AV Amp Crossover一問

DickLai@G

其實師兄對喇叭指示的 100hz -6db 多數是指他本身的 HPF 是用了 LR-2 (Second order Linkwitz–Riley crossover), 這樣配合一對同樣有 LR2 做 LPF 的超低音在100hz 分音就可以得到平宜的曲線了.

介不介意講下你用的是哪一牌子型號? 可助大家更了解你的題問.

MDLP

如果用-6dB就唔會係2nd嘅crossover
亦甚甚甚甚少喇叭仔低音會有HPF
而低音單元仲要串聯一粒電容
咁樣用家會好混淆
因為用他表他隻成品會誤以為唔通電
bass ext -6dB@100Hz其實係分頻指引
+/-3dB得120Hz估你隻低音大唔過3.5寸
用100/150都無所謂
以實際環境及自己聽感決定
沒有對錯

DickLai@G

MDLP 發表於 2019-5-25 11:08
如果用-6dB就唔會係2nd嘅crossover
亦甚甚甚甚少喇叭仔低音會有HPF
而低音單元仲要串聯一粒電容

師兄可參考一下這裏，他是這樣寫，我是這樣理解

LR2 就是 2nd order -6db.

或者我理解差，師兄你是對的

https://en.m.wikipedia.org/wiki/Linkwitz%E2%80%93Riley_filter

MDLP

DickLai@G 發表於 2019-5-25 13:47
師兄可參考一下這裏，他是這樣寫，我是這樣理解

LR2 就是 2nd order -6db.

你覆圖所見係2nd order -12dB音程斜度  在-6dB係個交疊位


以下資料係喺你上面條link度抄出來


First order       
Edit
First-order filters have a 20 dB/decade (or 6 dB/octave) slope. All first-order filters have a Butterworth filter characteristic. First-order filters are considered by many audiophiles to be ideal for crossovers. This is because this filter type is 'transient perfect', meaning it passes both amplitude and phase unchanged across the range of interest. It also uses the fewest parts and has the lowest insertion loss (if passive). A first-order crossover allows more signals of unwanted frequencies to get through in the LPF and HPF sections than do higher order configurations. While woofers can easily take this (aside from generating distortion at frequencies above those they can properly handle), smaller high frequency drivers (especially tweeters) are more likely to be damaged since they are not capable of handling large power inputs at frequencies below their rated crossover point.

In practice, speaker systems with true first order acoustic slopes are difficult to design because they require large overlapping driver bandwidth, and the shallow slopes mean that non-coincident drivers interfere over a wide frequency range and cause large response shifts off-axis.

Second order       
Edit
Second-order filters have a 40 dB/decade (or 12 dB/octave) slope. Second-order filters can have a Bessel, Linkwitz-Riley or Butterworth characteristic depending on design choices and the components used. This order is commonly used in passive crossovers as it offers a reasonable balance between complexity, response, and higher frequency driver protection. When designed with time aligned physical placement, these crossovers have a symmetrical polar response, as do all even order crossovers.

DickLai@G

MDLP 發表於 2019-5-25 15:35
你覆圖所見係2nd order -12dB音程斜度  在-6dB係個交疊位

師兄好

希望Google translate 幫到你

Linkwitz-Riley“L-R”交叉由低通和高通L-R濾波器的並聯組合組成。 濾波器通常通過級聯兩個巴特沃斯濾波器來設計，每個濾波器在截止頻率下具有-3 dB增益。 得到的Linkwitz-Riley濾波器在截止頻率下具有-6 dB的增益。

A Linkwitz-Riley "L-R" crossover consists of a parallel combination of a low-pass and a high-pass L-R filter. The filters are usually designed by cascading two Butterworth filters, each of which has −3 dB gain at the cut-off frequency. The resulting Linkwitz–Riley filter has a −6 dB gain at the cutoff frequency.

如文字不清晰，圖片也可

2條1 order Butterworth 便是1 條2nd order LR, 在cutoff frequency 有-6 DB 增益。完。

沒有可爭議的地方。

MDLP

DickLai@G 發表於 2019-5-25 16:30
師兄好

希望Google translate 幫到你

以1000Hz為例
對上一個octave係2000Hz
對落一個octave係500Hz
2nd order個斜度係-12dB
所以個交差喺-6dB

MDLP

DickLai@G 發表於 2019-5-25 16:30
師兄好

希望Google translate 幫到你

Second order Linkwitz–Riley crossover (LR2, LR-2)       
Edit
Second-order Linkwitz–Riley crossovers (LR2) have a 12 dB/octave (40 dB/decade) slope. They can be realized by cascading two one-pole filters, or using a Sallen Key filter topology with a Q0 value of 0.5. There is a 180° phase difference between the lowpass and highpass output of the filter, which can be corrected by inverting one signal. In loudspeakers this is usually done by reversing the polarity of one driver if the crossover is passive. For active crossovers inversion is usually done using a unity gain inverting op-amp.

Fourth order Linkwitz–Riley crossover (LR4, LR-4)       
Edit
Fourth-order Linkwitz–Riley crossovers (LR4) are probably today's most commonly used type of audio crossover. They are constructed by cascading two 2nd-order Butterworth filters. Their slope is 24 dB/octave (80 dB/decade). The phase difference amounts to 360°, i.e. the two drives appear in phase, albeit with a full period time delay for the low-pass section.

Eighth order Linkwitz–Riley crossover (LR8, LR-8)       
Edit
Eighth-order Linkwitz–Riley crossovers (LR8) have a very steep, 48 dB/octave (160 dB/decade) slope. They can be constructed by cascading two 4th-order Butterworth filters.

MDLP

只有LR2 LR4 LR8無LR1
煩係個分音器上有一粒電容一粒電容
都唔會係1st order

DickLai@G

回應樓主“ 我對喇叭如果Frequency Response 係120Hz ~ 20kHz(+/-3dB)，Bass Extension係100Hz(-6dB)”
所謂+/-X dB, 從來是講gain增益, 不是講slope斜度

我回覆樓主，100hz -6db多數是LR2 , 清楚明白
師兄如一時誤會是斜度，沒有所謂。對與錯都在google可以找到。
本帖從來冇人提過有LR1，請做認字特警前，先仔細閱讀內容。

“
2條1 order Butterworth 便是1 條2nd order LR, 在cutoff frequency 有-6 DB 增益。”

Since cascading two nth order Butterworth filters will give a (2n)th order Linkwitz–Riley filter, theoretically any 2n order Linkwitz–Riley crossover can be designed.


點都好，大家都係想幫忙主解決問題
對就是對，錯就是錯。
何必爭口舌？

只是想避免以下矛盾：
如果用-6dB（斜度？）就唔會係2nd嘅crossover
V.s.
2nd order個斜度係-12dB
所以個交差喺-6dB（增益？）

以後在文字/數字上加上單位，或許會減少誤會
謝謝


何況樓主跟本沒講明用哪隻喇叭，我自己都講明只係估估下，話“多數”係有LR2 filter 咁解。

MDLP

無錯係單位上嘅誤會
不過spec上+/-3dB係誤差範圍上響應
-6dB bass ext係指誤差外仍可用低音
一對正常喇叭99.9999%
唔喺低音單元上加個 HPF