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Thread: JBL 2245 : 10 or 12cft

  1. #46
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    Quote Originally Posted by rusty jefferson View Post
    Do you have first hand experience with this amplifier?
    I'm thinking about buying one instead of the Tannoy iwSA 500 D. My only concern is that it might not have the kind of current output I like.
    Quote Originally Posted by rusty jefferson View Post
    Is the high pass passive? Does it sound as good as the BX63-A?
    Doesn't matter, all that is handled by the surround sound processor these days and I'm not a big fan of subwoofers with two-channel systems, which is why I still can't get my head wrapped around what the HK 990 is for. I suspect it was probably designed with something like the JBL LS Series in mind .

    So, this Parts Express amp/crossover has a 3 dB bump filter at 25 Hz (or you can use the EQ at ~25 Hz instead if you need more boost), the 1500 Array has a 4 dB bump filter at ~25 Hz and the BX63/BX63A has a 6 dB bump filter at ~25 Hz. Some people don't like any bump filters with their B380 or B460 (it is room dependent). My point is, this Parts Express offering has a bit more versatility. Some people/manufacturers use plate amps instead.

  2. #47
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    What if I increased cabinet size to 12cft?

    Quote Originally Posted by Ian Mackenzie View Post
    What if I increased cabinet size to 12cft?
    If You pick a larger cabinet size Vb then the following formulas apply.

    f3 = fs * sqrt( Vas/Vb)
    fb = fs (Vas/Vb)**0.32

    You will have a "ripple" (deviation from flat response):

    R = 20 * log10(2.6 * Qts * (Vas/Vb)**0.35)

    There is a missunderstanding about fb and the box resonant frequency, fb *IS* the box resonant frequency, this is when the system of air mass in the ports together with the air "spring" in the box does resonate.

    If You build a passive xover then the Qt of Your speaker will change because of the DC resistance of the series coil in the xover. This has been explained several times here, and it is explained in the Thiele paper. See the technical references thread.

    Ruediger

  3. #48
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    what about a smaller box

    I see going larger than 10 cu ft but what happens when going smaller to the 8 cu ft box ? like what jbl has sold. what would be the trade off for 30 HZ to 340 HZ

  4. #49
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    There are more alignments than just one...

    Quote Originally Posted by kartsmart View Post
    I see going larger than 10 cu ft but what happens when going smaller to the 8 cu ft box ? like what jbl has sold. what would be the trade off for 30 HZ to 340 HZ
    ... see the Thiele paper. Many well-defined filters are possible, Butterworth of order 4 is just one possible choice, and even that only when the driver fits.

    You may as well apply the formula given in my last response. The response will have a positive ripple, the response will be peaked somewhat. The corner frequency will be higher. In too small a box a smaller driver may be better than a larger one.

    Ruediger

  5. #50
    Senior Member Ian Mackenzie's Avatar
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    On the basis of responding to the context of the 1st post in this thread please find the simulation per my previous post of the D.B Keele pocket calculator formula.

    The blue line is the woofer/ boxing system and the yellow line is with my customised room gain added.

    The current trend in bass reflex systems for domestic use incl current JBL K 2 systems is to tune the system so that it can be located near a room boundary and get a reasonable smooth and extended response.

    Your own room gain could well be less or more. In the case of a maximually flat tuning ie a smaller box Vb and higher tuning Fb where the system 40 hertz point is 0.00 db under room gain conditions this could be + 4 db or more leading to boomy bass.

    On paper tunings of this type do not turn heads but they sound better in a typical domestic environment hence the banana curve.

    In my own environment the in room response is -3 at 27 hertz with full power available at that frequency. For music this is excellent.

    The original JBL vintage monitors and the current blue series are tunings for maximually flat response where the modest size enclosure has the Fb pushed up for an elbow curve.

    In some cases the Fb of these systems is 32 hertz which make it sound quite aggressive as was the case when I heard them in Japan back in 2008.

    The banana curve is perhaps more Hifi as is the case with the overall sound of the newer K2 systems.

    On paper it looks impressive but like in a domestic situation it can be a PITA.

    . This looks good on paper but is problematic for the user who must drag the system one foot or so out from the wall and or erect the system on stands which is somewhat impractical given the overall size and height of the enclosures.
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  6. #51
    Senior Member ivica's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    On the basis of responding to the context of the 1st post in this thread please find the simulation per my previous post of the D.B Keele pocket calculator formula.

    The blue line is the woofer/ boxing system and the yellow line is with my customised room gain added.

    The current trend in bass reflex systems for domestic use incl current JBL K 2 systems is to tune the system so that it can be located near a room boundary and get a reasonable smooth and extended response.

    Your own room gain could well be less or more. In the case of a maximually flat tuning ie a smaller box Vb and higher tuning Fb where the system 40 hertz point is 0.00 db under room gain conditions this could be + 4 db or more leading to boomy bass.

    On paper tunings of this type do not turn heads but they sound better in a typical domestic environment hence the banana curve.

    In my own environment the in room response is -3 at 27 hertz with full power available at that frequency. For music this is excellent.

    The original JBL vintage monitors and the current blue series are tunings for maximually flat response where the modest size enclosure has the Fb pushed up for an elbow curve.

    In some cases the Fb of these systems is 32 hertz which make it sound quite aggressive as was the case when I heard them in Japan back in 2008.

    The banana curve is perhaps more Hifi as is the case with the overall sound of the newer K2 systems.

    On paper it looks impressive but like in a domestic situation it can be a PITA.

    . This looks good on paper but is problematic for the user who must drag the system one foot or so out from the wall and or erect the system on stands which is somewhat impractical given the overall size and height of the enclosures.
    This is very nice presentation, but if bass driver is planned to bi used above 100Hz, then the problem of the influence of the "image cancellation" one has to be aware.

    from: http://www.silcom.com/~aludwig/Physi...ity_modes.html

    or http://www.silcom.com/~aludwig/Room_acoustics.html



    it can be seen that about +14 dB gain can be get at low frequency, but -5dB loss (or more) on the higher frequencycan be expected too.

    Not to mention usual stereo arrangement.

    Some responses presented: http://www.nousaine.com/pdfs/Stereo Bass.pdf

    or in more detail: http://www.infinitysystems.com/home/...nf-rooms_3.pdf

    or http://www.bodziosoftware.com.au/Article_7.pdf

    From all mentioned above it is 'clear" that if we "want to introduce" the room acoustic in to the speaker response, then we would jump into the "deep mud" .

  7. #52
    Senior Member Ian Mackenzie's Avatar
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    That goes for any room and any loudspeaker unless configured like the early the Alison systems or NHT 3.3 with the woofer placed at the wall / floor junction and the id 4 feet from the floor.

    However, careful placement even small movement of the enclosure can provide an acceptable compromise.

    The actual response below 400 hertz is normally swomped with room modes . This tends to be more of an issue in small rooms.

    You can if you wish apply very modest equalization with parametric equaliser as some member have done but without suitable measuring kit and experience its best left well alone.

    The point here is however that it is industrious to design the system for a balanced response where tuning and room gain can extend and smooth the broad humps that can otherwise ocurr in a typical domestic environment. Its is there broad humps that are most noticable to the ear.

  8. #53
    Senior Member Lee in Montreal's Avatar
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    Reviving an old thread for everyone's benefit. It seems that an alignement of 5.7 is the golden rule for any woofer. Volume = 5.7*(Vas*(Qts^2)) which is around 12.5cft for the 2245. No early knee and no ripple.

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