Originally Posted by Nyal Mellor
Originally Posted by jevansoh
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.
Hi, I do not want to derail this thread, but I would like to answer some of your specific questions and also provide some more on where we are coming from.
The main thing to bear in mind is that our perspective is that acoustical model are just imperfect representations of reality. Each model is a by product of a particular time in history. As acousticians learn more and have better tools available to them the models change. I do not think you have to design a room based on any one acoustical model.
The white paper represents a 'stake in the ground' by Jeff and I and is a statement of our current knowledge, understanding and real world experience in designing and implementing room acoustic solutions for two channel systems. The targets describe a room that has good spectral balance in the direct and reflected sounds in the midrange/treble and reasonably flat response with low modal ringing in the bass frequencies. Many of the room models do not cover all the aspects of room acoustics that Jeff and I think are important. For example LEDE focuses nearly exclusively on the use of ETC, to the detriment of a lot of other things, and without covering the potential issues in general use of the ETC.
The targets are NOT easy to achieve in the context of a two channel system. I have measured many rooms and none meet the targets in the white paper without effort and acoustic treatment. Like I said earlier I believe that with EQ and subs the low frequency targets can be substantially tightened up for home theater applications. We think that if the targets are met and / or exceeded then your room will not be a detriment your overall reproduction experience. This is based on our real world experience of many hundreds
of two channel rooms.
There are many ways to meet the targets without having to be forced into designing to meet a LEDE, NE, or other type of room.
With the above high level overview of our position on acoustic models etc let me just briefly comment on some of your particulars...
Originally Posted by jevansoh
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?
- 10dB reduction is to ensure that the precedence effect does not break down and that reflected sounds are not audible as echos. You should read the target as 'AT LEAST' 10dB, not 'JUST' 10dB.
- I do not believe all 'strong early reflections' are destructive. I am in the 'Toole' camp when it comes to that.
- I do not believe in designing LEDE rooms for reproduction so any discussion of ISD is not relevant to me. LEDE was to me a product of a particular age of studio building and the use of particular speakers with poor off axis performance in that era.
Originally Posted by jevansoh
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?
- Of course I know there is no RT in small rooms.
- The main use of the 'T' measures is to look at how sound is decaying across different frequency bands. It's another way of looking at the spectral balance in the room.
- You are wrong that a room of 0.2s will sound dry. Small rooms with a lot of diffusion can have 0.2s and sound normal.
Originally Posted by jevansoh
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.
- our intent for the target was a 10dB window rather than +/-10dB. This needs revising. In the context of a two channel WITH NO SUBS OR ROOM CORRECTION this is a hard target to achieve.
- of course low frequencies should be smoothed. We don't hear the unsmoothed frequency response. It's only relevance is to precisely identify the frequency of peaks or dips.
Originally Posted by jevansoh
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.
- the targets for the time decay are relaxed in the ultra low bass for a number of reasons including general lack of musical content <35Hz (remember this is two channel, not HT) and the difficulty of achieving the targeted decay time targets in the low bass.
First I wish to thank you for responding in a civilized manor and without getting defensive.
I've read a lot of text books in my time, I've spent a lot of time on forums, and I've been involved in different aspects of business for awhile now, but no matter how much one reads and learns, experience counts the most in my opinion.
Based on what you stated in the text above, it seems as though I may have less than 10% of your real world experience at this point in my life and career, however, I do believe strongly in continuing education, gaining more experience both for knowledge sake and in that it means my bottom line continues to grow (I have work).
I'm sure over time my ideals may change a bit as I continue to learn and grow and I hope I never become a crotchety old man stuck in his ways.
But for now, I only have the education and experience I've gained so far to go on and have to respectfully continue to disagree with just a few of your ideals regarding the targets for 2-channel audio expressed previously.
I do respect where you're coming from and hope you understand that while I have some different viewpoints on certain aspects of what you believe, I don't know that either of us could say the other is "wrong" as all it boils down to is what make the customer happy.
For this thread I want to introduce folks to standard ways of doing things that aren't challenged by most and even if certain goals aren't totally met by each person, I know that nothing I'm teaching is going to make their rooms sound worse. There will always be room for improvement, but at least I'm doing no harm.
I'm sure through your experience you have found numerous reasons to come up with your own way of doing things and go down your own path, so to speak. At this point though, with my level of experience and knowledge, I simply feel more comfortable in teaching what I've learned and know works and for the most part is widely undisputed.
So I guess what I'm saying is, welcome. There is room for many different theories on what is "right" but the most important thing in my opinion is for one to decide what that path is going to be and follow it. If goals are set and worked towards to achieve them by passionate audiophiles, they will simply learn a lot along the way and enjoy their systems that much more and that enjoyment and knowledge gained will last a lifetime.
I'm glad to learn there is a typo in your document as quite frankly I mainly took issue with two of your points, one being a +/- 10db window is a "goal" and is acceptable, however, now realizing that is supposed to read +/- 5db I wholeheartedly concur. We are on the same page.
Where we remain opposed however is in regards to reflections. I never once stated all reflections are bad. In fact, I believe they are absolutely necessary.
I do believe that high gain early reflections are absolutely detrimental. I believe they cause smearing and muddiness as I've heard it myself. I also believe that nobody likes to listen in rooms approaching anechoic conditions therefore reflections after a certain termination point are necessary and they create the psychoacoustic effect of making the room seem larger than it is. Therefore, reflections become necessary, after a certain point and to a point, just not random uncontrolled reflections.
When creating a room that has a small period (12-25ms depending on the size of the room, budget, goals regarding focus on 2-channel or HT, etc) of low gain early specular reflections around -20db terminated by a high gain (around -12db or more) specular reflection and followed by a diffuse and infinitely decaying rate of further reflection, the direct sound will be heard, clear, no smearing or muddiness, and the room will sound spacious and live.
There are of course many other factors that if are not addressed will cause this effect to collapse, however, and I believe we are in agreement on most of them.
I don't think the goals for 2-channel and HT are all that different. Yes, there are differences, but let's face it, most rooms are multi-purpose including dedicated rooms as most folks (the folks reading this thread at least) don't have a dedicated 2-channel room and a dedicated HT).
I disagree that a room with an average 200ms decay time will not sound very dry, however. Maybe "dead" was a bit harsh, but 200ms sounds quite dry and you can't just fix it by adding a ton of diffusers and diffusers, by nature, also absorb and will reduce that further, plus too many diffusers, if not placed surgically and strategically in the room will cause other problems such as interfering with the early reflections you worked so hard to tame, lobing issues depending on the design, etc. If the diffusers are broadband then the room has to be large enough, too. So just placing a ton of diffusers all around a room with a 200ms decay time is NOT an answer IMHO.
As for the rest, we're pretty much on the same page.
I like to target +/- 5db with no EQ - full band. +/- 3db with EQ - full band.
Depending on the size of the room I like to target between 300-500ms and quite honestly will accept 250ms in smaller harder to control rooms and seldom reach much over 400ms in all but the largest of rooms. The target is always 10% but I'll be the first to admit I've yet to achieve it. 20% is more reasonable and I cannot disagree with your 25% recommendation fully, however, I do believe that should be the absolute limit.
With those targets, it's not necessary to state that the bass can decay slower than the specular region other than to say it is common for the lower frequency range to be the hardest to tame and it will take the most skill, time, and budget to get in line without affecting the specular region negatively. Why create two different targets then also state you need to keep the full band decay time within 25% relative?
So again, we may belong to some of the same clubs, pay membership dues to some of the same places, and have similar ideals with but a few differences, but one thing is sure and that is our experience differs by a great amount with you simply having more of it.
I hope we can speak again and would like to get to know you better.
I hope you can at least see that there is room for my philosophy and yours, and that the important thing for folks trying to learn is that they understand the differences, pick a model (yours, mine, or other) and start working towards it to accomplish true audio nirvana!
I hope our paths will cross again sometime, Nyal.