Monitor 7B schematics-XOVER upgrade.

Options
2»

Comments

  • Gym123
    Gym123 Posts: 14
    Options
    Nice to see some measurements as lots of people (myself included) don't have an LCR meter. Hopefully the dates on the crossovers match fairly closely with the dates on your drivers because those drivers were only found in the 7C, which came out sometime in late 1984 and was superseded by the Monitor 7 Series II sometime in 1990 I believe.

    Having the speaker sound better with a huge gaping hole in the back is indicative of something seriously wrong lol. Shouldn't be any bass to speak of with that arrangement with a passive radiator speaker, for one thing, and the alignment is a melding of the T/S parameters with the enclosure volume. Did I miss where you said that the spider was separated from the voice coil in your original comment? That would CERTAINLY mess things up badly. I had a crack in one of original MW6500s and that would occasionally cause some weird sounds with heavy bass material, but I can only imagine what a separated spider to VC joint would sound like.

    I don't know who sketched out that schematic for the 7B. The inductors should be 0.23mH and 1.55mH. Your schematic should be this one:

    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18772.pdf

    se4oc000x345.jpg


    Thanks for the real crossover- the other one was something I grabbed before I knew what these really were.

    I had another LCR meter and at some point before I needed to work on my guitar amp, (probably seconds before), it quit- seemed to think caps were resistors or inductors and I changed the battery & leads. Didn't matter, so I bought a new one. The new one was less than $30 and it tests well against more expensive ones.

    I doubt the inductors were wound on a precision machine- the difference isn't going to be huge. As the saying goes, "Electronics- always precise, never exact".

    You read it right- the spider is separated from the voice coil and I found that by thumping the back of the magnet with the heel of my hand. I may glue it and see if it makes the crunching stop- it's not my favorite sound. The dust cap is mesh, so the separation is causing a leak from the back to the front, so no seal is possible. It explains the sound quality and the increased bass with my Peerless, even though it's an 8 Ohm driver.

    Passive radiators aren't super precise, either- it isn't damped by having a voice coil connected to an amplifier and it usually requires empirical testing to find out if it will work properly. Whenever I get a chance, I'm going to work on an idea for a variable damped passive radiator, to see if it does what I think it will.

  • Gardenstater
    Options
    Gym123 wrote: »

    I doubt the inductors were wound on a precision machine- the difference isn't going to be huge. As the saying goes, "Electronics- always precise, never exact".

    You read it right- the spider is separated from the voice coil and I found that by thumping the back of the magnet with the heel of my hand. I may glue it and see if it makes the crunching stop- it's not my favorite sound. The dust cap is mesh, so the separation is causing a leak from the back to the front, so no seal is possible. It explains the sound quality and the increased bass with my Peerless, even though it's an 8 Ohm driver.

    Passive radiators aren't super precise, either- it isn't damped by having a voice coil connected to an amplifier and it usually requires empirical testing to find out if it will work properly. Whenever I get a chance, I'm going to work on an idea for a variable damped passive radiator, to see if it does what I think it will.

    Yeah but that is something like a 30% deviation from the proper 0.23mH. It would be interesting to see how the L crossover values compare with the R. The most important thing is probably that they match fairly closely.

    The spiders are incredibly leaky and "gauzy" so I don't know that the separation affects the rate of air leakage from the interior of the enclosure to the front of the baffle through the dust cap, very much. This picture shows how leaky they are on the MW6500:

    3bjvbizef1bv.jpg




    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gym123
    Gym123 Posts: 14
    Options
    A leaky spider is one thing, but a leaky cone with a path from behind the cone to the outside world is another- I used the kind of cement sold for attaching speaker cones to the basket on the spider, which is what tore, very close to the voice coil- it hadn't actually separated. I'll see how it does later today.

    On its face, this is just a 2nd order filter with resistance to drop the level of the tweeter and that really should have been done with a fixed L-pad.

    With the found values, this has become only slightly off of the 3K number that I have seen in forum posts. 5% only changes the crossover point by a couple of hundred Hertz in the crossover calculator I used. These aren't 1% components AFAIK, but I'll check that, too. The coil's accuracy is of less importance, it only makes the slope more steep. Even in this configuration, the cap being higher only lowers the F3 by about 100Hz. As long as Fs is at least 1-1/2 octaves lower, it's not a problem.
  • Gardenstater
    Gardenstater Posts: 4,281
    edited December 2023
    Options
    Before you said that the spider had separated from the voice coil. Well if it is the case that the cone has separated from the voice coil, then you may have to temporarily cut away the dust cap with an xacto knife and glue the voice coil back to the cone. Try to ensure that the spider looks flat rather than concaved or convexed.

    Since the speakers are not sounding right, my advice would be to fix everything you find that is wrong, and that includes the out of spec components and mismatched components from R to L. I wouldn't be happy with an inductor that is off by 30%, but that's just me and if it agrees with the one in the other speaker closely it might not be a big deal.

    I think the way Polk did the tweeter circuit with a series resistor and a shunt resistor basically does constitute a fixed L pad but I could be mistaken. << Oops sorry that is the way they did the 7B, not the 7C, but the shunt inductor has resistance so maybe it still could be considered an L-pad of sorts?

    If the yellow mylar capacitor has a "J" on it that is +/- 5%. I don't know what the electrolytics were but probably like 10% or more.

    PS - Probably best to start a separate thread or is it a bit late for that? lol
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gym123
    Gym123 Posts: 14
    edited December 2023
    Options
    Before you said that the spider had separated from the voice coil. Well if it is the case that the cone has separated from the voice coil, then you may have to temporarily cut away the dust cap with an xacto knife and glue the voice coil back to the cone. Try to ensure that the spider looks flat rather than concaved or convexed.

    Since the speakers are not sounding right, my advice would be to fix everything you find that is wrong, and that includes the out of spec components and mismatched components from R to L. I wouldn't be happy with an inductor that is off by 30%, but that's just me and if it agrees with the one in the other speaker closely it might not be a big deal.

    I think the way Polk did the tweeter circuit with a series resistor and a shunt resistor basically does constitute a fixed L pad but I could be mistaken. << Oops sorry that is the way they did the 7B, not the 7C, but the shunt inductor has resistance so maybe it still could be considered an L-pad of sorts?

    If the yellow mylar capacitor has a "J" on it that is +/- 5%. I don't know what the electrolytics were but probably like 10% or more.

    PS - Probably best to start a separate thread or is it a bit late for that? lol

    I can copy/paste comments about this to start a new thread- it's never too late.

    There's no second resistor and I saw a gap at the VC/spider, but in brighter light, I saw that the tear was about 1/16" from the VC's former. It's not disconnected from the cone, just the spider. The crossover is at the bottom.

    I reinstalled the woofer and after gluing the spider, the difference in sound is huge, but the voice coil still rubs, so I'll be replacing it. I guess a voice coil that moves and a cone that doesn't.....

    The inductor does have resistance, but an L-pad for a tweeter would be only resistors- the inductor's resistance is only 1.5 Ohms and with a 4 Ohm tweeter using a 2 Ohm series resistor, the paralleled resistor would be about 4 Ohms, according to the L-pad calculator in the link- I subbed various values for the attenuation and it works out to -6dB, if this crossover used an L-pad.

    Still, ±5% isn't what I would consider 'precise', as it would be in some circuits- I have also repaired tube guitar amps and the original cap tolerances were in the 20% range but those were cathode and coupling caps, so the effect of the differences isn't the same.

    https://sound-au.com/articles/l-pad-calc.htm
  • Gardenstater
    Options
    Welcome to the forum. Looks like you had your first post that got nuked by Vanilla.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gym123
    Gym123 Posts: 14
    Options
    Welcome to the forum. Looks like you had your first post that got nuked by Vanilla.

    Thanks for the welcome- new woofer has been ordered and the customer wants to think about updating the crossovers.
  • F1nut
    F1nut Posts: 50,086
    Options
    Customer is beyond stupid if they don't upgrade the crossovers.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • Gym123
    Gym123 Posts: 14
    Options
    F1nut wrote: »
    Customer is beyond stupid if they don't upgrade the crossovers.

    You need to understand that not everyone is a fanatic about their system and sound, in general. The vast majority of people who buy audio or AV equipment don't care as much, but they want decent sound. It's their decision, not ours. These weren't expensive when they were new and they don't sell for big bucks now- how much do you think he should put into 37 year old speakers?
  • F1nut
    F1nut Posts: 50,086
    Options
    Gym123 wrote: »
    F1nut wrote: »
    Customer is beyond stupid if they don't upgrade the crossovers.

    You need to understand that not everyone is a fanatic about their system and sound, in general. The vast majority of people who buy audio or AV equipment don't care as much, but they want decent sound. It's their decision, not ours. These weren't expensive when they were new and they don't sell for big bucks now- how much do you think he should put into 37 year old speakers?

    You are in the wrong business as you don't know what the hell you are talking about.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • plastic_avatar
    Options
    @Gym123

    The crossover refurb cost return on investment is Y-U-G-E.

    Even using straight Daytons would be an improvement.

    It's not a big cost, all things considered. The crossover for the 5 is similar, and the gains are substantial for the money.

    If you want to know if putting money (even the bare minimum of replacing the parts in the crossovers) into a pair of 5, 7, 10, 12, RTA, etc., is worthwhile, if you throw a dart into the forum blindfolded you'll hit someone who will tell you it is 100% worthwhile.

    I've got... lemme see... $500 worth of time/money in my 5B (plus discounts/gifts a couple of members gave me)... which might be an insane series of expenditures over 18 months, but these 40 year old speakers sound amazing. And they ended up being gifts for my father. 100% worth it.

    If I'd only spent $100 on upgraded Dayton crossovers? Still 100% worth it.

    d0gj330xe13i.png

    Pardon the Christmas setup clutter.

    The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage
  • Gardenstater
    Options
    Very nice. I am assuming there is a second Christmas Tree to balance out the soundstage?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gym123
    Gym123 Posts: 14
    Options
    F1nut wrote: »

    You are in the wrong business as you don't know what the hell you are talking about.

    How do I not know what the hell I'm talking about? Do you work in audio? I have done this for more than 45 years and to be honest, I'm tired of opinions from people who are outside of the conversation between me and customers. Beyond stupid? It's his choice, not yours and not mine.

    Being pretty judgmental, considering I'm not the owner of the speakers and these are used in a cabin up North. If these were mine, I would upgrade the crossovers, but trying to force someone else to do it when they're not the main speakers in their life isn't easy.
  • Gym123
    Gym123 Posts: 14
    Options
    @Gym123

    The crossover refurb cost return on investment is Y-U-G-E.

    Even using straight Daytons would be an improvement.

    It's not a big cost, all things considered. The crossover for the 5 is similar, and the gains are substantial for the money.

    If you want to know if putting money (even the bare minimum of replacing the parts in the crossovers) into a pair of 5, 7, 10, 12, RTA, etc., is worthwhile, if you throw a dart into the forum blindfolded you'll hit someone who will tell you it is 100% worthwhile.

    I've got... lemme see... $500 worth of time/money in my 5B (plus discounts/gifts a couple of members gave me)... which might be an insane series of expenditures over 18 months, but these 40 year old speakers sound amazing. And they ended up being gifts for my father. 100% worth it.

    If I'd only spent $100 on upgraded Dayton crossovers? Still 100% worth it.

    d0gj330xe13i.png

    Pardon the Christmas setup clutter.

    I agree, but again, the speakers aren't mine and it's not my decision. I built the speakers I use and the crossovers cost more than the drivers. Old crossover designs prevented good speakers from sounding great and the huge number of posts online and conversations between people telling of the improvements are proof.

    Did you use SEAS woofers?

    Nothing wrong with Christmas clutter.
  • F1nut
    F1nut Posts: 50,086
    Options
    Gym123 wrote: »
    F1nut wrote: »

    You are in the wrong business as you don't know what the hell you are talking about.

    How do I not know what the hell I'm talking about? Do you work in audio? I have done this for more than 45 years and to be honest, I'm tired of opinions from people who are outside of the conversation between me and customers. Beyond stupid? It's his choice, not yours and not mine.

    Being pretty judgmental, considering I'm not the owner of the speakers and these are used in a cabin up North. If these were mine, I would upgrade the crossovers, but trying to force someone else to do it when they're not the main speakers in their life isn't easy.

    I know because I've read your posts. If you knew what you were doing you wouldn't have said/asked half of what you did.

    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • xschop
    xschop Posts: 4,837
    Options
    Gym123 wrote: »
    F1nut wrote: »

    You are in the wrong business as you don't know what the hell you are talking about.

    How do I not know what the hell I'm talking about? Do you work in audio? I have done this for more than 45 years and to be honest, I'm tired of opinions from people who are outside of the conversation between me and customers. Beyond stupid? It's his choice, not yours and not mine.

    Being pretty judgmental, considering I'm not the owner of the speakers and these are used in a cabin up North. If these were mine, I would upgrade the crossovers, but trying to force someone else to do it when they're not the main speakers in their life isn't easy.

    I've always agreed the customer is always right.... but a good-paying customer is a down-right genius.
    Don't take experimental gene therapies from known eugenicists.
  • Gym123
    Gym123 Posts: 14
    Options
    F1nut wrote: »
    Gym123 wrote: »
    F1nut wrote: »
    I know because I've read your posts. If you knew what you were doing you wouldn't have said/asked half of what you did.

    Well, aren't you special?

    Care to enlighten me, or are you too busy feeling good about yourself?
  • F1nut
    F1nut Posts: 50,086
    edited December 2023
    Options
    Yes, I am special and thanks for recognizing that fact.

    BTW Rob, clicking insightful just makes yourself look ignorant.
    Post edited by F1nut on
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • xschop
    xschop Posts: 4,837
    Options
    It was an excruciatingly difficult decision whether hitting it or the lol button.
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,281
    edited December 2023
    Options
    Ha! A new forum member hult321lnc1d.png
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gardenstater
    Gardenstater Posts: 4,281
    edited December 2023
    Options
    ---
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gym123
    Gym123 Posts: 14
    edited December 2023
    Options
    Delete, please- it's not worth commenting anymore.
    Post edited by Gym123 on
  • Gym123
    Gym123 Posts: 14
    Options
    FWIW- I was requesting that my post be deleted, not the thread.