Setup question on bass management

[Vaughan Odendaa]

I have seen someone connect up a THX system (THX speakers and amp) and use the front left and right preout to feed the subwoofers (two of them). And then set speakers in bass management to large and subwoofer to off.

Which isn't typical at all. What exactly is going to happen here ?

It sounds odd.

--Regards,

 

[Davemcc]

The front left and right will run full range. The sub will receive full range front right and left signal and use its internal crossover to extract the LFE signal and play the combined LFE of the front right and left channels.

I think it would be the same as setting bass management to LFE + main.

P.S. I hope I'm right about this, but that's the result I would expect to achieve from that setup.

 

[Nick250]

I have seen someone connect up a THX system (THX speakers and amp) and use the front left and right preout to feed the subwoofers (two of them). And then set speakers in bass management to large and subwoofer to off.
Which isn't typical at all. What exactly is going to happen here ?
It sounds odd.

--Regards,

it seems pertty odd to me. Unless I am missing something, at best he is running his system as if there was no sub in all in his system.

Nick

 

[Vaughan Odendaa]

It's not typical especially for a THX setup. He has apparently told me that for stereo use, he wants the mains + subwoofers to be utilized when in "direct" mode on the AVR.

But that's about it. Crossover on subwoofer is set to 80 hz. Large setting in amp and subwoofer turned to "off". What are the consequences involved in running a THX setup this way ?

--Sincerely,

 

[no. 5]

I have seen someone connect up a THX system (THX speakers and amp) and use the front left and right preout to feed the subwoofers (two of them). And then set speakers in bass management to large and subwoofer to off.

Which isn't typical at all. What exactly is going to happen here ?

It sounds odd.

--Regards,

For one, this guy will be getting stereo subs, which may be nice when listening to two channel, also, he would be getting an unaltered LFE track; because in a typical setup, anything above the crossover point on the LFE track has the crossover applied to it (I am presuming that his receiver will send the LFE to the mains if the sub is set to ‘off’).

 

[jcPanny]

Sub connections

Interesting setup.
A couple side effects are that each sub is getting different information. The subs are not reinforcing each other to produce the same LFE info at a higher SPL. Another possible downside is that the info below the crossover for the Center and Surrounds might be lost OR if all speakers are set to Large then they might be less capable at producing the low frequencies than the sub. Also, unless there is an external high pass, the Mains will get the full range signal vs. the traditional crossover with the sub.

 

[Adam]

Also, unless there is an external high pass, the Mains will get the full range signal vs. the traditional crossover with the sub.

That's the only issue that came to mind for me. If he sets the cross-over on the subs to 80 Hz, but there is no such setting on the main speakers, then both the subs and the mains will be outputting frequencies between the low-end of the mains (e.g. 30 Hz) and final cut-off for the cross-over (80 Hz for full output plus higher frequencies at some level depending on the slope of the filter).

I agree, though...an interesting set up.

 

[Vaughan Odendaa]

The center and surrounds are set to small though in AVR settings.

--Sincerely,

 

[MDS]

If you set the Front speakers to Large and subwoofer = No then LFE and bass below the xover for the Small speakers goes to the Front speakers. The Front speakers are getting a full range signal plus the bass from the Small speakers.

With the subs connected to the Front pre-outs they see the same signal as the Fronts; ie the full range signal from the front channels and the bass from the small channels. The subs apply their own xover.

When playing in 5.1 (or 5.2 in this case), if the receiver's xover is set higher than the sub's xover the frequencies between the two xovers would be played mainly by the Fronts because the sub would filter out (actually attenuate according to its slope) those frequencies. Is that a real problem? Probably not one that I'd be able to detect.

I can understand the idea of using that setup so that the subs play in 2 channel 'Direct' mode because all they'd see is the full range signal from the Front channels.

 

[Vaughan Odendaa]

The thing is, this system is primarily for HT. It is a THX system in a dedicated room. Are there downsides to running the setup as I described ?

--Sincerely,

 

[AVRat]

We might be able to help more if we knew what gear he's running. If he's just using a receiver, driving the speakers full range may tax the receiver more than necessary.

 

[Vaughan Odendaa]

We are using the top of the range Denon AV receiver. Large setting for front speakers, small for center and surrounds. Subwoofer set to 'no'. In the crossover setting portion of the AV menu it is 80 hz-THX.

So, yeah. I have never connected up a THX system the way this installer has and I just don't know if there are any specific downsides. He also tells me that in an ideal world there would be four floorstanding speakers used for each main channel as per SkyWalker ranch.

He also tells me that B&W 802's are used for each channel. I don't know about that. Perhaps someone with more info on that can also chime in.

--Sincerely,

 

[jcPanny]

THX HT setup

For a THX HT setup your best but is to connect the sub to the LFE output and set the mains to SMALL. Before creating a unique setup like the one described above I would do some testing of the "Pure Direct" mode. There is likely little or no audible benefit to using this mode, especially if the system is mainly for HT vs. 2 channel.

 

[AVRat]

HEY, HEY, you’re using a Denon. That’s good news. Denons do use the sub in all modes including the “Pure Direct” mode. Current model Denons also offer better bass management options as well for more tweaking. Is this a 4/580# series receiver? Specific makes and models would really help.

Another note if I’m not mistaken, the LFE (.1) signal is only output through the sub-out on Denons, whether you have a sub or not. I can’t confirm this in the current manuals, but I thought it read this way in previous models’ manuals and can’t seem to find it now. Hopefully others can shed some light.

 

[Tomorrow]

HEY, HEY, you’re using a Denon. That’s good news. Denons do use the sub in all modes including the “Pure Direct” mode. Current model Denons also offer better bass management options as well for more tweaking. Is this a 4/580# series receiver? Specific makes and models would really help.

Another note if I’m not mistaken, the LFE (.1) signal is only output through the sub-out on Denons, whether you have a sub or not. I can’t confirm this in the current manuals, but I thought it read this way in previous models’ manuals and can’t seem to find it now. Hopefully others can shed some light.

You are correct regardless of receiver brand, I believe. The LFE channel IS the .1 in 5.1 or 6.1. It is a discreet channel. A setup that would yield the LFE includes the LFE out from the AVR or source device to a another subwoofer. The setup as described by the OP is playing only redirected bass (and not the LFE channel).

 

[MDS]

While it may be true that some Denon receivers will only play the LFE track if a subwoofer is present, it is not universally true - in fact it is the exception. If you indicate that subwoofer=no, the mains are automatically set to Large and the LFE is directed to the mains. If this were not true, you'd lose the LFE track and I highly doubt that current Denon receivers don't work the way all other receviers do.

 

[Tomorrow]

While it may be true that some Denon receivers will only play the LFE track if a subwoofer is present, it is not universally true - in fact it is the exception. If you indicate that subwoofer=no, the mains are automatically set to Large and the LFE is directed to the mains. If this were not true, you'd lose the LFE track and I highly doubt that current Denon receivers don't work the way all other receviers do.

I stand corrected. Thanks, MDS. My brain is thinking "Pure Direct" or "Multi-Channel" out of the source.

Where DID I put that other half of my brain?......

 

[Vaughan Odendaa]

So no downsides then ?

Cool.

--Sincerely,

 

[MDS]

I mentioned the only downside I see in my first reply and it is debateable as to whether it really is a downside.

If the xover on the subs and the receiver are different then the mains will be playing the frequencies between the two xovers. That could be considered a 'problem' if your intent is to let the subs do all of the low frequency content.

Without rehashing the whole thing, let me say you have to try to visualize the signal flow to see which component is doing what. The bass from the Small channels is redirected to the mains (because they are Large and subwoofer = no) but then you have the pre-outs which send the same signal to the subs. The sub's use their own xover so if it is lower than the receiver's there is a gap but that gap is still played by the mains because after all they got the same signal.

The setup is a good solution for the stated intent of having the subs active in 'direct' mode. Unlike Denon receivers which blur the distinction between the true meaning of Direct (or so I have read) most receivers will not utilize the sub in direct mode because if it did it wouldn't be direct (no processing), now would it?

 

[Vaughan Odendaa]

Got it. Thanks. Another question. Apparently at Skywalker ranch, they experts there use B&W 802's for all main channels. Is this considered ideal ?

My understanding is that 5 sources reproducing low bass is a recipe for disaster because of reinforcement/cancellation issues. What are your thoughts.

--Sincerely,