C4也属于低频有限类的。。。没啥奇怪。

上面的兄弟提到低频有限类里有许多大厂的品牌，这倒不奇怪，比方说C4，不管从指标上或听感上如果把它归为低频有限类我认为没什么不合理（没看到在Stereophile榜单里）。
我们来看看几个熟悉的品牌在2015年Stereophile榜单A级榜的分类：
全频类：
B&W 800D：25-33k-6db，32-28k+-3db
世霸Amati Futura：25-30k
威信Alexia：20-32k+-3db
低频有限类：
Q5: 18—50K+-3db
马田 Django XL：26-30k+-3db
C4: 27-25k+-3db（非Stereophile榜单）

从Q5的指标看，它甚至比全频榜中的800d和世霸好了不少，实际听感也是如此。Q5能发出那种感觉像地下爆破的低频声，而且非常干净层次分明。
A级榜低频有限类的许多音箱我不熟悉，无从判断。但Q5我比较熟悉，所以当成一个特例拿出来讨论。

Loudspeaker Systems
Editor's Note: Class A "Loudspeakers" are sufficiently idiosyncratic and differ enough from one another that prospective customers should read Stereophile's original reviews in their entirety for descriptions of the sounds. I have therefore just listed every system or combination that at least one of Stereophile's reviewers feels, as a result of his or her experience, approaches the current state of the art in loudspeaker design. (Note that, to be eligible for inclusion in Class A, the system must be full-range-ie, feature bass extension to 20Hz. It must also be capable of reaching realistic sound-pressure levels without any feeling of strain.)

For those unconcerned about the last few hertz of low-bass extension, we have created "Classes A, B, and C (Restricted Extreme LF)" for those speakers that are state of the art in every other way. Candidates for inclusion in this class must still reach down to at least 40Hz, below the lowest notes of the four-string double-bass and bass guitar.

In addition, such has been the recent progress in loudspeaker design at a more affordable level that we have an extra class: E, for "Entry Level." Someone once asked us why Stereophile bothers to review inexpensive loudspeakers at all: In effect, aren't we insulting our readership by recommending that they buy inexpensive models? Remember: It's possible to put together a musically satisfying, truly high-end system around any of our Class D and E recommendations. That's why they're listed-and why you should consider buying them


Read more at http://www.stereophile.com/conte ... cmvwIbv5lYGOS42l.99

扬声器系统
编者注：A级“扬声器”具有足够的独特性，并且彼此不同，潜在客户应该阅读Stereophile的原始评论，以了解声音的描述。因此，我刚刚列出了每一个系统或组合，至少有一个Stereophile的评论者认为，由于他或她的经验，接近扬声器设计中的现有技术状态。 （请注意，有资格纳入A级，系统必须是全范围的，即特征低音扩展到20Hz，还必须能够达到现实的声压级，没有任何紧张感。）

必须有一位评测人认为，低频能到20赫兹，声压级要足够，而且没有任何压迫感。

爆破的低频声直接就刷下来了

大证据也未必能进入A榜，不要奇怪。既有数据也要有听感！

q5低音的有效振动面积是多少？知道振动面积即可推算出单元直径了。

单元不管串联或并联对低频下潜一点贡献也没有，只有密度的贡献！

这是单元串并联的参数变化，你觉着单元的谐振频率能大幅降低吗？

看Q5的箱体结构，一个高音独立箱体、一个六寸中高频是独立箱体、一个九寸中低频是独立箱体、两个九寸低音是独立箱体（也许其中一个是被动辐射器）。

三个九寸所担当的任务不一样，不可能都加一起！谐振频率都一样咋样扩展九寸单元所不能达到低频输出昵