Top-mount Fastrac Cornwall horn questions

[tlarwa]

So I've been living with my stock (with the exception of re-capped crossovers) 1982 CW 1-1/2's for about 6 months now and I'm ready to do some upgrades.  I've read a million (or so it seems) posts and threads on the Fastrac mid-horn, and by all accounts this is the upgrade to make next.  My crossovers are the B1, and I have the K-55-V two-piece drivers with solder lugs.  So I plan to stick with the 1" throat horns and re-use the existing drivers.  From what I've read, and from what Dave has said, I should be good with the crossovers as they are (a crossover upgrade could happen in the future, but I'd like to see how they sound before I spend that $$).  I don't really want to cut up the motorboard, although I have the tools and ability.  So I'm thinking about top mounting the Fastrac horns.  I have a couple questions:

 

1. Do they have to be in a cabinet, or can they be "free air"?  I'm assuming they can, but wanted to make sure.

2. With the Fastrac horn, do I have the option of running them 2 or 3 way?  From what I gather the Fastrac horn can be used as a 2 way, but I'm not sure I'm reading that correctly.  If it stays a 3 way, and I top mount the mid-horn, would I then top mount then tweeter as well, keeping it above the mid-horn?  Also, if it can be run as a 2 way, do I just disconnect the tweeter fro the crossover and keep everything else as is?

3.  Does anyone have their Cornwalls set up with the horns on top of the cabinet, and can you send me some pics so I can see how you have them set up and what they look like?  

 

Sorry for all the questions that I'm sure have been answered a 100 times already.  I honestly searched and read a lot, but am still not comfortable I have all the info I need.  

 

Thanks for for any help, advice, guidance, wisdom, suggestions, etc.

 

Tom

[Honeybadger]

You can certainly set the mid-horn on top, but it benefits from being mounted near the woofer.

 

No need to move the tweeter on top of the cabinet.

 

Just disconnecting the tweeter will not work properly for 2 way operation. The K-55 doesn't go high enough for 2 way operation. 

 

The Fastrac is designed for 3 way. The Eliptrac can be used 2 way, but was also designed as a 3-way. Tractrix horns suffer from collapsing polars, therefore they are not good candidates for 2 way operation.

 

HB

[Chris A]

5 hours ago, Honeybadger said:

Tractrix horns suffer from collapsing polars, therefore they are not good candidates for 2 way operation.

 

I believe that it is "wide-mouth horns having a shorter height vs. width" (or vice versa) instead of "tractrix". 

 

Tractrix expansion by itself doesn't experience collapsing polars unless its mouth is modified to do that.

 

Chris

[Chris A]

11 hours ago, tlarwa said:

From what I've read, and from what Dave has said, I should be good with the crossovers as they are...

 

I'd like to see the measurements that make that statement true.  On this subject...I'm from Missouri.

 

11 hours ago, tlarwa said:

1. Do they have to be in a cabinet, or can they be "free air"?  I'm assuming they can, but wanted to make sure.

 

Most midrange horns of the size of the Heritage series midranges benefit from baffle mounting, although they can be used without their mouths mounted to a baffle.  The reasons for baffle mounting?  Clamping the mouth of the horn so that it doesn't ring (...even MDF moves around...), and providing a baffled exit for the horn extends and smooths its low frequency performance.  See the last page of the following article: https://community.klipsch.com/applications/core/interface/file/attachment.php?id=8074

 

11 hours ago, tlarwa said:

If it stays a 3 way, and I top mount the mid-horn, would I then top mount then tweeter as well, keeping it above the mid-horn?

 

The tweeter can be below the midrange horn if mounting both to a baffle, but the tweeter benefits from being able to move back until it's aligned with the midrange driver.  In that case, it needs to be on top on the midrange horn in order for its output to not be obscured by midrange horn mouth while you're listening to it.  The tweeter itself benefits much less than the midrange horn from baffle mounting. 

 

11 hours ago, tlarwa said:

Also, if it can be run as a 2 way...

 

You need a midrange driver that can go to 15-20 kHz.  The K-55 driver tops out at about 6 kHz.  Any straight horn can support higher frequencies (albeit narrow coverage angles if the horn's walls are curved).  It's curved axis and folded horns that attenuate the highs so that they cannot be used for tweeter frequencies. 

 

11 hours ago, tlarwa said:

...do I just disconnect the tweeter from the crossover and keep everything else as is?

 

You will have other effects by just disconnecting the tweeter electrically from its passive crossover.  Measurements of loudspeaker output to see the effects on the crossover electrical performance are usually required.  Of course, if you don't care about the resulting frequency response of the loudspeaker, you can do anything you want.

 

In general, ANY changes that you make to the drivers, horns, passive crossover, or the mounting of the horns/drivers with respect to each other and the loudspeaker cabinet--will change something in the frequency response of the speaker, both on-axis and off-axis. 

 

Any change in a loudspeaker's drivers, horns, or passive crossover usually requires some sort of test using a calibration microphone to verify the resulting loudspeaker output.  You can think of the situation like a large mobile hanging from the ceiling: if you reach up and grab a piece of mobile and pull downwards, the whole mobile will shift in somewhat unpredictable ways into a new shape.  Same thing for loudspeaker performance.  A test is required after a change in anything to make sure of the effects that occur.

 

Chris

[tlarwa]

Chris, 

 

Great reply, and I appreciate the thorough answer.  And I can't say I'm surprised by it ... I knew it couldn't be that simple!  So it sounds like I should baffle mount the Fastrac horn, and keep the tweeter in play.  The question then is whether or not the network needs to me modded or not.  I'll do more investigating about this, although I've read here that it's not necessary (but can help if it is modded).  As for the "free air" mounting of the horn,  I'm not sure I would have done that anyway, but it deserved the question.  

 

Tom

[muel]

I don't disagree with Chris nor will I argue but I will say that setting Eliptracs (in a small frame) on top of my La Scala's with BMS drivers installed was a wonderful improvement over stock!   Setting Fastrac's on top of my Cornwalls using the original k55 drivers was also an improvement.

Whatever the drawbacks were I was still enjoying a net gain!

 

I found that the response at my seat using AudioTools RTA was actually quite flat except for a 5-7db bump around 125-150hz.  I'm sure that I have other issues but I'm not unhappy with my setup.  I think I still need to work on my speaker placement a bit to work on that bump.  

[mkane]

  watching this like a hawk

[tlarwa]

4 hours ago, muel said:

I don't disagree with Chris nor will I argue but I will say that setting Eliptracs (in a small frame) on top of my La Scala's with BMS drivers installed was a wonderful improvement over stock!   Setting Fastrac's on top of my Cornwalls using the original k55 drivers was also an improvement.

Whatever the drawbacks were I was still enjoying a net gain!

 

I found that the response at my seat using AudioTools RTA was actually quite flat except for a 5-7db bump around 125-150hz.  I'm sure that I have other issues but I'm not unhappy with my setup.  I think I still need to work on my speaker placement a bit to work on that bump.  

Muel,

 

I have read some threads on your build.  In fact, that got me thinking about whether I should top mount or not.  Did you modify or replace your crossovers as well, or leave them alone?  And do you have the B or B1 variant?  And did you leave the tweeter in its original position in the baffle?  If you have any pics of your build that you could share I'd sure like to see them!  The way I look at it, I can always try them on top and then mount them in the baffle if necessary.  I'm pretty handy with woodworking, so building a cabinet for the horns isn't a big deal.  I would like to verify the crossover debate, however...

 

tom

[muel]

I'll talk about the Cornwalls with the Fastrac's.  I have the B2 networks installed which I upgraded from B1's (just a couple of parts).  I found that the mids were a little too loud so I attenuated them another 3db.  I think this is a matter of taste.  It is possible you would like the Fastracs with the crossovers stock so I would certainly try them that way first.  I didn't do any measurements so I don't know what would be more "correct" for sure.  Cornscala-wall crossovers from ALK engineering would allow you adjust as you like easily.   For the stock crossover you change the tap and add a resistor.  

 

I left the tweeters in the original position (mine are verticals from the 60's).   To place the mid driver and Fastrac outside the cabinet you obviously need to get it connected to the crossover.  I added new jacks for the input on the back of the cabinet and then used the old input as my connection for the mid driver.  Easy peasy!

 

With your woodworking skills you might find yourself a DYI project and build a whole new set!  

[tlarwa]

Muel,

 

I mis-spoke ... my networks are the B2, not the B1.  How did you attenuate the mids, exactly?  Just curious for when/if I end up there.  Is it just a resistor add and changing the tap on the network for the mids?  And if you get a chance, can you post up a pic of your CWs to show the horn mounted on the top?

 

Thanks!

[muel]

Thanks to some of the more knowledgeable here I learned that I could drop the squawker of the B2 by 3db if I move the squawker connection on the T2A from tap 3 to tap 2 and add a 15 ohm resistor across the squawker terminals.  

 

I looked and it seems I have no pictures of the CW's with the horn on top but it is actually just sitting on top.  I placed some wood shims under the rear of the horn to make it perfectly level. It might be better to fix them more firmly or build a cabinet for them but they have been working well as is.   I'll take a picture when I get a chance.

[tlarwa]

Thanks for the info, Muel.  Sounds like an easy enough adjustment.  If I decide to top mount I'll build a cabinet, so no worries on the pics.