Homebrew 4343

[4313B]

I don't expect it to match JBL since I do not have an anocheic chamber so I think it looks decent with no equalization.

JBL measured the 4343 on its back flush with the ground facing up into the sky so don't fret.

[Bill Shenefelt]

Bill,
If you want to to keep the vertical array and the other cards still dont help the falling response you can try and modify the low pass passive filter on the 2121. The problem with actively boosting the low end of the 2121 toio much is it will stress the amps dynamic headroom and the Xmax of the 2121. Just to show you how clever I really am...Muhhahaha the third graph shows the modelled effect of increasing the 1.7 mH inductor in increments of 1.9 mH, 2.15 mH and 2.38 mH. This has the effect of taming the rising response on the 2121 driver. This is simple enough to try by adding a few turns to the inductor (if you have an inductance meter) and doing some measurements with Smart Live to confirm what actually happens. You will of course need to need to modify the gain of the HF amp and adjust the mid, horn and slot levels to shelve the response overall.

The Doctor.

Is the 1.7 just a very slow slope to minimize the responce rise or is it part of the crossover at 300, or a phase thing? Should it be there at all with the active xover present? I'm using the JBL 1.7 mH so I cannot increase turns easily unless I just buy a bigger one and remove turns. I do have a meter for inducatnce now and an ohm meter capable of 0.001 ohm readout so that is not a problem. I really do not run it that hard so I doubt x max is a problem, especially with the 24/0ctave active. .

[Earl K]

Is the 1.7 just a very slow slope to minimize the responce rise or is it part of the crossover at 300, or a phase thing? Should it be there at all with the active xover present? I'm using the JBL 1.7 mH so I cannot increase turns easily unless I just buy a bigger one and remove turns. I do have a meter for inducatnce now and an ohm meter capable of 0.001 ohm readout so that is not a problem. I really do not run it that hard so I doubt x max is a problem, especially with the 24/0ctave active. .

- The 1.7 mH series coil together with the 20 uF conjugate capacitor, form a resonant 2-pole lowpass ( with an eventual slope of 12 db per octave ) on the 2121.
- It's essentially a 2-pole bump filter / that before it achieves the 12 db/octave lowpass / first "boosts" a selective range of frequencies .
- ie ; It is a significant contributor to the "rise" that you see in the 2121 .
- This midrange "boost" is quite apparent in the following "simmed" voltage drive ( courtesy of Giskard ).
- This extra bit of boost consistently shows up in your posted FR snap-shots ( & once you level the top to the surrounding topography you are left with a "hole" below the knowle ).
- At some point, you'll need to ask yourself if you want to keep this midrange rise on your 2121 / or / flatten it all out, by implemeting a different lowpass on that 10" ( by using a different LC design as IanM has started to work out for you ) .



- It's the green graph that represents the N3143 voltage drive . This was mentioned previously here !

[Ian Mackenzie]

Attachment 24774This is with the microphone on the floor rug as suggested by Ian.

Its not quite that simple. There are references on the www regards ground plan measurements.

Overall your plots are reasonable (for what we are dealing with)

Adjust the L pads over a period of weeks and see how you go.

I would not turn into a curve junky (tweaking) without doing a lot more listening on a variety of program material at this point. (Modification if the stock network is ill advised unless you are detouring off the road map...because you have an odd ball active filter at the moment I would leave as it.)

[4313B]

Yes, basically the L-Pads were kind of a bad idea. They've managed to cause alot of end users considerable angst over the years. They don't behave like perfect level controls and they shift crossover frequencies arbitrarily. The 250Ti is a classic example of going to the significant expense of proper shelving that has carried through in various systems right up to the Everest II. Where the 250Ti has a rather large range of shelving available the Everest II is quite subtle.