JBL 476MG Diaphragm Issue

[JamesBLansing]

Hi,

First of all happy holidays all.

I do need extensive information about JBL 476mg High Frequency Driver's Diaphragm, I do have some performance issues with my drivers, and as I have figured it out that the main cause is the diaphragm, I have searched for a new driver but unfortunately they are very expensive so I decided to change the diaphragms, there are several genuine JBL diaphragm's on the market with the same ohm's (I have stated below), I wonder if they will fit like the same as original or not, or will it be problems with the new diaphragms, unfortunately there aren't so many information about 476MG but I have figured it out that JBL produced same kind of technical type of high frequency drivers like 476mg, just their other parts are different but it seems the diaphragm and the shell are the same for instance 476mg is very similar to 2452H-SL and I did my best to find the most suitable ones by searching from different sources. Any additional information or leading to the right source of information will be much appreciated.

https://www.simplyspeakers.com/jbl-replacement-speaker-diaphragm-d8r2452-sl.html
https://reconingspeakers.com/product/jbl-2452sl-d8r2452sl-diaphragm/
https://www.ebay.com/itm/JBL-Factory-Speaker-Diaphragm-D8R2452-SL-for-2452-SL-8-Ohm-Horn-Driver-Repair-/141197184095

Thank you so much for the assistance.

All the best.

[Robh3606]

What's wrong?? Are you having a corrosion issue?? That was reported on this forum a while back. You should be able to fit the 2450 family diaphragms in the 476 Core.


The 476 Mg are 16 ohm drivers so if you have an existing crossover you will need to make changes!


http://www.audioheritage.org/vbulletin/showthread.php?41313-4365-has-quality-problems&highlight=476mg+corrosion


Rob:)

[JamesBLansing]

What's wrong?? Are you having a corrosion issue?? That was reported on this forum a while back. You should be able to fit the 2450 family diaphragms in the 476 Core.


The 476 Mg are 16 ohm drivers so if you have an existing crossover you will need to make changes!


http://www.audioheritage.org/vbulletin/showthread.php?41313-4365-has-quality-problems&highlight=476mg+corrosion


Rob:)


Actually no corrosion issue, one speaker started to play different than another, I have checked the crossover and other components but when I dismantle the drivers, the copper ring in the diaphragm was not in the same condition before somehow, so I wanted to change the diaphragm, it is very bad that ohm issue, I'm not sure I will be able to make changes on the crossover, I don't want the speakers to behave apart from the original, do you have any other diaphragm recommendation? By the way I again looked for my speaker's white paper, it has stated that the 476 MG's are 8 ohm's. (I have attached the screen shot of the white paper)

[Robh3606]

What you have in the white paper is the DCR not the same. In general Impedance is about 2X the DCR value. Take a look at the 2452SL techsheet H vs J. What you need are 16 ohm SL or coated diaphragms. You should probably change both. Call the stores they may be able to order them for you or try to go through JBL for a replacement under warranty.

http://www.audioheritage.org/vbulletin/showthread.php?21706-2452h-sl

Rob:)

[JamesBLansing]

What you have in the white paper is the DCR not the same. In general Impedance is about 2X the DCR value. Take a look at the 2452SL techsheet H vs J. What you need are 16 ohm SL or coated diaphragms. You should probably change both. Call the stores they may be able to order them for you or try to go through JBL for a replacement under warranty.

http://www.audioheritage.org/vbulletin/showthread.php?21706-2452h-sl

Rob:)

Rob, you are great! One additional question, is there a prediction that the sound will be the same as original? What should I do more to bring the speakers to the original condition?

[pos]

The 476Mg use magnesium diaphragms that are different from the titanium ones listed above.
Unless you manage to get your hands on magnesium diaphragms you will not get the same response as the original driver, and it will not work as intended.
Maybe at this point the best thing to do would be to order a usb measurement mic to see what you currently have.

[Mr. Widget]

Do you have a JBL system with 476Mg drivers installed, or did you buy the 476Mg drivers for a DIY project? Either way can you get support from whoever you bought the speakers from?

I do not think you can buy replacement Mg diaphragms. Unfortunately putting any other diaphragm in there will offer suboptimal performance. The magnesium diaphragms are extremely high performance units.


Widget

[JamesBLansing]

Do you have a JBL system with 476Mg drivers installed, or did you buy the 476Mg drivers for a DIY project? Either way can you get support from whoever you bought the speakers from?

I do not think you can buy replacement Mg diaphragms. Unfortunately putting any other diaphragm in there will offer suboptimal performance. The magnesium diaphragms are extremely high performance units.


Widget

Hi, I have a JBL system with 476MG installed, I have been having some sound issues tonal unbalance between midrange drivers, I found that the the copper ring on the diaphragm cause this problem (attached) I will not change the magnesium diaghpram in whole, I will only change the copper ring (attached) on the Diaphragm, I guess it will solve the problem, because of that, the matching copper ring will be suitable for me, I just need the suitable and %100 the same copper ring. You are right, I can't be able to buy mg diaphragms, they are sold as a whole driver. With the copper ring changed I think I will manage to solve the issue, what do you think?

[JamesBLansing]

The 476Mg use magnesium diaphragms that are different from the titanium ones listed above.
Unless you manage to get your hands on magnesium diaphragms you will not get the same response as the original driver, and it will not work as intended.
Maybe at this point the best thing to do would be to order a usb measurement mic to see what you currently have.

You are right, I just need to change the copper ring on it, this will solve the problem I guess, I have measured the drivers with a multi meter, they give the same ohm ratio, but the sound and the copper ring that I have attached before is different, I think that causes the unstablility with the two midrange drivers.

[Mr. Widget]

With the copper ring changed I think I will manage to solve the issue, what do you think?You are a braver man than I.

This reminds me of the time I lived abroad and when the windshield wiper motor burned out in our car, we went to a repair shop and they rewound the motor. It never ran at exactly the same speed as before, but it worked. Ordering a replacement motor from the USA would have taken months and been quite costly.

I would be hesitant to even remove the diaphragm from a modern JBL compression driver as they are precisely assembled and tested for performance. I suppose you can give it a try. Replacing the ring may be your best option if replacing the driver is not an option.

Where is the copper ring?


Widget

[JeffW]

I think he means the voice coil?

[JamesBLansing]

You are a braver man than I.

This reminds me of the time I lived abroad and when the windshield wiper motor burned out in our car, we went to a repair shop and they rewound the motor. It never ran at exactly the same speed as before, but it worked. Ordering a replacement motor from the USA would have taken months and been quite costly.

I would be hesitant to even remove the diaphragm from a modern JBL compression driver as they are precisely assembled and tested for performance. I suppose you can give it a try. Replacing the ring may be your best option if replacing the driver is not an option.

Where is the copper ring?


Widget

:))), Sometimes absence can make us do brave or silly things, I have to remove the diaphragm, and fix the copper ring on it because as you have seen from the pictures, they are damaged, and because of that, there is a %20 sound difference between the two drivers, and unfortunately I always hear the difference when I'm listening, I tested the crossovers, but they are the same and they all fine, I tested the woofers but they are the same also, I tested the uhf's, they are the same, just one difference in the system, that is midrange drivers so to speak "HF", when I opened the driver and see the diaphragm, I saw that the copper ring is fixed before, because of that I think this became a problem. ı don't want to make a deep renovation on the drivers but I couldn't find any other option, ı will to my best to keep them in original shape, I also got in touch with the JBL Dealer but they are selling the whole driver for nearly around 4.000 dollars each!, so I'm searching for the best suitable option. I have been searching for nearly one week, and I came across that 476 MG has huge similarities with other JBL drivers apart from their white papers, for instance the HF drivers of JBL 5732 cinema speakers seems identical with 476MG's.

[JamesBLansing]

I think he means the voice coil?

yes sorry for the non technical terms, voice coil.

[JamesBLansing]

What you have in the white paper is the DCR not the same. In general Impedance is about 2X the DCR value. Take a look at the 2452SL techsheet H vs J. What you need are 16 ohm SL or coated diaphragms. You should probably change both. Call the stores they may be able to order them for you or try to go through JBL for a replacement under warranty.

http://www.audioheritage.org/vbulletin/showthread.php?21706-2452h-sl

Rob:)
Hi Rob

Do you think that the 2452SL's diaphragm is identical with 476 mg?

[Mr. Widget]

yes sorry for the non technical terms, voice coil.
Oh geez!

Yes, it can be replaced, but the response will never be right.

Can you sell the pair of 476Mg drivers, and buy a matched pair of anything else? The only way you’ll be able to use this pair of drivers, you’ll need to ruin the good driver so they both have matching diaphragms.


Widget

[pos]

What make you think the voice coils are damaged?
I don't see anything obvious from the picture above.

At this point you should probably send the drivers to some competent shop and have them clean and reinstall everything correctly.

What is the history of these drivers? Did you get them new? Did you remove the diaphragms before?
Proper installation and centering is paramount here...

[JamesBLansing]

Oh geez!

Yes, it can be replaced, but the response will never be right.

Can you sell the pair of 476Mg drivers, and buy a matched pair of anything else? The only way you’ll be able to use this pair of drivers, you’ll need to ruin the good driver so they both have matching diaphragms.


Widget
Unfortunately I can't :(, I don't want to ruin my 4365's, because of that I'm searching for everyway possible.

[JamesBLansing]

What make you think the voice coils are damaged?
I don't see anything obvious from the picture above.

At this point you should probably send the drivers to some competent shop and have them clean and reinstall everything correctly.

What is the history of these drivers? Did you get them new? Did you remove the diaphragms before?
Proper installation and centering is paramount here...
87923879248792487925
The drivers are my 4365's drivers, which I have bought from a dealer as a demo product nearly 2 years ago, 3 months ago I have noticed that two speakers are playing differently both in mono and stereo soundtracks, I have checked all the options (there can be other also), because I have another pair of speakers which are 4367, with listening them all, I can easily say that 4365's are behaving not normally than it should be, I also have checked the attenuators of hf and uhf's but no solution, when I checked the driver that sousing the problem, I noticed that the voice coil had some operation (it can't be factory original in my opinion) if this voice coil is the factory original than I will have relief, and have another search only for the crossovers because there won't be any other option I guess, in order to give you detailed information I have attached additional photos of the diaphragm and voice coil, thank you for the responses and informations, I will be grateful if I know that I have missed a crucial point since I know JBL speakers very well and been using for nearly 20 years but in deep technical knowledge I have some gray areas.87922879228792287923

[grumpy]

Thinking outside the box a bit... TruExtent Be diaphragms might at least get you a matching pair... probably less than 1/2 your new driver quote.
Would take some serious homework to make sure they'd be suited for a 476Mg diaphragm swap out, but an option to consider. Someone here has probably run response curves for both...
Sorry if this was suggested earlier... came late to the party.

[HCSGuy]

If they were purchased legit, through a JBL dealer, wouldn’t they still be under warranty? Abuse not included, JBL should have a remedy, and I don’t see anything that suggests a melted voice coil.

[Mr. Widget]

Unfortunately I can't :(, I don't want to ruin my 4365's, because of that I'm searching for everyway possible. I agree with you. The 4365 is a great speaker and should not be modified. I did not realize that you were using actual JBL speakers… any departure from the original factory built 476Mg will be a terrible thing.


If they were purchased legit, through a JBL dealer, wouldn’t they still be under warranty? Abuse not included, JBL should have a remedy, and I don’t see anything that suggests a melted voice coil.In the USA and probably everywhere else, demo or not, they should have a 5 year warranty. I would ask the dealer to repair them at no cost and if he refuses to help you, find the Harman importer for your country and demand they repair them.



Widget

[Robh3606]

Here is a brand new DR82450SL and mine looks almost the same. You have to remember that you are dealing with a flat ribbon that gets twisted from the opposite side and gets twisted again to make a solder connection. One side is coming from the opposite side of the coil and that's the one I have a picture of. The other side looks much better because you only have to twist it 90 degrees to make the solder connection. Granted either one of them are not pretty but they pull this of in what a .025 gap!

You might just have a simple alignment issue/screw torque. When you took out the diaphragm did you notice if some of the screws were easier to break the torque on?? I once have a driver where one of the screws was "loose" and once I retightened it was fine again. JBL should help you with this.

Rob:)

[grumpy]

JBL should help you with this.

Seriously. Anything else is last-resort kind of stuff for a factory system.
Hope there is some success with the dealer, etc... that would be fantastic.

Off topic:
I need to get back into a mode where I can test drivers again, as now I'm curious
how well the aftermarket Be with the rolloff (vs the 476Be) tracks the 476Mg.

[JamesBLansing]

Here is a brand new DR82450SL and mine looks almost the same. You have to remember that you are dealing with a flat ribbon that gets twisted from the opposite side and gets twisted again to make a solder connection. One side is coming from the opposite side of the coil and that's the one I have a picture of. The other side looks much better because you only have to twist it 90 degrees to make the solder connection. Granted either one of them are not pretty but they pull this of in what a .025 gap!

You might just have a simple alignment issue/screw torque. When you took out the diaphragm did you notice if some of the screws were easier to break the torque on?? I once have a driver where one of the screws was "loose" and once I retightened it was fine again. JBL should help you with this.

Rob:)

Oh! that is a relief!, maybe that won't be a problem with the diaphragm, I will check the screws again, and I will change the diaghraphms between the speakers, to see whether I will have a difference or not, once a technician said that these horn drivers have some special liquid in it, and the liquid can cause sound differences, is there a thing like that? can it be the problem?

[JamesBLansing]

Seriously. Anything else is last-resort kind of stuff for a factory system.
Hope there is some success with the dealer, etc... that would be fantastic.

Off topic:
I need to get back into a mode where I can test drivers again, as now I'm curious
how well the aftermarket Be with the rolloff (vs the 476Be) tracks the 476Mg.

You are right but, I spoke with the dealer, and they requested to change the whole driver, unfortunately the parts of the driver isn't sold by JBL:banghead:

[JamesBLansing]

Thinking outside the box a bit... TruExtent Be diaphragms might at least get you a matching pair... probably less than 1/2 your new driver quote.
Would take some serious homework to make sure they'd be suited for a 476Mg diaphragm swap out, but an option to consider. Someone here has probably run response curves for both...
Sorry if this was suggested earlier... came late to the party.

You are right!, I'm very careful not to ruin the original drivers, since I have learn the exact problem, maybe it is not with the drivers, maybe it is the crossover, since I have measured all the parts of the crossover and they measure the same as factory crossover schematic, I don't what I should look further?

[Mr. Widget]

You are right but, I spoke with the dealer, and they requested to change the whole driver, unfortunately the parts of the driver isn't sold by JBL:banghead:I am also JBL dealer. Replacing the driver is the correct repair procedure for this model. JBL will replace a defective driver at no cost as a warranty repair. YOU should NOT be opening up the driver however, this may void your warranty! When your dealer provides the serial number of your 4365 and tells JBL that there is a warranty issue, he can order a replacement 476Mg.

ALSO, DO NOT SWAP THE DIAPHRAGMS! DO NOT OPEN THE GOOD DRIVER!!!


Widget

[Robh3606]

Off topic:
I need to get back into a mode where I can test drivers again, as now I'm curious
how well the aftermarket Be with the rolloff (vs the 476Be) tracks the 476Mg.

Hello Grumpy

The 476Mg runs out past 20K on the M2 waveguide and is clean on a CSD. It doesn't have the all the "noise" from the secondary resonances that the Ti diaphragm's have. The Be are also clean but don't have the extension that the Mg's have. In his speakers they run out the 476MG's and add a tweeter above.

If he goes to Be he will probably have a dip in response. If you look at the schematic the UHF trim is done by rolling off the 476Mg driver and diaphragm swaps would be a very risky proposition as far as keeping the original frequency response.

Rob:)

[JamesBLansing]

I am also JBL dealer. Replacing the driver is the correct repair procedure for this model. JBL will replace a defective driver at no cost as a warranty repair. YOU should NOT be opening up the driver however, this may void your warranty! When your dealer provides the serial number of your 4365 and tells JBL that there is a warranty issue, he can order a replacement 476Mg.

ALSO, DO NOT SWAP THE DIAPHRAGMS! DO NOT OPEN THE GOOD DRIVER!!!


Widget

I have already contacted with a dealer since my speaker is from 2013 it is out of warranty, the main purpose is not to ruin the original drivers, I'm still thinking that there is no problem with the driver, since Rob send the diaphragm pictures of his speaker and I'm convinced, I must find the problem of the unstability of the midrange sounds between two speakers, I have tried several options but right now I couldn't find the issue.

[Mr. Widget]

I'm still thinking that there is no problem with the driver, since Rob send the diaphragm pictures of his speaker and I'm convinced, I must find the problem of the unstability of the midrange sounds between two speakers, I have tried several options but right now I couldn't find the issue.I wouldn't expect to be able to see a problem by looking at it. Sometimes you can, but often an out of spec driver looks perfect.


On diving in and playing Rambo with your drivers.
Let's say you have a pair of identical Rolexes. If one was keeping poor time, would you pull the main spring out of one to test the other? Even if you are quite handy, I would expect you would end up with two watches that were not quite right or perhaps worse.

In the past JBL sold replacement diaphragms that trained repair facilities could swap out. Today the drivers are less forgiving so most do not offer this as an option and the repair procedure is a driver swap. Yes, out of warranty it is expensive, but if you own a "finished goods" JBL speaker you are entitled to have access to replacement drivers.

On the warranty.
In the US the warranty begins with the first sale to the end user and not the date of delivery to the dealer. I assume it is the same in your country.

If I bought a pair of new or demo JBLs and had issues I would be on my dealer and demand satisfaction regardless of the "bargain" he may have struck with me at the time of sale.



Widget

[Robh3606]

Found the Truextent measurements pos did them in a 2450SL core you can see the roll off. Similar to the 476Be


http://www.audioheritage.org/vbulletin/showthread.php?31657-Truextent-diaphragms-measurements


http://www.audioheritage.org/vbulletin/showthread.php?33761-476Be




Rob:)

[Earl K]

FWIW, I consider Giskards measurements to be the definitive ones for the Truextent//Be diaphragms ( no offense meant to POS or sebackman or 1audiohack or Rob or anyone else who has provided their measurements for our perusal ).

( Click the pic for his thread )

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=44871&stc=1&d=1269131225 (http://www.audioheritage.org/vbulletin/showthread.php?28127-Truextent-Diaphragms-in-JBL-four-inch-compression-drivers&highlight=Beryllium)

They are of much greater resolution than most others.

:)

PS;

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=44872&stc=1&d=1269131236

[Robh3606]

Hello Earl

Great thanks for posting them. That gives us a more complete picture of what to expect.

Rob:)

[JamesBLansing]

I wouldn't expect to be able to see a problem by looking at it. Sometimes you can, but often an out of spec driver looks perfect.


On diving in and playing Rambo with your drivers.
Let's say you have a pair of identical Rolexes. If one was keeping poor time, would you pull the main spring out of one to test the other? Even if you are quite handy, I would expect you would end up with two watches that were not quite right or perhaps worse.

In the past JBL sold replacement diaphragms that trained repair facilities could swap out. Today the drivers are less forgiving so most do not offer this as an option and the repair procedure is a driver swap. Yes, out of warranty it is expensive, but if you own a "finished goods" JBL speaker you are entitled to have access to replacement drivers.

On the warranty.
In the US the warranty begins with the first sale to the end user and not the date of delivery to the dealer. I assume it is the same in your country.

If I bought a pair of new or demo JBLs and had issues I would be on my dealer and demand satisfaction regardless of the "bargain" he may have struck with me at the time of sale.



Widget

Thank you all the time that you have shared with me, it's much appreciated having information from people that has deep knowledge, if is not with the drivers or the crossover, and I can't be able to change the driver, so what can cause this tonal difference between the speakers? Have you ever came across with these situation before? Can it be a simple fault? Or maybe I have to check other parameters? Let's imagine that all the enviroment of the speakers are same but we still have a sound difference between two drivers, what parameter would you check?

[HCSGuy]

Quick recap - you are in the UK and your speakers are a “few” years old. First, what is the JBL warranty for the UK - you may have to call the UK importer of JBL to find out. Second, as Widget said, the JBL warranty starts from when a current model speaker is invoiced to the final user - it does not matter if the speaker was used as a dealer demo for 2-3yrs. I am sure, however, that JBL would balk at a warranty repair on a speaker that has been out of production for quite some time, e.g. a speaker that was discontinued 10yrs ago cannot reasonably still be under warranty, just as JBL can’t still be held responsible for the speakers my father bought in the 60’s that had their old “Lifetime” warranty. The worst case in this scenario is that your dealer did not sell you Demo speakers, but instead resold you speakers he had bought back from someone else towards an upgrade - either originally purchased from him, or elsewhere. Either way, he can pursue a warranty claim on your speakers until it is rejected by JBL. I think you have much further to go on pursuing your claim here.

How do you know the problem is the driver? First, you need to carefully re-assemble your driver and listen to it. If that speaker still sounds off, make sure the alignment of the driver to the horn does not have any way to be shifted off, then swap just the 476mg from that speaker to the other speaker, then listen to them both again - did the bad sound follow the suspect driver (Driver is bad), or did it stay with the original (crossover may have a problem). Above all, as Widget said, DO NOT pull the diaphragm out of the good driver. If the bad sound stays with the driver, and you exhaust your efforts with JBL, then I would talk to Guido or find a really good speaker tech in UK or EU to send both drivers to, and have them test the bad driver and see if the diaphragm to driver fitment can be improved. If all that fails, which it shouldn’t, PM me about a replacement pair of drivers.

[JamesBLansing]

Quick recap - you are in the UK and your speakers are a “few” years old. First, what is the JBL warranty for the UK - you may have to call the UK importer of JBL to find out. Second, as Widget said, the JBL warranty starts from when a current model speaker is invoiced to the final user - it does not matter if the speaker was used as a dealer demo for 2-3yrs. I am sure, however, that JBL would balk at a warranty repair on a speaker that has been out of production for quite some time, e.g. a speaker that was discontinued 10yrs ago cannot reasonably still be under warranty, just as JBL can’t still be held responsible for the speakers my father bought in the 60’s that had their old “Lifetime” warranty. The worst case in this scenario is that your dealer did not sell you Demo speakers, but instead resold you speakers he had bought back from someone else towards an upgrade - either originally purchased from him, or elsewhere. Either way, he can pursue a warranty claim on your speakers until it is rejected by JBL. I think you have much further to go on pursuing your claim here.

How do you know the problem is the driver? First, you need to carefully re-assemble your driver and listen to it. If that speaker still sounds off, make sure the alignment of the driver to the horn does not have any way to be shifted off, then swap just the 476mg from that speaker to the other speaker, then listen to them both again - did the bad sound follow the suspect driver (Driver is bad), or did it stay with the original (crossover may have a problem). Above all, as Widget said, DO NOT pull the diaphragm out of the good driver. If the bad sound stays with the driver, and you exhaust your efforts with JBL, then I would talk to Guido or find a really good speaker tech in UK or EU to send both drivers to, and have them test the bad driver and see if the diaphragm to driver fitment can be improved. If all that fails, which it shouldn’t, PM me about a replacement pair of drivers.

Thank you for the detailed answered, sorry for the late reply, I have been dealing with health issues, for the JBL warranty issue, unfortunately I can't be able to take any action so I have cut my own rope.

I have tried swapping the drivers, same result, I have measured all the crossover capacitors - the crossovers give the same ratios, I have measured all the drivers - they gave the same ohm ratio, I have tried listening all the drivers seperately together - same result, I happen to hear a tonal difference between two HF drivers, I also believe the driver is ok but then the problem will be with the crossover, I think I need to check the crossovers with a good technician, I need to find the problem but unfortunately I couldn't so far

[JamesBLansing]

Here is a brand new DR82450SL and mine looks almost the same. You have to remember that you are dealing with a flat ribbon that gets twisted from the opposite side and gets twisted again to make a solder connection. One side is coming from the opposite side of the coil and that's the one I have a picture of. The other side looks much better because you only have to twist it 90 degrees to make the solder connection. Granted either one of them are not pretty but they pull this of in what a .025 gap!

You might just have a simple alignment issue/screw torque. When you took out the diaphragm did you notice if some of the screws were easier to break the torque on?? I once have a driver where one of the screws was "loose" and once I retightened it was fine again. JBL should help you with this.

Rob:)

Maybe it is from the crossover what do you think? I had k2 S5500's before and had a similar problem, it happen to be the crossover, but as far as I know I need to pull out all the capacitors from the crossover board in order to have the correct measurement, right?

[Mr. Widget]

I guess we all assumed you followed basic trouble shooting 101 before deciding to jump into opening up the drivers.

Did you try swapping your left channel 476Mg with the one on the right? This will immediately tell you if you have a network/wiring issue or a driver issue.


Widget

[JamesBLansing]

I guess we all assumed you followed basic trouble shooting 101 before deciding to jump into opening up the drivers.

Did you try swapping your left channel 476Mg with the one on the right? This will immediately tell you if you have a network/wiring issue or a driver issue.


Widget

Of course I have tried that, I also tried swapping the speakers in order to see acoustic defects but still the same, one hf is playin %10 lower than the other one

[HCSGuy]

Please, please, please, start with Widget's advice. Put the speakers together, take a listen. One of the speakers sounds better. Put a piece of tape on the 476Mg in that one and mark "Good" on it, or something, so you know not to mess with that one. Then swap the 476Mg's from one speaker to the other, and listen again. If the bad sound is still coming from the same speaker as before, it is not the 476Mg (***See below***). If the other speaker now sounds bad, it is the 476Mg, and you can move on to the next step.
88055

Which one of these is correct? Which one would you rather have? These are all simple 476Mg frequency response plots, with no horn, 5ms gate, in a 4'x2'x2' "tunnel" made of stacked acoustic panels, with the driver at one end, firing towards the mic 1M or so away at the other end. The conditions are not perfect, so do not judge the plots for their flatness. Instead, note that at some frequencies, they deviate by almost 8db from each other - yeah, it's at 4khz, but that would make one speaker sound alot brighter than the other. These three plots are the same 476Mg, with the same diaphragm, but I have adjusted the diaphragm fitment a little for each curve - before tightening the screws, I put a little pressure on the diaphragm outer ring towards the positive terminal, then the negative, then towards the driver label. So you see, installing a diaphragm is not quite as simple as putting a spare tire on your car. Which one is correct? In my case, it's the one that best matches the Frequency response plot I took first of the other 476Mg. *** It would be the same for you, as long as you don't remove the diaphragm on the good driver. If you have corrupted both drivers, you will have to figure out how to best measure what is a "Flat" response.

[HCSGuy]

Btw, I was typing my last reply while you posted yours, so sorry if I'm a little behind. So, you have determined that it is one of the 476Mg's, right? Also, you state that you are "On your own", implying you have no recourse with your dealer or JBL. If this is the case, you are going to need to spend a little money. First, you will need a calibrated microphone. I have been playing with the Dayton Audio OmniMic2, which we get here from Parts-express.com - I don't know what is available to you, but this one is about $300, and you need a PC and to download their test tracks. I would also get some acoustic foam and build a test "Tunnel" like I have so that you can make repeatable measurements with as little outside interference as possible. Then, you can take frequency plots of both your drivers, and adjust the bad one closer to the good one. Without all the test equipment, you could also try the diaphragm adjustments I did - just loosen the screws, push the outer ring one direction, tighten the screws, put the thing back together, and listen to see if it's better. Why do I think this would help? Here's my two 476Mg's before I adjusted one:
88056
And Here's after:
88057
I could hear the difference going back and forth between them before, but cannot now.

[1audiohack]

Awesome work HSCGuy!

Barry.

[Mr. Widget]

A bit off topic, but a forum member told me privately that he purchased a pair of JBL’s replacements for the 476Mg. They are called 877Mg and appear to be Radian drivers with JBL built diaphragms. Apparently the 476Be will also be replaced by the 877Be.

My guess is that due to the small numbers of systems being built and sold that use these drivers it no longer made financial sense to continue producing these high end drivers. I am not familiar with Radian’s 4” drivers, but I imagine they are not built at as high a level of precision of the former TOTL JBLs.

I would expect to hear about the updated Everests and K2s soon.


Widget

[Robh3606]

They must be changing the throat diameters on the Radians to 1.5" They are 1.4" and 2" available for stock drivers. Unless they drop a sleeve into the horns throats can't imagine them redoing the throats but it is possible.

Rob:)

[ivica]

A bit off topic, but a forum member told me privately that he purchased a pair of JBL’s replacements for the 476Mg. They are called 877Mg and appear to be Radian drivers with JBL built diaphragms. Apparently the 476Be will also be replaced by the 877Be.

...........

Widget

Hi Widget,

Does that mean that JBL still produce Be Diaphragms with 'diamond shaped suspension" (476Be) ?

Regards
Ivica

[Mr. Widget]

Hi Widget,

Does that mean that JBL still produce Be Diaphragms with 'diamond shaped suspension" (476Be) ?

Regards
IvicaThat is my understanding.


Widget