Crossover Help Needed With ANOTHER Pair of ALTECS

[voice of the theater]

Personally, I would remove the protection circuitry....unless you have some sort of mondo power amp and kids who like to crank the volume all the way.

Ron

Great idea--there's no way that I need the protection circuitry as these speakers are so efficient I doubt if I ever put much more than 10 watts per channel through them--they blow you out of the room if you go past that. Anyone out there know how to bypass the protection circuitry? I doubt if it will effect the sound but it just makes sense to not have the signal go through any more circuitry than is necessary.... Not sure if this schematic will help as it leaves out the protection circuitry..... (click on images for full size)

[SD-50]

Just wanted to contribute to this thread with a tweak poached from John Krutke's Zaph Audio site. It's simple resonance trap and does not require any soldering to try out. Did it to my A7s two weeks ago and found a subtle but worthwhile improvement.
Using alligater clips place a .1uf cap across the woofer's inductor. The schematic shows an example, inductor L6 with capacitor C12 across it. I'd be curious to hear comments from anyone who gives it a try.
Cheers

[voice of the theater]

Well--five and a half years later, I've decided I want to experiment with my Model 14 crossovers. When I did this recap in January of 2011, I wanted to replace the 30 year old caps with new caps of the exact same values as I did for both pair of my Model 19's and other Altecs I've recapped in the past. However, in the case of Model 14's, Altec manufactured three variations of the Model 14 crossovers--so if they rethought their design, I'm thinking that maybe I should try one of the other factory designs to see if I like it better than the one I'm now using. My 14's came with the 2 uF and 10 uF combination. If I'm reading Richard C's diagrams correctly, it looks like there was a factory version that used a 2 uF and 6 uF combination. I have three questions before I start my "experiment".

1) Are the two Altec factory designed networks identical other than the 2 uF / 10 uF combination being swapped for a 2 uF / 6 uF combination? In other words, if I swap out 10 uF cap for a 6 uF cap, will that convert my crossover to the other Model 14 variation that Altec manufactured, or are other changes involved as well?

2) I do have to turn down the midrange EQ "pot" on my Model 14 crossovers quite a bit to get them to sound their best. If I swap out the 10 uF cap for a 6 uF cap, will that result in less midrange from the Model 14 system (which would mean, among other things, that I won't have to turn the midrange pot on the crossover down as far)?

3) Does anyone know what the third variation of the Model 14 crossover was comprised of? Richard posted a photo of all three stock Model 14 crossovers, but only did a diagram for two of them?

To assist in the answering of these three questions, here's a photo of the three stock crossovers from Richard's photobucket page. Model 14 x-overs.jpg

Here's a link to Richard's photobucket page which has the above photo plus a bunch of crossover "schematics".

http://feed266.photobucket.com/album...io/account.rss

I'd really like to try at least one of the stock Model 14 designs that Altec manufactured and compare it to the stock version that mine came with to see which I prefer....

I had saved some of Richard C's original network studies onto an older computer .

Here they are ( with the Model 15s schematic thrown in as a bonus ) .

(A) First, 2 flavours of the M14s original network minus the protection circuitry.





(B) Then Richards' redesigned network .



(C) Then the Model 15 stock network .




<> EarlK

[Earl K]

( "Right-Click" ) the pic & open in a separate tab, to see it's full size .



The HF output ( ie; voltage-drive ) is displayed within the smaller window ( called the "Bode-Plotter" ).

The cursor within that window is set to around 2K.

One can see that the 6uF variant of this network employs a ( restorative ) response peak at around 2K ( right near the x-over point ).

I'd need to see some raw measurements of the speaker before commenting on whether the peak is truly needed.

All you can do is try this variant and see if you like it .

[voice of the theater]

Thanks Earl! I've never heard of a "bode-plotter" but your explanation is very helpful -- i.e. from listening to the Model 14's with my current crossover configuration, I am certain that what they don't need is a boost at 2k! I won't be trying that version of the factory crossover....

( "Right-Click" ) the pic & open in a separate tab, to see it's full size .



The HF output ( ie; voltage-drive ) is displayed within the smaller window ( called the "Bode-Plotter" ).

The cursor within that window is set to around 2K.

One can see that the 6uF variant of this network employs a ( restorative ) response peak at around 2K ( right near the x-over point ).

I'd need to see some raw measurements of the speaker before commenting on whether the peak is truly needed.

All you can do is try this variant and see if you like it .

- - - Updated - - -

In fact, looking at the bode-plotter for the two Model 14 factory crossovers and Richard's custom crossover, the factory version I'm currently using (with the 10 uF capacitor) looks to have the flattest response--rising gradually in the highest frequencies which is probably fine given the fact that human hearing falls off at those frequencies....

[Nickd]

In my Expierence, speakers having a rising response in the high frequency do not provide long term satisfaction. i have a hard time believing the Altec engineers designed the 14 with that rising top end on purpose?
Perhaps some part swapping occurred in the production run and no one caught it in the Q.C. Program if there was Q.C. Back then.

[Earl K]

You two are confusing the ( electrical ) voltage-drive ( as seen in the Bode Plotter ) with the acoustic frequency response of a speaker .

They are not the same thing ( & far from it ) .

Think of the voltage-drive as the necessary (EQ) signal that's required to result in a flattish acoustic measurement.

Here's what a JBL 2426h measures like on a largish Constant Directivety horn.

For this horn/driver combo to measure flat would require a voltage driver signal that is the inverse of the downward slope,
>>> hence a rising ( electrical ) response as seen in the Bode Plotter ( assuming the network was designed to flatten the HF response ).

[Earl K]

Here's the un-equalized response of the M14's horn-driver combo .

One can see that it needs the mid-range suppressed by some 6 to 10db ( between 1-6K ) so that the HF ( above 6K ) is brought back into a more reasonable balance .

[Nickd]

Thanks Earl,

When Voice of the Theater mentioned rising response, It threw me off a bit. I typically think of "Response" as measured acoustic output. In engineering speak however, you can relate the word response to many other aspects of a circuit.

Your last couple of graphs are a perfect explanation of what I understand

As you can see, I am neither an engineer or a lawyer. Apparently, I prefer to keep things simple and leave the heavy lifting to people who can make sense of an oscilloscope.
Best Regards,
Nick D

[voice of the theater]

At the risk of sounding (even more) ignorant--there are two response curves--what does the bottom one represent?

Here's the un-equalized response of the M14's horn-driver combo .

One can see that it needs the mid-range suppressed by some 6 to 10db ( between 1-6K ) so that the HF ( above 6K ) is brought back into a more reasonable balance .