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In Reply to: RE: Altec Model 19 - N1201-8A Crossover Question posted by Synthsayer on August 29, 2015 at 13:41:44
My understanding of that particular xover is that the resistors lower the output of the HF driver and the "cut" amount is used to boost the higher frequencies via the .3 inductor and 6uf cap.
The HF control does not really cut or boost the higher frequencies, it adjusts where, or at what frequency range the HF boost starts to kick in.
That EQ, along with the extended range 802G or 902 driver with phase plug used in the 19, results in a smoother midrange with extended highs.
Some people prefer the balance of say a Valencia or Flamenco with the rising mids and less extended HF response of the 806 driver and others perceive that as excessive midrange "shout" so it's one of those subjective or personal taste things.
It would seem logical that this type of EQ would work with other efficient HF horn drivers but I would think the values of the EQ components would need to be changed to suit a different HF driver.
There are HF horn drivers that have more extended highs without EQ than an 802G or 902 but do they sound better or worse than the Altec drivers?
Follow Ups:
Thank you very much, DaveV!This crossover's use of potentiometers and T-Filters? or Step-Filter?confuses me.
I am used to seeing L-Pads or attenuation circuits.
I found these posts related to Model 19 crossover on another forum:
"Here's the "T-filter" standing alone, top. Altec used it to provide supplemental HF compensation after some stock crossovers.
As you see in the M19 crossover, R2 may be varied to adjust the amount of compensation.
At the bottom here is shown a Zobel, which you'll also find discussed in Dickason, used to flatten the reflected impedance of the woofer as illustrated by Earl, above, so that the main filter behaves more predictably.
Yeah, 6.2 uF for C1 and 4 Ohms for R1s are fine. R2 and the Zobel components vary with the application. You can see that if R2 goes to a high value, providing the minimum of 6 dB compensation, it's basically 8 Ohms in parallel with C1, what I have suggested you try for starters here, as there's already some compensation in N800-F (maybe).... "
I am not understanding how the T-Filter functions here. How does it affect the high frequency response?
I have never used a T-Filter. Is it simply wired as shown in the diagram?
I have loads of resistors - no pun intended - so I thought I would do some experimenting with it.The driver I am using is an EV DH1012A with FaiTal LTH142 Elliptical Tractrix lens: http://www.faitalpro.com/en/products/HF_Horns/product_details/index.php?id=903020105
Thanks again for all the help.
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck
Edits: 08/30/15
Thanks for the great info on the mid compensation circuit.
I have been doing some experimenting with notch filters for the LP to remove some mids from the woofer aince LP filter is 1st order at 750Hz. I may go to 3rd order for LP but will have to order parts.
The LP has a Zobel, too.
I was looking at the graph for my horn and driver combo and the response fairly even. The horn is an Elliptical Tractrix.
Does the Model 19 use a CD horn?
Another question:
Do horn drivers combinations need Zobel or Res Fr Filters?
The spec sheets for my EV driver don't show impedance curves.
Does anybody here have impedance curve info for the DH1012 drive?
Thanks again for all the help.
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck
CD horn. The Model 14 does use a CD horn. The Model 19 uses a 811 B horn which if I'm correct is still a Bi-Radial horn.
A post on Audiokarma describes the controls this way:
The two L-Pads on the Z-19 crossover control the response of the HF section. One of them adjusts the output of the entire HF spectrum, and the other controls the droop or rise of the HF with increasing frequency.
I have never found a definitive explanation of exactly how this network works.
Hi DaveV,
I saw something over on either AK or AH forum that showed a graph that showed just how this Z19 work/s. I saw that it would raise and lower the mids to match this HF side while also doing the same with the HF side. The Z19 is from what Zilch said supposed to have the widest control/adjustment over these areas than anything before and the graphs showed this.
I wish I still had these to share the links. Last week my laptop with all this info crashed. The hard is toast and along with all my info on audio stuff. I will try to find that tread and post it here. very good stuff!
I saw that a few years ago. It's in a thread about the model 19 xover on the Altec Heritage Forum. It shows his circuit modeling graphs but it doesn't explain exactly how the circuit works. It's more about what the controls do.
I think you need to join that forum to view that original very long thread.
Zilch posted his circuit modeling showing what the original Model 19 xover does then I think he later, after developing his revised Model 19 xover, posted a model of his version that was basically the same except for the relocation of the .3mh inductor, the input split to use a bi-wire configuration, the use of the 3rd lug on the HF pot and the added 4uf cap.
In his list of parts he uses the Altec Schematic values of the inductors but my inductors don't measure the same values nor did those of some other Model 19 xovers where people posted the measurement of their inductors. In all cases they were lower in inductance. For instance, the 2.7 was more like 2.4.
I never tried the Zilch version but there was some Internet chatter that some think it was better and some think it wasn't. Maybe because of the inductor value changes and the use of low loss air core inductors?
Resistance in series with a driver isn't always bad and changing the inductor values does change the xover to some degree and it may or may not be audible.
His research was a result of a long thread about the weak HF response of the Altec 2 ways including the Model 19 and using an add on tweeter or changing to a BMS driver that had better HF response.
Thanks again for the great postings, DaveV.
All the best!!!
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck
i have a pair of M19s and my take on the X-over controls is:1. The controls while commercially avail L-pads are actually connected in-circuit such that they're really simple rheostats. One control makes use of the 8 ohm section and the other uses the 35 ohm section.
2. The 8 ohm control affects all frequencies above the ~1200Hz Xover point. The 35 ohm control is part of a bridged "T" attenuation network designed to introduce a variable midrange dip in response. The mid response dip is greatest when the 35 ohm control is set to 0 ohms and is minimum at 35 ohms. Since the Altec driver/horn combo has a pronounced midrange "prominence", the 35 ohm control appears to provide a midrange boost or cut depending on its setting.
I modeled the electrical response of the Xover some time ago. The plots from the model were "interesting". I'll edit a plot or two into this post if I can locate the model on my computer.
I found achieving proper adjustment of the controls to be counter intuitive compared to pretty much every other speaker I've owned because they greatly interact with each other. I ended up setting them by ear using an iterative process.
Edits: 08/30/15
Thanks a million for the great help, Steve O!!!
I built a slightly modified versoin of the N1201-8a crossvoer with a 1st order low pass and 3rd order high pass for my center channel speaker.
I wanted to see if I could build it and how it sounded before putting it into my front speakers.
Thanks again.
Have a great day!
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck
The "Optimum" setting produces the flattest response when measured in the anechoic chamber at Altec. So you'll have to play with it to find the best settings for your room.
Here are the response graphs for the 19. I'd recommend printing this out so you can study it. It took me a while before it finally sunk in.
Thank you very, very, much Timoteus.
You guys on this forum amaze me at the documents you know about and share for other members.
A million than you's!!!
All the best!!!
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck
Interesting info. From the text I take it that this is Altec's set-up info, correct? FWIW, I ended up with controls set to provide a bit more mid notching and high boost than the "optimum" settings. Looking at the plots, I suspect I did this in an attempt to knock down that 3-4dB peak ~ 1.5KHz in the "flat" plot.
The M19s are fascinating even if flawed by today's standards. This discussion makes me want to get mine back into the vintage system again. Just have to get rid of......
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