VOTT A7-500 EQ Circuit confusion (30923 vs N501-8B)

**altec-man** · January 30th, 2009, 01:54 AM

confused:
I was about to replicate the 30923 Equalizer Network as used in the 9846A/B and Biamped 9846BX Studio Monitor as this setup is the same as the mid 70's A7-500 (416-8B, 802-8D /808-8A, 511B and N501-8A) except for the 411-8A woofer. I was surfing this forum and noticed that in the early 80's Altec brought out the N501-8B xover which later became the N8500-8A, evidently these were designed for the A7-500 (416-8C, 902-8T, N501-8B/N8500-8A).
If this is so why are the component values different, especially the 6uF in the 30923 whereas the N501-8B has only 3uF.
The brochure for the 9846 Studio Monitor states that 30923 network suppresses the midband (1-6kHz) frequency response by 2 to 3 dB. Using the 6uF cap would equate to a first order broad frequency peak of 3300 Hz, which is right bang in the middle of the 1-6kHz band.
If the posted schematic of the N501-8B is correct then the first order broad frequency peak is 6500 Hz if using the 3uF cap.

Is this assumption correct?, if not please enlighten me as I want to do the correct EQ network first up.

**RonSSS** · January 30th, 2009, 02:13 AM

Later A7's, used the N1201-8A dividing network. This was for the A7-X systems.
Components were the 416-8B woofer and the 802-8G HF driver on the 511 horn. Same crossover as the M19. electrically identical.
This crossover allowed the user to shelve the mid freq, as well as the HF. It's quite good, even in stock form.
The EQ network you speak of was designed for the 411-8A and the 802-8G when used together in the 9846. Whole different animal than the A7....due entirely to the voice and efficiency of the 411 Woofer.
find some, you will be happy.
Ron
BTW...owner of A7's, M19's and the 9846 which I need to put together.

**altec-man** · January 30th, 2009, 02:41 AM

RonSSS
I understand what you are saying about the efficiency mismatch between the 411-8A and 416-8A but the 30923 (HF compensation circuit of the 30904 network) was incorporated into the Bi-amped version of this speaker making any efficiency mismatch moot.

**Old Guy** · January 30th, 2009, 09:18 AM

Well the efficiency difference isn't totally moot.

The circuit you mention is simply a filter that chops out the mid. Rather, some of it.

This essentially gives better sounding highs, at the expense of overall volume.

This can only be done if the woof is substantially less efficient.

The best solution is the later crossover.

As far as addressing component values, I don't have the circuit in front of me...but I have seen cases where caps were paralleled...or series, in those cases of course the value changes. I'll try to find a schematic for the xover you mention, and post later/ Am on my first coffee, brain not totally working yet.

**altec-man** · January 30th, 2009, 07:16 PM

I've added the schematic of the 30904 / 30923 for reference. The only reason I'm confident about this older circuit is that it was designed for the 802 / 808 (Alnico magnet)family of drivers whereas the N501-8B / N8500-8A was designed for the later ferrite magnet version with tangerine phase plug. Could there be some thing different between the two variants to make such a change in the horn compensation network. Utterly confused!!!!!