# Is the film industry's X curve suitable for home theater?



## Wayne A. Pflughaupt

* Is the X curve suitable for home theater?

Part 2: An X Curve for the Center Channel?*​*


House curve / X curve confusion*
In Part Three of my article, _House curve: What it is, why you need it, how to do it_, we saw that the film industry uses a standardized room curve for both production (soundstages) and reproduction (movie theaters), known as the X curve. On the home theater front, it’s not uncommon to see enthusiasts confuse the X curve with a house curve. The following quotes are from a couple of discussion threads that originated right here at Home Theater Shack (emphasis added):

_ “Vote for your favorite *Room Voicing Curve*.
1. Academy Curve
2. *X-Curve*
3. No Curve at all!”

“I am interested in what you think is a *house curve* ‘appropriate to the room’. I may be wrong but I think for a home-sized listening room, the appropriate house curve is zero. The need for an *X-curve* EQ gradually diminishes with room size from 100% for an auditorium or theatre, to zero for typical lounge or listening rooms.”

“Let us say an orchestra (or solo piano) is playing in a world class venue, and the recording mic is placed in the best seat in the house, say centre stage, 20 rows back. No EQ or compression is applied to the recording. When we play this back in our homes, what is the ideal *room curve*? It is flat, not *X curve*. Flat EQ will reproduce the same bass-to-treble balance in the listening seat as in the seat where the mic was placed. Playing the above recording through an X-curved system will sound far too dead due to the attenuated treble.”_

As you can see, these parties freely interchange the X curve with a house curve as if they are the same thing, and also assume the X curve is an option for a residential system. Therefore, it bears noting again that _the X curve is specific to the film industry._ No other professional audio field that I am aware of uses the X curve, or any specified room curve for that matter.

*Origins, applications, and practical limitations of the X curve*
To show that the X curve is wholly inappropriate for a residential/consumer audio system, it’s beneficial to know something about its origins and purpose. As best as I can tell by wading through Dolby Lab’s _History of the X Curve_, it’s something the film industry came up with decades ago to address the deficiencies in both optical soundtracks and the speakers of the day. Ioan Allen of Dolby Labs and other movie industry professionals did some experimenting on a soundstage in England back in the early 1970s, comparing hi-fi KEF speakers located near-field with old-school, two-way Vitavox film monitors located far-field, equalizing the latter until they felt a timbre-match with the former had been achieved (which strikes me as a futile exercise going in, but that’s a discussion for another day). 










After this exercise the film monitors' response was electroacoustically measured. All parties in attendance where surprised to find they exhibited not the KEF’s verified flat response, but a roll out of the high frequencies above 2 kHz. No one could readily explain the discrepancy, even though it seems there was no shortage of places to look. They could have started with the speakers themselves: The Vitavoxes were dead in the water above 8 kHz. Perhaps their prehistoric compression drivers sounded nasty with the highs suitably elevated, so the sound engineers instinctively kept them rolled back. Or perhaps the primitive equalizers the engineers used did the film monitors no favors. Who knows? What’s glaringly apparent is that the parties involved made no attempt to get to the bottom of it.

Regardless, the enhanced response measured for the Vitavox monitors was later adapted as the X curve. Subsequent testing and measurements in movie theaters of the day took reverberation into account and further validated the X curve’s high frequency roll off as suitable for maximizing *speech intelligibility* in movie soundtracks. A low-end roll off below 63 Hz was implemented to minimize distortion from overloading the full-range speakers commonly used at that time (before commercial subwoofers were commonplace).











*An outdated standard?*
“Speech intelligibility”: that should tell us right there that the X curve was never intended to maximize the capabilities of extended range, high fidelity sound systems. One could argue that since the highest fundamentals of the human voice – the sibilants – are about 7.5 kHz, there’s no need for a speech-optimized speaker to have extended range. But there are numerous musical instruments with harmonics that can reach an octave or more higher – violins, cymbals and other percussion instruments. Instruments like electronic synthesizers can generate fundamentals above 8 kHz, as can sound effects generated by Foley artists. Apparently it’s not enough that a movie’s music soundtrack will typically be mixed at a lower level than the dialogue. The concern seems to be that if not squelched, the music track’s extended high frequency content will swamp the upper registers of the dialogue, rendering it unintelligible. 










*1950s Vitavox Trade Publication Advertisement*​

Whatever the reason, over the decades as advancements in professional loudspeaker design have improved both low- and high-end extension, the film industry has rigidly adhered to the X curve, essentially keeping movie theater sound “dumbed down” to the level of the limited-range speakers used back in the ’50s and ’60s. Adding insult to injury, modern theaters are much more- and better-dampened than they were in the past, diminishing the effect of reverberation on both measured response and speech intelligibility; yet the X curve remains. Small wonder that modern movie theaters sound as dull and lifeless as they do. 

It should take only a small leap in logic to determine that an X curve will not sound good in a home theater system. As explained in Part One of my house curve article, it has problems going in simply because it is a type of rigid-value slope that presumes to be the reference standard for any and every room, no matter what the size. Bottom line, the X curve was never intended for our tiny rooms and has no place in a residential setting. The only possible exception I can see would be for the center channel speaker. 



Thanks to:
brucek for his excellent Excel program, from which we created our X curve chart.
Donna Pflughaupt, for creating the Excel chart.


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## Wayne A. Pflughaupt

*Part 2: An X curve for the center channel?*​
An exception I can see for the “no X curve” rule, as well as the “minimize per-program tweaking” rule, would be for the center speaker, which is primary dedicated to reproducing dialogue. After years of constantly adjusting my treble control up and down to compensate for poorly equalized voices, I’ve come to the conclusion that perhaps some kind of dedicated curve is necessary for the center channel. Not to address relative distance from the display or reverberation in the room as the movie industry’s X curve does, but to compensate for program content that is poorly equalized. 

*Why can’t they get voices right?*
After bass, voices seem to be the most abused thing in the world of audio reproduction, as far as proper equalization is concerned. It’s not uncommon to hear male voices that are unnaturally “boomy” because of excessive low-end boost, but most often the problem is the treble – more specifically, sibilants that are not properly balanced with the rest of the voice. Too often they are either exaggerated or muffled. Sometimes you can hear examples of both present in the same program, which is especially maddening. A common example is news shows that have remote, on-location interviews piped to the studio: One talking head will have well-balanced voice equalization, while the other has exaggerated, “crispy” sibilants. Not that TV shows and movies are exempt – I’ve seen it there as well.

It’s easy enough to determine if you’re hearing natural-sounding voices from your system. Just have someone stand in front of your display, while you’re sitting in the primary listening position, and repeat some phrase rich in sibilants, such as “Simple Simon savors luscious twinkies.” (You will probably want to come up with your own phrase.) Have them repeat it until you have a good “feel” for how the “s,” “sh” and “t” phonemes sound in relation to the others. Then turn on your system and see how well a program source compares to the real person in front of you. Most likely you’ll hear right away that the voices from the program sound unnatural. Sure, different voices will sound different, but the relative level of the sibilants should be similar to the live voice. 

Obviously, it’s impossible to accomplish an EQ adjustment that will make voices sound completely natural in all instances, just like a house curve will not always deliver perfect sound quality (see article linked in first paragraph). Once again, we’re at the mercy of the program’s sound mixer. Even if your speakers are capable of reproducing voices indistinguishable from the real thing, you’ll seldom get such a thing from programming. 

*A quick and easy faux X curve*
Unfortunately, I haven’t found a perfect answer for this problem. The best thing I’ve come up with is a pre-set shelving filter on my center channel equalizer hinged at about 4.5 kHz and cut 5-6 dB - in short, a kind of X curve for the center speaker. This filter allows me to easily switch between flat response (which restores some “life” to muffled sibilants) and attenuated highs (which takes the “sizzle” out of exaggerated sibilants). The hinge (a.k.a. “turnover”) frequency for the shelving filter isn’t critical and can be set according to what sounds best with your speakers. A shelving filter doesn’t continually drop at higher frequencies as the X curve does, but levels off to flat response (see picture below). However, this won’t matter since voice fundamentals don’t extend beyond 7.5 kHz anyway. Besides, there may be other sounds, harmonics and sound effects in the center speaker that extend beyond 7.5 kHz, and we want to be able to hear them.










As luck would have it, most receivers’ treble controls are shelving filters, so this adjustment should be readily available for most people. Easy access to quickly change from one setting to another may be different story, however. (Such are the benefits of outboard parametric equalization over navigating cumbersome menus.) If you’re fortunate enough to have adjustable frequency settings for your treble control, you will probably want to set it no higher than about 5 kHz. As the picture above shows, shelving filters begin their action well beyond the turnover frequency (represented by the vertical line), and the action is forced further out as gain (boost or cut) increases. Be forewarned though, unless your receiver’s manual specifically indicates dedicated center-channel EQ is available, any tone-control adjustments will affect all three front speakers, and perhaps even the rear speakers as well.

If your receiver’s treble control is the rare one with a bandpass filter with adjustable center frequencies instead of a shelving filter, setting it somewhere between 6-9 kHz will do the trick. 

As noted, it’s impossible to accomplish an EQ adjustment that will always make voices sound natural. This “A or B” method isn’t perfect, but I’ve found that one EQ setting or the other will deliver acceptable-sounding voices for most program material.


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## Home Theater Guy

Wayne A. Pflughaupt said:


> Adding insult to injury, modern theaters are much more- and better-dampened than they were in the past, diminishing the effect of reverberation on both measured response and speech intelligibility; yet the X curve remains. Small wonder that modern movie theaters sound as dull and lifeless as they do.


In dubbing stages and commericial theater environments, acoustic treatments are selected to bring the reverb time within specification (the target reverb time is based on room size), and the room is equalized to hit the X-curve target. Thus, the X-curve is not the response of the speakers, or the EQ settings, but the resulting electro-acoustical response of the sound system after acoustic treatments and EQ have been applied.

If modern theatrical soundtracks are mixed in dubbing stages that use the X-curve (I don't know of any exceptions), then playback in an environment that uses a different curve will result in a different sound (different, but not necessarily better). The playback environment must replicate the environment where the content was created.

As for modern movie theaters sounding dull and lifeless, I can only say that I think you need to change theaters. Maybe the seatbacks are too high? I don't know. But don't blame the X-curve. I have heard some really ugly sound in a lot of theaters, and there are currently only 2 theaters where I live that I am willing to step foot into. They both sound fantastic because they do everything by the book (they happen to be THX certified). They never sound dull or lifeless. On the contrary, they represent a standard that I dare say most home theaters fail to achieve, in one way or another.



Wayne A. Pflughaupt said:


> It should take only a small leap in logic to determine that an X curve will not sound good in a home theater system. As explained in Part One of my house curve article, it has problems going in simply because it is a type of rigid-value slope that presumes to be the reference standard for any and every room, no matter what the size. Bottom line, the X curve was never intended for our tiny rooms and has no place in a domestic setting. The only possible exception I can see would be for the center channel speaker.


Since you recognize the need for the X-curve (or at least a similar curve) on the center channel, why does it not apply to the rest of the speakers? I cannot understand how a different EQ curve for the center channel could be acceptable. Constructing a coherent soundstage is impossible when the center channel has a different EQ curve than the other channels in the system.

Now, I agree that the X-curve is inappropriate for a home audio system...until you play a movie. Remember, we need to duplicate the mix environment. That is where modes like THX re-eq come into play (some non-THX gear has similar modes, such as Onkyo's Cinema Filter or Denon's Cinema EQ). You set up and EQ the system to produce a smooth and natural frequency response in your domestic setting. Then the re-eq applies correction to the signal so that the X-curve is replicated, and the original character of the soundtrack is maintained. After the movie, you can turn off the re-eq to listen to music. There is no need to have a "compromise" curve setting.

I do understand that some DVD and Blu-Ray titles are remixed for home theater, so the re-eq would not be used on those titles.

Thanks for listening...


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## Wayne A. Pflughaupt

Thanks for the comments, Joe. :T



> As for modern movie theaters sounding dull and lifeless, I can only say that I think you need to change theaters. Maybe the seatbacks are too high? I don't know. But don't blame the X-curve. I have heard some really ugly sound in a lot of theaters, and there are currently only 2 theaters where I live that I am willing to step foot into. They both sound fantastic


Only two? Thanks for proving my point.  I assume that all theaters have their sound systems set up and tuned according to the X curve standard. So I blame the X curve for their bad sound, plain and simple.




> If modern theatrical soundtracks are mixed in dubbing stages that use the X-curve (I don't know of any exceptions), then playback in an environment that uses a different curve will result in a different sound (different, but not necessarily better). The playback environment must replicate the environment where the content was created.


 Sorry, but this is not relevant to a home theater. The playback environment movies are mixed for – at least initially - is a movie theater. Unlike movie theaters, there is no standard for dimensions, construction or acoustical treatments for living rooms or dedicated rooms. This is only one reason why the X curve does not sound good in a residential setting.




> Since you recognize the need for the X-curve (or at least a similar curve) on the center channel, why does it not apply to the rest of the speakers? I cannot understand how a different EQ curve for the center channel could be acceptable.


As I thoroughly discussed, it’s merely for the purpose of _per-program tone-control,_ to compensate for poorly-mixed voices.

Let’s not forget that many people don’t use their systems exclusively for watching movies. For non-movie programming like TV, etc. the X curve does not apply (I haven’t seen anything to suggest it’s used anywhere but the movie industry), so equalizing is all over the map. 

Even with movies the X curve is, in reality, not as rigid a standard as one may think. If you know anything about professional audio systems, you know there is one major difference between them and home systems (at least for the purpose of this discussion). With a home theater, equalization (if it is used at all - think Audyssey or user-adjusted outboard equalization) is a global, “set and forget” application.

Naturally, a pro system like those used for soundstages has the same kind of “set-and-forget” system equalization, but with an important difference: The mixing console has separate EQ controls for each input that can be used at the engineer’s discretion. So, with a simple twist of a knob the engineer can fully override the system’s X curve if he so desires, as it would apply to that particular input. Naturally, he would EQ each input signal based on his own preferences or hearing capabilities. If he happens to like things bright, or subdued, then that’s going to come out in the theater, irrespective of its X curve calibration. 

For instance, it would take no more than for the engineer to set the treble EQ adjustments for all channels (which are often shelving filters) to +5 dB @ 5 kHz, and the X-curve would be rendered virtually flat all the way out to 8 kHz, instead of being down -6 dB at 8 kHz. For all practical purposes, that movie would sound like the theater had had the system totally re-calibrated to something with more high end than the X curve. Similarly, the way they get such prodigious low bass levels is to apply enough EQ to override the X-curve’s low frequency droop.

Thus, global system tuning and equalization can be easily over-ridden by _after-the-fact equalization._ You can easily do it in your home theater with the bass or treble controls your AVR has, and the engineer at a mixing facility can do the same thing with the numerous equalization tools at his disposal. This is why despite an X-curved soundstage, a movie like _U-571_ has noticeably brighter voices than say, _The Dark Knight_, which is pretty near perfect.

Then you have the fact that there is no industry standard to specify what mics (brand, model) are used in the various aspects of movie recording (music, foley, etc.), or which speakers are used for the soundstage. Naturally, no two mics sound alike, nor do speakers. If, for instance, a particular mic makes voices sound “honky” on a wide variety of speakers, but by chance not the ones used in a particular mastering facility, then that won’t be corrected, and the film gets out to the public with honky-sounding voices. 

While DVDs for the most part have more consistent EQ than TV and other programming, I’ve come across enough with excessive highs in the voices to make center-channel, per-program EQ capability a nice feature that makes the movie more enjoyable, if it’s called for. Especially since I don’t have Re Eq. Even if I did I probably wouldn’t use it, as it would attenuate the highs in all the channels, not just the center. Personally I’ve never seen DVD where I felt the highs in the other channels needed taming. I only see that in the center channel.




> Constructing a coherent soundstage is impossible when the center channel has a different EQ curve than the other channels in the system.


I suggest studying up on the finer points of equalization, both from the production and end-use “points of view,” as it were. I’d also note that there is no “soundstage” with a multi-channel system, as we have with basic two-channel stereo. The rules of two-channel equalization for a playback system do not apply to multichannel, especially for home theater, where the equalization can and will change throughout the course of a movie in the various channels depending on what sound effect is being generated at any particular moment.




> Now, I agree that the X-curve is inappropriate for a home audio system...until you play a movie. Remember, we need to duplicate the mix environment.


Really? How are we supposed to duplicate a 40 ft. sound stage in a living room or dedicated home theater?


Regards,
Wayne


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## Home Theater Guy

Wayne A. Pflughaupt said:


> Only two? Thanks for proving my point.  I assume that all theaters have their sound systems set up and tuned according to the X curve standard. So I blame the X curve for their bad sound, plain and simple.


I disagree that all theaters sound bad. If they do, then why do we all want one in our living rooms? Anyway, the point I was making regarding commercial theaters is that the ones that sound good adhere to film industry standards, not deviate from them. In fact, some of the worst sounding theaters in my area use little to no acoustic absorption in the auditoriums (they have purple painted drywall instead :scratch. Contrary to your earlier statements (that the absorption combined with the X-curve in modern theaters makes them sound dull and lifeless), these untreated auditoriums sound extremely muddy, with muffled voices and no detail or sparkle to the high frequencies. My hometown has many, many theaters, but as I said before, there are only two of them I will see a movie in. _Update: I've discovered a couple more that offer an excellent presentation. Non-THX, but they still seem to do everything right._ A few years ago I saw one movie (Pirates of the Caribbean: At Worlds' End) in multiple auditoriums, all THX certified, and they all delivered a repeatable, consistent, excellent presentation. When I saw the same movie in another theater (the purple-walled one), that is when the experience became dull and lifeless. The majority of theaters may indeed sound dull and lifeless, but as I said before, the X-curve and absorption are not to blame.

Regarding the above paragraph, _please_ don't infer that I think that the X-curve and absorption are the only factors that influence sound quality. They are merely the subject at hand.



Wayne A. Pflughaupt said:


> As I thoroughly discussed, it’s merely for the purpose of per-program tone-control, to compensate for poorly-mixed voices.
> 
> Let’s not forget that many people don’t use their systems exclusively for watching movies.


I never implied that I advocate using a home theater solely for watching movies. On the contrary, I suggested setting the system up to have a "smooth and natural" frequency response curve, meaning one that is appropriate for your room size, then engaging the re-eq on program material that was mixed using the X-curve standard. I personally listen to about 50/50 music and movies.



Wayne A. Pflughaupt said:


> For non-movie programming like TV, etc. the X curve does not apply (I haven’t seen anything to suggest it’s used anywhere but the movie industry), so equalizing is all over the map.


I think you've made a pretty good case for standardization in the TV and music industries!



Wayne A. Pflughaupt said:


> Naturally, a pro system like those used for soundstages has the same kind of “set-and-forget” system equalization, but with an important difference: The mixing console has separate EQ controls for each input that can be used at the engineer’s discretion. So, with a simple twist of a knob the engineer can fully override the system’s X curve if he so desires, as it would apply to that particular input. Naturally, he would EQ each input signal based on his own preferences or hearing capabilities. If he happens to like things bright, or subdued, then that’s going to come out in the theater, irrespective of its X curve calibration.


This is a good place to point out the distinction between the creative process and the playback system. The engineer and film director can give a film exactly the sound they want. That is part of the creative process. The EQ on the inputs, the type of mics they use, etc. (but not what speakers are used on the dubbing stage, that is the playback system), are all part of the creative process and have absolutely nothing to do with the "set and forget" EQ of the playback system. The engineer does not "override" the X-curve by adjusting a particular input.

The playback system, on the other hand, is not part of the creative process. Whatever the engineer puts into it, that's what you'll get out, not irrespective of its X-curve calibration, but _because of its X-curve calibration._ If the engineer wants a bright or dull soundtrack, that's what you'll get in the theater, because the theater is set up to sound the same as the dub stage. There are many more similarities than dissimilarities in dubbing stages and screening rooms, and there probably less than 15 major dubbing facilities worldwide, so there is much consistency between them (compare this with thousands of music recording studios). A soundtrack recorded at any of the facilities will sound very similar (if not almost identical) when played back at another facility. I think this is where many home theaters (as well as the aforementioned commercial theaters) fall short. With all of the freestyle arrangements out there, strange EQ curves, and a plethora of other variables, it's no wonder there is so much confusion and inconsistent sound out there.



Wayne A. Pflughaupt said:


> I suggest studying up on the finer points of equalization, both from the production and end-use “points of view,” as it were. I’d also note that there is no “soundstage” with a multi-channel system, as we have with basic two-channel stereo. The rules of two-channel equalization for a playback system do not apply to multichannel, especially for home theater, where the equalization can and will change throughout the course of a movie in the various channels depending on what sound effect is being generated at any particular moment.


Constructing a coherent and immersive soundstage is at least as important in multichannel recordings as 2-channel. As long as there is a need for imaging between speakers (close your eyes and point) or envelopment (close your eyes and you are there), then there is a need for a "soundstage". The same rules of equalizing apply whether you are using two speakers or 20. More speakers just means more skill and care is necessary on the part of the calibrator to construct an immersive soundfield. I would rather hear the aural environment created by the speakers than hear the individual speakers themselves.



Wayne A. Pflughaupt said:


> Really? How are we supposed to duplicate a 40 ft. sound stage in a living room or dedicated home theater?


Thankfully, we don't need to ("Honey, why is there a Euphonix console on the coffee table?"). All we need to do is replicate the layout (three speakers up front, surrounds to the sides and rear, etc.), get the acoustics right, and make use of the tools at our disposal that are already built-in to most of our processors. If we understand how sound behaves differently in a smaller room compared to a larger one, and how our brains interpret sound in a smaller room, then we can get a faithful translation of the original sound character at home, just on a smaller scale.



Wayne A. Pflughaupt said:


> While DVDs for the most part have more consistent EQ than TV and other programming, I’ve come across enough with excessive highs in the voices to make center-channel, per-program EQ capability a nice feature that makes the movie more enjoyable, if it’s called for. Especially since I don’t have Re Eq. Even if I did I probably wouldn’t use it, as it would attenuate the highs in all the channels, not just the center. Personally I’ve never seen DVD where I felt the highs in the other channels needed taming. I only see that in the center channel.


I agree that most DVDs do have more consistent EQ than other programming, but I don't believe that it is only by mere coincidence. Most DVDs have soundtracks that were originally mixed in a dub stage, built to the same audio specs as other dub stages and movie theaters, with the same general acoustics and X-curve EQ in place.

Although I have not listened to every single movie, music, and TV program out there, I have never personally had the center channel need its own tone control. Is your center speaker identical to your left and right speakers? A non-identical center speaker (even if the manufacturer says it's voiced-matched) can cause the kind of tonal problems you speak of. I only use three identical LCRs across the front, and have never had that problem.

Before anyone accuses me of it, let me say that I'm not trying to tell everyone how they have to set up their home theaters. If someone wants it a certain way, that's fine. If someone doesn't want to use re-eq, that is a personal decision and I respect that. But re-eq is a tool that we can use and it is very effective for enjoying movies and music on the same system. My whole point is that there are certain standards in place that make it easy for us to get consistently great sound. A home theater is not a home theater if it cannot reproduce films accurately, but there is no reason that same home theater cannot also be the best music system you have ever heard.

And it doesn't need to be complicated.

Thanks,


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## gsmollin

I read the X-curve explanation, and was surprised: The X-curve is the exact "house curve" I used equalizing sound reinforcement systems in auditoriums, churches and similar venues in 1973. I actually had no idea the movie industry was using it. It was credited to Altec-Lansing at the time. (Whoops, the A7 was the Voice of the Theater, wasn't it?)

Anyway, I experimented with the house, err, X-curve on numerous occasions, probably all occasions I used it. I found that trying to raise the high end of the curve produced a rather harsh and bright sounding sound reinforcement, with accentuated sibilant sounds. It also tended to blow out tweeters. The high frequencies also beamed a lot, and one could point to the location of the tweeter horn, or multi-sectoral midrange if there was no tweeter. The relaxed X-curve provided a system where the electronic speakers could disappear, and the sound appeared to come from the human speaker. Providing high frequencies across long distances in an auditorium is never easy, because humid air is an acoustic low pass filter. The near seats would get a very "hot" signal, and the far seats would still have a roll off of the treble frequencies. The X-curve roll off mitigated that problem and gave everybody the same signal.

The low frequencies were rolled off to avoid problems with HVAC equipment. You haven't suffered until you've had to deal with air moving rumbles and ductwork resonances. I also thought the systems sounded pretty boomy if we tried to raise the low end below the 63 Hz third octave band. Once again, the booms may have been unlined ducts.

None of this translates well to a stereo or HT system in somebody's den. The tweeter may be 12 feet from your ear, and getting a flat curve is pretty easy.


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## Home Theater Guy

"You haven't suffered..." :rofl: Hilarious!

Seriously, it's really interesting to hear of your real-world experience and the effects of EQ in sound reinforcement systems.


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## gsmollin

Home Theater Guy said:


> "You haven't suffered..." :rofl: Hilarious!
> 
> Seriously, it's really interesting to hear of your real-world experience and the effects of EQ in sound reinforcement systems.


Yuck it up, yuck it up, guys. We did it all without a single computer. I drew the eq graphs _by hand._ The equipment was a General Radio third octave analyzer and pink noise generator. Not MLS, real pink noise. The filters where 1/3 octave plug-ins. Passive. Later we got a strip chart recorder. It took minutes to sweep room, not seconds. By the time we got to finding HVAC resonances, it was 2 AM, and I just wanted to go home. You push a button and in two minutes have amultipoint eq. Woosses.


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## tnargs

I think we can well say the X curve is not only inappropriate for home use, it is outdated for cinema too. In fact Newell et al (2011) write that the use of the X curve has been detrimental to the enjoyment of cinema!

So pleeeease don't use it for home cinema setup. 

As a starting point I recommend the use of the Bruel and Kjaer 1974 curve that they derived for use when listening to music at home.


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## Mitchco

tnargs said:


> As a starting point I recommend the use of the Bruel and Kjaer 1974 curve that they derived for use when listening to music at home.


+1 Here is a link to the B&K curve. Note Figure 5. 

Another interesting curve came from Sean Olive's excellent research on The Subjective and Objective Evaluation of Room Correction Products. Note the curve (or straight line slope) at top of slide 24.

I use Audiolense DRC and have tried both of those curves and many others (including flat).

Personally, I like Sean Olive's the best and what I have been listening to for a while. It is also very similar to the results Sieglander posted in what does a good curve look like.

Another Audiolense user (Brad) is using the Sean Olive curve on a multichannel tri-amplified HT system. Be sure to check out the pics.

Cheers, Mitch


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## tnargs

Thanks Mitch, great extra info. 

The Olive 'line' is the same as the default target that Behringer uses in their DEQ2496 analyser-cum-equaliser.

Both the B&K and Behringer targets will do some good and some harm. Doing it right needs a little more subtlety.

Like I said though, good starting points, much better than the X curve!


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## Wayne A. Pflughaupt

tnargs said:


> As a starting point I recommend the use of the Bruel and Kjaer 1974 curve that they derived for use when listening to music at home.


Indeed, it’s good to note that any recommended “ideal curve” from any source is just that – a starting point. Every room is different, so you may well have to tweak their “ideal curve” so that things sound right in your room.

Regards, 
Wayne


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## AudiocRaver

Wayne A. Pflughaupt said:


> Indeed, it’s good to note that any recommended “ideal curve” from any source is just that – a starting point. Every room is different, so you may well have to tweak their “ideal curve” so that things sound right in your room.
> 
> Regards,
> Wayne


Beg pardon if this has already been brought up, if so, I missed it. How about contributions from individual differences in hearing sensitivity? Not necessarily hearing loss, although that can be a factor too, but Listener A might have a hearing sensitivity curve at 80 dB (for instance) with greater sensitivity through the upper-mid frequency range than the hearing sensitivity curve at 80 dB for Listener B, therefore what sounds perfect to Listener B sounds too bright to Listener A? The Fletcher Munson curves are averaged over a population, of course. We are not machines, genetic variation must include some differences in individual frequency sensitivity curves that would show up in target curve preferences. I have long been convinced, even in playing with different target curves, that my own hearing is 1 to 2 DB more sensitive above 2 kHz or so than the norm.

Echoing Wayne's last post, they are just starting points.

Hey, Wayne, just catching up on this recently-revived thread and your initial articles. Nice work, well-thought-out, got a lot of people thinking, a real contribution. Thanks for all the work.:clap:


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## tnargs

AudiocRaver said:


> Beg pardon if this has already been brought up, if so, I missed it. How about contributions from individual differences in hearing sensitivity? Not necessarily hearing loss, although that can be a factor too, but Listener A might have a hearing sensitivity curve at 80 dB (for instance) with greater sensitivity through the upper-mid frequency range than the hearing sensitivity curve at 80 dB for Listener B, therefore what sounds perfect to Listener B sounds too bright to Listener A? The Fletcher Munson curves are averaged over a population, of course. We are not machines, genetic variation must include some differences in individual frequency sensitivity curves that would show up in target curve preferences. I have long been convinced, even in playing with different target curves, that my own hearing is 1 to 2 DB more sensitive above 2 kHz or so than the norm.
> 
> Echoing Wayne's last post, they are just starting points.


Hi, I don't think the FM curves or personal variations of it have any relevance to setting a target curve.

There is a big misunderstanding in audio circles that we need to correct for FM curves. I even see articles written on how to determine your personal correction curve based on your personal frequency sensitivity.

In fact it is an input-output issue. Floyd Toole once wrote something like "we live with these contours from birth, they are part of everything we hear, whether live or reproduced". Our brains are fully adapted to our individual sensitivity curves. We hear all natural sounds through it, and we expect to hear all reproduced sounds through it. Therefore please do not take your sensitivity curve into account when thinking of a target response.

P.S. it was me who called the Olive and other target curves 'starting points'.


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## Wayne A. Pflughaupt

AudiocRaver said:


> Hey, Wayne, just catching up on this recently-revived thread and your initial articles. Nice work, well-thought-out, got a lot of people thinking, a real contribution. Thanks for all the work.:clap:


Thanks for the kind words, Audiocraver. :T



AudiocRaver said:


> How about contributions from individual differences in hearing sensitivity?


I agree that not all people hear the same; as you mentioned you have determined that your ears are more sensitive above 2 kHz than most. I think it’s been established that people with acute hearing loss, brought on by their occupation, hobbies (e.g. hunting) etc., are more sensitive to sounds in the 2-4 kHz range (IIR) than other people. And of course, everyone knows that high-frequency sensitivity decreases with age. There’s nothing wrong with people tuning their systems to compensate with hearing deficiencies they might have – it’s their system, after all, and they have a right to enjoy it. :T

And I agree with tnargs that it’s senseless to set your system according to the Fletcher-Munson curves. They are primarily with our hearing capabilities with regards to differing _volume levels._ As I’ve noted in my house curve articles, a room curve is actually (and correctly) compensation for the _room,_ not your ears: It will be different in a small bedroom than in a large open-concept family room.

Regards,
Wayne


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## tnargs

Nice comments Wayne, as always, and I fully agree with them.


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## primetimeguy

I think people do need to take the Fletcher Munson curves into account. Most people do not listen at reference level and I'll throw out a number of -25 from reference being more typical and for an example. One can look at the curves to determine how much bass boost they need as compared to the higher frequencies to maintain a frequency response that more closely matches reference by comparing the curves that are 25db apart.

But at reference level the mixer has essentially already taken the curves into account by mixing to what sounds correct to him.


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## tnargs

Agree, -- you are talking about the need for a 'loudness' button. Some amps implement a simple version, some are quite sophisticated. Rarely seen in audiophile amps these days, along with tone controls.


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## AudiocRaver

tnargs said:


> Hi, I don't think the FM curves or personal variations of it have any relevance to setting a target curve.
> 
> There is a big misunderstanding in audio circles that we need to correct for FM curves. I even see articles written on how to determine your personal correction curve based on your personal frequency sensitivity.
> 
> In fact it is an input-output issue. Floyd Toole once wrote something like "we live with these contours from birth, they are part of everything we hear, whether live or reproduced". Our brains are fully adapted to our individual sensitivity curves. We hear all natural sounds through it, and we expect to hear all reproduced sounds through it. Therefore please do not take your sensitivity curve into account when thinking of a target response.
> 
> P.S. it was me who called the Olive and other target curves 'starting points'.


Allow me to clarify. My point was simply to echo the previous comments about target curves being starting points, and to state the belief that there can be numerous reasons to consider departing from that starting point, including the _possibility_ of differences in hearing sensitivity. Indeed, we hear through our sensitivity curves 24/7, yet we audio nuts are refining our hearing muscles and training them to be more flexible all the time. The individual's sensitivity curve is not some brick wall that is impossible to see beyond.

To go a step further: To someone whose eyes are hypersensitive to light, direct sunlight always seems _really bright._

If the target curve always seems _really bright,_ and all the right room treatment steps have been taken, then use a different target curve - as you say, it is only a starting point.

Appreciate the feedback.


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## tnargs

AudiocRaver said:


> If the target curve always seems _really bright,_ and all the right room treatment steps have been taken, then use a different target curve - as you say, it is only a starting point.


Hi, I liked your post, thank you. I just want to comment on the section above.

This is true enough, but for the person that it applies to, if it is due to their frequency sensitivities then such a person will also find live natural sounds _really bright_, they will find the sound of a perfectly tuned live orchestra from the optimal seat _really bright_, the sound of traffic in the street will be _really bright_, the sound of someone pottering around in the kitchen will be _really bright_.

Such a person might well be advised to use a different target curve, just because he or she can't stand normal sounds.

I think the real reason to tweak a target curve is because it will usually be the case that trying to force the speaker/room system to meet a target curve often forces that speaker/room system into operating at points where it is not behaving well. No automated correction system can take this into account.


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## AudiocRaver

tnargs:

Agree, always start with "is my room right?" not "are my ears right?"


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## psg

I wanted to use Klipsch KPT series (Pro Cinema) rear surrounds for my Klipsch heritage HT, or maybe something from the JBL pro lineup. The implemented x-curve in their crossover stopped me. I suppose I could compensate for it using a few channels of my miniDSP but that seem overly complicated. Too bad they don't have a switch to turn it off!


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## sdurani

Mitchco said:


> Here is a link to the B&K curve. Note Figure 5.


There was a paper from Jan Pedersen of Lyngdorf about trying to determine a default target curve that sounded "natural" to listeners. Turned out it had something in common with the B&K curve: elevated bass, at least compared to the mids and highs. Looked similar to the curve that JBL had been using on their Symthesis systems for years. 

Pedersen found that keeping naturally occuring room gain was essential to listener preference: _"This system also provides a more natural timbre to room correction systems by recognizing the fact that part of the influence of a room is perceived to be natural and should not be removed by a room correction system."_


Mitchco said:


> Another interesting curve came from Sean Olive's excellent research on The Subjective and Objective Evaluation of Room Correction Products. Note the curve (or straight line slope) at top of slide 24.


Yup, and just as important is slide 25, which shows how listeners perceived the measurements in slide 24. Note that the curves with a downward tilted response (e.g., Lyngdorf at #3) were heard as relatively flat, while the curves that aimed for a flatter response (e.g., Audyssey at #6) where heard as tilted up. Makes sense, since our human hearing is less sensitive in lower frequencies, so a boost in the bass region would make the low frequencies sound as loud as the rest of the frequency range. 

Judging by the preference ranking, seems listeners prefer a preceptually flat response to a measured flat response. Hence that similarity in the target curves from B&K, Lyngdorf, JBL Synthesis, Harman and others. Speaking of others, a few years after Sean Olive's comparison, DTS publised a paper on their proposed room correction system. The target curve they used looked exactly like the Harman curve used in Olive's comparison: straight line, 10dB down from bass to treble.


Mitchco said:


> Personally, I like Sean Olive's the best and what I have been listening to for a while.


That curve was cobbled together by Olive and Alan Devantier in a couple of hours (no joke) in preperation for the comparison. They went through Harman's exhaustive speaker comparisons and looked for sound power responses of loudspeakers that were the most preferred. And there's your tilt. Not very complicated. The speaker comparisons also showed that smoothness of response contributed to listener preference, so that became the other main priority for Harman's room correction.


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## tnargs

sdurani said:


> Note that the curves with a downward tilted response (e.g., Lyngdorf at #3) were heard as relatively flat, while the curves that aimed for a flatter response (e.g., Audyssey at #6) where heard as tilted up. Makes sense, since our human hearing is less sensitive in lower frequencies, so a boost in the bass region would make the low frequencies sound as loud as the rest of the frequency range.


Hi, your explanation based on human sensitivity curves is a bit off track, as explained in earlier posts. The reason flat target curves sound sharp is because the listener responds mostly to the sound of the direct on-axis energy from the speakers, whereas the microphone is measuring direct and reflected energy, i.e. the ungated pink noise curve that is being measured is the sum of direct and reflected sound. A loudspeaker with 'perfect' (flat) on-axis response will measure in-room as down-tilted because the reflected sound contains less treble energy and relatively more bass energy. But it will sound great to the listener, who is sensitive to the on-axis sound. If we equalise to a flat target with the above 'perfect' speaker, it will will involve turning down the bass and up the treble, which will be detected by the listeners.




> Judging by the preference ranking, seems listeners prefer a preceptually flat response to a measured flat response.


That goes without saying, actually. If it is perceived as flat, it sounds right. If it is perceived as tilted up or down, it sounds wrong. :T



> They (Olive et al) went through Harman's exhaustive speaker comparisons and looked for sound power responses of loudspeakers that were the most preferred. And there's your tilt. Not very complicated.


Not very correct, either. The sound power response is not the same as the in-room response.



> The speaker comparisons also showed that smoothness of response contributed to listener preference, so that became the other main priority for Harman's room correction.


No, that is smoothness of direct energy response (used for speaker design), not smoothness of in-room response (used for room correction). 

I think you are well-read, but slightly confused in a number of areas. I hope I have been helpful.

Have a careful read of earlier posts in this thread, especially mine  such as post #11. No matter what the automated room correction algorithm and target is, it can be improved upon by individual customised adjustments. Olive, Pedersen, etc, they are all just starting points.


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## sdurani

tnargs said:


> A loudspeaker with 'perfect' (flat) on-axis response will measure in-room as down-tilted because the reflected sound contains less treble energy and relatively more bass energy. But it will sound great to the listener, who is sensitive to the on-axis sound.


Not a question of sounding great or not, since that is up to personal preference, my point about Olive's comparison was that a 10dB drop from bass to treble was perceived as flat. It's two separate things, albeit related. Erasing room gain, as Audyssey (RC6 on Olive's comparison) does by using a relatively flat target curve, tends to lower statistical preference. But preference doesn't explain why bass that is 10dB louder than treble is perceived as equal in level.


tnargs said:


> Not very correct, either. The sound power response is not the same as the in-room response.


When I was at Harman for a training class on their ARCOS room correction system, I asked Olive how they came up with that tilt and he mentioned using sound power as a guide (rather than predicted in-room response).


tnargs said:


> No, that is smoothness of direct energy response (used for speaker design), not smoothness of in-room response (used for room correction).


Not from what we were told at Harman. For both speakers and room correction, they pointed out that the smoother the frequency response (fewer bumps and dips), the more it was preferred. The Harman curves (RC1, RC2) had tilts similar to Lyngdorf, but the smoother response is why they scored higher. 

As far as using in-room response, are you sure you're not confusing Harman's room correction with Lyngdorf? The latter uses in-room response for their target curve. As does Anthem room correction (RC5) to some extent, which forces their target curve to be dependent on the speaker. From what Toole told us at the training, had they used a better speaker for the comparison, Anthem would have scored on the other side of no room correction (RC4). 

As for the Harman curve, it has changed a few times in the 20 months since ARCOS was released. It was originally closer to the straight line in Olive's comparison; by the time of my training class 5 months later, it had gotten curvier (like the old JBL Synthesis curve); by CEDIA this year it had become a bit straighter, like it originally was. The basic idea (downward slope) hasn't changed, but the more feedback they get from the field, the more they keep refining the curve.


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## Wayne A. Pflughaupt

sdurani said:


> Yup, and just as important is slide 25, which shows how listeners perceived the measurements in slide 24. Note that the curves with a downward tilted response (e.g., Lyngdorf at #3) were heard as relatively flat, while the curves that aimed for a flatter response (e.g., Audyssey at #6) where heard as tilted up. *Makes sense, since our human hearing is less sensitive in lower frequencies, so a boost in the bass region would make the low frequencies sound as loud as the rest of the frequency range.*


As explained in Part 2 of my original house curve article, a house curve is compensation for the room, not the ear. 

For instance, the first time I tried to tune the system in a largish church auditorium I initially dialed in the same great-sounding curve I was using at home, only to find that the sound was extremely bass heavy. When I finally got things sounding correctly, the curve was virtually flat all the way down to 40 Hz or so, with only only a 2-4 dB boost needed in that range. Drastically different from the typical curve needed in residential listening environments.

On the flip side, people who are into high-performance car systems will tell you they usually need a really steep curve of maybe 30 dB for those tiny "rooms."

Regards,
Wayne


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## tnargs

Thanks for the extra discussion Sanjay. Rather than focus on details, let me reiterate what I think are the big points for this thread:

For home listening rooms, don't use the X-Curve or near variants as your target in-room response. Use a steadily downward-trending target curve.

Consider using a Pedersen-stye 'bump' in the target curve in the bottom 3 octaves, but be aware of the stress this might put on your low-frequency sound system, depending on its ability.

If you choose to use an automatic equalisation system, make sure that it can display the various cuts and boosts that it applies, and that it allows you to make post equalisation adjustments to these settings. If it does not do this, its ability is ultimately compromised.

Treat the achievement of a target curve, any target curve, as a starting point not an end point.

And finally, any discussion of human hearing sensitivity (as an explanation of the shape of target curves) is a diversion, and does not really belong in this thread.


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## sdurani

Wayne A. Pflughaupt said:


> As explained in Part 2 of my original house curve article, a house curve is compensation for the room, not the ear.


Never said that target curves should compensate for human hearing, merely pointed out _why_ the downward tilted curves in Olive's comparison were heard as flat, which does have to do with human hearing (measured flat vs perceptually flat).


Wayne A. Pflughaupt said:


> For instance, the first time I tried to tune the system in a largish church auditorium I initially dialed in the same great-sounding curve I was using at home, only to find that the sound was extremely bass heavy. When I finally got things sounding correctly, the curve was virtually flat all the way down to 40 Hz or so, with only only a 2-4 dB boost needed in that range.


If you're going to do final fine tuning of a target curve by ear, then at some point not only does human hearing figure in the shape of that curve but so does preference.


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## sdurani

tnargs said:


> If it is perceived as flat, it sounds right. If it is perceived as tilted up or down, it sounds wrong.





> _And finally, any discussion of human hearing sensitivity (as an explanation of the shape of target curves) is a diversion, and does not really belong in this thread._


What do you mean by "sounds right"? Sounds right to who? Wait, don't answer that, because then you'd have to discuss human hearing in reference to target curves, and that does not really belong in this thread.


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## tnargs

sdurani said:


> Never said that target curves should compensate for human hearing


I am just responding to this incorrect statement you made in post #23: 


> Note that the curves with a downward tilted response were heard as relatively flat, while the curves that aimed for a flatter response where heard as tilted up. Makes sense, since our human hearing is less sensitive in lower frequencies, so a boost in the bass region would make the low frequencies sound as loud as the rest of the frequency range.



That is not why it makes sense: it is not due to human hearing being less sensitive in lower frequencies, as explained in posts #14 and #15.

It is due to the presence of the room and all the reflected sound therein. If you conduct the preference test outdoors or in a non-reflective room, there is no downward tilt to the preferred response, it is flat.




sdurani said:


> What do you mean by "sounds right"? Sounds right to who? Wait, don't answer that, because then you'd have to discuss human hearing in reference to target curves, and that does not really belong in this thread.


Sarcasm noted. Sounds right means more preferred by listening test subjects; sounds wrong means less preferred. Didn't need explaining.


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## sdurani

tnargs said:


> If you conduct the preference test outdoors or in a non-reflective room, there is no downward tilt to the preferred response, it is flat.


You have data from a preference test (like the one Olive conducted) which shows that measured-flat response was preferred?


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## tnargs

sdurani said:


> You have data from a preference test (like the one Olive conducted) which shows that measured-flat response was preferred?


Not me, but Sean Olive does. Dig around his writings and you will find the data you seek.

So, the downward tilt in preferred response is all due to the room.

So, the amount of downward tilt to use for a target response is room (and speaker) dependent.

So, any auto-calibration tool that sets a fixed amount of downward tilt is only going to be a starting point, IMHO.


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## sdurani

tnargs said:


> Not me, but Sean Olive does. Dig around his writings and you will find the data you seek.


I did dig around, including his entire room correction AES paper that goes with the slide pack linked to earlier, and I couldn't find mention of a measured-flat response being preferred in either his room correction comparison or his (or Toole's) various speaker comparisons. Can you point to which of his writings contains this data?


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## tnargs

sdurani said:


> I did dig around, including his entire room correction AES paper that goes with the slide pack linked to earlier, and I couldn't find mention of a measured-flat response being preferred in either his room correction comparison or his (or Toole's) various speaker comparisons. Can you point to which of his writings contains this data?


Slide 22 in the slide pack refers to the objective measurement of "in-room amplitude", which is code for saying the measured curves that follow slide 22 are "ungated", or "room-dependent". That is why the preferred curves have a downward slope.

Olive's 'Generation Y' blog post refers to a flat anechoic on-axis response as being the most preferred. "_The comprehensive set of anechoic measurements for each loudspeaker is compared to its preference rating. There are clear visual correlations between the set of technical measurements and listeners’ loudspeaker preference ratings. The most preferred loudspeaker had the flattest measured on-axis and listening window curves ..._" He goes on to say this is in good agreement with the preferences of trained Harman listeners.

The best summary of listener preference for flat frequency response curves is Toole, _Sound Reproduction_, 2008, pp390-395.

In conclusion, the downward tilt in preferred response (in Olive's paper on room correction products) is all due to the room. It is unrelated to human hearing being less sensitive in the lower frequencies.


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## sdurani

tnargs said:


> The best summary of listener preference for flat frequency response curves is Toole, _Sound Reproduction_, 2008, pp390-395.


Finally got a chance to read the above pages: the "flat" response that Toole is talking about is anechoically measured, not what the listeners heard in-room during the speaker comparisons. As I asked earlier, do you have data from a preference test (like the one Olive conducted) which shows that measured-flat response was preferred? It can be a preference test that was done outdoors, like what you alluded to earlier.


tnargs said:


> In conclusion, the downward tilt in preferred response (in Olive's paper on room correction products) is all due to the room. It is unrelated to human hearing being less sensitive in the lower frequencies.


Where did I say that the tilt comes from human hearing being less sensitive in the low frequencies? Instead I posted:


sdurani said:


> Pedersen found that keeping naturally occuring room gain was essential to listener preference: _"This system also provides a more natural timbre to room correction systems by recognizing the fact that part of the influence of a room is perceived to be natural and should not be removed by a room correction system."_


My comment about human hearing wasn't in regard to generating the target curve but about why we hear a downward tilted response as flat (measured flat vs perceptually flat). That's why I pointed to the two slides in Olive's slidepack (measured vs perceived).


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## tnargs

sdurani said:


> Finally got a chance to read the above pages: the "flat" response that Toole is talking about is anechoically measured, not what the listeners heard in-room during the speaker comparisons.


Precisely my point.



> As I asked earlier, do you have data from a preference test (like the one Olive conducted) which shows that measured-flat response was preferred?


As previously answered.



> Where did I say that the tilt comes from human hearing being less sensitive in the low frequencies?


As previously answered, see posts 23 and 30.



> My comment about human hearing wasn't in regard to generating the target curve but about why we hear a downward tilted response as flat (measured flat vs perceptually flat).


And your comment is mistaken because you say the reason is human hearing being less sensitive in low frequencies, whereas in fact the reason is an artefact of the measurements being ungated, continuous pink noise, in-room. This is the third time I have said this.

Sanjay, I am ending this dialogue because you are going in circles.


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## Wayne A. Pflughaupt

tnargs said:


> I think we can well say the X curve is not only inappropriate for home use, it is outdated for cinema too. In fact Newell et al (2011) write that the use of the X curve has been detrimental to the enjoyment of cinema!


Well, Joe (Home Theater Guy) seems to think the X curve is simply wonderful. 

Here’s the paper from Newell and Holland you mentioned. It discusses many of the things I mentioned, such as speech intelligibility and outdated speakers, that there is no “one curve fits all” situation,” and that generally there is no longer a need for the X curve in movie theaters.

Regards,
Wayne


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## Cam Man

Hi guys,
I stumbled on this thread while doing a bit of research after learning of an enthusiast using pro gear utilizing the X-curve. They seemed to not have any idea whether this might be appropriate for their room.

First, to an answer of the title question of the thread, I propose "maybe" rather than definitely not. Like many contributors to the thread, I agree that the selection of a target curve is very dependent on the room. But what I am missing from any of the discussion here is a more thorough list and discussion of the factors that will determine whether the X-curve may or may not be appropriate in a "home theater" room ... or any room for that matter.

I suspect that I might get broad agreement that two obvious factors in evaluating a room and this question are: room volume; and acoustic characteristics, specifically reverberation above 2.5KHz. Maybe I'll get broad agreement, but nobody mentioned them, IIRC.

If we have a home theater room that is quite large (it might not be a dedicated room; an open floor plan media room, for instance) and acoustically "lively," then are we not going to have reverberation times of high frequencies ringing about for quite a long time (not to the exclusion of lower frequencies, of course)? If the room is on the order of 9000+ cubic feet, and acoustic treatments and/or furnishings and other things in the room do not lower the reverberation time of the higher frequencies, then there is the potential that the room might benefit from a curve that might be similar to the X-curve. But that potential would be influenced by other factors, too.

Two important factors will be the distance of the main listening area from the speakers (primarily the LCRs) and the directivity (index) of the speakers. Acoustic Critical Distance will become a factor to consider. If the ratio of direct sound from the LCRs and their non-direct sound from the room become equal in energy, dialogue intelligibility and imaging may suffer, and the perceived level of energy of the upper frequencies will be higher. Use of speakers with higher directivity and/or shortening the distance between speakers and listener will be beneficial in such a room.

In the case of multi-channels audio systems, though, we have multiple surround speakers that generally are designed to have wide dispersion characteristics. These speakers will contribute to the overabundance of perceived treble in a large volume room that does not have significant attention to absorption, right? So, it seems that a large volume room at home can certainly have a problem with a perception of an unpleasant upward tilt.

So, what curve is "correct" for such a room ... which, let's face it, is more common than not? I agree with those here who say that a cookie cutter curve is not appropriate in an unpredictable/unstandardized environment such as home theaters. Much like "target" reverberation time is room volume dependent for a given frequency, the "appropriate" curve for a room will be dependent on several factors. Those must be considered, then the room measured before correction, then again after correction, then there must ultimately be a subjective evaluation made by the calibrator with demo program material with which he is very familiar. I suspect that may be considered heresy by some, but that verification evaluation by an ear that is trained and seasoned with that material on high quality systems in various acoustic environments is essential.

As automated room correction systems go, I do like MultEQxt32. IMO, it does a remarkable, if imperfect, job despite the fact that it presumes its one and only correction pass is correct, therefore never re-evaluates/compares it with an additional run. I'm sure you have noticed that Audyssey Pro permits several target curves from which to select with MultEQxt32. Each has a different slope in the upper frequencies. The X-curve is one of the choices ... for all the reasons I have presented here. I like this approach because it gives us some room to be flexible.

Back to the fellow that was going to use surround speakers with the X-curve in his home theater. From photos, I can see that room is around 3500 cubic feet. We would all hear the X-curve roll off. Would we agree that it is inappropriate in that room? I would. But in my giant, imperfect room ... maybe not.

Please consider my statements here as questions or invitations to discussion, not definitive by any stretch.

So, what say all of you?


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## Cam Man

I found this article _after_ I posted here. It supports the observations in my post,  but also many others who contributed to this thread. With all due respect, everyone here should give this one a good read, as it is the definitive article on the subject, IMHO.

http://www.hometheaterhifi.com/volume_9_2/feature-article-curves-6-2002.html


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