主题：各位老师您们好！我想设计一间9平方的小消音室，请各位多多指教。

其实我可以说我是一个喇叭开发低能儿,但我绝对是一个电声测量大师.

我的强项就是电声测量了.不好意思.

国明，你这习惯不好，不要批改作业，你还没资格做我的老师呢！

看了你的帖子，我可以打包票你没试过1/2自由场！！你不知道1/2自由场测试是不要障板的吗（我还假设你知道呢）？我们现在讨论自由场和1/2自由场的问题，既然1/2自由场不IEC障板，那不就只有一个选择了吗？

中高频这两种测试情况是样当然是提升6dB（这时的提升是和理论公式吻合的），低频因为自由场中IEC障板上的扬声器正反向声波不会隔断，出现声短路现象，导致低频声压下降，不信你可以自己测一下，算一下，查一下（IEC的资料），而1/2自由场就不同了，正向和反向的声波是完全隔开，解决了声短路的我问题，低频测量和理论上吻合的！

你的判断是错的，liyyMM我不知道，我是用过的！

国明，这么简单的问题要我来回讲，我都有点不耐烦了，这好象不应该是你水平吧？有时间再去翻翻书好吗？

呵呵，言重了，其实我觉得你“喇叭”做得比测量好，真的！

其实是个误会吗,你说的"一致"是指"曲线形状一致", 而我认为的"一致"是"两者声压相等",
由此看来大家的观点其实是相同,只是表达的不同,就没什么好争的了啊.

此主题相关图片如下：

看一下音箱的模拟,都没障板的.供参考!

附加说明一下:箱体容积20升,闭箱,单元为FOCAL 27KX 1W模拟

呵呵，技术探讨，这样很好，争论也没什么问题的，只要不相互攻击！

纠正一下，中高频时，我认为的“一致”是“曲线形状一致”“两者声压相等”！

呵呵，到此为止吧？

这次讨论问题的气氛还不错，继续吧！

那你不了解我了, 我最感兴趣的就是电声测试了, 测试系统我没用过的还真不多.从民用的到专用的.
从电声到水声的,从最便宜的LMS麦克风到B&K的水听器.

南大办班也是先从"测试班"开始,慢慢再到"开发班",不是吗

谢谢水仙兄提供曲线，能说明问题了！

有时间请国明先生给大家讲讲测试仪器吧！！

我觉得水仙模拟的有些不对劲,不一定准确,
对了,你Anechoic的那条线有问题,应该是平的而不是上翘. 否则LMS的说明书就错了,这样LINEARX就是自相矛盾了.

另外所谓"1/2自由场"或"半自由场"是指露天发射的, 只有面向天空才不会有任何反射波,
我不认为把半场建在消声室内是很有趣的玩法.那样做就丧失了半场的真正内涵, 因为声压级的提高,
引发的反射更大, 反而更加不准确, 所以诸位以前如果有过"在房间里玩半场"的经验,是不是有些问题呢.
真正玩过半场的人很少, 因为很少有公司在室外搞测试活动的


此主题相关图片如下：

Half-space or pit measurements are made by recessing the loudspeaker in the
ground with the drivers facing toward the sky, and the microphone placed
above the enclosure. Again, the mic should be directly in line above the high
frequency driver. This is shown in the figure below.
Since this type of measurement places the baffle board of the enclosure in an
infinitely large plane, measurements made in half-space do not exhibit the
rising response that occurs with anechoic or ground plane measurements.
However like the ground-plane, the radiation field is half of a full sphere so the
level is 6dB higher than a free field or anechoic measurement.
As with ground plane measurements, there should be no obstructions for a 15-
30 foot radius around the area for low frequency work.
Pit measurements can be one of the very best for producing SPL response
curves of the transducer/enclosure free of any reflection defects caused by the
environment. Many loudspeaker researchers and manufacturers have employed
this method for years.
In some cases the size of the plane can be reduced. If mid and high frequency
response plots are required, a smaller plane is permissible. A plywood table 8
feet square with a hole cut in the center for the transducer would provide good
results down to about 200Hz. The table can be above the floor and will act as
an infinite plane at these frequencies.

此主题相关图片如下：

呵呵，不要钻牛角嘛！严格意义上来说根本没有所谓的自由场，消声室也不是，只是在模拟（或者说近似，逼近）自由场环境而已。

Anechoic measurements require either a specially constructed anechoic chamber,
or placement of the speaker in mid-air far from any surfaces. The only
surface is that of the baffle board of the enclosure. This method includes the
enclosure diffraction effects.
The purpose of an anechoic chamber is to absorb all sound striking the walls
so that none is reflected. This is typically handled by covering the walls of a
room with sound absorbing materials. A chamber is shown below.
However, even well designed chambers still do not approach the ideal anechoic
behavior at low frequencies. At low frequencies, total absorption is extremely
difficult to achieve. For this reason most chambers degenerate to the behavior
of a constant pressure enclosure as frequency is decreased.
At these frequencies the pressure field will cause a rise in level with decreasing
frequency typically 12dB/Octave. In the mid and high frequencies the
chamber will usually have good anechoic characteristics.
Given the difficulty of either building an anechoic chamber or dealing with
microphones and loudspeakers suspended high in mid-air, true anechoic
measurements are not convenient for most people.

此主题相关图片如下：

Ground plane measurements are very nearly identical to anechoic measurements.
Because the measurement includes both the direct sound from the enclosure, plus
the mirrored image from the ground plane, the SPL for the same microphone
placement distance will be 6dB higher than the anechoic SPL level.
The only requirement for a ground-plane measurement is a large reflective surface,
such as a parking lot or drive-way, with no obstructions for a radius of 20-30 feet
or more. The procedure is to place the loudspeaker on its side on the ground, and
then place the microphone on the ground in front of the speaker.
Ground plane measurements, like anechoic measurements, will have a rising
character in the response caused by diffraction off the loudspeaker baffle board.
This occurs in the mid range region. The increase in SPL is about 6dB, the frequency
being determined by the total area of the baffle.
If you are measuring a multi-way enclosure with low, mid, and high frequency
drivers, the enclosure should be positioned on its side with the high frequency driver
nearest the ground. The microphone should be aligned on axis with the high
frequency driver as well. The off-axis angle relative to the wavelengths of the mid
and low frequency drivers will typically not be significant.
Many times it is a good idea to slightly tilt the enclosure downward toward the
microphone. The important goal here is to try to keep the microphone on-axis with
the high frequency driver.
The ground plane method is a very good choice and does not require any expensive
or elaborate set up. All that is required is a flat surface with some open area around
it. See the figure below.

此主题相关图片如下：

西西，这个论坛太猛了，这个话题也玩完了啊？还搞了那么多E文，至于吗？

小消音室

好贴!!!