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Thread: JBL Cinema sub and solid state amplification with 2 channel horns, advice sought

  1. #1
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    JBL Cinema sub and solid state amplification with 2 channel horns, advice sought

    Hi all, this is a repeat (sorry) of my post in the amplification section, it might sit better here

    I am very interested in researching the best solution for my 2 channel system to fill in the bottom end. I have a pair of Living voice Tone Scouts that are all over by 50Hz, sound amazingly dynamic and can fool you into thinking they do every note at the bottom end, but they miss that bottom octave or perhaps 2. I bought the first pair from Kevin Scott of definitive Audio and have sought Kevin's advice. In short he is not a fan of anything available in the domestic/AV world and his solution with his latest horns (The Vox Olympian) is very large horn loaded subs, he did say that he had very good results with efficient big JBL cinema subs and solid state amplification.

    I run a valve preamp and a 211 SET power amp, so my current thinking is one JBL 4642A and possibly a crown DSi 2000, as this covers EQ and the X-over. I have also considered a Marchand MB42 unit http://www.marchandelec.com/mb42.html or use a Marchand x-over and alternative power amplification (perhaps a secondhand gutsy Bryston). My horns are 104 db/W and the range of low end is likely to be 20 to between 50 and 90, no clue on the slope.

    Any ideas as I'm moving house I cant give room dimensions, but hopefully reasonable UK size, likely to be an old Goegrian/victorian house with tallish ceilings. Any thoughts greatly appreciated






  2. #2
    Senior Member 1audiohack's Avatar
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    The 4642 is a great box. I have four of them. I also have three of the 5749's which are functionally identical with the exception of the JBL stamp and terminal connections are oriented for vertical installation, and the drivers. The 4642's use 2441's, the 5749's use 2242's. In identical boxes these look to have very similar performance but to me the 2242's sound better and dig considerably deeper.

    This isn't something I had hoped for as it cost me substantially to load the four 4642's with 2242's but after having them side by side the same amps, I just had to do it.

    In a relatively small room either would be great. These theater subs are tuned lower than their touring brothers and to me sound much more natural especially if using just one.

    I have t looked up the amp you referenced yet but can tell you the bigger the amp, the more weight the will carry down low.

    All the best,
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    My background is Cinema Audio, so I can give you a little insight.

    The models listed by 1audiohack are good choices, but I would choose the models with the 2242 driver. The single driver version of that subwoofer is the 4645C. Make sure you feed it LOTS of power, something like a QSC DCA 3022 or 3422. These boxes are designed with B6 tuning in mind, so if you go with QSC route, add a SF3 crossover filter to your order. That way the subwoofer is something like -3db down at 22hz, and flat.

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    Thanks guys.

    I will be using this is a modest size room for music, not film (I have a separate system for film). The room is currently 15.5' by 28' (two room knocked through) 10' ceilings, suspect going much above 100 db continuos will be unusual. I will aim for live jazz venue levels and listen to a lot of jazz. Interested in you comments regarding the 2242 vs 2241, does the 2242 sound better at low volumes too ?

    Thanks for the 5749 reference, looks like the 2242's are a little more sensitive as well

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    Senior Member louped garouv's Avatar
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    generally folks like the 2242 for dedicated LFE channels b/c
    they are VERY rugged...

    I believe the 2241 may reach just a but lower according to specs....
    but I forget the exact numbers both report...

    as a side note, I run a pair of 4642a cabinets with either a single qsc mx3000a
    or a pair of them bridged, depending on the output I am requiring at the time....

    they are solid units, even with just the 2241 drivers....

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    Quote Originally Posted by louped garouv View Post
    generally folks like the 2242 for dedicated LFE channels b/c
    they are VERY rugged...

    I believe the 2241 may reach just a but lower according to specs....
    but I forget the exact numbers both report...

    as a side note, I run a pair of 4642a cabinets with either a single qsc mx3000a
    or a pair of them bridged, depending on the output I am requiring at the time....

    they are solid units, even with just the 2241 drivers....
    The specs are interesting the 5749 goes lower at -3db (30Hz) than the 4645 and 4642 (35Hz), but less at -10db (25Hz vs 22Hz). This is without EQ, I would be interested in comments about the character of the 2242 vs 2241 as the price for a 5749 is 'only' a few hundred pounds more than a 4642. I won't be pushing it hard as this is for vinyl replay at home to recreate live music levels in a room that is currently 15' by 30' (Although this is two rooms with a large opening (Probably used to have 'wedding doors')

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    Senior Member louped garouv's Avatar
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    Hi

    I am very satisfied over my two JBL4641 subs driven by one Crown MAi5000, mono in and dual out. Working range is from 25-80Hz.
    They do a great job playing the low octaves

    Read all about it here

    http://www.audioheritage.org/vbullet...l=1#post320209

    Frankly, all the suggested subs from Cinema series will do the job and not only for movies. I my self mainly listening to music from CD, vinyl and internet.

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    Interesting and thanks for all the inputs so far.

    I am moving towards stereo bass using either crown or Marchand or possibly BK Electric amplification (something that has all I need in one box to start and sub £1k or all bar the speaker) I am looking at two 4645 or 4641's as an alternative to a 4642 or 5749. Not sure yet.
    Room treatment is interesting as well

    Keep the feedback coming all very helpful

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    Here's my plan....

    Two 4645c's used with two of these BK plate amp http://www.bkelec.com/Modules/bsbpv500.htm. I think this will be a good start as this is class AB and I can experiment with some of the later Cinema amps like the Crown DSI's, depending on how I find things. This will get me going for £2k, I have measured my horns from 300Hz to 20Hz and this set up with a 6db lift at 20Hz should be spot on with crossover at 80-90Hz. I can place the subs either to the side or behind the Horns, in my current room they would snugly fit in either way and have the cone clear of the back or side of the speaker, so a neater option than one large central box.

    Can't wait !

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    I can also consider 2245's as well at a later stage.

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    Senior Member Mctwins's Avatar
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    Quote Originally Posted by IWC Doppel View Post
    Here's my plan....

    Two 4645c's used with two of these BK plate amp http://www.bkelec.com/Modules/bsbpv500.htm. I think this will be a good start as this is class AB and I can experiment with some of the later Cinema amps like the Crown DSI's, depending on how I find things. This will get me going for £2k, I have measured my horns from 300Hz to 20Hz and this set up with a 6db lift at 20Hz should be spot on with crossover at 80-90Hz. I can place the subs either to the side or behind the Horns, in my current room they would snugly fit in either way and have the cone clear of the back or side of the speaker, so a neater option than one large central box.

    Can't wait !
    With those amps you will have low power for those subs, you will only have 250Watts in 8ohm. The amp will go into clipping before you can use full benefit of the subs.

    You schould have a amp of 1600Watts into 8ohms load for 4645C subs. It is Ok to use an amp of 800Watts minimum into 8ohm.

    Read here...

    http://www.jblpro.com/catalog/suppor...pe=3&docid=626

    This has to be understood, mentioned in the specsheet.

    1
    AES continuous pink noise (25 - 250 Hz), 2 hours duration.
    2
    Continuous program power is defined as 3 dB greater than AES continuous pink noise
    and is a conservative expression of the transducer’s ability to handle normal music
    program material.
    3
    Peak power is defined as 6 dB greater than AES continuous pink noise, reflecting the
    6 dB crest factor contained in the pink noise signal.

    Spend your money on a good amp

  13. #13
    Junior Member Turner's Avatar
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    That room shouldn't need B6 tuning, check an online room mode calculator.

    Power requirement (assuming B6 filter not used):

    2 4645C, each 97db 1w@1m 40-100Hz

    Listening position @ 2/3 length of room = 18.6 ft

    Subs 1/4 space loaded (wall and floor)

    10 watts = 98 dB
    50 watts = 105 dB
    125 watts = 108 dB (109 - 1 dB power compression)
    250 watts = 110 dB (112 - 2 dB power compression)
    800 watts = 114 dB (117 - 3 dB power compression)

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    Db and power

    Looking at the specs and comparing to my horns, they are circa 105db/W at 1m, but with my settings I suspect nearer 102-3 db/W, my 211 is if a 18W I had thought it was 11W but checking its nearer 20W

    I listen below 100 db in room, measuring at 1m away, which is more than enough to recreate live jazz, so looking at the spec it appears 1m away to be circa 103db/W at 1m between 40-100 Hz without EQ in the position I would place them, so if look for say 108 db maximum. This would only require similar power that I get from my 211 SET. Looks like I would have a good 10db extra to play with before EQ to Match the max db from my horns. Believe me they can go very loud in room with 18W

    Any guidance for realistic maximum in room volume levels ?

  15. #15
    Junior Member Turner's Avatar
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    2 horns, each 103 dB 1w@1m

    18 watts each = 119 dB @1m, 103 dB @ 18.6 ft

    The above calc assumes the horns do not benefit from boundary loading and since it is a system, it's response is relatively flat - any low end gain from boundary loading is either a feature or filtered out.


    2 4565C, each 97 dB 1w@1m - 1/4 space

    18 watts each = 116 dB @1m, 100 dB @ 18.6 ft

    36 watts each = 119 dB @1m, 103 dB @ 18.6 ft

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