Fastrac Cornwall horn pros and cons

[Rjk1972]

Could someone please explain to me the pros and cons of the Fastrac Horn. What is measured by Polar Response. I've actually spent sometime Googling that and can't really find anything. Why are some people so against the Fastrac mod for Cornwalls?

 

Thanks

Russ

[Honeybadger]

1 hour ago, Rjk1972 said:

Why are some people so against the Fastrac mod for Cornwalls?

Some people don't want to cut their Cornwalls.

Others feel that they will turn your Cornwalls into a Jorjen 3, and no longer Klipsch.

Klipsch die hards believe if it's not made by Klipsch it cant be any good.

 

I like Tractrix myself, I think it is an improvement over exponential horns.

[Honeybadger]

Time for the 2 way crowd and the anti upgraders to chime in, these are the usual responses.

 

Get a K-510 2 amplifiers and an active crossover, or better yet get a K-402. (Be sure you get a Yamaha active crossover)

 

Have you seen the directivity of those horns they are terrible, you need a Constant directivity design.

 

Tractrix horns are beamy at high frequencies, you need a Oblate Spheroid design.

 

Horns with curved walls cause high order modes, you need straight sided horns.

 

I am sure I missed a few.

[Rjk1972]

Thanks for the responses. I get the not wanting to cut them. Mine are a minty, beautiful pair of CWO with risers. 

 

I've come across some comments about them. Sort of more generalizations. People saying g things like they measure worse than the stock horn and have a horrible polar response.

 

I'm not interested in bi or tri amping with actives. I've heard a few systems that went that route and outside really expensive Genelex and ATC speakers haven't heard anything I like. I have a sweet little Toolshed Amps customized EL84 amp arriving this week. My system as is is pretty good. A NOS Valve restored 500c retubed with all nice NOS tubes. A Rega DACr and Rega RP6 with a 2m Blue and my 1985 Cornwall 1s.

 

I'm looking for a little more smooth/lushness and detail than I have right now and maybe a little more bass and extension up top in my speakers. My crossovers are the original 31 year old crossovers. So I trying to figure out if I should go with the ALK crossover / Fastrac modification or just get a really nicely rebuilt set of crossovers, something like the Cornwall crossovers in the Garage Sale section.

 

So what is the "polar response" of a drive and what does it measure.

 

[Honeybadger]

I am by no means an expert.

 

I do like Tractrix horns and ALK crossovers. I have heard numerous great Cornwalls, amazing Jubilee's, Klipschorns stock, and modified, I love them all. 

 

Polar response is the horns ability to distribute sound on and off axis.

Why is polar response important? Having good polar response is necessary for clubs and theaters when the listeners are off to the sides of the speakers.

Constant directivity horns or constant coverage horns typically have good polar response but have to be equalized.

 

Tractrix and Exponential horns are Controlled directivity and tend to beam at high frequencies but typically do not require equalization.

Controlled directivity horns are typically used in a home where the listeners are sitting on axis with the speakers. Properly designed Controlled directivity horns can minimize floor and ceiling bounce due to narrower beam width.

What is POLAR RESPONSE CURVE?

 

The curve which indicates the distribution of the radiated energy from a sound reproducer for a specified frequency. Also the relative response curve of a microphone for various angles of incidence of a sound wave for a given frequency. Generally plotted on a radial decibel scale.

Have fun with your project.

 

HB

 

Anyone who does not like this response please refer to the opening statement.
 

 

[Chris A]

18 hours ago, Rjk1972 said:

Why are some people so against the Fastrac mod for Cornwalls?

 

Pros: doesn't lose vertical coverage just below 2 Hz (it probably holds its coverage down to 600 Hz), it has a tractrix mouth expansion (resulting less abrupt loss of coverage close to the horn's resonant frequency with driver attached), and it looks fairly nice. 

 

Cons: it won't sound as good as a K-510 (from Klipsch) down to ~600 Hz (...it's that coverage vs. frequency thing that Honeybadger clearly doesn't want me to talk about...as well as that "horn sound"), it's a large horn for its performance--in terms of coverage and "fc", and it apparently costs a lot more than other horns that are third-party sourced with similar performance (starting at ~$39.90US per horn). If trying to reuse the Cornwall's passive crossovers without sufficient modification/testing, its performance will suffer over a stock Cornwall.

 

 

You can do better for less money.  There are alternatives...but all require some modification to EQ (i.e., in passive crossover or upstream in the electronics) to achieve the same level of frequency response flatness as the K-600/K-55 with stock passive crossover filters, requiring a little testing/iteration...

 

Chris

[Mighty Favog]

14 hours ago, Rjk1972 said:

I've come across some comments about them. Sort of more generalizations. People saying g things like they measure worse than the stock horn and have a horrible polar response.

 

 

Think I know where that came from..........

[Honeybadger]

4 hours ago, Chris A said:

Cons: it won't sound as good as a K-510 (from Klipsch) down to ~600 Hz (...it's that coverage vs. frequency thing that Honeybadger clearly doesn't want me to talk about...as well as that "horn sound"),

 

Refer to opening statement.

13 hours ago, Honeybadger said:

I am by no means an expert.

 

Talk away

[profsbg]

Chris,

 

Please explain what are the K-510 advantages if sitting on axis, and if the advantages are significant   (e.g., due to room response). Also, is there any advantage to the (larger) tractrix sound when in fact sitting on axis? Thanks

 

 

[muel]

I imagine there are more technical reasons than I realize that I shouldn't use my Fastracs set up the way I have them.  

 

I'm unwilling to cut into my Cornwalls as well.  I set the Fastracs on top of the cabinet with them supported so they are perfectly level.  I have K-55m drivers mounted and connect the drivers to the original input connection on the back of the speakers.   That connection is wired to the squawker connection on the crossover.  I have new inputs installed on the back for my speaker wire connection.   As good as this sounds, it makes the mids a little bit too hot.  I bumped down the mids 3db on the crossover.  

 

The Fastrac sounds better to me than the original horn even though it evidently shouldn't.  It sounds much more "open" to me and I would say that it actually sounds better than the original off axis as well but I'm almost never off axis.  This setup is on a secondary system now.  What I like most about it is that I can easily convert everything back to its original state.

 

[Chris A]

There's a fairly large amount of difference in a K-500/K-55 (i.e., the Belle midrange horn) and a K-510 with 2" K-69-A in terms of neutrality of sound and coverage horizontally and vertically.  It doesn't take very long to become very aware of those differences: it's immediately audible, truth be told. 

 

The Belle's K-500 horn is an unmodified exponential horn which loses its directivity in the vertical direction below 2 kHz.  The Cornwall's K-700 is basically the same horn profile except it's cutoff frequency is ~200 Hz higher.  Both of these midrange horns (K-500, K-700) sound very similar to my ears, but the horn-loaded bass on the Belle sounds cleaner but less deep.

 

The K-510 is a straight-sided pyramidal horn--which many describe as "conical" but which isn't really conical--which holds it's horizontal and vertical coverage well down to ~600-700 Hz, and gradually loses polar control below that point.  It also has a tractrix mouth flare and "mumps" in the corners of the horn that together avoid coverage anomalies (an initial  "waist-band" narrowing, followed by an increasing widening of coverage, then complete loss of coverage control vs. frequency toward its low frequency cut-off region).  The K-510 is "well behaved".  The difference in holdover transient decays and horn edginess is fairly striking with the K-510 being the most neutral horn that I've heard--not counting the K-402. Note the difference in timbre with the above K-500 and K-700 is not so great once the horn/driver is time aligned with the tweeter and bass bin/woofer.  But the neutrality of the transients and the solidness of coverage vs. angle isn't difficult to hear.

 

The Fastrac appears to be a conical-tractrix horn (i.e., top and bottom sides flat and expanding, sides curved to a tractrix profile).  It sounds intermediate in performance between to the K-700/K-55 and the K-510/K-69-A in terms of edginess and holdover, with much less issues in terms of floor-ceiling bounce.  I believe it is this latter characteristic (avoidance of lower frequency loss of vertical coverage control) that is the most significant cause for the listening differences and preference among its owners.

 

Chris

[muel]

The   K-510/K-69-A  combination has been suggested to me before.  Doesn't this require a passive crossover change or would the original work?  Not so much an issue for you as I know you prefer active crossovers.  

 

"  (avoidance of lower frequency loss of vertical coverage control) that is the most significant cause for the listening differences and preference among its owners. "

 

Not sure I'm translating this correctly... so are you saying some frequencies are ultimately being attenuated a bit by using the Fastrac?  or am I Off-trac ?  I'm trying to wrap my head around what you are saying.

[Chris A]

1 hour ago, muel said:

Not sure I'm translating this correctly... so are you saying some frequencies are ultimately being attenuated a bit by using the Fastrac? 

No, not at all.  I'm saying that the Fastrac sounds better because it isn't doing that "collapsing polar" thing that all the other Heritage midrange horns do.  That collapsing polar characteristic is responsible for a lot of compliants by novice Heritage owners that aren't used to dealing with that extra 400-1700 Hz energy on their ceiling and floor. PWK liked that design.  I don't, and apparently many Heritage owners also have trouble with it. 

 

____________________________________________________________________________________

 

Now that I've got some listening time and experimentation under my belt, I should probably also describe the sound of the K-402-MEH (multiple-entry horn) vs. the K-510/K-69-A with a tweeter for comparative purposes so that you can see the progression of listening differences for progressively better and more controlled midrange/midbass horn polars:

 

1) Mid-bass continuity (i.e., tuning fork "A" down to 100 Hz, over two octaves below) is much more apparent in the K-402-MEH.  I believe that many people must have gotten used to the narrow coverage of the folded bass bins of the Khorn, Belle, and La Scala, and the direct-radiating Cornwall and Heresy at frequencies close to a 1/4 wavelength across the woofer cone diameters (i.e., indicating a narrowing of coverage at those frequencies).  The K-402-MEH really makes speech intelligibility much, much better.  The sound of speaking voices and midrange instruments is a bit startling at first, since there is no "disconnect" between the bass bin and the midrange horn--it's totally integrated.

 

2) The timbre of the K-402-MEH also is fuller and more consistent regardless of listening angle.  I know this characteristic isn't something that comes up in conversation, but nevertheless is something that is quite attention-getting.  [I find that there are a lot of mid-bass issues with all loudspeakers, and when you happen across one that doesn't have those issues, it grabs your attention.]  The octave between 200-400 coverage and offset/alignment problems aren't problems any more, and male voices, pianos, and guitars (unmastered recordings, that is) sound much more life-like, balanced, and focused.

 

3) The K-402-MEH has a much more "integrated" bass and deep bass potential, I attribute this to the point source effect, avoiding the driver-offset issues in typical loudspeakers.  If you get a chance to listen to a Danley Synergy horn (preferably the SH-96, and also the SH-50 or SH-60 would be good candidates), I'd take the opportunity to listen, particularly to the integration of midbass instruments and voices.

 

[I offer the above discussion only as a logical progression of what happens as you continue to address and solve the issues with midrange horn coverage vs. frequency and integration with midbass coverage.]

 

Chris

[Deang]

18 hours ago, Chris A said:

The Fastrac appears to be a conical-tractrix horn (i.e., top and bottom sides flat and expanding, sides curved to a tractrix profile).  It sounds intermediate in performance between to the K-700/K-55 and the K-510/K-69-A in terms of edginess and holdover, with much less issues in terms of floor-ceiling bounce.  I believe it is this latter characteristic (avoidance of lower frequency loss of vertical coverage control) that is the most significant cause for the listening differences and preference among its owners.

 

When you speak through the two horns, the sound is very different. One sounds natural/uncolored - the other one does not. Bruce Edgar did this demonstration for many years to show the difference between exponential and tractrix - so I don't think "floor-ceiling bounce" is dominating here.

[Deang]

17 hours ago, Chris A said:

... I'm saying that the Fastrac sounds better because it isn't doing that "collapsing polar" thing that all the other Heritage midrange horns do.  That collapsing polar characteristic is responsible for a lot of compliants by novice Heritage owners that aren't used to dealing with that extra 400-1700 Hz energy ...

 

I'm not quite following you here Chris, because these horns definitely collapse the vertical plane. 

 

Even though the Fc is higher and much closer to the crossover point, Dave's horns show significantly less distress when using low order filters. I agree with John Warren, and believe the long narrow throats cause what he calls "throat overload distortion".  

[Chris A]

5 hours ago, Deang said:

...these horns definitely collapse the vertical plane. 

If you're talking about the Fastrac horn shown in the bottom photo below, it's basically the vertical mouth dimension that controls the frequency at loss of polar control.  If that dimension is twice the height of the K-700 horn, then it loses vertical polar control about an octave lower, etc.  That would make the loss of vertical polars around 700 Hz  or lower rather than 1700-2000 Hz for the K-700. 

 

 

 

5 hours ago, Deang said:

...I agree with John Warren, and believe the long narrow throats cause what he calls "throat overload distortion".  

While that discussion wasn't part of my discussion above, one thing that you'll notice about all Klipsch acoustic horns is that they tend to expand more rapidly at the throat than a strict exponential/tractrix curve (which are the same curves at the throat end, if you look at the equations).  This is the so-called "rubber throat" of PWK that significantly reduces thermodynamic (condensation) distortion as well as generation of "frying bacon" (higher order modes) that will interact with the midrange driver up to about 8 kHz, at which point these HOMs will exit the horn mouth.  So to say that Klipsch has throat distortion and other third-party vendors' horns don't--probably isn't terribly accurate.  However, the degree of throat distortion may be lower in other horns due to a more rapid throat expansion than the K-600, K-500, or K-400 horns. 

 

 

[Honeybadger]

I am more concerned with the sound than all of this polar control jargon.

 

All I am saying is the Tractrix sound better to me than the exponential.

 

The horn above doesn't look at all like my old fastrack cornwall.

[Chris A]

28 minutes ago, Honeybadger said:

All I am saying is the Tractrix sound better to me than the exponential.

The tractrix profile horn will only sound different at lower frequencies, if the only difference is tractrix vs. exponential,...because that's the region where the two expansion profiles differ.*

 

*One thing that you might not realize is that straight horn expansion further than a 1/4 wavelength at the axial point from the throat really doesn't affect the sound wave at that frequency. So the throat end of the horn produces the high frequencies, and the entire length of the horn including the mouth end produces the low frequencies.  Only the changes in horn profiles can change the sound emerging.

 

If you carefully read my above posts, the discussion of horn coverage differences was specifically aimed at "how one horn profile sounds different from another" rather than just a discussion of physics or mathematics.  Only a cursory discussion of the "why" was included to give an intuitive idea of what's occurring to those that might have an interest.  That's why I took the time to write it the way that I did.

 

Chris

[Honeybadger]

27 minutes ago, Chris A said:

The tractrix profile horn will only sound different at lower frequencies

To me the K-600 and Fastrack Cornwall horns sound very different. It doesn't sound like it is restricted to the lower frequencies only.

 

HB

[Honeybadger]

21 hours ago, Chris A said:

No, not at all.  I'm saying that the Fastrac sounds better because it isn't doing that "collapsing polar" thing that all the other Heritage midrange horns do. 

 

21 hours ago, Chris A said:

That collapsing polar characteristic is responsible for a lot of compliants by novice Heritage owners that aren't used to dealing with that extra 400-1700 Hz energy on their ceiling and floor. PWK liked that design. 

 

I am not sure if you agree the Tractrix sounds better than the exponential or not.

 

If not- I have to agree to disagree. No amount of calculations is going to make me think the increased clarity I get from tractrix doesn't sound better than exponential horns.

 

I assume this is exactly how you feel about CD horns.

 

HB