+ Reply to Thread
Page 4 of 5 FirstFirst ... 2345 LastLast
Results 46 to 60 of 63

Thread: JBL 2245 : 10 or 12cft

  1. #46
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,406
    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
    Senior Member
    Join Date
    May 2007
    Location
    Ingolstadt in Germany
    Posts
    339

    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
    Senior Member
    Join Date
    May 2005
    Location
    Glass City Toledo Ohio
    Posts
    203

    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
    Senior Member
    Join Date
    May 2007
    Location
    Ingolstadt in Germany
    Posts
    339

    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
    Join Date
    Apr 2003
    Location
    The Tardis
    Posts
    5,950
    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.
    Attached Images Attached Images  

  6. #51
    Senior Member ivica's Avatar
    Join Date
    Jan 2008
    Location
    serbia
    Posts
    800
    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
    Join Date
    Apr 2003
    Location
    The Tardis
    Posts
    5,950
    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
    Join Date
    Sep 2010
    Location
    Montréal
    Posts
    1,915
    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.

  9. #54
    Senior Member Champster's Avatar
    Join Date
    Apr 2014
    Location
    San Diego
    Posts
    146

    2245

    So Lee, what did you build? As you know, I am just now getting my 2245's and planning to build them into a true subwoofer with an upper limit of about 80hz.

    I really am tempted to build this 12cf cabinet in this article. I am going DSP with fully active amplification, so the electronic boosting will be simple.

    Has anyone built either of the cabinets in this article?

    Thanks,
    Paul
    Last edited by Champster; 04-28-2014 at 07:39 PM. Reason: typo

  10. #55
    Senior Member
    Join Date
    Feb 2007
    Location
    Christchurch, NZ
    Posts
    1,392
    I think Greg Timbers always said that the 2245 would benefit from a 12cuft box. He also said the 4345 was always limited buy the box size.

    Allan.

  11. #56
    Senior Member svollmer's Avatar
    Join Date
    Dec 2004
    Location
    Looking 4 Squirrels!
    Posts
    410
    Quote Originally Posted by Champster View Post
    So Lee, what did you build? As you know, I am just now getting my 2245's and planning to build them into a true subwoofer with an upper limit of about 60hz.

    I really am tempted to build this 12cf cabinet in this article. I am going DSP with fully active amplification, so the electronic boosting will be simple.

    Has anyone built either of the cabinets in this article?

    Thanks,
    Paul
    I built four of the 12cf models as described in Greg's article. I changed the dimensions to fit my space, but other than that, they're the same. I have them crossed over at 60Hz (18db/octave if I remember correctly) and they KILL! Mine are close to a corner stacked floor to ceiling.

    If you do the 12 footers, I'm sure you will love them!

  12. #57
    Senior Member Lee in Montreal's Avatar
    Join Date
    Sep 2010
    Location
    Montréal
    Posts
    1,915
    The 2245 can use 8cft to 12cft depending on if you prefer underdamped to overdamped. 8cft will yeld a tighter bass. 12cft will go lower.

    I made mine at around 10cft. with two 6" ports. Roughly 33" x 23.5" x 23.5" (or if you make a draft from an 8'x4' - make 36"x24" and 24"x24" panels, minus blade thickness)




  13. #58
    Senior Member
    Join Date
    Apr 2007
    Location
    Maryland
    Posts
    398
    Quote Originally Posted by Allanvh5150 View Post
    I think Greg Timbers always said that the 2245 would benefit from a 12cuft box. He also said the 4345 was always limited buy the box size.

    Allan.
    That is why, when I built my JBL 4345 Clones, I made my enclosure a little deeper, so the internal volume of the enclosure (net of the dogbox) was around 12 cubic feet

  14. #59
    Senior Member Champster's Avatar
    Join Date
    Apr 2014
    Location
    San Diego
    Posts
    146
    Ok so I'm going with the 12cf box tuned to 20hz. When I put the vent into WinISD I get 2 - 4" vents about 11" long. What is vent mach? Does that sound right?
    Name:  Screenshot (3).jpg
Views: 112
Size:  95.3 KB

  15. #60
    Senior Member svollmer's Avatar
    Join Date
    Dec 2004
    Location
    Looking 4 Squirrels!
    Posts
    410
    Quote Originally Posted by Champster View Post
    Ok so I'm going with the 12cf box tuned to 20hz. When I put the vent into WinISD I get 2 - 4" vents about 11" long. What is vent mach? Does that sound right?
    I’m certainly no expert and many here would know for sure, butI thought Greg’s plans called for a large vent because of the high velocity of air produced by the sub.The larger the vent, the less “chuffing” occurs.The B460 used three vents to simulate one large vent because JBL was afraid that small animals could get into one large vent (or at least that’s what I’ve heard).I just copied Greg’s plans, but I altered the dimensions (same net volume) and I changed the round vent to a square vent.I think my vents are something like 8”x8”, or close to that (I'd have to measure them at home).I just calculated the area of the 9” vent described in the article and changed it to the proper dimensions for a square vent so the area was the same.


    I chose the 20” version which is 25hz unassisted.I can verify that it will produce startling infrasonic frequencies with the subs near one corner and thorough bass traps in each corner.I use an Audio Control Richter Scale III xover/eq at 60Hz (sometimes 40) and I have never had to boost the lowest frequencies.I keep it flat and the bass is deep and tight.



+ Reply to Thread

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. jbl 2245 H
    By gene in forum Lansing Product Technical Help
    Replies: 105
    Last Post: 08-28-2012, 01:11 AM
  2. A 2245 is a?
    By toddalin in forum Lansing Product Technical Help
    Replies: 5
    Last Post: 11-10-2006, 11:49 AM
  3. A7/2245 (x2?)
    By moldyoldy in forum Lansing Product DIY Forum
    Replies: 2
    Last Post: 01-04-2006, 12:16 AM
  4. Sub/2245
    By dieterj in forum Lansing Product General Information
    Replies: 5
    Last Post: 03-20-2005, 06:22 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts