What is the LFE input??? - AVS Forum
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post #1 of 10 Old 07-30-2007, 09:46 PM - Thread Starter
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I'm getting the subwoofer for my home theater setup, but I'm really confused when it comes to the inputs. I believe there are three different inputs on the back of most subwoofers, red & white rca looking ones, the spring(?) connectors that are look like regular speaker ones, and finally the LFE.

My knowledge is very limited in such regard however, as far as I understand it, the single-cable input so called "LFE" is for the 5.1 home theater setup whereas it represents the 0.1 from 5.1. Also, I heard something about LFE is to bypass the crossover(?) section of the subwoofer, and this is where I get really lost.

What does the LFE stand for, and what does this input do? Can this be considered as the digital input of the subwoofer (not compressed) like the opticals and coaxials???
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post #2 of 10 Old 07-30-2007, 10:08 PM
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which subwoofer are you looking at?

LFE stands for low frequency effects

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post #3 of 10 Old 07-30-2007, 10:26 PM
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Quote:
Originally Posted by Gaytoray View Post

I'm getting the subwoofer for my home theater setup, but I'm really confused when it comes to the inputs. I believe there are three different inputs on the back of most subwoofers, red & white rca looking ones, the spring(?) connectors that are look like regular speaker ones, and finally the LFE.

My knowledge is very limited in such regard however, as far as I understand it, the single-cable input so called "LFE" is for the 5.1 home theater setup whereas it represents the 0.1 from 5.1. Also, I heard something about LFE is to bypass the crossover(?) section of the subwoofer, and this is where I get really lost.

What does the LFE stand for, and what does this input do? Can this be considered as the digital input of the subwoofer (not compressed) like the opticals and coaxials???

LFE stands for Low Frequency Effects. LFE effects are recorded in the the .1 channel in multichannel DTS, DD, etc recordings and is recorded at a higher DB level.

When setting up a sub the reason you see most recommend to bypass the subs crossover is because the receiver will have a crossover settings also and you don't need 2 crossover settings possibly conflicting with each other.

All you need to do is set this in the receiver and the one in the sub is not needed. Some subs will have a crossover bypass switch and others will not. All you do on those is turn the crossover knob all the way up which is basically the same as bypassing it.
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post #4 of 10 Old 07-31-2007, 02:20 AM - Thread Starter
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Quote:
Originally Posted by Jakeman02 View Post

When setting up a sub the reason you see most recommend to bypass the subs crossover is because the receiver will have a crossover settings also and you don't need 2 crossover settings possibly conflicting with each other.

Okay, so the best way to connect the subwoofer to receiver is with the LFE. This may be a bit off the question, but I keep thinking that the receivers would power the subs if use any kind of bypassing method. The 200-watts sub will always do 200 no matter what the receiver's output is?
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post #5 of 10 Old 07-31-2007, 09:54 AM
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Quote:
Originally Posted by Gaytoray View Post

Okay, so the best way to connect the subwoofer to receiver is with the LFE. This may be a bit off the question, but I keep thinking that the receivers would power the subs if use any kind of bypassing method. The 200-watts sub will always do 200 no matter what the receiver's output is?

Short answer - yes. The receiver is simply sending LFE audio information to the sub; the amplifier in the sub is providing the power to drive the speaker, regardless of what the sub's crossover is set for.

Ross
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post #6 of 10 Old 07-31-2007, 10:03 AM
 
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Quote:
Originally Posted by Gaytoray View Post

Okay, so the best way to connect the subwoofer to receiver is with the LFE. This may be a bit off the question, but I keep thinking that the receivers would power the subs if use any kind of bypassing method. The 200-watts sub will always do 200 no matter what the receiver's output is?

NO...Most every AVR's LFE output level is controlled by the AVR's volume control thereby effecting the subs output level...Eg...The AVR's volume is set @ '5' and the Subs gain is set to '50%' of the total output amount...The sub will not be outputting 100Watts...The AVR if turned to '50' will in turn have the subs output increased due to the increase of the input level which is controlled by AVR's LFE output...

Now IF you use fixed outputs from the AVR and NOT the LFE jack and you set the sub to '50%', then yes the sub will always output 100Watts no matter the volume the AVR is outputting...

Make sense now?
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post #7 of 10 Old 07-31-2007, 10:19 AM
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Quote:
Originally Posted by Splicer010 View Post

NO...Most every AVR's LFE output level is controlled by the AVR's volume control thereby effecting the subs output level...Eg...The AVR's volume is set @ '5' and the Subs gain is set to '50%' of the total output amount...The sub will not be outputting 100Watts...The AVR if turned to '50' will in turn have the subs output increased due to the increase of the input level which is controlled by AVR's LFE output...

Now IF you use fixed outputs from the AVR and NOT the LFE jack and you set the sub to '50%', then yes the sub will always output 100Watts no matter the volume the AVR is outputting...

Make sense now?

Agreed, as far as the absolute amount of power/volume is concerned, but the receiver is not providing the power to the subwoofer - the sub's amplifier is doing that. If the sub gain is set to zero, the receiver is not going to drive the sub. And the bypass setting on the sub doesn't influence that.

Ross
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post #8 of 10 Old 07-31-2007, 12:37 PM
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... nor is the "power" constant or absolute. It is determined by the voltage provided by receiver to the amp in the sub. The amp will allocate the power to reproduce that voltage into a signal (volume) based on the received voltage at any given instant, whether the output is fixed, variable or LFE, on the source material (movie soundtrack). Depending on how it's interconnected, either the AVR/Pre-Pro controls the voltage (for LFE) or the internal x-over of the sub divvies up the signal(s) to either go to the sub's driver or back to the receiver, minus the desired lower frequencies (for what you refer to as "fixed").

If you're referring to "fixed" outputs as a tape loop. That's not a good recommendation for a sub. If you refer to "fixed" as Pre-in/Main-out, then that's a whole different setup and requires settings in the AVR or Pre-Pro and the sub that are totally different than for what "LFE" is intended.

As an example, setting the volume control on the sub at 50% and the receiever's sub output level to +5 only sets a "limit" it does not specify a contant power/wattage. So no... it will not "always" output 100 watts.
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post #9 of 10 Old 08-02-2007, 12:22 AM - Thread Starter
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Quote:
Originally Posted by RTracey View Post

the receiver is not providing the power to the subwoofer

Thanks all for replying. I guess this is the answer I was looking for, or the question I should've asked. Does the receiver provide power to the subwoofer like it does to the regular speakers. Hmm... that sounds confusing lol

Oh, almost forgot. What's the difference in SQ between using LFE inputs and the red & white inputs?
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post #10 of 10 Old 08-02-2007, 03:36 AM
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The SQ of the speaker stays the same.

The LFE input bypasses the crossover. It's used with the receivers "sub out" as the receiver has already channeled the lower frequencies to it.

The red and white are used with receivers that have stereo (R/L) sub outs (ex. H/K 745 7.2 and their stereo receivers) or with R/L pre out when there is no sub out available. Then the sub's built in crossover should be used.
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