High Level Subwoofer Inputs: A Necessary Feature?

[Kal Rubinson]

Anyone can easily add high-level inputs to subs missing them - all that is needed are a few resistors, wires, connectors and a soldering wire.

Of course. A convenience.

Although I agree with Mark Seaton post above, we should remember that in audio the proof of the pudding is in the eating - I also have listened to excellent sound using high-level inputs.

There are many different standards of proof. I, too, have listened to excellent sound systems using high level inputs but, imho, it is no longer the optimum way to integrate subwoofers into a sound system.

 

[stehno]

The argument is that high level inputs to one's subwoofer(s) are necessary to keep the character of the mains amplifier(s) to the subs.
The argument seems legitimate, but I have never tried low level or LFE inputs. Any thoughts on this?

I remember you mentioning the REL subs and their high-level conneciton only and I actually ended up writing a short list of concerns but can't seem to find it. Based on my Class D amps, all caution not to perform high-level outputs or bad things will happen so I'm left with speculation only.

But the more I think about high-level amps connnections with subs the less logical it seems to me. For example.

- High level connections will induce the main amp's sonic signature into a sub's active amps and I just don't see any logic there unless perhaps somebody thought the sub amps induce no sonic signature of their own. And that is highly unlikely.

- In the case of the REL subs the user is forced to use REL's cables. When is the last time anybody ranted about REL being a stellar cable manufacturer?

- Every cable potentially induces its own sonic signature as I'm sure REL sub cables do too. I'm a big believer that the sub cable should be identical to other interconnects used elsewhere to absolutely minimize sonic differences and maximize bass uniformity / continuity betweeen mains and subs. The REL cables cannot offer much relief in this regard.

- Timing? I just don't see how lower frequencies passing thru two amplifiers to make sound at the subs can possible help regarding any potential timing issues with regard to the mains.

I actually had about 4 more things to list but even with these 4 above, I just don't see much logic in a config's subwoofer utilizing high-level inputs. I certainly wouldn't bet the farm that high-level inputs offer superior sonics. But it's still pure speculation on my part.

 

[stehno]

Another thing that comes to mind and hopefully nobody would disagree with me when I say when using high-level inputs, in addition to getting the main amp's sonic signature you're also getting the main amp's more distorted signal at output. Surely nobody thinks a component's output signal maintains the exact same fidelity of the component's input signal. Small-to-large percentages of the music info are gone at the output signal.

So the high-level signal that has already been compromised at the main amp due to internal distortions must now make a second pass thru the sub's amplifier which in turn will compromise the fidelity of its input signal.

The more I think about high-level inputs as superior sub config's the more I'm compelled to ask, what were they thinking?

 

[Kal Rubinson]

So the high-level signal that has already been compromised at the main amp due to internal distortions must now make a second pass thru the sub's amplifier which in turn will compromise the fidelity of its input signal.

I thought that was implicit.

 

[stehno]

I thought that was implicit.

Indeed. I'm just adding up all the implicits, Kal. As I'm sure you know, striving for improved performance ain't always a cakewalk. Especially when it come to the bass regions. Why start out behind a bigger 8-ball when you can start out behind a smaller one? There's no fun in that.

 

[Al Stewart]

@stehno I'm not attempting to disagree with any of your thoughts laid out above. But, it is worth noting that on REL subs, current models allow a wireless connection from the main amplifier to the REL; there is no REL cable running from the main amp to the REL. Also, if one chooses to use the REL with cables there are many different manufacturers' cables designed as "sub" cables for the REL format. A while back I followed some really good advice from Duke LeJeune on subwoofer application (the DBA). I run 4 REL subs in my room (2 wired and 2 wireless) placed asymmetrically in the room, at different crossover levels, and different volume levels--although the volume on each is rather low. It works wonders. I use the high level input on all of them. I have used the low level input in the past, but using long RCA-type cables via this route can result in a grounding hum. In fact, it did with my 2 wired RELs. So, with a REL, I would recommend using the high level input.

 

[stehno]

I personally greatly prefer using high level inputs on my subs. My experience is that its much harder to integrate (my) subs through the low level inputs from my DAC/preamp than from the high level inputs of my amps. I've found this to be true for the last three solid state amplifiers I've owned, and I did the legwork.. I would assume this to be even more true if ones' man amplifiers are tube or SET based designs that deviate even more from the 'straight wire with gain' design objective.
If you have both high level and low level inputs, I suggest you try both and see if you don't reach the same conclusion.

I'm a bit confused, Kerry. I think you stated in your OP that you'd never tried low-level inputs but here you seem to be saying you did all the necessary legwork and you much prefer high-level inputs.

Still, I was under the impression from your OP you were seeking arguments for and against high-level inputs and I can't think of a single argument in favor of high-level inputs but I've numerous arguments against them.

Per your OP, I would think if one were seeking to retain the main amp's sonic signature by use of high-level inputs, any hope of retaining such character would be lost based on my arguments listed above. Or if per some odd chance the main amp's sonic signature was retained (seems impossible) it would have to be at the expense of perhaps anything / everything else.

I'm probably missing something here but if high-level inputs are your preference and meet your needs that's all that really matters, right?

 

[musicfirst1]

I guess I misspoke with the use of the term low level inputs here. Using the outputs of a preamp is something I have never used to feed a sub, as I've been without a pre for some years. Using the variable outputs of my DAC is something I've tried, not with much success, so for me its been DAC/pre to amps into high level inputs of the sub amps. I have no experience with using a preamp to feed a subwoofer.

As you indicated John, there are often difficulties for some low level devices (DACs and Preamps) to drive low level cables, especially if they are longer lengths, which might be another reason one might prefer high level connections.

And yes, I asked the question to promote discussion, especially for those who have SOTA Pre's that may prefer the low level route. I find it interesting that there are many highly regarded subs that don't offer high level inputs

 

[Kal Rubinson]

I, too, no longer use a preamp (most of the time) and drive my amps and subs from DAC outputs using direct low-level (I prefer to say, line-level) connections. No noise or signal issues with 10m balanced cables.

 

[Lagonda]

I, too, no longer use a preamp (most of the time) and drive my amps and subs from DAC outputs using direct low-level (I prefer to say, line-level) connections. No noise or signal issues with 10m balanced cables.

Same here 10m balanced cables work fine in my setup.

 

[Lagonda]

I guess I misspoke with the use of the term low level inputs here. Using the outputs of a preamp is something I have never used to feed a sub, as I've been without a pre for some years. Using the variable outputs of my DAC is something I've tried, not with much success, so for me its been DAC/pre to amps into high level inputs of the sub amps. I have no experience with using a preamp to feed a subwoofer.

As you indicated John, there are often difficulties for some low level devices (DACs and Preamps) to drive low level cables, especially if they are longer lengths, which might be another reason one might prefer high level connections.

And yes, I asked the question to promote discussion, especially for those who have SOTA Pre's that may prefer the low level route. I find it interesting that there are many highly regarded subs that don't offer high level inputs

Do your REL’s have continues phase adjustment for best integration ?

 

[musicfirst1]

Do your REL’s have continues phase adjustment for best integration ?

Alas, no. I haven't found one sub that offers the trinity (low level, high level and continuous phase adjustments..

 

[Kal Rubinson]

Alas, no. I haven't found one sub that offers the trinity (low level, high level and continuous phase adjustments..

JLaudio E110 and E112. Of course, with their small size, many will have to use a few of them. I do.

 

[sleepysurf]

One other consideration, depending upon circumstances, is potentially easier phase/time alignment with main speakers when using speaker level sub inputs. For example, my C-J preamp is phase inverting (as is my C-J Premier 350 amp). I have two ML BF 210 subs, and although they have adjustable phase settings, I've found it easier to phase/time align the subs to my ML Expressions using speaker level inputs, since I have 180 degrees less phase shift to start with.

 

[Kal Rubinson]

That's polarity, not phase. The JL's and many other subs have polarity switches in addition to phase adjustments.

 

[musicfirst1]

That's polarity, not phase. The JL's and many other subs have polarity switches in addition to phase adjustments.

Kal
Can you explain the difference between polarity and phase? It is my understanding that phase is essentially a delay characteristic of the subwoofer, while polarity can be either A/C or audio polarity.

Also, do you have any thoughts as to why JL Audio has eschewed high level inputs on their big Gotham and Fathom models, while offering them on their lower models?

 

[Kal Rubinson]

Can you explain the difference between polarity and phase? It is my understanding that phase is essentially a delay characteristic of the subwoofer, while polarity can be either A/C or audio polarity.

Polarity indicates whether an AC signal (audio, power, any) is inverted or not and is not frequency-correlated. It is 0deg or 180deg and not any nothing in between.
Phase is a delay characteristic, is incremental and which can affect different frequencies differently. For example, filters used in crossovers will shift the phase of frequencies above and below the nominal crossover frequency differently depending on the slope and configuration of the filter.

Also, do you have any thoughts as to why JL Audio has eschewed high level inputs on their big Gotham and Fathom models, while offering them on their lower models?

It is an acknowledgment that their more advanced models will most likely be used in more sophisticated systems where high level inputs are not needed or, even, considered. Inclusion in the lower models acknowledges that some accomodation is made for systems with constraints.

 

[sleepysurf]

That's polarity, not phase. The JL's and many other subs have polarity switches in addition to phase adjustments.

So, CJ (and others) should really say their preamps (or amps) are Polarity Inverting. Regardless, I think it still makes a difference when trying to optimally "time align" subs with main speakers. If the sub signal is inverted (relative to the mains), wouldn't that create "destructive interference" that impacts the perceived bass response (depending upon speaker/room interaction)?

BTW, I found this recent video illustrating the differences between polarity and phase...

 

[admin1959]

I subscribe to this REL high-level (speaker level) input philosophy. So does Evolution Acoustics.

But, as with everything in our subjective hobby, opinions vary. Notably JL Audio and Wilson Audio do not provision their subwoofer cross-over controllers for high level inputs.

JL Audio do have high level inputs.

 

[Al M.]

JL Audio do have high level inputs.

Not their more advanced models, see Kal's post #37 above.