Help with figuring port sizes.

[Zilch]

Geometry is a bit different from Hamilton's MTM setup.

I'm thinking NL200t3 is fine.

Maybe move the LF rolloff up a bit?

Lettin' the LF play full range will interfere clear up to 10 kHz. Not good, right?

Suggestions, please....

[Hamilton]

Hey Zilch, yep, you are getting a flatter response than I, here are some RTAs (2426/2342/2118J) :

1. Stock nL200t3
2. nL200t3 - LF 2mH, 6uF, reverse polarity on 2426
3. nL200t3 - LF 1mH, 1uF, reverse polarity
4. nL200t3 - LF 1mH, 2uF, standard polarity *

I ran one more test using the nL200t3 with no LF, the RTA was near identical to #4, but sonically it was too bitey in the upper mids.

*sounds best to my ears.

[Zilch]

Your #2 looks best to me, actually. I suspect that notch at 800 Hz is the reversed polarity on the 2426H. Try it with normal polarity.

Listening is the final test, of course, but we want to be selective in terms of the final intended use. This is a HT center channel. It's gotta be voiced properly for dialog. Using music may not be the best test.

I suggest we move the LF rolloff up somewhat as you have done, but keeping the filter slope similar (right curve, below). Use 2.0 mH for L1 and 10 uF for C2. R1 should be 20 Ohms to take the "bite" out of the HF via attenuation. This combination of drivers seems generally well balanced with respect to overall output levels.

I'm opposed to just letting the paired 2118's play full range, no matter how good the RTA looks. This MTM (Mid-Tweet-Mid) already has two drivers (the 2118's) playing the same program material, but the geometry is optimized to use that to advantage, providing a wide sound field at the center with minimal phase conflict. Letting the woofs play well into the 2426H's upper mid- and high-frequency range will generate unwanted phase cancellations up there. Bad practice for home listening, I'd say....

May we see a pic of your cabinet, please?

[johnaec]

I suggest we move the LF rolloff up somewhat as you have done, but keeping the filter slope similar (right curve, below).

Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that??

John

[Hamilton]

Here's a pic of the unpainted center cab with crossover parts scattered all across the top. The width of it is 60", the internal speaker cab is 1.2 cu ft, 3" ports 4" long.

[Hamilton]

Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that??

John

[Zilch]

UT, oh!

Izzat a B380 I spy on the left there?

["This ain' no foolin' around...."]

[Zilch]

Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that??

Well, I DID have the HF shown there, but took it out so's not to surprise you, John....

Actually, that's how I made sure the slopes were ROUGHLY parallel....