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Schoeps話筒麥克風 BLM3g 話筒 Schoeps麥克風 BLM 3G 界面話筒
界面話筒 BLM 3g
專用于在聲學界面上使用的話筒拾音頭（壓力傳聲器）
當拾音角度變化時，聲音的“染色”不會改變
出色的低頻再現能力
更適合于管弦樂隊的錄音
界面錄音可以提供不引人注意的話筒擺放方式；無需使用立式或懸吊的固定設備。如果使用壓力傳聲器，它具有與頻率無關的半球形方向特性；因此無需對準話筒，即使拾音角度改變，本質上音質仍是相同的。
該技術以物理效應為基礎，即：沿著聲反射面的聲音，其聲壓將加倍。如果壓力傳聲器直接放置于聲音反射面或內部，如BLM 3，其對于直達聲的靈敏度將是同等傳聲器在自由聲場內的2倍。它對于自由聲場的響應不會改變，但對于在給定距離時的話筒拾音，其清晰度卻可以得到顯著的提升。
理論上講，該類型理想的傳聲器應當具有一個無窮小尺寸的振膜，并被安置在一個無限大的、完美的聲音反射表面上（內）。實際中，安置小型傳聲器BLM 3g的金屬底板只反射高頻和中頻。要反射低頻（更長的波長）聲音，界面的尺寸相對來說就要足夠大。因此話筒要被放置在地板上、墻面或天花板，或安置在其它足夠大的表面上，這樣才能反射所需要的最低頻率。
由于BLM 3g的金屬底板只有5mm厚，傳聲器不能安放在它的中心，而金屬板的邊緣對于聲音的拾取影響非常小。BLM 3g不會妨礙自然聲場；偏離軸向（off-axis）上極低頻率的聲音也能辨別出來。即使移動聲源，聲染也很低，這是因為，本質上在半指向拾取模式內所有角度拾取的聲音其頻響都是一樣的。
用于靠近聲音反射表面的話筒通常會產生梳狀濾波效果。但這不會在BLM 3g上發生，這是因為在安置傳聲器的分界處，直達聲及其反射聲沒有相位差別。
對于高頻處的直達聲和反射聲，通常，壓力傳聲器在靈敏度上會呈現出差異。無論如何放置界面話筒，這個差異在所有頻率處都會發生。直達聲的聲壓在聲音分界線處是雙倍的（增加6dB），由于擴散場反射聲相位的關系導致界面話筒的靈敏度只增大3dB。因此界面話筒將會抑制擴散聲，即便它不是指向性的。它將拾取少量的“環境聲”，它的錄音效果比全向話筒聽起來“更干澀”。
拾音頭本身是一個經典的靜電壓力傳聲器，它能在擁有高信噪比的同時，還可以確保低頻的正確再現以及典型專業電容話筒的穩定性能。
該類型傳聲器對風和顫動不敏感，BLM 3g的錄音效果比較重，這是因為它僅拾取非常小的固載噪聲。舉例說，當錄制腳步聲時，絕大部分到達話筒的聲音都來自空氣而不是地板。
典型的應用包括：舞臺對話的拾音，樂池內拾音，作為環境話筒和特殊的拾音。由于話筒通常放在地板上，就存在被踩踏而被破壞的可能性，通過精心的設計，這類破壞的可能性已經大為降低。一般來說，普通的鞋子并不能損傷拾音頭。
與其它Colette系列話筒拾音頭類似，BLM 03g（界面話筒拾音頭）也需要話筒放大器（如CMC、CMD 2U或M 222），從而組成一只完整的話筒。
還可以增加衰減器（DZC）和有源附件，如可變低頻切除濾波器（CUT1或CUT2）或是附加有源線纜（KC）。
界面話筒十分適合A/B（間隔話筒）擺放方式的拾音，也可以用于M/S方式，但需要使用特殊的MSBLM附件。
尺寸：金屬底板： 200mm × 200mm × 5mm
話筒放大器連接器凈高：21mm
重量：570g（不含話筒放大器）
表面工藝：磨砂灰
附件（包括）： 拋光木盒
BLM 3 BOUNDARY LAYER CAPSULE
PROPERTIES
plate with 200 mm edge length
preferred use: as a room microphone
DESCRIPTION
Boundary-layer recording offers unobtrusive microphone placement possibilities; no stands or hanging fixtures are required.
When pressure transducers are used, the result is a hemispherical directional characteristic that is independent of frequency; thus it is not necessary to aim the microphones, and if the angle of sound pickup changes, the sound quality remains essentially the same.
The technique is based on an effect in physics by which sound pressure doubles along a sound-reflecting surface. If a transducer is placed directly on such a surface, or is built within it as with the BLM 3, its sensitivity to direct sound will be twice that of an equivalent transducer in a free sound field. Its response to diffuse sound remains unchanged, however, causing a notable increase in the clarity of pickup for a given miking distance.
In theory an ideal transducer of this type would have a membrane of infinitesimally small size, and would be mounted flush with an infinitely large, perfectly sound-reflecting surface. In practice, the plate in which the small transducer of the BLM 3 is mounted assures reflection of only the high and medium frequencies.
To reflect sound at lower frequencies (greater wavelengths), the dimensions of the surface must be correspondingly larger. So the microphone should be placed on a floor, wall or ceiling, or mounted on another surface large enough to reflect the lowest frequencies of interest.
Since the plate of the BLM 3 is only 5 mm thick and the transducer is not mounted at its center, the edges of the plate have very little effect upon the sound pickup. The BLM 3g does not interfere with the natural sound field; off-axis sounds thus encounter very little frequency discrimination. Sound coloration is low, even for moving sound sources, because the frequency response is essentially the same for all angles within the hemispherical pickup pattern.
Microphones used near sound-reflecting surfaces ordinarily produce comb-filter effects. This does not occur with the BLM 3, since at the boundary in which the transducer is mounted there can be no phase difference between the direct sound and its reflection.
Ordinary pressure transducers show a difference in sensitivity between direct and diffuse sound at high frequencies. In a properly placed boundary-layer microphone, however, this difference occurs at all frequencies. The sound pressure for direct sound is doubled at an acoustic boundary (6 dB increase), while the essentially random phase relationships of reflections in the diffuse sound field cause the boundary-layer microphone's sensitivity to increase by only 3 dB. Thus a boundary-layer microphone will suppress diffuse sound somewhat, even though it is not directional. It will pick up less “room sound“ and the recording will be slightly “drier“ than it would be with an omnidirectional microphone.
The capsule itself is a classic electrostatic pressure transducer, which assures accurate reproduction of even the lowest frequencies along with the high signal-to-noise ratio and stable performance typical of professional condenser microphones. This type of transducer is inherently insensitive to wind and vibration and the BLM 3 is comparatively heavy, so it picks up very little solid-borne noise. For example, when footsteps are recorded, most of the sound reaching the microphone will be conducted through the air rather than the floor.
PRACTICE
Typical applications include pickup of stage dialogue, or in orchestra pits, as an ambience microphone and for special public address applications. Since the microphone may well be used on the floor, the likelihood of damage from its being stepped on has been reduced by careful design and construction. As a rule, the capsule will not be harmed by normal footwear.
The BLM 3 (boundary-layer microphone capsule) resembles any other microphone capsule of the Colette series in that it needs a microphone amplifier CMC to form a complete microphone. This arrangement allows Active Accessories such as the low-cut filter CUT 60 or the Active Cable (KC) to be added as well.
Boundary layer microphones are particularly useful for unobtrusive recording with A/B (spaced microphone) methods, but M/S recording is also possible, using the special MS-BLM accessory.
TECHNICAL SPECIFICATIONS
Pickup pattern
Half-space
Frequency range ：20 Hz - 26 kHz with CMC 6 / CMR,20 Hz - 43 kHz with CMC 6xt
Sensitivity ：-36 dB (V/Pa), 16 mV/Pa with CMC 6
Equivalent noise level (A-weighted) ：12 dB with CMC 6
Equivalent noise level (CCIR) ：23 dB with CMC 6
Signal-to-noise ratio (A-weighted) ：82 dB with CMC 6
Maximum sound pressure level (THD < 0.5 %) ：130 dB-SPL with CMC 6
Length ：200 mm
Width ：200 mm
Height ：5 mm
Weight ：570 g
Surface finish ：matte gray
