Midrange driver distortion

[lofi-ear]

Good summer to everyone!

I was listening to Vijay Iyer's excellent CD "Historicity" and observed that piano was sounding somewhat "hard" and straining to the ear. First I though it was because of the room, but later decided to play some sinetones and instantly noticed something's wrong. The midrange driver was audibly distorting with an 900Hz sine wave.

The 804ti driver of my TI10K speakers takes care of a very narrow frequency range of 1200Hz-3500Hz, taking off some burder from the tweeter; it has a 40mm voice coil and a very high mechanical excursion considering its frequency range, so I find it extremely odd that this driver could become faulty just like that. The driver has never received any external impacts and I've never pushed these speakers much over 100 decibels.

This very same phenomenon has happened to me before with a tweeter that was distorting. Removing the tweeter diaphragm and reassembling it resolved the problem. Now all I could do is rotate the driver 180 degrees and hope it's just the voice coil rubbing the magnet and time will fix the problem.

If not, I've contacted JBL service and they say they've got a replacement driver for the TI6K for 130 euros. I assume the drivers are identical in both models?

I've been very satistifed with these speakers but am afraid what time will do to them in the future. :crying:

[rdgrimes]

1st, swap the driver with the same driver in the other speaker. Does the distortion now happen in the other speaker?

yes: bad driver

no: bad crossover

Given the cost and prowess of these models, nothing short of a replacement of defective parts should be considered. Strike while the parts are still available.

[DavidF]

I am not familiar with the driver. I am aware of circumstances with other drivers where the diaphragm assembly bolts/screws loosen and get the assembly out of alignment. The remedy is to loosen all screws, reset the assembly and retighten the screws. The best approach is drive the unit with a test tone which allows you hear a clear tone when the alignment is correct as you tighten down the screws in sequence. The frequency of tone is not criticalim but it should be in the bandwidth of the driver, of course. A final sweep from FS to 10k or so to ensure no issues.

Hopefully, this is all you need to relieve your worries.

[Don C]

The 804TI does seem to be the same in the Ti10K and the T16K, according to the tech sheets.
Have a close look at the rubber surround, it's possible that it is coming unglued and flapping against the cone. I've seen this on my PT800s.

[BMWCCA]

The midrange driver was audibly distorting with an 900Hz sine wave.

The 804ti driver of my TI10K speakers takes care of a very narrow frequency range of 1200Hz-3500HzJust curious how you determined it was the 804ti mid-range rather than the 806G-1 mid-bass at that frequency if you didn't already swap the drivers? :dont-know:

[lofi-ear]

Thanks for your responses.

The 804ti is the faulty driver because I connected it directly to the amplifier with the same result. However, I ordered a new driver from the service (expensive!), there's not much I can do with it and the surround seems OK. Maybe re-coning would help, but luckily that wasn't the only option here.

Next I'm going to rotate the rest of the drivers upside down to increase their longevity hopefully...

[lofi-ear]

I noticed that PT800 has "904ti" as its midrange, which seems look the same as 804ti and according to specs the DC resistance is exactly the same. But how about sensitivity and frequency curve? Would it be possible to replace 804ti with 904ti without any changes in the XO network yet have balanced sound?

[rdgrimes]

I noticed that PT800 has "904ti" as its midrange, which seems look the same as 804ti and according to specs the DC resistance is exactly the same. But how about sensitivity and frequency curve? Would it be possible to replace 804ti with 904ti without any changes in the XO network yet have balanced sound?
An excellent question and one with no answer. The most likely 1st issue would be mounting differences, if any. 2nd would be it's behavior on the specific crossover. DCR isn't the whole story. I'd ask JBL directly. If you did that you'd want to replace both not just one. But again, these are high end and high priced speakers so they should be kept stock at all costs.

[lofi-ear]

The replacement driver finally arrived in the mail. Got to install it on the weekend.

http://s47.photobucket.com/albums/f159/air-breather/?action=view&current=804ti-2.jpghttp://i47.photobucket.com/albums/f159/air-breather/804ti-2.jpg

The definition of hi-tech lies in the image :p