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Thread: 250 DIY BASS RENONANCE - HELP

  1. #1
    Senior Member gerard's Avatar
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    Unhappy 250 DIY BASS RENONANCE - HELP

    Hello

    I just finished my 250 Diy and would like to thank first the people who help me for drawings , crossover etc ... .
    I use
    LE14A-LE8T-LE5-5-035TI
    CROSSOVER XPL200

    2214H is too hard to find and I had an LE8T!
    My choice for xpl200 crossover comes because 250Ti crossover was hard to find ,very expensive and due to age would have need to change all caps I believe ; making a brand new one crossover for a first Diy speakers was not the best solution and xpl200 was not so far for the crossover and compnents used , the xpl200 crossover was cheap and new (ebay) .

    Now:
    the midrange is very good , precise , clean beautiful .
    Treble is not as good as in my 434x clone with 2405 , may be it's beacuse i am used to a tweeter taking up at 9khz and this one takes 5 khz ! but the 2405 makes silky anf finest uhf .

    The problem is with the Bass .
    I have very big resonance between 50 to 150 hz
    playing standart cd or records it's ok but if I play a test record for bass : David Crosby ( If I only remember my name ) then it's a nighmare .

    I stuff my speaker with fiberglass already ; my port behind the speaker is a little small ( 9.5 cm diameter = 4 inch ) I wanted 5 inch but I found a pvc audio port who suits very well !!!.

    Can I have any advise to solve this ?

    regards

    Gerard

  2. #2
    Administrator Robh3606's Avatar
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    Do you have more pictures?? Did you brace per the JBL drawings??? From your avatar they look nice but can't really see what's going on. You do realize the XPL crossover is optimized for a different driver set.

    Rob

  3. #3
    Senior Member gerard's Avatar
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    Hello


    here is a picture

    I did brace , may be not enough I do not knwo , it is made of 19mm Mdf .
    Brace every 60/70 com and all along the corners
    fiberglalss was glued on someparts but not with staple !
    here is a pic attached .

    Gerard
    Attached Images Attached Images  

  4. #4
    Administrator Robh3606's Avatar
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    OK attached is a drawing that shows the bracing. What is the ID on that port tube?? That look real small. What is the cabinet tunned too?? To get 31Hz with an Le-14A in 4 cubic ft took 2 3" ID ports about 8 inches long and even with that I can get quite a bit of port noise when they really get going.
    Attached Images Attached Images  

  5. #5
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    Hi
    Gerard, nice work it looks good !
    My post consider only the noice in the port and nothing else.
    It sounds like a mis-tuning of the port !

    If the port-diameter is to small (for the given resonans-freq and the amount of moved air).
    It can mostly be solved with a bigger diameter to avoid turbulence in the port.
    It can also be solved (2.nd best) with filling up the port with drinking straw !
    Yep, and I have NOT been drinking all night, and i know it would never work in commercial speaker-industry.
    You can also glue felt on the inside of the tube.
    Give it a try its not expencive.
    Thanks
    Jens

  6. #6
    Senior Member gerard's Avatar
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    ok


    I did brace following this drawing .
    I check again with a cd and a record ; Resonance seems to be between 45-90 hz .

    Jpb : Resonance is really big ; if you sepak French can you explain for the straw ? .

    Regards

    Gerard

  7. #7
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    Hi Gerard,
    In first try i will keep it in english for the others to follew and give comments. If You like i can send You the same post in french in PM or by mail.

    I think we must make clear that we are dealing with two or tree problems here and not just one.
    1. filtering,... ( i will not comment that here as i bulive other guys can do that better, by their experience)
    2. Wrong tuning of the port.. (resonance up to 90hz sounds really wrong)
    3. Noice-reduction due to turbolence in the vented area. (the port)

    2. If You have a multimeter, some resistors, and a sine-generator we can easily help you to find a good balance in your speaker regarding the resonance of the port and the general behavior of your woofer. (from a electrical point of wiev) Later You might have to play around a bit with the to find the dimension that also sounds good.

    Tell us what You've got.

    3. When nr.2, is in order you maby not even have to think about step-3, but if you do it just as simple (and crazy) as it sounds. You buy a few packs of straw and fill up the port with them so they sit tight ! Many small tubes in one big. This will give a slight air-flow resistance in the vented area, and some say Whauuuu, and others shake their head..

    I think its like 10 -20 years ago when people expected HiFi-freaks discussing cables and capasitors to be member of a secret spooky society.. The fact is that HighEnd speaker manufactors have worked with this princip for 10-20 years maby even more.. Its just never been in production except for Danish Dynaudio and ScanSpeak. (as far as i know)
    Lets hear what You do
    Jens

  8. #8
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jpb_dk
    I think its like 10 -20 years ago when people expected HiFi-freaks discussing cables and capasitors to be member of a secret spooky society.. The fact is that HighEnd speaker manufactors have worked with this princip for 10-20 years maby even more.. Its just never been in production except for Danish Dynaudio and ScanSpeak. (as far as i know)
    Dynaudio called theirs a variovent. It is a type of aperiodic tuning and is really a very different animal from the classically tuned JBL cabinet.

    Quote Originally Posted by gerard
    I did brace following this drawing .
    I check again with a cd and a record ; Resonance seems to be between 45-90 hz .
    Are you sure that it is the cabinet and speaker and not a room mode that is being excited?

    If you have the capability to measure the impedance of the woofer, you should run the impedance sweep both with and without the network. This can be very useful in finding an anomalous cabinet resonance.


    Widget

  9. #9
    Senior Member duaneage's Avatar
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    To fix this easiest you need a Audio Wave Generator. This can generate pure tones from 10 Hz to 200 Hz.

    If you have one of these, you can determine the frequency the port is operating at. Guessing, measureing other systems, even following precisely the jbl plans will not work. Almost all speakers need to have the port tuning finally adjusted to be correct.

    Allow the drivers to break in by playing music for a few hours at a moderate level.

    Adjust a tone from 20 Hz to 150 Hz through an amplifier. Play it just load enough to see the cone move a little. As you move from 20 to 150 Hz take note of when the speaker cone actually does not move anymore. The air from the port will be strongest at the same time. This is the port frequency.

    If it is too high make the port longer, or add solid volume to the cabinet ( like a book or wood blocks)
    If it is too low cut 1-2 cm from the port and test again. See how much it changed and cut again if needed. Do not cut too much at one time. You could also add more fibreglass to raise the tuning frequency.

    Each cabinet may end up with different ports.

    Do this with the crossover connected, the resistance in the coils affects the port frequency.

    YOu may be able to use WinISD to generate tones on your computer and feed them through an amp into your speaker. You can actually feel the cone come to a stop at resonance even though sound is being produced. The port DAMPS the driver at the resonance, controlling cone movement, and most sound comes from the port at this point.

  10. #10
    Senior Member gerard's Avatar
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    Thank you all for your help .


    1. I can check with the straw
    Do not have a sine wave generator


    2.With My 434x I have no resonance speaker at the same place .
    But I remember i HAD SOME RESONANCE before changing my caps for bass ( 52uf) . when I changed my caps from oil caps ( 20 yars old ) to solen 52uf I had a big improvment in cleaning the bass section in my 434x .


    3.Duaneage : can i use a Cd having mp3 sound from 20 t0 500 hz directly ? and test the cone displacment . I notice the cone was even moving sometimes too much !

    4. Woofer impedance : I can do that also .

    I will try tomorrow 1 and 3 , 4 and keep informed .


    gerard

  11. #11
    Senior Member Guido's Avatar
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    Gerard, original reflex port of 250ti is dia 103mm duct 130mm.


    What do you have?

  12. #12
    Senior Member gerard's Avatar
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    Guido


    Port dia 75 mm length 75 mm !!!

    Gerard

  13. #13
    sa660
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    Port agjustement

    The volume of the port is important.
    Some audio Book (jean Hiraga) is recommending to keep a constant volume.

    3 options.
    A. Change the lenght of the port to keep the same volume as orginal 75x245mm
    B. Create 2 ports of 75x122.5mm each.
    C. increase holes size to get the right port size (Dia 103mm duct 130mm).

    The later one can be found in carpet shop. Some big roll of carpet are made on carton roll very strong and heavy.

  14. #14
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    gerard, Nice work! I use ( If I only remember my name ) as "Test" material as well. I've tamed the "Nightmare Bass" a bit by wrapping the outside of the port tubes with two layers of sound deadening material. 1st is a layer of fiberglass insulation, covered by a layer of fiberfill (pillow stuffing/sheet form). That helped some. I may try wrapping the port tubes with a material used for "Roofing" called freeze guard, to insure the port tubes are "Dead Quiet". It is a dense/sticky/rubber/tar-like sheet that would quiet a bell, but once on, VERY hard to remove. Maybe try the fiberglass wrap first, to "See" if the sound improves. The simple test could show if the tubes are part of the problem. But, it just might be David's way of shaking the "Soul"...

  15. #15
    Senior Member gerard's Avatar
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    Well I just inverted the wire connection to the speakers and that'all everything is ok for me .

    I know the wire connection was straight but when I did connect the woofer I did the white wire on the red plug and the white+ stripe with black plug Am I wrong ?

    Rek50: "the nightmare bass " is ok now I think it's a nice test for bass !

    Guido : if you read this I would like your input about what is your feeling compare 4343 to 250 Ti as I know you had both ( or anyone feeling ) :
    Bass - midrange - tweeter- soundstage - Dynamic feeling -

    I have no way to compare my 250 diy as I never listen to original . I just have 434x to compare to my 250 xx clone .

    I will post some picture later if somebody is interested , for now I go on with my test , and later will change the port or use the straw !

    Thank for support .
    Gerard

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