5.1 surround source material played with 4.0 speaker configuration

I want to attach 2 sets of speakers to my 5.1 surround sound receiver. I plan to connect one set as the front left and right speakers, and the other set as the rear left and right speakers.

My receiver has various options to describe how many speakers are attached and one of these options is “4.0”, so far so good.

So, what happens with the center speaker and subwoofer signals when I play 5.1 source material with my receiver configured with a 4.0 speaker setup ?

I suspect the subwoofer signal will be sent to all speakers (or maybe just the front two), but my main concern is the center channel signal. Will it be sent to both front speakers, or will it just be dropped ?

Center is summed equally between front left and right.
Bass is just sent out normally, no dedicated LFE

I have exactly that configuration, 2 large front speakers and two small rear ones, and it’s perfectly satisfactory. It’s been a long time since I configured my receiver, but all 5.1 channels are downmixed appropriately, nothing is dropped. The center channel goes to the two front speakers equally, as does the low-frequency channel, which will work well if your fronts have good low-frequency response. IIRC most of this is configurable, including relative volumes of the virtual channels and channel balance of physical ones, but how much you can control will vary by receiver. You certainly would not want the center channel dropped as that contains most of the dialog! But not having a physical center speaker IMHO is no problem whatsoever, and in fact the physical placement of such a speaker is often a damn nuisance.

I have no idea what your “4.0” option does as I haven’t seen this, but it probably just sets defaults pretty much the way I described them.

Well I guess you can’t play the sub (very low frequency ) channel , the .1 , without a woofer to do it with. The sub channel is usually going to cause crackles or even real damage and destruction if sent to the regular speakers… maybe there is an option to do it, with the warning “this can cause actual damage”…

One thing that can help dramatically if you have a number of people watching the TV, and no centre speaker is to angle the front speakers in quite significantly. Actually point the speakers so that they point at the person on the other side of the sofa (or whatever). So the left speaker points at the person on the right. This can have the effect of ameliorating the variation in sound level from the speakers that a row of people receive. This level variation is the prime reason the centre channel is used at all. In cinemas (for which the movies are mixed) it is necessary to have a sound source that is located with the screen, otherwise dialog has the habit of coming from the speaker nearest to you - which for many patrons is off to one side of the screen. In a home theatre you have a different mix of compromises, and so long as you hear roughly the same volume from both left and right speakers you won’t miss the presence of a centre speaker. As noted above, you do need to ensure that the system is configured to know there is no centre speaker, so that it directs the centre signal to the left and right front speakers. Playing about with the speaker angles may make a useful improvement in the overall sound stage for you.

The sub channel will not damage your main speakers unless you’re actually sending an amplified LFE signal to them, which you wouldn’t be. A 5.1 receiver will mix the sub channel to the mains with the appropriate cutoff. It’s extremely difficult to screw this up, because normally the sub channel is its own output, so either it will show up there, or be mixed by the receiver’s internal circuitry which knows what it’s doing.

All that said, 4.0 (or 4.1) is not an ideal configuration. It can lead to obnoxious and distracting imaging issues, as was discovered when they briefly tried to make quadrophonic records. (That’s why they invented the center channel in the first place.)

But if that doesn’t bother you or you don’t notice any problems, go for it. It will work fine.

As others have indicated, just what your equipment is doing when selecting “4.0” cannot be answered as “4.0” in and of itself is meaningless. If your equipment actually has a mode called “4.0”, you would need to refer to the products documentation to discern exactly what “4.0”'s intended use was. Is it downmixing various 5.1 sources to four channels or, more likely, is it simply downmixing to stereo which is then output to both the front and rears.

At any rate, your manual should clarify what this “4.0” mode is for and just what it does to the LFE, center and rear tracks and just what sort of control over the output.

As I understand it, the “4.0” referenced by the OP is not a mode as such but just a description of the speakers connected to the amplifier. The actual mixing technique will depend on the source and the selected mix. If the source is 5.1 and the amplifier mode is selected to 5.1 then it should just mix the centre channel to the front left and right.