Short version.
I'm trying to understand the mid section of the xover - NP L300.jpg
I'm also trying to work out the needed values for the bass section.
Long version.
I've rebuilt a pair of speakers and now need to redo the xover.
There a copy of the 4333, which is the 'pro' version of the L300.
As far as I can see, both use the exact same xover, the 3133, and pretty much the same drivers.
(Why one is classed as pro and other domestic I also don't understand, but meh, whatever)
Drivers I'm using are all JBL pro series.
2215B 16ohm 15" bass
2420 16ohm 1" compression mid with 2307 2308 horn/lens assy
2405 8ohm slot tweeter
8 cubic foot (227 liter) cabinets.
I have been using the crossover "3133 modified" as this was worked out by a gentleman on the lansing heritage forums as being a replacement for the original JBL crossover.
This has points of 800 and 8500
I want to replace these with NP's version (NP L300).
This has mid/woof at 700hz, and the tweeter is now a 6db at 15khz.
The L300 and 4333 all use 8ohm bass drivers crossed at 800, where as mine are 16ohm.
The zobel is designed as being the same for 8 and 16.
Apparently with the zobel the xover will 'see' the bass driver as a 10 ohm driver.
Those on the lansing forum also say that there is no difference in 8 or 16 diaphragms for the 2420 mid, and that they all measure at 10-12 ohms.
I'm having trouble understanding the following;
Entire mid section.
Purpose of the 8ohm series resistor in the mid section.
What values I should use in the bass section to get the 16ohm driver to xover at 700hz.
And lastly, what values for the zobel.
Thanks.......
I'm trying to understand the mid section of the xover - NP L300.jpg
I'm also trying to work out the needed values for the bass section.
Long version.
I've rebuilt a pair of speakers and now need to redo the xover.
There a copy of the 4333, which is the 'pro' version of the L300.
As far as I can see, both use the exact same xover, the 3133, and pretty much the same drivers.
(Why one is classed as pro and other domestic I also don't understand, but meh, whatever)
Drivers I'm using are all JBL pro series.
2215B 16ohm 15" bass
2420 16ohm 1" compression mid with 2307 2308 horn/lens assy
2405 8ohm slot tweeter
8 cubic foot (227 liter) cabinets.
I have been using the crossover "3133 modified" as this was worked out by a gentleman on the lansing heritage forums as being a replacement for the original JBL crossover.
This has points of 800 and 8500
I want to replace these with NP's version (NP L300).
This has mid/woof at 700hz, and the tweeter is now a 6db at 15khz.
The L300 and 4333 all use 8ohm bass drivers crossed at 800, where as mine are 16ohm.
The zobel is designed as being the same for 8 and 16.
Apparently with the zobel the xover will 'see' the bass driver as a 10 ohm driver.
Those on the lansing forum also say that there is no difference in 8 or 16 diaphragms for the 2420 mid, and that they all measure at 10-12 ohms.
I'm having trouble understanding the following;
Entire mid section.
Purpose of the 8ohm series resistor in the mid section.
What values I should use in the bass section to get the 16ohm driver to xover at 700hz.
And lastly, what values for the zobel.
Thanks.......
Attachments
Hi,
The 8ohm series resistor replicates the loss of the autotransformer
driving the the 8 ohm L-pad. There is a large difference in source
impedance between the two schema, and without extensive
modelling, which I'm not prepared to do, not knowing the
drivers, I can't really comment on the veracity of the schema.
Though I will note that C3 with R3/R4 and C4 give a fixed 8ohm
impedance to ground at high frequencies, and with the treble
unit guarantee a 4 ohm high frequency impedance, which is
in my considered opinion a very poor design arrangement.
However the original x/o does the same thing, I have
no idea why, its very bad use of valve amplifiers.
rgds, sreten.
The 8ohm series resistor replicates the loss of the autotransformer
driving the the 8 ohm L-pad. There is a large difference in source
impedance between the two schema, and without extensive
modelling, which I'm not prepared to do, not knowing the
drivers, I can't really comment on the veracity of the schema.
Though I will note that C3 with R3/R4 and C4 give a fixed 8ohm
impedance to ground at high frequencies, and with the treble
unit guarantee a 4 ohm high frequency impedance, which is
in my considered opinion a very poor design arrangement.
However the original x/o does the same thing, I have
no idea why, its very bad use of valve amplifiers.
rgds, sreten.
Last edited:
Pete, Ta.
And no I only have the jbl docs. see attached.
Streton, Also Ta
So your saying that neither would be 'safe' for valve amplifiers.
And neither is 'technically' better than the other.
I wonder if that 4ohm high freq loading is to help protect or smooth out the compression mid ?
Currently their driven with a PL J2 (25w rms class a transistor).
Ive also attached the Pass article on his rebuild.
*** All docs are freely available from all the authors, so no worries about copyright etc. ***
EDIT, that Nelson Pass pdf has some impedance graphs in it from memory. No idea if there of use ?
And no I only have the jbl docs. see attached.
Streton, Also Ta
So your saying that neither would be 'safe' for valve amplifiers.
And neither is 'technically' better than the other.
I wonder if that 4ohm high freq loading is to help protect or smooth out the compression mid ?
Currently their driven with a PL J2 (25w rms class a transistor).
Ive also attached the Pass article on his rebuild.
*** All docs are freely available from all the authors, so no worries about copyright etc. ***
EDIT, that Nelson Pass pdf has some impedance graphs in it from memory. No idea if there of use ?
Last edited:
Ta Pete.
I tried various online calcs, but unless I made the driver imp 5 ohms, i couldn't get them to line up with any of the values.
Other thing that bothers me is, shouldn't I work out the xover with the driver and zobel as as whole ?
Or does the zobel only affect the impedance at its tuned frequency (function of cap and resistor ?)
Yes, I know, I should really get the right impedance to work with before 'guessing' at things
I tried various online calcs, but unless I made the driver imp 5 ohms, i couldn't get them to line up with any of the values.
Other thing that bothers me is, shouldn't I work out the xover with the driver and zobel as as whole ?
Or does the zobel only affect the impedance at its tuned frequency (function of cap and resistor ?)
Yes, I know, I should really get the right impedance to work with before 'guessing' at things
What a nightmare! Redesign a crossover for two largely unknown drivers!
Well, it may not be too bad. It looks like the 2420 mid was always 16 ohms, so I think the mid and treble crossovers are unaffected.
We are now down to getting the bass crossover right. Replacing an 8 ohm 15" bass driver with the 16 ohm version.
How's it sounding at this point?
If I was going to guess, I'd say you double the coil and resistor in the bass section, and halve the capacitors, so that's 4.4mH, 20R and 10uF. That might be overdoing it a bit though. A 3.3mH coil and 15R and 12uF caps probably would be quite close too on a 3/2 ratio.
The level adjust on the other two drivers should get you out of jail. Modifying the crossover further is a bit of an ask, I'd stick with the JBL original.
Well, it may not be too bad. It looks like the 2420 mid was always 16 ohms, so I think the mid and treble crossovers are unaffected.
We are now down to getting the bass crossover right. Replacing an 8 ohm 15" bass driver with the 16 ohm version.
How's it sounding at this point?
If I was going to guess, I'd say you double the coil and resistor in the bass section, and halve the capacitors, so that's 4.4mH, 20R and 10uF. That might be overdoing it a bit though. A 3.3mH coil and 15R and 12uF caps probably would be quite close too on a 3/2 ratio.
The level adjust on the other two drivers should get you out of jail. Modifying the crossover further is a bit of an ask, I'd stick with the JBL original.
LOL.
yup. its my dads system thats hes had for 35 odd years.
he decided he wanted to replace the cabinets. was 140ltr, now 227ltr.
bass has changed dramatically (for the better).
so now i need to up the mid and tweeter levels.
but then i found Nelsons article.
currently the bass section has a zobel of 13.5uf and 10 ohm, with a 800 xover of 3.3mh and 12 uf.
so now the hunt begins to try and get the best possible i can out of them.
thats why im trying to relearn what ive forgotten about xovers, and hopefully not waste hundreds off dollars on unsatisfactory parts.
as for the sound, not to bad, bass mid area was a bit muddy, so i need to extend the ports, and raising the mid ~3db has helped greatly, now need to raise the tweeter maybe 2db.
But, before i go playing with all that, if nelsons is sonicly better, then id rather start with that, then waste time and money with the 'modified' version of the original.
so yes, im trying to get one xover out of two, or possibly even more..
yup. its my dads system thats hes had for 35 odd years.
he decided he wanted to replace the cabinets. was 140ltr, now 227ltr.
bass has changed dramatically (for the better).
so now i need to up the mid and tweeter levels.
but then i found Nelsons article.
currently the bass section has a zobel of 13.5uf and 10 ohm, with a 800 xover of 3.3mh and 12 uf.
so now the hunt begins to try and get the best possible i can out of them.
thats why im trying to relearn what ive forgotten about xovers, and hopefully not waste hundreds off dollars on unsatisfactory parts.
as for the sound, not to bad, bass mid area was a bit muddy, so i need to extend the ports, and raising the mid ~3db has helped greatly, now need to raise the tweeter maybe 2db.
But, before i go playing with all that, if nelsons is sonicly better, then id rather start with that, then waste time and money with the 'modified' version of the original.
so yes, im trying to get one xover out of two, or possibly even more..
Ah right. Different cabinet too...everybody wants more bass...
What I can tell you is the formula for a 8R to 16R bass conversion works reasonably well, albeit the 16R driver will be a tidge less sensitive. Maybe 1-2dB down. As it stands, the 16R driver will sound overly bright on the 2.2mH 8R bass filter, the bafflestep is underdone, you see.
Speaker cabinet tuning parameters of Vas and Qts probably aren't much different either with 8 or 16 ohms.
I think you need to remember the KISS principle here. Keep it simple and change as little as possible. You don't have the resources of Nelson Pass or JBL. I can't speak for the other monkeys on the internet, who may or may not know what they are doing here.
What I can tell you is the formula for a 8R to 16R bass conversion works reasonably well, albeit the 16R driver will be a tidge less sensitive. Maybe 1-2dB down. As it stands, the 16R driver will sound overly bright on the 2.2mH 8R bass filter, the bafflestep is underdone, you see.
Speaker cabinet tuning parameters of Vas and Qts probably aren't much different either with 8 or 16 ohms.
I think you need to remember the KISS principle here. Keep it simple and change as little as possible. You don't have the resources of Nelson Pass or JBL. I can't speak for the other monkeys on the internet, who may or may not know what they are doing here.
Last edited:
These 2215's are quoted as being best in a "6-8 cu foot"
so dad being dad, said, "I want 8cu ft".
The old cabs were obviously strangling the hell out of the bass.
There really is that much difference its not funny.
So far it sounds like i should try Nelson's version for mid and tweeter, keeping the current bass section.
Then play from there.
Guess ill go and order some parts now and see how it goes..
Thanks to all, i'll let ya know how it goes....
so dad being dad, said, "I want 8cu ft".
The old cabs were obviously strangling the hell out of the bass.
There really is that much difference its not funny.
So far it sounds like i should try Nelson's version for mid and tweeter, keeping the current bass section.
Then play from there.
Guess ill go and order some parts now and see how it goes..
Thanks to all, i'll let ya know how it goes....
ok, hang on a sec..
the current xover, that is in use, for the bass, has a zobel of 13.5uf and 10 ohm.
and a xover of 3.3mh and 12uf.
I've just checked the dc resistance of the bass driver as being 12 ohms.
so that means a zobel of 15ohms and ? around 13uf (assuming an Le of .0008 - which is guess work as i dont have that figure)
isnt that what you suggested back a few posts ?
or have i misread your post ?
EDIT, so im planning on changing the resistor from 10 ohm to 15 ohm..
the current xover, that is in use, for the bass, has a zobel of 13.5uf and 10 ohm.
and a xover of 3.3mh and 12uf.
I've just checked the dc resistance of the bass driver as being 12 ohms.
so that means a zobel of 15ohms and ? around 13uf (assuming an Le of .0008 - which is guess work as i dont have that figure)
isnt that what you suggested back a few posts ?
or have i misread your post ?
EDIT, so im planning on changing the resistor from 10 ohm to 15 ohm..
Hi,
Good plan though the new bass section only needs
two new caps which you should be replacing cheaply
anyway, re-using the inductor and resistor.
FWIW the NP version has much better treble impedance.
rgds, sreten.
Just been reading up on zobels.
even found some previous posts by Streten.
If I understand the function and effect of a zobel correctly, the only real effect its going to have for me, is reducing the bass drivers sensitivity.
The effect on the amplifier and frequency response will be zero as I'm using a 'modern' transistor amp.
Theoretically I'm thinking I can delete the zobel, and just fine tune the actual xover point.
Yes No ?
even found some previous posts by Streten.
If I understand the function and effect of a zobel correctly, the only real effect its going to have for me, is reducing the bass drivers sensitivity.
The effect on the amplifier and frequency response will be zero as I'm using a 'modern' transistor amp.
Theoretically I'm thinking I can delete the zobel, and just fine tune the actual xover point.
Yes No ?
Hi,
In this case no. The redesign is more trouble than its
worth and you don't understand when and when not
a zobel should be used or could be omitted.
It is not true here it has no effect with a modern amplifier.
Your best bet is to follow N.P.'s update, and replace
the bass 20uF originals with new cheap 22uF NP's.
(It will then be the same as updated effectively.)
Understand the point of N.P.'s update is to make
the speakers better with low powered amplifiers,
at the cost of reducing maximum power handling.
rgds, sreten.
Your lucky in that someone like Nelson Pass has
spent a lot of time on the issue, and consequently
it is the only approach available worth considering.
Last edited:
Alrighty, I'll take your word for it.
Primarily as I suspect you might have just a little bit more experience and knowledge than me.
Sooooooo, that has me thinking, considering im using a 16ohm vs his 8ohm, should i change the zobel from 10ohm/22uf to a new 15ohm/12uf ?
I did measure the driver last night, out of circuit it measures 12ohms.
or is the different impedance of no real importance ?
Lower power handling wont be an issue, even with his 25w class a, they produce massive volume without effort.
Primarily as I suspect you might have just a little bit more experience and knowledge than me.
Sooooooo, that has me thinking, considering im using a 16ohm vs his 8ohm, should i change the zobel from 10ohm/22uf to a new 15ohm/12uf ?
I did measure the driver last night, out of circuit it measures 12ohms.
or is the different impedance of no real importance ?
Lower power handling wont be an issue, even with his 25w class a, they produce massive volume without effort.
yes, its all a bit of a head f... hence my struggle to work this out.
Both the L300, and the 4333, use the same xover, the 3133.
that xover is drawn up as suiting two different bass, two different mids, and two different tweeters... just to really confuse things
The bass drivers for the L300 and 4333, are rated as 8 ohm. the 3133 xover specs the bass driver as 8ohm as well.
The drivers I am actually using;
The bass driver I'm using is a 2215h which is 'rated' as 16ohms. (measures as 12ohm dc resistance)
the midrange is available as a 8 and 16, BUT, experts etc have said they are the exact same diaphram and they both measure as 10-12 ohms.
the tweeter in all cases is 8 ohm.
EDIT, so to directly answer your question.
The non original driver is the bass driver, and mine is a 16ohm version. its also a different model to whats used in the L300 and 4333......
Are we having fun yet ?
Both the L300, and the 4333, use the same xover, the 3133.
that xover is drawn up as suiting two different bass, two different mids, and two different tweeters... just to really confuse things
The bass drivers for the L300 and 4333, are rated as 8 ohm. the 3133 xover specs the bass driver as 8ohm as well.
The drivers I am actually using;
The bass driver I'm using is a 2215h which is 'rated' as 16ohms. (measures as 12ohm dc resistance)
the midrange is available as a 8 and 16, BUT, experts etc have said they are the exact same diaphram and they both measure as 10-12 ohms.
the tweeter in all cases is 8 ohm.
EDIT, so to directly answer your question.
The non original driver is the bass driver, and mine is a 16ohm version. its also a different model to whats used in the L300 and 4333......
Are we having fun yet ?
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.