Help with surround driver choices

[Zilch]

But Zilch I do not understand : " note how one of the 2118's is a LF helper like in 4435 "

One of the two 2118J's has a 1.2 mH inductor in series with it in the crossover. I believe that's a 6 dB/octave low pass filter at about 1500 Hz, depending upon the actual driver impedance at the design frequency. Apparently, a single 2118J has sufficient output in the upper midrange, but two are required for good balance below that frequency.

I have a pair of them here, and I wouldn't hesitate to use them as mains, even.

A single 2118H was used as midrange between 2404 and E145 in 4628(B), another one of my favorite systems.

See also http://www.jblsynthesis.com/products...=US&Region=USA

[stevem]

Can the 2012's get low enough for them to be used??? =Rob

Unfortunately the 2012H in a sealed enclosure starts to roll off about 500Hz (I think). It is about 4-6 db down at the crossover frequency, and I have to use a bit of EQ to flatten it. I'm about to build ported enclosures that should flatten it to 100hz or so, and I am hoping this will not have an adverse effect on the transient response. To answer your question, I don't think the 2012H would be suitable for use as the LF driver in the center speaker.

[pentictonklaus]

One of the two 2118J's has a 1.2 mH inductor in series with it in the crossover. I believe that's a 6 dB/octave low pass filter at about G&Language=ENG&Country=US&Region=USA

Thank you very much. I finally get it now. I had totally neglected my math on crossovers and filters since I run everything active, which is no replacement for the school of the old masters. Keep up the good work.

[Zilch]

I run everything active....

Run them active in parallel with that inductor in there on one of them.

[pentictonklaus]

Run them active in parallel with that inductor in there on one of them.

I have done some calculations for the fun of it :

16 Ohm cut off at 2100 hz = 1.213 mH
8 Ohm " " " " " = 0.606 mH
16 Ohm " " " 1500 hz = 1.698 mH

8 Ohm high pass at 3 khz = 6.631 uF

That's all for 6db 1st order

Thank's again Zilch for your input.