benwongkk 發表於 2017-5-11 09:57
師兄,小弟覺得段片亦有不足之處. 若果只單純用longitudinal wave去解釋有點籠統. 喇叭震動所產生既sound...
師兄你所講mechanical wave祇係單元震膜震動
震膜震動就產生sound wave
而sound wave就一定係longitudinal wave
唔會可能係transverse wave
MDLP 發表於 2017-5-11 10:15
師兄你所講mechanical wave祇係單元震膜震動
震膜震動就產生sound wave
而sound wave就一定係longitudina ...
sound wave should be inclusive Longitudinal and transverse waves. 點解師兄會否定transverse?
https://www.acousticfields.com/wavelengths-in-our-rooms
Earphone works the same way as speakers. Sound is transmitted through air. This is indebatable fact.
The only difference is the distance to the ear drum. Earphone can produce bass like 20hz. 20Hz bass MAY not be audible in small room is due to reflections and bounce back etc. It is the cancelling effect which makes it not audible. While there is no cancelling effect in your ear canal so you can hear bass via earphone. If you put your ear close to the woofer you can easily hear the bass.
So it is correct to say bass MAY not be audible in small room. But it is mainly due to cancelling effect, not entirely right to say it is due to a room smaller/shorter than the wave length. It is the small room which cause the wave to bounce back and in turn leads to cancelling effect.
I am no expert in this but the above article explains this phenomenon clearly and precisely.I think in any argument the precise choice in wording is important.It's not a game of playing words. But if the use of words is not precise, concepts can be mis- represented. What is the point of arguing when you can't present your side of argument clearly.
benwongkk 發表於 2017-5-11 09:24
2.耳筒不同喇叭需要空氣空間傳送聲波，而是直接震動耳膜。
師兄我都確信耳筒原理亦都須要空氣作媒介去傳 ...
如果耳機震膜通空氣去耳膜
就要服從返340m/s做V去計
除非個耳機同耳道密封產生高壓
耳道空氣密度上升以使V加大而λ下降
但這點在現實不可行
先唔執好著可否20Hz單元去到定耳仔聽唔到
就算有50-100Hz都無乜意思
因為以以上咁講法
耳機震膜去耳膜得4cm
除一除咁咪只可聽到8500Hz ????
mdo 發表於 2017-5-11 10:19
https://www.acousticfields.com/wavelengths-in-our-rooms
Earphone works the same way as speakers. So ...
So it is correct to say bass MAY not be audible in small room. But it is mainly due to cancelling effect
同意我上面都講過
房間出唔到到某個低頻當然同"重疊/抵消/駐波"不能混為一談
benwongkk 發表於 2017-5-11 10:19
sound wave should be inclusive Longitudinal and transverse waves. 點解師兄會否定transverse?...
有無聲音經空氣傳送係transverse waves嘅例子？
So it is correct to say bass MAY not be audible in small room. But it is mainly due to cancelling effect, not entirely right to say it is due to a room smaller/shorter than the wave length. It is the small room which cause the wave to bounce back and in turn leads to cancelling effect. 其實大房聲壓夠都一樣可以同時有"重疊/抵消/駐波"
由於距離長聲音要較長時間返彈仲多一樣叫殘響
如果大地方無問題的話
演奏廳就唔洗做room treatment
mdo 發表於 2017-5-11 10:19
https://www.acousticfields.com/wavelengths-in-our-rooms
Earphone works the same way as speakers. So ...
謝謝師兄講解。
這是很好的一個解釋，我一直找到的資料，都只說到耳筒和喇叭不同，無需經過空間（無需空氣是錯的，謝謝指正），但沒有說明無需經過空間的分別，只有「偶合」/「直接」等字眼，用詞確是會令人誤解。
師兄指出的「頻率未經抵銷」，就解釋到耳筒如何出到二三十赫低頻而又沒有違返波長的理論了。
本帖最後由 MDLP 於 2017-5-11 13:25 編輯
波長的理論只係音響佬術語
聲音從單元出嚟都唔係水平擴散
房間除咗長度仲有高度同闊度
就算有抵銷都唔會在某波長以下全數抵銷
koalaau 發表於 2017-5-10 18:23
類比係連續訊號，反而冇數碼的上下限。
一個普通mm唱頭頻應20hk-30khz都好平常，我不知之前的師兄為何會 ...
唱針和唱臂是沒能力把該頻段重放
