工作室声学第2部分:驻波

This mini-series sees Joe Albano demystifing the science of studio acoustics. In Part 2 we look at low-frequency standing waves which can get in the way of getting a well balanced mix.  

这一系列的第一部分 ,我列出了一些可以实现良好的录音和混音的方式获得室内声学问题。在这篇文章中,伊利诺伊州将开始在细节,用的问题得到一个很好的平衡搭配最常见的原因之一开始,和混合的能力去旅行wellto声音在其他地方好。这个问题是低频驻波。

站在我旁边

每当发生在一个封闭的空间的声波,它们与房间boundariesthey相互作用可以反射离开它们,将它们吸收,或穿过它们。驻波,又名房间模式,是反射波的函数。在中频和高频波围绕一个房间反弹,他们可以导致一个愉快的感觉ambiencelivenessor引起不愉快的文物,像扑回波。但是,当低频波反射出房间表面,他们表现自己有点不同。

Fig 1 A typical Studio Control room layout

图1一个典型的工作室控制房间布局

没有进入它的物理太多,所有的音频波具有的声音产生对象的振动的特定fhrequencythe率,在振动周期每秒或赫兹下测量。波本身是一系列的空气的压力变化(比正常pressurecompressions更高,并且低于正常pressurerarefactions),从源发出出并传播穿过房间。当这些波的一个满足室内表面(墙,地板,天花板),它会反射回来进了房间,从表面反弹至表面。在中,高频率,这可以是细微的,但是低频率存在,因为其波长不同的情况下,。

龙和它短

每一波具有波行进在房间是它需要以完成振动的一个周期时的wavelengththe物理距离。由于低频波振动速度比中频或高点,它们的波长更长。音和高音可能从几英寸到几英尺的任何地方波长,但低点往往有接近和超过房间面积自身的波长。当这样的一个波在一个房间的两个平行面之间的反射,它的两倍回到它自身上,造成的干扰,在增强材料和取消的形式,在与该波长相关的特定频率。

当发生这种情况与音和高音,这些取消和增援分布在整个房间。然而,随着时间越长,低频波,则取消与增强件被定位在室的特定区域。其结果是,在房间的低音响应是不均匀的,在一定frequenciesthere将太多的低音在房间里的一些点的特定频率,并没有足够的其他人。

Fig 2 Standing Waves reinforcing and canceling a particular frequency and its Harmonics at various locations in a room

图2驻波增强和取消在各种位置的特定频率及其谐波的房间

如果工程师/搅拌机,或扬声器,在这些景点之一,然后听到房间里的声音将是什么样的录音低端是真的很喜欢灯红酒绿。通常情况下,这将导致该EQ补偿,一个室低频率的问题,而不是在该记录本身实际问题作出决定。当所产生的组合是听到其他房间,其中不共享这些完全相同的低频违规行为,他们的声音baduneven低端,要么太薄或桶状,整体。

它映射出

为了解决这个问题,首先映入眼帘的事情是必须做的是确定哪些频率,什么地点在一个给定的房间会受到影响。幸运的是,对于特定的房间,将发生驻波的特定频率,并且该问题区域的位置,可根据房间的尺寸来计算。我不是要去通过所有的物理公式thistheres任何空间,他们可以在任何数量的工作室书中找到acousticsbut我会提到一个或两个可以做最基本的计算。

所有并行室dimensionswalls(长度和宽度)和地板之间产生的驻波

当特定频率的波长,正是一个房间尺寸的倍数时,将发生在该频率处的驻波。此外,由于复杂的音乐波都有谐波,这是基本频率的整数倍,那么谐波波长也将是相同的房间尺寸的倍数,也将导致

不要害怕公式

这可以计算和映射outwithout任何必要的测试设备或特殊物理knowledgewith简单的公式11302L(其中2L =房间尺寸×2,和1130是声音的速度)。这给你的频率,驻波将形成在roomstanding波也将形成在该频率(谐波)的整数倍。

所有的驻波的频率将有增援在两个wallsthese被称为腹。主

Fig 3 The distribution of the Nodes and Antinodes of the first three (of one set of Axial) Modes in a room.

图3的在一个房间的第一个(一组轴向的)三个模式中的节点和波腹的分布。

音频例如1如何

[音频ID =“32631”]

前三个或四个轴向模式,在最低频率,通常是最problematicabove 300赫兹左右的节点和波腹被如此并拢,它们平均出一个更均匀的响应,在那些较高的频率。但要记住,这些节点和波腹出现为三个平行室boundarieslength(前

该怎么办

而其容易够确定在房间里的反应可能是最不均匀,解决了这个问题可以更有挑战性一点。商业解决方案包括多种产品,如低音陷阱,被置于对着墙壁,或者,更可能的是,在角落,打散

如果youre涉及记录/混合空间的初始结构,从一开始,然后腔可设计成在壁本身抵抗的影响

中庸

最小化的负面效应的一个方法

Fig 4 Some established “Golden Mean” room dimensions

图4建立了一些中庸的房间尺寸

驻波洗牌

即使你没有应用任何提到的治疗方法的选择,可以做的至少是确保工程师/搅拌机甜蜜的初级离开。7监督positionand扬声器的位置,都没有正确的一个节点的中间或腹。这意味着,具有音箱靠墙可能是最好避免,除非这些扬声器的布局是专门设计的。虽然低音响应可以有一个控制台或桌面放置较少的魅力,低端可能会更加均匀,并且那远比骨霍霍低音更重要。如果你映射出最强的位置

Fig 5 Top) A studio with speakers and engineer/mixer’s “Sweet Spot” coinciding with standing waves Nodes & Antinodes (problematic); Bottom) The speaker position and “Sweet Spot” relocated to avoid the Nodes & Antinodes of the most prominent standing waves (better)

图5顶),与扬声器和工程师/搅拌机甜蜜点与驻波的节点重合一室

最重要的是,你需要去了解房间的声音,以免使EQ选择,只能在那个房间里有效,并会混合声音更糟糕的其他地方(音频例2)。

音频例2的4条通道重复4次:A)原非EQD组合,因为它会听到在一个房间里,没有驻波

[音频ID =“32632”]

要做到这一点,组装好,商业录音收集,并用它们来了解如何低端的声音在你的房间与已知有合适的低频平衡混合。然后使用这个作为你什么你自己的混音低端的平衡应该听起来像在你的房间的参考,而且,只要有可能,请检查您的混音在其他系统上,在其他房间,最后确定之前。它当然可以做好的,平衡混合,甚至在一个房间由于低于完美的响应

下一次,伊利诺伊州继续这个系列一看一个中等和高频率的反射。

Joe is a musician, engineer, and producer in NYC. Over the years, as a small studio operator and freelance engineer, he's made recordings of all types from music & album production to v/o & post. He's also taught all aspects of recording and music technology at several NY audio schools, and has been writing articles for Recording magaz... Read More

Discussion

Jabun
Good article, though you should give units for the values in the formula, otherwise it won't work properly. The speed of sound is 1130 ft/s as you give it, so the room lengths will have to me measured in feet to get the correct frequencies.

Alternatively, you could go metric by using speed of sound = 344 m/s, then your room lengths would need to be in meters.
james
Joe, first: I know nothing. So the question may be total stupidity. Are standing waves the reason why music on the car stereo sounds better with the windows fully open? Or is this due to sound from the outer environment acting as carrying waves for treble within the car? Or it all an illusion?
Joe A
Opening (opposite) car windows would eliminate one source of parallel reflections within the car, which could have a noticeable effect on both mid/high-frequency reflections (clarity, flutter echoes) and lower-frequencies (mud, masking).. (Keep in mind that any standing waves in a car interior--even in a larger SUV--would form at much higher frequencies than in even a small room, due to the smaller distances between (more or less) parallel reflective surfaces).. Also, opposite reflective surfaces in a vehicle are probably not entirely parallel, which makes the whole issue a bit more complicated..
Irene M
Hello Joe,

I'm a student, and I'm doing a math paper on how to build a room with the dimensions of the golden ratio to increase sound quality. Your article was beneficial in understanding about frequency and how wavelength is a significant factor.

In your article, you mentioned the dimensions of the golden ratio to design a room, but how did their numbers come to be? Could you either explain or maybe direct me to the source that you used to get this information.

Feel free to reply here or contact me through my email: irenemahanyu@yahoo.com

Thanks.
Joe A
Hi Irene -

AFAICR the origins of the theory go way back to ancient Greece -- for background and practical applications of golden ratio/golden mean theory there are several books by F. Alton Everest that are generally considered reference texts on studio acoustics, including "Master Handbook of Acoustics" and "Sound Studio Construction on a Budget", among others. If you Google "recording studio acoustics" on Amazon you'll find them along with additional texts. Also, the websites for the companies that make acoustic treatments (Auralex, RealTraps, etc) often have useful information/white papers on studio acoustics and theory, and if you're an AES student member you may be able to find relevant Journal articles there as well. Googling "recording studio golden mean or "recording studio golden ratio" should turn up additional sources of information.

Cheers,
Joe

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