This is topic JBL Loudspeakers - Bi-Amp Questions in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Manny Knowles (Member # 1171) on 05-21-2002, 10:55 AM:
I have a set of JBL 4675C speakers (built-in crossover network) and I'm wondering if it would be better to use the built-in crossover, or use the one in the processor and then bi-amp.I prefer the whole idea of bi-amping but I'm wondering if this is a case where it wouldn't be a good idea.
What about the 4670D? It's essentially the same speaker with a smaller horn.
------------------
~Manny.
Now...where was I ?
Leonard Shelby, MEMENTO.
Posted by Gordon McLeod (Member # 33) on 05-21-2002, 11:28 AM:
Bi amping is always preffered
It leads to lower distorion for several reasons
1 time alignment of the drivers at the crossover frequency (not provided in the cp45 internal crossover)
2 Improved amplifier performance as the powersupply rails don't get swampped as easily
3 equalization of the horn
and better driver protection
Posted by Pete Naples (Member # 761) on 05-22-2002, 02:47 AM:
Yup, all that!The 4670D is just that Manny, same thing with a different horn, suited for different size of theatres.
One of my favourite loudspeakers too! I've also been using the Screen Array series JBL lately, and am quite well pleased with those.
Posted by David Koegel (Member # 25) on 05-22-2002, 09:20 AM:
There's a very good manual on JBL's website titled "Cinema Sound System Manual" that covers these speakers, their specs, bi-amping, etc. If I'm doing the UBB'ing correctly here, you should be able to download it by clicking here:SoundManual
JBL's Professional main website is at:
http://www.jblpro.com/
Posted by Manny Knowles (Member # 1171) on 05-26-2002, 11:43 AM:
Thanks for all the help. I really appreciate the info and the tips.One more question about the 4670D and the 4675C...
They both have a built-in crossover network (4638-TH)...Is it necessary (or advisable) to bypass the JBL crossover since I'm using the Dolby circuitry to separate HF and LF?
My fear is that removing the crossover from the speaker cabinet would change its acoustical properties. But...at the same time...Do I really want a signal that's already been "filtered" to pass through another "filter" ?
Right now, I'm feeding the LF signal to the speaker via its built-in crossover...nothing connected to the HF output of the network. The HF is getting its signal directly from its corresponding amplifier.
Just reading through their catalog...JBL doesn't seem to recommend these speakers for bi-amping...they're pushing the 4675-8LF instead.
These 4670D's and 4675C's are the speakers that are already in these auditoria and the owner isn't interested in upgrading them at this time (and besides, they're good speakers, right?).
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~Manny.
Some people can read "War and Peace" and come away thinking it's a simple adventure story while I, on the other hand, can read the ingredients on a chewing gum wrapper and unlock the secrets of the universe.
Lex Luthor, "Superman: The Movie"
Posted by Richard Fowler (Member # 893) on 05-26-2002, 03:41 PM:
Manny,
you can safely convert the 4670D and 4675C to bi-amp if done properly with a electronic crossover. the 4638TH bass cabinet handles less power than the 4648 bass cabinet supplied with the 4675-8 or 4LF system...it has to be a judgement call based on the cubit size of the room....if they have been working fine passively in the existing situation, they will probably fly......We stock JBL and have done training seminars with their assistance and other manufacturers.
Richard Fowler
TVP-Theatre & Video Products Inc www.tvpmiami.com
Posted by Steve Guttag (Member # 268) on 05-26-2002, 08:20 PM:
>>"cubit size of the room"<<Cubit? Whats a cubit? ... RIGHT!
Steve
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"Old projectionists never die, they just changeover!"
Posted by Richard Fowler (Member # 893) on 05-26-2002, 08:34 PM:
Cubits are those munckins that ran off with your Rockports in the Kinoton booth at ShoWest 
Total volume of room expressed in feet or meters...My association with JBL products goes back when Norm Schneider ( Smart ) was the rep for the Southeast USA in the early 1970's 
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com
Posted by Gordon McLeod (Member # 33) on 05-26-2002, 08:50 PM:
I believe that the cubit was a ancient unit of measure of the egyptions
Posted by Richard Fowler (Member # 893) on 05-26-2002, 09:29 PM:
Those pryamids where a hassle to run background music lines and speakers when I was a small tyke 
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com
Posted by Steve Guttag (Member # 268) on 05-27-2002, 09:26 AM:
Haven't any of you hear the Bill Cosby routine on Noah and the Ark? Called "RIGHT"Steve
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"Old projectionists never die, they just changeover!"
Posted by John Pytlak (Member # 331) on 05-28-2002, 02:57 PM:
What's a cubit?
http://jr.co.il/humor/noah4.txt
http://www.clown-ministry.com/Ministry/Skits/Noah-skit.html ------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Sean M. Grimes (Member # 445) on 05-28-2002, 04:23 PM:
Steve -How long can you tread water?
One of his best skits ever, RIGHT....
Posted by Ray Derrick (Member # 1001) on 05-30-2002, 05:49 AM:
John, are we talking Royal Cubits here (20.5 Pyramid Inches) or garden variety cubits?Richard, how many cubits does it take to change a light bulb?....ah never mind.
Manny, you should bypass the built-in crossover in your JBLs completely if you are bi-amping the system, otherwise you will end up with a nasty hole around the crossover frequency.
------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
Posted by Manny Knowles (Member # 1171) on 05-30-2002, 10:12 AM:
Ray, that's what I was curious about.Any suggestions on how to do that without leaving a big square hole in the side of the LF cabinet (where the xover is now) ?
Wouldn't such a hole change the acoustic properties of the LF module ?
Does anybody sell a speaker terminal the same size ?
------------------
~Manny.
Some people can read "War and Peace" and come away thinking it's a simple adventure story while I, on the other hand, can read the ingredients on a chewing gum wrapper and unlock the secrets of the universe.
Lex Luthor, "Superman: The Movie"
Posted by Gordon McLeod (Member # 33) on 05-30-2002, 10:56 AM:
Drill a small hole and wire right to the speaker and fill the hole with caulking
Posted by Steve Guttag (Member # 268) on 05-30-2002, 10:07 PM:
Or if you are really lazy...reach in through the ports!...just don't let the cable vibrate on anything!Steve
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"Old projectionists never die, they just changeover!"
Posted by Manny Knowles (Member # 1171) on 05-30-2002, 10:50 PM:
Aw...now I don't mind drilling a hole.This operation would effectively convert these speakers to 4675C-4LF...Right?
I know that JBL makes an 8-Ohm version as well (4675C-8LF) and I was wondering if somebody could explain the different scenarios for which the 4-Ohm and 8-Ohm models are intended.
In other words, I'm wondering if I should buy the 16-Ohm transducers to convert these LF's to 8-Ohm..?
------------------
~Manny.
Some people can read "War and Peace" and come away thinking it's a simple adventure story while I, on the other hand, can read the ingredients on a chewing gum wrapper and unlock the secrets of the universe.
Lex Luthor, "Superman: The Movie"
Posted by Richard Fowler (Member # 893) on 05-30-2002, 11:54 PM:
Manny,
the end result would not have the same power handling capacity as the 4675C/4LF since the bass cabinet you are converting ( 4638 ) is rated 1/3 less power capacity than the true 4648A used in the 4675C/4LF. The four and eight ohm systems allow for flexibility regarding usage such as in large rooms where using a double stack of 4648A or A8 bass cabinets for each channel may be neccessary.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com
Posted by Manny Knowles (Member # 1171) on 05-31-2002, 11:10 AM:
How much closer would I be to having 4675C-8LF loudspeakers if I replaced the 2035H transducers with 2226H?~Manny.
Posted by Richard Fowler (Member # 893) on 05-31-2002, 11:22 AM:
Manny,
going for the other components would make the box act like the 4648A.....
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com
Posted by Manny Knowles (Member # 1171) on 08-21-2002, 10:32 PM:
Okay, I've received the new transducers and I'm about to do this drilling procedure. Anybody wanna chime in with their idea of where exactly to drill the hole? Will the location of the hole really be an issue?
I was figuring on drilling to the right of where the crossover is.
~Manny (The man in the hat is back!)
Posted by Richard Fowler (Member # 893) on 08-21-2002, 10:45 PM:
NOT THERE MANNY!!! 
Seriously anywhere that is convenient, cabling wise 
A terminal strip would be nice for a neat install and a little chalk.
Richard Fowler
TVP-theatre & video Products Inc. www.tvpmiami.com