Acoustic Benefits of Front Projectors
John Meyer, Newform Research, Inc.
December 31, 2002
Did you ever think about the impact of your video system on the acoustic performance of your home theater? Few people do. But the surprising fact is that there are important acoustical advantages to be gained by using a front projection system instead of a big-box rear projection television.
Many of the first video enthusiasts came from the ranks of audiophiles. Equipment and performance driven, they expanded their fascination of music reproduction to include the whole home entertainment spectrum. This meant taking a TV and plunking it down between their carefully placed hifi loudspeakers.
Of course, some budding videophiles were sufficiently well-heeled to allow them to have separate rooms for music and home theater. They didn't even try to achieve great sound in their home theater room because both the equipment and the soundtracks were, until recently, way below audiophile standards.
That has all changed. Although still variable, many movie soundtracks now deliver excellent acoustics and, dare I say it, true hifi sound. And the equipment is now fully on a par with the best from the two-channel music world. So two separate rooms are no longer necessary. Two-channel audiophile performance and high performance home theater can be blended into a single system.
But what happens when you drop a big TV into a carefully tuned music system? In a word--disaster. The soundstage becomes much more two dimensional. Both horizontal and depth focus significantly degrade. And timbre is altered as well. There is no good news here except that when the TV is on it provides enough of a distraction to make the flaws less noticeable.
Why is a TV an acoustic nightmare? From an acoustic point of view, a tube or rear projection TV is a large box consisting of reflective and resonating panels and sharp corners. Instead of the generous space in which the speakers were placed with a wall well behind them, they find themselves roughly on the same plane with this large reflective surface. Effectively now each speaker is in a bit of an alcove. The typical rear projection TV with room for its cabling in the rear, effectively moves the wall forward 2 ½ to 3 feet. That is a big loss of space. (Anyone still living with a large TV should place the speakers as far ahead of the plane of the TV as possible).
Where once the sound radiated out from the speakers in an uninterrupted hemispheric pattern, the side wave now encounters the TV chassis and reflects both back towards the speaker and forward toward the listener. These delayed waves arrive shortly after the main direct wave from the speaker. This multiple arrival time smears the soundstage focus.
Furthermore, because the reflective surfaces of the TV are not 100% solid, they are more reflective for some frequencies than for others. Thin plastic, glass and wood panels are less of an obstacle to low frequencies than they are to high frequencies, so they reflect more highs than they do lows. Hence there is a tonal imbalance introduced as well.
Those same thin panels move with the sound that hits them. Once moving, they don't stop when the music does. They now have a (short) life of their own. Tap on any panel of your TV and listen to its individual sound. This tone is playing, excited by the soundwaves from your main speakers, sub etc., when your sound system is on. And each panel speaks with a different voice--a low level cacophony. TVs are simply not designed with any thought of acoustic performance.
The British picked up on this early on. That's why, in a high-end British audio shop, there was only one pair of speakers in the room at any one time. If you wanted to listen to another pair, the first speakers were removed and the second pair brought in. This eliminated the effects of having a set of large boxes upsetting the sound from the working speakers. A large screen RPTV is like having several sets of large speakers at the front of the room. The effects are not subtle once you have tried it both ways, and you'll be aware the situation is less than ideal until you get rid of the problem.
With our own Ribbons, which extend above the top of most RPTVs, standing up will reveal a tremendous depth of soundstage and openness while sitting down the soundstage flattens out and the sound closes up. This is distinct and completely unavoidable even with damping on the sides of the TV cabinet to reduce the effect.
Front projectors change all of this. Essentially, they and the screens they project onto are acoustically invisible. They return the room to its state before the arrival of the 3 cubic metres of living surfaces which is a rear projection TV. They give the speakers space and act much the same as the wall behind them. If video screen material is acoustically reflective, it is at a vanishing level. If the screens resonate (everything does at some point) it is imperceptible and probably un-measurable. Video screens suspended several inches off the wall simply get out of the way of proper and natural sound propagation.
The bottom line is this: front projectors give you your music back. We have long maintained that in the future a great music system will be a great home theater system with the video switched off. Despite an acoustically rough start for home theater, front projectors have now made that ideal an attainable reality for the great majority of music and video enthusiasts. Home theater capability is no longer an impediment to the finest reproduction of music.