Building some horns

[tigerwoodKhorns]

Check out this one. Scroll down and there are three shots of it on a dark K Horn:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220324803599&translate=no&ssPageName=LanguageToggle

That is a big horn! Are they limiting the K Horn to maybe 300 Hz or lower? If so what are they using on top?

EDIT - I reread the ad, it looks like a 200 Hz horn and an Altec 288 driver by my guessing.

[djk]

• I should mention that the Jabo horns are exponential, not tractrix.

• Posted by

PK (A) on November 11, 2008 at 02:50:11

In Reply to: RE: beautiful Jabo horns (from Germany) -opinions? posted by Angaria on November 10, 2008 at 11:10:25

Hi Angeria,

I have a pair of Jabo KH-50B's as well as a pair of the smaller horns from Stereolab (to be used above 1000 Hz) - the company that djk is referring to. I think both horns sound good. The Jabo KH-50's appear slightly less damped than the Stereolab horns which seems to be completely dead. The Jabo KH-50 is an older version, and according to Werner Jagusch who make the Jabo horns, the newer versions (e.g., KH-55 and KH-30) are slightly better and hence more expensive. Note that the curvatures are different: While all the Jabo horns use an exponential curvature, all the Stereolab horns are tractrix.

Best regards

Peter

-------------------------------------------------------------------------------------------------------------------------------

The depth of the 72cm and 75cm horns is not listed, so it would be difficult to calculate what they may do.

" 1/4w and 1/2w - what is the "w" so that I can do the calcs? Is that an octave? How do you arrive at 565 hz for this 400 HZ horn?"

W is wavelength. The speed of sound is about 1130 feet per second, so the wavelength of a 100hz note would be 11.3 feet. The peak amplitude of a sinewave is at the 90° (1/4W) point, so the horn will load the driver down to this point, but may not have useable response. In a cone driven bass horn the front and rear cavities may be adjusted for flattest response in the bottom octave, something that is difficult to do in an HF driver (although RCA made an HF driver that you could vary the rear cavity volume).

"I have asked this question a bunch of times and your is the best answer so far. I was told before that about 1/2 octave below the cutoff frequency is what I need, or 300 hz for a 400 hz cutoff (200 to 400 being the octave below the cutoff frequency). "

A half-octave is 1.414 (or .707) depending on whether you are going up or down in frequency. How much overlap in response you need is in large part a function of how steep the drivers/horns cut off, and how smooth you want it to be.

[tigerwoodKhorns]

• I should mention that the Jabo horns are exponential, not tractrix.

• Posted by

PK (A) on November 11, 2008 at 02:50:11

In Reply to: RE: beautiful Jabo horns (from Germany) -opinions? posted by Angaria on November 10, 2008 at 11:10:25

Hi Angeria,

I have a pair of Jabo KH-50B's as well as a pair of the smaller horns from Stereolab (to be used above 1000 Hz) - the company that djk is referring to. I think both horns sound good. The Jabo KH-50's appear slightly less damped than the Stereolab horns which seems to be completely dead. The Jabo KH-50 is an older version, and according to Werner Jagusch who make the Jabo horns, the newer versions (e.g., KH-55 and KH-30) are slightly better and hence more expensive. Note that the curvatures are different: While all the Jabo horns use an exponential curvature, all the Stereolab horns are tractrix.

Best regards

Peter

-------------------------------------------------------------------------------------------------------------------------------

The depth of the 72cm and 75cm horns is not listed, so it would be difficult to calculate what they may do.

" 1/4w and 1/2w - what is the "w" so that I can do the calcs? Is that an octave? How do you arrive at 565 hz for this 400 HZ horn?"

W is wavelength. The speed of sound is about 1130 feet per second, so the wavelength of a 100hz note would be 11.3 feet. The peak amplitude of a sinewave is at the 90° (1/4W) point, so the horn will load the driver down to this point, but may not have useable response. In a cone driven bass horn the front and rear cavities may be adjusted for flattest response in the bottom octave, something that is difficult to do in an HF driver (although RCA made an HF driver that you could vary the rear cavity volume).

"I have asked this question a bunch of times and your is the best answer so far. I was told before that about 1/2 octave below the cutoff frequency is what I need, or 300 hz for a 400 hz cutoff (200 to 400 being the octave below the cutoff frequency). "

A half-octave is 1.414 (or .707) depending on whether you are going up or down in frequency. How much overlap in response you need is in large part a function of how steep the drivers/horns cut off, and how smooth you want it to be.

I have not seen the equation but 1.414 and 0.707 look like multiples derives from an exponent, which makes sense in a log scale.

So lets look at a K Horn with a desired 400 Hz cutoff.

The full octave is 200 hz (200 to 400 hz). So do we multipy 0.707 by 200 Hz and wind up with 141 hz or build a horn that is 140 Hz less than 400 hz, or a 260 Hz horn? Is this correct?