Flatscreen between speakers

@asctim 

So phantom centre describes imaging where the subject is dead centre!  Are there terms for where all the other sound sources might be located?

In the old days of classical stereo, recordings were made using a very small number of microphones (two or three being common) and the imaging "trick" was pulled off to great effect - no need for "multiple, near identical, time aligned sound sources" to be electronically processed

It’s not necessarily just dead center. Phantom imaging is any image generated some place between the speakers when they both play the same thing in phase. Or if they play the same thing with a time delay on one of the speakers. It’s only dead center if both speakers are at the exact same level and in phase, which means the comb filtering is at it’s worst. (There are potential combinations of level difference and phase/timing difference that can bring the phantom image back to dead center.) A lot of content has a lead singer or instrumentalist panned dead center, so it makes sense in a lot of ways to move that to a center speaker. The devil is in the details of how to do that, so it’s no surprise that audiophiles have often not been satisfied with the results of a center channel. It depends a lot on what characteristics of the sound they are most sensitive to.

If two or more omnidirectional microphones that are not coincident in location are used to record an orchestra, there will be delay characteristics introduced into the recording that may be considered technically less than optimal. I personally think a lot of the Mercury Living Presence recordings sound great despite this issue. Blumlein demonstrated that two coincident microphones could produce a coherent stereo image that was correct in both amplitude and phase at each of the listener’s ears for imaged sound objects placed anywhere between the speakers, with no delay echoes introduced as the microphones are right on top of each other, just pointed in different directions. Unfortunately it only works perfectly when sounds are hard panned to one speaker or the other. Anything in between will sound like it’s coming from the correct direction, but the tone will be increasingly corrupted by interference patterns, with it being at its worst when the imaging is dead center. The interference patterns are not caused by the microphones, but by the 2 speakers when they play the recording back, and this happens with 2 speakers regardless of how the mics were set up.  Fortunately this doesn’t sound as bad as it looks like it should. But still, it doesn’t sound as clear and pure of timbre as does a hard panned sound. So, center channels, and perhaps a couple more speakers between the center and side speakers have desirable potential. The problem is how to make the recording, or how to upmix a good 2 channel recording to more channels without doing more harm than gain. 

I learned recently that there are some French multi-channel recordings that were made with 5 microphones spaced apart in a row in front of the orchestra. The intent is to play the recording back with 5 speakers arranged in your room with the same spacing as the microphones. This allows for a proximation of wave front reproduction that a 2 speaker system cannot reproduce at all. Unfortunately it also generates lots of comb filtering/interference from delays when played back, which could be alleviated to various degrees with more microphones and more speakers. 100 channels would probably do a marvelous job of pushing comb filtering/interference patterns above the critical range, but would also be ridiculous to pull off. 100 speakers and 100 amp channels. Yikes! I’ve thought about ordering some of these 5 channel recordings and having a listen, but honestly I’m enjoying 2 speakers well enough and it’s considerably more convenient. 

@asctim 

When thinking about cancellation and reinforcement of sound, I would encourage you to think about the wavelengths of sound waves in the audible spectrum - Google AI thinks:

The human audible spectrum encompasses frequencies from approximately 20 Hz to 20 kHz. Correspondingly, sound wavelengths within this range in air at standard temperature and pressure vary from about 17 meters (56 feet) at the low end (20 Hz) to 17 millimeters (0.67 inches) at the high end (20 kHz). 

So there is usually lots of distance between speakers and listeners to hold many complete waves for most frequencies, and even between the drivers in one speaker!  There are pictures in this thread where the distance from a main speaker to one driver in the centre channel is about the same as the distance between the outer drivers in the centre channel.  No wonder it sounded better with a smaller centre speaker.

I would also encourage you to explore multi-channel recordings from France and other parts of Europe mainly to the North.  Several thousand classical SACDs are available, for example from Presto.  Most include a CD layer, so you can compare two-channel CD quality with DSD, which is usually on the disk both as two-channel and multi-channel.  SACD has now been around for almost a quarter of a century and these days most cost the same as a CD.  It is hard to find a streaming service that offers multi-channel DSD?

Studios have offered more than two channels since the 1970s, both on tape and quadraphonic records. The CD standard mentions expansion to 4 channels.

Today Dolby Atmos offers up to 32 channels - something being used by some engineers.  Dark Side of the Moon is quite something.  But the best exponent in my opinion is from Norway - Morten Lindberg and his label 2l.no.  I remembered rave reviews in Gramophone for the classic recording Reflections which was released in 2016 in a pack containing a SACD plus a Blu-ray audio disk with many options including Dolby Atmos and 9.1-channel Auro-3D.

Morten Lindberg is willing to leap on anything new - he uses 64-bit formats and floating-point numbers, not the whole numbers we are used to with PCM.  For a lot more depth see Merging Technologies - Use Cases

@richardbrand. Thanks for your thoughtful comment. My personal opinion is that stereophonic was designed to be sufficient for the reproduction of live music. By definition 
“Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective”

When done correctly, two speakers can put you right in the venue where the performance is recorded. If you listen to Charles Mingus, Miles Davis and most recordings from that era, you will realize that the weakness in the reproduction chain is the album itself or more precisely, the recording. Take two CDs of the same performance, one from Japan and the other from the USA and you will quickly realize that a lot can be missed from the same performance. If you’re not familiar with BACCH DSP, do a quick search and see how Dr Choueiri was able to restore a lot of that magic back. The problem with multichannel is that it requires a much higher expenditure in money and space. Stereo on the other hand seems simple and clever. 

@spenav 

Not sure where you got that definition of stereo!  The word stereo actually stems from the Greek word for solid.  In modern usage it refers to playback through two or more speakers.  I don't think two-channel stereophonic was designed per se, rather it evolved and continues to evolve, especially outside North America.

The problem with multichannel is that it requires a much higher expenditure in money and space. Stereo on the other hand seems simple and clever.

Never thought an audiophile here would baulk at the cost!  Agree a little bit on space, I've had to find room for two rear tower speakers, but then I deliberately shun a centre channel.  The four height speakers are flush with the ceiling.  On the other hand, my TV (home theatre) shares the same living space as my 'stereo'.

It is quite obvious to me that if you have say 9 channels available, you can always choose to use just two.  Many multi-channel classical recordings tend to use the extra channels for ambience, but some really open up the immersive experience.  Add in video from the Berliner Philharmoniker's Digital Concert Hall and you may be in for a real treat.

Not so much in the pop/rock space but try Dire Straits on SACD, or Pink Floyd in Dolby Atmos.

Personally, I prefer a simple microphone approach, exemplified in the US by Mercury Living Presence, RCA Living Sound and then Telarc.  Set the microphones and recording gear up and let the performers control the balance.

In Australia there was a series of adverts for the Northern Territory, about the most remote tourist destination imaginable.  The tag line was "If you never ever go, you'll never ever know".

@richardbrand 

I've had some experience with multi channel classical, jazz, and rock on SACD and DVD-A. I never had a really good multichannel system so it's fair to say I really haven't tested the possibilities yet.  My house needs to have a bunch of clutter cleared out of a couple rooms. When that's done I may have the space to get a decent multi-channel setup going. I still own the discs. 

@richardbrand. You and I both have a hybrid system. I have a 9.4.4 Dolby setup.  As for the definition, check here. That’s what the patent for Stereo Phonic Sound System calls for. I would encourage you to read it. The idea that stereo systems are supposed to be flat is misleading. When done right, the musicians are placed in time and space very realistically. It can be spooky at times. Of course, the recording itself must be done right. People sometimes refer to it as speakers disappearing: it’s not magic, it’s by design.

@spenav 

Amazing how two people can interpret the written word so differently!  From your Wikipedia definition:

Because the multi-dimensional perspective is the crucial aspect, the term stereophonic also applies to systems with more than two channels or speakers such as quadraphonic and surround sound. Binaural sound systems are also stereophonic.

Then you quote a US patent filed some 40 years after the pioneering work by Alan Blumlein which was patented in the UK in the 1930s!  In Australia we have a clear distinction between Patents and Trademarks

The word "stereophonic" itself is not trademarked. It's a descriptive term referring to sound reproduction using two or more channels, and therefore cannot be trademarked

The Wikipedia article discusses the use of close microphones and subsequent artificial mixing for pop/rock and then notes:

Classical music recordings are a notable exception. They are more likely to be recorded without having tracks dubbed in later as in pop recordings, so that the actual physical and spatial relationship of the musicians at the time of the original performance can be preserved on the recording

I absolutely agree that two-channel recordings can be stunning - I currently buy anything Decca (London to you?) puts out on CD with Klaus Makela conducting (unlike most European classical record companies, Decca does not seem to do SACD).  My main speakers emulate point sources of sound and throw a huge soundstage with a sweet spot you can walk around in.

Many years ago I auditioned Duntech Sovereign speakers which each contain 7 drivers in a vertical d'Appolito configuration.  They weigh 190-kgs each and are precision time-aligned.  I found that moving my head vertically by just a couple of inches suddenly produced the huge soundstage, then just as suddenly it disappeared.  John Dunleavy used the apparent point source Quad ESL-63 as his reference, which were many times cheaper and had a huge sweet spot but could not play as loud!

Most centre-channel speakers use d'Appolito configurations, but sideways.  Enough said?

What do you do with your centre channel when you are playing two-channel?

@richardbrand.

I am not sure I get your point. Which part of the definition you disagree with? (“Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective”). I listen to my stereo every day and that's exactly what it does (multidirectional and 3-dimensional). The better the recording, the stronger the effect, it was designed by the inventor of the format to do exactly that. By the way, the number of drivers in the speaker has nothing to do with the effect. The single driver Audience 1+1 does it as well as any speaker system.

By the way, when I listen to stereo, my center channel (single Audience 1+1) speaker does nothing.

@spenav 

Ah, but you used the term to strongly imply two-channel and you also imply there is only one format and that it was designed by "the inventor" rather than evolved over time.

My personal opinion is that stereophonic was designed to be sufficient for the reproduction of live music. ...  When done correctly, two speakers can put you right in the venue where the performance is recorded

Morten Lindberg, I think correctly, says audio is an illusion.  Somehow our ear / brain system builds up a ’picture’ and basically it can be fooled into ’seeing’ a soundstage just as the eye / brain system is fooled into seeing moving images.

I would encourage you to go online to 2l.no and buy a copy of Reflections.  You probably already have a Blu-ray player to feed your Dolby 9.4.4 setup.

I think single apparent source speakers improve the illusion because they don’t muddy the waters with interference effects from different pathlengths, and they don’t produce incoherent reflections from walls, floors, ceilings and maybe TVs.  The Duntech example I gave is the other extreme, where the multiple, separate drivers interfere quite severely between themselves.

I could only find the ClairAudient 1+1 V5 on the web and in its blurb was amused to discover that it is the most unique (there are no degrees of uniqueness, it either is or it isn’t) and that it eliminates the need for desperate drivers (plenty of those where I live)

The 1+1 V5 Personal Reference Monitors are the most unique small footprint loudspeaker in the world. They feature a highly refined proprietary wideband driver eliminating the need for desperate drivers

I see it actually has two full-range drivers in a bipole arrangement, and passive radiators.  You are worried that your plasma TV needs damping but passive radiators are OK?  By the way, if I did want a centre channel, the Audience might well be ideal!

@richardbrand.

Your first sentence is correct. When audiophiles talk about stereo, they are strictly referring to the two front channels. Yes, stereo has not evolved over time. The format was invented and patented by an inventor. My best stereo recordings are from the 50’s and 60’s. Stereo is not in your gear, it is in your recording. I am using two mono amplifiers to play stereo and if something is wrong with them, I use two channels of my multichannel home theater amplifier. The term has been used loosely for the most part. 
Stereo is an illusion just like seeing your image in a mirror is an illusion. There is not two you in the room but the image is real. It is however happening in the optical domain just like a phantom stereo center image happens in the acoustical domain. It’s not a mind trick per se, it’s real but in the acoustical domain. 
I intuitively feel that the big glass surface of my plasma TV is affecting the sound of my stereo system. I should be able to assess this objectively in a couple of days. It’s in the acoustic domain and I don’t have the tools to measure it accurately. Stay tuned. 
 

@spenav 

The image we see in a mirror is virtual not real.

Surely, hearing a central image in stereo is a trick of the mind. The ears detect two equal signals in phase coming from the loudspeakers, but we interpret them as a single sound coming from a point midway between the speakers.

@newton_john. 
You are correct. My choice of words was incorrect. I hope my meaning wasn’t lost in translation. My point is that the image is not a magic trick but something that can be explained, manipulated and repeated. In other words, it’s physics not voodoo. 

I asked Google Gemini for treatment options. One of the options was using sound absorption to the left and right, behind and below the wall hanging TV.  I used 24x48x2 panels (thicker panels would not fit behind TV) extending behind by 3” & below by 5”. Gemini claims this largely mitigates the problem. 
It recommends experimenting with speaker distance (mine are 30” out) from rear wall and ensuring there is no resonance from the TV & mount. Since the bottom of the TV rests on the absorption panels, that should help mitigate any resonance. 
Lastly, it states ’if you want to go the extra mile’ try placing thin removable panels or dense velvet/felt over TV during critical listening. Hope this helps. 

@signaforce. 
Funny, that’s what I have now currently. It’s not doing a lot but seems to be better than nothing. I am very close to something (2 days tops). I will tag you when I get it up. Thanks. 

I’ve always been more concerned about the internal loudspeaker of the TV resonating in sympathy with the sound in the room. My acoustic guitar does this when not in use so I dampen the strings with a soft cloth. Removing the surround loudspeakers from my listening room improved stereo performance.

Unless the stereo loudspeakers are toed in sharply and have front baffles close to the front wall or the TV projects out a long way, I can’t see how mid range and high frequencies that might cause problems could directly reach the screen.

@newton_john Although I no longer have a TV between speakers, I did for several years, and it was quite close to the wall and above the main speakers.

Covering the TV significantly improved stereo imaging.

I also have an acoustic guitar in the room and it never occurred to me that it could be resonating - I just had a listen and it most certainly is - a lot! - but damping the strings made no difference. Not surprisingly, the resonance is from the body, which is essentially a Helmholtz resonator. THX!

@macg19 

Thanks for the advice. I’ll give covering the TV a shot. Also will pay more attention to guitar - maybe putting the cloth over the sound hole will help. I suppose I could move it to another room.

Folks, the results are finally in. It took me a while, but the conclusion is undeniable. Yes, my flat screen glass, Plasma TV was definitely affecting negatively the performance of my music system.

I have so many people to think for their advice and contribution: @ghdprentice ​​@jeffbij, @bugredmachine, @erik_squires, @karlss0n, @elliottbnewcombjr, @mihorn, @shooter41, @atanarjuat99, @wooly_mammoth, @avanti1960, @mswale, @tablejockey, @richardbrand, @asvjerry, @gruvjet, @asctim, @bhrapp, @tweak1, @knownothing, @kubla36, @samoh, @newton_john.

I started in the direction of a thick cover and ordered one from Digital Deck Cover. They are not cheap at $120. I was planning on modifying it to make it more substantial. One common mistake with acoustic panel is to think that any thickness will do. And then kubla36 chimed in and showed a picture of a panel that he designed. That was actually my original idea, but I thought it would have been expensive. Turned out it just looks expensive. The material can be found at Amazon here and here. Wood working is my hobby, so I had all the tools I needed to make it happen. My design is a little different from his, but the possibilities are endless. The pictures can be seen in my Virtual System. I couldn't load that many pictures in the thread.

So how does it sound? Exquisite. Soundstage height is finally right; soundstage depth is much deeper. I will do some measurement later, but for now I need to relax and enjoy the fruits of my labor   I got to admit, it took me longer than I anticipated. Designing a mechanism to hang it on the wall in front of the TV is the most challenging. The panels construction itself was very easy. I use double sided tape to attach the 12"X 12" panels to the board and the frame construction was kept simple. The two panels system was ideal for me because I could keep them light. The whole project costs less than $200.

Looks fantastic!  I lack carpentry skills.

So its not just my wishful thinking on soundstage (lots of options for panels). I forget to put it up while casually listening and after about two news articles its always, "something's wrong with the music".

@spenav  Yay!  Always good to hear (literally) that you've found and executed a solution that Works above your expectations....

To misquote the Super, "Our work here is done...."

...for the time being, anyway....*L*

Enjoy, play Loud, J

Congratulations! Hard work and thought is rewarded in this pursuit. Happy to hear about your results.

Nice work. As cousin Eddie said, "BINGO!"

Looks great! Glad it sounds great too.

Great job!

Cool!

@spenav

Thanks for reporting back on the fruits of your labour!  Must admit I like the look of the diffusing panels.

I've now had a virtual look at your system and see you already have everything you need for 'immersive' sound, except possibly silver disks for the source!

I know you believe that for 'solid' sound, two channels are necessary and sufficient. I argue that two channels are necessary but not necessarily sufficient.

So can I suggest another experiment for you to report back on, which is even less expensive.  Just pop an "immersive" disk (multi-channel SACD or Blu-Ray) into your Oppo and let your Marantz processor use all its channels as it thinks best. Preferably connect them via an Ethernet-capable HDMI cable.

Many of the recordings from Norwegian label 2l.no ship with hybrid SACD and Blu-Ray containing an assortment of hi-res formats.  I've suggested Reflections which is classical but there are many Grammy nominations in their catalogue.

Love to get your reactions .

@richardbrand. I am a veteran of multichannel. I have plenty of concert DVDs, my favorite being Hell Freezes Over from The Eagles. That’s the reason I have an AVR instead of a preamp. The reason two channels are sufficient for music is because at a live performance, the sound is coming from the front. There are no musicians on the side or in the back or on the ceiling. These are necessary for movies but kind of unnatural for music. I am not saying it can’t be done. My AVR can do Auro 3D and Dolby Atmos music. I prefer stereo though. There is a reason the format has been around so long and is so successful. It is simple and clever. When done right, it really takes you there. Enjoy the music. 

If I could go back I would not buy a tv and buy a projector

@rtacconi. Everything has its negatives. Projectors require that you watch in the dark only, they are still much more expensive than a comparable flatscreen. It you have a home theater dedicated room, then by all means…

Yes but there are now projectors with high luminosity and you don’t have to be in the darkness. Yes they cost more but they are still relatively affordable like with 2k you can have a great 100 inch picture with less eye fatigue 

I see. It’s worth considering. They also seem to be affordable. 

A few observations that I made since using this panel:

I would still use it if don’t have a TV anymore between my speakers. 
It is doing much more than removing the glare or whatever the glass was adding to the equation. 
It can be configured with a combination of absorption and diffusion to resolve particular issues in different situations. Mine has very few absorbing tiles (3).
It probably would look better using white tiles. The black tiles look kind of austere for lack of a better word. But that’s probably a matter of taste. 

I am planning to use a pull down TV wall mount that is built to allow a TV mounted above a fireplace to be pulled out and down. 

Instead of mounting a TV on it, I would mount a diffuser slightly larger than my TV that would be above the TV when I am watching television and would swing down to cover the Tv when I I am listening to music.

My only concern is that the TV would be too far off the wall when is is the down position. to that end i am still looking for one that swings more "down" and less "out".

@tony1954. You might have to build whatever you want. Set your design parameters then solve them one by one. Mine were that the gadget be light, not expensive, functional and elegant. I have achieved all of them to varying degrees. Some were even exceeded. Like I said, you might have to create it yourself. Good luck. 

@spenav 

Had a look at your setup and your solution with hanging a panel on the TV seems to be a more practical (and less expensive) solution.

If I make it so it can either hang the panel on a French cleat situated above the TV when I am using the TV, or hang it on the TV itself when listening to music, then It should be the best of both worlds.