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Thread: Help for right volume 2231H

  1. #1
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    Help for right volume 2231H

    Hi,
    years ago (1994) I assembled a cabinet like L250 (same form) but using different woofer and tweeter. This four way system uses a woofer 2231h, mid bass 2118h, mid high 2105h and 2403h tweeter. I don't know the crossover's cuts but I woud like to know the right volume for the 2231h because for me the guy which calculated the volume, made a terrible mistake calculating a volume very very less than the right for this woofer.
    Thanks
    Giuseppe
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    Your data please

    Several combinations of box volume and port dimensions are possible.

    Please do tell me the box volume and the number and dimensions of ports.

    If possible find out the DC resistance of the series coil (bass coil) in the crossover as well.

    Ruediger

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by audiophile.1963 View Post
    years ago (1994) I assembled a cabinet like L250 (same form) but using different woofer and tweeter.
    Very interesting project!

    In answer to your question, you will get the most linear performance from that woofer with a 5 cu ft box (~142 liters) with a port or pair of ports tuned to 30Hz.


    Widget

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    Administrator Robh3606's Avatar
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    Download some box software and try yourself. It's easy. It thats a correct size L250 box it's about 4 cubic ft for the woofer. The sub enclosures for the 2118 and 2105 should be the same as 108H and 104H

    WinIsd

    http://www.linearteam.dk/default.aspx?pageid=winisd

    Rob
    "I could be arguing in my spare time"

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    Thank you very much for your reply Ruediger.
    Today I have measured the box inside.
    The volumes of the three loudspeakers:
    2231h 78784 cm3 = 79 litres
    2118h 10120 cm3 = 10 litres
    2105h 225 cm3 = 2,2 litres
    The woofer has four reflex tubes deep 30,5 cm with a diameter of 7,5 cm and there are 13 cm between the centre of every hole. The volumes of the cabinets were calculated in 1993 by a guy with a mic and a software (I don't know what software) but I fear that the volume should be less than the right because with a 15" woofer I would listen a bass more low (It should be my impression, because I listen these loudspeaker from a lot of year). Now they are in the laboratory of my woodworker for a restyling: I could increase the volume with other 11 litres, more litres it should be a great problem. I don't know the crossover's cuts but I think very very low for the woofer, aroud 150hz. Please let me know your impression, thank you
    Giuseppe

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    Not sooo bad, can be fixed

    Quote Originally Posted by audiophile.1963 View Post
    Thank you very much for your reply Ruediger.
    Today I have measured the box inside.
    The volumes of the three loudspeakers:
    2231h 78784 cm3 = 79 litres
    2118h 10120 cm3 = 10 litres
    2105h 225 cm3 = 2,2 litres
    The woofer has four reflex tubes deep 30,5 cm with a diameter of 7,5 cm and there are 13 cm between the centre of every hole. The volumes of the cabinets were calculated in 1993 by a guy with a mic and a software (I don't know what software) but I fear that the volume should be less than the right because with a 15" woofer I would listen a bass more low (It should be my impression, because I listen these loudspeaker from a lot of year). Now they are in the laboratory of my woodworker for a restyling: I could increase the volume with other 11 litres, more litres it should be a great problem. I don't know the crossover's cuts but I think very very low for the woofer, aroud 150hz. Please let me know your impression, thank you
    Giuseppe
    1st the usual disclaimer: I may have made an error in my calculations.

    The relevant Thiele Small parameters for the 2231H are:

    fs = 16 Hz, Vas = 736 liter
    Qt = 0.21, Qm = 5.5, Qe = 0.22, Re = 6.3 Ohms

    Only one alignment from Thiele's tables fits: Alignment #2, QB3 (Quasi Butterworth 3rd Order)

    f3 / fs = 2.28
    f3 / fb = 1.32
    Vas/Vab = 7.48
    Qt = 0.209

    Calculate the values for the 2231H:

    f3 = fs * 2.28 = 36.5 Hz
    fb = f3 / 1.32 = 27.6 Hz
    Vab = Vas / 7.48 = 98.4 liter

    I calculated the box resonant frequency for the current volume which is 79 liters. The result is 4 Hz. This is definitely wrong and reason #1 why the bass is so weak.

    The f3 (36.5 Hz) is great for such a small cabinet! The 4430 monitor is not any better.

    For a proper alignment we would need 98.4 liter. 79 liter plus 11 liter is a bit short but it would work.

    The current volume (79 liters) is reason #2 for the weak bass.

    Question: did You already subtract the volume occupied by the pipes from the box volume?

    I will check if we can steal a bit volume from the 2118H, if it can live with less. If that was possible, could You do that? Make the chamber for the 2118H smaller?

    ==> BUT <== here comes the other side of the coin: the DC resistance of the series coil in a passive xover will make Qt larger, which is bad for us. A tube amplifier with output transformers will do the same.

    Measure the DC resistance of that coil and tell me the inductance (milliHenry). Then I can check for a coil with a core and a low DC resistance.

    In the worst case You must go "active".

    Ruediger

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    Senior Member JoMoCo's Avatar
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    Check out this possibility...

    Here is one simple, very practical, and really rather elegant way of increasing box volume through adding a stand courtesy of Zilchlabs...

    http://www.audioheritage.org/vbullet...ad.php?t=21007

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    Thanks Ruediger,
    ... I forgot the volume of woofer and tweeter... what can I do to increase with no modifie the cabinet? ...and about the tubes, four tubes 30,5x7,5 cm, is it correct for you? I will can send you better informations next week: I have sent the crossovers to a serious laboratory and I will have real knowledge about cuts and the components only next week.
    Ciao Giuseppe

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    No worries, does not look so bad

    You told me the volume for the bass was 79 liter. Is the space for the 4 tubes included in this? If the 4 tubes were removed, how big would be the volume for the bass?

    Ruediger

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    An other thing that I had not thought… the tubes have a volume to embezzle ulteriorly!

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    An Idea should be change the woofer with another JBL 15" (BUT WHAT?) but in this case I must change the crossovers too and I'm not very able to do this... considering that I don't know how much the filters are correct!

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    Action Items

    Quote Originally Posted by audiophile.1963 View Post
    An Idea should be change the woofer with another JBL 15" (BUT WHAT?) but in this case I must change the crossovers too and I'm not very able to do this... considering that I don't know how much the filters are correct!
    The bass is okay, keep it.

    Some "action items" for You.

    1.) Get a circuit diagram of the crossover. Include all information which You have (DC resistance of inductors etc.).

    2.) Calculate the volume of the bass cabinet when the bass speaker and the tubes are removed.

    3.) See if it is possible to remove the internal box for the 2118 and replace it with a smaller one.

    Take it easy! Ruediger

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    Thank you very much for all information Ruediger. Next week I will send the crossovers to a real technicist who lives in Tuscany and I have just asked him a plan of the crossover, so I will have a real knowledge of the situation. I will inform you about all news. Thank you too, you are very kind
    Have you a nice weekend.
    Best regards, ciao
    Giuseppe

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    Hi Ruediger,

    1.) Get a circuit diagram of the crossover. Include all information which You have (DC resistance of inductors etc.).
    I have sent to the laboratory a picture and they said me that it will be very very difficult "to translate" te filter (see the picture)

    2.) Calculate the volume of the bass cabinet when the bass speaker and the tubes are removed.
    The five tubes are 5 liters + 2 liters speakers

    3.) See if it is possible to remove the internal box for the 2118 and replace it with a smaller one.
    The volume for the 2118H is correct and I can't touch.

    A solution should be to copy the original filter of L250 (the first) modifing only the bass (2231H) and the high (2403H) part of the filter because the other components (mid bass/high) are the same. The cuts are OK for the loudspeakers. But I don't know if it is possible and is yes, how. About the volume I will take a solution.

    Ciao
    Giuseppe
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    Hi Giuseppe,

    That network looks like a plate of spaghetti

    I do not want to modify the crossover. I wanted to see if there were resistors in series with the drivers, and what their values are.

    If possible, I would like to know the resistance of the 7.4 mH bass coil. To measure that a "Milliohmmeter" would be good. A general purpose multimeter will not do unless the person who does the measurement really knows what he's doing. He might also build a Wheatstone bridge with a couple of resistors. To access the bass coil use the "+" input to the crossover and the "+" wire to the bass.

    I do not understand Your remark about the 2403 tweeter. I did not want to change that.

    If I got You right
    1.) the volume of the bass cabinet is 79 liter
    2.) plus another 11 liter available somehow(?)
    3.) plus 5 liter occupied by the tubes
    for a total of (79 + 11 + 5) liter = 95 liter? Is that true?

    As soon as I have Your answer I will calculate and make a suggestion.

    Ruediger

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