Altec 9844-8B

[Zilch]

When Jackgiff opened his, it just kinda crumbled away, mechanically. In the "Babies" thread.

There's likely a double-cap flatpack in there, and the values are written on it.

[Earl K]

Hi Skywave-Rider

- FWIW; Yesterday I took my 902s and put them on about 8 different horns. One thing became apparent. The horn ( & it's classification type ) can either exaccerbate or minimize the notches. The included 909 info also reflects this somewhat.

Thanks Earl, that's interesting. I wonder if Zilch has tried this on the PT waveguide. I should have, but did not think of it b4 sending the 902s out.

- I was able to make ( with real CD horn compensation ) a very respectable line/curve ( with only 1.5 db notches at 3 & 8K ) on an RCF 9041 CD-type horn ( which is much like a smaller 2370 ).

Using standard 6 dB/octave CD horn compensation?

- Yes, except that the compensation was what I would call "Type 2" CD horn compensation .
- FWIW, All the networks for the older Altec stuff incoporating radial/sectoral horns use "Type 1 compensation " .
- Really, the only difference is where the 3 db down point ( F3 ) of the cap is placed .
- Type 1s' "F3" occurs lower, and as such, counts on adding its' 3 db "HF-boost" to the @ "3 db HF boost" one gets from an exponentail horn ( as its' HF pattern narrows ). Together, they achieve the final 6 db type slope above the F3, set point .

- I came to the conclusion that the network will play a significant role in minimizing or expanding the notches ( into holes ) as large as what's seen with the M19 network . IMO, that network needs to be redesigned for use with the 902/811 combo.

Could the incorporation of series notch filters into either the N800 or M19 constitute the redesign, or do you mean scrapping, entirely, the HF section of the x-over, making something totally new?

- Yes, the HF section of the M19 or N800 would be completely scrapped .
- Last weekend I kludged together a network that included 3 series notch filters for use with ( exponential type ) horns .
- Overall, it's midband attenuation is around 12 db / making it ( I think ) only useful for someone who is biamping or using it with a 16 ohm woofer/8 ohm horn combo .
- I'll post some details this coming weekend .

[Skywave-Rider]

- Yes, the HF section of the M19 or N800 would be completely scrapped .
- Last weekend I kludged together a network that included 3 series notch filters for use with ( exponential type ) horns .

Hi Earl.
It'll take me a while to digest your info, thank you.

I believe the 811B is a bi-radial horn. Are you working with an exponential horn to see what the filter is doing without having to factor in bi-radial or CD horn rolloffs? That is, to more directly observe the filter's effect?

I look forward to your results.

Note: Zilch corrected me, the 811B is a radial horn.

[Zilch]

I was corrected on that one earlier. The sectorals are not constant directivity, and not biradial, rather simple radials, an exponential profile rotated horizontally about a vertical axis.

Altec's implementation of constant directivity was MantaRay....

http://aa.peavey.com/downloads/pdf/qwp1.pdf

[Eric Best]

Skywave, How did the seleniums sound on your 811B?

[Skywave-Rider]

I was corrected on that one earlier. The sectorals are not constant directivity, and not biradial, rather simple radials, an exponential profile rotated horizontally about a vertical axis.

Altec's implementation of constant directivity was MantaRay....

http://aa.peavey.com/downloads/pdf/qwp1.pdf

Thank you Zilch. I seem to have forgotten the difference between radial and bi-radial; and I'll go back to the Peavey .pdf to straighten myself out.

Eric, I put the Seleniums on for the hell of it, as I bought them for a different project. Since I did not have the proper compensation, only what is in N800F, stock, the FR was not optimal. Imagine too much 8kHz and rolling off above that. Zippy, a little sibilant, but not extended. My impression is that it would be good if dialed in.

Somewhere, someone must have a Selenium DT220Ti compensation filter worked out for the 811B; seems like a popular application. Try this thread over at AK:
http://www.audiokarma.org/forums/sho...=147170&page=8

Let us know if you do it.

[Zilch]

Returning the drivers to Skywave, now.

[Zilch]

Last one:

[geaugafletcher]

Zilch, forgive my ignorance, but what are we looking at in that last graph?

[Skywave-Rider]

Zilch, forgive my ignorance, but what are we looking at in that last graph?

Re. Zilch's last graph:

I'll try my hand at this but I know I've got something wrong, part of what I see does not make sense.

Sine wave for a duration of 5.58 ms, through the 902/811 horn combination. The crossover is active cx3400 Behringer, with CD horn compensation engaged. However, what I do not understand, also from Zilch's legend, is a frequency of 179.10 Hz. Can't be so low, but I am needing reading glasses so maybe I cannot see it well enough. The duration and and frequency don't seem to jive.

My conclusion: I'm not much help, sorry. I'm sure Zilch will fix us up soon enough.

Aren't those waterfalls interesting. Those I've recently learned to read pretty well, and the horn "ring" is visible. Yes, the 511 has smoother frequency response, but the 811 comparatively less ring.

I hope Zilch will be able to post same tests on same horns but with BMS 4552ND drivers.

Awesome graphs!

[Zilch]

I hope Zilch will be able to post same tests on same horns but with BMS 4552ND drivers.

Sure, but I have to catch up on other stuff first. I don't have answers on Step Response yet; have to read up.

In the meantime, here are more Waterfalls, this time normalized. You can see it has flattened the response across the top. This gives a more fair comparison, since the 20 kHz peak of 811B no longer skews its picture. 511A still loses at the high end, but it's better down low.

On gated sinusoidal, 511A rings with sustain on virtually every note, 811B only in the region of 1.5 kHz, if I recall correctly. It'd be interesting to damp them selectively, comparing the results, to ascertain where the problem areas are, and develop a solution.

[Not my job.... ]

[Zilch]

Here, for comparison, is the $9.90 JBL PT waveguide driven by a cheap Selenium driver, "EconoWave":

[grumpy]

Question:

511A and 811B plots are non-baffled? (not mounted to a board)
Just that difference would be mildly more interesting... that metal horns
ring if not mounted should surprise no one.

[Zilch]

Question:

511A and 811B plots are non-baffled? (not mounted to a board)
Just that difference would be mildly more interesting... that metal horns
ring if not mounted should surprise no one.

Certainly true.

Then again, 511 is rarely "baffled" in common use, and 811 only marginally secure in Altec products such as Valencia et al.

The primary source may be the "lips."

People have sawn out the vanes, and reported no difference listening, but nobody's actually measured, to my knowledge.

I've also seen one with the lips removed. Looks like a bowtie horn. More

It's all part of "That Altec Sound." Yet again more ....

[grumpy]

If/when I get around to mounting either (probably 811b first), I'll try to
remember to give this (before/after) a go. Thanks for the clarification.