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The LFE test....

 

Silver Member
Username: Thx_3417

Post Number: 777
Registered: May-05
Introduction

Films with that big shaking rumble in the tummy abyssal depths of low end with almost unrelenting pressure....

The L.F.E Low Frequency Effects, over the years the L.F.E as provided some fantastic effects to the on screen action, if not more for taking on some with high dynamics that get most home cinema users reaching for the sub bass volume before it has been driven to the point of Armageddon?

So with this thread, I'll be looking at the films that have highest range along with the frequency response, looking at the response on a VU meter which controls the flow of sub bass and L.F.E on a multi-channel audio mixer, I've set the AVR Kenwood KRF-X9050D THX select to 0db and using the DTS calibrating disc to align the inputs and outputs from all RCA phones.

The reason for this is clear EQ as to be apply to the whole program set-up to get smother timber balance of the fronts and the split-surrounds and some other channels too, like the centre back and the upper centre channel, but I'm not hear to give a total discussion on that the goal hear is to explore the L.F.E.

First I'll start of with, Star Wars Episode 4 A New Hope.

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Well this was a whole of fun, so hears my report.

Opening the star destroyer rocketing overheard with the LFE, adding the extension to the scene and giving the wow feeling responding from 25Hz though to 40hz and 60hz with 25Hz having the highest peak, but this doest overpower nor spoils with too much.

Less is more, because as the film continues to play on the LFE will get big with its dynamics with what is presented on the screen, so playing at 98dbc @1m and giving me an accurate response on the films playback is satisfactory.

I've gone though the whole film note the time and the SPL level against frequency response on the RTA as well, the results so me that its better and wiser to keep to the technical tolerances of the THX sound system operational parameters.

At 56mins the death star destroying the planet with a devastating huge explosion 105dbc @1m and peaking at 25Hz 40hz slightly less and 62Hz all adding to the feel and the awesome power that this planet destroyer can unleash.

With lots of LFE effects playing at randomized times throughout the destruction of the death star coming in at 107dbc @1 topping of the film the wave of low frequency air pressure swooping down from 40Hz and climbing upwards to 25hz as it gently presses on me, I'm happy this as played well the JBL 4645 THX professional cinema sub bass unit can easily peak @ 120db but I'll keep this to a realistic cinema level, while the fronts and the split-surround-EX can also measure up to the same level.

The next film I'll be looking at will be Superman the Movie, and leaving the levels and settings as they are I'll be very impressed with its mighty powerful mix LFE style that's going to blow me away, I wish....
 

Silver Member
Username: Thx_3417

Post Number: 802
Registered: May-05
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So with the opening of "Superman The Movie" the score by John Williams gives the power of this classic film slam on the LFE at 1m 48s there is a huge slam at 100db @1m with peak at 40Hz (-7dbvu) the style of the opening is one of openness.

The highest peak in the film or peaks, when Krypton explodes with a devastating KABOOM, coming in at 21m 40s 109db (-3dbvu) frequency 25hz third in the scale 40Hz being the first 62Hz being the last peak, the JBL 4645 handled it without no strain or popping.

When one of the rockets reach there target, with the impact coming in at 109db (-3dbvu)
40Hz with most random LFE effects at 2h 2m 10s 100db and 106db (-5dbvu) when lightning strikes the air-force one KABOOM.

When Superman pushes the huge rock over to block the path of thousands of tons of water comes crashing towards a small town, the rock kicks at a small 91db 2h 9m 7s and climbs up to 105db (-4dbvu)

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With the closing credits rolling the LFE is neutral with just the bass from the three-screen and the split-surrounds in there EX mode.

So what's next "Apocalypse Now" is a long film and with two versions of it to test, this will take two days to complete this.

In my written notes there is a whole lot more, and it was trying and taxing too, do I what to really do this again yes, its fun.
 

Gold Member
Username: Paul_ohstbucks

Post Number: 1931
Registered: Jan-05
Just about any of the new action adventure releases have incredible LFE effects.

Dont ya think??
 

Silver Member
Username: Thx_3417

Post Number: 805
Registered: May-05
Paul

There are indeed some real aggressive films with cursing distortion or popping with the possibility of bottoming out, and some owns having chosen the wrong type of sub bass unit for there home cinema.

If you where to buy some additional audio equipment, to add on to your home cinema a simple audio mixer and send the LFE input into one of the mixers line inputs, and outputting it to the sub bass units line input, or inputs.

Next play a film like "Star Wars Episode 4 A New Hope" and there are a few parts in this film where the LFE really does go over the top, the part where the Death Star blows up the planet the peak level should not go over the 0db level.


If you have THX, I think you do have THX don't you Paul, if so set the THX peak management to 0dbmaking sure the sub is turned off as this THX peak management outputs a raw pink noise!

Once done turn the sub back on and playing the planet being destroyed bit over a few times the LFE on this ranges from 25Hz peak with 40Hz peaking secondly and 62Hz peaking lastly just as the sound starts to fade slightly but still the LFE climbs upwards, it is the LFE that you should be looking at closely and keeping it at 0db peak.
 

Gold Member
Username: Paul_ohstbucks

Post Number: 1934
Registered: Jan-05
there aint nuthin' that can touch my SVS.

The CVs??.......sure, but nothing exists that can touch the SVS monster.
 

Silver Member
Username: Thx_3417

Post Number: 817
Registered: May-05
Well after going though a few films now, this test is starting to show some interesting results.

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1# Master and Commander with peaks at (0dbvu) and down to 25Hz the aggressive cannon firing at the opening so far I haven't seen a film that surpasses it.

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2 # The Lord of the Rings part 2, with peaks at (-2dbvu) down 40Hz, there is huge explosion when the castles walls are breeched.

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3 # I' Robot (-2dbvu) peaks at 25Hz, the opening dream sequence, showing "Spooner" being saved by a robot, the score by "Marco Belrami" as lots of low end but short of "Master and Commander."

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4 # Star Wars Episode 4 A New Hope (-2dbvu) down to 25Hz the Death Star, as it unleashes it devastating power, and utterly destroying "Alderann."

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5 # "Superman The Movie" (-3dbvu) down to 25Hz, Krypton explodes due to there own star in the galaxy KABOOM!

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6 # "U.S Marshals" (-18dbvu) down to 40Hz, with very little happen on the so called (SVS) plane crash scene, but still entertaining throughout.

I'll have to give, "The Fugitive" another go, to see if the fright-train scene is higher in the LFE department?

With "The Lord of the Rings" only partly analysed due to the running time it's the peaks that I'm looking at on the LFE and not sending the loudspeakers to small, sending the loudspeakers to small creates confusion with the LFE issue.

With these films playing on the JBL 4645 THX cinema approved sub bass, it difficult to find a film that it's not going to like, and since I've gone though some power house films so far with no signs of distortion or popping sound, I'm confident in its performance.

So with "U.S. Marshals" at 6 # that will drop like a fright-train?
 

Silver Member
Username: Thx_3417

Post Number: 822
Registered: May-05
So why not implement these techniques this into your home cinema, the use of an Audio mixer and EQ will make it less problematic, and you will gain more flexibility over the whole system.

It's easy and affordable with this you'll able to keep an eye on levels.
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