【聚焦】影音中国“大师问答Ask the Guru! ”第七期
“大师问答Ask the Guru! ”第七期的内容，我们来了解一些和屏幕增益有关的问题，对于小房间环绕声系统的选择、不规则形状的房间如何改善声音效果等实用的问题，大师们也都给出了自己的答案。
如果我想观看更大的画面，应该选择一款更大增益的屏幕吗？或者你有其它的建议？
Gregg Loewen（THX视频培训首席讲师、Lion AV顾问公司创始人）：
An excellent question that could warrant an entire article of response (ie: The question of screen selection). Due to design limitations, a particular model of projector will only allow for a certain amount of light output. The larger the screen size the dimmer the image. There are many light output calculators that will assist you in making educated decision in regard to this question. The parameters of: lightout, size screen, screen color, and screen gain, while considering the ability to control ambient light and also needing to consider room reflectivity (is the room painted white or black) need to be considered.
这是一个好问题，我敢说我能写一整篇文章来回答（关于屏幕选择的问题）。因为设计上的限制，一台特定的投影机只能有一定总量的光输出。屏幕尺寸越大，图像越暗。有很多亮度输出的计算器可以帮助你做一个明智的决定。参数包括光输出，屏幕尺寸、屏幕色彩、和屏幕增益，也需要考虑到控制环境光的能力和房间的反射（房间被粉刷成白色还是黑色）。
Gregg Loewen先生
如果我想看3D电影，对屏幕增益有要求吗？
Gregg Loewen（THX视频培训首席讲师、Lion AV顾问公司创始人）：
The challenge with 3D is the lack of light output as the use of 3D glasses can decrease the amount of light output by up to 75%. The minimal goal of light output for a 3D projected image should be 4.5 fL. If the projector and screen combination cannot achieve this target then the screen gain will need to be increase to meet the light output target. Also, remember that as the gain is increased the viewing angle is decreased. Other options include changing to a projector with more light output and getting a smaller screen size. Lastly, ambient light control is critical when viewing 3D.
3D的挑战在于亮度输出的缺失，因为3D眼镜的使用会减少超过75%的输出亮度总量。一个3D投影图像的最小输出亮度目标应该是4.5FL。如果投影机和屏幕的组合不能达到这个目标，那么需要增加屏幕的增益。同时要记住，当增益增加时，观看角度会变小。其他选择包括换上输出亮度更高的投影机或更小尺寸的屏幕。最后，当观看3D电影时，环境光的控制也至关重要。
哪一个4K投影机技术是最好的？TI UHD 4K, JVC 4K D-ILA 还是Sony SXRD? HDR功能重要吗？
Gerry Lemay（THX视频培训首席讲师、Lion AV顾问公司创始人）：
There are many factors involved in the perception of image fidelity and only one them is the native resolution of the imaging chip. Far more important is the absolute black level followed closely by the contrast ratio. Seating distance, screen size and material, and lense quality also factor into this perception of image fidelity, so there is no best technology but rather the best technology for a given situation should be considered.
HDR is an exciting development in the home theater market. To enjoy HDR the viewer not only needs to have an HDR capable PJ (meaning accepts an HDR signal) but also needs to have a PJ that is able to process at 10 bits, have increased color gamut, and have increased light output of 2 to 3 times the SDR light output value. On a side note, generally speaking the ability to have a good black level is essential when trying to achieve a great HDR image.
影响图像还原准确性的因素很多，只有一个是成像芯片的原生分辨率。更重要的是绝对黑位，紧跟其后是对比度。还有座位距离，屏幕尺寸和材质，以及光学镜头质量等因素，所以没有最好的技术，只有在特定情况下应该考虑的最好技术。
在家庭影院市场，HDR是一个令人兴奋的发展。享受HDR的内容，观看者不仅需要有一个支持HDR的投影机（意味着能接收HDR信号），也需要它能达到10bit色深，更广色域，2-3倍SDR亮度输出，另一方面，通常来说，在获得一个好的HDR图像时，投影机呈现优秀黑位的能力也很重要。
在一间小房间里安装7.1或7.1.4系统有必要吗？会不会5.1系统已经能得到不错的环绕声效果？
Gerry Lemay（HAA家庭声学联盟创始人与主席 ）：
The answer to this question should be based upon the specific room. For example, in a small room adding more surround speakers can complicate seating layout. This is because speakers that are too close to any listener can disrupt and even collapse the surround field. We call this the “exit door effect” since localizing a nearby speaker makes you aware of the speaker and you lose the illusion of the movie created by the sound track… just like someone interrupting the movie by flooding the room with light by opening the exit door. In such rooms, you might be better minimizing the surround channels so you can place them farther away from your listeners. As you say a 5.1 system can be very good, however adding more channels can create a better sense of envelopment and immersion. In most cases, I would add ceiling speakers to fully enjoy Dolby Atmos or DTS:X. In rooms will tall ceilings (3 meters or higher), you could easily add ceiling speakers, but in lesser height rooms Dolby Atmos Enabled speakers which reflect sound off of the ceiling might be a better choice. Larger rooms give you more options but you still must avoid having speakers too close to listeners.
这个问题的答案要以具体的房间为基础。例如，一个添加太多环绕音箱的小房间会使座位布局复杂化。这是因为离任何聆听者太近的音箱会破坏甚至使整个环绕声场崩溃。我们将这种现象称为“出口效应”。因为你离旁边的音箱太近，导致你只意识到那只音箱，而失去电影所营造出来的声音幻象。就像有些人突然打开门照亮房间而打断你看电影。在这样的房间中，你可能最好还是减少环绕通道的数量，这样你可以将它们摆放得离聆听者更远。就像你所说的，一个5.1声道可以非常好了。然而，增加更多的声道可以创造更好的包围和沉浸感。在大部分的案例中，我会增加天花音箱来享受完整的杜比全景声或DTS:X效果。在一些有着3米或更高天花板的房间中，你可以轻松增加天花板音箱，但在天花板高度更低的房间中，选择能将声音反射到天花板的 Dolby Atmos Enabled 音箱会更好。更大的房间给你更多的选择，但你仍然必须避免让音箱离聆听者太近。
Gerry Lemay先生
如果我不想改变房间的不规则形状，有没有什么简单的方法能改善声音效果？
Gerry Lemay（HAA家庭声学联盟创始人与主席 ）：
There are two problems with irregular rooms: 1) Depending on the shape of the room, it may be difficult to properly place speakers. 2) This makes predicting low frequency modes much more difficult to deal with. As you might understand, the ability to solve either of these problems depends on the shape of the room. In the case of low frequency modes, we try to predict where these modal resonances cancel bass and avoid placing seats there. If you don’t have the ability to predict such things, the best solution is to use an audio generator playing a sine wave to find the lowest mode frequencies by changing frequency until the tone becomes very loud. You then can find the cancellation points and avoid them when placing seats. This process is taught in the THX-HAA Advanced class and is much easier if you also have a high resolution RTA to use.
不规则房间会有两个难题：1、根据房间形状的变化，合理地摆放音箱可能会变得很困难；2、这也会让能预测到的低频模式会变得更加难处理。就如你可能理解的，解决这些问题中的任何一个都要依靠房间的形状。在低频模式的例子中，我们试着去预测这些模态共振取消低频的位置，然后避免把座位放在那里。如果你没有能力去预测这些事情，最好的解决措施时使用音频信号发生器播放出一个正弦波信号，改变音频信号的频率，如果发现声音变大了，就能寻找最小的房间模式频率。然后你可以找到相消的点，并在放置座位的时候避免放在这些点上。这个过程将在THX-HAA高级课程中讲授，如果你可以使用一个更高分辨率的RTA实时分析仪，过程将会变得更加容易。