|   Those well decorated hometheaters you see in magazines...... | Terrence
Jul 6, 2001 1:59 PM | | May look great, but I am beginning to believe that they don't sound that great at all. This is now the fifth time I have run into this recently.
I was asked by a friend to come look at his theater(megabuck I might add)and tell me why it doesn't sound as good as my screening room.
When walking into his room, one of the first things I noticed was how dead sounding speech was. So I'm thinking "good, acoustics are well controlled, one less problem". So I thought. I then went to check the eq, and found that the highs were very boosted, and the eq was all over the place. I thinking what the heck is this. Next thing is to look at the screen setup. He had his speakers placed carefully behind the preforated screen, in a nice straight line just like in a theater.(FLASHING RED LIGHT) So I go to check the front speaker delay settings on the pre-amp, and found that they were all the same distance. "Thats not right" I thought, that would put the center closer to the listening position than the mains. With tape measure in hand, I marked the distances from all the speakers to the listening position. Then I reset the delays. One down. One of the first things I notice when I peeked behind the screen, no baffle wall, and no acoustical foam to control reflections. Thats bad, real bad. As sound leaves the speaker, most sound passes through the screen, some is reflected back. The higher the frequency, the more dense the reflections behind the screen. That is one of reasons the eq was all screwd up. I also noticed he was using a older B & W THX speaker system. I hated to let them know that these speakers perform poorly when behind a screen. Domes, and cones have no place behind a screen. When their sound passes through the screen, it spreads way too much on the other side, since their directivity is not controlled. High frequencies disperse more quickly the farther you are from the source, so the perception of a loss(at the listening position)of highs is there, when in fact there is enough highs in the room already. When combined with an overly damped room, you have problems. The installer must have misread his RTA, because the speakers were distorting the highs, they were so boosted. Only horn loaded speakers do well behind screens because of their controlled dispersion pattern. When sound reaches the other side, it is more focus toward the listening position.
There in a nutshell is this hometheater problem. I end up recommending that he have a baffle wall installed behind the screen. When that was completed a week later, we went searching for speakers. Genelec's all the way around won out. With baffle wall installed, new speakers installed, aimed, and balanced, we tackled eq. When the baffle wall was installed, I put some pretty thick acoustical foam around the rear, and side of the screen speakers to control any residual reflections. Next I setup mikes for measuring the room. I found then, that very little eq was needed to flatten out the sound. None was used above 300hz, and very little below that.
When I was completed, my friend had spent quite a few dollars, but he was super enthusiastic about how much better the sound was.
This is a lesson to those who go to the designers of those fancy looking theaters. It may look great when finished, but it doesn't always sound as good as it looks.
Terrence |
| Delay question.. | Josh Studrawa
Jul 6, 2001 2:11 PM | | On my 1801, I have options for distance and volume (for lack of a better word) for all speakers. Does the distance setting automatically calc the delay? Or do I have to find it somewhere in there and set it? Seems logical that it would, but I'm known for overlooking that one little last thing. |
| short answer, yes it does (nt) | Terrence
Jul 6, 2001 2:15 PM | | |
| Damn good post nt | Adam
Jul 6, 2001 2:26 PM | | |
| Good Info, good post (nt) | nick4433
Jul 6, 2001 3:24 PM | | |
| One thing that escape me is why........ | Smokey
Jul 6, 2001 7:32 PM | | Why would a home theater designer that is working from ground up would design the speakers to be placed behind screen. I mean sound account for 50% of a good home theater set up and by placing the speakers behind the screen you are leaving its sound and radiate quality to the wind.
Also by placing a speaker behind the screen, a designer have to worry about the placement of baffle wall and acoustical foam behind the speakers to control reflections coming from the screen. No matter how transparent the screen is to speakers( it will be more transparent at lower frequency) at higher frequency >1 kHz, there would be reflective problems because of the nature of line-of-sight property of higher frequency.
I guess my question is why jeopardize a system higher frequency integrity by placing the speaker behind the screen. Don't you think it will more logical to design the speaker placement some where along or front of the screen, rather than placing them behind screen and then come up with solution to absorb the reflective high frequency sound wave reflecting back from the screen. Two wrongs don't necessary makes one Right. |
| Well smokey..... | Terrence
Jul 6, 2001 10:41 PM | | Smokey,
There isn't anything wrong with placing the speakers behind the screen. If you know which ones work back there, and which don't, it is actually a BETTER experience than if they were below, or above the screen. If you can't see the speakers, then the images just float across the screen in a well setup system. Because cones and domes tend to radiate their output more broadly in both the horizontal and vertical plane(especially when screen spread is added), they take more work to adjust. Typically, you would end up having to use drastic eq to make it sound balanced throughout the room. That usually drives the tweeters and mids quite hard. That is why they have to damp the walls so heavily, thereby drying out the room. Do you see the mistake? Excessive spread, more walls treatment, dead highs, boosted highs, distorted tweeters and mids.
With horns, it is a different story, they beam(according to the horns flare)like a flashlight. When screen spread is added, they tend to cover more of the listening position, as opposed to the whole room. Side wall reflections are kept to a minimum and less acoustical material is needed., better balance throughout the room.
Horns, and tweeters and mids with waveguides tend to work best. The answer lies in understanding how theaters do it.
I have found over the years that front projection systems using preforated screens work best with a baffle wall in place. Doing it this way seperates the front wave, from the rear reflections. Since most of the problem with typical hometheaters stems from proximity effects of L/R speakers close to the side and rear walls, with a baffle, the rear reflections(which are out of phase)can be damped to inaudibility. With this done, more than half of your acoustical problems would be solved. At that point, very little eq needs to be used.
So it actually can benefit a dedicated install to have a baffle wall.
Terrence |
| Terrence, please don't give me any more advice!! | Smokey
Jul 7, 2001 12:40 AM | | Any time I read yours or somebody' elses posting about HT improvement, it make me think that how I can implement that improvement in my HT setup.
For example, few day ago you gave some advice about center speaker and how it should match the L/R speakers, and now you got me thinking about replacing my center speakers and actually going shopping for it.
Then in your above statement you are talking about installation of baffle walls and how it will eliminate sound reflection from behind speakers and now I am thing about where can I buy some cheap baffle Walls.
What is going to be next.....you or somebody else will propobly give advice about the HT surrounding and how it can be improved and next thing you know I will be thinking about tearing down all of my walls and install red curtain all around my room to minimize sound reflection....hehehe (:^)
Thanks for info. |
| Terrence, quit giving advice period!! | Robert393
Jul 7, 2001 8:18 AM | | Yeah......exactly what Smokey said! This MUST stop!
I am actually sitting here this early Sat morning an laughing my ass off! Oh boy......this forum has taken on it's own character now! Mnay thanks to the dot (.) guy who ever you are!
I thought I had a lot of knowledge about HT, but I hang around here and learn more from all of you guys each day. That can be good and bad. The knowledge is good, but the problem is that after I have the knowledge I must then do something with it i.e. change my stuff HT around!! I am in the process now of completely relocating/repositioning my entire HT. Resulting improvements include lowering my monitor to proper viewing level, getting my center channel more in-line with L/R mains, elevating and moving to proper side listening of the L/R side/effect speakers, mounting rear centers above and behind listening position. And lastly, but the thing I am probably most excited about is getting my Silicon Image DVDO Iscan Pro Monday! Can't wait to see Sat. and OTA in 480p! I'll report to you guys after I have a few days to play with it, and I'll let you know how well it performs!
NOW I get to learn (worry?)more about sound deadening and wall baffles........your killing me! LOL!!!!!!!!!
You guys are great.......it was time we all loosened up a bit....
Have a great w/e!
Robert |
| Terrence, quit giving advice period!! | mtrycrafts
Jul 7, 2001 3:03 PM | | Its only money:-) YOu cannot take it with your:-) |
| Terrence, please don't give me any more advice!! | mtrycrafts
Jul 7, 2001 3:01 PM | | "What is going to be next....."
Stand by for a need for more $$$ :-) |
| I was afraid you're going to say that. | Smokey
Jul 7, 2001 4:54 PM | | |
| Great | mtrycrafts
Jul 6, 2001 8:14 PM | | Thanks for the input. Hope many will read it and remember some of this advise. |
| re: Those well decorated hometheaters you see in magazines...... | miamifunk
Jul 6, 2001 9:58 PM | | Speaking of bad magazine adds, did anyone notice the Paradigm add in Sound&Vision a few months ago? The speakers were set up in a room with solid brick walls and a hardwood floor. Even worse, the listener was sitting between the speakers...LITERALLY between them...with one at each side of her chair and the front baffles facing away. Anyway, it was good for a laugh. |
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