Measuring free air resonance on a 2235H?

[Flodstroem]

Hello folks! Last pair of refoam work done was on a pair of 2235H. Everything went OK and the job was easy. But................ when measuring the speakers free air resonance I got som unexpected results: both speakers had an fs of 17.7 and 17.6 Hz!!??

When looking at the JBL T/S specs list for the T/S parameters on a 2235H it says 20Hz. Then I discovered that the LE15, 2215H etc also had an fs of 20 Hz and this is a bit of unbelievable because of the difference between the two speakers cone weights (Mms). The LE15 is 97 grams and the 2235H is 155, with same fs? how does it comes? Spider differences?

Also, measuring the fs to be 17.7/6 Hz for the two 2235H, whats wrong? :blink:

[DavidF]

Hello folks! Last pair of refoam work done was on a pair of 2235H. Everything went OK and the job was easy. But................ when measuring the speakers free air resonance I got som unexpected results: both speakers had an fs of 17.7 and 17.6 Hz!!??

When looking at the JBL T/S specs list for the T/S parameters on a 2235H it says 20Hz. Then I discovered that the LE15, 2215H etc also had an fs of 20 Hz and this is a bit of unbelievable because of the difference between the two speakers cone weights (Mms). The LE15 is 97 grams and the 2235H is 155, with same fs? how does it comes? Spider differences?

Also, measuring the fs to be 17.7/6 Hz for the two 2235H, whats wrong? :blink:

Published specs are always subject to variations in production changes. Actually, having the two drivers within a tolerance of 0.1 is a far better outcome.

[Mannermusic]

Published specs are always subject to variations in production changes. Actually, having the two drivers within a tolerance of 0.1 is a far better outcome.

What he said! And, you can measure the "in box" tuning with signal generator and I'll bet it is pretty darn close; 30 - 32 Hz. It's not a critical value in terms of actual user performance - 10% is just fine; the "null" point is quite broad and flat. Depends on your room, what you like. One test is worth 1000 expert opinions. Mike

[Flodstroem]

Thanks guys for your positive comments. Actually as you said, its -10% and not far from the stock specs. But as normally after refoaming I had expected this tolerance to be in the upper region something like 22-24 Hz. Thats my experience before braking in......... :)

[Mannermusic]

Thanks guys for your positive comments. Actually as you said, its -10% and not far from the stock specs. But as normally after refoaming I had expected this tolerance to be in the upper region something like 22-24 Hz. Thats my experience before braking in......... :)

Yes, but that was how many years ago? This stuff (as well as we users!) is getting old - quite a few variables in the equation. I figure if we manage to make it sound good we're in the window! And, we can't get correct parts. Do you know what your new surrounds are; who the supplier was? This is the global economy. I recently changed the water pump on my 1993 LT1 /Corvette and the carton said GM Delco but when I examined the part it had China stamped on it. The dowells weren't quite right so I did and instant "engineering repair" and bolted the thing on and crossed my fingers. Works O.K. I think we have to be ready to "adjust as required." :confused: So it goes.

[Robh3606]

Nothing is wrong mine measured the exact same way I would not worry about it

Rob:)

[Flodstroem]

Yes, but that was how many years ago? This stuff (as well as we users!) is getting old - quite a few variables in the equation. I figure if we manage to make it sound good we're in the window! And, we can't get correct parts. Do you know what your new surrounds are; who the supplier was? This is the global economy. I recently changed the water pump on my 1993 LT1 /Corvette and the carton said GM Delco but when I examined the part it had China stamped on it. The dowells weren't quite right so I did and instant "engineering repair" and bolted the thing on and crossed my fingers. Works O.K. I think we have to be ready to "adjust as required." :confused: So it goes.

Hmmm, I guess you are right here Mannermusic, thats my experience too.
But, for those who wanders: foam surrounds came from Rick Cobb, and the fs was measured twice with two different methods and all shoved the same results :)

Im glad you answered my question (also thanks to Robh) and for the customer of mine to those 2235H I can only say: happy building with such a good speakers.............. (damn, I want them myself :crying: )..........