High Frequency Driver Extension

[Altec19]

Which of the the Altec small format drivers has the greatest amount of high frequency extension? I'm thinking an 802-8G or 902, both with the tangerine phase plug and a 34647 diaphragm. I'm wondering if I can improve upon the high frequency response of the 802-8Ds used in my A7-500s. Or, is there room for high frequency improvement in the crossover???

Thanks All!

[Art J.]

The method Altec used in the crossover was to install the 30923 attenuator
in series with the horn. This device lowered the output of the horn about
2db in its lower range. Then by increasing your l-pad 2db, you effectively
gain 2db in the higher range of the horn. This modification is very easy to
build. It was used in many Altec designs. Compare the one used in the
Model 19 diagram on Jeff's fine page
http://home.earthlink.net/~jmarkwart/id7.html
to my note book scribbling of the 30923.
http://img1.uploadimages.net/974615Altec9846-8A.jpg
You see they are essentially the same. Even though I bi-amped my
speakers, I left the 30923 in the circuit with very pleasing results.
I have been wanting to study the results on my spectrum analyzer
but it seems I'll never get around to it. Their will be a slight phase
shift by using this series capacitor, if that is an issue with you. It
showed up on my dual trace scope at the time I was experimenting
and it was expected. Then implementing bypass capacitors really was the
icing on the cake. Have fun, Art.

[djnagle]

Hi Altec Fan, wanted to do something similar but ended up buying a pair of Beyma CP25 SuperTweeters instead. I am triamping through a Rane 23. I think that my mids sound just a touch better because they are not working in the upper freqs. I have them crossed at 5000 and am driving them with the Sonic Impact $27.00 digital amp. Cheers.

[Altec19]

Hi Art,

I understand the approach with the 30923 attenuators. I don't have any of those handy but I did find two brand new 30904 eq/attenuator modules in my box of stuff. I don't have the specs for them but they appear to be similar in purpose to the 30923. Any idea what the 30904 modules are for???

Thanks!

[Altec19]

Hi Igor,

I've thought about getting a Rane and doing the bi-amp or tri-amp thing. Haven't quite talked myself into it yet. But I may!

Later . . .

[Art J.]

I forgot to ask.
Can you open the box and read the component values? Thanks

[Art J.]

I think the 2 attenuators are the same. You are lucky to have them.
They have the exact same function.
Mine are an open circuit board
http://www.lansingheritage.org/image...-8a/page03.jpg
and yours are in a closed box.
http://www.lansingheritage.org/image...nal/page14.jpg
The capacitor determines the point where attenuation begins
and the resistors determine how much attenuation. That's it.
They must be the same.

Use the horn wire leads (in and out) but do not use the woofer leads
at all. Those are for a Zobel only for a 411-8a woofer.
Its definitely worth a try. See if you like it.

The Guys around here talked me into bi-amping,
and I'm glad they did.

[Altec19]

Hi Art,

The 30904's are just components mounted to terminal strips mounted to a metal plate, like so:

30904 Front Panel View

30904 Component View

If not legible, the component values from left to right are:
3.9 ohms 10W
6.5 ohms 10W
3.9 ohms 10W
6uf 50VAC
18uf 50VAC
5 ohms 15W

In comparing your 30923 drawing with the 30904 they appear to be indentical. Why two part numbers? It appears that they both are intended to help the 411-8A woofer match the compression drivers a little better.

[Art J.]

Very good, thanks for solving the mystery. The 2 different part
numbers is kind of strange.
Their is one more attenuator board that I know of made by Altec.
It was identical to ours but with only the horn circuit, on a smaller board
and nothing for the woofer.
Their was no part number on these but 2 of them came unattached in my speakers
when I got them. I pretty sure these were meant to use with any 511b
horn no matter which woofer is used. This is why I recommended
it in the first place to improve your highs. If you try yours and like what it does,
it can be improved even more by changing the old capacitors to new ones.
It really sharpens up the highs. Keep me posted about what your going to do.

[Richard C.]

Art J.

I modeled this 30923 attenuator in "Multisim 2001" to the best of my ability. I found the initial attenuation at 600 to 700 Hz to be about 9 dB with a nice gradual rise to only about .5 dB at 20kHz. This is almost the same attenuation with the same that amount of lift that I use in my model 14's. (1800 Hz crossover) With 1/3 octave warble tones, my system measures very flat up thru 13 kHz and is about 4dB down at 16hHz. I had a 10 dB peak at 1700 Hz until I installed a Zobel network. Now it's beautiful - hardly any EQ required. I use an Le value of .15 mh which is what I measured on my 902 drivers. This inductance added into the model changes the trace a little. I know that drivers are inductive, so I try to find out about what the Le really is. I haven't modified the crossovers on my 19's, yet. My model 14's were too HOT in the 2 to 6 kHz region for me. To me it was very fatiguing.

I also measure the phase shift at crossover, it is about 90 to 100 degrees in that region, and that probably somewhat matches my driver voice coil offset.

I will try to post some pictures if anyone wants to see what this looks like.

Richard C.