4" coil Nd driver history, revisited

[subwoof]

Had a unique chance to get a group picture of the entire generation of JBL 4" coil
Neodymium drivers here, and have labeled them so it's an easy view should
someone find unlabeled drivers secondhand.

A bit of history ( as far as I can remember )...

The first Nd driver was a combination effort:
The internally shielded 475 as used in the flagship K2
And the 2450 as used in the last gen Concert series.
There is a good article on this but cannot find it right now.

Now of course many prototypes and other applications must of been used
but this is what was generally disclosed and marketed by JBL.

During this time the new generation horn design / size ( 1.5" ) was being introduced
to address the nagging throat cancellation / HF roll off that the 2" driver/horn combo's
had. Large touring systems had a hard time meeting response, distortion and of course,
WEIGHT requirements. So Nd drivers ( then the cones ) became the new norm.

Since the 1.5 horns are essentially throat-less, and the phase plug is right at the exit,
new computer modeling allowed superior performance from all area's.

And of course keeping JBL's " continued improvement " mantra meant that each newer
version becomes smaller, lighter and less costly to manufacture. Here are the drivers to date
( as of fall 2013 )

From left to right:

2450 2450SL 2451 2452 2453

Note the mounting hole pattern is different for the 2450SL and the 2451
- otherwise the motors are identical.

A group picture of a few 1.5" horns ( and a 2311 for ref ) shows the mounting flanges.
NOTE that since many of the newer PT horns have SMALL flanges the wider 2451
( and the sister ferrite 2447 ) cannot bolt to them HOWEVER the larger horns for the
most part can be re-drilled to accept the smaller pattern ( the 2383 is shown modded )

sub

[subwoof]

Before 200 posts / questions get put up, in general the following applies to the WHOLE FAMILY of JBL 4" coil compression drivers....

(1) YES they are ALL interchangeable if you are experienced at doing this and can sweep test,clean,etc etc. Otherwise let a service dealer do it.

(2) The Phenolic models ( 2480/82/85/375HP ) and the OEM models sold to heath, RCA, Dukane, etc have wider mounting hole patterns and different gaps so NO you can't do it. And if it's a 375 being sold on ebay with a dukane model number that has a *P* on it, it's phenolic and NOT a "375" no matter what the seller says..

(3) The older alnico's have guide pins and SOMETIMES a given dia won't align in a given motor...again, have a service guy beat on it before you wreck yours. Murphys law is especially harsh here.

(3B ) YES there is only ONE correct position for a dia in *each* model driver so the lead wires and coilwire points fit. ( see #1 )

(4) The newer ferrites and Nd's have shoulder alignment with larger ( sometimes..?? ) gaps ( esp at the coilwire places ) so are easier BUT #3 can still haunt you.

(5) The dia for the 2452 is the stock 2450 with some small hardware / posts ( included ) that poke through the back cap.

(6) The $$$$ replacement dia for the 476 is identical to the 2450SL.. consumer/pro labeling. Don't let the ebay guys blow smoke...

(7) The diaphram on the 2453 is ATTACHED to the cap so most probably the replacement IS a new cap also...haven't seen one yet.

(8) Some coated types were NOT available in 16 ohm from PRO - maybe from consumer or by special order. For some reason the EU did??

And finally the nagging number FIASCO that JBL created with the 2450:

2450 = 2" exit driver with ribbed diaphram
2450SL = 1.5" driver with COATED, SMOOTH ( 2445 ) diaphram
2450SL-a = 1.5" driver with COATED, RIBBED ( 2450 ) diaphram

[subwoof]

Yeah - my "wonder list" of the PT horn models and P/N has proved elusive to find -
I have both of those horns her and yes - it was the 475..

fixed..

I should do a side by side between the 2350/2440 in a plywood case and the 1010/2453.
110lbs vs 7lbs...damn.

[jerv]

Wow - truly an excellent post!
This common overview on all the newer big-format drivers is really useful.

It seems (to me) that the 2451 is the odd one out here - with a bolt pattern on a much bigger radius that the other ones.
What horns fits that one?

The 2450SL, 2452 and 2453 looks to have identical bolt patterns. According to spec sheets, this is 82,5 mm. Is this correct?

The newer PT waveguides: what bolt circle on those?

[subwoof]

all the PT horns I have are the smaller bolt circle - the flanges are just too small otherwise.

The array 90 degree horn ( 2332 ) is drilled for BOTH at the factory - that horn was used in a lot of models / combinations for a long time. I would have to look and see if the 45 and 60 horns were also.

The large theater 1.5's ( 235X ) have the hole pattern for the 2451 / 2447 but can be redrilled to accommodate.

I will add posts showing those family's - I actually have one of each also..go figure...

SKOL

*cheers*

[Mostlydiy]

Wonderful! Thanks for sharing

/mostly

[spkrman57]

Thanks for sharing all that info.

After meeting you in person and seeing your toys was impressive!

Especially Thanks for the education on installing diaphrams correctly! They are sounding great!

This thread should end up a "sticky".

Regards, Ron

[ivica]

Before 200 posts / questions get put up, in general the following applies to the WHOLE FAMILY of JBL 4" coil compression drivers....

(1) YES they are ALL interchangeable if you are experienced at doing this and can sweep test,clean,etc etc. Otherwise let a service dealer do it.

(2) The Phenolic models ( 2480/82/85/375HP ) and the OEM models sold to heath, RCA, Dukane, etc have wider mounting hole patterns and different gaps so NO you can't do it. And if it's a 375 being sold on ebay with a dukane model number that has a *P* on it, it's phenolic and NOT a "375" no matter what the seller says..

(3) The older alnico's have guide pins and SOMETIMES a given dia won't align in a given motor...again, have a service guy beat on it before you wreck yours. Murphys law is especially harsh here.

(3B ) YES there is only ONE correct position for a dia in *each* model driver so the lead wires and coilwire points fit. ( see #1 )

(4) The newer ferrites and Nd's have shoulder alignment with larger ( sometimes..?? ) gaps ( esp at the coilwire places ) so are easier BUT #3 can still haunt you.

(5) The dia for the 2452 is the stock 2450 with some small hardware / posts ( included ) that poke through the back cap.

(6) The $$$$ replacement dia for the 476 is identical to the 2450SL.. consumer/pro labeling. Don't let the ebay guys blow smoke...

(7) The diaphram on the 2453 is ATTACHED to the cap so most probably the replacement IS a new cap also...haven't seen one yet.

(8) Some coated types were NOT available in 16 ohm from PRO - maybe from consumer or by special order. For some reason the EU did??

And finally the nagging number FIASCO that JBL created with the 2450:

2450 = 2" exit driver with ribbed diaphram
2450SL = 1.5" driver with COATED, SMOOTH ( 2445 ) diaphram
2450SL-a = 1.5" driver with COATED, RIBBED ( 2450 ) diaphram

It would be very nice if any skill-full member would IN DETAIL EXPLAIN the WHOLE procedure in installing 4" diaphragms.
Here, SUBWOOF has been mentioned that ALL JBL 4" drivers have very precise guiding pins or 'shoulders' so original diaphragm almost can not be moved, but only can be moved UP (putting 'shim paper' under the ring that holds the diaphragm and voice coil.

Me, and a fiend of mine, have such experience with the new original JBL 4" diaphragms. What is the reason that JBL production QC allow that such products can be delivered to the JBL users? Is it so expensive and technically difficult to organize a kid of final QC in order to prevent such , some time, tedious 4" diaphragms installations, or such problems is "inherent to" the diamond-shape diaphragm suspension, may be because of the material thermal and/or plastic/elastic deformation or thermal treating?


Regards
Ivica

[ivica]

Before 200 posts / questions get put up, in general the following applies to the WHOLE FAMILY of JBL 4" coil compression drivers....

(1) YES they are ALL interchangeable if you are experienced at doing this and can sweep test,clean,etc etc. Otherwise let a service dealer do it.

(2) The Phenolic models ( 2480/82/85/375HP ) and the OEM models sold to heath, RCA, Dukane, etc have wider mounting hole patterns and different gaps so NO you can't do it. And if it's a 375 being sold on ebay with a dukane model number that has a *P* on it, it's phenolic and NOT a "375" no matter what the seller says..

(3) The older alnico's have guide pins and SOMETIMES a given dia won't align in a given motor...again, have a service guy beat on it before you wreck yours. Murphys law is especially harsh here.

(3B ) YES there is only ONE correct position for a dia in *each* model driver so the lead wires and coilwire points fit. ( see #1 )

(4) The newer ferrites and Nd's have shoulder alignment with larger ( sometimes..?? ) gaps ( esp at the coilwire places ) so are easier BUT #3 can still haunt you.

(5) The dia for the 2452 is the stock 2450 with some small hardware / posts ( included ) that poke through the back cap.

(6) The $$$$ replacement dia for the 476 is identical to the 2450SL.. consumer/pro labeling. Don't let the ebay guys blow smoke...

(7) The diaphram on the 2453 is ATTACHED to the cap so most probably the replacement IS a new cap also...haven't seen one yet.

(8) Some coated types were NOT available in 16 ohm from PRO - maybe from consumer or by special order. For some reason the EU did??

And finally the nagging number FIASCO that JBL created with the 2450:

2450 = 2" exit driver with ribbed diaphram
2450SL = 1.5" driver with COATED, SMOOTH ( 2445 ) diaphram
2450SL-a = 1.5" driver with COATED, RIBBED ( 2450 ) diaphram

It would be very nice if any skill-full member would IN DETAIL EXPLAIN the WHOLE procedure in installing 4" diaphragms.
Here, SUBWOOF has been mentioned that ALL JBL 4" drivers have very precise guiding pins or 'shoulders' so original diaphragm almost can not be moved "left-right", but only can be moved UP putting 'shim paper' under the ring that holds the diaphragm and voice coil.

Me, and a fiend of mine, have such experience with the new original JBL 4" diaphragms. What is the reason that JBL production QC allow that such products can be delivered to the JBL users? Is it so expensive and technically difficult to organize a kid of final QC in order to prevent such , some time, tedious 4" diaphragms installations, or such problems is "inherent to" the diamond-shape diaphragm suspension, may be because of the material thermal and/or plastic/elastic deformation or thermal treating?


Regards
Ivica

[subwoof]

Well there are a few tricks for each mounting method - in general for the older pin diaphrams drill out the locating holes from 1/8 to 9/64 and that should give you plenty of room to "wiggle" This is a common procedure around here..

For the shoulder types, the dia is held in position at each mounting screw position against a small portion of a shoulder that is milled into the top plate.

Take a NEW, decent size tool steel *right angle* edge ( as would be found on a wood chisel SIDE or machinists block ) and shave down the diaphram where it meets this shoulder. DO NOT USE A FILE, SANDPAPER, KNIFE EDGE, LAWN MOWER or something LAYING AROUND...Buy it NEW if you aren't a machinist!

Because slight offsets and material size differences when making the diaphram assembly happen ( it is a sandwich if you look close ), there are burrs / waste material / etc etc.

By shaving down these areas ( ALL EIGHT ) the diaphram can move around. Bingo...be sure to remove the burrs you CREATE !

NOW THAT YOU KNOW THIS - it is IMPORTANT to have a low distortion oscillator to align the diaphram - AND THE DRIVER must have a nominal air mass load at the exit otherwise you will get false response / harmonics that will FOOL you..

NOTE: methods for aligning the NEWER Nd drivers with the dia glued into the back cap are not yet hacked. Someday I will find a need but HELLO, they never blow up right??

Anyways I made a wood box with various holes with wood dowels for guides and lined it with insulation.. stuck a cheapo microphone in the side and connected to the oscilloscope and compared in/out. Wearing earplugs and headphones you can actually hit a driver with some decent power to see if there's any breakup but it REALLY pissed off the cats.

Worked great until I gave it away to a tech and never bothered to make another.

Hmmm...Maybe I have a market here..

[ivica]

Well there are a few tricks for each mounting method - in general for the older pin diaphrams drill out the locating holes from 1/8 to 9/64 and that should give you plenty of room to "wiggle" This is a common procedure around here..

For the shoulder types, the dia is held in position at each mounting screw position against a small portion of a shoulder that is milled into the top plate.

Take a NEW, decent size tool steel *right angle* edge ( as would be found on a wood chisel SIDE or machinists block ) and shave down the diaphragm where it meets this shoulder. DO NOT USE A FILE, SANDPAPER, KNIFE EDGE, LAWN MOWER or something LAYING AROUND...Buy it NEW if you aren't a machinist!

Because slight offsets and material size differences when making the diaphragm assembly happen ( it is a sandwich if you look close ), there are burrs / waste material / etc etc.

By shaving down these areas ( ALL EIGHT ) the diaphragm can move around. Bingo...be sure to remove the burrs you CREATE !

NOW THAT YOU KNOW THIS - it is IMPORTANT to have a low distortion oscillator to align the diaphragm - AND THE DRIVER must have a nominal air mass load at the exit otherwise you will get false response / harmonics that will FOOL you..

NOTE: methods for aligning the NEWER Nd drivers with the dia glued into the back cap are not yet hacked. Someday I will find a need but HELLO, they never blow up right??

Anyways I made a wood box with various holes with wood dowels for guides and lined it with insulation.. stuck a cheapo microphone in the side and connected to the oscilloscope and compared in/out. Wearing earplugs and headphones you can actually hit a driver with some decent power to see if there's any breakup but it REALLY pissed off the cats.

Worked great until I gave it away to a tech and never bothered to make another.

Hmmm...Maybe I have a market here..

Hi SUBWOOF,

Many thanks for Your explanation. I believe that a lot of members would be happy while reading your short but effective explanation.

Regards
Ivica

[awedio]

Sorry to dig up an old thread..

Do any of these drivers employ a 5-slit phase plug?

[pos]

No, but the Radian 950PB and 951PB do, and you can put JBL diaphragms in them, as well as Meterion/Truextent ones.

[awedio]

Thx for clarifying

I was aware of the Radian's & also the TAD's

[more10]

No, but the Radian 950PB and 951PB do, and you can put JBL diaphragms in them

I believe you are wrong here. Radian makes repalcement diaphragms for JBL, not the other way around.