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Thread: Box design for JBL 2205A

  1. #1
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    Box design for JBL 2205A

    Hi,

    Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

    Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.

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    Senior Member LE15-Thumper's Avatar
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    Quote Originally Posted by acmv View Post
    Hi,

    Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

    Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.
    Search the old library, you'll find plenty of options there.
    LE15-Thumper
    "Give me JBL, or give me death"

  3. #3
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by acmv View Post
    Hi,

    Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

    Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.
    As I recall the 2205 was first an Alnico design (2205A/B) which, after the switchover to ferrite (2205H/J) because of external reasons, soon morphed into the 2225H/J with what changes I do not know. You might be able to deduce some of them by studying the T/S parameters. For rear-loaded horn the C34/4530 style enclosure would be OK for that driver.

    Also, for bass reflex for hi fi use decide what kind of alignment you want and use one of the enclosure design software programs to get dimensions and porting details.

    For SR use the JBL Pro Enclosure Guide will provide data. (GI)

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    Your Thiele Alignments

    The relevant Thiele Small parameters for the 2205A are:

    fs = 30 Hz
    Qt = 0.21
    Vas = 297.3 liter

    Qt will become a bit larger when a passive crossover is used. The combined resistance of amplifier, cables and the crossover’s series inductors determines Qt. See below for details.

    Of the alignments in Thiele's tables only two are feasible with this driver.

    No. 2, QB3, f3/fs = 2.28, f3/fb = 1.32, Cas/Cab = 7.48, Qt = 0.209
    No. 3, QB3, f3/fs = 1.77, f3/fb = 1.25, Cas/Cab = 4.46, Qt = 0.259

    There result the following boxes.

    No. 2, f3 = 68.4 Hz, Vab = 39.7 liter
    No. 3, f3 = 53.1 Hz, Vab = 66.7 liter

    Any Qt with 0.209 <= Qt <= 0.259 is feasible, You need to do a non-linear interpolation between Alignments No. 2 and No. 3. For that You need Thiele’s tables. Somebody with a good design program could do that for You.

    Alignment No. 3 will supply good midbass with punch Depending on Your taste You may need a sub then.

    This post contains the "formula" how to calculate the resulting Qt.

    http://audioheritage.org/vbulletin/s...&postcount=105

    The data for the 2205A is:

    Qa = 5
    Qe = 0.22
    Re = 5.5 Ohms

    Ruediger


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    Thank You for the replies. But being an amature in speaker building, I am unable to understand the phrases used here. Things like Q values, alignment, etc.

    So please pardon me. Is there any thing that I can read up, or maybe a few suggested designs that I can follow? Your effort will be most appreciated. Thank You.

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    I see two choices

    Quote Originally Posted by acmv View Post
    Thank You for the replies. But being an amature in speaker building, I am unable to understand the phrases used here. Things like Q values, alignment, etc.

    So please pardon me. Is there any thing that I can read up, or maybe a few suggested designs that I can follow? Your effort will be most appreciated. Thank You.
    You can either build:

    a rearloaded horn which will be 60 cm x 60 cm x 110 cm. Plans are readily available, for example JBL 4530. This will not supply really deep bass.

    or:

    a vented box, ca. 70 to 75 liters net volume. This will have a -3dB frequency of ca. 53 Hz. That is plenty of bass from a very small cabinet. For really deep bass You will need a subwoofer.

    Make up Your mind, then we can proceed.

    Ruediger

  7. #7
    Dang. Amateur speakerdave's Avatar
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    Use this enclosure guide: here's the link: http://www.jblpro.com/pub/manuals/enclgde.pdf

    Here's the first page: Build #6.
    Attached Images Attached Images  

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    Thank You everybody for the reply. After reading thru the information, I have come out with my prefered dimension on the interior of the box. I am looking at 25" High by 20.5 Wide and 18" deep. Having a port of 1.4" high by 20.5" wide and length of 11" at the bottom. Is these dimensions workable? Please give your advice, your feedback will be most appreciated. Thank You.

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    Not okay

    The box is too large. You cannot pick any box and any tunnel and combine them with any speaker.

    I calculated box net volume and box resonant frequency from Your data.

    Box net volume: 25 x 20.5 x 18 in**3 = 9225 in**3 = 151 liter
    Effective radius of vent: R = sqrt( 1.4 x 20.5 / pi) = 3.02 in
    End correction for tunnel, both ends flanged: L” = 1.70 R = 5.13 in
    Effective length of tunnel: 11 + 5.13 + 0.75 in = 16.9 in
    Volume occupied by tunnel: (11 + 2.57) x (1.4 + 0.75) x 20.5 = 598 in**3 = 9.8 liter
    Box net volume corrected: 9225 in**3 – 598 in**3 = 8627 in**3 = 141 liter
    Box resonant frequency wb: wb = 2 pi fb
    Lv / Sv = 1.84 x 10**8 / wb**2 Vb
    fb = sqrt( 1.84 x 10**8 Sv / (Vb Lv) ) / (2 pi)
    = sqrt( 1.84 x 10**8 x 28.7 / (8627 x 16.9) ) / (2 pi)
    = 30.3 Hz

    If I made a mistake let me know.

    This gives a response which is down -1 db at 250 Hz and -7 dB at 35 Hz.

    Ruediger

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    Hi Ruedider,

    Thank You for your reply, your reply is quite technical for me to understand, can you help me to change the design to fit the requirement? I am looking at a general purpose bass box of about 30 to 40 Hz. Look forward to your reply. Thank You

  11. #11
    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by Ruediger View Post
    The box is too large. . . . This gives a response which is down -1 db at 250 Hz and -7 dB at 35 Hz . . . .
    Maybe just right for his room.

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    Quote Originally Posted by speakerdave View Post
    Maybe just right for his room.
    No, that is a sick response curve.

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    Quote Originally Posted by Ruediger View Post
    No, that is a sick response curve.
    I am unable to semanticize "sick" in this context into technical or any other relevant terms. Do you mean one with a bump in the bass followed by a steep fall?

    The picture I have of the curve is that it might be a smooth "banana" roll off, which JBL has used for a good number of years for speaker systems that will be used in relatively small rooms. In a typical domestic setting the room is part of the LF system from the lower hundreds downward. Some of the effect is a more or less gradual room rise, which a banana roll off may mate with well, and some is unfortunately peaky resonance modes which must be dealt with separately. In small rooms the classic extended shelf bass alignment results in a nice fat hump somewhere, not a desirable feature. The gradual roll off gives more extended VLF, though at a reduced SPL,as I understand it, which the room may support.

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    Pathological ?

    Quote Originally Posted by speakerdave View Post
    I am unable to semanticize "sick" in this context into technical or any other relevant terms.
    ill-designed, not properly designed, mal-functioning, heavily overdamped.

    Plot the frequency response in something like WinISD and You will see.

    First I intended to write "pathological response" but then I thought it sounded too academically, so I wrote "sick".

    Do a Google search for "pathological equation". See?

  15. #15
    Dang. Amateur speakerdave's Avatar
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    This is not at all helpful.

    Quote Originally Posted by Ruediger View Post
    ill-designed, not properly designed, mal-functioning, heavily overdamped.

    Plot the frequency response in something like WinISD and You will see.

    First I intended to write "pathological response" but then I thought it sounded too academically, so I wrote "sick".

    Do a Google search for "pathological equation". See?

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