[Jonathon Janusz]

Beg my pardon for maybe asking to dig a little deeper into the question, but I know - from being told and listening - that putting a big, flat panel LCD/plasma TV in the middle of the wall between speakers (like many people do in non-dedicated 2-channel rooms) ends in problems compared to not having the TV in place.  Often the common advice is to throw a comforter over the TV, which helps, but still isn't quite the same as having no TV at all.

What I'm wondering is, from a technical perspective, why this is the case.  Specifically, I wonder about some of the newest, thinnest, wall-mounted TVs.  Sure, the TV is still taking up real estate that could have some other treatment put there, but why would what is effectively a large format framed picture on the wall at this point cause so much issue with the soundstage even as compared to the previously mentioned actual framed picture?

I'm wondering what specifically it does and why it does it.  I don't have any other practical agenda in asking, just curious from an academic standpoint.

Thanks for any thoughts!

[glynnw]

I have a flat panel TV on the wall between the speakers which are 4' out from the wall and I have no problem with it - imaging is awesome.  I did originally build a removable 2" thick soft sound absorbing panel to cover it , but I never could tell a difference with it in place.   No visitor has ever complained that the TV mucks up the sound.  I cannot deny that some may hear a difference due to the TV, but not me.

[JRace]

Painted drywall will  absorb more 'sound' and reflect less back into the room compared with the protective glass on a LCD/Plasma TV.

http://www.studiotips.com/absorb1.html

Drywall, 1 layer 1/2", on 2 x 4's,

 125Hz  250Hz   500Hz   1000Hz  2000Hz  4000Hz
0.29      0.10      0.05      0.04      0.04      0.04

Glass:
0.10      0.05       0.04     0.03      0.02      0.02

1.00 means 100% absorbtion.

Not much difference, but there is.

[zoom25]

It's a problem that a lot of us have. In home theatre rig, it's the 60" TV. In the nearfield, it's the iMac. Like you, I've also noticed that as the screen is moved back, the sound gets better. Although, the degree of toe-in angle also makes a difference. I do toe-in all my speakers to various extents depending on the overall room and listening position. I think the directionality of the FR for each cabinet also factors into the equation.

I haven't yet been able to flush mount the TV or iMac, but do recognize that as the distance between the screen and front wall changes, there is indeed an impact on bass. I also prefer the sound without having in the middle.

Another thing that I was looking at for my home theatre rig was to perhaps one day get a very quiet projector with an acoustical screen. I'm not sure how feasible it is and the advantages/disadvantages in the long run.

[Wayner]

I have a 50" between my Martin-Logan reQuests and there is no problem at all. Just pull your speakers a little in front of the TV.........

[Jonathon Janusz]

I have a 50" between my Martin-Logan reQuests and there is no problem at all. Just pull your speakers a little in front of the TV.........

I'm sure (hope) that the idea of placing the baffle face of the speakers out ahead of the plane of the front of the TV is generally understood as best practice.

Maybe the term "problem" wasn't the best choice of words.  I'm curious - for those who can or do discern a difference, or those who have measured a difference in-room with or without a TV and noted a statistically significant difference - why acoustically there is a difference, in particular in light of that modern TVs are little more than picture frames.

JRace I think is getting somewhere with an answer.  I also thought about flush mounting a screen, but I would be concerned that one might get some sort of issue from putting a large surface area, albeit shallow, cavity in the front wall, unless the display were somehow both flush and sealed along the surface of the wall.

Some of the more prevalent comments I have heard regarding a TV in place is a slightly diffused center image compared to no TV, and a collapse of greater soundstage depth - a flattening of the sound stage, if that makes sense.

Good stuff; please do feel free to elaborate further!

[abernardi]

I've been having problems in my room with peakiness that I haven't quite nailed down.  I've posted about it before I believe.  I had a lot of reflective surfaces in my listening/living room.  I had wood floors, huge windows on the back wall, 65" plasma over the fireplace with the speakers on either side.  The peakiness to my ears seemed to be around the 700Hz area, like an ice pick in the ear.  But it varied from day to day, some days worse than others.  I thought it was my ears, my power, a bad amp, my DAC, digital glare (but it actually is worse with records), my speakers, my active crossover!, I tried everything and swapping out different components changed things, but never quite solved it.  So finally (and I know I should have started here...) I addressed the acoustics.  I put a rug on the wood floor, heavy curtains on the back windows, acoustic panels behind the speakers and covered the TV with a thick throw.  I did these one at a time.  The throw on the TV had the biggest effect, which I totally didn't expect.  My speakers are very front firing and there's not a lot of energy coming from the back or sides of the speakers, but the throw really helped.  The problem is still there, but it's much better. 
I would add that the angle of the flat screen would also contribute to the problem I would think.  My TV is angled down a few degrees for optimum optics.  I'm sure that would also make whatever sound is being reflected off the glass than much worse. 
Also, my house was built in 1953, before drywall, all lathe and plaster.  I'll bet I'm getting more reflections from the walls than most...

[Rocket_Ronny]

The problem is the reflective surface. Same goes for large componant stands and gear piled up in between the speakers.

To improve imaging you want "At Least" 10 milliseconds of delay between the first sound wave and reflective sound waves. Think 1' of distance as a millisecond. Pulling your speakers out from the wall 5' will give you 10 milliseconds. Having absorption on the wall reduces sound waves bouncing at certain frequencies which helps. For me, 5' is a minimum distance and prefer much more up to 12'.

Rocket Ronny

[kernelbob]

I've been looking for a larger flat panel TV to replace the one between my speakers.  Any thoughts on whether there's any difference good or bad between a flat versus curved display?

[zoom25]

Curved TVs are thought as worse for the sound.

[Rocket_Ronny]

Same issue, reflections. I would think curved is worse as it would direct all the reflections to the seating position.

Rocket Ronny

[JRace]

I have a 50" between my Martin-Logan reQuests and there is no problem at all. Just pull your speakers a little in front of the TV.........

Those speakers are dipoles and have a null at the sides which has the benifit of little acoustic energy being directied towards the TV in the first place.

OP: the further you can move your speakers from the TV the better.Dipole speakers (like Wayner's MLs) will reduce the potential problem.

Flush mount (the TV) or not the problems are the same as you have only moved the TV a couple of inches. Moving the speakers a foot or more would have better results and far less work.

[zoom25]

Moving the speakers forward from the screen can be good for imaging and getting a tight phantom center. However, also factor Speaker Boundary Interference Response into it. You might end up doing more harm in other areas. Play around with it. Of course, treatment and room build comes into play.

[Wayner]

My MLs are (of course) dipole, but they are toed in so that 3 people can enjoy the sweet spot. However, most dynamic drivers are only forward facing and getting the TV out of the first boundary refection area is very important. Because most folks have huge (in my mind) TVs, the toe-in angle of their primary drivers may be considerable and pulling them out a little into the room/setting back the TV is one of only a few options.

I also am one of the lucky guys to have a large room for all of this to happen in (32' X 28') and I have my system an TV along the long wall, so my speakers are fairly far apart. I have no center channel to be concerned with as my Sony TA-E9000es preamp can create a phantom center channel (where all of the dialog is) and do it very well. So basically, I'm 4.1 if you will. The REL T-5 sub sits in the corner and the surrounds are on columns that straddle the listening position. I like this arrangement because it puts the first reflection target from the MLs basically behind me.

The other point is that the MLs are very tall (as tall as me) and that may take some of the sound energy out of this plane. So, maybe there is another direction some can try, by raising their speakers a bit and/or lowering the TV. Most drivers have a diminishing off axis response as the angle from front on increases. If there is a frequency range that could be affected by the TV, it would be the lower mid-range.

Oh yeah, my equipment rack is right next to my TV on the left side.