Film-Tech Forum ARCHIVE: JBL parts structure list

This is topic JBL parts structure list - wiffle tree and driver Q in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by John Walsh (Member # 168) on 09-18-2008, 01:01 PM:

Does anyone have a list that shows all the parts that go together to make up JBL speakers? For example:

4675C-4(8)LF
Bass cabinet: 4648A / Bass transducer: 2226H / Recone kit: ????
HF horn: 2360A / HF Driver: 2446H / Replacement Diaphram: D8R2450
HF horn mount: 2506B

The old timers around here used to call that 'structured' listing a wiffle tree.

Also, is there any real reason someone would install a bi-amped speaker where the bass was 8 ohms, but the HF driver was 16 ohms?

Posted by Phil Ranucci (Member # 3820) on 09-18-2008, 01:48 PM:

Can't help on the 'wiffle tree', but in a bi-amped system, the HF driver is connected directly to an amp and requires so little power that a 16 ohm driver would add a little protection from overdriving. On the other hand, low frequencies require more power to move the air so 8 ohm would allow the low amp to put out more power to the woofer. Lots of touring rigs use amps that can drive 2 ohm loads for the subwoofers.
If you're changing a HF from 8 to 16 ohm you may have to adjust the amp output to maintain the frequency response you currently have.

Posted by Gordon McLeod (Member # 33) on 09-18-2008, 04:12 PM:

By the tome you add the CD horn correction and screen loss most high frequency drivers are being driven fairly hard
I believe I read once that when THX was being developed there was a paper published debunking the myth that HF needed a smaller amp than the bass section in biamped cinemas

Posted by Mark Gulbrandsen (Member # 72) on 09-18-2008, 06:47 PM:

I've always used the same sized amp in each position... just about for ever... Its drawn much criticism from other techs who think its allowing excessive headroom and so on. Hey, amps are the cheapest part of the booth and one amp makes thngs way lots easier to deal with when things do go wrong and you're on the other end of the phone. I've also rarely ever lost a hf diaphram! Now with 3-way systems its another story...

Mark

Posted by Steve Guttag (Member # 268) on 09-18-2008, 08:26 PM:

As certified reconer for JBL...I do have access to various lists, as well as exploded views on various JBL systems. Mind you, not all are published AND, doing some searches on the JBL PRO web site may also allow you to find the "Technical Specifications" sheets in PDF form.

The components list can be had here

Some of the exploded views can be had
here

Steve

Posted by John Walsh (Member # 168) on 09-20-2008, 08:45 AM:

Thanks, Steve, that was exactly what I was looking for. I must admit I get a little mixed up with JBL numbers because they are 4-digits with a '2' or a '4'; I don't use them enough to get used to them....

I ask about a 8 ohm bass cabinet with a 16 ohm horn because I have that at a theater. I'm beginning to think it's a, 'we had a few 16 ohm drivers left over' rather that a technical reason, or maybe someone replaced the original 16 ohm diaphram with an 8 ohm and didn't make a note. In the same auditorium, someone used a 2447H HF with a 2380 -style horn for just L-R channel, and a 2445J with a 2360 -style horn for center. I thought it wasn't a good idea to mix speakers, but it's all good stuff, so hopefully the EQ'ing will remove any differences.

Posted by Steve Guttag (Member # 268) on 09-20-2008, 09:30 AM:

John,

There is a bit of a history to the JBL speaker evolution. The 4675 did start out with 16-Ohm highs with 16-Ohm lows so the LF system came to 8-Ohms. Furthermore, all of the systems were intended to run with a passive crossover (3152, IIRC). When the 3160 crossover came out, the LF cabinet (4648...though they were not calling it that then) since JBL sold the system piece-meal...it was a 4508 cabinet with (2) 2225H drivers, 2360 Horn, 2445J HF driver and 3160 network.

JBL thought of cabinets as a means to sell components and there cabinets were nothing to write home about...technically sound but their construction left (and leaves) something to be desired.

That changed and JBL seemed to be much more system oriented where very few components are offered for sale as separates.

When this transition occurred (as bi-amping became much more common in cinemas)...JBL came out with the 4648-TH that had an inset crossover that was based on an 8-Ohm HF. The bi-amper also would desire a more efficient HF also would want 8-Ohm.

Since the crossover in the 4648-TH could only handle 300-watts, JBL figured it was silly to use a PAIR of 600-watt drivers so the cheapened the system and replaced the 2226H drivers with 3" v.c. versions (who's number escapes me now...it is probly something like a 2035 and is not available as stand-alone driver). The LF-system was renated 4638-TH and looks identical to the 4648-TH but the drivers can only handle half the power.

So, to make a longer story shorter...there were factory versions of the 4675 and 4670 with both 8 and 16 Ohm HF sections and the LF section could be loaded with 16-Ohm (-8LF) or 8-Ohm (-4LF)!

The 2447 uses the same diaphram as the 2446 but has a 1.5" throat and mates to the "optimized aperture" CD horns from the 2350 family. God knows, they couldn't have gone to the 1.4" throat since that would have meant that Altec had it right many years ago!

Steve

Posted by Louis Bornwasser (Member # 3063) on 09-20-2008, 05:01 PM:

The 2447/2352 is an optimized design that lowered distortion almost 6%. It is smaller/cheaper than the 4675 with only a few problems (dispersion and punch). If a theatre was mono, then had Dolby added it sometimes got mismatched speakers, especially in Mass & CT where we used the Kelmar 120 for mono to start. Louis

Posted by John Walsh (Member # 168) on 09-21-2008, 06:49 PM:

OK, Louis, that makes sense .. I didn't think about what was done to upgrade a place. As I said, it's all good quality stuff, so it should still sound OK.

I'm replacing some subs (2242H) and found an interesting problem .. it seems the wires that run from the cone to the termination block on the speaker itself were 'oversoldered' meaning there was so much solder, it ran down the wire. This made the wire stiff and not flex as the cone moved in and out. The result was the same as when you bend a piece of wire repeatedly; it breaks. Found several like that.

Phil's' idea about reduced power to HF horns is interesing, but I think I would agree with Gordon, but for the slightly different reason that I would want all the power I had. I could always turn down the gain somewhere.

Posted by Steve Guttag (Member # 268) on 09-21-2008, 09:20 PM:

John,

Don't forget, those 2242s can be reconed.

There is a delicate balance of getting a good connection and wicking too much solder. One should let more than a 1/8" wick up above the terminal. Also one should ensure there is enough lead to avoid flexing the joints. Lastly there shouldn't be too much lead such that the wires could touch each other.

Steve

Posted by Phil Ranucci (Member # 3820) on 09-22-2008, 02:32 AM:

I'll stand corrected about HF power needs.
Every time I open up a JBL cabinet I'm always amused that we go to the trouble of running 10 or 12 gauge wire to the cabinets and they use 14 or 16 gauge inside the box. Pinching pennies or what?

Posted by Steve Guttag (Member # 268) on 09-22-2008, 06:10 AM:

Phil,

The are running what? 2 to 3 feet of wire as compared to what you are running?

The voice coil wire is even thinner wire. The reason for running the large gauge wire it keep down Ohmic losses and also to handle the power. It absolutely is a funciton of length.

Steve