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SP1200, 1700, or 2500 Crossover Diagrams

Discussion in 'Exclusively Sansui' started by Culpeper, May 17, 2017.

  1. Culpeper

    Culpeper Active Member

    Messages:
    191
    Yep, it is sort of daunting. I keep running into road blocks.
     

     

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  2. Culpeper

    Culpeper Active Member

    Messages:
    191
    Ragan, when you get back on xsim tinker with a zobels on the mid and tweets. Brings down -3dB and flattens FR at high freq after raising the cap value on the tweeter. Looks like another possible tweak.
     
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  3. Culpeper

    Culpeper Active Member

    Messages:
    191
    So, got tired of working with the whole band pass and HF filters. I have a couple of MCM $19 woofers with just 1.0 mH inductors on them that have pretty good specs for some reason. For the tweeters I started out with just the 2.2 uF capacitor but the tweeters are pretty sensitive and was about 12dB too high. So, I swapped out the capacitor with 1.2 uF and a 30R shunt resistor. This got everything into line. Since the bass and tweeters are 1st order we don't have to worry about phase alignment. This really opens the door to the tweeters with plenty of protection. Bass is very nice and holds its own like a Heresy III. I left the ports as is. The midranges are left at the Natural (1.062 mH setting). I used SPL Copy to put together a FRD and ZMA file. Those got me started using Xsim to get a good idea of the electrical response. Polarity on the band pass is reversed. Frequency response graph below was measured in the cabinet and the listening room at near field. So, it is an acoustic response. Sort of ironic that this is so simple and yet so good. I'm thinking on bypassing the parallel midrange cap and transformer and make it a full 1st order. That will need a different cap on the tweeter.

    Woofers:
    http://www.newark.com/mcm-audio-select/55-2952/12-woofer-with-paper-conecloth/dp/80R7003
     

    Attached Files:

    Last edited: Mar 20, 2018
    sragan likes this.
  4. Culpeper

    Culpeper Active Member

    Messages:
    191
    figured out why the midrange and tweeter driver sections are reversed polairty from the factory. When set to Clear it is coming out normal polarity from the crossover and reversed on the drivers. When on Natural or Soft the polarity is reversed from the crossover. Something to remember when modeling in Xsim. Also, explains the advertised 750Hz crossover frequency. It is based on the system response crossover with the woofer and not the actual crossover between the midrange and woofer. Here is another example of a 1st order modification with the same MCM woofer. One with the -180/+180 vertical line is reverse polarity on the midrange with a very acceptable flat system frequency response. Regular polarity has the near linear system phase. Very nice. Hard to decide but easy to determine by listening in the room. No noticeable HF bleeding into the LF or LF breakup. Converting to 1st order on the tweeter and midrange is really simple. Remove the 16R resistor. Disconnect the transformers and keep the switches on Clear or solder the switch just to keep it there.
     

    Attached Files:

    Last edited: Mar 23, 2018
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  5. Culpeper

    Culpeper Active Member

    Messages:
    191
    At the end of the day I settled on using the MCM with a 2.0mH inductor and regular 22uF cap before the midranges. Basically, a two way 1st order. The midranges have an L-Pad consisting of 2R/12.5R. There is no need for the tweeters. Frequency response is less than +/- 3dB between 170-17,000 Hz using ERB. To complement this set I have a pair of HUMAN Model 81. My second set of SP-2500 has a 100W Dayton subwoofer amp in the rear and a GRS subwoofer in the other box. They connect together using the original speaker inputs. The sub crossover is 80Hz and the gain is set -5dB below the MCM woofer. MCM woofer is sold by Newark and the rest came from Parts Express. Total cost was about $60 for the drivers and $100 for the sub amp. The inductors was one of their factory buyout specials and the resistors were Dayton. The capacitor is the regular $1 variety. I decided the OEM crossover is obsolete and only using it for the inputs and to mount the capacitor. The transformer switches need to be set/solder to Clear and the resistor disconnected. All the inductors disconnected and jumper to replace the series 351. This is so the squaker outputs can still be used. Same thing for the tweeters if used with 1st order capacitor. Woofer inductor is mounted inside the box. The L-Pads are connected inline.

    As a result I have plenty of spare parts. Also, these boxes are a good candidate for the Two Pi speaker kit. Came close to going this route and may eventually go there :)
     

    Attached Files:

    Last edited: Apr 26, 2018
  6. vha

    vha New Member

    Messages:
    30
    I brought back and connected my very old speakers SP1200.
    except that one of the 2" 50mm tweeters cone is damaged (not completely) they seem to work ok.
    I will have to replace it..
    I read most of the interesting full of information discussions from start and I noticed if not mistaken that most of them are based in replacing the woofer.
    I was thinking why not keeping the old woofer and replace all mid-rage and tweeters with a mid-high or even with two 4inch drivers of 30w 8Ωms each and cut the woofer lower somewhere between 300 and 700Hz.
    I guess that just a lowpass filter is needed in that case by using one of the original coils in series and add a bipolar capacitor on the new fullrange/tweeter driver?
     
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  7. Culpeper

    Culpeper Active Member

    Messages:
    191
    10_Jun_2018_12_50_06.jpg I used the original network board bypassing the inductors. Set the tone control to Clear and soldered in place. One series capacitor for the midranges and one for the tweeters on the board. A single separate coil for MCM woofer mounted in the cabinet. Disconnected the original midrange resistor and added a -3dB L-Pad after the network board for the midrange. The tweeters just utilize the existing parallel resistor on the network board. I have a nice FR between 170-15khz. Use Xsim to simulate to make a determination on your best combination. Main thing is the original network super chocked up the tweeters and midranges so they are normally well preserved for a little hot-rod changes. Also, boxes are bettered sealed if not using original woofers with no inductor. You'll need to do the math.
     
    Last edited: Jun 10, 2018
  8. vha

    vha New Member

    Messages:
    30
    thank you for all the detailed description
    I will try to be more familiar with this technical terms and get back to you.
    As a first approach I was thinking the keep the woofer and replace the rest with two 4" med/high drivers.
    But first I will make some tests by connecting the speakers several different
    amps (one 70s Sansui and one 90's Luxman vintage among them) and class D amps too.
    and make some frequency measurements too before of (or if.. ) any changes.
    If we change the woofer we get something completely different, will have to change the other drivers too.
    The idea of a more powerful new speaker system in the old beautiful enclosure..
    Then the Sansui SP1200 will probably lose its value?
    Ill get back to you with sharing this
    Thank you
     
  9. Culpeper

    Culpeper Active Member

    Messages:
    191
    Yes, I came close to a complete rebuild inside myself. Something like the Two Pi loudspeakers with a single port tuned for the Sansui box.
     
  10. vha

    vha New Member

    Messages:
    30
    do you have a picture to share?
     
  11. Culpeper

    Culpeper Active Member

    Messages:
    191
    Last edited: Jun 14, 2018

     

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  12. vha

    vha New Member

    Messages:
    30
    Yes this is another speaker with 2 drivers and a port and with about the same size box.
    Maybe I misunderstood I thought you had SP Sansui speakers that you upgraded??
     
  13. Culpeper

    Culpeper Active Member

    Messages:
    191
    Yes, mine our SP 2500s. Your 1200s would be a good box for the Two Pi kit. It is just an idea I was throwing out there. There is nothing wrong with your idea to upgrade the sound. As for losing value. I wouldn't worry about it. You're creating a sound for yourself.
     
  14. vha

    vha New Member

    Messages:
    30
    I am very curious to see the sansui how you changed them
    Can you send me pictures?
     
  15. Culpeper

    Culpeper Active Member

    Messages:
    191
    Schematic


    schematic.jpg


    The four boxes. The two outboard are the schematic above. The left inboard has a subwoofer amp (Dayton SA100) mounted in the back. The right inboard box has the actual 12" subwoofer (GRS 12SW-4). Sub crossover is set at about 70Hz and the gain is set about 5dB below the main woofers.

    KIMG0022[1].JPG

    Subwoofer amp. Speaker cable goes to the right inboard box.

    KIMG0041[1].JPG

    Connection to the subwoofer driver. Ports are blocked so that it is a sealed box.

    KIMG0042[1].JPG

    Inside the left outboard showing the in-line midrange L-Pad and the 2mH Inductor

    KIMG0029[1].JPG

    Inside left cabinet showing hookups. No reverse polarity.

    KIMG0034[1].JPG

    Front of left cabinet. Sealed ports.

    KIMG0035[1].JPG

    Midrange and tweeter baffle mounting. Above and below the midranges are 1/2" weather stripping to diffuse baffle response. Between the tweeter horns and the sound diffuser is 30 ppi 1/2" Filtration Foam to diffuse the horns and baffle response. This part is all sheet metal. There is factory thin padding in the rear but not any in the front. This part of the box really needs to be calmed down.

    KIMG0039[2].JPG

    Left crossover network. All inductors disconnected. Copper jumper wire installed to bypass inductor 351 using its own connection holes on the board. Tone control set and soldered in the Clear position so that the midrange and tweeter connections can still be used based on network board layout. Parallel 16W resistors removed. 2.2uF series capacitor for the tweeter (blue). 22uF series capacitor for the midrange (black). The parallel 4.7uF capacitor for midrange removed.

    KIMG0032[2].JPG

    Frequency response sweep (without subwoofer). You can see why no resistors on the tweeter. The 30 ppi filter in front of the tweeter is dampening the high end. This is desirable since the horns are harsh at very HF. -10dB at 15khz is fine. Total cost for this change-up is about $60 for parts plus shipping. Didn't go high end on capacitors or inductor. There is no need for that with these cheap woofers and 47 year old OEM speakers.

    FR.jpg
     
    Last edited: Jun 29, 2018
  16. vha

    vha New Member

    Messages:
    30
    Really thank you for the photos.
    You did a very good job. Do you enjoy good sound quality?
    Did you have 2pairs of them before or you bought them later ?
     

     

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  17. Culpeper

    Culpeper Active Member

    Messages:
    191
    I like good sound on a budget. Not into buying into it. I got each pair separately within a year before becoming a member here. It wasn't until I started this thread that I decided to radically change it up.
     
  18. ericc129

    ericc129 AK Subscriber Subscriber

    Messages:
    230
    Location:
    Shreveport, LA
    This crossover stuff is outta my level/expertise.....but man, because of the efficiency and quality of the mid and highs with the speaker, it's making me want to biamp them with my SE tube amp driving the highs and to replace and amplifiy the woofer with a stronger solid state amp.....or some sort of frankenstein setup, etc....it is weird that the stock crossover just sends the signal straight to the woofer ?Anyone else try bimaping the SP2500 with good success....it seems like its a great efficient speaker for mids and highs with a striaght up subwoofer just also just stuffed straight into the speaker box.....decisions decisions. This hobby is maddening sometimes
     
  19. Culpeper

    Culpeper Active Member

    Messages:
    191
    The OEM woofer rated @6 ohms was designed to cutoff without the aid of the external crossover. If you replace the OEM woofer you will most likely end up putting a filter before it.
     
  20. vha

    vha New Member

    Messages:
    30
    On this kind of speakers in-order to ameliorate the sound quality, I would say to keep the vintage woofer and replace the tweeters. Do not make any changes on the crossover except to replace the caps with new plastic ones.The electrolytic capacitors are those worst affected by aging because they dry out. Replacing them may help on the sound. But, there are limits to the miracle.
    This one produces 80W. If you want more with biamp options you will have to replace everything and keep just the enclosure. (if you replace everything send me the parts...!)
     

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