Runnng 4350's with completely passive crossovers. Not Biamping

Hi

Title pretty much sums up my question but is it feasible to run the 4350's completely passive???

I dug through the forums and I can't find any information regarding this. I would rather not run them with a active crossover due to the additional expense and added ancillaries (interconnects, power cables and also floor/rack space).

Unless having the dual fifteens makes for a speaker with a nasty impedance I don't see the need to biamp in this day and age. I have a 400 watt Krell that is an absolute powerhouse and should be up to the task of running the speakers passively.

If this is all possible is there 250hz passive network for the 4350's anywhere? Am I able to alter the values in the woofer circuit in a pair of 4343/4344 networks to change the frequency from 320hz to the required 250hz?

It's feasible, but as you've discovered you'd be the first ( meaning you'd have to pay all the costs for the necessary R+D to actually make it all work properly ).

Once those passive part values are determined ( some of which would need to be finessed via listening tests ) it shouldn't be that complicated a build .

The actual costs shouldn't be that off-putting ( as long as one uses surplus HVAC motor-run capacitors for the majority of the needed capacitance ).

Inductors would need to be very low DCR, ( which points the way to using laminate core types ).

You really want to partner-up with a current 4350 user who's interested in the same outcome ( + who has the needed measuring equipment to design the necessary network parts ).

:)

PS#1; Surplus Motor-Run ( HVAC ) caps can be had quite cheaply ( from time to time on eBay ).
- Depending on the actual slopes used ( as well as actual impedance's ) I calculate you'd need to buy as much as 350uF in capacitance distributed between the 4 crossover legs of the 2 new crossovers ( ie; 115uF x 2 , 60uF x 2 >> for 12db Butterworth like slopes ).

Here's an outfit the ships internationally that's selling multiple lots of surplus/used Motor Runs ( with reasonable shipping rates I might add ).
- Remember, one can directly add the value of capacitors when they are paralleled together.

PS#2; Here's the type of inductor I would first try out. ERSE SuperQ 14ga

It's not as simple as you think you are going to have to pad down the upper drivers in a passive network as well as working out the high-pass for the 2202.

The high-pass for the 2202 was done as part of the original active crossover network. All of these components "talk to each other" so as soon as you add the high pass on the 2202 you are going to have to re-tweek the network because the added poles may/probably will change the voltage drive where you don't want it changed.

You need to match the original voltage drive to the 2202 or you won't have 4350's. I have done it going the other way from passive to active and it's not something to be taken lightly. As Earl says it takes the proper tools including a good measurement system and crossover design software to plug the measurements into.

Rob:)

Ok I give up running them completely passive.

The 4350 was the pioneering product for Jbl as far as bi amp operation of a monitor was concerned.

Quote:

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Originally Posted by kelossus

Ok I give up running them completely passive.

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Well, maybe someone else with some 4350's will get interested in this project ( never say never ! ).

There are established precedents for going this route ( ie; going all passive for twin-15 monitors ).

One only needs to study the products of WestLake Audio for that confirmation.

:)

PS; There's really no magic here ( especially with older JBL networks ).
- The active cards look to be either standard 12db/octave butterworth types ( or 18db BW as used in the newer 4344, 4345 & 4355 ).
- Those slopes superimposed on the natural response of the drivers result in the final acoustic response.
- There's no reason to think a passive 12BW filter ( designed around the drivers actual impedance & FR response ) won't give similar results.

http://www.audioheritage.org/vbullet...1&d=1058110102

The challenge will be attenuation of the 2202, 2440 and the 2405.

You may try Lpads.

The other issue will be the interactions of the 2202 motional impedance with the network and impact on the wooferresponse around 100 hertz. The 2022 voltage drive may not be ideal. The woofer low pass filter may exhibit passive gain around 100-150 hertz which is not ideal.

Bi amp is far more dynamic approach with better bass.