4430 l-pads

[speakerdave]

Oh, I see. You mean the same from speaker to speaker. Yes, I think ordinarily you would. Can't you do it?

[Figge]

not by the db scale i cant...since it dont match the knob...on one speaker that is...the other is just perfect!

[speakerdave]

I think I understand. A photo showing the difference would help. You may be stuck with trusting your ears, not a bad thing. Perhaps you can balance them be centering pink noise on mono. If you don't have a test CD with pink noise, try interstation hiss from the FM tuner. Switch the tuner or preamp to mono, put yourself in the prime listening position and see if the sound is centered between the speakers. Be aware other factors may influence this, such as asymetrical speaker placement. If you can get a test CD with tones in the relevant frequency bands that would be more accurate. Be careful not to play test tones too loud.

Another thing you might do is try a sweep tone (again, on a test CD). If it seems to move as you sweep through the low mid and high frequency bands, then there is an imbalance. Sometimes you can discern the same thing with passages of music that go up or down the scale, but with a speaker whose first crossover is at 1000 cycles, that may not be true.

David

[Figge]

well look at them pic:s i posted...the knobs are supposed to stick out of the holes a little... on the pic u see the knobs on that speaker is behind the foilcal and not centered in the hole wich makes inaccurate readings towards the scale.

i really dont understand how they have become this was...or how to correct them....

i cant imagine jbl letting them out of the factory this way...so someone must have been there screwing around behind the foilcal..

[Mr. Widget]

Originally posted by Figge


i cant imagine jbl letting them out of the factory this way...so someone must have been there screwing around behind the foilcal..

I am sorry to say that even our beloved JBL let's things out of the factory they shouldn't when Jim Lansing's ghost is taking a break and not keeping an eye on quality.

Seriously, you can't fully rely on the screen printed graphics. Those numbers are indications and are not laboratory calibrated. If you want to set them up so that the response is reasonably accurate and the same left to right, you need a test signal source. It could be an audio generator or test CD and you need at least an SPL meter and preferably an SPL meter and a RTA of some type.

With these simple goodies you can rough in a balance in a few minutes and after extended listening, if something bugs you, you can tweak by ear.

Widget

BTW Get some curtains or Sonex panels or other room treatment. It will make more of an improvement than changing any cable in your system. Even between Radio Shack to $1000 a meter interconnects.

[Figge]

ok now i´v got HP:s sony TA-E86B preamp and i "borrowed" a son of ampzilla from.. ole daddy and this shure made a big diffrence from the quad driven by my home made volume-pot! infact it like day and night...not that the quads are bad amps....just that they are pretty hard to drive with other pre-amps the quads own! i used my homebuilt pot for a luxman M120A once and it was Sweet!

[herki the cat]

Here's some background on JBL compression driver and diaphragm evolution. There is more detail here:

http://www.audioheritage.org/html/pr...logy/435be.htm

From the very first JBL compression driver of 1948 (the D175), until 1980, there was no change in the basic engineering of JBL's small format compression drivers. They all used an Alnico motor with an aluminum diaphragm and tangential surround. 1980 saw the first major change with the development of the diamond surround. While still constructing the diaphragm out of aluminum, the surround was pressed into a series of diamond shaped polygons. The reason for this was to increase the HF extension by taking advantage of a phenomenon known as parasitic resonance. The smaller diamond polygons increase the second resonance to the point that it reinforces HF response in the highest audible octave. This was primarily intended for the large format 375/2440, which otherwise was restricted in response to 10khz. Using parasitic resonance, extension could be pushed to 18khz and eliminate the need for three-way systems in most pro applications. While the small format compression drivers were in less need of this HF boost, they were found to benefit as well and they were converted to diamond surrounds at the same time.

However, there was a penalty to be paid for this change that did not become fully apparent until a high profile incident in 1982. The problem was that the diamond peaks concentrated stresses to a much greater degree than the previous tangential geometry. The stress concentration led to premature failures of the diaphragms. The incident in question was the premier of the brand new JBL installation at the Academy of Motion Picture Arts and Sciences theatre. It was considered quite a coup for JBL to replace the old Altec sound system with their then state-of-the-art cinema system (for which JBL would later win an Academy Technical Award). However, during the premiere, the diaphragms on nearly all of the 2441’s failed. As a result, an edict was issued from on high at JBL to immediately fix this issue. Six months later, the result was the titanium diaphragm.

Titanium is an order of magnitude more resistant to fatigue failure. The diamond surrounds, with their increased HF response, could still be employed, but power handling was increased by 30% with greatly increased longevity. Nonetheless, there were tradeoffs involved. As Giskard stated, titanium has poorer internal damping than aluminum. Further, titanium has reduced stiffness meaning that it is driven to breakup at a lower frequency than aluminum. The net result is increased distortion. This increase is relatively miniscule, but many listeners find it audible in critical applications like monitoring or home hi-fi.

For this reason, JBL has reverted to aluminum and introduced beryllium diaphragms on their latest compression drivers. The use of a composite mylar surround has solved the fatigue problem. The use of beryllium has solved the diaphragm breakup issue so that these drivers have the lowest levels of distortion of any compression driver yet built by JBL. The smaller diaphrams (3" vs 4") of these newer drivers furhter pushes the frequency of breakup modes and increases overall HF response. Finally, applying EQ allowed these drivers to have the same UHF extension without the need for parasitic resonance and its attendent distortion.

cheers, herki