Homebrew 4343

[Bill Shenefelt]

It would not be a big thing to add some internal volume to the box if that in some way would help the transient response which is a concern I have. I can saw a 9 inch by 9 inch hole in the internal back and put a couple of 6 inch spacers and a new back expanding to near the 1000 cubic inches that way. Just do not want to bother if it does nothing for me. Costs no $ but a new box with new verneer wood, glue and all would be one to two hundred bucks I think.

[Robh3606]

Hello Bill

The 4343 internal volume is .5 cubic ft net so that's what you need. You don't need to add the driver volume to the .5 cubic ft. That means the driver is working into about .4 plus what ever virtual volume is added by the fiberglass.

Rob

[Earl K]

Hi Bill

I am only using the low pass part (1200 down) of the 2121 JBL passive crossover and using the Marchand at the 300 cps

- Please confirm; that you included ( or not ) within the bandpass portion of the circuit for the 2121H , the 16 ohm variable Lpad, as well the "T" pad ( which is comprised of a 2R series resistor followed by a 30R shunt resistor followed by another 2R series resistor ).

- Assuming that you did include this 16 ohm variable Lpad, where is it usually set, ( within its' relative rotation of; full CW & full CCW) ?

- The 52 uF cap ( 56 uF in some later systems ) and the 2.8 mH coil appear to form a fairly resonant 2 pole high pass. FWIW; These 2 poles have swapped ( inverted ) their usual relative positions to each other. This inversion is in the "classical" sense of what most of us are used to seeing ( ie; large coil & small cap / this circuit uses ; large cap & small coil ) . This inversion will dramatically effect the damping of the filter.
- A quick guesstimate of some working AC impedances suggests that this filter is fairly resonant ( higher Q or lower damping than is typical ) in the 300 to 400 hz area. This "resonance" looks to actually give a bit a lower midrange response boost. This would make sense considering the very low total "Q" of this driver ( 2121H )
- As a result , I would include these 2 passive elements in the bandpass circuit for your 10" (or else have Marchand design a custom card for use in your XM-44 crossover by recreating the transfer function of these 2 omitted passive elements ) .

- It would be handy if someone with the LEAP crossover software ( or a decent Spice program ) would figure out what is really going on in this part of the 3143 network . I see a fairly resonant circuit / but then I don't have this actual 10" to test / plus I have no SPICE program / just a calculator and some formulas .

so I guess I should let the box alone unless (or until) I later build a brand new box to replace the widened baffle?

- I blew up the photos of your old avatar , as well as your new one.
- From these 2 very grainy photos , it looks to me that your 2121H is housed in a "ported" 1.0 to 1.5 cu' enclosure .
- Am I just seeing things that don't exist / or ???
- Do you really have a .5 cu' doghouse there ( maybe it's created by a partition ) ?

Anyways, moving forwards ;
- Increase the size of the baffle board as has been discussed / as well as recreate the orginal component spacing as has been discussed . They won't fix all the problems that have resulted from your deviation from JBLs' original design / but they are a step in the right direction .
- Then do something about including the 2 missing passive elements in your crossover .

[Bill Shenefelt]

[quote=Earl K;160276]Hi Bill



- Please confirm; that you included ( or not ) within the bandpass portion of the circuit for the 2121H , the 16 ohm variable Lpad, as well the "T" pad ( which is comprised of a 2R series resistor followed by a 30R shunt resistor followed by another 2R series resistor ).
YES

- Assuming that you did include this 16 ohm variable Lpad, where is it usually set, ( within the relative rotation of ; full on & full off ) ?
Midpoint to slightly higher, say "2 oclock"

- The 52 uF cap ( 56 uF in some later systems ) and the 2.8 mH coil appear to form a fairly resonant 2 pole high pass. FWIW; These 2 poles have swapped ( inverted ) their usual relative positions to each other. This inversion is in the "classical" sense of what most of us are used to seeing ( ie; large coil & small cap / this circuit uses ; large cap & small coil ) . This inversion will dramatically effect the damping of the filter.
- A quick guesstimate of some working AC impedances suggests that this filter is fairly resonant ( higher Q or lower damping than is typical ) in the 300 to 400 hz area. This "resonance" looks to actually give a bit a lower midrange response boost. This would make sense considering the very low total "Q" of this driver ( 2121H )
- As a result , I would include these 2 passive elements in the bandpass circuit for your 10" (or else have Marchand design a custom card for use in your XM-44 crossover by recreating the transfer function of these 2 omitted passive elements ) .
I could give the 15 inch a 400 cps crossover and keep the 10 inch at 300 as a means of boost there maybe

- It would be handy if someone with the LEAP crossover software ( or a decent Spice program ) would figure out what is really going on in this part of the 3143 network . I see a fairly resonant circuit / but then I don't have this actual 10" to test / plus I have no SPICE program / just a calculator and some formulas .



- I blew up the photos of your old avatar , as well as your new one.
- From these 2 very grainy photos , it looks to me that your 2121H is housed in a "ported" 1.0 to 1.5 cu' enclosure .
NO it is sealed and about 1/4 cuic ft.
http://www.sheneskillies.com/speakers/frontview.jpg
The box itself is about 16 inches deep to sit on top of the bass enxlousre but there is a rear face of the doghouse installed about 6 inches back from the front baffle limiting the size to 1/4 cu ft.
- Am I just seeing things that don't exist / or ???
- Do you really have a .5 cu' doghouse there ( maybe it's created by a partition ) ? Yes

Anyways, moving forwards ;
- Increase the size of the baffle board as has been discussed / as well as recreate the orginal component spacing as has been discussed . They won't fix all the problems that have resulted from your deviation from JBLs' original design / but they are a step in the right direction .
- Then do something about including the 2 missing passive elements in your crossover .
What do I do bypass them inserting the signal between the 52uF cap and the 1.7 ohm inductor? I will be feeding the highpass of the Marchand. Somehow I don't think using the 12/0ctave JBL active for biamp does that since they switch out the big inductor and cap. Also since it is a general active not specifically tayiored for eht 4343 I doubet they do anything unusual.

[Earl K]

What do I do bypass them inserting the signal between the 52uF cap and the 1.7 ohm inductor? I will be feeding the highpass of the Marchand.

- As I suggested, feed the eletronically crossed over signal into a Hipass section that would now include either a 52 or 56 uF cap, and 2.8 mH coil // or // have Marchand build the equivalent 2-pole HP with the proper "Q" and omit these 2 passive elements ( the 52 uF cap & 2.8 mH coil ) .

Somehow I don't think using the 12/0ctave JBL active for biamp does that since they switch out the big inductor and cap. Also since it is a general active not specifically tayiored for eht 4343 I doubet they do anything unusual.

- Doubt if you must, but ;

- Typically JBL "did fiddle" with the Q in the custom electronic filter cards that JBL sold for specific Studio Monitors ( these cards were specified for use in their 5234/5 crossovers ) .

- Even the Everest II ( DD66000 ) recommends a fairly high Q for the HiPass filter / when biAmping with an external crossover .
- Look at the included .jpg to see just what EQ ( & group delay ) JBL is adding to the horn circuit .

- FWIW ; the pictured voltage drives for the horn circuit in the Everest II, are a result of inverted relative positions for the 2 poles within the passives' High Pass Filter ( similar to what is found in midbass portion of the N3143, ie; large cap, small coil ) .


*

[Bill Shenefelt]

-
- Typically JBL "did fiddle" with the Q in the custom electronic filter cards that JBL sold for specific Studio Monitors ( these cards were specified for use in their 5234/5 crossovers ) .


*

Thanks for the additional information. What I can do is increase my baffle, stuff the enclosure and try the current crossover with the active and no 52 cap network parts and look at what I get in the room using a little 1/3 octave RTA I have. I know that Marchand can provide secondary cards for " baffle step compensation, notch/boost filters, delay sections and bass boost filter (Linkwitz transform)". In addition the cards are independant for high and low pass slopes and filters. Once I see what the response looks like I could check with him to see what might be best. Thinking about it when I first got the 10 inch drivers I bought "the JBL crossover card" for their active crossover which was to be used in the 2121 high pass network. It was a single card with a 12dB/octave slope but I did not know it ahd some other factors built into it. Also maybe some others on the Forum that have done the biamp that know what additional features the card must possess. I don't want to add the big cap and inductor since that is what everyone on the forum discussing the 4343 wants to remove by the biamp setup since it also impacts the higher drivers as they are in its circuit also. Thanks for the info.

[Earl K]

I could give the 15 inch a 400 cps crossover and keep the 10 inch at 300 as a means of boost there maybe.

- Yes, you should try that out scenario. Give it a listen & Post your impressions .
- This won't be the same as using a HP filter that has the same Q as the original passive / but it's certainly worth a listen. It may get you close enough to a pleasing result, to call it a day .
- I'd also recommend measuring this scenario with your RTA for future reference .

( If using 24 db, 4-pole network cards , start out by wiring the woofer and 10" midrange with identical polarities / this should offer the best summing throughout the crossover region )

[Earl K]

I don't want to add the big cap and inductor since that is what everyone on the forum discussing the 4343 wants to remove by the biamp setup since it also impacts the higher drivers as they are in its circuit also.

- Yes, I can understand that sentiment / plus / the cost of passive componets at these sizes is quite a bit more than another 2, XM44 crossover cards .
- Still the problem remains, that the 4343 network ( & 2121H ) was designed to offer more than just simple crossover filtering . My quick analysis indicates that the high Q of the HP on the 10" is there by design. High Q also equates to more group delay in a filter. Group Delay is just like it sounds / a select area of frequencies are delayed ( due to the resonant nature of the filter ). Delaying the 10" ( in the crossover region ) relative to the horn circuit ( and maybe the woofer ) is likely a good thing .

- FWIW: You could add these 2 passives to just that portion of the network fltering the 10" midbass . This approach will maintain your existing design deviation ( which you're apparently enjoying ) and still remain true to the original design objectives of the network ( somewhat an assumption on my part ) .

- If I was a paying customer of Marchand Electronics ( like you ) I would email the principal ( Phil ?? ) and ask if he will design a custom set of 4343b cards for your XM44 crossover to work with the your fourways . Provide him with the N3143 schematic / some specific load impedance info, / & / he should be able to design a pair of 2 pole cards that recreate the same electrical transfer functions ( as found in the N3143 ). He may also be able to approximate those transfer functions into 4 pole network cards. That would be a real bonus if you could maintain absolute polarities . You'll likely need to offer to pay for his design time ..

[Robh3606]

Why JBL put in the 52uf cap in series with the HF and UHF

About the 52uf capacitors I have sent and email to a higher level for qualification. From both the technical and historical viewpoint we really need to have this correctly documented on the Forums.

Apparently the 52 uF capacitor was used as protection if the system were to be switched to Bi-Amp as amplifiers from that day made a turn-on transient that could damage the compression driver diaphragms. In more recent times amps are well enough behaved that that part is no longer necessary.

Ian

Rob

[Earl K]

- Rob, why don't you fire up your LEAP software package and help out here ?

- Will LEAP tell you the "Q" of the resulting filter ( when one combines a 52 uF cap with a 2.8 mH coil ) ?
- Will LEAP tell you the resulting Group Delay ( in ms ) for the range of affected frequencies within the crossover region ?
- FWIW ; I use 12.5 ohms ( or vary 12R to 13R ) as the combined load impedance ( of 2121H driver & the 16 ohm Lpad & that T-pad in place ).

[Earl K]

- Bill, if you closely read the underlined section you'll see it has some applicability to your initial observations & complaints .

- Your XM44 filters are likely the same transform as the quoted info for the XM1 .

- As such, I would be giving standard 24db, 4-pole Butterworth filters an audition. A pair of these HP Butterworth filters should be a no brainer for Marchand to make up. ( Butterworth filters have probably the best power transfer throughout the crossosver region / though they have their well publized drawbacks ).

- Picking a filter type is a lot like choosing your poison .

[Robh3606]

Hello Earl

Will it tell the Q??? Don't know at this point in the game. Simply not enough experience with it. Looking at it quickly I don't think it will however it will easilly give you Group Delay. Here's a quick look at those components with a 12.5 load.

Rob

[Earl K]

Thanks Rob !

- Though ( thinking outloud ) without the LP portion included into a full band-pass FR / I'm sure the overall idea one gets ( of resonant boost, in relative db ) is a bit skewed .

[Robh3606]

Though ( thinking outloud ) without the LP portion included into a full band-pass FR / I'm sure the overall idea one gets ( of resonant boost, in relative db ) is a bit skewed .

I think you are right. If I get a chance latter I will load up the LF portion with a resistive load sum them and see.

Rob

[Bill Shenefelt]

I think you are right. If I get a chance latter I will load up the LF portion with a resistive load sum them and see.

Rob

This is getting very interesting but a bit beyond me. Once I see what comes out, I will forward whatever you guys can recommend for him to make to Marchand to get some cards. In the interim I will reinstall the drivers on tuesday (in the existing 0.25 box with the baffle extensions) On Tuesday when the RCL meter arrives I can re size the 0.25mH coil (now a 0.27 of unknown match in resistance to my unknown resistance JBL iron cores) in the assembled passive and try the 300/300 and 300/400 active card combinations and take some photos of the RTA readings of each and post them.