jbl sr4735 questions

garynb

looking to set up the following system with a driverack pa.
jbl sr4735
ev t-18 subs

my main questions r, do i need any delay between subs and 4735's.
i have heard about the phase of the 8" driver of the 4735. can someone explain this to me. jbl says u need to invert the driver. need explanation.. can anybody help with this system. thank u Gary.
these r the original 4735, not the a, or x series.

Dennis

garynb wrote:

looking to set up the following system with a driverack pa.
jbl sr4735
ev t-18 subs

my main questions r, do i need any delay between subs and 4735's.
i have heard about the phase of the 8" driver of the 4735. can someone explain this to me. jbl says u need to invert the driver. need explanation.. can anybody help with this system. thank u Gary.
these r the original 4735, not the a, or x series.

Yes, you probably need delay on the sub. I'm not sure what the necessary amount of delay would be without measuring it.

There can be various reasons for inverting polarity between components in a speaker cabinet. Polarity has a different meaning than phase...the words are not interchangeable so what you meant to say was "I have heard about the polarity of the 8" driver of the 4735". As an example, if the crossover point between 2 components was comprised of 2nd order (12dB per octave slope) filters on both the low-pass and high-pass, the two components will automatically end up 180* out of phase with each other...it's the nature of 2nd order filters. Reverse the polarity on either component and the two of them will be in phase.

That is one reason for inverted polarity between components in a box. Don't fight it...don't fix it. It was designed that way.

Dennis

Gadget

I believe that driver is reverse wound.. I looked to see if I could find the document but ran out of time today... that is to say, JBL reverse wound some of their older drivers so that unlike most drivers, with a 9 volt battery and the '+' on the battery to '+' on the speaker and the 2 minus terminals hooked together as well, the speaker cone would move INWARD instead of outward as most speakers (even the new JBL speakers).

I would think you might want to delay the TOPS since the T18's are a "turbo" design that takes a tiny bit of time to get out. That and there is a 7.5 second propagation delay in the driverack (at least for the LR24 filter). I have the LABsubs and they have a 10.5 foot horn and I ended up delaying the tops about 18.2 ms.

The T18's however have a very tiny delay by comparison, similar to the EV S-181's which I have and I don't think are more then 4-5ms +propagation delay.. I think I use 8.5 -9ms total.

Gadget

garynb

Ok did some research.. jbl says use the tunings for the 4735x.
i would be triamping the system SO.....
the tunings say output 3-4 should be "INV" which is inverted polarity. this would be the 15" woofer correct??

1-2 would be subs
3-4 low mid 15"
5-6 mid high

the driverack pa "understanding the driverack" manual says the signal cable should have pins 2-3 swapped if any of the tunings call for an inverted polarity.

should i leave it alone or make a cable with pins 2-3 swapped?? what would u do?

Thanks for the help. Gary

Gadget

As I understand it the SR4735 is a three way design, but the 1/4" inputs have the 8" and horn on the hf input and the 15" is on the low input. So, if you are going to use the 1/4" ins you will either have to reverse the pins 2 and 3 on the cable from the DRPA to the amp, or the speaker cable from the amp to the speaker OR better yet make up a jack panel for the back of the amp rack and reverse the polarity to the jack plate so no "movable" cables will have to be modified and marked VERY WELL..
G
P.S. I'd put Speakon connectors in those cabs and be done with it... If you need a schematic ..let me know..

Dennis

Yup...what Gadget said. The BUT 12 filters that JBL calls for on the sub/mid xo point leave you no choice but to invert the signal going to the 15".

Dennis

Gadget

12 filters? :shock: :shock: :shock: Dennis, perhaps you could be a bit more specific in your post.. are you saying that the reverse wound ( I just added an FAQ from JBL regarding the issue of black terminal + versus red terminal + and it appears the 2226H is right in the middle of the reverse wound cone speaker list..) 2226H should be reversed again... like red to positive?
Sorry not very clear to this old fart..
G

Dennis

First of all, define "reverse wound"...as far as I knew, the only thing reversed was the color on the terminals and that was a long time ago. I have never seen a reversed 2226 but to be fair most of the 2226s I have owned or worked on have been 2226G (4 Ohm). This is what was used in the SR Series so this whole "reverse" conversation does not apply here.

As far as 2nd order filters go, the following explanation might be completely backward but the outcome is the same either way. A 2nd order hi-pass filter will result in a +90* phase shift and a 2nd order lo-pass filter will result in a -90* phase shift. This will put the two components being crossed over at 180* out of phase from each other. Reverse the polarity of either component and they are back in phase with each other.

Dennis

Gadget

Very good, thanks. JBL used the BLACK terminal to indicate positive (going counter to the rest of the industry) until the release of this:

As of a few years ago, JBL Professional began manufacturing transducers with the IEC standard of positive to red.

I think JBL thought their standard would prevail. I have to assume that they were predicting the need to reverse the polarity between woofer and horn, and not wanting to have to answer a bunch of questions, and polarized the woofers opposite the current horn drivers.

Look for a regression in the JBL product. It has ceased production in the USA and has moved ALL of it's manufacturing facilities to China. Suffice it to say...JBL will NOT be able to respond quickly to a crisis, and the quality will be suspect... until proven otherwise. 8)
G

Dennis

I remember the reverse color thing but it was well back into the 80s...By the early 90s I think they had pretty much turned it around.

All JBL has to do is keep their bills paid up with the Chinamen and they should be able to respond to a crisis a lot quicker than another set of companies that we are all familiar with.

Dennis

garynb

Thank you gentleman for your response.. That is what i was looking for.

Gary

garynb

Gadget, Yes i would like the schematics and a parts list for the conversion to speakon.

Thanks, Gary

Gadget

Problem here is if you take out the 1/4" jacks you won't have fullrange capability any more. First off, I need to know if you would ever want to use the fullrange capability... If yes, you would need to (interrupt the paths trough the HPF and LPF of the onboard crossover by inserting ... plugging in, a 1/4" jack in the Hi and low inputs of the speaker cab... no wires, just 1/4" male jacks to interrupt the signal path) hook the NL4 connectors to the 1/4" jacks on pins 2 and 6 of the HF input, and pins 2 and 6 of the LF jack and you would need to put a 1/4" jack ... if this doesn't seem silly, or you wish to only have the speakers be bi-amp I can provide you with a schematic...
G

garynb

i will be running them fullrange for small events so thatprobly wont work. thank you for your time