主题：[求助]关于开孔式音箱的近场测试

倒相箱某点的声压决定于喇叭正反俩面在此处的体积速度，只是反面的经过箱体和孔的作用改变了相位。正面的体积速度为Usp,反面的体积速度为Up,那结果应该为Usp-Up, 而Up经过箱体和孔后发生了相位改变，而此相位改变是包含在Up以内的，简单讲如果Up变成了负数，实际上就是相加了--这正是倒相的原理。

对倒相式音箱使用近场测量的方法要注意：

1。要注意转化到远场后相位延迟，水仙DX的MALLSA的帖子中有详细

2。如果喇叭离孔太近，那么会有相互影响不过LINEARX正在解决此问题，见他们工程师的帖

此主题相关图片如下：

这个问题理论上讲应该相加，但是LMS是相减，昨天咨询了LINEARX公司，他们回答了为啥相减，看来和测试系统有关系。大家如果有其他关于LMS测试问题，可以到他们网站上参加讨论

If you are generating the phase using the Minimum Phase transform, there is no polarity reference possible so you have to subtract them. They are both the same polarity. You have to subtract them so that the port curve is treated as opposite phase. Regards, Chris N. Strahm / Engrg LinearX Systems Inc. 9500 SW Tualatin-Sherwood Rd. Tualatin, OR 97062-8586 USA Tel: (503) 612-9565 Fax: (503) 612-9344 Web: www.linearx.com Email: chris@linearx.com

到此，DX对于这个问题最终解释清楚了

你没有完全领会上述帖子。如果一个理想的测试系统，能够测量出SPL和相应的相频响应，那么分别测试喇叭和孔后，那么最终的结果应该是将此2个曲线进行相加，相加的时候系统会自动根据相位进行相加。而LMS 不能测试相频曲线，其产生的相位曲线是计算出的最小相位，不是真正的相位，如你所知道的，喇叭的前后震动是相反的，所以在LMS里面应该是相减。至于DASS系统现在忘记了，等再看过说明书后再回答

摘自DAAS说明书，供参考

3.1.9 Combine curves
The disadvantage of the free field correction via impulse response is the reduction of
the frequency resolution. This is especially problematic in the lower frequency range.
The free field curve contains only few details of the true frequency response here.
A possibility to avoid this disadvantage is to combine a free field frequency response
curve with a near field curve. So you can get a complete frequency response curve
without the problems we mentioned before.
To combine curves do as follows:
1. Carry out the frequency response measurement of the speaker under test
2. If necessary calculate the free field frequency response curve
3. Position the microphone near to the speaker (near field measurement)
4. Press [F7] – [F1] and enter the chosen combine point.

The measurement then will be repeated and the frequency response curve values below
the chosen combine point will be replaced by the new measured values.
The combined curve can be saved and loaded like each other curve.
Note that the phase will not be combined, only the magnitude.