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LFE vs. RCA Subwoofer input question

REK2575

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Are there any advantages/disadvantages to LFE as opposed to RCA inputs on subwoofer? If the sub offers both inputs, and your preamp can connect to either -- is there a good reason to choose one over the other? I read somewhere in these forums that LFE has a passover ceiling of 120Hz. Is that true? Does it matter? (Just for context: I'm thinking about a single subwoofer as part of a 2.1 setup w/ bookshelf speakers, used for music listening only, not movies/AV.)
 

Kal Rubinson

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Where and how are you implementing the crossover between the main and sub?
What sub is it?
 
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REK2575

REK2575

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Where and how are you implementing the crossover between the main and sub?
What sub is it?

I'm considering buying a single, 8" sub, frontrunners being SVS 3000 Micro and Cambridge Audio Minx X301. Gotta keep it small due to space limitations.

I'm not entirely sure I understand the first question. I thought the crossover was set through the subwoofer itself? My setup is:

[Audio sources] --> Rotel RC-1572mkii Preamp -XLR-> Rotel RB-1552mkii Amp --> ELAC DBR 62s

The Preamp has 2 dedicated sub outs and single pair of rca pre-outs. The XLR outs go to the power amp.

I'm assuming I could hook up to a Subwoofer via either of the dedicated sub outs or via the unused rca pre-outs. Bad assumption on my part? If not, is one better than the other (LFE vs. RCA)?
 

GDK

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When I got my subs, I emailed SVS and they said to use the LFE input (which is simply the R channel of the RCA inputs) even though I was not using it for home theatre.
 

Kal Rubinson

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I'm not entirely sure I understand the first question. I thought the crossover was set through the subwoofer itself?
No. The SVS sub has an adjustable low-pass filter which only affects the upper limit of its output. There is no provision for rolling off the low end of your main speakers.
The Preamp has 2 dedicated sub outs and single pair of rca pre-outs. The XLR outs go to the power amp.
Those "dedicated sub outs" are just the mono sum of the main L/R output of the Rotel. There is no crossover function in the amp itself.
I'm assuming I could hook up to a Subwoofer via either of the dedicated sub outs or via the unused rca pre-outs. Bad assumption on my part?
You could since you will have only one sub. You could use one (or both) of the "dedicated sub outs" or both (not just one) of the unused rca pre-outs. I would recommend the use of the "dedicated sub outs" because I do not know how using both the XLR and RCA outputs of the Rotel at the same time might affect its performance.
 

Chrispy

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Often the LFE input on a sub will automatically bypass the sub's low pass filter since its assumed you're using a unit with bass management. I really hate when a sub labels a low pass filter as a crossover....its just misleading.
 
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REK2575

REK2575

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No. The SVS sub has an adjustable low-pass filter which only affects the upper limit of its output. There is no provision for rolling off the low end of your main speakers.

Thank you for the information and advice. How does one solve this problem though, provisioning for rolling off low end of main speakers -- is this the "High Pass"? (Forgive the extreme ignorance!) Options for setting a High Pass filter?
 

radix

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Thank you for the information and advice. How does one solve this problem though, provisioning for rolling off low end of main speakers -- is this the "High Pass"? (Forgive the extreme ignorance!) Options for setting a High Pass filter?

When I last spoke with SVS, they recommended using passive in-line high-pass filters on the sub pass-through outputs. They said none of their current subs will high-pass the output, it's only pass-through. I think Amir reviewed some of those passive filters a while ago. SVS suggested using Harrison Labs passives.

Marc
 

Kal Rubinson

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Often the LFE input on a sub will automatically bypass the sub's low pass filter since its assumed you're using a unit with bass management. I really hate when a sub labels a low pass filter as a crossover....its just misleading.
I agree, especially in this case where the LFE input is also the Line input for one channel. Also, in this case, the sub's low pass filter can easily be bypassed from the control app.
When I last spoke with SVS, they recommended using passive in-line high-pass filters on the sub pass-through outputs. They said none of their current subs will high-pass the output, it's only pass-through. I think Amir reviewed some of those passive filters a while ago. SVS suggested using Harrison Labs passives.
The use of the Harrison Labs filters is a clumsy solution since it is generally necessary to fiddle with the HP and LP filters in order to get them right. Fixed filters make that difficult.
Thank you for the information and advice. How does one solve this problem though, provisioning for rolling off low end of main speakers -- Thank you for the information and advice. How does one solve this problem though, provisioning for rolling off low end of main speakers -- is this the "High Pass"? (Forgive the extreme ignorance!) Options for setting a High Pass filter?
The Harrison filter will work but an adjustable HP filter would be better. I know they exist.
 
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REK2575

REK2575

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Still a little confused about Low Pass and High Pass - ?

If I understand correctly, Low Pass sets the freq. ceiling of the Subwoofer. If I set to 120Hz, sub ignores all signal above 120Hz. (correct on a purely conceptual level, i.e. leaving aside question of whether LFE or preamp override subwoofer's Low-Pass setting - ?)

High Pass though -- How do I prevent my DBR62s from outputting the low frequencies I want to restrict to the subwoofer?
 

radix

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Still a little confused about Low Pass and High Pass - ?

If I understand correctly, Low Pass sets the freq. ceiling of the Subwoofer. If I set to 120Hz, sub ignores all signal above 120Hz. (correct on a purely conceptual level, i.e. leaving aside question of whether LFE or preamp override subwoofer's Low-Pass setting - ?)

High Pass though -- How do I prevent my DBR62s from outputting the low frequencies I want to restrict to the subwoofer?

You need a filter between the preamp and amp. Passive RCA or active XLR or a miniDSP or an active crossover.
 

Chrispy

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Still a little confused about Low Pass and High Pass - ?

If I understand correctly, Low Pass sets the freq. ceiling of the Subwoofer. If I set to 120Hz, sub ignores all signal above 120Hz. (correct on a purely conceptual level, i.e. leaving aside question of whether LFE or preamp override subwoofer's Low-Pass setting - ?)

High Pass though -- How do I prevent my DBR62s from outputting the low frequencies I want to restrict to the subwoofer?
Keep in mind a crossover is where the slopes of a low pass filter and a high pass filter cross over each other.....a low pass filter is not a brick wall in any case, it is setting a rolloff point for the low pass filter....but if your preamp can't set crossovers (i.e. use bass management) all you have is the lpf on the sub to use and "blend" with your speakers. If you are thinking about the inline filters you might look at this https://www.audiosciencereview.com/...ison-labs-in-line-crossover-review-rca.33475/
 
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Chrispy

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There's also units like this
 
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REK2575

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I really appreciate all this information. So, specs on my preamp say this:

Tone Controls:

Bass: ± 10 dB at 100Hz

Treble: ± 10 dB at 10kHz

Does this mean that the Low Pass is set at 100Hz? There's definitely no option that I can see to set/adjust the crossovers myself.

(And not sure how to interpret the Treble. I get that I can boost or reduce signal by 10dB at 10kHz. But why 10kHz specifically? This is not the 'high pass' filter, right?)
 

Chrispy

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I really appreciate all this information. So, specs on my preamp say this:

Tone Controls:

Bass: ± 10 dB at 100Hz

Treble: ± 10 dB at 10kHz

Does this mean that the Low Pass is set at 100Hz? There's definitely no option that I can see to set/adjust the crossovers myself.

(And not sure how to interpret the Treble. I get that I can boost or reduce signal by 10dB at 10kHz. But why 10kHz specifically? This is not the 'high pass' filter, right?)

No, that's just a tone control. More like a two band equalizer....
 

DVDdoug

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Are there any advantages/disadvantages to LFE as opposed to RCA inputs
"LFE" is "strange terminology"... LFE (low frequency effects) is normally the "point one" channel in surround format and it doesn't include "regular bass" in the other channels. The LFE gets routed to the subwoofer ONLY so if you don't have a sub you lose the LFE.

AVRs have a built-in crossover and "bass management" options so the bass from all channels can be mixed and routed to the sub. And of course that includes regular 2-channel stereo sources. Usually that's called a "small speaker" setting, and it's the most common home theater set-up because most people don't have room for 5 or 7 (or more) full-size speakers that can reproduce bass.

Usually the easiest & best solution is get an AVR, which will have the full crossover with high & low pass. Or, many people just run full-range into the main speakers. You can also buy an active crossover or a MiniDSP. But, you still need a proper surround decoder and bass management if you want to get the LFE from surround tracks and mix it with the regular bass.
 

Chrispy

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FWIW a lot of two channel gear doesn't provide bass management, there are some units out there, tho. Many, if they even have a sub pre-out it is full band. Audiophile fear of subwoofers or something. :)
 

Chrispy

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"LFE" is "strange terminology"... LFE (low frequency effects) is normally the "point one" channel in surround format and it doesn't include "regular bass" in the other channels. The LFE gets routed to the subwoofer ONLY so if you don't have a sub you lose the LFE.

AVRs have a built-in crossover and "bass management" options so the bass from all channels can be mixed and routed to the sub. And of course that includes regular 2-channel stereo sources. Usually that's called a "small speaker" setting, and it's the most common home theater set-up because most people don't have room for 5 or 7 (or more) full-size speakers that can reproduce bass.

Usually the easiest & best solution is get an AVR, which will have the full crossover with high & low pass. Or, many people just run full-range into the main speakers. You can also buy an active crossover or a MiniDSP. But, you still need a proper surround decoder and bass management if you want to get the LFE from surround tracks and mix it with the regular bass.
Another peeve like lpf being labeled crossover :) I can see LFE being important if for some strange reason that's all you use your sub for, but to indicate external bass management is just annoying.
 

Kal Rubinson

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High Pass though -- How do I prevent my DBR62s from outputting the low frequencies I want to restrict to the subwoofer?
Exactly the issue. Using a low-pass filter will help balance the transition between the main speakers and sub and, equally important, it will remove the lows from the main speakers. The latter will increase power handling in the whole system.

OTOH, the SVS controls are quite effective and you can use them to optimize the sub's output by following the instructions.

It is unfortunate that, at this time, a stereo preamp or integrated amp that provides subwoofer output does not include an option for HP filtering of the main speakers. It is unfortunate but common.
 
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REK2575

REK2575

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"LFE" is "strange terminology"... LFE (low frequency effects) is normally the "point one" channel in surround format and it doesn't include "regular bass" in the other channels. The LFE gets routed to the subwoofer ONLY so if you don't have a sub you lose the LFE.

When you say LFE "doesn't include the regular bass in the other channels" -- that's very surprising to me. Doesn't one want the 'regular bass' signal sent to the subwoofer? "LFE" makes it sound like only the quite low 'effect' frequencies from AV content -- explosions in movies and the like -- are getting channeled to the sub, and your stereo speakers are left to carry the 'regular bass'. Is that correct?

And if it is, isn't that an argument for using the RCA pre-outs from the preamp to a subwoofer?
 
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