At The Listening Position
> The 1/20th octave, manual, single-band parametric EQs I've used have, in every circumstance, been able to have a positive, tunable effect up to 100Hz. <
Yes, at one specific location, anyway
Hold that thought. The basis of effective room tuning, as taught by Dr. Floyd Toole of Harman International, Tony Grimani, ex-THX and a veteran of over 150 high-end Home theaters and John Dahl of THX is that we are giving advice which solves the most-common, in-Home-Theater-environments single bass peak
at the listening position.
We believe the four CEDIA seminars posted on our site so far support your points regarding passive room correction. (Our specific case in point regarding passive room correction is the top-view illustration of a suggested layout from CEDIA Seminar #3, found at the bottom of this post.)
Graphs which are helpful in explaining a point or issue are of course welcomed. Please be aware however that we at Audioholics would like the intent of such graphs to be as an aid in helping our readers understand both sides of the discussion from the viewpoint of a level playing field.
Specifically we would request any SPL vs. frequency graph conform to our format shown here:
http://www.audioholics.com/productreviews/loudspeakers/AV123RocketUFW-10Subwoofer8.php
The example above is our 20Hz to 500Hz x-axis, 40dB Y-axis scale which we use for subwoofer testing. We would also request that if a z-axis is to be included that it be labeled clearly for easy readability.
These posts are read by an audience with widely diverse familiarity in chart reading. So we feel that standardization is the only clear approach to making a fair comparison. For any future submissions we would require:
-A standard 40dB Y-axis scale. We have had loudspeaker manufacturers intimate that their products might look better on a 90dB or 100dB scale which would of course make the measured response look flatter. And we have published such graphs in the past. Since I've come on-board doing speaker reviews and room acoustics, however, we've set the scale to what I've always used in speaker design which is the 40dB scale. And that's where it will stay. Conversely, in our opinion, a 30dB y-axis scale tends to exaggerate a problem and does not present the facts on a level playing field. (I have trouble comparing varying scales and I believe others do too..)
-Regarding the X-axis. The bandwidth about which we're speaking is 20Hz - 100Hz. Please keep this bandwidth for any submissions on this thread.
-if using the Z-axis such as with the Hamming chart presented please annotate with numbers and hash marks so the scale is easier to read. It would also be helpful if a good portion of the left -to-right x-axis lines are eliminated because without segmented hash marks it's hard for anyone to get more than a general picture of what is trying to be portrayed.
Having said all that we can now reply to the submitted charts-
-There is no labeling on this chart designating where in the room this reading was taken.
-Referring to the three peaks within the 20Hz -100Hz bandwidth I can truthfully say that I've never measured,
at the listening position, such a severe, triple-peak case in any room I've ever encountered.
-Nor have I seen such an example brought up in any of the five CEDIA seminars I attended last October which dealt with room acoustics.
-Dr. Floyd Toole of Harman International, Anthony Grimani, ex-THX and a veteran of over 150 high end installs and John Dahl of THX taught these classes and all three were unanimous in defining the vital task of passive room correction. That task, overall is to obtain a listening space with an RT60 of between .2 and .4 seconds through the full frequency bandwidth shown at the bottom of this thread (From CEDIA Seminar 3). It will be noted that below 200Hz the .4 reverberation time is allowed to rise quite substantially but it is at this juncture that
the main criteria of this discussion, flat low bass response, reverts to our initial stipulation.
"At The Listening Position".
-I have seen a chart such as this. It was for a sealed, reverberant room with nothing inside but hard surfaces. So from our stance these two charts are red herrings. Again, we've got three known acousticians teaching hundreds of CEDIA grads (and now our Audioholics readers) how, and to what point passive room correction is most effective. Let's move on...
-We now concentrate on the listening position or positions and are giving our readers what we feel is a much more incisive and effective method for dealing with low frequency anomalies. At this point,
flat frequency response at the listening position becomes the matter of primary import. We believe and support Dr. Toole's assertion that single-band, parametric equalization, either manual or automatic is the most direct, cost effective and acoustically correct answer. This is the simplest of options because it is so definable by actually doing the calibration
at the listening position.
A couple of last points>>
The brilliance of Floyd Toole is that he has the gift of making the confusing simple. One of his 400 slides says "The problem is standing waves, room resonances, room modes, eigenmodes, etc. These are all the same phenomenon."
Now try Googling "modal resonances" and see who's name comes up. I found all three of the acousticians who taught the CEDIA courses use the same terminanology. It is helpful to those who read these forums. Please respect this request.
Again, EQ can help to flatten the low frequency response, but it does nothing for modal bandwidth or decay time, both of which are at least as important as the raw LF response.
Flat Frequency response, at the listening position, is and always has been our primary concern. Given the amount of attention and our endorsement for the benefits of passive room correction, the supposed importance of
model bandwidth or decay time in other areas of the room are no longer of import to us enjoying our music and film
at the listening position.
