Altec 9844-8B

[89-300ce]

Thanks Earl,

I'll try it once I get an RTA set-up of my own so I can see what I'm doing. I'm curious though. Why do you recommend a 16 ohm lpad? The R1 fixed resistor in the Tpad is/was a 4 ohm and the variable R2 resistor in the M19 is a 0-32 ohm. An 8 ohm lpad seems to be a closer match to the Altec design, just the R1 resistor being variable as well.

Jorg

[Zilch]

I ran sims, and that kinda works. The shapes of the curves change somewhat as the values are adjusted, but not fatally.

With an 8-Ohm L-pad, you begin at 3 dB of compensation, and the midpoint is 6 dB, so the useful range is in the lowest settings.

With a 16-Ohm L-pad, the starting point is 6 dB.

Changing the fixed R to 8 Ohms with that gets 10 dB compensation at midpoint, and 15 dB max (all at 1.2 kHz,) which I consider a useful range.

I'd have to build it up and measure the reflected impedances; too tough for me and the calculator to figure.

Aside from its inherent symmetry, (you appreciate that the left side of the "T", your connection to terminal 3, varies from 8 (or 16) Ohms to zero Ohms (CW) depending upon the control setting,) I consider the original circuit to have the advantage of but one wiper contact when made adjustable, with the parallel leg of an L-pad easily serving as the adjustable R.

I am clueless as to how the reflected impedance of that varies with the setting, as well, and would have to measure. Note that Altec typically used this filter AFTER the main crossover attenuation L-pad, i.e., between that and the driver, providing an element of isolation as Earl recommends above.

And finally, this compensation filter should not be conceived or used as attenuation, which must be otherwise provided for balancing. Presumably, the amount and character of compensation should not vary with level, and once correctly established for a particular driver/horn combination, attenuation should be idependently adjusted for the desired balance with the woofer.

The Model 19 crossover does not operate this way, and worse, attenuation and compensation adjustments are interdependent. Hardly anybody gets how to use it, and it was widely ridiculed by pros who didn't understand it. Markwart apparently abandons M19's attenuation adjustment and uses compensation for level balancing.

For the truly gluttonous, here again is my M19 XO analysis:

http://audioheritage.org/vbulletin/s...26&#post128826

With respect to Skywave's project, I expect this is all academic; he's likely out of headroom with the compensation already provided in N800-F....

[MrT]

Hi Zilch

Just finished cloning n800f with the parts I already had in my hands. Turned on the music. Sounds good. Turned on my laptop and opened up the Lasing Heritage forum. What do I find? More options. I noticed that N800f has attenuation as you said they were 25ohm pot and 20ohm parallel to the LF. My question is does T filter goes before or after the attenuation or does it matter? I am confused.

Thanks

Tim

[Zilch]

I noticed that N800f has attenuation as you said they were 25ohm pot and 20ohm parallel to the LF. My question is does T filter goes before or after the attenuation or does it matter?

After's fine. I'd suggest you try what Skywave's doing, just the 6 uF with 8 Ohms in parallel, the combination in series with the HF driver. In your case, that provides 3 dB more compensation. If the HF no longer plays loud enough to balance with the LF, you're out of headroom.

The 8-Ohm version of that crossver, N800-8K, uses an L-pad for attenuation in lieu of the pot and fixed resistor. Use a 16-Ohm L-pad with N800-F as alternate for a 16-Ohm HF driver, or an 8-Ohm one with an 8-Ohm HF driver....

[MrT]

Will do!

For Zobel for 16ohm LF, am I doing the same thing as Skywave?

Thanks.

Tim

[Zilch]

Skywave's not doing Zobel yet, I don't think.

But for dual 16-Ohm 414s in parallel, what Earl said.

18 uF and 7.5 Ohms for starters.

8 Ohms's fine, too....

[MrT]

Ok. I will wait then.

Tim