WMcD Posted April 22 Share Posted April 22 Typically horn flare rates (areas)are described by the term "cut-off" frequency aka "Fc"; at freques below this this the horn just about stops working. You put Fc into the exponential equation however, PWK often used the term "lamedh" (I'll use "Ld") to describe the horn area expansion; It is the lengh of travel down the horn in which the area doubles (or halves). Therefor the expansion works like animals / bacterium doubling every time period. If my math is correct, the cuttoff wavelength (I'll call it "Lc) is 18.1 times the length to double. We can examine the LaScala's two paths (combined) and notice the area at the throat is 0.5 ft^2; then the paths go across the back to the interior corners where the area is 1 ft^2; then toward the front for a foot to where the area is 2 ft^2; then another foot to the mouth where the combined area is 4 ft^2. Therefore we see the Ld is 1 foot or 12 inches. The Lc is thus 18.1 * 12 and we dived the velocity of sound 15,00 in/sec by that wavelength to get an Fc of 62 Hz. We can check the PWK article on the K400 horn and notice that the length to double is given as 2.75 inches. The math like the above shows that it's Fc is 270 Hz. PWK was really getting it to go as low as possible to where the bass bin on the Khorn is running out of steam! Good night all, WMcD 7 Quote Link to comment Share on other sites More sharing options...
Woofers and Tweeters Posted April 22 Share Posted April 22 5 hours ago, WMcD said: WMcD Hello Gil, Thanks for the information. I have wondered about the formulas used to make speakers sound as great as they do. I hope you're doing well. Glad to see you posing again and please keep posting when you can. James 3 Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 22 Author Share Posted April 22 It is instructive to look at US Patent 4,210,223 (Note this is corrected)which concers the big MCM bass horn woofer. The Length to double area is 23.3 inches which gives an Fc of 31.95 Hz. You can find the document at USPTO.GOV or Google Patents. There is in that patent document some design information. And Klipsch and Gillim use the 18.1 figure (so I was correct!) Many thanks toJames and also to John A for helping me through this stroke time. WMcD 7 Quote Link to comment Share on other sites More sharing options...
Deang Posted April 22 Share Posted April 22 Glad to see you back Gil. 4 Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted April 22 Share Posted April 22 This place is much better with you Gil … 🙂 2 Quote Link to comment Share on other sites More sharing options...
Woofers and Tweeters Posted April 22 Share Posted April 22 2 hours ago, WMcD said: Many thanks to James and also to John A for helping me through this stroke time. WMcD Glad to help. You have been so much help on here for many years. I saw this thread this morning and thought it was one from years ago. It made my day when I saw it was a new one from you. Glad you're back. Quote Link to comment Share on other sites More sharing options...
JohnA Posted April 23 Share Posted April 23 Hey Gil! Good to see you posting again. Musta worked out the computer issues. Do you like tablets? Sometimes they are easier, but typing is slower, one or 2 fingers. But I love the pinch/zoom. 1 Quote Link to comment Share on other sites More sharing options...
babadono Posted April 23 Share Posted April 23 Oh how wonderful to see you back here Gil. God Bless you. 1 Quote Link to comment Share on other sites More sharing options...
babadono Posted April 23 Share Posted April 23 Don't know too much(if anything) about the math behind horns..but sure love how they sound. Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 27 Author Share Posted April 27 Since I've been writing about US Patents . . . Please consider the bass horn shown in the Klipsch Papers i.e. Bell Labs' Symposium. I shows up in US Patent 1,970, 926 titled "Sound radiator" to E.C. Wente and assigned to Bell Labs. (It is likely the same IMHO) It seems best charactized as a giant re-entrant horn (like a bull horn) in a box. It does not seem adaptable to home construction. But take a look. It claims 300 to40 Hz with a 5 square foot mouth and 3' 8" depth. Stackable. 'Good Night, WMcD 1 Quote Link to comment Share on other sites More sharing options...
JohnA Posted April 28 Share Posted April 28 Weird. Built in halves and bolted together. Wente stated horns with large mouths became directional. Is that true? Quote Link to comment Share on other sites More sharing options...
WMcD Posted Tuesday at 01:58 AM Author Share Posted Tuesday at 01:58 AM I took another look at the Symposium bass horn and see the throat is 50.27 in^2; the mouth is 3,600 in^2; the length is 131.76 inches (approx). From those I calculate the Fc to be 34.83 Hz. Thanks to John A for the graphic. Good Night All, WMcD 3 1 Quote Link to comment Share on other sites More sharing options...
Bill W. Posted Tuesday at 03:43 AM Share Posted Tuesday at 03:43 AM I would love to hear one of those to understand their capabilities, seems like a groundbreaking achievement in their day. Quote Link to comment Share on other sites More sharing options...
Dave MacKay Posted Tuesday at 09:29 PM Share Posted Tuesday at 09:29 PM I've been reading an old (1972) book (How To Build Speaker Enclosures by Badmaieff and Davis). A topic that I found to be of interest was how the area of the mouth of an exponential horn determines the lowest frequency that the horn can reproduce. I tried applying the logic to my vintage La Scalas, but the answers I get don't seem to be very satisfactory. I measured the area of the mouths of: a) the lens used with the K-77M tweeter (4" x 1.5") b) the K-400 horn used by the squawker (16.75" x 5.75") c) the La Scala bass bin (22.25" x 22") I then used those areas to figure out what the circumference of a circle with the same area would be (i.e., Radius=sqrt(Area/pi) and Circumference = 2pi*Radius). The thinking is that the lowest wavelength the horn can support should match the circumference, I divided the speed of sound (1125 ft/s) by the wavelength to get the frequency (in Hz). Here's what I came up with for the lowest frequencies supported by the different horns: a) lens used with the K-77 tweeter ---> 1555 Hz b) the K-400 horn used by the squawker ---> 388 Hz c) the La Scala bass bin ---> 172 Hz I thought the the K-400 got its name because it was intended for use down to 400 Hz, so the figure for it (i.e., 388 Hz) seems reasonable. However, from what I've read on this forum, I thought that the La Scala bass bin was supposed to be good to about 104 Hz, which is well below the 172 Hz that I calculated. I'd be grateful if anyone would care to help me understand this better. Quote Link to comment Share on other sites More sharing options...
JohnA Posted Saturday at 04:38 AM Share Posted Saturday at 04:38 AM Memory is a ethereal thing, but I recall that rge K-400, on a baffle, had an fc of 273 Hz. I ksonthought the *length* of the horn controlled its fc and the mouth area determined the response ripples it had (or didn't). I seem the remember the La Scala bass horn had an fc of about 70 Hz and acted more like a woofer in a corner from 70 to 55 Hz or so. 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.