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Old 29th August 2018
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After carefully reading all the posts here, and all the linked papers, I think there are 3 main questions:

1. How important is the control room curve?

2. If it is important, which curve is the goal? -> I.e. can we assume we know what the majority of listeners are used to?

3. Are we comparing apples to apples? -> I.e. -> What is the difference between steady-state (long gate) vs. direct sound (short gate) measurements in domestic rooms vs. treated/control rooms.

I'll start with:


After careful examination of the Toole paper (including some references) and my own measurements - my conclusion is this:

EDIT: It seem that this (a) is more wrong than right, but it doesn't really change much in regards to the rest of the post.

a) For any given room, the direct and steady-state curve shape is virtually identical at HF, regardless of room size and absorption properties. If present, the "tilt" downwards is explained by HF air absorption (if slightly larger distances) and off-axis measurements.

I know this goes against what some of you were saying, but I encourage you to double-check the paper, and your own measurements, if you have any of less-treated environments.

See below:

Originally Posted by Toole
“… the thinking was that “if a room is tuned with pink noise as a test signal to have a 3 dB per octave slope from 2 kHz, the first-arrival signal will be closer to flat than the 3 dB per octave seen on an analyzer would suggest.“ This morphed into a common belief that seeing the X- curve high-frequency rolloff in steady-state measurements at the 2/3 listening distance ensured a flat direct sound. We now know that is not true with today’s loudspeakers in today’s dubbing stages and cinemas—direct and steady-state sounds above about 1 kHz are essentially identical

Originally Posted by Toole
"The SMPTE/ISO method of calibration cannot deliver a flat direct sound. The high-frequency rolloff is identical in both the direct and steady-state sound fields. The low frequency direct sound will exhibit varying amounts of at- tenuation depending on the directivity of the woofers and the reflectivity of the venues—the shaded area. Only in dead rooms will the low-frequency direct sound be approx- imately flat."

NOTE: The superimposed topmost curves are directivity indices, NOT FR measurements.

So no, HF being equal in steady vs direct measurements is not true just for very treated rooms, it is true almost always, as can be deduced by carefully examining all provided ACTUAL (not only predictions) measurements in the Toole paper! Please do. All is explained by off-axis measurements and air attenuation (assuming flat speaker). Same steady vs. direct.

b) The progressive boost at LF is something that does happen in non (or less) treated environments. Most obvious in very large rooms, because the Schroeder frequency is low.

On the other hand, in smallish rooms this effect is still present, but it's hard to say how useful it is to even consider it while pondering the "curve shape" of home listening environments. And this is why:

Originally Posted by Toole
"Below the transition/Schroeder frequency the room resonances and the associated standing waves are the dominant factors in what is measured and heard. These are unique to each room and are strongly location-dependent. Only on-site measurements can reveal what is happening and different loudspeaker and listener locations will result in different bass sound quality and quantity"
I'm sure you know how extremely erratic the LF response is in small, untreated environments. Let me illustrate with an example:

We see relatively typical low-end response for an untreated room. The slope/average curve is in black. Is that really what is always perceived for LF? I see attenuated bass below 110 Hz, with a huge bump at 50 Hz. Sure, for some material this will result in "more" low end, but for some material this curve will de-emphasize the bass.

So, for smaller rooms, it is debatable whether the area below the Schroeder can be considered as being simply "boosted". It most definitely is "messy and boomy", and it is tilted... But my point is that:

Saying domestic rooms exhibit a bass boost is true, but is an oversimplification of what is actually happening

To reiterate - For steady-state measurements -> there is no HF "cut" present only in the steady-state measurement. If it's there, it's there also in the gated measurement. There is a progressive boost towards lower frequencies, most obvious in the diffuse field (above Schroeder), and the amount off boost is a function of room size, reflective surface absorption, and air absorption. Even if I'm wrong about the HF, that doesn't change much, if anything, for further points.

So back to the original question. Can we compare treated room FRs and domestic room FRs, so that we bring the listening experience in one, closer to the other?

IMO, not really. Perhaps in the non-modal region. I'll further explain why in the follwing point:


I would say most definitely not, I completely agree with the following:

Originally Posted by scraggs View Post
whether the room has a 'flat' curve or your beloved B&K curve, the end user listening experience is an impossibly wide moving target.

cars, Beats, iphone speakers, laptop speakers, horrible Bose garbage with ridiculous bass, etc etc. and maybe there are some people out there who actually have a decent 'home system', but for sure it's in a room with no treatment and the FR is going to be all over the place.

How can we possibly figure out what's the "standard" from all this? One thing is certain, the following chart is not the answer:

If anything, this shows that there is a discrepancy between what pros prefer, and what casual listeners prefer as their playback environment.

But it doesn't tell us what the average listening environment is! And that is the main question here. Understanding that there is a difference between "taste in playback FR" and "actual average playback FR" is crucial.

Thinking that a "Hi-Fi listening room" study (B&K) from the 70's is somehow representative of the current "standard listening environment (which includes headphones, laptops...)" is, IMO, wrong (DanDan sorry to use your least favourite word ).

As a side-note, it is more than obvious, to anyone who carefully read the Toole paper, that even the famous cinema X-Curve is an obvious mistake! But ironically, it is kind of useful because dubbing stages mostly use it also... So both the cinema goer and the mix engineer hear the same "wrong" thing. I.e., - a standard. Funny!

Originally Posted by Toole
If a flat direct sound was the objective in calibrating cinemas, the attempt failed.
Final question, perhaps the most important:


For all the reasons above, I agree that it is most likely not very important, and mostly comes down to taste. Of course, within reason. You don't want a certain frequency range boosted by 20 dB, so that it masks everything else. I still think "neutrality" (as in; no huge irregularities in FR), controlled decay times, and good stereo imaging are more important than the actual curve.

In conclusion, DanDan, to answer your question:

Originally Posted by DanDan View Post

Can you offer a view on how a desired/achieved tonal balance established anechoically could possibly remain the same when listened to in a 6-10dB dulled environment?

Because (assuming a treated room), you can listen to your references before mixing, and calibrate your brain. The music of the past is your "control", your "taste", call it "style"; and it establishes the "frame" within which you draw (i.e. - mix). My opinion is that with proper references and an acclimatisation period, the FR becomes less important (within reason, of course).

The shape of the FR can be another personal "taste", but this layer is superimposed to what I desribed above. I.e., the FR doesn't change your style. But only if you have calibrated your brain properly.

On the other hand, if someone works a lot in various studios, and doesn't like using references... I can see how lack of standards would be a problem. Lucky movie sound guys with their flawed X-Curve (sarcasm alert)!

Also, I can totally understand that there are people who, for whichever reason, simply cannot stand a specific house curve. But claiming that somehow this should be true for everybody, and is a biological truth - is weird. Stubborn if you will.

Since you all are counting stripes, I went to check my uniform. I'm from a small country, so no Billboard top 100, sorry. But I earn a living from working in audio, and have mixed 800 songs in the past 6 years (some also recorded, some also produced). And I like my more-less flattish HF curve in my well treated room.

Finally, thanks to everyone for you contributions here, I really have learned a lot from this exchange. And it is really saddening to see the unnecessary bad vibes created. But that's the internet I guess, could be worse

P.S. - I would appreciate it, if you (anyone) find a flaw in my reasoning, to point it out. I'm trying hard to figure out what's "real" here, and would rather know the truth than (falsely) think I'm right.
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Last edited by ReDRuMx; 29th August 2018 at 11:21 PM..