Subwoofer connection for B&W 805

[Aussie Geoff]

I've posted this question I recieved in a PM from "Bullit731" (and my answer) because it is an intersting topic and I know there are quite a few different opinions and options on this one...

Geoff,

I have a couple of quick connection questions. I have been reading subwoofer threads associated with my Sig 805s. If I understood the posts correctly I could run a digital coax from my 1072 to my 1056 being used as my preamp and RCA cables from the 1056 to my 1080 as the power for my 805s. Then I could run the RCA analog outs from the 1072 directly to the RCA analog ins of a powered sub.

This is said to generate the cleanest signal from the 1072 in each case. My question is if this is correct, how do you limit the 805s to the midrange frequencies and above. I know you can control the frequencies of the sub by adjusting it crossover. I any case can you let me know how you would recommend setting these componets up.

Thanks, Ed

[Aussie Geoff]

Ed,

This is a good question and there are several answers depending on the capabilities of your subwoofer...

The simplest connection option is to put a coax cable into the RSX-1056 and use it to crossover to a sub by setting your speakers to small with a crossover of 80 Hz or 60 Hz (listen to see which you like).... The subwoofer is connected to the Receiver using a single RCA cable from the Sub/ LFE out of the Receiver and the subwoofers crossover is turned off or set to as high a frequency as possible so that the receiver is controlling the sound and the crossover.

The advantage of this is that it only uses one set of Digital to Analog connections and the bass crossover is done perfectly by the Receiver... If you use this option get a good coax digital cable to maximise the sound quality. However the disadvantage of this option is that you loose the benefits of the CD optimised DACs in the RCD-1072 CD player…

So another option is to run analogue cables from the CD to the Receiver, run the Receiver in pure stereo mode (i.e. no processing, no crossover etc) and feed the left and right pre-outs from your receiver to your sub via a pair of RCA cables into the subwoofers stereo inputs. You then set the subwoofer to crossover at about 40-50 Hz (frequency varies depending on room, speakers and taste) using the subs own controls (many subwoofers have separate stereo and LFE inputs for the two different approaches.) Here the 805s are being fed a full range signal (including all bass) but they will roll off the bass (depending on room and placement) at around 40-50 Hz. The subwoofer is also fed a full range signal but will roll off the high frequencies…

The advantage is if all this works well, you can get some very clean stereo sound… However the disadvantage is that the Receivers is still trying to drive the deep bass into the 805s (which will strain it a little at higher volumes) and the 805s are trying to play the deep bass (which can strain the drivers with too much power / too great and excursion at loud volumes with deep bass…)… The other issue is that this really only works well for stereo, it is hard ot set-up for 5.1 or 7.1 listenning unless you have a second subwoofer or also coonect the LFE cable to the subwoofer and have a sub that will automatically switch between the LFE and Stereo inputs...

There are some other options with specialist stereo subwoofers such as those from REL – but you need to let people know what you have…

Too me the option people are suggesting to you is an unfortunate compromise between the two... My recommendation is that you listen to both in your room and decide which you prefer.

I hope this helps and I’m sure you will get some more ideas from other posters…

Geoff

[Indytown]

Geoff, what are you doing in the second example, running a (y) connector for the left/right front channels so the 805's are also receiving a signal?

Indy

[Aussie Geoff]

Indytown,

Geoff, what are you doing in the second example, running a (y) connector for the left/right front channels so the 805's are also receiving a signal?

If it was a processor (like the RSP-1068 or 1098 ) I'd need do that but since it is a receiver (the RSX-1056), most receivers keep their Pre-outs (which you can use for external amplifiers) active even then using the internal receiver’s amplifiers... So no need for the Y splitter - just a normal left and right out signal from the pre-outs to the left and right input that most subwoofers have... The Receiver will keep driving the 805S’s just the same with a full range signal in bypass mode…

As I mentioned if you have a subwoofer with a separate LFE input to the left and right inputs, you can usually do even better and also run an LFE signal from the subwoofer out on the receiver so that when you are not using pure direct mode (e.g. for home theatre) the processors normal SMALL speaker logic can kick in and send all bass via the LFE line to the sub, cutting it off from the 805s to avoid over driving them.

Geoff

[Ash]

Hello Aussie,

As always, this is some great advice you provided in this thread. :T

I have the same dilemma here, and it has been haunting me for a while.

My N805s struggle when they get a full signal, which in turn is not optimal for stereo listening ( with heavy bass tracks, they vibrate vigorously and sometime my receiver shuts down, which scares me :E ). So I bought two ASW675 subs to help with this problem (I didn't want to give up on the 805 without a fight).

The way you suggested to connect to a sub through the pre-outs from the receiver seems very logical, but as you mentioned, that the 805s will still get a full signal, thus will still struggle. However, you have mentioned that they will roll off at 40-50hz, what does roll off means exactly??

I also came to know that you can connect some B&W subs (not sure about other makes), If you have a separate processor / amp, by connecting RCA cables in the following way processor=>sub=>amp=>speakers, connecting both right & left pre-outs from the processor to the sub RCA ins, and from the sub RCA outs to the power amp ins, setting the crossover freq on the sub.

In this way, you can still get the benefits of stereo direct but the signal will first go to the sub, retaining the low freqs and sending the remaining higher freqs to amp and finally to the 805s. Thus the 805s will not have to play the lower freqs and can concentrate on providing better mids; furthermore, the amps won't be strained.

If you have two subs, you can connect the right channel from the processor to one sub and the left channel to another sub, thus getting stereo subs (if placed next to the right & left mains), which I intend to do in the future when I get separates ( my current receiver doesn't even have pre-outs ).

A disadvantage of this set-up is having the additional cables and subwoofer crossover introduced in the signal path. I'm not sure how much will this effect the sound quality. Does any have an idea?

My biggest concern with the above set-up is the HT performance. If I use two subs connected as above, I will not have an LFE channel. Although I heard that, if you set the sub as off in any receiver and set the fronts as large, then the LFE channel will be re-directed to the fronts, where the subs are connected, I don't know how effective this will be or if it is actually true, does anyone have an idea?? If this is true, then this will be the optimal way to connect the subs!

I have another option, I can connect one sub to the 805s as describe above and connecting the other one to the LFE channel. This way, only one sub will be working in stereo mode (shame to have one sub working when I have two and I will lose one sub per channel capability), and both subs will be working in movies (if I set fronts as large).

I'm not sure, which one would be the optimal set-up. I would appreciate any inputs.

Thanks , I hope this helps as another way to connect to a sub for anyone deciding on sub connection.