FAQ - High Level and Low Level Inputs

Member 639844

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Every now and again I see questions asking about these inputs on subs, and there seems to be some confusion, so I thought I would post a thread explaining this that could perhaps be added to the FAQ section. I'll try answer this to the best of my knowledge.

The basic answer to what these do, is essentially they do the same job, they just do it a slightly different way. They are both inputs, and they both take a signal from a source to produce the bass content in material. The main difference is that the low level input is designed to work with the LFE channel encoded into movie material you find on DVD's and BR's. The high level input is designed to work with the normal speaker channels, and is really left over from the days before processors and digital soundtracks with a .1 channel existed.

For a more detailed explanation of what they do and how to use them, I'll explain them one at a time.

First is the normal LFE input. This is typically seen on all modern processors and AVR's. The LFE channel is a discrete channel the carries the Low Frequency Effects added to movies. This is in addition to the standard speaker channels. Some processors have 2 sub outputs, but they both use the same singular LFE signal, so for the sake of this guide, we'll ignore this and talk of the LFE as a single sub channel. A typical LFE input on a subwoofer is a phono socket input, and his input will have its own crossover and gain controls. The gain is used to match the subwoofers output to the rest of the system. The crossover is used to select the crossover frequency at which the subwoofer will cross into the frequency range of the speakers. Pretty much all processors I know of also have these controls integrated into the processor, so the controls on the sub are somewhat not needed, but they are included anyway just in case.

The main use for the LFE input is for use in a bass managed system, like a home theater with a dedicated subwoofer output.

The high level connection does not use the low level phono connection. The high level connection instead takes a full range speaker signal. Typically this is done with a cable that connects to the front left and right speakers. This cable reads the signal, and then the subwoofer reproduces the bass present in this signal. This connection also has a crossover and gain control, and in the case of the high level connection, this is important, as there are no controls for this for this connection method in a normal processor. The gain works the same as for the low level connection, and balances the output of the subwoofer to match the rest of the system. The cross over also controls the crossover point at which the subwoofers frequency range crosses into the frequency range of the speakers.

The main use for the high level input is for using a subwoofer in a stereo system, or other non bass managed system.

I'll try and explain the differences in how these two connection methods should be used. To do that though, we first need to understand how the channels are encoded for a digital soundtrack, so I'll cover that for the benefit of anyone that doesnt fully understand this first. If you know this stuff, you can skip the next paragraph.

In a normal full range speaker system the full frequency range is sent to the front left and right speakers, and any other speakers that the system might have. With a digital sound track, this remains unchanged, but we have the addition of the .1, which is the LFE channel. In a multi channel system, the speaker channels still have this full bass content in them, as well as this LFE bass channel, but the processor gets involved. When you tell the processor you have a subwoofer connect, the processor will filter out the bass content from the speaker channels, and re-direct this bass to the subwoofer. This is what the speaker crossover settings do. The result is then that the subwoofer is responsible for playing this re-directed bass from the speakers, as well as the LFE content.

So, how to best use the connections. Well in a typical bass managed setup, like a home theater setup, there isnt really any need for the high level connection, as the low level connection takes care of this by means of the redirected bass being sent here, as well as the LFE content in movies. This doesnt mean that the high level cant be used in a HT system, because it can, but for it to work, the system has to be used a certain way. The high level connection requires that the speakers get a full range signal, so to use the high level connection method in a bass managed setup, you must ensure that the speakers receive a full range signal. Typically, this would never happen in a home theater setup, so it requires user input to ensure this does happen if you want to use the high level connection method.

This might lead you to ask if there is any point using the high level connection, but for some there might be. Firstly there is a subtle difference between the crossover typically used in the high and low level connections. In simple terms, the crossover for the high level connection will usually use a more gradual slope, which in theory could lead to a smoother integration between sub and speakers, where the speakers are full range. This leads to the second important point. Speakers being run in full range mode will not crossover according to the setting in the processor, instead they will output material down to what ever frequency response they are capable of, so this is why the crossover on the subwoofer for the high level connection is more important. The crossover frequency should be matched to the natural low end frequency response of the speakers being used, and this will vary from speaker to speaker. If you are using small sats, then there seem little point in using the high level connection, but if you have larger more full range speakers, then for music this may be preferable. In my own experience, larger speakers will have their character changed when filtered by a processor at 80hz, and this can impact music negatively. If this is the case, then running the high level connection can restore the speakers natural character, while still allowing a subwoofer to improve the low end response, and the end result can be positive for musical listening experiences.

There are two main ways I have seen high level connections offered. I have owned subs with both but only ever used one. The first is via a single input using a Speakon connector. This will read the signal from both the front left and right speakers, and produce the bass content in them upto the crossover frequency you select on the sub. The speakers have no filtering provided for this type of connection so will run full range.
The second is with speaker terminals on the subwoofer, with an input and output. This type of connection allows you to filter off the low frequency response of the speakers off if you choose. As the signal from the amp if fed into the subwoofer, the bass is produced by the sub, then the remainder of the signal is fed to the speakers. This essentially provides the same function os the crossover settings in an AV processor, so the low end frequency response of the speakers is filtered off with this setup according to how you set it on the subwoofer.

Hopefully that should cover the issue well enough to explain it, and allow people to decide on if the high level connection is for them. Hopefully it will also resolve some of the confusion as well.

If there are any glaring errors anyone can see, feel free to add to the thread and I will make corrections where needed.
 
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very good write up dan and this should be a sticky, so if a mod could sort it that would be great.
 
I know :D
 
In a normal full range speaker system the full frequency range is sent to the front left and right speakers, and any other speakers that the system might have. With a digital sound track, this remains unchanged, but we have the addition of the .1, which is the LFE channel. In a multi channel system, the speaker channels still have this full bass content in them, as well as this LFE bass channel, but the processor gets involved.

I've often been curious about this. In a surround sound mix, why would/do they send full frequency range to the speakers? Do cinema's have full frequency range speakers for front mains and surround? Majority of people at home don't seem to have speakers effectively capable of full range 20Hz-20Khz.
Every time people have the "large" vs "small" discussion, its recommended best to let the subwoofer handle the lower frequencies. When they mix for surround sound, couldn't they just limit the front and surround channels to a certain frequency and then send everything below that to the subwoofer channel?
 
I've often been curious about this. In a surround sound mix, why would/do they send full frequency range to the speakers?
What if you dont own a sub?

When they mix for surround sound, couldn't they just limit the front and surround channels to a certain frequency and then send everything below that to the subwoofer channel?
They sort of already do, as this is what the LFE channel is. Its that the normal channels still contain all the frequency range just in case someone wants or needs the speakers to play below 80hz.
 
What if you dont own a sub?

They sort of already do, as this is what the LFE channel is. Its that the normal channels still contain all the frequency range just in case someone wants or needs the speakers to play below 80hz.

Dan does the main fronts do lower than 20Hz or is that there role off point.
 
The full range is encoded into the speaker channels, but it wont have the potential to be 10db hot like the LFE channel is. If the speakers cant go down to 20hz or whatever, then there will be components in the crossovers inside the speakers that will filter out the low end they cant produce.
 
Can I add a "bit", subject to it being correct? I've also seen questions about bass management several times and answered a few, so an FAQ is a great idea!

In terms of input signals, most cases will either present a two-channel stereo input (2.0) or a multichannel mix with a dedicated LFE channel (that's what the .1 is in 5.1). In the case of a two-channel stereo mix or a multichannel mix without a dedicated LFE channel (ie: 3.0 or 5.0 for example), each channel has the potential to have full frequency range information. Conversely in a mix with a dedicated LFE channel, each non-LFE channel still has the potential to have full frequency range information, but you ALSO have the .1 LFE channel which has additional LFE and (as already mentioned) is usually mixed 10dB hotter.

High Level inputs on a simple stereo system

If all you have is a simple stereo amp with only (speaker) high-level power amplified outputs, then the simplest choice you have is to connect your subwoofer's high-level inputs to the high-level outputs of the amp. On an active subwoofer, its high-level input impedance is many orders of magnitude higher than the speakers' impedance (eg: 100KOhms vs 6 Ohms), which effectively means that the subwoofer is drawing an insignificant amount of current from the amp's output - so you're not going to be starving your speakers of any power if you connect this way.

Since the sub would now be getting exactly the same frequency ranges as the speakers, you need to filter the signal so that the sub only reproduces the very low end; therefore subs have an adjustable low-pass filter (crossover) which should be tweaked so that the sub integrates well with where the two stereo speakers' low end drops off.

Low level inputs & multichannel mixes

I think the easiest way to explain this is with a 5.1 movie soundtrack; this will contain five surround channels, plus a dedicated LFE channel. Provided you have a speaker setup with a subwoofer, the LFE channel will be sent to the subwoofer via the AVR/processor LFE Output straight away. On top of this, the system-wide or per-channel crossovers that you can set on AVRs/processors apply to the 5 full-range channels, and define below what point the AVR/proc will redirect those 5 channels' signal to the sub; this then gets added to the LFE track and sent to the sub. This is not a hard cut point of course.
Some subs also have a crossover setting for the low-level LFE input, or the same crossover applies to both low and high level inputs. If you've only connecting an AVR to the sub, then you can safely set the sub's crossover to bypass or its highest frequency setting; all this means is that the AVR is doing all the filtering, which is what you want.
If however you're connecting both high and low level inputs and you only have one crossover on the sub for both, it means you have to fiddle a bit more and go between bypass for low-level and whatever integrates best for high-level...

A few things to note here on additional AVR settings:
"Pure Direct" or whatever each manufacturer calls it: in the simplest terms, what's in, goes out. If you have a two-channel input, the receiver bypasses all processing / filtering / etc and outputs just two-channel stereo. Nothing gets redirected/copied to the sub.
"Large speaker" setting: all this means is that you're telling your AVR/proc that that particular speaker can handle the full frequency range. If you don't have a sub, then the AVR will probably redirect the LFE channel to your "Large" speakers as well.
"Extra Bass" setting: provided you have "Large" speakers defined, all this does is send the unfiltered full-range channel signal to that particular speaker, and ALSO copy the filtered low-end of that channel to the LFE Outputl. This may sound appealing at first, but it will usually end up sounding quite muddy due to the same low frequency signal coming from physically different sources in different positions; don't get confused here: having two identical subs may improve things, but having a sub and two speakers trying to do the same thing just doesn't work nearly as well.

Other things to keep in mind
In some cases, you can of course connect both low and high level inputs of a sub to the same system. The low-level will function as usual; the high-level will also function as usual, and as long as the crossover setting on the sub is set correctly (and below the AVR's setting for the channels you're using for the high level connection), then you should be fine. It's confusing though and a little complicated, so don't do it unless you have to and you understand it. If you're connecting two different systems to the sub (one to low and one to high level inputs) then you should also be fine, but again if you only have one crossover on the sub which applies to both inputs you have to do a lot more manual fiddling.

Hope this helps!
 
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Great thread guys. I've got a proper sub on order to replace my present weakling sub. I'm intending to use both high and low imputs simultaneously to extend my 38Hz mains musically and get LFE for AV work.

As far as big vs small goes, I have my fronts set to large as they are capable of reasonable bass and the sub can simply be turned off late in the evening without loosing everything. Ideal after a back-shift... So, another reason for a full range mix being used.
 
Many of us have speaker arrays with various crossovers.


As so much equipment uses a global crossover point (processors & players when using analogue outs) often a compromise has to be reached.

It is not be unusual to see folk using:

Front three speakers capable of 50/60Hz and the rears may be 80/100Hz

This leaves the front stage too “small” to set to “large” (not physical size) as well as the rears needing “small” of course. Hence you have to use a global crossover of 80/100Hz (could even need to be slightly higher)

At this point a subwoofer can start to draw attention to itself, which is not good.


SO, using the speaker terminal method on the sub can this work?

Downsides?

Or fatally flawed, don’t attempt!


Set rears to large and use high level connections to those speakers and set the high level sub crossover accordingly?

Then use a more appropriate crossover for the front three (50Hz in this scenario)

This would only have the sub drawing attention to itself on the lesser used rear channels?


Hope my description makes sense? and would value any thoughts

@Member 639844 @sergiup

EDIT Update:

Ahh just thought you probably cant use both hi/low level at the same time?:( or it is sub design dependant?
 
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Hi - yes, that does make sense. I'll start off by saying that any reasonable sub should be able to play up to 120Hz or so without attracting attention to itself.

If you can set different crossovers for each channel then do so and just get the rear channels playing as low as they're comfortably able to, and everything else will go to the sub.

I wouldn't overcomplicate it by having high-level from the rears only - too much of a headache to figure out and EQ.
 
Hi all :)

I have successfully managed to connect my all-in-one sub speaker out to my BK XLS200 high level input.
Very happy with the sound, however when I turn the AIO off I get a fairly loud hum from the sub.
Ground loop I guess and, if yes, how do I get rid off it?

TIA ;)
 
Anybody know whether when using the high level inputs if the high level out from the subwoofer applies of high pass filter to the speaker signal as well as the low pass filter to the subwoofer? Essentially is it a crossover like you use in your AVR or does it still send a full range signal to the subwoofer?
 
Some subs have high pass on the speaker level outputs, ie SB12+ so need to add that to your FAQ. This functions to a Bose/PC speaker system where you go source--->sub--->speakers so source sends full range audio to the sub, then the sub filters out low diverts it to cone (low pass) but passses high frequency to the speaker outputs (high pass)
 
Hi everybody:

First of all I would like to thank you for all the useful advices I can found in this forum. Said that, I have a question, maybe out of date, regarding the next quote posted by Member639844...

If you are using small sats, then there seem little point in using the high level connection, but if you have larger more full range speakers, then for music this may be preferable.

I want to pair a Marantz NR1506 (5.2) to 5 CA Minx Min22 (120 Hz - 20 KHz) with two Canton ASF 75 SC subs, due to space issues. Since the lowest frequency value for the Minx is 120 Hz, I thought that connecting the subs to the LFE output of the receiver I would lose the stereo imaging of frequencies above 80Hz (thaose you can still locate in space?). To solve this I thought that it would be a good idea to connect the subs using the High Level Input, thinking this connection would be more appropiated for small sats than for bigger speakers. But the quote posted says is the other way around and I don't really understand why (I'm newbie here). Is because these kind of speakers shouldn't receive a full range signal? In that case could it be fixed by connecting a crossover before the speakers and the subs. In case it would be doable, i guess I'd have to set the system without subwoofer, fronts to big and the rest (center and surrounds) to small.

Thanks for your help, and please, apologize me for me English :)

Regards,

Carlos.
 
I think in your case it will work to use the high-level input. As you say, there can be some stereo bass. If you only had a single sub, it would make sense to use the LFE output but as you have two, and presumably will colocate one with each sat speaker, go with high level and hopefully you'll enjoy a nice full sound in full stereo :)
 
This is a very good writeup,

In a HT situation, if I have a sub which ONLY has line level inputs, am I missing anything by using these?

i.e. does the LFE content get redirected to the front L+R when setting the receiver to 'no sub'?

If not then using a line-level input on a subwoofer on a HT system will result in some sounds/effects/gain on certain freq effects being missed.

As far as I can tell, the LFE gets redistributed to L+R but it's hard to clarify this.
 
Do you mean line or speaker level?

If you mean line level (usually a single RCA from the receiver to the sub) then if you set the receiver to "no sub" then the sub is doing nothing.
 
This is a very good writeup,

In a HT situation, if I have a sub which ONLY has line level inputs, am I missing anything by using these?

i.e. does the LFE content get redirected to the front L+R when setting the receiver to 'no sub'?

If not then using a line-level input on a subwoofer on a HT system will result in some sounds/effects/gain on certain freq effects being missed.

As far as I can tell, the LFE gets redistributed to L+R but it's hard to clarify this.
Technically an AV Receiver manufacturer can re-direct LFE into the speaker channels when you select no subwoofer, but there are no manufacturers I know of currently that do this as it has the potential to damage speakers.

Line level essentially just takes your left and right channel signals and sends them to the subwoofer, so your subwoofer when connected to the front left and right channel pre-outs will play a copy of the bass the speakers are producing, very similar to what the Rel high level connection does. The net result, unless stated otherwise by your manufacturer, is that you would lose the LFE dedicated channel. What content you actually lose if you lose the LFE part of the sundtrack when doing this depends in part on how each discs soundtrack is mixed, as the sound engineers have licence to mix the channels as they please.
 
Technically an AV Receiver manufacturer can re-direct LFE into the speaker channels when you select no subwoofer, but there are no manufacturers I know of currently that do this as it has the potential to damage speakers.

Actually, this is incorrect. Yamaha explicity describe what happens to the LFE .1 channel under various conditions, see below. The manual for my RXV681 also explicitly states that 'Large' speakers with 'No Sub' will redirect LFE to front left and right and describes various situations. I have also seen but can't confirm similar from Denon.

This makes sense as the AV receiver manufacturer doesn't want you to miss out on the LFE channel (which as you say, can vary in it's utilisation per engineer/sound mixer). What happens if you've got a set of gigantic floorstanders with 10'' woofer cones but don't want a sub? ;)

What effect does the Speaker Size and LFE/Bass output settings on my Yamaha A/V Receiver affect the output sound? - BD-S671 - Blu-ray Disc Players - Blu-ray Disc™ Players - Audio & Visual

The question regards slightly older Av receivers and the settings nowadays are different. I can confirm that the brand new RXV681 manual has a similar clarification on page 112. The more modern units require less fiddly settings - simply setting front speakers to 'Large' and sub to 'No Sub' will redirect LFE to fronts.
 
Actually, this is incorrect. Yamaha explicity describe what happens to the LFE .1 channel under various conditions, see below. The manual for my RXV681 also explicitly states that 'Large' speakers with 'No Sub' will redirect LFE to front left and right and describes various situations. I have also seen but can't confirm similar from Denon.

This makes sense as the AV receiver manufacturer doesn't want you to miss out on the LFE channel (which as you say, can vary in it's utilisation per engineer/sound mixer). What happens if you've got a set of gigantic floorstanders with 10'' woofer cones but don't want a sub? ;)

What effect does the Speaker Size and LFE/Bass output settings on my Yamaha A/V Receiver affect the output sound? - BD-S671 - Blu-ray Disc Players - Blu-ray Disc™ Players - Audio & Visual

The question regards slightly older Av receivers and the settings nowadays are different. I can confirm that the brand new RXV681 manual has a similar clarification on page 112. The more modern units require less fiddly settings - simply setting front speakers to 'Large' and sub to 'No Sub' will redirect LFE to fronts.

As I say, its left up to the manufacturers to do what they want with the LFE. Things change that much from year to year this isnt somethign I spend time on keeping up with that much. The main speaker channels carry the full audio range. The LFE channel can then duplicate the low frequency part of the speakers content plus add in any LFE specific content, again as the sound mixer decides. The problem with sending LFE to the speakers is that the LFE channel specifically has an additional 10dB extra dynamic range, and the reason the speaker channels dont have this is they just cant handle it. The potential is there to damage speakers trying to play the LFE content correctly, but an AVR manufacturer can account for this and reduce LFE material (down)mixed into the speaker channels if they wanted to. This becomes a bit of a grey area if you ask me though, and you could argue down-mixing the LFE into the speaker channels without the 10dB additional dynamic range is also a bit pointless, as this extra range is often required to make LFE specific effects noticeable.

Ultimately, I dont think its much of an issue to lose the LFE channel (if you do on your particular receiver). You still get 99.xxxxxx% of the frequency spectrum anyway. Whether you use a sub with high level only or just have highly capable floorstanding speakers, from a purely 'whats on the disc' point of view, you can still enjoy movie soundtracks just fine. Obviously, adding in a subwoofer to any system will improve its bass response, and I personally dont see the point of not utilising the LFE channel when you have a subwoofer in your system.

With respect to the Yamahas (Im going to check up a little more on this with the new AVRs), I would advise caution to anyone setting up their AVR to send LFE content to their speakers, and its not something I would do personally with anything but the most capable of speakers.
 
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This becomes a bit of a grey area if you ask me though, and you could argue down-mixing the LFE into the speaker channels without the 10dB additional dynamic range is also a bit pointless, as this extra range is often required to make LFE specific effects noticeable.

You're right about different manufacturers making a choice - Yamaha is fairly out of your hands but others do treat it differently.

We're discussing a hobby where people argue about the effectiveness of a shielded mains cable on their amplifier performance - you're damn right I don't want to miss my LFE (even down stepped by 10dB through a speaker that can't reach that frequency range) ;)

The purpose was generally to ask - if I take the speaker level signal to a subwoofer (not line/sub-out level) - will I miss out on the LFE channel and it just clarifies that you won't miss out. Front speakers aren't the ones intended to benefit from the LFE being sent to the fronts, ironically enough.

This is likely to be the purpose of sending LFE to the fronts - for a subwoofer without a line level input, not for the benefit of the fronts. You can compensate for the 10dB drop on the sub gain itself.
 

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