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Thread: Discussion Thread JBL 4343 to 4344 upgrade

  1. #181
    Administrator Robh3606's Avatar
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    Your braces look good. In my boxes I use pine 2X3 on edge and wraped them round the box on 3 sides and had a baffle stiffener across the front as well. Have 1x2 as well. Did them in odd intervals like your to try to break the panels up into different sizes. Also have the front and back panels connected through the dog house.

    Rob

  2. #182
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    Looks good

    Ian

  3. #183
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    I have been refining the previously mentioned active crossover.

    The unit it such that it would appear to be the final arbitrator of all post signal elements

    I have attempted to a/c couple the balanced outputs for safety. This will require some research and evaluation as prior art passive devices appear to loose the elusive being there boogie factor.

    I have ordered some Black Gate N / Nx series for trial in Super E configutation and charge coupled configuration.

  4. #184
    Senior Member saeman's Avatar
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    4344

    Hello Ian: I'm at a stand still on my first 4344 cabinet. I need to know the port duct tube length JBL used on their 4344's. I've combed thru your thread and cannot find a number on length. I have 4" diameter. Do you know or is there someone out there who owns 4344's and can take a measurement. Thanx - Rick

  5. #185
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    Off hand I don't know...Lancer might..!

    I spent months trying to find out the tuning of the 4345. In the end I sent a request to JBL, Greg Timbers wrote to me the next day... It should be noted JBL tuned some of their monitors empirically.

    I am sure a few members to come up with some suggestions..........

    We really need to know your net enclosure volume to provide an accurate model of the tuning using the driver T/L parameters and if you plan to use one or two ports and the inside diameter. Please confirm.

    Try a search for 2235 tunings in the technical forums. A couple of hertz either side of the idealised tuning will give a satisfactory result....according to taste and your room acoustic.

    Go here, Giskard covers the subject perfectly..as always.

    http://www.audioheritage.org/vbullet...ht=2235+tuning

    Regards the port length, tuned to 30 hertz in 5 cu ft3 requires two 4 inch ports 10.3 inches long according to BassBox Software, or one 4 inch port 3.5 inches long with normal fill 1 inch fibrelgass on all sides except front baffle QL = 10 F3 = 31.4. Bassbox as a rule is quite accurate at determining these data, but its only as good as the assumptions made in the simulation.


    If you are tehncially inclined......the scientific approach

    Technically, QL is quality factor for expressing box losses (leaks, panel flexure, cone leakage) and is an unknown factor effecting bass response in a model simulation (and in reality) .

    In a very rigid box with no leaks you can expect QL= 10 or more and this will tend to cause a rise the response 1/2 a db in the tuning region over a nominal QL=7. A QL = 3 is a lossy box and will cause a drop on the response at tuning.

    Also the driver QTS (or total Q = electrical Qt = mechanical QM) is effected by series Dc resistance of the cables, crossover network and amplifer output impedance. If this is large (0.5> ohms) it will effect the bass quality at tuning and transient performance of the system will suffer. For example modifying the QTS by 10%+ will cause a 0.8 db rise at 50 hertz (ripple) .

    These effects can be adjusted to a degree by either adjusting the tuning slightly (+-2 hertz) or the net volume (+-10 %) although siginificant changes in QL or QTS should be avoided.


    Practically speaking .........

    I suggest you start out with a longer length port and test the tuning wth a low level sine wave signal and monitor the physical movement of the cone which will be at a minimum at resonance.

    The actual impediance is not a reliable means of determining tuning at resonance as the curve is almost flat and the lowest point on the curve is not necessarily the point of resonance(due to reactance of the driver motor).

    Let us know how you go...and have fun.

    Ian

  6. #186
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    Another thought for those intending to biamp.

    http://www.audioheritage.org/vbullet...&postcount=181

  7. #187
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    From the Kitchen table

    Remember the old rule for turning off your power amp and preamp.

    On first and off last.

    The same applies to other devices in the signal chain such as an active crossover or graphic equaliser. Some commercial units have a built in turn on delay and mute on turn off.

    I built the unit below to be installed in the custom active crossover for the JBL 4344/4345. It operates from the unregulated supply and shorts the balanced outputs for a 4 seconds and instantly after turn off thus avoiding any start up or turn off transients.
    Attached Images Attached Images   

  8. #188
    Senior Member saeman's Avatar
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    4344

    Hello Ian: Do you have Christmas in Australia in December or in June - since you're on the other side of the world. Yeh, Yeh - everyone like a little ass nobody likes a smart ass, right. I'd trade weather with you right now. Anyway - I'm getting closer on the 4344 project and thought I'd post you a couple of pics of the effort. I've got one cabinet built; without skin right now as the veneer is still a week out. I brought it into the house temporarily to make room to build the second cabinet - and I couldn't resist putting the components in it to have a look. 2235H, 2122H, 2425J/2307/2308 and 2405. Since my rosewood 4350B's ran away from home I'm going to do this pair in rosewood so I can have some in the house. I'll get you some more pics when the cabinet is finished. Happy holidays - Rick
    Attached Images Attached Images    

  9. #189
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    Nice.

    Ian

  10. #190
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    Quote Originally Posted by riessen
    I'm getting closer on the 4344 project and thought I'd post you a couple of pics of the effort. I've got one cabinet built; without skin right now as the veneer is still a week out. I brought it into the house temporarily to make room to build the second cabinet - and I couldn't resist putting the components in it to have a look. 2235H, 2122H, 2425J/2307/2308 and 2405.
    Looks much better than the stock 4344. Very nice!

  11. #191
    Super Moderator yggdrasil's Avatar
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    Looking goooood!
    Johnny Haugen Sørgård

  12. #192
    Administrator Robh3606's Avatar
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    Those look sweet!!! Wait till you power them up. They will sound even better than they look.

    Rob

  13. #193
    Senior Member saeman's Avatar
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    Thanx Rob - Getting the veneer on them will make a real difference but the bigger problem now is the lack of continuity between the rear terminals and the components. Unless I can program the incoming electrons to jump thru air to the right driver I've got a problem. I now need to get busy on the cross-overs. For now they'll have to look better than they sound.

    Rick

  14. #194
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    What crossover configuration have you decided on?

    Sorry I shoud never ask such difficult questions:dont-know

    Ian

  15. #195
    Tom Loizeaux
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    Quote Originally Posted by Ian Mackenzie
    What crossover configuration have you decided on?...
    Ian
    You've done a great job with those cabinets! And yes, we're all waiting to see what crossovers you use!
    I do know of a pair of 4343 stock crossovers, but with the 2122 mid drivers you probably need slightly differant slopes. I think, if I were in your position, I'd bi-amp these and try Ian's custom passives (tweaked for your drivers).

    Anyway, good work...keep us posted!

    Tom

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