(From Speakerlab's Technical Compendium TC-10 1979, by Pat Snyder)

"A Shortcut (pun intended)

"You will find that bass horns designed strictly to the forumula are quite long. Olson demonstrated (Reference 1, p. 114) that the horn can be shortened considerably, with little adverse effect on the bass response, by using a faster taper rate in the throat end. In addition this extends the high frequency range of the horn.

"The Speakerlab K uses a 100 hz taper rate for the first 8 inches of horn path from the throat, then a 48 hz taper rate thereafter. A line for the SK is plotted on figure 5.

"References

"1. H. F. Olson, Elements of Acoustical Engineering, 2nd Ed., Van Nostrand, New York, 1947. Out of print."

• "A low frequency horn of small dimensions"

The plans show the same 50Hz flare rate used by the original Klipschorn. Also the remaining "K" flares are 32 and 38Hz respectively with the same overall horn pathway length (approx. 64 linear inches). Both horns employ a 78 sq. in. throat area cross-section. A virtual Khorn knowckoff with a couple of improvements, funny since they were originally included in the 1946 Klipsch plans (a 12" driver size) but were subsequently dropped by Klipsch production some time later. These include back chamber "stuffing" and back chamber/channel axially aligned bracing to reduce vibration.

Most likely, the THROAT CAVITY OPENING of the Speakerlab "K" is the so-called "wrong" part, evidently copied directly from a post-1962 Klipschorn, being that it is 3" wide versus the 6" wide typically used for a non-K33 driver, such as the W1508S 8 Ohm driver used by Speakerlab. This is where the SL "K" MAY have been improved BUT I heard a pair of "K"s at the time, and in no way do I think that they suffered in the least from using the smaller slot size. I've NEVER heard a Klipschorn that beat them on the bass-end to this day.

DM

As I said, this is from a Tech paper from Speakerlab.

From Speakerlab's Technical Compendium TC-10 1979, by Pat Snyder

This paper, as well as about a half inch thickness of other technical papers, were what Speakerlab sent out as their "Speaker Design Book". Most were written by Pat Snyder, one of their engineers, and were papers presented at AES meetings.

If you wish, email me. I'll try to scan it, but it is printed on green paper. I'll see if I can lighten it up enough to read. I quoted Mr. Snyder accurately.

Clearly the 100Hz reference is a direct and mistaken ripoff from the original 1945 Klipschorn patent document, which was concerned with a smaller version featuring a single 12" field coil driver which DID indeed use a 100Hz flare rate at the throat. So much for copying the at-the-time-and-still-current-flavor of the larger 15" driver version of the Klipschorn and not knowing why it's the way it is...

However, the 1970's Speakerlab "K" used the familiar 15" driver and the normal 50Hz throat expansion rate, as indicated in the Speakerlab "K" plans. Anyone with a ruler can figure it out. Wavelength/18.1 = exponential area doubling length, and that isn't going to amount to 100Hz (that would double its area every 8 inches (approx) of linear travel)!

The throat area cross-section doubles, according to the plans, at at approx. 16 inches, measured center of channel, which would be 50 Hz, thereabouts.

DM

Gives me the willies that Speakerlab was so blatently uninformed about what they were doing! Blindly copying.

But at least its not a bad copy, anyway. Couple of improvements, to boot!

DM

• Klipsch KPT-MCM-4-T Grand

I imagine the scale and power of the MCM stack would be impressive (and I don't just mean the footprint), to say the least, but I haven't heard them. But I have studied the available documentation about them, though.

Stacked in a pair, the throat size is correct for the "official" 30Hz in 1/2 space according to the Gillum patent document if I remember correctly. I would expect to be impressed, at any rate.

I have played around with a 2" tractrix midrange horn (DIY), and they have a distinctive "flavor", quite addicting actually. It has to do with the way that the sound propogates, rather than having a particular "sound" in its response. It's rather like when a nice speaker system broadcasts into a large, quiet, non-reflecting space. Except it's in your room. A positive effect, to say the least.

DM

I'd like to see that MGM, as I don't know anything about it except what I see in the picture. The midhorn and tweeter are pretty easy to see, but you can't know what configuration the basshorn uses from the picture. It looks like a W-bin, but I can't know for sure.

Tell me where - and it's there!

DM