Bass missing on LFE channel - hi/Lo level inputs?

[ChrisA]

Hi

I was reading some sub reviews this week and noted in one a comment about poorly engineered LFE channels on 5.1 discs. It commented that this was the reason some brands allow connections at high and low level, the theory being that if the engineer misses anything on the LFE channel the amp will strip it out of the mix and pass it along the left/right outputs. It cited a couple of, apparently commonly known, examples, one being a missing elephant stomp in th eLion King.

Has anyone any experience of this? Is it a common phenomenon?

I’d always been led to believe the two connection types were to allow different settings for movies and music utilising the two types of connector – which is it?

Regards

Chris

PS you can probably tell that I don’t currently use a sub myself!!

[Cynar]

I can't see the point of a high level connection unless you have no low level connection available as with a lot of stereo amps.
If you have a receiver you should set all your speakers to 'small' so all the low frequencies (not just the LFE channel) are directed away from them and to the sub via it's low level connection anyway.
There's not many speakers about that can reproduce the lows as well as a sub can.

Originally Posted by ChrisA

Hi

I was reading some sub reviews this week and noted in one a comment about poorly engineered LFE channels on 5.1 discs. It commented that this was the reason some brands allow connections at high and low level, the theory being that if the engineer misses anything on the LFE channel the amp will strip it out of the mix and pass it along the left/right outputs. It cited a couple of, apparently commonly known, examples, one being a missing elephant stomp in th eLion King.

Has anyone any experience of this? Is it a common phenomenon?

I’d always been led to believe the two connection types were to allow different settings for movies and music utilising the two types of connector – which is it?

Regards

Chris

PS you can probably tell that I don’t currently use a sub myself!!

[ChrisA]

Thanks Betty, but I thin you're missing my point. If I do this with just a single .1 cable attached, am I going to miss things that have not been properly mixed by the engineer?

C

[mojogoes]

Hi........i have my monolith sub connected in both ways and must admit i've never come across such as you describe when playing a movie.......although i have both gains set at 11oclock when i'm watching TV or playing a cd (music) disc the sub output is less for some reason and the only way of upping the spl output is to then raise the frequency switch to around 80hz.

Some dts disc's i've had when set to just dts don't give 7 channel output only 5 and some dts formats do.....you then after change over to noe6 or dd ex but the sub channel response in which ever scenario still gives good consistent out imo....or i have found.

[Cynar]

Originally Posted by ChrisA

Thanks Betty, but I thin you're missing my point. If I do this with just a single .1 cable attached, am I going to miss things that have not been properly mixed by the engineer?

C

Nope, you're missing the point.

In the scenario you describe, the information missing from the LFE channel is sent to the main speakers and reaches the sub via the high level connection.
For this to happen the speakers must be set to 'Large' on the receiver.
If they were set to 'small', as I suggest should be the case, the information would not be sent to the speakers, but be sent direct to the sub via the low level connection anyway.

[mojogoes]

Originally Posted by betty_swallocks

I can't see the point of a high level connection unless you have no low level connection available as with a lot of stereo amps.
If you have a receiver you should set all your speakers to 'small' so all the low frequencies (not just the LFE channel) are directed away from them and to the sub via it's low level connection anyway.
There's not many speakers about that can reproduce the lows as well as a sub can.

Hi does this also count for floorstanders......i have it connected in both ways but find that when i'm watching tv or a cd none .1 even though both line level and high level gains are set at the same place , when watching tv etc the sub output is much less........i guess i'll set them back to small even thought odyssey puts them to fullband.....plus take the high level connection off and see what i get.

[Cynar]

Originally Posted by mojogoes

Hi does this also count for floorstanders......i have it connected in both ways but find that when i'm watching tv or a cd none .1 even though both line level and high level gains are set at the same place , when watching tv etc the sub output is much less........i guess i'll set them back to small even thought odyssey puts them to fullband.....plus take the high level connection off and see what i get.

I don't know what your floorstanders are, but I'd suggest even if they are capable of reproducing fairly low frequencies, it won't be as low or as well as your monolith can!
If you set them to small, anything below the crossover frequency on your amp will go to the sub and not to them.
You actually get a double benefit as not only does the sub do the lows better, but the other speakers can reproduce the rest of the frequencies better too as they're not struggling to do the lows as well.

It's normal to get less output from your sub when your source isn't .1 as there's usually less low frequency information when there's no dedicated LFE channel.

[Ightenhill]

In simple terms this will/should only happen (ie you may miss some sub information) if you set your speakers to lge and dont allow the receivers crossover to do its work..

However and heres a big (I have know idea why moment).. I set my Sub using both hi and lo and tune both crossovers independtly. ie. the low is crossover bypassed and controlled by the processor and the high is set to the centre speaker roll off and takes a high lead from the center.. For some reason the vocals in speech etc are much more natural this way and there is a noticeable dirfference in the initial leading edges of very dynamic notes such as a gunshot punching its way out of the center speaker..

[Cynar]

Originally Posted by Ightenhill

However and heres a big (I have know idea why moment).. I set my Sub using both hi and lo and tune both crossovers independtly. ie. the low is crossover bypassed and controlled by the processor and the high is set to the centre speaker roll off and takes a high lead from the center.. For some reason the vocals in speech etc are much more natural this way and there is a noticeable dirfference in the initial leading edges of very dynamic notes such as a gunshot punching its way out of the center speaker..

I've seen this mentioned a lot, and I know MJ and REL are both proponents of simultaneous Hi and Lo level connections.
I'm not saying it doesn't produce an improvement, but I do struggle with the logic as to why it does.
Surely if the receiver's crossover is set a fair way above the speaker's roll off, and the sub's high level crossover is set low enough for the speaker's roll off, then there should be nothing output from the sub from the high level connection anyway.

[Ightenhill]

Not 100% sure of the terminology bit but its something to do with the impedence of the hi versus the lo connection, speaker loading and the amps roll off(even with a selected crossover) and what then happens to the signal. The hi as its receiving the same load and signal as the speakers is better matched. Told you it was double dutch.

One thing that does puzzle me is why the hi connects to the terminals on the reciever and not the actual speaker its underpinning for this seems to be the best way to ensure the sub is seeing the exact same load as the speaker. I know this is the recommended method for Naim equipment as I used to use N-Sats and n-sub

[russ.will]

The recommendation for connecting the high level inputs at the amp is simply because the two sets of speaker terminals are adjacent which simplifies stereo connection which is where this modus operandi is envisaged as being used. The alternative being high level cables running to both speakers and yet more cables on the carpet.

In electrical terms it makes no difference. The electrical properties of any decent speaker cable are so vanishingly small that whether you connect at one end or the other (amp or speaker) to all intents and purposes, it's the same thing. As far as the amp is concerned, it is at the back of the speakers. Remember, the inductance, resistance and capacitance of cables are measured in units per kilometre in order for them to be meaningfully large. Over the distances involved in domestic runs it makes no difference.

Now, the input impedance of the subs high level input is about 10kΩ and as such draws virtually no current from the amp what-so-ever - it presents no load. What it does, is just read the voltage swings of the electrical signal being applied by the amp across the speakers and then amplify this signal to send it to the subs driver. It is just like applying a volt meter across the speakers/amps terminals and deriving the signal to be amplified from the swinging needle.

It's just another one of these myths that falls down when you think about it a bit. For instance, if there were significantly different electrical conditions at the back of the speaker 3, 4, 5, whatever metres from the amp, how different are these same conditions going to be by the time they've traveled down the additional 5m of high level cable? If the reasoning made any sense, you'd want the sub at the end of exactly the same length of cable from the amp.

The wider debate about high v low v dual level connections is a common one and it is one that I suspect is fuelled by manufacturers trying to exaggerate a useful feature into some sort of perceived advantage.

Unless you are running some really serious gear, I can think of no reason for running any speaker attached to an AV amp full range in order to support a high level connection that's just not needed. There are two related reasons for this.

One is that running five or more speakers is already quite demanding for even decent amplifiers, especially if you like your volumes high. Bass places high current demands on the amp and the further you push something, the more it distorts giving a harder, less clear sound. The demands are also increased by the amplifier having to control the reactive load of all of these cones it set in motion in the first place as they become electric motors generating their own signals as they try to spring back to rest.

The second is that the speakers themselves distort more the further their cones travel. The deeper the bass, the greater the travel and you can see where this is going by the time you add this to the amplifiers issues.

If you take a look at a serious active speaker, you'll see about 50w for the treble unit, 100w for the midrange and 200w for the bass and that's in each speaker. So why use over half of your amps total pot, to reproduce bass it doesn't have to? With a bass managed subwoofer, you have the opportunity to take this onerous task off the amp and speakers. You can redirect all of the bass to a box designed and optimised for the job of doing bass and bass only.

Even if we ignore the superior quality of bass from a good sub, the rest of the frequency range left to the amp and speakers just took a huge boost in performance. With massively increased reserves now available, the treble and midrange will have a much easier ride, maintaining their clarity and composure to much higher volume levels, resulting in an easier, less fatiguing sound.

So running any channel full range is to hamper it's performance.

I don't buy the 'sub connected to centre speaker' method either. Of all the channels that could really do with the load being lightened, it's the motherload carrying centre channel. If all of the above makes sense, it goes double for the centre which carries the all important dialogue and needs to do it clearly inspite of what else is going on in the average soundtrack.

If using the amp to bass manage the bass to the sub results in a loss of clarity to voices and reduced dynamic impact, then that's a sign of setup issues being shown up. Natural reproduction of voice is always a great test of system integration and if it falls down here, running the centre as large is papering over the cracks by reducing the subs input, rather than getting the input right in the first place, be that because of setup issues or just as importantly, a poor sub.

A good sub is capable of producing not only cleaner deeper and louder (if you want it) bass, but it offers the chance to tune the bass to suit the room in a way that the speakers can't, due mainly to them having to be anchored to where the soundstage needs to be. Moving the single sub source of bass around can help tune room modes in a way that would be hard with speakers and reduces the posibilities of cancellations between multiple bass sources. Of course, multiple sources can help spread a more even bass around the room, but the possibilities to tune this with speakers is limited due to their placement being dictated by other tasks.

There is a really good white paper by the Harman Group here for anybody fancying a technical read on multiple bass sources and if I haven't bored you enough already, I spent a week playing with multiple subs here although that's focused primarily on whether its worth splitting your budget for two subs.

Russell

[Ightenhill]

My solution is try the Naim and Linn solution, tunedem the methods for there PRAT and if theres an improvement fine, if not don't. Don't worry about why, its the final sound that matters .

Now do I buy this HI-Line I have on dem:-- the wifes ears will have to decide