科普一下，密闭箱箱体谐振频率计算 [复制链接]

谢谢3L大烧
能与众分享是大德

T/S参数定义：VAS，驱动器的空气等效容积。VAS具有的声顺等于驱动器振动系统的声顺。

VAS=ρ·c↑2·CAS

其中CAS是驱动器支撑的声顺。

换种说法：VAS是令驱动器谐振频率提高到自由空间中数值的√2倍的密闭音箱中的空气容积。

BTW：单元厂商提供的VAS数据都是实测值，不是推算出来的。

业余条件下，可造一设定体积的密闭箱体，将单元装入，测定Fc后计算VAS.
VAS=Vc·｛（Fc/Fo）↑2-1｝

轻描淡写即将电声界最经典的理论推翻，楼上名符其突。

嗟叹都觉得多余，藕收口。

原帖由 强悍制箱 于 2012-7-7 16:34:00 发表 惠威W5的振膜为PP材料，使得其音域较宽，从其灵敏度曲线上看，即使到1400Hz，灵敏度数据变化也不大，它还带导向锥，中频到1400Hz时音质有保证。在低频方面，其谐振频率为57Hz，有一定的低频下潜度。它与惠威的K1高音喇叭配合，可以做成性能较好的两分频小型倒相式音箱，其音质应超过惠威那配F5喇叭的M1成品箱（喇叭搭配不当） W5喇叭的音圈直径为25毫米，属于小直径，适合用胆机或小功率的乙类石机推，加上两分频的方案，成本很低廉，那么这箱适合于初烧和对音响器材要求不高的用户在客厅使用 此类箱客户都要求尺寸尽量小，但要保证面板上能装下两喇叭，倒相管，还需保证有足够的尺寸在面板的四条边上车出园或斜边 经过优化最后音箱的外部尺寸定为：高311毫米，厚251毫米，宽206毫米，用18毫米厚的高密度中纤板制造，面板上装两支50毫米直径排水管做的倒相管，长度为57毫米，音箱的净体积为8.7升 经计算：音箱如果作为闭箱时的谐振频率为121Hz，那么倒相箱的谐振频率也就定为121Hz 好了，明天上音箱计算结果数据

原帖由 强悍制箱 于 2012-7-7 16:34:00 发表 惠威W5的振膜为PP材料，使得其音域较宽，从其灵敏度曲线上看，即使到1400Hz，灵敏度数据变化也不大，它还带导向锥，中频到1400Hz时音质有保证。在低频方面，其谐振频率为57Hz，有一定的低频下潜度。它与惠威的K1高音喇叭配合，可以做成性能较好的两分频小型倒相式音箱，其音质应超过惠威那配F5喇叭的M1成品箱（喇叭搭配不当） W5喇叭的音圈直径为25毫米，属于小直径，适合用胆机或小功率的乙类石机推，加上两分频的方案，成本很低廉，那么这箱适合于初烧和对音响器材要求不高的用户在客厅使用 此类箱客户都要求尺寸尽量小，但要保证面板上能装下两喇叭，倒相管，还需保证有足够的尺寸在面板的四条边上车出园或斜边 经过优化最后音箱的外部尺寸定为：高311毫米，厚251毫米，宽206毫米，用18毫米厚的高密度中纤板制造，面板上装两支40毫米直径排水管做的倒相管，长度为135毫米，音箱的净体积为8.5升 经计算：音箱如果作为闭箱时的谐振频率为61.78Hz，那么倒相箱的谐振频率也就定为61.78Hz 好了，明天上音箱计算结果数据 强悍制箱 最后编辑于 2012-07-13 22:30:36

惊天大逆转

原帖由 强悍制箱 于 2012-7-10 5:22:00 发表 楼主摆出的这个问题，使我在计算的过程中发现了以前有两个换算系数搞错，一个是力阻，另一个就是力顺，是从喇叭振动系统的速度状态转换为气体流量状态的换算系数，这个问题曾经困扰了大半年，到近月才想出了些眉目，总是感到还是有些迷糊，果真只搞对了力质的换算关系，这次经楼主提醒，再通过昨晚的反复思考，终于彻底搞明白 楼主的闭箱计算谐振频率公式是对的，但惠威厂家给出的等效体积数据有误，如果是通过只装入闭箱测出来的，就比较可靠 我按等效容积的定义，严格遵循科学原理推导出的计算式为：V=P×K平方×C，P为大气压力，在广州地区为一个海平面标准大气压，数值为9.807×1.0332×10000牛顿/平方米，K为喇叭运行一米时振膜推动一面的空气体积，W5喇叭用积分的方法计算为：0.01751立方米/米，C为W5喇叭的力顺：0.000802米/牛顿，代人计算出W5喇叭的等效体积为24.92升 用8.7升闭箱体积再代人楼主计算公式，就可计算出W5喇叭装入8.7升闭箱后的谐振频率为112Hz

原帖由 强悍制箱 于 2012-7-7 16:34:00 发表 惠威W5的振膜为PP材料，使得其音域较宽，从其灵敏度曲线上看，即使到1400Hz，灵敏度数据变化也不大，它还带导向锥，中频到1400Hz时音质有保证。在低频方面，其谐振频率为57Hz，有一定的低频下潜度。它与惠威的K1高音喇叭配合，可以做成性能较好的两分频小型倒相式音箱，其音质应超过惠威那配F5喇叭的M1成品箱（喇叭搭配不当） W5喇叭的音圈直径为25毫米，属于小直径，适合用胆机或小功率的乙类石机推，加上两分频的方案，成本很低廉，那么这箱适合于初烧和对音响器材要求不高的用户在客厅使用 此类箱客户都要求尺寸尽量小，但要保证面板上能装下两喇叭，倒相管，还需保证有足够的尺寸在面板的四条边上车出园或斜边 经过优化最后音箱的外部尺寸定为：高311毫米，厚251毫米，宽206毫米，用18毫米厚的高密度中纤板制造，面板上装两支40毫米直径排水管做的倒相管，长度为135毫米，音箱的净体积为8.5升 经计算：音箱如果作为闭箱时的谐振频率为61.78Hz，那么倒相箱的谐振频率也就定为61.78Hz 好了，明天上音箱计算结果数据 强悍制箱 最后编辑于 2012-07-13 22:30:36

既然承认顶楼的公式是对的，再玩玩，顶楼的公式逆推：VAS=Vc·｛（Fc/Fo）↑2-1｝
将音箱的净体积为8.5升，闭箱时的谐振频率为61.78Hz代入，得→VAS=1.48 升，合理吗？

原帖由 强悍制箱 于 2012-7-13 0:35:00 发表 对于本帖中各种相互矛盾的公式及数据，我查阅了有关的资料，对自已推导出来的公式和用于计算的原始参数认真地梳理了一遍，所有问题基本清楚了 1.书本上等效体积的计算公式问题： 声音的速度=√γ×P/ρ，将其平方后代人书本上等效体积的计算公式中后，公式就成为：V=γ×P×S平方×喇叭力顺 其中γ为空气的绝热系数。P为大气压力。S为喇叭振膜的有效辐射面积。 这个公式中的逻辑关系混乱，无法让读者搞明白，因此也就不敢相信它 对比我推导出的公式： 音箱内气体等温压缩时：V=P×S平方×喇叭力顺 音箱内气体绝热压缩时：V=P×S平方×喇叭力顺/γ 书上一些公式经常是故弄悬殊，搞得高深莫测，故意不让读者明白 2.通过对基础数据的梳理，以前计算惠威W5喇叭有效辐射面积时错将振膜的直径当成半径，结果算出的面积0.01751平方米，还超出喇叭振膜直径115毫米的面积0.01039平方米，经过更正后为0.004379平方米，按此计算等效体积：9.807X1.0332X10000X0.004379X0.004379X0.000802=1.558升 如果将喇叭的振膜全面积0.01039平方米代入公式中：9.807X1.0332X10000X0.01039X0.01039X0.000802=8.773升，正好是惠威公布的等效体积数据，如果这样计算，在科学原理上讲不通，试想喇叭的音圈如果移动1厘米，只有与它相连的振膜部分才会跟随移动一厘米，而最外圈的与橡皮边相连的振膜部分就根本不会动，要用积分的方法计算有效辐射面积，不能将整个振膜面积当成有效面积 因此不可迷信书上的公式和厂家数据 强悍制箱 最后编辑于 2012-07-13 00:56:42

留个证据，再编辑也好对照。

微笑一下

这里请教几个问题,一.公式里除VC外都是巳定数,任意VC都可改变FC值,关键是VC如何确定才合适.二.影响箱体谐振频率除了箱内空气容积外,是否还有其它因素,如箱体三维尺寸比例,箱体内外形状,加强结构形式,箱体自重和构成箱体材料的性质,三.箱体谐振频率激发的条件和优缺点,谢谢.

老车，你嘅问题问你老友贺兄更合适。

藕不应该一而再再而三多嘴......

整理补充，需要的朋友可参考。





Fc：箱体谐振频率
Fo：单元谐振频率
Vc：箱体净容积
Vas：单元等效容积





ρo：空气密度
C：声速
SD：等效辐射面积
Co：顺性



T/S参数定义：VAS，驱动器的空气等效容积。VAS具有的声顺等于驱动器振动系统的声顺。

VAS=ρ·c↑2·CAS

其中CAS是驱动器支撑的声顺。

换种说法：VAS是令驱动器谐振频率提高到自由空间中数值的√2倍的密闭音箱中的空气容积。





ρo：空气密度
C：声速
SD：等效辐射面积
Co：顺性

验证一下这条的式子

SEAS H1488-08 L16RNX




ρo：1.18 Kg/m↑3  C：344 m/s  SD：.0104m↑2  Co：0.0011m/N
计算结果 VAS=0.0166 m↑3，即16.6 Litres，seas提供的数据为 16 Litres




Fc：箱体谐振频率
Fo：单元谐振频率
Vc：箱体净容积
Vas：单元等效容积

验证一下这条的式子

seas H416 P17REX

VAS: 30.5 Litres，Fo: 34Hz，装入净容积 12 Litres闭箱，计算结果：FC=63.9 Hz.






无声室测试结果，看看阻抗曲线，准确性如何？



The Laboratory

  The Seas laboratory is located in the south end of the Seas building, resulting in a very little traffic noise, and as far away as possible from our mechanical production. We have an anechoic chamber, a reverberation room (used today as a storage room), a laboratory with lots of measurement systems, offices, listening room, and two meeting rooms.

The south wall has only one opening of 1 x 1 m for free field measure infinite baffle measurements. This is today more an interesting curiosity since it’s no longer being used. In the basement, we have a well isolated room for long term power handling tests of loudspeakers. We also have an enormous storage room in the basement for physical storage of different projects and samples going back, more than 30 years


The anehoic chamber
The anechoic chamber consists of a shell of concrete and Leca that rests on coil springs (16 x 3 ) to dampen noise from vibration in the ground. The mass (approx 200 tons) together with the springs results in a 2. order low pass filter with a cut off frequency of 2.5-3 Hz. The dimensions inside the shell is ( L x W x H ) 960 cm x 650 cm x 755 cm.

All walls inside the anechoic chamber are covered with mineral wool wedges placed 5cm from the walls. These wedges together with the 5cm air layer represent an absorber/resonator which gives an absorption coefficient of more than 0.99 for frequencies above 70 Hz. The floor in the anechoic room is a net made from tensioned steel wires.

The entrance into the room consists of two coupled steel doors which opens outwards, together with a 1m thick frame construction with wedges which open inwards. Loudspeakers, microphones etc. can be connected to the measuring equipment outside the room with a sophisticated cable system. The cables are led into the room through noise traps.

A system of hooks from the roof and the floor gives us the possibility to mount different installations in different ways. The available room within the wedges above the wire floor is (Lx W x H): 750 cm x 440 cm x 480 cm. The room can be used for all kinds of free field measurements.




Our measurement systems

Klippel
We’re using the Klippel measurement system to develop and document.
WinMLS
The WinMLS is another very good measurement system, developed by Lars Morset in Norway.

SeasGraph
SeasGraph is our own viewer for all the different measurement system. We needed a really good program to compare and present our measurements, and ended up by designing our own computer software.

Comments to the datasheets

The resonance frequency (f0) and the impedance at resonance (Z0), are measured using a 2 VRMS sine signal.

Our woofers are measured in a closed cabinet with outside dimensions according to the table you will find here. The cabinet is loosely filled with damping material.

All loudspeakers are measured at 0.5 m/2.83 V on axis in our anechoic chamber using the TRF-module from Klippel GmbH. The microphone is a B&K 4133.

Before measuring the T/S-parameters the driver has been run in at near maximum excursion in free air using a sine signal at f0 for 2 min. The resonance frequency and impedance at resonance are measured using a 2 VRMS sine signal.
The moving mass and the BL-product are measured with the laser equipment from Klippel GmbH.

  

Below, you will find some information which may make it easier to interpret the technical data.

Power data is given with reference to IEC 168-5. The signal is white noise, shaped to a defined spectrum, and amplitude limited so that the peak voltage is two times the RMS voltage.
The maximum noise power which the drive units can take without permanent damage for sixty cycles consisting of one second ON and one minute OFF is the specified short term maximum power.
The specified long term maximum power is defined as above but with ten cycles consisting of one minute ON and two minutes OFF.
The mounting conditions in the above tests and during the sound pressure frequency response measurement are identical.

Voice coil inductance is a controversial topic since the loudspeaker impedance towards higher frequencies can not be represented by a simple inductor. We have calculated the inductance value at the frequency where the impedance has risen 3 dB from its minimum above the resonance frequency.

Resonance frequency fs is measured using 2 Vrms sine wave. Please be aware that differing power levels and measurement methods may give significantly different fs, and consequently different values for other parameters dependent upon fs.

Suspension compliance Cms (the inverse of the suspension stiffness or spring constant) is related to the moving mass Mms and the resonance frequency fs by the equation:

                                  ( 2 ∏ fs) ² . Mms .  Cms = 1

Linear coil travel is the total distance peak to peak which the coil can move with no significant change in the force factor.

Maximum coil travel is the total distance peak to peak which the coil/cone can move without experiencing gross mechanical non-linearities and limitations.

藕非卫道士，楼上继续轰吧。