
I'm finding most people on this thread are probably going to go one way or another.
So here's how I (and just about everyone else who is in this industry and knows what they're talking about) would recommend folks starting out, what goals to set, and what it should ultimately look like.
If you are more interested in 2-channel, meaning you more critically listen to it, whether or not you listen to it more than watch movies, then you want to work towards a LEDE/RFZ design.
If you are more interested in movies and mostly watch movies, plus aren't too critical of your 2-channel (don't sit with your head in a vice or buy special recliners with low backs, etc) then you are most likely going to work towards an NE model.
Here's the main difference regarding reflections.
First, reflections ARE NOT BAD!!! We have to quit saying that.
High Gain EARLY reflections (less than about 20ms) are bad. This goes for either room model and in fact ALL common acoustic models.
So, after the direct sound, you should have reflections no higher in gain than -15db and the real goal, especially if going for the specific NE or LEDE model should be -20db.
At around 20ms is where the models change. For NE, this simply continues. It should evenly decay more and more beyond about 20ms to infinity. Where this decays into the noise floor, looking at the ETC (NOT RT60 as that doesn't EXIST in small acoustical spaces) is your decay time and this is how you can figure out how live/dead your room is. (This is a real quick/dumbed down answer but we'll go into more detail later)
So if you mostly listen to movies and aren't too critical of or don't listen to a lot of 2-channel only music, you simply want to make sure you don't have any reflections higher than about -15db in the first 20ms (but really try to make that -20db) and that should simply continue at and after around 20ms to decay more and more, and EVENLY, into the noise floor.
Even AFTER 20ms, if you have a high gain reflection here and there, you need to take care of that too.
Plus, even with NE, you can have a "Too Dead" room so you needn't only use absorption and can still take advantage of redirection and diffusion. Nobody says an NE room has to sound dead. It's just that there aren't high gain reflections, whether early or late, so the response is "effectively anechoic" - but not dead.
Now, for what I think most people will want to work towards as most of us use one room for both movies and music...
Same as above for up to around 20ms but at or around 20ms you need to have a high gain reflection. But not just one. That EARLY energy, if not absorbed and taken away forever, should be reintroduced laterally/behind at a level as close to around -12db or higher as possible and THEN - Naturally decay EVENLY into the noise floor. You NEED diffusers and simply cannot do this with just absorption/insulation/fluffy/fuzzy stuff.
You will most likely need redirection/reflection, too, because people use way too much fuzzy stuff/insulation and there is a finite amount of energy to work with.
The goal with this model is to hear only the direct sound followed by about 20ms of effectively anechoic (no high gain EARLY reflections) - then create a sense of a larger room and be able to hear all the sonic characteristics of the room the original recording was created and mixed. You need that ISD gap to achieve this, but if you don't then TERMINATE that ISD gap at around 20ms (depending on size of room) you are really just creating an NE room.
This is where those reflections become important and NECESSARY. All reflections are NOT bad and are needed to create a lively room that will let you hear ALL the information on the recording as is intended and you cannot really do this (2-channel rooms or 2-channel mode in a multi-channel room) without reflections.
If you just have one HIGH GAIN reflection at around 20ms but then the next several ms are back under -20db, then have another sparse high gain reflection here and there, you're just creating a mess and this is not what we are going for.
You have to be careful to not use too much absorption.
Jerry's room is looking great. But most other rooms are ALREADY under .2ms.
So, if you are going to look at the TOPT in the RT60 field, even though there are better ways, since it's been brought up and people are posting their graphs, even though this is also way ahead of where we really are (and if the previous information is adhered to this will take care of itself) here is what you should be looking for.
First, looking only at 500hz to 1khz is RIDICULOUS!!! That's taking 500hz of a sample even though the specular region is from about 350hz to 20000hz and makes no sense. I've NEVER heard of this recommendation anywhere else.
You should look at this in 1/3rd octaves. REW defaults to 1/1 so you need to change this in preferences.
You should be looking at THE FULL SPECTRUM. You do not need to zero in / zoom in on specific frequencies.
It SHOULDN'T matter whether you use one speaker, two, or all 7-11 for this.
If your room is properly treated (but see, we're not that far along yet and are jumping ahead, plus not really using the right tool for this - although if we are going to use the RT60 tab in REW, TOPT is the closest to accurate for our small acoustical spaces - so it's the best compromise, but make no mistake, it is a compromise and doesn't tell the whole or even necessarily accurate picture) this should be pretty even no matter which speaker(s) you use or what SPL you take the measurements at.
The goal should be no less than .2s across the range. If you have a VERY small room like Keith's then .2 is okay. If you have a lot of diffusion then .2 is okay. In fact, my own 20x26x8.8ft room, at 4500cu ft is right at .2. But it's even and there is proper diffusion. My ETC looks good and the room isn't dead.
If you are only using absorption and have a small room then that .2ms is going to sound a lot different.
You should NEVER be more than .5s.
It's okay for the Modal and Transition region to be a little higher than the specular region (let's say above 300hz for this thread) but not by a whole lot and even that should be even.
For instance, the modal/transition region graph showing .4 second (40hz to 300hz) then from around 300hz on the TOPT graph showing .25 second is fine. But if the whole frequency range from the graph limits of around 60hz up to 20khz ranges from .25s to .4s up and down up and down etc, that is NOT okay.
The BBC made some really good targets their studios had to adhere to, and while this is difficult to accomplish, we do need to at least set goals.
Their rule is no octave should be more than 10% below or above the previous/next octave. I think we can change that to 20% and be fine.
From the graphs that have been posted so far, although the rooms are on the dry/dead side for the most part, it's also true that most of them (pleasantly surprising to me, honestly) are pretty even. That's GREAT!
A good target for most rooms is about .3 seconds, but not less than .2 and few will get up past .35 to .4 and NONE should be more than .5. These need to be as even as possible from one octave to the next and it's okay for the modal/transition region (only due to compromise and not because acoustically it's okay - only because the lower frequencies are harder to threat, though) about 30% more than that.
Now, I know this post is jumbled and yet another novel as I don't seem to be able to make short posts, but Jerry, Keith, et al - If you would/could take this information and "pretty it up" so more people can read, understand/interpret, and be able to put this to use in a more clear/concise format I'd be forever grateful.
Thanks a bunch, and let's keep the conversation moving forward...
--J