High level connection with (Rel) sub.

frogcarmichael

Standard Member
Hello all.
I might will be completely missing the point here, and this might be a real newbie question, but here goes.
I have a pair of LS50s running off a NAD M1 amp with two Rel T5i subwoofers.
I had thought that the benefits of using separate subs were the following:
1) lower to get good bass extension.
2) Flexibility to place the subwoofers in the correct position.
3) ability to use DIRAC more effectively, given the subs are driven separately and therefore can be “tuned” separately.
4) The fact that the sub takes the low frequency means that the main speaker doesn’t have to produce this low frequency. The crossover diverts this lower frequency to the sub. This gives the main speaker less work to do, and therefore means it performs better.
Basically it’s easier to create a clean sound when you have less frequencies to produce.

if I use the high level connection, however, I am not getting the advantage of (3) and (4)
I get that the high-level connection means I will have the same sound signature coming from the amp. But to be honest I’m not sure my ears would really notice difference.
Am I better off using the subwoofer output from my amp and gaining the benefits of (3) and (4) as noted above?

thanks for any insight, especially on point (4).
 

wine man

Active Member
The sub(s) should be set/tuned to the point at which your main speaker's bass capability starts to roll off. In other words the partnership of sub & main speakers should be seamless. It doesn't matter which connection you use, the controls surely work the same? I have a BK sub with a pair of £4k speakers, it took a couple of weeks to gradually tune the sub in to the main speakers but once done they worked in unison rather than two separate sound sources.

I see Dirac as similar to a parking aid on a car dashboard, very clever and nice to have but I prefer to set my own sub/speakers by ear.
 

dogfonos

Well-known Member
thanks for any insight, especially on point (4)

Although I don't use a sub and I'm not familiar with the REL T5i or the KEF LS50, I believe your point 4 is very important in many, setups - including your own.

Reason is, I see the KEF LS50 as a precision instrument and, ideally, it should be treated accordingly. I don't see the KEFs as a 'general purpose' hifi speaker. In other words, if D&B, or similar, at realistic volumes in anything other than a tiny room, is your thing then the KEF LS50 is not for you (assuming the KEFs are used full-range).

Whilst I've not seen any objective or subjective testing that confirms the KEF sounds better and plays louder when deep bass is removed (and reproduced by a sub), I suspect it would, assuming ideal sub integration (which you should be able to achieve with the NAD's sub out). The KEF's are renowned for their excellent midrange but if the bass/mid driver is forced into large (deep bass) excursions, then I doubt the midrange would be quite so impressive.

I've noted a few cases of the KEF LS50 suffering a crumpled bass/mid driver and the users don't seem to be aware of the cause:


Again, just a suspicion, but squeezing generous levels of deep bass out of a relatively inefficient passive 5" bass/mid driver is asking for trouble and I think that's what causes this crumpled cone effect. As a cone material, the magnesium/aluminium coned KEFs will likely be more suseptible to such permanent deformation than a paper or plastic cone.

Unless you listen exclusively to music that contains little deep bass, I'd remove deep bass from the KEFs. Besides, the KEFs aren't considered particularly brilliant in the bass department anyway.
 

gava

Active Member
No harm trying it both ways.

I found with LS50s & one REL T5i that it was cleaner and more seamless to use the high level input. And set at a much higher crossover frequency than you might first expect. I found +-110Hz was about right, them adjust the volume until you can't tell where the speakers end and the sub starts.

You need to try lots of music to find the best balance. Mine was pretty good but with Dirac I'm sure you will be able to get it perfect. I don't see any reason why Dirac won't work just as well with the high level input, it's just applying an eq curve after all.
 

andycc72

Active Member
No harm trying it both ways.

I found with LS50s & one REL T5i that it was cleaner and more seamless to use the high level input. And set at a much higher crossover frequency than you might first expect. I found +-110Hz was about right, them adjust the volume until you can't tell where the speakers end and the sub starts.

You need to try lots of music to find the best balance. Mine was pretty good but with Dirac I'm sure you will be able to get it perfect. I don't see any reason why Dirac won't work just as well with the high level input, it's just applying an eq curve after all.
What do you have the crossovers set at on
both subs when running 2?

I’ve got the same speakers and subs as you and after lots of tweaking I’ve got the crossover at around 55hz on both and the volumes at 9 o’clock on both. This works best so far. Any higher on the crossover and the bass starts to get a bit muddy.

saying that every time I think I’ve cracked it a song will come on where the bass sounds
bloated and the temptation to start fiddling with it again is immense.
 

andycc72

Active Member
Hello all.
I might will be completely missing the point here, and this might be a real newbie question, but here goes.
I have a pair of LS50s running off a NAD M1 amp with two Rel T5i subwoofers.
I had thought that the benefits of using separate subs were the following:
1) lower to get good bass extension.
2) Flexibility to place the subwoofers in the correct position.
3) ability to use DIRAC more effectively, given the subs are driven separately and therefore can be “tuned” separately.
4) The fact that the sub takes the low frequency means that the main speaker doesn’t have to produce this low frequency. The crossover diverts this lower frequency to the sub. This gives the main speaker less work to do, and therefore means it performs better.
Basically it’s easier to create a clean sound when you have less frequencies to produce.

if I use the high level connection, however, I am not getting the advantage of (3) and (4)
I get that the high-level connection means I will have the same sound signature coming from the amp. But to be honest I’m not sure my ears would really notice difference.
Am I better off using the subwoofer output from my amp and gaining the benefits of (3) and (4) as noted above?

thanks for any insight, especially on point (4).
What do you have the crossovers set at on
both subs when running 2?

I’ve got the same speakers and subs as you and after lots of tweaking I’ve got the crossover at around 55hz on both and the volumes at 9 o’clock on both. This works best so far. Any higher on the crossover and the bass starts to get a bit muddy.

saying that every time I think I’ve cracked it a song will come on where the bass sounds
bloated and the temptation to start fiddling with it again is immense.
 

gava

Active Member
What do you have the crossovers set at on
both subs when running 2?

I’ve got the same speakers and subs as you and after lots of tweaking I’ve got the crossover at around 55hz on both and the volumes at 9 o’clock on both. This works best so far. Any higher on the crossover and the bass starts to get a bit muddy.

saying that every time I think I’ve cracked it a song will come on where the bass sounds
bloated and the temptation to start fiddling with it again is immense.
I only have one sub.

What amp are you running?

I guess room acoustics are of paramount importance if there is such a huge difference in the best setting. It could just be taste of course, but I suspect not.
 

andycc72

Active Member
I only have one sub.

What amp are you running?

I guess room acoustics are of paramount importance if there is such a huge difference in the best setting. It could just be taste of course, but I suspect not.
Sorry I replied to the wrong person !!

I'm running a new Cyrus One amp. The room is about 9m x 4.5m I have the system on the long wall at one end of the room.

My personal taste bass wise is that I'm very keen on it, hence the two subs I listen to a lot of reggae house and soul music.

I started with the crossover at 70hz on each and it was way too muddy. Generally really happy with the current settings, but like I said the odd tune makes me want to keep tinkering.
 

gava

Active Member
I suspect that the power difference between your amp and mine is important. Mine only claims 60W/8Ω and yours claims 100W/8Ω. I think my limit on the LS50s was that the amp wasn't powerful enough for high volume, though I'm in a room which is quite a lot smaller.

I found at high volumes the bass got loose, until I set the crossover much higher at 110Hz, and at that point everything seemed to come into alignment and suddenly was nice and tight again.

Lots of variables. :)

I am getting a Behringer A800 to play with, because I suspect the LS50s actually will benefit from a really powerful amplifier. I don't use them on my main system anymore and can't decide between selling them and using them as a near-field setup. I am hesitant to get rid of them because I like them so much.
 

jamieu

Well-known Member
3) ability to use DIRAC more effectively, given the subs are driven separately and therefore can be “tuned” separately.
4) The fact that the sub takes the low frequency means that the main speaker doesn’t have to produce this low frequency. The crossover diverts this lower frequency to the sub. This gives the main speaker less work to do, and therefore means it performs better.

if I use the high level connection, however, I am not getting the advantage of (3) and (4)
I get that the high-level connection means I will have the same sound signature coming from the amp. But to be honest I’m not sure my ears would really notice difference.

Not overly familiar with your NAD.

But if it correctly implements bass management (ie. correctly diverting L&R channel content above and below the crossover frequency) and allows you to set both sides of the crossover ie. a LPF on the sub and a matching HPF on the L&R channels. Then if setup correctly (which may require measurement using a program like REW and a AVR/Amp capable of letting you set adjustments) you should have more chance of creating a smooth crossover point as you have complete control over both sides of the crossover curve.


In terms of DIRAC it shouldn't really matter (unless you're also using the bass management features of DIRAC 2) as all DIRAC is doing is correcting the overall in-room frequency response. Although in practice is often useful to get DIRAC to analyse the sub channel separately from the L&R channels when creating correction curves. So yes 'ability to use DIRAC more effectively' is somewhat true.

You're also correct that "The fact that the sub takes the low frequency means that the main speaker doesn’t have to produce this low frequency". Although in practice most good speakers will roll off naturally when used full range. The advantage is when your mains attempt, but audibly struggle, with low frequency content (i.e smaller bookshelf speakers). In those sort of setups you'd be better off stopping them from trying to reproduce those frequencies (via the crossover/HPF) and passing that content to the sub instead.

I expect many people prefer using the high level inputs esp. if using full range speakers and a lowish crossover point as it's fairly easy in those sort of setups to adjust the subs gain and crossover point by ear to match the natural rolloff of the mains. You're effectively just 'filling in' the missing sub-bass / giving your mains some extra 'bottom end'.

There may also be something to be said for not wanting to use electronic crossovers (and hence a sub output) in a 'pure' HiFi setup. Not sure I fully agree with it, but I understand the sentiment. In fact most HiFi amps won't even give you the option, hence the need to use the hi-level connections.

Once you start to raise your crossover points higher, for example with smaller bookshelf or satellite speakers, then having control of both the LPF and HPF crossovers (and their slopes) for your mains and subwoofer starts to make a lot more sense as your more likely to notice (audibly) a non-smooth crossover at those frequencies. In those situations I'd use the subwoofer output (and measure the response around the crossover with REW).

If you already have a measurement mic with your NAD and want to get your head around this, then I'd really recommend taking a few sweeps using REW to see how smooth the frequency response is around the crossover point. It will also be useful when working out the best point to crossover your speakers and sub. You can try both connection types and see what looks/sounds best, at least you'll have a clearer picture of what is happening.

In short using the subwoofer output in combination with the electronic crossovers/bass management in the NAD will give you more control — and IMO is the better option. But it probably also opens up more room to get things wrong.

If you're using full range speakers and a low-crossover point you may be better of using the high-level connections and trusting your ears (along with a quick frequency sweep in REW to make sure your ears aren't completely off).

Conversely, if you're using the hi-level input with full range speakers and a high-crossover point (and haven't measured your overall response) I expect you run the risk of having both your mains and sub reproducing the same frequencies, in effect raising the overall levels at those frequencies. Although this is incorrect, I sometimes wonder if people with this kind of setup prefer the sound due to that effect.

btw. "high-level connection means I will have the same sound signature coming from the amp". We're taking subwoofer frequencies here, there isn't really going to be any 'sound signature' from the amp that you can hear other than some potential distortion/noise possibly introduced by the power amp itself and the attenuating resistor on the subs high-level input (likely at frequencies the sub can't even reproduce). In short this is just hi-fi marketing nonsense, you shouldn't let it affect your decision re. connections — both have their places/uses and both (in most situations) should work equally well if setup correctly.
 
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