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Centre speaker in mono for TV viewing, will it be any good?

neRok

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I'm not a big movie watcher and don't feel the need to have a home theatre system (even when I used to have a stereo with 3 way floor standers connected to my TV and HTPC, I never used it for anything but listening to music), but I wouldn't mind a bit better audio than the TV puts out. I saw the video Why Is EVERYONE Buying This Soundbar??? the other day and figure that's the sort of thing that would suit me, except it seems a bit lame, so I don't want to get one. Instead I might try out some old bookshelf speakers I have lying about. I ordered (but am still waiting for) a Fosi 2.1 amp the other day, which I will try out on my TV soon...

1) But then I was reading the thread Group delay produced by stereo and wondered if listening in mono is a good idea? A lot of the TV shows I watch have a lot of talking, so having clear dialogue is probably the most important factor. So maybe listening to 1 speaker in mono is a good idea? Has anyone done this? What are the results like? Is there much lost by not having stereo?

2) But then I was thinking, 1 bookshelf speaker sitting in the middle under the TV would look pretty dumb, so maybe I could run a centre speaker there? Something with a coax driver and 2 woofers like a KEF Q650C would probably give a great point source for vocals, and deep enough bass to be pleasing even without a subwoofer. But would a single coax driver have enough horizontal dispersion to have good clean vocals at all the sitting positions? Or would a different sort of mid+high driver be better?

This got me thinking about looks some more, because I don't particularly like the contrast of a "narrow" (compared to the TV) yet bulky centre speaker sitting under the TV - it just looks wrong to me. Soundbars look better IMO (less distracting because they blend in better). So this got me thinking about DIY solutions, because then I could build a box roughly as wide as the TV and get some great performance from some 6.5" woofers (flat down to 50Hz should be achievable). But I'm not here to talk about DIY possibilities in this thread, but this did lead to me thinking about...

3) How can I handle the signal side of things (and/or, what is there to consider)? Pretty much everything I watch is streamed through the browser on my HTPC, and I presume it is 2ch stereo. I don't think what I stream has surround sound, and I'm not sure how that is handled on the PC anyway, AND I don't have a receiver or anything (so I presume I can't use any Dolby etc tech). So what is the best way to make a mono centre signal from 2ch audio? Should I just sum the channels, or would it be best to do some sort of fancy processing that boosts the vocals and what not? What are my options here?

And here are some bonus questions;
4.1) If I made or adapted a speaker that is woofer-coax-woofer, would it be a good idea to send left and right bass/low-mids to the respective woofer, and maybe that would give a bit of a stereo effect? Like a pseudo 3chan L-C-R.
4.2) Following on from the "3 channel" idea, what if the PC still output normal 2chan, and each woofer got it's own signal (and the woofers would have analogue LPF). And then the coax driver was wired so that it bridged both channels, thus getting its mixed signal that way?
4.3) This is a very general thing, but is it possible during processing (in EqAPO say) to transform the bass frequency? Say if it could monitor all the bass from 20-50Hz, and whatever the peak amplitude in signal is, reproduce that amplitude as a "slam" at 50Hz. Is there a name for such a technique?

TLDR, I have the following questions;
1) Is using only a centre speaker in mono good for "non critical" TV viewing?
2) Which type of centre speaker would be best for listening mono?
3) What is the best way to create a mono signal from a 2chan source?
 
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neRok

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I did some tests on this other day. My TV viewing room is like below. The room is 6m wide, so the speakers are a considerable distance from the side walls. Also I pretty much only "lounge" (lay down) on the couch, so my head is in 1 of 2 positions (which are mirrored for all intents and purposes). I tried the book shelf speakers orientated straight and angled (toed in).
lounge.png

Whilst in normal stereo: Whichever side I was sitting on, the closest speaker would "beam" straight into the relevant ear (ie. sitting on left means left speaker has short path to left ear). I felt like there was minimal input from the opposite speaker, so any stereo imaging wasn't particularly effective, and dialogue on the opposite side was at a disadvantage. And actually, because 1 speaker was responsible for so much of what I was hearing, it made it sound like voices were coming from off the screen.

2 speakers playing mono: So I used EqAPO to copy both L and R audio to both speakers. This obviously improved the legibility of opposite-side sounds, and it helped center the sound into the TV a bit (not too much from what I recall), but it seems a bad option (2 speakers to do 1 "sound" seems unnecessary). But that lead to...

Using some stereo "crosstalk": So I worked out EqAPO could copy a volume adjusted version of each channel (I presume this is known as crosstalk), so I added what I presume was 70% (=0.7) off the opposite channel to each speaker. This helped narrow the sound to the confines of the TV, and kept some stereo feedback. It was a decent result. I guess this crosstalk is effectively what a center channel speaker is doing = helping deliver the opposite channel and thus pulling the sound into the center of the TV.

I then tried single speaker in mono below the TV. Obviously the sound was now central to the TV, but it sound "too central". By this I mean the sound was so obviously coming from right there in the middle, not spread out across the TV, if that makes sense? And also it was so obviously coming from below the TV. This was with the speaker "flat", so then I tried tilting it up, which didn't particularly help. I thought maybe having different parts of the audio split between the vertically aligned woofer and tweeter was making things worse (dragging the sound down much lower than the top of the speaker), so I also tried the speaker on its side. I can't recall exactly, but this may have been a tiny bit better in regards to the "height" of the sound.

For mono vs stereo (for TV shows, not movies), I'm not really sure how much was "lost" by not having stereo. Usually when a sound occurs on the screen, you can also see where it comes from, which may render the mono listening experience satisfying enough? For example I watched a video of a plane flying from right to left on the screen, and the audio had obvious stereo panning when in stereo, but when in mono it still faded in and out whilst at the same time I could see it going from this side to that side, and so it was still pretty good. So yer, dunno how important it is.
But as an argument against stereo, there was a scene that was shot from behind a character, and their phone went off in their right hand, and the audio was somewhat panned to the right. But then the camera changed to looking at the character front on, and so now the phone making noise is on the left of the screen. I can't remember what the audio did in that brief moment (perhaps it panned to the center), but the fact all sound effects are "temporary" and "insignificant" makes me wonder if LR or LCR is required at all.

So I'm not really sure what to think now. The fact that my LR tests and mono-below tests so obviously pulled the sound off the TV was not a good outcome for me. Would LR bookshelfs beside the TV with a C below the TV help locate the sound "within" the TV, or does the differing heights have other negative effects? Would any sound source below the TV ever not sound so obviously below the TV? Do actual Atmos soundbars with their upward firing speakers help in this regard?

Perhaps for a DIY solution, a single point source located as high in the box as possible might help? I guess this could be a coax speaker, or a waveguided compression driver, or a big dome tweeter, or just a decent full range driver? SPL requirements and not particularly high, so there should be many decent options. And I did start looking into the DIY front recently and found some decent posts starting here: Diy Soundbar - how would you design the best sound bar? | AVS Forum
I do wonder what the "minimum" required solution is though;
1) The "mono soundbar" would be so easy from a DIY perspective because any 2channel dac+amp could handle it with digital crossover (1 channel for bass, the other for midrange+). I am somewhat adverse to analogue crossovers because it seems so unnecessary when it can be done digitally, hence my thought process.
2) The 2.1 amp I obtained recently (Fosi BT30D) might be an easy way to have stereo hi-range drivers with bass woofers, but it would be a compromised solution (the .1 amp having a LPF that is likely lower than ideal, whilst it would still require an analgoue HPF for the other drivers).
3) Recently I learned about the mid/side processing technique of stereo sounds, and I wonder if it could be applied to a DIY soundbar? Perhaps a substantial center driver could be used, along with 2 small dome tweeters at each end. The dome tweeters would play their respective "side" channel, which might be enough to give the stereo imaging effect? Alternatively, perhaps the bass woofers can be run with mono bass but also the "side" sound. This effectively makes them full range woofers, but because they are only playing a small amount of "side" audio, that might not be a problem? Both of these options need more than 2 channel outputs though.

Lastly I will just brielfy mention that the "basic" bookshelfs I tested did sound pretty nice whilst providing in room "F0" of like 50Hz. Speach sounded better, and having some bass effects was valued (so at least things like the "bung bung" from SVU have some impact). I don't feel the need for proper deep bass or mega SPL for watching the shows I watch, and this testing further confirmed that.
 
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neRok

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I did a bit more reading last night about center channels. These threads provided some info;
1) Why do we need a center channel in a home theater system?
2) Optimizing Center Channel Performance - Dispersion, Placement & Image
3) CC Speaker: Design & Placement Issues, particularly post #4

There wasn't any discussion about mono, but all my observations regarding speaker position vs sound "location" seem normal. Quotes such as the following suggest my observation with the plane are correct, and thus mono might work?
When the speaker itself has the inherent property of not being localized, and nearby reflections are attenuated sufficiently, other cues like seeing a person on the screen talking places the sound firmly on the screen, even if the speaker playing is placed at a different height.
So the visual cues may be able to add a stereo effect to a mono sound. But the same post also says;
It works for moving sound that is already there, by chancing the frequency distribution of this sound while playing. You hear the sound, then fr. is changed, you hear it moves up.
It does not work to move the perceived location of the sound source from one speaker. There is no reference for the sound playing, so changing its frequency distribution before anything is playing does not move it up or down.
So a few posts were saying that EQ tricks might be able to be used to "raise" the sound stage, by increasing the FR around 8 kHz as per many posts, and even up to 15 kHz according to the post#4 linked above (which refers to a post by Toole).
Or you need you take advantage of psychoacoustic cues to raise the image closer to the center of the screen, if you use a center below the screen. Such as peaking around 8 kHz.
But when considering that against the second quote, perhaps the effect won't work because the sound hasn't moved? It's still a sound coming from a single source, but now with a bright spot at 8 kHz?

Unfortunately the speakers I was testing with are now gone, so I can't test any more. But in those threads I came across this info;
Sony OLED TVs (some models) use the entire surface of the panel as a speaker.
So I looked that up and found the feature is called Acoustic Surface Audio+™, and there were a few posts I saw on reddit of people saying that the sound was very good for a TV, even rivalling budget sound bars. And as it just so happens, I kind of purchased a Sony OLED late last week! I got it for a great price from a discount/deals website, so I just need to wait and see if the retailer actually honours it. Because if so, I might not need a "sound bar" after all!
 

Cbdb2

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Almost all tv and movies for the last 25 years have 3 channels of audio in front. The stadard used to be all (most) all dialogue in the center channel and most of the music and sound effects in L R channels. This makes for clear and centered dialogue no matter where you sit. Both stereo and mono are a compromise. Is your source mutichannel or stereo?
 
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neRok

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Is your source mutichannel or stereo?
I use HTPC and stream from websites. I presume it's all stereo.

Edit: I ripped a bit of the stream, and it is indeed stereo. Also I checked the rip in Audacity and can see very minor differences in the channels generally. But I found one scene where a push bike with a clicking sprocket passes in front of the camera and goes off to the left, and the audio appears for ~1 second in both channels, and then fades off in the left channel only for 1.5 seconds. Listening to this scene in mono on my PC headphones does not give the auditory effect of movement. I will go try it on my TV soon. But also, this is a very detail not even relevant to the main action, so would anything be really lost moving to mono? I guess I will find out when I test the TV soon...

Also new Sony TV is coming tomorrow! I don't know if my specific model has the feature, but some allow you to integrate the TV as the center channel of an AVR. Maybe I can just use a cheap powered "LFE" subwoofer to give a bit more bottom end? I will see about this too.

Edit2: The effect (or lack thereof) was the same on my old TV too. But I noticed the TV's audio was effective at making the stereo effect of the bike moving to the left even when I was sitting to the right. I'm not sure if LR speakers like I tested before would have been so effective (due to the dominance of sound coming from the nearest speaker when not sitting in the center).
 
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hnash53

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To make a 3.0 system, using a stereo receiver with A and B speakers, using the "B" speakers on my receiver, I connected the center speaker to + and + and got a good output.
Pretty simple way... at least to me.
 

JktHifi

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I think the AVR center speaker ourput is different from mono amp speaker output. The AVR will give you so much clear voice of people talking in TV. You better use a soundbar that has EQ for News/People Talking
 

Beershaun

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I would not recommend a mono solution. If esthetics and size are important just get a stereo sound bar and be done and happy. A mono sound bar or just center channel speaker will kill any stereo imaging and separation that is very common and prevalent in modern TV programming. There is also a lot of music in TV shows and low frequency effects that you would lose as well. I wouldn't overthink it and get a solution that is at least stereo.
 

jsilvela

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I'll echo others that advise against abandoning stereo altogether. For music, a single speaker really does miss out.

But, as you mentioned "I wouldn't mind a bit better audio than the TV puts out", well, a single speaker would likely be better than the TV speakers, yes.

If you're set on single speaker, there are cheap little boxes that can convert stereo RCA into mono RCA. I got one for about 40 eur / usd.

But, I wonder about the logistics: I see you don't have an AVR, so Left-Right-Center seems out of the question.
Would a DAC-with-remote-volume + powered speaker be the type of thing that could work for you?
You could do TV / HTPC -> DAC -> stereo-to-mono-box -> Powered speaker.

I use a single speaker for my desktop. I like it much more than stereo, for Zoom calls and Youtube talks.
The vocals are sharper, and they seem much more realistically like a person talking. The phantom center has a "voice of god" feel I personally don't like. But, personal preferences there, etc. etc.

You mention the imaging. My experience personally is that once you let a movie roll, you adapt to believing the sound is coming from the action and not from the dedicated center speaker below. There's the ventriloquism effect coming to the rescue.
You might find you can live with that, without having to resort to EQ tricks.
 
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