Originally Posted by Nyal Mellor
Originally Posted by djbluemax1
Since this topic has already popped up, I figured I'd comment.
As far as the time range for waterfalls, there are 2 approaches:
1) as Jerry states, increase the decay time setting till you can see the majority of the peaks fall to the noise floor (set at 40db or your individually measured noise floor). This is great for folks curious to see what their room is doing and can help ID modal ringing.
2) set the decay range to 300ms as the goal is to have everything above ~40Hz decay in under 300ms (or by about 200-250ms in ideal conditions).
It's not only important to have the frequencies decay by a certain time, it's also important that the frequency range decays at similar rates over the entire range.
For example, if the octave from 60-120Hz decays much slower than 30-60Hz and 120+Hz, that octave will dominate what is heard. It will also mask/blur everything else.
Because it's harder to damp/absorb bass frequencies than mids and highs, the type and amount of absorption used to control the bass may inadvertently absorb too much of the higher octaves, resulting in drastically shorter high frequency decay rates, which will produce tight bass, but a 'dead' sounding room.
How much treatment is good and how much is too much is something we'll get to later I'm sure, but to get back to the specific issue, if it takes more than 600ms for the bass to decay into your noise floor, you seriously need bass traps anyway, and showing a waterfall to 1000ms is unnecessary, except to show just HOW badly bass traps are needed.
BTW, when folks begin producing waterfalls, they'll see just how powerful XT32 is for reigning in bass ringing, but of course, the better the situation prior to running Audyssey, the easier it is for Audyssey to do its thing and the better the outcome.
I believe some of those targets you quoted are from the white paper
I co-authored with Jeff Hedback. There is a ton of pretty detailed discussion about each measurement and relevant targets. You guys should read it, if you haven't already. There's a whole bunch of targets defined in there for things like frequency response, time decay, ETC and so on.
Maybe people missed it (or ignored it) earlier on. To whet your appetite here's the summary page:
And here's the decay target graph:
Please note those targets were for two channel. Am happy to brainstorm with you nice people what the modifications for HT might look like. At a high level they would involve bringing in the bass response frequency response targets quite a bit, decay, ETC, mid/high frequency response and likely T60 targets would remain as is.
We haven't had the pleasure of meeting or speaking before. Although I don't know you and am not familiar with your work, I know Jeff and his work very well and respect him very much.
I'd love to have further conversations with you since we don't exactly have the largest pool of acousticians and acoustical consultants to pick from when seeking new friends with our common interests.
With that being said and with all due respect, I must humbly disagree with several recommendations your white paper recommends, though.
I actually did read the paper shortly after you published it, but didn't give it too much thought as at the time it didn't concern me or affect anything I was personally involved in and I'm definitely not one to criticize just to stir up trouble.
If you will kindly read the first page (second post) of this thread, you'll see that I started this thread to help people set goals and work towards achieving them regarding the acoustics of their listening rooms.
I've offered my time and participation in this thread to give back to this community for all the invaluable information and knowledge I've received from this forum and forums like it over the last several years.
I know what it's like to spend a lot of time reading, learning, and then through further research and way down the line find out I was given so much misinformation that I have to try and unlearn and then start all over relearning things the right way and I want to try to teach people the "right" way from the beginning.
The problem is, "right" isn't necessarily fully defined unless your goal includes an acoustical model in which you are trying to achieve.
The first main post of this thread states just how critical it is to set this goal as otherwise, what exactly are we working towards?
Once one has chosen an acoustical model, there are absolute guidelines that are in place to assure certification spelled out in great detail as to what each of the parameters your white paper has mentioned above should actually be, and quite frankly a lot of what you state is simply not supported by these models.
I understand that most people reading this thread and planning on taking measurements and applying treatment to their rooms aren't going to have them LEDE certified for instance, but I strongly believe you must set a goal and have specific ideals to work towards if you ever hope to accomplish anything close to what you set out to do.
In the second post of this thread, I recommended, and for those reading this, am recommending again, that you all read this fine document that details each of the most popular room models from which to choose then pick one to model your own room after. http://www.eetimes.com/design/audio-design/4015907/Acoustics-and-Psychoacoustics-Applied--Part-1-Listening-room-design
Another great article comparing the different acoustical models is from RPG and it goes into even more detail yet is very well written and easy to understand. http://www.rpginc.com/docs%5CTechnology%5CPresentations%5CStudio%20Design%20From%20Mono2Surround.pdf
The point is that this thread is geared towards learning what the different acoustical models are, picking one (setting that as the ultimate goal) then working towards achieving it, starting with learning how to use REW and progressing through all the different graphs and functions of REW, what they mean, how to interpret them, and what to actually "DO" about whatever problems your room has so you can achieve your initial goal.
We're obviously in the very beginning of this process with most here not even having their mic's yet and very few folks are comfortable using REW past very basic measurements and I'm sure it will be quite some time before we get into intricate details on exactly what some of these parameters are and how they'll end up in most folks rooms.
With all that being said and understood, I have to say I believe your white paper can very easily confuse people and deter them from following the proper steps already set in place to participate in this thread.
I suppose what I mean by that is that your white paper is simply arbitrary targets that don't adhere to any standard, especially any standard for an actual and proven room model which people have built and use either to record or for critical listening.
If there were no standards then this would be fine.
Since the whole purpose of this thread is for folks to pick an existing and well proven standard acoustical model, most of which I assume will work towards LEDE/RFZ or NE standards, what exactly do you hope to accomplish here by posting "your" targets?
I mean no disrespect at all and welcome you to continue participating in this thread as I know the knowledge you have was not easily attained nor did it happen overnight. I also know you have surrounded yourself with folks whom I deeply respect and admire, so you're not all bad...
But I have to say, I do discourage folks from selecting these arbitrary numbers/targets you've set, at least until you can explain exactly what you're trying to accomplish with them.
Are you suggesting a new acoustical model? Are these the targets for this new model? Why do you feel we need a new model/targets? What's wrong with what we have to choose from?
I don't believe the many different acoustical models (which accommodate many different needs and purposes already) need to be changed as they have all worked quite well and are proven and have been around for many years. Do you?
I'm not trying to be rude or harsh, but I just want people to learn the "right" way to begin with. Most of these folks probably have no idea who Don and Carolyn Davis are and don't know of Trevor Cox's work, or Manfred Schroeder, and all the other pioneers in acoustics. They may have heard of Floyd Toole (whom I also admire and respect, but...) who has his own ideas which are very different from the norm on reflections and the ISD for instance. Most of the folks on this thread aren't going to read the text books that we read/have read and aren't in this due to their passion for acoustics and furthering their education.
Most folks (I'm assuming again) are here to learn how to measure their rooms and make them sound better/perform better.
We've done the hard work and have amassed a lot of information over the years but we have to be very careful in how we disseminate it as it is very frustrating to try and unlearn or relearn something, sometimes to the point that one simply gives up or worse yet, doesn't know they have learned "wrong."
So to keep it "right" I am going to specify exactly what I disagree with and I welcome you to let me know why it is you made the recommendations you did in your white paper and what you're trying to accomplish by changing the standards already set in place long ago that have been working quite well for everything from recording/mastering studios to critical listening rooms for several decades now with few updates/changes to the models in which they're based.
First, why do you feel the ETC should show "10db reduction by 40ms?" Do you not believe in an ISD Gap? Do you not believe early reflections high in amplitude are destructive? Do you not believe in the termination of the ITG?
LEDE standards are pretty clear that energy should not be above -20db from 0 to "around" 20ms or so to create an effectively anechoic gap which is then strongly terminated to increase the apparent size of the room and so the direct signal has time to form free of clutter. This will reduce muddiness and improve the listening experience with absolutely no argument against doing this from most well respected people in the field. What would the purpose of having a ton of high energy reflections all the way out to 40ms only 10db down be?
Second, you reference RT60, 30, 20 yet there is absolutely NO REVERB TIME in Small Acoustical Spaces!! I'm SURE you know this. You stated these targets you set were for two-channel and you may amend them for home theater so this paper was obviously not written for concert halls, yet you reference taking RT measurements!
While looking at modal decay times and insuring they are even and contained to the appropriate range for the size of the room and the actual proven acoustical model targeted is necessary you won't find it by looking at the RT60 nor will that measurement help for the mid-hi frequencies either.
You can simply use the ETC and Cumulative Spectral Decay plot to find decay times and setting specific decay targets without taking into consideration the model, the room, etc, in my opinion is far from ideal.
You suggest targeting between .2 and .5 seconds with not much more explanation than that, but that is a HUGE difference. A room that has an overall average decay time of .2 seconds will sound quite dead no matter the size, especially considering you stated this document was created with two channel in mind, whereas with HT you'd at least have the surrounds so .2 wouldn't be so dead and dry, yet .5 in small rooms can be WAY too long. So have you defined specific targets for specific rooms in this new model of yours? What are the "why's" behind these numbers or are they just arbitrary limits you selected?
Next, you suggest a +/- 10db FR in the low frequencies at 1/24th smoothed! That isn't much of a goal! First, low frequencies should NEVER be smoothed at all. We need to see all the resolution possible here. Second, a 20db swing is worse than most people that have taken 5 minutes to "try" will ever see, especially now that RC software like Audyssey is now so popular. Anybody that would actually be reading your paper or this post is not going to accept a 20db swing in the most important frequency band in the audible spectrum whether 1/24th, 1/48th, or totally unsmoothed, which is the only way the FR should be viewed in this range.
The effects of what you've recommended here are much more devastating than those of what you recommended for the ETC.
As for decay times, should not the target be simply as even throughout the entire audible spectrum as possible with as little deviation as possible?
Again, it may not be likely that everyone will be able to get to within 10% of the full spectrum regarding decay times like the BBC demands for its rooms, but if you don't set the goal and understand the importance of ringing and vastly different decay times, especially in the lower frequencies, then your "critical" listening room is going to sound pretty bad.
Nyal, I know reading this probably upsets you and may even come across as preachy or arrogant but I assure you the intent of this reply is nothing more than an attempt to keep everyone on the same page and encourage them to read up on the TRUE - ACTUAL Acoustical Room Models that are proven with specific targets that which rooms have been built to for decades now.
There is no reason to invent the wheel. The information is out there. The acoustical models we have now work. I'm simply trying to condense as much of the information that is already out there as possible and slowly work through each step in this thread so that in the end, or at least months down the road, other folks will have a reliable source to visit and learn correct and proven factual information so they too can hopefully achieve acoustic nirvana.
I actually agree with all the points in your white paper that I didn't specifically call out, and there are more things I agree with than I don't, but some of the things I don't agree with are critical to the acoustical response of a room and quite frankly are too "easy" and I'd bet a lot of people reading this thread are already within most of your specified targets.
Sorry for this novel of a post and sorry if you take offense to this. I've not once written one post in my tenure at AVS that I feel is likely to offend anyone, yet I'm afraid this may be my first, although I honestly assure you that the education and enjoyment of the readers of this thread are all I truly care about and I wish to preserve the integrity of this thread and all of the masters of this industry that paved the way and wrote the true manuals for us to achieve the best listening rooms possible.
I do hope we can talk again under more pleasant circumstances and get to know each other.
Also, as I'm sure regular readers of this thread have figured out, I am a few days behind as I'm launching a new company soon and just don't have the time I wish I had to dedicate to this thread right now, so if you reply, I may be a bit behind on getting back with you but rest assured I will respond.