Pro Cinema Speakers, the X-Curve, and other Target Curves at Home - AVS Forum
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post #1 of 84 Old 07-27-2014, 04:43 PM - Thread Starter
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Pro Cinema Speakers, the X-Curve, and other Target Curves at Home

The advent of Dolby Atmos coming home has us all considering an expansion, or maybe upgrade, to our present compliment of speakers. It's logical to possibly consider some of the professional cinema models in our homes, especially as we eye what is in the commercial Atmos theaters.

I am certainly a proponent of the consideration of some professional models in some circumstances, rooms, personal tastes, or other factors. On the other hand, there are number of situations/rooms where some professional models would not be a good choice. I'm not speaking of the obvious size that some screen arrays would impose on real estate. I'm addressing the issue of the X-Curve that is "baked in" on some pro cinema speakers, including most surround speakers, and the utilization of the X-Curve (or not) in the home theater environment.

The thread I found recently that addressed this was this one about the JBL Pro 3677 that an installer utilized as LCRs in a client's home. The installer posted his reasons for this choice. You can find that here. JBL Pro 3677 Speakers

I have to hand it to CriticalListener for succeeding with his client in this project. That said, I think it is worthwhile to point out a number of details that are revealed in the posts, and some that are not brought out in the ensuing posts, lest there be folks who will not enjoy success with the use of products from the same class.

One post points out that this speaker's FR conforms to the commercial X-curve. Another post asks the question "What's wrong with theX-Curve?" The answer to that and a further discussion will reveal one contributing factor to the success in this case, but also why it might be a miserable failure in others.

As I mentioned, the CriticalListener gets credit for using residential protocol to achieve “success." What everyone must acknowledge,though, is the fact that customer subjective opinion is the final arbiter in the residential world, even if that results in serious compromise of objective/scientific reality. Hence the difference between the professional world verses the residential world.

In the professional world, an "engineered" outcome is pursued whether it's a huge cinema or a small mixing stage so that a given media will be rendered with a reasonably consistent experience. The final result in that world does have a subjective component, but it rarely results in major changes. A reference piece of media that the engineers know well is run just to verify that nothing significant has slipped by. There are so many more variables in our home environments that this approach is more difficult, may require more adjustments, and the end user subjectivity overrules anyway.

My point is that everyone should recognize that the success in the use of this particular JBL model (3677) as LCRs, and other pro speakers in this instance, was for two reasons: the room's big volume was somewhat supportive; and secondly, the end user was willing to accept some serious performance compromises in favor of other priorities.

A quick look at the ARC graphic JBL Pro 3677 Speakers shows you a speaker that conforms to the standard X-Curve. It's cooked into the design of the speaker. That leads to the obvious question of whether that is appropriate for that room ... or any room, for that matter.

I contend that from strictly an "engineered outcome" protocol, this particular JBL speaker is a terrible choice. It is a dinosaur from 70s technology. Modern cinema sound tracks are definitely of very high fidelity, and lossless digital codecs will certainly deliver them that way. Modern professional cinema screen speakers no longer have the X-Curve baked in, and they might be a viable choice in home environs. Most pro cinema surround speaker models do have the X-Curve built in. Whether that will be acceptable in a home theater will depend primarily on the volume of the room and its reverberant characteristics.

The legacy JBL Synthesis LCR speakers are an interesting relative of the 3677. The technology of the components used are from the same era. A big difference is the cabinet size, but very notably the frequency response. The JBL Synthesis speakers do not conform to the X-Curve. They have a ton of slam that comes with pro components, but they are 3dB down at 16KHz rather than the 3677 being down 12dB at 16KHz. That’s a huge difference!

I recently had the opportunity to do a fairly thorough comparison of the JBL Synthesis S2C and a modern speaker, the KlipschKL-650-THX. We chose them because we felt that they were fairly similar in design characteristics, but we wanted to seek out any perceivable difference. Each was installed identically in the same system, and each calibrated utilizing MultEQxt32 with the standard Audyssey curve. As a reference scene, I used a fairly short, quiet dialogue sequence in Batman Begins. Despite it being mostly dialogue, there were modest ambient acoustic effects of the environment in which the scene is played. Upon hearing them both, I was quite surprised that the newer speaker delivered nuance that the S2C could not. That nuance was in the range above that of the JBL, but the Klipsch reached. Each speaker could deliver the slam in louder passages, but the Klipsch KL-650-THX won the nuance of refinement. I’m a huge fan of the legacy S2C, but that’s how it fell. More than an endorsement of the KL-650-THX, I would say that modern speakers with good directivity of designs similar to the Klipsch, whether residential or pro, can be a very good choice. Modern professional cinema screen speakers will have the extended frequency response that impressed me in this comparison.

Could I be happy with a system made up of S2Cs for LCRs? You bet! I would probably be happier, though, with modern pro cinema screen speakers such as some of you have from JBL or Klipsch. Neither utilize the X-Curve.

But ... the X-Curve may or may not be viable as a target curve in your room. How do we know?

To answer this, it's time to first understand the X-Curve.This is a superb article for that. http://www.hometheaterhifi.com/volum...es-6-2002.html

I contend that LCRs with the X-Curve baked in are a terrible choice for professional or home cinemas. Surround speakers with the X-Curve might be okay, depending on the many factors. In a common size room around 3500 cubic feet in volume, the X-Curve roll-off will be very noticeable and verifiable. What curve you select for your room should depend on the factors of room volume, its acoustic characteristics, the distance between your MLP and the LCRs, and the directivity of the LCRs. As many of you know, Audyssey Pro provides target curve options … and one is the X-Curve. I like that flexibility. Since it is the residential world, you get to decide.

I've said more than enough. What say you?

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post #2 of 84 Old 07-28-2014, 08:40 PM
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I noticed that Klipsch has some new surrounds and interestingly, the details page says they are "75Hz-20kHz +/- 3dB per X curve -10dB 49Hz".

I would have thought they rolled off well below 20khz if they incorporated the xcurve.

http://www.klipsch.com/kpt-8000m/details

The model it replaced also had the xcurve but it was 72Hz-17kHz (+-) 3dB.

The implementation of the xcurve seems very inconsistent but Klipsch surrounds with the xcurve roll off at higher frequencies than the JBL surrounds do.
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post #3 of 84 Old 07-28-2014, 09:19 PM
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Double blind tests have shown that in a small room our binaural hearing system largely uses the spectrum of the direct sound to determine percieved spectral balance. Rolling off the direct sound per the X-curve will only make the subjective balance way too dull and lacking in detail. This is a major mistake which has no place in a high fidelity system.

The JBL 8340a is another speaker I see touted around here a lot that has the X-curve baked in, along with a narrow dispersion and sound power problems that make it a really poor choice for a consumer surround speaker in most respects.

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post #4 of 84 Old 07-28-2014, 10:06 PM - Thread Starter
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Originally Posted by SyntheticShrimp View Post
Double blind tests have shown that in a small room our binaural hearing system largely uses the spectrum of the direct sound to determine percieved spectral balance. Rolling off the direct sound per the X-curve will only make the subjective balance way too dull and lacking in detail. This is a major mistake which has no place in a high fidelity system.

The JBL 8340a is another speaker I see touted around here a lot that has the X-curve baked in, along with a narrow dispersion and sound power problems that make it a really poor choice for a consumer surround speaker in most respects.
I would agree in the case of small/"normal" size home rooms.


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Originally Posted by Davecraze View Post
I noticed that Klipsch has some new surrounds and interestingly, the details page says they are "75Hz-20kHz +/- 3dB per X curve -10dB 49Hz".

I would have thought they rolled off well below 20khz if they incorporated the xcurve.

http://www.klipsch.com/kpt-8000m/details

The model it replaced also had the xcurve but it was 72Hz-17kHz (+-) 3dB.

The implementation of the xcurve seems very inconsistent but Klipsch surrounds with the xcurve roll off at higher frequencies than the JBL surrounds do.
I've noticed that. I'll contact one of their engineers and see if he can explain.

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post #5 of 84 Old 07-30-2014, 11:53 AM
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I know the x-curve is a part of the speaker crossover network, but I assume that one could still EQ it flat (or flat enough) with enough correction in the 8khz-20khz region. I am sort of surprised that those posted ARC room correction measurements of the 3677 did not show just that. There is certainly a point where the rolloff is too steep for correction but Audyssey XT32 should be able to flatten out more than that ARC graph shows
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post #6 of 84 Old 07-30-2014, 12:41 PM - Thread Starter
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Originally Posted by Davecraze View Post
I know the x-curve is a part of the speaker crossover network, but I assume that one could still EQ it flat (or flat enough) with enough correction in the 8khz-20khz region. I am sort of surprised that those posted ARC room correction measurements of the 3677 did not show just that. There is certainly a point where the rolloff is too steep for correction but Audyssey XT32 should be able to flatten out more than that ARC graph shows
You could possibly do that with a shelf filter in an external PEQ, but I would be suspicious of how that might sound. XT32 certainly would not attempt to do that. I'm certain that XT32 presumes that speakers are well designed and reasonably anechoically flat, and it would presume a poor design or malfunction in a speaker with X-curve. Maybe someone has some experience with that, and knows different.


BTW, the Klipsch engineer is on vacation, but said he'll get back to me.
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post #7 of 84 Old 07-31-2014, 06:08 AM
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Originally Posted by Cam Man View Post
I was quite surprised that the newer speaker delivered nuance that the S2C could not. That nuance was in the range above that of the JBL, but the Klipsch reached. Each speaker could deliver the slam in louder passages, but the Klipsch KL-650-THX won the nuance of refinement. I’m a huge fan of the legacy S2C, but that’s how it fell. More than an endorsement of the KL-650-THX, I would say that modern speakers with good directivity of designs similar to the Klipsch, whether residential or pro, can be a very good choice. Modern professional cinema screen speakers will have the extended frequency response that impressed me in this comparison.
Nuance?

Andrew Robinson need his ears checked?
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post #8 of 84 Old 07-31-2014, 10:38 AM - Thread Starter
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Nuance?

Andrew Robinson need his ears checked?
Your response doesn't fit the comparison I made in my post where I was comparing the JBL Synthesis S2C and the Klipsch KL-650. I made no listening comparison of those speakers to the 3677. Plus, in my comparision, I'm implying nuance character revealed by the KL-650 higher frequency response compared to that of the S2C. Comparison to the 3677 would only be inferred and would hardly be fair using only spec sheet data. "Nuance" may well be perceived at lower frequencies of the 3677 by Andrew or any of us ... but obviously not the ones in the higher frequencies to which I referred. Clear as mud.


One might infer that the S2C would sound somewhat more like the 3677, but I'm sure that most of us would still hear the X-curve effect on the 3677 in an A/B comparison.


I guess the question is: What is a speaker with the X-curve roll-off (designed for reverberant-field/large room acoustic environment) going to do with higher frequency program material/sounds when it is placed in a near-field/small room acoustic environment? Will it render it faithfully, or subdue it to lower than the high fidelity character that it was mixed to deliver?
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post #9 of 84 Old 08-01-2014, 12:45 AM
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Originally Posted by Cam Man View Post
Your response doesn't fit the comparison I made in my post where I was comparing the JBL Synthesis S2C and the Klipsch KL-650. I made no listening comparison of those speakers to the 3677. Plus, in my comparision, I'm implying nuance character revealed by the KL-650 higher frequency response compared to that of the S2C. Comparison to the 3677 would only be inferred and would hardly be fair using only spec sheet data. "Nuance" may well be perceived at lower frequencies of the 3677 by Andrew or any of us ... but obviously not the ones in the higher frequencies to which I referred. Clear as mud.


One might infer that the S2C would sound somewhat more like the 3677, but I'm sure that most of us would still hear the X-curve effect on the 3677 in an A/B comparison.


I guess the question is: What is a speaker with the X-curve roll-off (designed for reverberant-field/large room acoustic environment) going to do with higher frequency program material/sounds when it is placed in a near-field/small room acoustic environment? Will it render it faithfully, or subdue it to lower than the high fidelity character that it was mixed to deliver?
Clear.

But I do have an experience with Klipsch speakers where I need to engage both the Audyssey movie curve & Denon Cinema EQ together. That's two HF-roll-off filters. Without them engaged, I can't tolerate them at loud volumes (about -5dB volume). My room has reflective floor tiles with brick-concrete construction of walls, ceilings & floor. However, when I clap my hands, there's no flutter echo.

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post #10 of 84 Old 08-01-2014, 08:13 AM - Thread Starter
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Originally Posted by Skylinestar View Post
Clear.

But I do have an experience with Klipsch speakers where I need to engage both the Audyssey movie curve & Denon Cinema EQ together. That's two HF-roll-off filters. Without them engaged, I can't tolerate them at loud volumes (about -5dB volume). My room has reflective floor tiles with brick-concrete construction of walls, ceilings & floor. However, when I clap my hands, there's no flutter echo.
What's the volume of your room and your listening distance from those? What Klipsch speaker model? What is your AVR model or amp output wattage for that/those channels? Where are you crossing that/those Klipsch(es)?

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post #11 of 84 Old 08-02-2014, 12:02 AM
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What's the volume of your room and your listening distance from those? What Klipsch speaker model? What is your AVR model or amp output wattage for that/those channels? Where are you crossing that/those Klipsch(es)?
16x25x9 feet room (but I'm only using the front half). Listening distance 11 feet. Denon 3312 AVR. Klipsch Synergy B3 speakers, crossover at 120Hz to relieve the load. I do understand that this is just a low-end model.
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post #12 of 84 Old 08-02-2014, 12:50 AM - Thread Starter
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16x25x9 feet room (but I'm only using the front half). Listening distance 11 feet. Denon 3312 AVR. Klipsch Synergy B3 speakers, crossover at 120Hz to relieve the load. I do understand that this is just a low-end model.
Well, you seem to know the issues and are doing all you can.
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post #13 of 84 Old 08-28-2014, 04:06 AM
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The advent of Dolby Atmos coming home has us all considering an expansion, or maybe upgrade, to our present compliment of speakers. It's logical to possibly consider some of the professional cinema models in our homes, especially as we eye what is in the commercial Atmos theaters.

I am certainly a proponent of the consideration of some professional models in some circumstances, rooms, personal tastes, or other factors. On the other hand, there are number of situations/rooms where some professional models would not be a good choice. I'm not speaking of the obvious size that some screen arrays would impose on real estate. I'm addressing the issue of the X-Curve that is "baked in" on some pro cinema speakers, including most surround speakers, and the utilization of the X-Curve (or not) in the home theater environment.
I make no apology for my stand against commercial equipment being used in a home environment, for many reasons. The only X-curve i am aware of was from Dolby and DTS sound sound tracks on 35MM film print. X-curve is a very mute subject for todays digital audio processing. So how does labeling JBL Pros 3677 as 70's tech matter when all loudspeakers are essentially 1912 tech? The 3677 is the only PRO speaker i would even recommend to anyone for use in a medium to large room, as i question why anyone with a 10x10x8 foot room is even looking at 85 pound speakers to start with.

And the payoff is never certain: Some observers contend that a generation has already been trained to be content with the small screen.
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post #14 of 84 Old 08-29-2014, 11:18 AM
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I've owned the 3677 and heard the kl650 several times. The 3677s blow them away IMO. Midbass, dynamics, sound stage and are a lot smoother than the kl650...it's not even close! IMO.

But seriously how can dual 6.5" woofers compare to a very high quality 15" driver when you're trying to produce 80-115 hz at reference levels at 15' away or whatever distance in a dedicated theater...I don't think the kl650 can even come close to handling the power or excursion it would take to move that much air to hit those spl at any reasonable distance yet the 3677 can do it cleanly and effortlessly. And would you really want to hand 2 6.5s off to a theater with multiple 18s and expect it to keep up? kinda of an apples and grapes comparison. Of course it carries a THX ultra 2 cert...which is only good for 12' and that's on a good day.

Sure the 3677 rolls off at 12k but many can barely hear over that anyway and room correction can bump that up if you like. I never missed anything on the high end and thought they were exceptional across the board....actually the best speaker for a serious HT I've heard or owned which is a fair amount of speakers and several owned and in the same treated HT room on the same gear.

As for being old...Flat is flat within its range... and the drivers are still used in newer designs and as for the woofer you'll find it in some of JBLs best speakers costing over 3k each. The ears tell the story and IMO they are insane HT speakers. Of course to get the best sound they need to be in a treated room and set up properly. But every one has their own opinion.

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post #15 of 84 Old 08-29-2014, 12:33 PM
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FWIW, I just bought 5 QSC 2150s for my new theater, I planned on getting 5 3677s as they are hands down the best most fun HT speakers I've ever heard or owned, but I found a deal on the QSCs new in box that was just too good to pass up. And If the QSCs don't favor as well after I'm done I'll be going back to the sure thing... the 3677.

I actually called QSC and spoke with their lead cinema installer. Because the 2150 is for smaller rooms with seats from 8 feet and up to 55 feet back they are perfect for screening rooms. I got tons of advice and installation tips, he even wants pics and I'll be asking him questions as I build.

I asked him about the xcurve. Basically even if the speaker has an Xcurve built in it should be eq'd even for screening rooms (basically large home theater). They take measurement but also pay attention to how it sounds. Sometimes they boost the curve sometimes they stick to it. It's room dependent.

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post #16 of 84 Old 09-07-2014, 12:19 AM
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Originally Posted by cdy2179 View Post
FWIW, I just bought 5 QSC 2150s for my new theater, I planned on getting 5 3677s as they are hands down the best most fun HT speakers I've ever heard or owned, but I found a deal on the QSCs new in box that was just too good to pass up. And If the QSCs don't favor as well after I'm done I'll be going back to the sure thing... the 3677.

I actually called QSC and spoke with their lead cinema installer. Because the 2150 is for smaller rooms with seats from 8 feet and up to 55 feet back they are perfect for screening rooms. I got tons of advice and installation tips, he even wants pics and I'll be asking him questions as I build.

I asked him about the xcurve. Basically even if the speaker has an Xcurve built in it should be eq'd even for screening rooms (basically large home theater). They take measurement but also pay attention to how it sounds. Sometimes they boost the curve sometimes they stick to it. It's room dependent.
I seriously hope you have a large room. A very large room. The QSC 2150 screen array loudspeakers have a 90° horizontal x 40° vertical sound cone. I know what QSC says, i would rather be 20 to 40 feet from that speaker for the best performance. QSC has been "filling the home theatre void" left by the other commercial manufactures, but still, it's way more to it than just running wires.

And the payoff is never certain: Some observers contend that a generation has already been trained to be content with the small screen.
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post #17 of 84 Old 09-07-2014, 12:41 AM
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I seriously hope you have a large room. A very large room. The QSC 2150 screen array loudspeakers have a 90° horizontal x 40° vertical sound cone. I know what QSC says, i would rather be 20 to 40 feet from that speaker for the best performance. QSC has been "filling the home theatre void" left by the other commercial manufactures, but still, it's way more to it than just running wires.
Yeah my room is going to be of decent size. And they have a great pattern than will easily meet my requirement. And qsc doesn't play these off as home theater, just as jbl has speakers for smaller screening rooms and smaller cinemas, so does qsc. This isn't my first home theater, nor my first cinema speaker. These and others like them have been extremely successful in home theaters of comparable sizes.

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post #18 of 84 Old 09-07-2014, 01:22 AM
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Yeah my room is going to be of decent size. And they have a great pattern than will easily meet my requirement. And qsc doesn't play these off as home theater, just as jbl has speakers for smaller screening rooms and smaller Co email, so does qsc. This isn't my first home theater, nor my first cinema speaker. These and others like them have been extremely successful in home theaters of comparable sizes.
JBL monitor speakers will over power your average HT room. I use a pair of older QSC SC-422C that i use for outside special events, birthday parties, etc. A lot of people see them set up and go, "Only two speakers?" Once there powered up and playing it's "Damn! Turn them down someone's gonna call the cops." It's all about room size, or lack there of.

And the payoff is never certain: Some observers contend that a generation has already been trained to be content with the small screen.
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post #19 of 84 Old 09-07-2014, 05:39 AM
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JBL monitor speakers will over power your average HT room. I use a pair of older QSC SC-422C that i use for outside special events, birthday parties, etc. A lot of people see them set up and go, "Only two speakers?" Once there powered up and playing it's "Damn! Turn them down someone's gonna call the cops." It's all about room size, or lack there of.
But that's the goal, isn't it? It's mine at least . To keep things from getting out of control I use a special high end in-line attenuator, aka the volume knob.

I have never, ever, (and I really mean ever ) heard too much headroom or dynamic range at reference volume. But the opposite is all too common.
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post #20 of 84 Old 09-07-2014, 07:06 AM
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as i question why anyone with a 10x10x8 foot room is even looking at 85 pound speakers to start with.
As somewhat a rhetorical question.... what dos the weight of the speaker have to do with anything?


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post #21 of 84 Old 09-07-2014, 10:00 AM
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With several home theater of the months using these cinema speakers, and achieving sound that has over and over been given raving reviews.... Well... That kinda says it all.
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post #22 of 84 Old 09-08-2014, 02:59 AM
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Originally Posted by cdy2179 View Post
With several home theater of the months using these cinema speakers, and achieving sound that has over and over been given raving reviews.... Well... That kinda says it all.
Very true. I don't have a large room and pro line speakers have been a giant upgrade over anything else I have had. Music and movies it's effortless, huge, and so clean. I could never go back.. Never.
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post #23 of 84 Old 09-09-2014, 09:15 PM
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But that's the goal, isn't it? It's mine at least . To keep things from getting out of control I use a special high end in-line attenuator, aka the volume knob.

I have never, ever, (and I really mean ever ) heard too much headroom or dynamic range at reference volume. But the opposite is all too common.
It's rather odd to be sitting in a overpowered HT and still hear the last sound echoing around the room 3 seconds later. Doesn't do it for me.

And the payoff is never certain: Some observers contend that a generation has already been trained to be content with the small screen.
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post #24 of 84 Old 09-09-2014, 09:27 PM
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As somewhat a rhetorical question.... what dos the weight of the speaker have to do with anything?


Weight and size go hand in hand. Bigger speaker, more weight, more amps, etc. It's a never ending circle.
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And the payoff is never certain: Some observers contend that a generation has already been trained to be content with the small screen.
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post #25 of 84 Old 09-09-2014, 11:02 PM
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Originally Posted by CinemaAndy View Post
It's rather odd to be sitting in a overpowered HT and still hear the last sound echoing around the room 3 seconds later. Doesn't do it for me.
A long reverberant decay time has nothing to do with the output capability of the speaker, except maybe at higher output levels delayed energy is more audible. In any case, the speaker isnt the problem, the environment is.

Theee seconds would only happen in a large room, one with basically no furniture, or one with cubical proportions.
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post #26 of 84 Old 09-10-2014, 01:39 AM
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There's a bit of misunderstanding of what the X-curve actually is. For example, you see a FR graph with a 3dB/oct. drop above 2KHz, it looks like the X-curve has been "baked in". That's actually not what's going on.

The X-curve is a measurement technique, not an EQ curve. It was developed so that large reverberant cinemas would reproduce the same sound quality heard in small, dead mixing rooms. The curve arose from an anomaly encountered when measuring steady-state pink noise in a reverberant space, where the reverberant spectrum is integrated with the direct spectrum, actually causing the measurement to be inaccurate. Adjusting a 1/3 octave EQ in a large reverberant cinema so that a 1/3 octave RTA displays the X-curve results in a better subjective match to what was heard in the mixing room.

Simply, it's a way to measure, then EQ a large theater to get it to match a small room. The actual correction applied will be different for different rooms, and of course, different speakers.

To quote Ioan Allen of Dolby, "The target of standardization of monitor characteristic, whether cinema, television, music recording, indeed any environment, has to be that material can pass from one to another without requiring any by rote equalization." (“The X-Curve” by Ioan Allen, SMPTE Motion Imaging Journal, July/August 2006) That means, if all is working well, the same track will play on any size system in any size room with any reverb time and sound basically the same. Unfortunately, that's not quite what happened. The X-curve became a rigid standard everywhere, and thus got misapplied. We ended up with tracks being mixed in a small dead room that had been EQd based on X-curve measurements, which of course, was wrong. Today, most of that has been straightened out.

The X-curve has no place in the home theater at all, because an HT is a small, non-reverberant (by comparison) room already, so match to the mixing room has basically already been done. Further, because the problem X-curve tries to address involves measuring continuous pink noise with a real-time analyzer, you can't replicate the same result using a time-domain analysis system like REW, which by its very nature tends to window-out reverberant spectral build-up from the measurement. The correction of X-curve would still be necessary in a large theater, but a time-domain measurement technique would achieve a different result.

So how could a speaker manufacturer bake in an X-curve? He can't, because he doesn't know how reverberant, or how large the space is. It's not a fixed EQ curve at all, is a measurement that includes the speaker, room, and continuous pink noise displayed on an RTA. You can't predict the X-curve and bake it in because you don't know what room you're correcting for.

Any speaker manufacturer making HT speakers for small home theaters claims to have built-in the X-curve has basically not done his homework, and is doing his customers a disservice.

There are also some issues with the X-curve's accuracy. It has an error built into it caused by the measurement equipment of it's time of origination (1972). That error is the basis for THX re-equalization in home systems, and is also the basis for some of the "Cinema EQ" settings found in AVRs. However, the correction is no longer uniformly required, and as a result, Cinema EQ and THX Re-EQ cannot simply be left on. Unfortunately, there's no tagging on media to indicate if Re-EQ is necessary for the home, so you just have to listen. If the track sounds consistently bright, it's time for Re-EQ.

Audyssey would partially compensate for speakers with the X-curve built in, but probably not well because Audyssey has a maximum gain of 9dB, which corresponds exactly to where 16KHz response would be on the X-curve. If the curve were extended to Audyssey's full 24KHz correction bandwidth, it clearly falls outside of the maximum gain. Even if the curve is extended out to 20KHz, flattening that out would be beyond Audyssey's gain range. There's some doubt that it would fully un-do the X-curve though, because nothing really measures smoothly, so I'd expect Audyssey to "give up" at some point. Audyssey does include two target curves, Reference (basically, a curve to correct for the mistranslation built into the whole X-curve mess), and Flat (music). I'd be willing to bet hardly anyone ever switches between them...

Just to be clear, no home theater should be adjusted to match the X-curve, no speaker anywhere should have an X-curve baked in. And the X-curve is not a target EQ curve, but a measurement technique involving continuous pink noise and a real-time analyzers.
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post #27 of 84 Old 09-10-2014, 01:56 PM
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Well said, but note claimed "SMPTE/ISO2969 Curve X high frequency de-emphasis" on the JBL 8340a.

Also note what appears to be a high frequency de-empasis in the 3677 in another poster's spatially averaged in room measurements of them.



For comparison, here is an example of my own Revel M105s measured in the same way, with the same program.



Given the wide adoption of these speakers in commercial cinemas and, more recently, home cinemas, perhaps not as many people as we'd hope are on the same page?

Theater room: Sony VPL HW30ES, DIY 100" screen with Seymour Centerstage XD, 5 Revel M105, 2 JBL Studio 210, 4 SVS SB12-NSD, Anthem MRX-300
Living room: Panasonic TC-P60VT60, 3 KEF LS50, Pioneer SW-8, Marantz NR1603

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post #28 of 84 Old 09-10-2014, 03:11 PM
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Originally Posted by SyntheticShrimp View Post
Well said, but note claimed "SMPTE/ISO2969 Curve X high frequency de-emphasis" on the JBL 8340a.
At best, the claim is only correct for a specific application, and is actually the wrong way to do it. It's easy to understand: how would anyone know what the response at the speaker should be to hit the X-curve without knowing the room it's working into?

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Originally Posted by SyntheticShrimp View Post
Also note what appears to be a high frequency de-empasis in the 3677 in another poster's spatially averaged in room measurements of them.



For comparison, here is an example of my own Revel M105s measured in the same way, with the same program.



Given the wide adoption of these speakers in commercial cinemas and, more recently, home cinemas, perhaps not as many people as we'd hope are on the same page?
It doesn't matter what they do to speakers, the final calibration includes the speaker and the room. At best, they've made it so that when you start from "flat", there's a bit less adjustment to do to get to the X-curve.
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post #29 of 84 Old 09-10-2014, 03:27 PM
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At best, the claim is only correct for a specific application, and is actually the wrong way to do it. It's easy to understand: how would anyone know what the response at the speaker should be to hit the X-curve without knowing the room it's working into?



It doesn't matter what they do to speakers, the final calibration includes the speaker and the room. At best, they've made it so that when you start from "flat", there's a bit less adjustment to do to get to the X-curve.
But there is always the "close enough" factor. It's hard for me to believe that every theater has a professional calibrator come in and EQ when new speakers are installed. In fact, given the cost I would bet that even if the theater had the space professionally EQ'd it probably happened before the grand opening and likely will never happen again unless they are very successful and profitable. Very few businesses spend money where they don't have to in my experience and the JBL's will probably be "close enough" to the x-curve by just mounting them on the wall, so why spend the money to EQ them?

I could certainly be wrong about that, but there must be a market for speakers with this approximation of the x-curve baked in or JBL wouldn't bother with it. If you're using EQ a baked in x-curve is senseless, but if you're not it makes total sense.

This is is all just deductive reasoning on my part, so take for what it's worth
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post #30 of 84 Old 09-10-2014, 05:22 PM
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But there is always the "close enough" factor. It's hard for me to believe that every theater has a professional calibrator come in and EQ when new speakers are installed. In fact, given the cost I would bet that even if the theater had the space professionally EQ'd it probably happened before the grand opening and likely will never happen again unless they are very successful and profitable. Very few businesses spend money where they don't have to in my experience and the JBL's will probably be "close enough" to the x-curve by just mounting them on the wall, so why spend the money to EQ them?

I could certainly be wrong about that, but there must be a market for speakers with this approximation of the x-curve baked in or JBL wouldn't bother with it. If you're using EQ a baked in x-curve is senseless, but if you're not it makes total sense.

This is is all just deductive reasoning on my part, so take for what it's worth
It's actually not quite that bad. The larger chains have theater techs that keep things working by making periodic maintenance visits, and yes, theaters are EQ'd and periodically checked. The standard EQ is built into Dolby processors (the "B" chain). Back when I was familiar with those things, there was actually a 1/3 octave equalizer card that you put on an extender to get it out of the card frame, tweak little trimmers to get it right, then re-insert it back into the cage out of harms/hands way. Not sure how the current product does it, but I'd guess via computer interface. THX has a rather well defined means of confirming theaters meet spec, but their re-certification program kind of fell apart. It's the small, independent theaters that would probably not keep things maintained, not picture either. The smaller "art houses" are often quite well done.

Typical theater EQ is done by using a spacial/temporal average with a real-time spectrum analyzer. For THX, they use 4 mics spaced around the room, then "multiplexed" during an averaging interval.

Theaters do blow drivers, and routine tech visits catch them if someone doesn't complain first. I don't go to the theater much at all anymore since HT, but it was rare for me to get through reel 1 without getting up to gripe about something. Since digital cinema, I haven't done that much, though a blown center channel HF driver will cause me to demand a refund. Which, by the way, is what we ALL should do. A theater MUST account for refunds, it's the only way to accelerate maintenance. Just a rain-check won't trigger the same chain of events. Demand a full refund, and be ready to leave, the theater will get fixed right up quickly.
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