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Horn and driver upgrades

Do your Klipsch speakers sound harsh or give you a headache after listening for a while? It's a very common reaction and the reason is the squawker horn. Not the K55 driver, the HORN! This is the fix.

B&C drivers and complete tweeters to replace the K77 are available directly from ALK.

All the Fastrac horns are compatible with the original Klipsch drivers and crossover networks, but once you experience the improvement in sound quality these horns deliver you will find a new love for your heritage Klipsch speakers and will want to move on to fix the other big shortcoming, the networks!

The "stock" grill frame assembly.

On the right is a grill frame from a Belle Klipsch. It's the K500 squawker horn, K55V driver and "Z-bracket" K77M tweeter. A frame out of a Klipschorn, on the left, looks the same except everything is a little bigger. It uses the K401 horn and K55M driver instead. Both frames are held to the sides by 4 long screws. The screw positions are marked by red arrows in the pictures. Remove those 4 screws and the entire thing slides out the front! They are very easy to remove and replace.

At this time the only replacement horn available is the Eliptrac 400 kit from Dave Harris. The Fastlane Audio web site is no longer available but you can contact Dave Harris by email: fastlaneaudio@aol.com

DRIVERS: 1-Inch, 2-Inch or keep the K55?

Modern trends are pushing manufacturers to make drivers with light metal diaphragms that go high in frequency. Modern 1-Inch drivers will not tolerate any power at the lower 400 Hz limit of the Klipschorn midrange. They will also generate distortion when reproducing these low frequencies. The stock K55V or K55M drivers use a tough phenolic material for their diaphragms and a throat that is slightly less then 1-Inch in diameter. Better drivers with a true 1-Inch throat like this are nearly impossible to find today.

The Belle Klipsch and La Scala can be crossed over at 500 Hz. 1-Inch drivers can still be found that will operate cleanly at 500 Hz but they are expensive. One such driver is the JBL 2426. The intermodulation plots shown below compare the stock K55V and the JBL driver on the K500 horn of the Belle Klipsch and on a 1-Inch wood Bruce Edgar type Tractrix horn. The lowest of the two tones is 550 Hz. The volume level is a respectable 100 dB SPL (Sound Pressure Level) 2 feet from the speaker. It's easy to see that the K55 isn't bad at all!


If you have a Klipschorn, the JBL 2426 just won't cut it! The next intermod plot compares the K55 and JBL drivers on 1-Inch horns trying to reproduce two tones. The lowest one is 450 Hz at 105 dB SPL. The JBL is far worse than the K55. To make matters worse, the Klipschorn midrange must operate even lower, down to 400 Hz! The plot at the far right is the 2-Inch B&C DCM50 driver on a 2-Inch Edgar Tractrix horn like the Trachorn 410. It is clearly the only way to improve on the stock K55. The DCM50 was deigned for the 400 Hz crossover frequency required by the Klipschorn.


There are quite a few 2-Inch drivers that will operate cleanly down to 400 Hz even though they were not designed to do so. The B&C DE85 and DE750 are to examples. These will also operate 2-way because of their light diaphragms. The economic reality seems to be that you should either keep the K55 and mate it to a 2-Inch horn with an adaptor, or go directly to a 2-Inch driver, even in a La Scala!

3-way Klipschorn systems

The most appropriate 2-Inch mid-range driver, the B&C DCM50


ALK suggests the B&C DCM50 2-Inch driver which is an ideal driver for use in the Klipschorn. These are designed for the 400 Hz crossover required by the Klipschorn. Larger drivers designed to go lower provide no advantage and simply cost more! No known 1-Inch driver can replace the stock K55V without distortion.

NOTE: If you do decide to replace the K55 with a better driver you should realize that your "stock" Klipsch network will no longer be usable. All of them depend on the natural roll off of the K55 at 6000 Hz to form the crossover. Very few quality drivers do this. They usually operate far higher. This means the squawker and tweeter will both be making a sound simultaneously. Better drivers will normally be louder too. Only the networks from ALK Engineering will do.


TIME ALIGNED mid-range and highs

A true 2-way system

Several drives have been found that will provide a true 2-way system with the 400 Hz crossover required by the Klipschorn woofer. One is the B&C DE85TN. It has low distortion and frequency response to well beyond the hearing range of most of us. Another is the B&C DE750TN.

Woofer / squawker network: Either high frequency setup you choose must be crossed over from the Klipschhorn woofer at about 400 Hz. The recommended low frequency network is the ES400 strapped for 2-way operation, but the AP12-400, AP12-AK3 or the high-frequency amplifier of a bi-amp setup are options. The stock Klipsch crossover networks are NOT suitable.

For the stock Cornwall: 2-way or 3-way


The B&C DE85TN driver mounted to an Eliptrac 400 horn will fit nicely into a stock Cornwall. This combination is actually not as deep as the Stock K600 Cornwall horn and K55 driver!

You will need to upgrade the crossover though. The stock crossovers are not compatible with wide-range drivers like the B&C. This would work nicely with the AP12-400 or AP12-500 low frequency crossovers in a 2-way system. Adding the AP15-6000 or ES5800 will let you keep the 3-way configuration using the K77 tweeter.

True 2-way or conventional 3-way? You can have it BOTH WAYS!

It's easy: Click the picture for details

All of the crossover network combinations from ALK Engineering are compatible with true 2-way or 3-way operation by removing a single strap. A simple switch can even be used in place of the strap to select between 2-way and 3-way operation in seconds if you have a conventional tweeter. The diagram at the left shows how the orange 3-wire cable provided with the squawker / tweeter (high frequency) networks (ES5800, AP15-6000 etc.) can be connected to make the change on a whim!

The transformer located on the woofer / squawker (low frequency) network will remain to set the level of the wider range driver in the 2-way switch position! The tweeter will simply make no sound. All you need to make this work is a driver like the DE85 or DE750 that is capable of operating all the way up to tweeter frequencies.


A direct comparison of popular 2-Inch driver choices for the Klipschorn.

Compare Intermod distortion: DCM50 and DE85TN
  • B&C DCM50: Provides the best impedance load to the network. Has only a small impedance peek that is located below the 400 Hz crossover because it was designed for the 400 Hz crossover required by the Klipschorn. It also features a composit rather then titanium diaphragm. It is usable only in a 3-way system.
  • B&C DE85TN: Is the least expensive of the two and the only one capable of 2-way operation. It was designed for a 1000Hz crossover but test show it functions will down to 400 Hz. Its power handling capability below 1000 Hz is therefore unspecified by the manufacturer but easily generated 105 dB SPL at 400 Hz 2 feet from the horn. It has a very diffuse impedance peek at about 600 Hz which is easily controlled by any horn designed to operate below 600 Hz. This includes any horn usable in the Klipschorn, La Scala or CornScala. This driver is the best choice for a limited budget.

ALK Engineering is a authorized B&C dealer. B&C has an extensive line of horn and driver products.

B&C Drivers


There remains a debate between a 2-way system or a 3-way system as to which sounds better. In our experience, a 3-way system using extreme-slope crossover networks yields the best results. The mid-range horn required in a 2-way system simply can't handle the highs as well as the smaller horn of a tweeter designed specifically to be a tweeter. The choice of what tweeter driver and horn then becomes the issue in a 3-way system.

The stock K77 tweeter should be the last item on your upgrade list. It is not a bad tweeter but can be easily damaged. There are better tweeters available. Here are several to consider.

A new tweeter to directly replace the K77 from ALK and Fastlane Audio

Introducing the Eliptrac HF

The Eliptrac tweeters will directly replace the K77 in the stock top compartment of the Klipschhorn, Belle Klipsch or La Scala. It can fit neatly between the squawker horn and the top providing a flush mount with the front baffle no matter if the old tweeter was directly mounted or with "Z-brackets". Unlike other direct replacements using the APT50 driver it will have high sensitivity and good transient response equal to the K77 and with good frequency response on and off axis!

Transient response: One method of evaluating transient response is to apply a short burst of pure tone into a tweeter and look at what comes out with an instrument microphone and oscilloscope. Does the tone stop when the applied burst stops or does it continue to ring like a bell after its struck. The picture at the left shows the tone burst of a stock K77 with the details identified, Click the picture for tone burst tests on six popular tweeters and drivers.

The APT50 rings like a Christmas bell! Any tweeter you may have that uses the APT50 driver should be replaced with either the stock K77 or a new tweeter using the B&C DE120 or DE110!

The Eliptrac HF horn is designed to allow the driver to mount flush to the horn. There is no air gap between the driver and the horn throat. There is no need for a "kludge" screw-on adaptor. With the DE110 or DE120 driver the entire tweeter is small enough to replace the K77 with no modifications to the speaker.

  • 1 - The B&C DE10. The DE10 has the smoothest response in the critical region between 6 and 17 KHz and still very good for use with a 4 KHz crossover. It is the least expensive of the drivers. Its ferrite magnet makes it too large to be a direct replacement for a K-77 in a stock Klipschorn, Belle Klipsch or La Scala. It can be used in a Cornwall. It's the preferred choice for a CornScalla or where the tweeter has been moved to the side of the squawker horn.
  • 2 - The B&C DE120. With its Neodymium magnet, the DE120 will fit anywhere a K-77 was used. It has the nicest frequency response of the two neodymium magnet drivers all the way to and beyond 20 KHz. This has been the best driver for most applications. B&C Speakers will soon discontinue the DE120. It will be replaced by the DE110.
  • 3 - The B&C DE110. The DE110 is soon to replace the DE120. It has equal performance, is slightly smaller and slightly less expensive. It also uses a Neodymium magnet.


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  • Shipping box: US Postal medium flat rate box. $13.60
  • Shipping weight: 4 Lbs.
  • [-Price-list-]

Eliptrac HF horn polar directivity:

Horizontally is the way to mount it!


When mounted vertically:


Mounting dimensions:


An all B&C alternative


The B&C DE10 tweeter with the B&C ME10 horn is also available directly from ALK Engineering.