X-over schemo for 604(a) 20 ohm etc.

[sean sweeney]

I'm Sean, in St Louis (even if it says Michael, as I grew up with hundreds of them). I am a local tech and do all sorts of stuff here... but I'm currently reconing a single 604 (a), the later one with the grey crackle-coat and Yellowish/Blue-greyish label, with no (b), but looking pretty much JUST like a B, but 20 ohm... I can't find info on this one, whether the horn is 20ohms like the woofer, or less... to build a crossover for it and hopefully plans for a cabinet that would do it justice when I'm done. I got the correct kits for the recone of the woofer, 20 ohms and all, but the tweeter is original 40s and it tests about 8 ohms DC resistance... as does the woofer, but we know the woofer is 20 ohms allegedly, as the kit is correct on it. I guess I'm curious about crossover schematics and have had a HECK of a time finding anything on these! I do want to build a cab for it and keep it, as I have been wanting one like this, beat up, but good enough to keep and restore.
Thanks for any help you may have!

 

[EarlK]

8 Ohms DCR ? ( for both LF + HF ) ?

5 Years after the labels ( decals ) were put on that driver, Altec might have called that same driver a 12 ohm ( er ) .

2 different naming conventions ( for the same parts ) are at work here.

( FWIW ), JBL offered up the same confusion to its customers ( alternately calling the same damn driver , 8 or 16 ohms at various times ).

Since impedance is a curve, choosing any point along the curve can give radically different values.
- Naming conventions flipped between approximating the "curve" after it had flattened out above the Fs peak versus choosing an average value of the Fs peak .

If your woofers recone kit comes from GPA it's most likely of the newer 16 ohm variety ( with an approx. dcr of 12 ohms )..

The GPA woofer kit when coupled with the older #20275 type original diaphragm somewhat equates to the parts found in a 604E.

Building up the crossover that accompanied the 604E would be a good starting point.

 

[Dswankey]

Not sure if this helps but might be worth a quick read

https://www.technicalaudio.com/pdf/Duplex_Speakers_related_to_Altec_604/DUPLEX.html

https://www.technicalaudio.com/pdf/..._to_Altec_604/604_1944_604_Duplex_Speaker.pdf

 

[sean sweeney]

Ok, yea, I had considered such things, but just wondered if they held any water in this quandary. I guess the only way to truly tell is to gently sweep them and work towards a 2k xover point. Or aim for where that coil leaves the woofer, if it's not too low.

8 Ohms DCR ? ( for both LF + HF ) ?

5 Years after the labels ( decals ) were put on that driver, Altec might have called that same driver a 12 ohm ( er ) .

2 different naming conventions ( for the same parts ) are at work here.

( FWIW ), JBL offered up the same confusion to its customers ( alternately calling the same damn driver , 8 or 16 ohms at various times ).

Since impedance is a curve, choosing any point along the curve can give radically different values.
- Naming conventions flipped between approximating the "curve" after it had flattened out above the Fs peak versus choosing an average value of the Fs peak .

If your woofers recone kit comes from GPA it's most likely of the newer 16 ohm variety ( with an approx. dcr of 12 ohms )..

The GPA woofer kit when coupled with the older #20275 type original diaphragm somewhat equates to the parts found in a 604E.

Building up the crossover that accompanied the 604E would be a good starting point.

 

[bowtie427ss]

Best sounding factory network for the older paper hinged 604's with true multicells was the N1000(stock network for some 604B's).

I'd be aiming for an XO much closer to 1k than 2k.