Hi,
Basic question please 😱.
Ho to make the difference in a low pass filter of a bass driver between a serie RC in parralel with the driver for a top Z curve flatening purpose and/or a second order low pass C with an added in serie resistor to ground ?
Why I ask that ? In my main loudpeaker the bass section which I believe to be a 6db low pass has in // with the bass driver a serie RC with a 100 uF low ESR bipolar lytic with 0.75R.
The loudspeaker while still making good bass for a 30 yo loudspeaker has this condensator measured ! Both L & R speakers. 130 uF instead 100 uF of the marking, uh !
Ok, we still are in the 20% plus of lytic capacitance variability... but :
the loudspeaker is said to be an high end one and I assume the lytic were matched, though I don't know if towards the 100 uF of the marking or higher (where). In the meantime 30 years of use makes these lytic probably drifted !
Why I matter ? I swapped for a fresh 100 uF lytic -measured- with a Little worse ESR as the former ones furiously look like smooth foils ones. ...And the bass are playing lower but boomy and their never were before -I bought 25 yo ago the loudspeakers second hand and the model was 5 years old design-
I forgott : the lytic is // with a 0.1 uf Styren by design despite having after in serie this 0.75 R resistor ??
Why do I have a boomy bass now please ? Too low capacitance whatever the marking ?
Basic question please 😱.
Ho to make the difference in a low pass filter of a bass driver between a serie RC in parralel with the driver for a top Z curve flatening purpose and/or a second order low pass C with an added in serie resistor to ground ?
Why I ask that ? In my main loudpeaker the bass section which I believe to be a 6db low pass has in // with the bass driver a serie RC with a 100 uF low ESR bipolar lytic with 0.75R.
The loudspeaker while still making good bass for a 30 yo loudspeaker has this condensator measured ! Both L & R speakers. 130 uF instead 100 uF of the marking, uh !
Ok, we still are in the 20% plus of lytic capacitance variability... but :
the loudspeaker is said to be an high end one and I assume the lytic were matched, though I don't know if towards the 100 uF of the marking or higher (where). In the meantime 30 years of use makes these lytic probably drifted !
Why I matter ? I swapped for a fresh 100 uF lytic -measured- with a Little worse ESR as the former ones furiously look like smooth foils ones. ...And the bass are playing lower but boomy and their never were before -I bought 25 yo ago the loudspeakers second hand and the model was 5 years old design-
I forgott : the lytic is // with a 0.1 uf Styren by design despite having after in serie this 0.75 R resistor ??
Why do I have a boomy bass now please ? Too low capacitance whatever the marking ?
That is a damped second order, not a 6dB and zobel. A zobel will only flatten Z with the coil removed. A damped 12dB will not flatten the Z with the same criteria. A damped second order normally has a lower value resistor and a larger cap than required for Z flattening.
The change in cap value is smaller and higher Fc and then allows more midbass to the woofer.
Wolf
The change in cap value is smaller and higher Fc and then allows more midbass to the woofer.
Wolf
diyiggy,
you are burdening yourself unnecessary with flattening voice coil impedance. The whole idea is nonsense. You shall design a lp filter that fulfills your design criteria, whether that involves true zobel impedance compensation, a variation of it or not, is unimportant. The shape of the FR is all that matters. You can achieve a perfect one with 2 parts or a dozen, depending.
In regard to your perceived change in SQ while introducing a new 100 uF cap, well the capacity is now changed, so is the response.
I am not sure how you calculated 130 uF in relation to 100 uF is still within 20% tolerance.🙂
you are burdening yourself unnecessary with flattening voice coil impedance. The whole idea is nonsense. You shall design a lp filter that fulfills your design criteria, whether that involves true zobel impedance compensation, a variation of it or not, is unimportant. The shape of the FR is all that matters. You can achieve a perfect one with 2 parts or a dozen, depending.
In regard to your perceived change in SQ while introducing a new 100 uF cap, well the capacity is now changed, so is the response.
I am not sure how you calculated 130 uF in relation to 100 uF is still within 20% tolerance.🙂
Many thanks guys, very helpfull. 🙂
@ lojzek : it's not a diy design but a loudspeaker designed by Phil Jones.
About the capacitance : I measured both few weeks ago, so I have no idea of what did the designer ?! The genuine capacitor here is marked 100 uF but both channels I measured 130 uF exactly on each while the Loudspeaker is 30 yo now - so with a capacimeter and the caps desoldered fastly no to waste it with the temp -! I think I tried to explain that incertitude in my first post : I dunno if it drifts from 100 uF (marking) or the caps were sorted out near 130 uF. At least they are symetric on both channel : exactly 130 uF each !
Now I know this is not a first order filter as a famous review explained. The bass cabinet is a bandpass and the loudspeaker was made in the suburb of Boston !
At this point I should try any value by 10 uF jump I surmise, but my questions are motivated to avoid any error by knowledge miss... As I refurbished many commercial loudspeakers for friends but only almost designed only one by myself, my main thought was about an ESR and capacitance drift here !I was disapointed this swap wasted the sound, but maybe because on the habits of the sound I know (psychoacoustic)... while I have heard an have loudspeakers enough to know what is or not a boomy bass ! Maybe the room just not liked the true response or indeed 100 uF is not the right value the designer had in mind - Ked did that on reference series : the sorted out values are not exactly the marked one but the capacitance value maybe in 20% of the marking while sorted out at 2%... the hassole of passive components 😉
@ lojzek : it's not a diy design but a loudspeaker designed by Phil Jones.
About the capacitance : I measured both few weeks ago, so I have no idea of what did the designer ?! The genuine capacitor here is marked 100 uF but both channels I measured 130 uF exactly on each while the Loudspeaker is 30 yo now - so with a capacimeter and the caps desoldered fastly no to waste it with the temp -! I think I tried to explain that incertitude in my first post : I dunno if it drifts from 100 uF (marking) or the caps were sorted out near 130 uF. At least they are symetric on both channel : exactly 130 uF each !
Now I know this is not a first order filter as a famous review explained. The bass cabinet is a bandpass and the loudspeaker was made in the suburb of Boston !
At this point I should try any value by 10 uF jump I surmise, but my questions are motivated to avoid any error by knowledge miss... As I refurbished many commercial loudspeakers for friends but only almost designed only one by myself, my main thought was about an ESR and capacitance drift here !I was disapointed this swap wasted the sound, but maybe because on the habits of the sound I know (psychoacoustic)... while I have heard an have loudspeakers enough to know what is or not a boomy bass ! Maybe the room just not liked the true response or indeed 100 uF is not the right value the designer had in mind - Ked did that on reference series : the sorted out values are not exactly the marked one but the capacitance value maybe in 20% of the marking while sorted out at 2%... the hassole of passive components 😉
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Boston Lynnfield 500L and 400L
I can affirm than the hifi review didn't understand those speakers that are crazy goods -just need indeed a little work on the tweeter that is after as sota as some Be and I had mail exchanges with P Jones himself, very nice guy btw-)
They are drived by a Chord and the Dac is more than good as the pre and the cables and the room... well maybe the listener but it's another story 😉
I can affirm than the hifi review didn't understand those speakers that are crazy goods -just need indeed a little work on the tweeter that is after as sota as some Be and I had mail exchanges with P Jones himself, very nice guy btw-)
They are drived by a Chord and the Dac is more than good as the pre and the cables and the room... well maybe the listener but it's another story 😉
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... will try, with a little help from my friends. Have to understand what the capacitance value was though . (I had no doubt a capacitance change has moved the frequency response).
oh no, hope it will not finish as Stereophile judgement : throw it to the garbadge, lol !
oh no, hope it will not finish as Stereophile judgement : throw it to the garbadge, lol !
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I'm going to try a // cap to the 100 uF as per wolf-teeth inputabout what the filter is doing there.
It should be ok as the lowest ESR with a // cap of two rough foil lytic caps should more or less cope with the former standalone smooth foil lytic cap... I hope. Seems it's important as I read the word 'damped' 😕 and I assume a precise resistance of this serie RC was planed.
What does it damp please ? The Q of the second order filter there ?
I have not exact idea how a 30 yo lytic cap drift here. And I know from experience that a cap towards ground before the voice coil of the speaker don't drift in capacitance value the same way than a serie with the driver coil having refurbishing few loudspeakers.
Experienced guys of the forum said me than first the ESR was increasing making the lytic more resistive, then the capacitance will drop, then after more aging the capacitance of the lytic could increase.
Lojzek indeed talked about the 20% of M grade precision with a lytic but it can be less most of the time with a bipolar made for speaker filter... closer to the 10 to 12% with brandnew caps (btw whatever the marking precision is saying... depends of the brands... bad for a Mundorf, quite good for a JB, very precise from a F&T (that are making imho Mundord caps under license).
I couldn't measured the coil yet, but from Stereophile the filter is 125 hz electrical, 90 hz acoustical....
It should be ok as the lowest ESR with a // cap of two rough foil lytic caps should more or less cope with the former standalone smooth foil lytic cap... I hope. Seems it's important as I read the word 'damped' 😕 and I assume a precise resistance of this serie RC was planed.
What does it damp please ? The Q of the second order filter there ?
I have not exact idea how a 30 yo lytic cap drift here. And I know from experience that a cap towards ground before the voice coil of the speaker don't drift in capacitance value the same way than a serie with the driver coil having refurbishing few loudspeakers.
Experienced guys of the forum said me than first the ESR was increasing making the lytic more resistive, then the capacitance will drop, then after more aging the capacitance of the lytic could increase.
Lojzek indeed talked about the 20% of M grade precision with a lytic but it can be less most of the time with a bipolar made for speaker filter... closer to the 10 to 12% with brandnew caps (btw whatever the marking precision is saying... depends of the brands... bad for a Mundorf, quite good for a JB, very precise from a F&T (that are making imho Mundord caps under license).
I couldn't measured the coil yet, but from Stereophile the filter is 125 hz electrical, 90 hz acoustical....
500L is a load difficult enough to trigger some amps short circuit protection. I would modify to yield a more friendly one.
The mid high-pass for the caps is measured on the two speakers at 280 uF and 283 uF (instead of the marking on the caps that are 260 uF).
After few online simulation taking close 125 hz cut-offs and the 130 uF of the bass filter, it could match if the two 6 bass drivers are wirered in serie giving a 8 ohms and the mid being a 4 ohms driver !
Well no problem with the amp, it's a chord, protetions never happened, but I don't listen to at PA levels.
If all these caps drifted in 30 years of the loudspeaker existence, then it drifted very symmetrical on both L&R loudspeakers ! The both bass caps in // with the bass drivers are exactly 130 uF each. And the serie caps with the mid at 280 uF and 283 uF, shows only a little 3 uF.... As it is made from a marked 220 uF and 60 uF // caps, I think it shows some sorting out at the production plant... They were Boston Acoustic High End though killed by unfair review of Stereophile... maybe an ads problem, who knows.
Ok ... maybe the caps didn't drifted that much or ar still ok on capacitance but the ESR ?
After few online simulation taking close 125 hz cut-offs and the 130 uF of the bass filter, it could match if the two 6 bass drivers are wirered in serie giving a 8 ohms and the mid being a 4 ohms driver !
Well no problem with the amp, it's a chord, protetions never happened, but I don't listen to at PA levels.
If all these caps drifted in 30 years of the loudspeaker existence, then it drifted very symmetrical on both L&R loudspeakers ! The both bass caps in // with the bass drivers are exactly 130 uF each. And the serie caps with the mid at 280 uF and 283 uF, shows only a little 3 uF.... As it is made from a marked 220 uF and 60 uF // caps, I think it shows some sorting out at the production plant... They were Boston Acoustic High End though killed by unfair review of Stereophile... maybe an ads problem, who knows.
Ok ... maybe the caps didn't drifted that much or ar still ok on capacitance but the ESR ?
Thirty years ago, serious manufacturers would measure the component's values and select the desired value before installing them in the crossover. The imprints were only used as rough guides as tolerances of 20% were pretty normal (you ought to know how caps, resistors and coils are sorted and labeled in their respective factories). Serious manufacturers today still practice this. A good consideration when restoring old speakers. 😉
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Yes I know, I already refurbished the filter of some old english ladies like Spendor, or Kef reference serie.... a nightmare despite you can have the shematic ! Not saying thatn simulating the filter to understand the values also drive you nowhere if the filter is asymetrical.
Here symetrical, the values of the HP and LP seen together could be a second order LR or Bessel, according the drift or not ! Because also a cap in serie or in // is not drifting about his capacitance value and ESR at the same speed ! (no pun intended)
I'm glad to know it's not a zobel but a second order. Which has sense as the bass cabinet is a bandpass ! I assume it's about taming the first resonance peak after the acoustical first drop of such a load...
Here symetrical, the values of the HP and LP seen together could be a second order LR or Bessel, according the drift or not ! Because also a cap in serie or in // is not drifting about his capacitance value and ESR at the same speed ! (no pun intended)
I'm glad to know it's not a zobel but a second order. Which has sense as the bass cabinet is a bandpass ! I assume it's about taming the first resonance peak after the acoustical first drop of such a load...
So knowing now this low pass filter on the woofer being a second order, I'm playing with the capacitance values of both the low pass cap and the high pass caps in the medium part that makes the cut-off with the bass area I' talking about.
I made some simulaions with the Hifi Audio web site that has the option of seing the passive parts value according both the drivers resistance and several different slopes : butterworth, Bessel, LR, etc. Crossover Calculator LR2, Bessel, Butterworth & Cheybyscheff
Ears are a fantastic instrument. The marking of the high pass caps on the medium is marked 260 uF and I measured on each channel 280 uF and 283 uF after 30 years of drifting. Replacing with 280 uF gives a close result, certainly due to less ESR with the fresh caps vs the 30 yo formers.
At 125 hz which is the acoustical cut-off on the loudspeaker manual and simulations made, the closest result on that online calculator is a Bessel filter. I have not measured the T&S characteristic of the drivers nore the coils, so it's 2 cents trial and error refurbishing till I finish my Arta box. At 125 hz the difference between 260 uF and 280 uF is the mid driver being at cut-off 3R3 or 3R6 !
And it changes it all. At 280 uF, the bass are not present anymore and my ears gave this habit little by little during these 2 decades and half.
260 uF is too much boomy for my 40 square meters LR (living room).
With try and error, I' now at circa 269 uF of MKP instead. And that makes the loudspeakers eachtime different.
I made a mistake above in the post, the lytic cap of the second order in the bass filter low pass is marked 100 uF and was measured both channel at 111 uF not 130 uF. I apologize for that if an owner of this loudspeaker is reading that and want to start a capacitor refurbishing job. Correction made now😀.
The new cap is a lytic here as it is in serie with 2 x 1R5 resistor so the whole ESR is important I assume as inputed above by an experienced member saying it's a "damped second order filter" and not a zobel as I belived .
Here again between the 111 uF with some assumed aging drift and the marked 100 uF on the body cap, the difference of Z at 125 hz is between 4.6 and 5.2 ohms ! Btw the drivers are measured raw with an LCR meter...are 4.6 ohms on the voice coils. I surmise two 4 ohms woofers in series as there are two 6" bass drivers in the band pass bass cabinet. At 125 Hz the Bessel second order slope is giving a 103 uF cap which exactly is the fresh new litic cap.
The values have to be found as it's changing not only the spl curve at listening checking but also how is damped the bass (group delay change, resonance of the room, etc ?)
I have also a mismatch spl level between the two loudspeaker on the mid-treble filter as I'm refurbishing them as well.
A question please, how much db are ears level for spl mismatch between R&L channels ? 0.5 decibel ? How much should be the capacitance and resistance precision of the passive filter parts please ? On the bass filter I'm in 100% matching (high pass are sorted out MKP and the the electrolytic cap in the low pass are F&T caps : very precise out of the manufacture and both sorted out by me here !
Is there maybe also a difference between two raw drivers ?
I made some simulaions with the Hifi Audio web site that has the option of seing the passive parts value according both the drivers resistance and several different slopes : butterworth, Bessel, LR, etc. Crossover Calculator LR2, Bessel, Butterworth & Cheybyscheff
Ears are a fantastic instrument. The marking of the high pass caps on the medium is marked 260 uF and I measured on each channel 280 uF and 283 uF after 30 years of drifting. Replacing with 280 uF gives a close result, certainly due to less ESR with the fresh caps vs the 30 yo formers.
At 125 hz which is the acoustical cut-off on the loudspeaker manual and simulations made, the closest result on that online calculator is a Bessel filter. I have not measured the T&S characteristic of the drivers nore the coils, so it's 2 cents trial and error refurbishing till I finish my Arta box. At 125 hz the difference between 260 uF and 280 uF is the mid driver being at cut-off 3R3 or 3R6 !
And it changes it all. At 280 uF, the bass are not present anymore and my ears gave this habit little by little during these 2 decades and half.
260 uF is too much boomy for my 40 square meters LR (living room).
With try and error, I' now at circa 269 uF of MKP instead. And that makes the loudspeakers eachtime different.
I made a mistake above in the post, the lytic cap of the second order in the bass filter low pass is marked 100 uF and was measured both channel at 111 uF not 130 uF. I apologize for that if an owner of this loudspeaker is reading that and want to start a capacitor refurbishing job. Correction made now😀.
The new cap is a lytic here as it is in serie with 2 x 1R5 resistor so the whole ESR is important I assume as inputed above by an experienced member saying it's a "damped second order filter" and not a zobel as I belived .
Here again between the 111 uF with some assumed aging drift and the marked 100 uF on the body cap, the difference of Z at 125 hz is between 4.6 and 5.2 ohms ! Btw the drivers are measured raw with an LCR meter...are 4.6 ohms on the voice coils. I surmise two 4 ohms woofers in series as there are two 6" bass drivers in the band pass bass cabinet. At 125 Hz the Bessel second order slope is giving a 103 uF cap which exactly is the fresh new litic cap.
The values have to be found as it's changing not only the spl curve at listening checking but also how is damped the bass (group delay change, resonance of the room, etc ?)
I have also a mismatch spl level between the two loudspeaker on the mid-treble filter as I'm refurbishing them as well.
A question please, how much db are ears level for spl mismatch between R&L channels ? 0.5 decibel ? How much should be the capacitance and resistance precision of the passive filter parts please ? On the bass filter I'm in 100% matching (high pass are sorted out MKP and the the electrolytic cap in the low pass are F&T caps : very precise out of the manufacture and both sorted out by me here !
Is there maybe also a difference between two raw drivers ?
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