Think We May Have a Keeper Here!!!

[Earl K]

...(snip).... I think where I'm headed is that the 500 Hz "problem" is apparent in running the woofer just by itself, in this cabinet, with no crossover, which I'm about to further verify in a different room..

- Okay,, makes sense .

Actually been there/done that. Disconnected the cap entirely as well as trying various resistances between the cap and gnd. Adds very little upper end boost to the woofer, such that it is audible, but the analyzer doesn't see it and the spectrum remains pretty much the same...

- That makes sense when cross-referenced against Zilches full-range woofer measurements .

So Guys, what common measurement ( in both of your setups ) does a dimension/distance of 13" to 15" represent ? ( Floor Bounce Cancellations can create big "V" notches in a woofers' response & they are very hard to overcome )

[edgewound]

How did it sound with your ears before you listened to it with your 10 band analyzer. You really can't expect to get accurate results to compare without having the same test equipment as your designer...there's gonna be band overlap that is skewed (or is that skewered?) on your 10 band that a 31 band can look at with more precision. The 10 band has to do something with all that info and put it somewhere. Maybe it's putting it where it's just screwing things up visually rather than audibly. Just my thoughts...feel free to correct me.

[Zilch]

So Guys, what common measurement ( in both of your setups ) does a dimension/distance of 13" to 15" represent ? ( Floor Bounce Cancellations can create big "V" notches in a woofers' reponse & they are very hard to overcome )

Here in Berkeley, woofer is centered 18" off the floor.

I'm suspecting the culprit is the baffle being recessed 4" back from the cabinet face. The recess is 22.5" H x 29" V. The sides are "vented." The 29" correlates....

[Earl K]

Now punch it into spice and see what's up.
Or else just hook it up to the "Standard JBL Test Jig" and run a voltage drive.

***

Oh, also, go ahead and punch in the whole enclosure/woofer system into BB6P and model it. Then open a second instance and insert that 16 ohm series resistor. Compare the data if only for future reference.

- Zilch, are you able to do this ?

- I don't have BB6P or a Spice modeller.

- A voltage drive of the built network , would be illuminating .

[toddalin]

How did it sound with your ears before you listened to it with your 10 band analyzer. Just my thoughts...feel free to correct me.

As I noted, I can hear the 500 Hz dip as a loss of intelligibility, especially of the male voice. That's what led to the testing.

[Zilch]

- Zilch, are you able to do this ?

- I don't have BB6P or a Spice modeller.

- A voltage drive of the built network , would be illuminating .

Yeah, all that suff.

Giskard modeled it in the original thread:

http://audioheritage.org/vbulletin/s...0&postcount=41

Ignore the yellow and white, which show the HF boost in the original, from which this one is derived. Todd's design LF and MF are the green and orange.

Part of the problem here is that the project is now in multiple threads.

Next time I see Todd in person, I'm gonna konk him for this.

Me, I'm the champion of the "Single-thread" aproach....

Here's the history:

http://audioheritage.org/vbulletin/s...ead.php?t=8507

http://audioheritage.org/vbulletin/s...ead.php?t=9009

http://audioheritage.org/vbulletin/s...ead.php?t=9134

http://audioheritage.org/vbulletin/s...ead.php?t=9176

[Earl K]

I'm suspecting the culprit is the baffle being recessed 4" back from the cabinet face. The recess is 22.5" H x 29" V. The sides are "vented." The 29" correlates....

- Well, I'll leave it to you to suss that out .

- If you have one, put a shorter-coil 15" JBL in the box ( like a 2225 or a 2205 ). Maybe the L200 box was deliberately engineered to cancel out a 500 hz bump from one of those older type woofers which I think are hotter in this area .

- Okay, I'm just grasping at straws now, so I'm signing off .

[Zilch]

Ok, then verify that the voltage drive of the actual physical network matches the model. Remove it as a suspect.

Get a bigger flashlight on it like edgewound suggests. Use CLIO.

Go ahead and investigate the physical aspect of the driver enclosure/relationship like you're thinking about. You might have to go with EQ or a passive notch filter to solve the problem. Don't be too afraid of the notch filter. Yeah, alot of people would scoff, but JBL used one in the Everest and it worked.

Thanks, Giskard.

I've suggested that Todd might send one of the three he built up here for testing. Voltage drive will be easy to verify.

We'll be asking for your help in fixing this with a notch filter, if it comes to that.

This SHOULD be a good generic (read "no autotransformers") 800 Hz network for the common JBL compression driver/ring radiator three-way with extended-bass woofer. It's well worth working through these difficulties, I believe.

[Not to mention continuing the amusement value.... ]

[edgewound]

Thanks, Giskard.

I've suggested that Todd might send one of the three he built up here for testing. Voltage drive will be easy to verify.

We'll be asking for your help in fixing this with a notch filter, if it comes to that.

This SHOULD be a good generic (read "no autotransformers") 800 Hz network for the common JBL compression driver/ring radiator three-way with extended-bass woofer. It's well worth working through these difficulties, I believe....

If I may....I think one of your variables that is not so common in your equation, is the midrange horn/driver combo being used in this setup. The 2235 variant being used was teamed up with the LE85/2420-H92/2312, rather than the 175 driver and the smaller horn. It seems to make sense to me that there will be a hole in your response by using a crossover in this range with these components....the 175 driver just doesn't have the muscle to reach into 500Hz territory, and there might be time alignment phase cancellation issues with the shorter horn. If you stick with your new crossover, maybe you'd find that an LE85/2420(2421)-H92 horn would work better....otherwise shift the crossover point up to about 1000-1200Hz.

[Zilch]

If you stick with your new crossover, maybe you'd find that an LE85/2420(2421)-H92 horn would work better....otherwise shift the crossover point up to about 1000-1200Hz.

Yes, we went over that pretty thoroughly in the original thread.

See the sim curves. The MF is down 25+ dB at 500 Hz. It's in the woofer/cabinet, if it's real. Note also the LF Q is high, there, perhaps in partial compensation.

Though I'm reluctant to bring it up, we may be able to tweak it some in the Zobel.

Also, though I've been pretty adamant about the 16 Ohms series resistance thing here, I recall measuring the original LF inductors at a surprisingly high value.

Naw, they was just 0.81, 0.84 Ohms. That's not it....

[Zilch]

The 2235H simply isn't going to like a whole lot of Q added to it. It just isn't. There's no point in using a nice big wonderful transducer like a 2235H if you're going to go ahead and stick a big-ass resistor in front of it and choke it off.

We'll wait and see what else you find.

Yup, agreed. I'm gonna quit typin' and go test more, now.

This is plenty good fun, and learnin' new stuff, too!

[Well, new HERE, at least.... ]

[Zilch]

1) Second unit above, in a different room. Same deal.
2) Insulation all around.
3) Ports closed.
4) Yup, a woofer in there.

Standing waves inside, maybe?

[Off to Home Depot for more insulation....]

[Zilch]

Run an impedance curve a couple hundred Hz above and below your suspected frequency. Let's look for an anomoly.

No problem. Gonna be a 30 ft."long wire" reading, though.

[Hand truck's at the warehouse.... ]

[toddalin]

While you're in there, try putting a horn on it and running up the ~500 eq bands for a flat response and see if that doesn't clear up male vocal intelligibility.

People been putting 2235's in L200 cabinets for ??? years and I'm the first to notice this 500 Hz suck-out phenonom???

1) Second unit above, in a different room. Same deal.
2) Insulation all around.
3) Ports closed.
4) Yup, a woofer in there.

Standing waves inside, maybe?

[Off to Home Depot for more insulation....]

[Zilch]

Yup. It goes flat at 450 and 900 Hz.

What's that mean?

Cabinet's O.K.

All I heard was it got louder approaching 1 kHz.

I'll run it higher res....

Edit: 2 X res, port open, looks the same.

Note: Small world, folks. These were Giskard's 2235H's.