Altec N500D,E,G series Crossover network Question

Does anyone have an idea why Altec used the 3 different Crossover networks, N500D, N500E, N500G for the identical components in the A7-500 cabinet.

Attachment 87235

I understand the N500E is 8-16 ohm version so that you can use either the 8ohm or 16 ohm taps on the amplifier, but is still rated for 16om operation. But the remaining two are supposed to be 16ohm. But why the different “D” & “G” ? What are the differences in the 3?


Also according to Altec literature, if you use the A7-500 cabinet with the N500E, the polarity should be reversed. Why?

I am assembling the Altec "Magnificent" utilizing the N500E Crossover.

Thanks for any information you can provide.

Quote:

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Originally Posted by pantoramasan

Does anyone have an idea why Altec used the 3 different Crossover networks, N500D, N500E, N500G for the identical components in the A7-500 cabinet.

Attachment 87235

I understand the N500E is 8-16 ohm version so that you can use either the 8ohm or 16 ohm taps on the amplifier, but is still rated for 16om operation. But the remaining two are supposed to be 16ohm. But why the different “D” & “G” ? What are the differences in the 3?


Also according to Altec literature, if you use the A7-500 cabinet with the N500E, the polarity should be reversed. Why?

I am assembling the Altec "Magnificent" utilizing the N500E Crossover.

Thanks for any information you can provide.

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Can you please point me to a link that states this ( bolded words in your posts ) ?
( - I'd like to try to puzzle-out that directive ).

Having said that, the N500E IS notably different from the the other N500x variants you've mentioned in that it combines the function of the HiPass capacitor with that of the capacitor size typically found in a HF compensation circuit.
- The resulting capacitor size is unusually small for any network that purports to have a 500hz crossover point.

The cap in question here is the 4 MFD ( uF ) cap seen in the HF leg of the crossover of the following pic.

http://www.audioheritage.org/photopo...00/N-500-E.jpg

Normally, that cap size would be much larger ( such as seen in the N500C ).
- The pic shows 2 x 18.9 uF caps ( within that cardboard box ).

http://www.audioheritage.org/photopo...C_inside_B.jpg

The N500F and N500G are most decidedly designed for 8 ohm loads ( according to their different/included LC values ).

http://www.audioheritage.org/photopo..._schematic.jpg

http://www.audioheritage.org/photopo..._N500G_001.png


I'm not going to bother trying to reconcile why Altec ( or JBL for that matter ) decided to suggest some of these networks were usable with different/newer/lower impedance loads ( I would need the actual components to run those type of tests or simulations ).



:)

FWIW, here's one simulation I created using available resources that put the N500E to the test.

Attachment 87238

One can see the actual crossover point is a lot higher than 500hz.

:)

Thanks for your explanation. On the bottom of this page it refers to phasing and reverse connection to the HF driver when using either the N500E or D networks only.


Attachment 87239

Quote:

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Originally Posted by pantoramasan

Thanks for your explanation. On the bottom of this page it refers to phasing and reverse connection to the HF driver when using either the N500E or D networks only.

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If you are wondering why some versions would require a phase reversal and others not, is likely due to the fact that some are 2nd order networks and others are 3rd order networks.


Widget

Quote:

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Originally Posted by Mr. Widget

If you are wondering why some versions would require a phase reversal and others not, is likely due to the fact that some are 2nd order networks and others are 3rd order networks.


Widget

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The only 3rd order networks that Altec had ( that I'm aware of ) was the HiPass section for the M19 ( N1201-8a ) and some of the networks used for the later models 604-8xx's .

All the networks I posted pics for are 2nd order.

:)

I didn’t actually look at the schematics. There I go assuming again. :banghead:

Any ideas why some would be affecting the phase differently than others? If they are all 2nd order, you would expect them all to be 180 degrees out of phase at the crossover.


Widget

I think the hint was the horizontal (front/back) displacement of the woofer and horn phase centers on some models.
Roughly a foot would be 1/2 wavelength at 500 Hz. Other factors could make this "correction" be for smaller or shorter distance offsets. But I'm guessing the end result is to make the crossover region flatter for continuous tones.

Quote:

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Originally Posted by pantoramasan

Thanks for your explanation. On the bottom of this page it refers to phasing and reverse connection to the HF driver when using either the N500E or D networks only.


Attachment 87239

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OK, back to the beginning;

When I read through the text seen within that pic I don't see anywhere > where Altec used the word "ONLY" .

I don't even see ( or agree that ) the word was being implied.

What I do see being implied is that anytime one uses an Altec crossover that is 2nd order > and where the voice coils ( of the horn-driver and woofer ) are vertically aligned > then one should flip the polarity of the horn driver > so that at crossover, the best acoustic summation is achieved.
- If the voice-coils are not vertically aligned, then one should wire both horn and woofer with the same polarity ( according to the words in the pic ).

As well, all my research has shown that the N500C shares the same LC values as the N500D ( meaning there's no reason to exclude it from the stated wiring protocol ).
- The functional difference between the N500C and the N500D is that the "D" variant has 2db more ( maximum ) attenuation ( this sameness/difference somewhat helps explain the somewhat awkward way the N500C is included in the directions > or left out dependent on ones perspective ) .

- One other notable difference between the 2 models is that the "Green-Boxed" N500D selects horn attenuation through a 5-position switch ( while the N500C used buss bars to choose horn attenuation ).
- There was an ancient "Black-Boxed" N500D that also used buss bars > further confusing the historical lineage.

- The lack of any mention of the N500F or N500G may simply be date related ( iow; the pictured directions predate their existence ).


That's my take on this Altec info.

:)

PS; Worth noting ( really ! ) in regards to this whole 16 ohm versus 8 ohm fiasco , is that Altec clearly shows multiple woofers loaded onto the same LF outputs of their crossovers ( here + there ) effectively lowering the load impedance ( without any regard or mention as to what this does to the "so-called" 500hz crossover point.

- All-in-all , my eyes glaze over the more I think about all this ;)