Networks

[Singer-Man]

A newbie, here, who desires enlightenment.

Can someone explain to me why DIY folks say that copying the networks / crossovers of these old JBL systems can be one of the more difficult aspects of their build?

In many instances we have the old speaker systems intact as well as some of the schematics, so we know what resistors and capacitors etc. are being used, and we know at what Hz. the crossovers are being implemented.

I'm clearly missing some principle in this process.

[hjames]

A newbie, here, who desires enlightenment.

Can someone explain to me why DIY folks say that copying the networks / crossovers of these old JBL systems can be one of the more difficult aspects of their build?

In many instances we have the old speaker systems intact as well as some of the schematics, so we know what resistors and capacitors etc. are being used, and we know at what Hz. the crossovers are being implemented.

I'm clearly missing some principle in this process.

The hard part of making clones using the old networks is getting exact matches for any
Tapped inductors they may have used ... and specific values were not always shared.
Easy for JBL to build/buy quantities for production runs, hard to do/DIY as a 1-off (or 2-off, as it were).

of course, as was said in another thread - the tough part is WHICH network we are talking about.
The network for a basic 2-way speaker system isn't bad,- 3-ways are more complicated, and 4 ways can be much more complex.

[JeffW]

And yet, even with the old speaker systems intact and the schematics on hand, you'd be amazed at how many pages are spent trying to get the new crossovers actually working.

[gdmoore28]

I don't see why it should be THAT difficult. If the schematics are correct (sometimes, a big"if") it should be a simple matter of duplicating them. I've run across a few folks who will custom wind inductors at about $50 a pop, and caps are readily available, as are resistors and Lpads, etc etc. Of course, whether they work properly will be determined by whether they are used with the original drivers.

GeeDeeEmm

[speakerdave]

The schematics are created for JBL and dealer techs. They may include values and part numbers for inductors but not DCR.

Equivalent networks without tapped inductors have been worked out by the Techbot and GT for the 4355 and the 4344/45. There may be a workaround for the 4315. Beyond that, any network that used a tapped inductor must be reengineered.

It seems to me the concerns about networks more often come up with people wanting to substitute drivers. They are often difficult to convince that the networks are engineered for specific drivers and that any substitutions will require network tweeks at a minimum and possibly major reworking. That work requires prototyping, access to many values of components, testing facilities and equipment and expensive software, not to mention actual knowledge and experience. In other words, it is beyond the capabilities of most diyers.

[hjames]

A newbie, here, who desires enlightenment.

Can someone explain to me why DIY folks say that copying the networks / crossovers of these old JBL systems can be one of the more difficult aspects of their build?

In many instances we have the old speaker systems intact as well as some of the schematics, so we know what resistors and capacitors etc. are being used, and we know at what Hz. the crossovers are being implemented.

I'm clearly missing some principle in this process.
Don't forget, cap values age and shift over time. (Inductors and resistors rarely do, of course)
Plus, frankly, there may be better ways to engineer a crossover for specific set of drivers
than was done 30-50 years ago with a cost conscious design in mind.

I can only speak of the big 4 ways as I spent a lot of time comparing them at one time,
but just look at the evolution of the crossovers for the 4341 vs 4343 vs 4345 systems,
and even THOSE have evolved since they went out of production.