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post #1 of 39 Old 05-28-09, 08:33 PM Thread Starter
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Is the film industry's X curve suitable for home theater?

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).


Is the film industry's X curve suitable for home theater?-x-curve-original-nearfield-vs.-farfield-testing-1972.jpg


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).


Is the film industry's X curve suitable for home theater?-x-curve.jpg



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.


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1960s 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 ’60s and ’70s. 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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post #2 of 39 Old 05-28-09, 08:38 PM Thread Starter
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Is the film industry's X curve suitable for home theater?

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.


Is the film industry's X curve suitable for home theater?-shelving-filters.jpg


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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post #3 of 39 Old 05-02-10, 05:06 PM
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Re: Is the film industry's X curve suitable for home theater?

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Wayne A. Pflughaupt wrote: View Post
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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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...

Joseph Gaydosh
First Run Home Cinema
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Re: Is the film industry's X curve suitable for home theater?


Thanks for the comments, Joe.

Quote:
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.


Quote:
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.


Quote:
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.


Quote:
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.


Quote:
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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post #5 of 39 Old 05-10-10, 02:51 PM
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Re: Is the film industry's X curve suitable for home theater?

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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 ). 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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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!

Quote:
Wayne A. Pflughaupt wrote: View Post
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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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.

Quote:
Wayne A. Pflughaupt wrote: View Post
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,

Joseph Gaydosh
First Run Home Cinema

Last edited by Sonnie; 01-08-11 at 05:36 PM. Reason: Updates and additions supplied by Home Theater Guy
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post #6 of 39 Old 01-04-11, 03:08 PM
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Re: Is the film industry's X curve suitable for home theater?

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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post #7 of 39 Old 01-08-11, 06:39 PM
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Re: Is the film industry's X curve suitable for home theater?

"You haven't suffered..." 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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post #8 of 39 Old 01-09-11, 07:55 AM
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Re: Is the film industry's X curve suitable for home theater?

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Home Theater Guy wrote: View Post
"You haven't suffered..." 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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post #9 of 39 Old 12-10-12, 11:23 PM
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Re: Is the film industry's X curve suitable for home theater?

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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post #10 of 39 Old 12-11-12, 12:16 AM
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Re: Is the film industry's X curve suitable for home theater?

Quote:
tnargs wrote: View Post
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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