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Altec Model 19 - N1201-8A Crossover Question

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Posted on August 29, 2015 at 13:41:44
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 Is it true that the High Pass section of the N1201-8A crossover had a 'midrange suppression' circuit that helped balance the midrange and upper high frequencies?

The schematic seems to show 2 each of 3.9 ohm resistors parallel with a 6 uf cap after the 3rd order filter section???

I am working on some two way crossovers for system with a horn HF driver and wondered if this is a good way to get a little better response from the HF horns above 3k?

Would I use a Contour Filter to achieve similar results???

Thanks in advance




"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

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RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 07:54:15
DaveV
Audiophile

Posts: 513
Location: SC
Joined: December 26, 2009
 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?

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 09:45:36
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 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

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 13:22:42
DaveV
Audiophile

Posts: 513
Location: SC
Joined: December 26, 2009
 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.

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 18:05:13
Steve O
Audiophile

Posts: 12359
Location: SE MI
Joined: September 6, 2001
 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.

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 19:34:55
timoteus
Audiophile

Posts: 94
Location: greater Kings Canyon/Sequoia Natl. Parks
Joined: June 21, 2000



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.

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 30, 2015 at 20:08:57
Steve O
Audiophile

Posts: 12359
Location: SE MI
Joined: September 6, 2001
 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......

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 31, 2015 at 13:00:08
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 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

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 31, 2015 at 13:04:03
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 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

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on August 31, 2015 at 13:05:16
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 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

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 1, 2015 at 19:15:48
Cougar
Audiophile

Posts: 4574
Location: SoCal
Joined: June 25, 2001
 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!

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 1, 2015 at 19:48:12
DaveV
Audiophile

Posts: 513
Location: SC
Joined: December 26, 2009
 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.


 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 2, 2015 at 09:09:26
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 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

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 2, 2015 at 11:20:53
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 The low freq cutoff of my HF driver and horn is 800HZ.

Would it be best to crossover at that point or above that at 1kHz or 1.2?

Thank you
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

Altec Model 19 does not use a..., posted on September 2, 2015 at 11:22:43
Cougar
Audiophile

Posts: 4574
Location: SoCal
Joined: June 25, 2001
 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.

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 2, 2015 at 11:31:39
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 I was mistaken about the cutoff for the horn and driver; it is at 500Hz whcih is close to the lowest useable pint for the driver.

Looking at the the horn's specs again, I saw that there is an asterisk next to the freq response. The note says freq response up to 12k which explains why I don't hear cymbals and hi hats as well as I would like.

I can add a tweeter. I just have to figure out how to mount it.

I have JBL 2402 or Selenium/JBL ST200.

"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 2, 2015 at 13:01:37
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 I used the T Filter from the above diagram and changed R2 to 2 ohms. That seems to have smoothed out the mids around 1.5k and made the higher frequencies come through very well.

This sounds much better than using a regular attenuation L circuit.
"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

RE: Altec Model 19 - N1201-8A Crossover Question, posted on September 3, 2015 at 09:33:45
Synthsayer
Audiophile

Posts: 113
Location: Lexington, KY
Joined: December 20, 2009
 The T-Filter with 2 ohm resistor at R2 transformed my okay sounding 2 way system that uses EV DH1012A driver with FaitalPro LHT142 into one of the best sounding speaker systems I have ever heard.

Even running off a measly 100W Denon AVR, the sound jumps out of these things the way it should with a high efficiency system. In addition to that, they seem to blend well with the other speakers in the surround system.

My center channel speaker is built using an old Sears Roebuck mahogany record cabinet my father bought in Memphis in 1949. I sealed off the top section of the record storage and put an MCM 10 inch 'pro' :-) woofer in it, then set a horn cabinet on top of it. My AVR, cable box and Roku are in the bottom.

If anyone is experimenting with passive crossovers and filters for systems that use horn loaded high freq drivers, they should strongly consider trying the Altec 30904 style T-Filter seen in the above diagram.

I wish I had a way to do some testing to see exactly what the response is but I don't. All I can say is that I can hear cymbals and hi hats, synth noise effects, and reverb effects in music much, much better; way better than I ever expected. I listen to a lot of old Bob Marley and reggae dub like Scientist that has lots percussion and synths.
Here's a link to a nice album by Scientist:https://youtu.be/B8LjzHKMLh4

I do have the new Dayton measurement mic for iPhone, so I may try some measurements if I can figure out how it is done.

Since this system only uses a 1st order LP filter, another dramatic improvement came from using a Parallel Notch Filter for cone break up areas to give the impression of a steeper crossover and as Baffle Step Attenuation. After using 4th Order LP filters, I really like the sound of the system this way much, much better.

Good luck and thanks to all who contributed to this effort. Your help was invaluable.

TLP


"Ad Astra Per Alia Porci", - To the stars on the wings of a pig: John Steinbeck

 

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