Altec 9844-8B

[Zilch]

The Markwart crossover(s), as example, set the VHF at max and adjust the balance by increasing or reducing the amount of compensation.

I don't believe you have enough headroom to do the Patten HF boost.

Build the "T" filter using tabs 1 and 2 of your 8-Ohm L-pads for the adjustable resistor, and use that to balance your lows and highs. Tweak your Zobel for the smoothest response through the crossover region.

With that, I think you're done until you go active....

[MrT]

Hi Zilch

That sounds awesome to me. I heard T sounds better than L-pad. So I will do. That's the same scheme we see in model 19 hf section. Correct?

Would you draw T filter schematic for 806As using 8ohm L pads, the values of the resistors, etc? I would really appreciate that.

414 sounds much better! That's for sure.

Thanks Zilch. This has been my first project. A lot of people helped me. I thank them all.

Over and out for now.

Tim

[Zilch]

The T-filter is shown in this post at the top:

http://audioheritage.org/vbulletin/s...9&postcount=48

Substitute L-pad terminals 1 and 2 plus a 2-Ohm resistor in series for R2 to replicate the adjustable Model 19 version. 3.9 Ohms is not available from Parts Express in either Mills or Dayton, so use 4 Ohms. 6.2 uF is fine for C1, or a pair of 3.0 in parallel if you want to be spot on.

The contours generated by this filter are slightly different from those of a simple resistor and capacitor in parallel. I think the T-filter is better for your application....

[MrT]

Thanks Zilch. I am going to finish it this weekend.

Tim

[DonM]

The T-filter is shown in this post at the top:

http://audioheritage.org/vbulletin/s...9&postcount=48

Substitute L-pad terminals 1 and 2 plus a 2-Ohm resistor in series for R2 to replicate the adjustable Model 19 version. 3.9 Ohms is not available from Parts Express in either Mills or Dayton, so use 4 Ohms. 6.2 uF is fine for C1, or a pair of 3.0 in parallel if you want to be spot on.

The contours generated by this filter are slightly different from those of a simple resistor and capacitor in parallel. I think the T-filter is better for your application....

Zilch,

As you know I'm also working on a new filter for my Altec 806's.

Could you post the final complete network drawing for the HF?

Once again thanks for all your hard work and research on these drivers.

Don

[Zilch]

Could you post the final complete network drawing for the HF?

Well, it's not "Final" anything, of course, merely the adjustable "T" filter added on to the N800-F HF filter.

With LP1 set to full 35 Ohms, it provides 3.3 dB more compensation, and set at 10 Ohms, ~6.3 dB

The combined contour varies somewhat from both the stock N800-F (yellow) and the T-filter alone, above.

R4 represents the stock crossover attenuation control set to "0"; it doesn't have to be there.

The intent here is to squeeze the most available compensation out of this crossover and 806A. Depending upon what woofer is used, there may not be enough headroom available to do even this.

Again, my current recommended approach to 806A is to active biamp and engage the CD compensation. With the inexpensive Behringer CX3400, that produces flattened response and HF out to ~14 kHz on the 811B horn. If you don't like the sound of that compensation, use the adjustable "T" filter with it, instead, or an alternative contour filter such as a derivative of the Patten 605A (806A HF, different horn) filter posted earlier.

[DonM]

Zilch,

My current passive crossovers are very close to the N800-F. I'll take your diagram and add on the CD compensation.

Yes it is better to bi-amp. I also have the DCX2496 however my 4 channel amp left with my Son to University this year.

Thanks again,

Don

[MrT]

Hi Don

Would you share your schematic of N800f? I am curious to know what type of mods you made. I would really really appreciate that.

I am finishing up mine. And Just wanted to compare mine with yours.

Hey Zilch. I looked at the active crossover at the Partsexpress. Really tempting. In fact, I am looking at my rack to see if there is a space for it and an additional amp. Mid-high: tube and bass: SS. Makes perfect sense.

Tim

[Zilch]

Hey Zilch. I looked at the active crossover at the Partsexpress. Really tempting.

Guitar Center may still have it on sale for $99.

If not, just tell them you want it for that....

[DonM]

Hi Don

Would you share your schematic of N800f? I am curious to know what type of mods you made. I would really really appreciate that.

I am finishing up mine. And Just wanted to compare mine with yours.

Hey Zilch. I looked at the active crossover at the Partsexpress. Really tempting. In fact, I am looking at my rack to see if there is a space for it and an additional amp. Mid-high: tube and bass: SS. Makes perfect sense.

Tim

Tim,

Since I still do not have all the equipment required to test the response of my system (Altec 806a/416a/811b) I have been following all the tests that have been posted by Zilch.

My current HF includes a 2.4 uF capacitor (instead of the 4.0 uF), a fixed 8 ohm resistor in parallel (instead of the variable 35 ohms) and a 3.5 mH coil.

I'll be purchasing the parts recommended by Zilch in the above post.

Regards,

Don

[MrT]

Thanks Don.

Tim

[Skywave-Rider]

For these tests I reverted to 2-way using the stock N-800F crossover. I was only able to test one speaker, but I believe previous tests indicate the drivers are close. I set the HF pot to “2” because that is the factory ref. and also happens to be a spot which is not intermittent. I used a dummy load when removing drivers as previously. One set of readings with the stock crossover, another with contour filter added (6.2uF+8Ohm paralleled in series with 902 as shown.) I also reversed the phase of the 902 for comparison.

I used a distance of 3ft, mic positioned to center of 811B horn (this works out to approx. 3ft high,) excepting the woofer nearfield reading which is 3in., same as last time.

Listening impressions:
First thing I noticed was that the pink noise output sounded softer, I didn’t need muffs this time, though I wore them anyway. (I kept amp level and pink noise output exactly as before.)

Unfortunately there was no extra time to listen much, but I rigged mono signals to both the 2 and 3 ways. No time to listen with contour filter. The 2 way sounded great compared to the 3 way. Much more balanced mids, highs were actually better, less smearing there. Sounded well extended too. The 3 way was horn forward and “pointy” in that range. Sounded like it had less bass, and rather irritating in comparison.

This was a listening test which I did during cleanup, about 15 mins, but the change is large and easy to hear. Sorry I did not have time to listen with contour in. But to my eye, the measurements don’t show an enormous change with it in, though there is clearly an effect.

I was amazed to see how high the 902 goes. And I thought to myself, especially after listening, “why did I want to change this?” Well, please remember that previously I had loading caps on the 902s, and never heard this system in 2way with the bigger back covers on. I believe that is one factor. Another is the relative auditioning. The comparison to the 3 way which is not optimized. (I went back to look at the 3 way RTA and found it looks smoother overall, hmmmm.) One thing is for sure -- hearing this monitor 2 way for 15 mins has excited me again about the potential it has.

I’m still reading. Eager to hear all your comments and absorb the expertise. I’m definitely willing to experiment much further in pursuing the maximum potential from the 9844s. Zilch I know you’ve helped a lot and I don’t want to be presumptuous.

Pics below, and I think I can take the plastic off the DEQ2496 now....

[Zilch]

Well, there it is again, I must say!

I worked quite a bit in the Valencia thread with trying to add a tweeter to 811B, and it just didn't happen worth a poop until I mounted a small one inside the horn mouth itself, and even then, there were issues, but none so major that, using this approach, Jackgiff was able to integrate one successfully. You're hearing substantially what I heard, most likely: standing separate, an add-on tweeter sacrifices coherency, and it's quite audible.

You've also found, as I did, that the 811B horn supports VHF, and with even the modest compensation provided by the N800F crossover, 902 will play fully out through 20 kHz. If you move up and down, you'll find that response is somewhat beamy, but the beamwidth is at least 30° vertical, and JBL's UHF drivers like 2402 and 2405 are about the same. The horn needing to be at listening height in order to hear the VHF adequately is the compromise. Bottom line on which it would appear we agree: Two way is better. Make it work.

What first struck me in these most recent measurements is the nearfield LF response. Compare what you measured to the simulated voltage drive of the N800-F, the blue line here:

http://audioheritage.org/vbulletin/s...2&postcount=55

The filter has assumed control of the woofers, and the response is flat as Nebraska. We're quick to criticize Altec engineers for their apparent cavalier approach in using this 16-Ohm crossover with an 8-Ohm load. Here, again, is evidence there's more to Altec designs than might casually be observed; it's US who are the fools.

Tuning now to the HF, generally, with the attenuation at "2" you're still playing that too "hot," by as much as 5 dB, perhaps. Crank it down for better balance. Watch what happens on the RTA display as you do that. The HF should be just slightly lower than the LF for optimum balance. That's encouraging, because it says there's sufficient headroom for a better compensation contour, which I will suggest below.

We again have a notch at 3K15. Let's find out if it's real before doing anything about it. Two suggestions: get that on the display again, and then rotate the horn slightly off-axis, so that the mic is aiming in the first open area off center, i.e., not at the central vane, which may be shadowing that frequency, or generating reflective interference.

Second, lay several layers of fiberglass insulation (or a thick fluffy comforter, folded) on the floor between the speaker and the mic, 6" minimum, paper only on the bottom layer, against the floor. We may be looking at a cancellation due to floor bounce at that frequency. That's the first reflection with a different path length (think inverted triangle,) and it WILL interfere with the measurements.

If neither of those measures mitigates the notch, and you don't discover something else which does, that notch is then coming from the driver/horn, not the filter, and it should not be there. Order up a pair of the Radian diaphragms for these drivers from Parts Express, install one, and compare the response measurements.

There's one more thing I'd like you to try the next time you set up for measurements, and that is to disconnect one of the woofers and see how that alters the total system response. You'll have to crank down the HF more to restore optimum. Do nearfield measurement on the single woofer also. I'm suggesting you try this because there's a simple way to use the second woofer as a "helper" to augment the LF response at the low end.

Finally, with respect to optimizing compensation, Altec used the "T" filter in later iterations of these "Pro" monitor products as well as in Model 19. The schematic differs from M19 in that it does not rely upon a connection in the LF filter path, and thus may be used independently. I'll draw that up and post it here. You may want to build both the LF and HF sections, so you have yet another LF option to try. We can almost certainly improve upon the HF response N800-F is generating in your system.

Thank you again for performing these tests and posting your measurement results. Know that you are contributing to expanding the knowledge base regarding these vintage Altec products and designs, and it is appreciated....

Edit: Model 19 crossover with N604-8H VHF attenuation:

[MrT]

Skywave

Thanks for the excellent post. I learned a lot. I heard 902s are one of the better Altecs. And that they are clean and crisp. I've never auditioned them myself. But the graphs are saying a lot. On the other hand, I heard that 806As are warmer and smoother. Further, I did hear that 806As don't go up high.

Zilch. I have a question. My understanding is that N800Fs are used both for 8 ohms and 16 ohms. If so, how is that possible?

Thanks guys. To me this post helped me most in regard to 414s.

Tim

[Zilch]

I heard that 806As are warmer and smoother.

Further, I did hear that 806As don't go up high.

They're largely the same thing, I would say.

Zilch. I have a question. My understanding is that N800Fs are used both for 8 ohms and 16 ohms. If so, how is that possible?

It's an 8-Ohm crossover when used with 8-Ohm drivers, and a 16-Ohm one when used with 16s, the primary difference being that the voltage drives, and thus the frequency responses, are different in the two cases. Where they cross acoustically, in combination with the drivers in the system, defines the crossover frequency, NOT the electrical drive.

See the link I posted immediately above....