Think We May Have a Keeper Here!!!

[Zilch]

Have we not already gone over these old networks sufficiently? You just keep going around in circles dude.

I dunno. I'm merely pointing to additional information for Todd (and others, perhaps,) to consider in understanding their testing of the performance of these networks. Seems like several members may already be working with them....

[Zilch]

I think that is what you aren't getting Zilch. People actually read this freakin' forum and then go out and do all this shit. They actually take all this crap posted all over this forum and apply it.

There are few subjects that have been more thoroughly massaged on these forums than biasing and bypassing crossover capacitors. With respect to this particular project, we discussed it in the initial thread. You recently posted in another thread regarding JBL's use of Solens in their latest designs. In my view, this is all good an useful information for everyone interested to consider.

I believe even the earliest information posted here indicated that biased crossovers using Solens don't require bypass capacitors. It's not my intent or responsibility to undertake a comprehensive exposition of all of the relevant design issues in the course of participating in a DIY project, though I believe I do a creditable job with the fundamental considerations known to me.

You seem to be arguing that it would be better not to do it at all. Here, again, this is not about bypass capacitors, but rather, the larger question of whether such endeavors belong in these forums, and I believe the vote is long since in on that one....

[briang]

I hesitated to write this at first...it might be unwelcome.

Thanks to Zilch for posting all this work.

[toddalin]

Boy, I'm one heck of a trouble maker!

When I initially asked for a design to build the crossovers supplemental to replacing the 130A's with 2235's in my L200 cabinets, I knew nothing about biasing and by-pass caps in crossovers. This was all learned on the fly.

Zilch stepped up to the plate and suggested the N200B as a viable option. He suggested the use of Dayton caps to save costs and even revised the circuit for biasing at my request. When the circuit diagrams were presented for consideration, there was talk of by-pass caps for use with the Daytons.

When I ordered the components, I decided to stay with one brand for the big caps that didn't cost an arm and a leg. Solen had the values I wanted, was only a little more expensive than the Daytons, and I had heard good things about them. The PE website also talks of by-pass caps and no mention is made that they are not necessary with Solens.

After the parts order was in, it came up that the Solens didn't need the by-pass caps. I already had them on order so figured WTF, may as well use them..., couldn't hoit, and as long as I was going to the trouble to build these things, what's another $20 each in the grand scheme of things?

Do by-pass caps help the sound of the Solens? Did JBL leave them off the Solens because there was no difference in sound or was it ultimately $$$ consideration of the bean counters? Would they have used them if $$$ was no object?

If the world wants to know if they make a difference in this instance, Zilch feel free to remove them for trial (no easy task I know as they are all tucked up tight under the bigger components). However, I am of the impression that if they do make a difference, it will be extremely subtle and unless you can instantaneously A/B the crossovers without and with the Theta's in place, you would never know. Not everything the ear hears can be quantified using our rudimentary instrumentation.

[Zilch]

Boy, I'm one heck of a trouble maker!

If the world wants to know if they make a difference in this instance, Zilch feel free to remove them for trial (no easy task I know as they are all tucked up tight under the bigger components). However, I am of the impression that if they do make a difference, it will be extremely subtle and unless you can instantaneously A/B the crossovers without and with the Theta's in place, you would never know. Not everything the ear hears can be quantified using our rudimentary instrumentation.

'Zactly.

I'm gonna build up a pair with spaces for bypass caps. I'll put Thetas in one and none in the other. We'll A/B 'em at the Lansing Heritage Weekend Expo!

[Earl K]

As noted, I did some more testing today. Using a sine wave generator through a working speaker system (under the actual load it is to drive), and using an a/c volt meter on the speaker input terminals the electrical minus 3 dB points are approximately:

Woofer LP is electrically (1/2 voltage) down 3 dB at about 700 Hz.

Mid HP (from woofer) is down 3 dB at about 650 Hz.

Mid LP (to tweeter) is down 3 dB at about 7,500 Hz (50 mH coil).

Tweeter HP (from mid) is down 3 dB at about 5,500 Hz (50 mH coil).
- ( I'll assume these 50 mH coils are actually .5 mH )
These pretty much confirm what the scope saw on the bench.

- Well, okay, I'm baffled .

- I just used the 1/2 voltage method ( on a partially reconstructed horn circuit / ie ; minus its' low pass section , but the rest of the horn circuit is present ).
- Capacitors are Solen ( I have boxes of them ) .
- All the test equipment signal grounds are referenced back to the amps output ground / so there is no floating ground .
- I built a woofer circuit & loaded it with an 8 ohm dummy load ( looking for interaction between the 2 network branches ) I didn't find any, though I didn't build up the Zobel . Maybe that's next .
- My reference frequency is 3000 hz ( to stay above this circuits' "bump-filter" ).
- Volt Meter is my old AC powered B&K 290 . Useful for its' huge metering . All the AC powered stuff is "warmed-up" .

And still:
- I get a 3 db down point for the horns' hipass at @ 760 hz ( with the 16 ohm Lpad fully open ) .
- With that same Lpad attenuated ( 10db, measured acoustically ) the new 3 db down-point has risen slightly to @ 775 hz .

So :
- Anyone have any ideas where the discrepencies might be arising between Todds' and my measurements ?

- Anyone want to comment on my testing methods and offer up some insights ?

Thanks !

[toddalin]

'Zactly.

I'm gonna build up a pair with spaces for bypass caps. I'll put Thetas in one and none in the other. We'll A/B 'em at the Lansing Heritage Weekend Expo!

Actually..., what would provide the best representation would be a single crossover with a multi-pole relay on-board that could instantaneously kick the BP caps in/out at the flip of a switch. Alternatively, the relay could kick between two crossovers, but that introduces other differences (e.g., no two caps/coils are exactly identical so the crossovers are not identical and we are looking for what may be very small changes here). 6+pdt relays are common and cheap.

[toddalin]

Sorry, but I am a scientist (show me) and work in sound and noise and recognize that at least my ear has a poor acoustic memory and for me an A/B/X test would be the acid test.

I think you will find that it is easier to distinguish the difference by listening to the bypassed version for awhile until you become acclimated and then removing the bypass capacitors.

[Zilch]

I hesitated to write this at first...it might be unwelcome.

Naw, no problem. We're just havin' plenty good fun with JBL stuff here, is all.

[None of this is fatal, or even disfiguring, for that matter. Just keep the SPL within reason.... ]

Yes, but compared to your others and personal experience, how do they sound???

Well, I'm gonna say your crossover is smoother sounding that the vintage 3110/3105 combination I have used here recently.

Johnaec dropped off a second 2446J/2380A today. I'll set up a system with that and the old crossovers for A/B listening comparison.

Here it's running on your crossover with a 2405H slot tweeter, which he also brought to try. This combo works, too. Michael's (Nestawasright) system is gonna sound mighty good, if this is an indication. These 2" drivers and larger horns seem to have an inherent effortlessness and transparency to their sound, and the slot, well, everybody knows....

[Also, with 2407H on $10 PT-F95 horn, bottom pics.]

[hapy._.face]

I think the consensus amongst those who have limited knowledge of this sort of thing (myself included) is that the technical information on this forum should be chased with a pound of salt. Two major variables influence my decision to spend any time or money on anything discussed herein:

1. The SOURCE of the information

2. The supporting data found elsewhere

One quickly realizes "who knows what" on this forum- even when you, yourself, may not know much at all. Anyone jumping into the whimsical suggestions of just any ol' member is taking the kinds of chances that (likely) he or she has taken many times before (JBL aside). That's their thing. OTOH, if people want to have fun tinkering with something that others think is a waste of time, so be it- so long as the 'tinkering' isn't a sermon on the new world order of doing things.

Taking all this into account, my best lessons learned were from actual mistakes- it's a beautiful thing, sometimes! This forum is interesting because you oftentimes get to watch others make them and work through them. It can also yield an amazing new discovery. I'm gonna learn something either way!

[toddalin]

Potentially my sine wave generator is off. I'll see how close it comes to A-880 on my digital keyboard tomorrow.

- Well, okay, I'm baffled .

- I just used the 1/2 voltage method ( on a partially reconstructed horn circuit / ie ; minus its' low pass section , but the rest of the horn circuit is present ).
- Capacitors are Solen ( I have boxes of them ) .
- All the test equipment signal grounds are referenced back to the amps output ground / so there is no floating ground .
- I built a woofer circuit & loaded it with an 8 ohm dummy load ( looking for interaction between the 2 network branches ) I didn't find any, though I didn't build up the Zobel . Maybe that's next .
- My reference frequency is 3000 hz ( to stay above this circuits' "bump-filter" ).
- Volt Meter is my old AC powered B&K 290 . Useful for its' huge metering . All the AC powered stuff is "warmed-up" .

And still:
- I get a 3 db down point for the horns' hipass at @ 760 hz ( with the 16 ohm Lpad fully open ) .
- With that same Lpad attenuated ( 10db, measured acoustically ) the new 3 db down-point has risen slightly to @ 775 hz .

So :
- Anyone have any ideas where the discrepencies might be arising between Todds' and my measurements ?

- Anyone want to comment on my testing methods and offer up some insights ?

Thanks !

[JuniorJBL]

my best lessons learned were from actual mistakes- it's a beautiful thing, sometimes!

Sometimes EXPENSIVE!! but it can be a wonderful thing

[briang]

Sometimes EXPENSIVE!! but it can be a wonderful thing

That describes nearly all my mistakes... ...

[Zilch]

I built up this networks' band-pass portion about 10 days ago. I measured an electrical 3 db down point ( with actual horn load in place ) of @ 780 hz ( if my memory is correct .) I used the "db counter" function on my Loftech/Goldline generator to measure the electrical drop . I did need to approximate the .8mH coil with 3 .56mH coils arranged in a parallel/series topology / so that would introduce a margin of error in my findings.

Yeah, but do you LIKE it?

18 dB/octave HP and 12 dB/octave LP, no? And then 12 dB/octave HP to the UHF?

Is the 800 Hz crossing to the LF 12 dB/octave LP "asymmetric," then?

[Earl K]

- Well, okay, I'm baffled .
...........snip, snip, snip,...............
And still:
..........snip, snip, snip,...............
- With that same Lpad attenuated ( 10db, measured acoustically ) the new 3 db down-point has risen slightly to @ 775 hz .

- Okay, my best guess ( for Tues. ) is that the "tight-pack" layout of Todds' construction is forcing the .8mH coil into being a larger "virtual" value. I'll have to try some parts substitutions ( Wed. ) to see what value coil would cause this lower reading in F3 . ( Coils interact with other coils when placed in close proximity )

- In the meantime Zilch, you should verify Todds F3 numbers . Once finished ; lift the .8 mH coil from its' present location / extend with 12" of wire on either end of the coil/ replace the "new coil" into the circuit & remeasure the horns' F3 for its' high-pass .


- A couple of notes ; the .6 mH coil in the 3105 omits the use of both 20 ohm load resistors ( compared to the 3106 ) . Todds use of .5 mH coils begs the question ; "What about the usage of load resistors ? Impedance plots should be run with & without the resistors inplace . Then full voltage runs should be worked-up for each scenario so one can study the consequences of ad hac parts substitution .

Yeah, but do you LIKE it?

- My opinion, on the whole is pretty well beside the point / except to say / both Todds' and your declarations, that this "workedup design" is a done deal and ready to implement ,,, is vastly overstated - to put it mildly.

18 dB/octave HP and 12 dB/octave LP, no? And then 12 dB/octave HP to the UHF?

- A study of the actual derived "acoustic" slopes is enlightening .

regards