2435HPL vs. 435Be

[speakerdave]

Originally posted by jim henderson
The "echo" comes about 1.4 ms after the pulse response. Does that seem to be too long to be stored energy in the diaphragm surround or back chamber?

I don't know. Too long for the diaphragm surround, probably. Figured on the back of an envelop that's enough time for sound to travel a little less than a half-meter, so "echo" may not have been a good term to use. I was really thinking that the energy might be being "stored" in something that is flexing and then springing back the way a cabinet panel does. Ever since Bo and Widget posted those photos of the fins on the 435 I've wondered about them. If they are for heat dissipatiion why would they be needed more on a domestic driver than on one used in the big concert arrays? Could they be there to give the back chamber total rigidity? Is it possible the relatively plain back cover of the 2435 has a ring to it? If that's what is happening wrapping the back of the driver in a thick layer of modelling clay should reduce that artifact you are seeing.

Do we in fact know that the internal dimensions of the back chamber are different? Is there damping material in there similar to what is in other drivers? If the answer to both of these questions is yes, is there MORE damping material in the 435?

Jim, Widget, I totally understand your hesitancy to remove the back cover of those drivers. Maybe we can get this information from JBL.

Subwoof has had his apart. Subwoof, what's it like in there?

I wonder what the chances are of the back cover of the 435 showing up on the miscellaneous parts list.

Is it possible that "echo" or "artifact" is not big enough to worry about?

Also, I see a blip in the 035 trace with approximately the same delay. Could the source be elsewhere in the setup?

Lots of questions.

David

[jim henderson]

Subwoof,

Can I safely remove the back shell without affecting the diaphragm alignment?

[subwoof]

no problem...just be sure to align the input terminals when re-assembling. To save space, the old "lead wire" method is replaced by ittybitty spade leads.

sub

BTW - I am selling off the entire "I'll get around to building these someday" collection of components. I have all the parts to build a set of DMS-1 and 4345's....and about 50KW of crown power...

need stuff????

[jim henderson]

I removed the back shell to see what's inside and was surprised to find that the diaphragm is attached to the back shell and not the body as I expected. The 3" dome occupies most of the tiny back chamber leaving very little volume behind the diaphragm.

[johnaec]

Jim - did you ever come to any conclusions about the anomolous pulse respone you were seeing with the 2435/2232 combination, or is that what you're tracking down with opening the drivers?

John

[jim henderson]

I'm trying to track down the cause of the 1.4 ms pulse. I planned to open the back shell and measure the pulse while it was open, but I can't do that because the diaphragm is in the back shell and the magnet is in the body.

The next challenge will be EQ. They get very efficient in the upper vocal range and that needs to be tamed somehow.

[Mr. Widget]

Greg Timbers at JBL initially suggested we use the 2435HPLs for the Project May. He told us that to better the performance we would want to increase the rear chamber. We never pursued this as shortly there after JBL donated the 435Be drivers. I have no idea what the improvement would be.

Are your drivers ferro fluid cooled?

Widget

[Don McRitchie]

Actually, Greg's original suggestion was to use 2430's since these aluminum diaphragm drivers were much less costly than either the 2435 or 435Be. However, I believe that his comment regarding the rear chamber was equally valid for both pro drivers. However, as with Mr. Widget, I'm not sure what the difference would be. Greg did mention that the AL versions really needed to be aquaplased for hi-fi use to smooth out an otherwise harshness in the midrange.

[speakerdave]

Originally posted by Mr. Widget
Greg Timbers at JBL initially suggested we use the 2435HPLs for the Project May. He told us that to better the performance we would want to increase the rear chamber. We never pursued this as shortly there after JBL donated the 435Be drivers. I have no idea what the improvement would be.
Widget

I'm going to guess this has to do with the lower crossover frequency. In the arrays I'm aware of using the 2435 it is used above the neodymium 8" midrange. What do you all think?

[johnaec]

Originally posted by Don McRitchie
Actually, Greg's original suggestion was to use 2430's since these aluminum diaphragm drivers were much less costly than either the 2435 or 435Be.

It's good to hear Greg holds the 2430 as good enough for this application, since those are the versions I'm primarily interested in. I'd really like to hear someone's impression and/or measurement of those with the 2332 horns. Actually, I think what got me started on those in the first place was someone else's thread here in the past about their positive impression incorporating that combination in a custom system...

BTW, I'd be crossing them over above the 2012H midrange, (realizing EQ will probably be necessary, barring a good passive crossover design).

John

[Mr. Widget]

speakerdave,

What is your x-over frequency? The Project May will be around 800Hz.

I would assume a larger rear cavity will lower the driver's resonance allowing a lower x-over point. I would assume your x-over point is above 800Hz, so that might be the thinking.

Widget

[speakerdave]

In the VT4889 array the 2435 is used above the neodymium 8" midrange. Crossover frequencies are not given in the spec sheet I've seen. I would think it to be much higher than either the 650 or 800 the 435Be cuts in at in the K2 or Synthesis speakers. What do you all think?

[speakerdave]

Originally posted by Mr. Widget
speakerdave,
What is your x-over frequency?
Widget

I'm not there yet, but for some reason I've had a hunch I would need to add a driver between the 1400nd and the 2435. Right now I'm dreamin' 2250, but they're $500 each.

David

[speakerdave]

Also, in the array the 2435 is the tweeter and is spec-ed out to 16k. Some of that high end would be lost with the larger chamber. If I use it stock I may not need a supertweeter and could put that savings toward the midrange. (heh heh). Only thing is, it's not a K2 anymore; it's a hybrid three-way that JBL never bothered to build, and that gives me the willies. Also, I would be completely without a starting point on crossover design--not even frequency response curves for the drivers. Without a genius-level crossover it would be a mere collection of very expensive drivers. Just thinking out loud here. The chances of my making it sound more accurate than the LSR32 are practically nil.

David

[speakerdave]

Here's a picture of the neodymium 8" midrange. I've put it up so everyone can see what I'm talking about.