jdm56 Posted February 16, 2005 Share Posted February 16, 2005 I was just wondering about this after looking at some internal Cornwall pictures someone posted. Nearly all modern vented speakers use tuned ports; usually a tube of certain dimensions, to vent the box. Measurement will show this tuning frequency output to be as distinct as a separate driver. But a speaker like the cornwall, is it using the same principal? Is there a "tuning frequency" there, too? Would the slot output graph as nicely as a well-designed tuned port enclosure? I'm thinking that maybe older designs used slots instead of ports simply because paper or plastic tubes weren't available. --Just a guess. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted February 16, 2005 Share Posted February 16, 2005 JD, Tubes weren't invented yet. Theil and Small had not yet done their landmark reasearch either. PWK developed the box and slot size the old fashioned trial and error way. After Theil and Small published teir papers PWK calculated the parameters for the Cornwall and remarked at how close his final version was to the calculations. If you look at the other speakers of the era you will see an assortment of round holes and slots in the Altecs and others with no tubes. Rick Quote Link to comment Share on other sites More sharing options...
jdm56 Posted February 16, 2005 Author Share Posted February 16, 2005 Hm, I didn't realize that the "Thiele/Small" research was that recent. I guess I just assumed it was from back in the '20s or '30s. I do remember that there used to be a lot more vented speakers that were like you said - they just had holes or slots in the cabinet, not tubed ports. And this would have been as recently as the '70s. So, Mr Know-it-all , what is the tuning frequency of a cornwall? I'd guess it's pretty high. I remember mine had a fairly broad peak in the 60-80Hz range. Maybe that wasn't due to the box tuning, though. Maybe it was just a room thing. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted February 17, 2005 Share Posted February 17, 2005 jdm, You might be interested in the Belgian Audio School's rather comprehensive test report of the Cornwall at http://www.belgaudio.com/kcmap.htm They seem to rather enjoy the Cornwall sound. From the Frequency curve supplied with the CWII tear sheet, there is a distinct hump at 45 Hz, a boader one from 70-90 and a dip at about 52. From my understanding, this dip is the 'resonant frequency' that would be a severe spike in the reponse of a 'free air' speaker, but is tamed by the cabinet volume. I could be totally wrong. The Cornwall curve is amazingly flat compared to the LaScala's bumpy ride! It's truly within 3 db from 38 to 20,000 Hz. The response about the Cornwall cabinet and port volumes being developed entirely by trial and error well before Thiel and Small's research is correct. I think I read somewhere that PWK was only off from the optimum cabinet volume by something like 3%. Pretty astounding, but then again, the US put a man on the moon prior to the IBM PC having been invented. so why is it that I still get the awful headaches...... Michael Quote Link to comment Share on other sites More sharing options...
jdm56 Posted February 17, 2005 Author Share Posted February 17, 2005 Michael, Thanks for the link. That may be the most comprehensive test I've seen of a cornwall. You know, there are a lot of people who actually think the cornwall was the best sounding loudspeaker PWK ever designed. I think I may be in that group, with the only exception being a k-horn in a really big, really GOOD room. So if you accept the notion of the corn being the best midsize-room speaker PWK built, what is the best midsize-room speaker klipsch (the company) has ever built? cornwall? KLF30? RS7? Quote Link to comment Share on other sites More sharing options...
formica Posted February 17, 2005 Share Posted February 17, 2005 The theory behind port "tuning" comes from the resonant frequency of the air contained within the port. Round or square it makes no difference... it's just a question of aesthetics and cost. Large ports are usually easier to build rectangular, while smaller ones as tubes. Notice the new Klipsch THX subs use large slot ports... The larger x-section area the port has, the longer it has to be to maintain the same tuning, but it is less subject to port noise. Passive Radiators (PR) are also ports and are basically a compact version of a vent. BTW, A speaker's tuning frequency ideally doesn't create any form of hump in the response curve... rather it picks up as the speaker is naturally rolling off in the low end. Also note that although ported enclosures extend the usable low-end response... they roll off very quickly (in the 24db per ovcatave range). Given this, it's safe to figure that if the speaker's response is 38Hz to 16000Hz ± 3db... that it is probably tuned between 35 and 40Hz range. Later... Rob Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted February 17, 2005 Share Posted February 17, 2005 Thanks Rob, I was unsure as to how to read the 'resonance frequency' from the response curve, So the resonance freq (of the cabinet, not free-air speaker), is lower than the last 'hump', which is what pulls up the very low end before the curve collapses, or something like that, yes? I was misreading that the resonance, or 'tuning' was what 'flattened' the curve and took what would have been a single large bump in the low end and inverted part of it to form two lesser bumps. Shows what I know- hey it was late. At any rate, I love the Cornwalls so much I'll have 5 of them soon. My home has baseboard radient heat, almost no square corners without those in them, therefore massive placement problems for Khorns. I like the size, shape, and options the Cornwalls give me. The Belgian Audio School basically says that the Cornwall is the best all-round speaker ever built for the bucks. ANyone care to counter that claim? JDM- "So if you accept the notion of the corn being the best midsize-room speaker PWK built, what is the best midsize-room speaker klipsch (the company) has ever built? cornwall? KLF30? RS7?" great subject for another thread, why don't you post it? Michael Quote Link to comment Share on other sites More sharing options...
dodger Posted February 17, 2005 Share Posted February 17, 2005 One other reason for the use of tubes is the ability for the sub Manufacterer to provide different tubes, thus giving the Consumer the chance to "tune" the sub to their Room. ddger Quote Link to comment Share on other sites More sharing options...
formica Posted February 17, 2005 Share Posted February 17, 2005 ---------------- On 2/17/2005 7:03:58 AM colterphoto1 wrote: So the resonance freq (of the cabinet, not free-air speaker), is lower than the last 'hump', which is what pulls up the very low end before the curve collapses, or something like that, yes? ---------------- Actually it's the "port's" resonant frequency. The cabinet (the sides of the enclosure) ideally resonate entirely outside of the audible range... but that is the gist of it. I'm also a Cornwall fan... and definitely preferred it's sound over that of the LaScala/Belle. It just sounds more balanced given it's better bass extension and less efficient mid horn. I'm not sure about being compact though... Now that I have Khorns as well, I can see the LaScala's place as a bass limited centre channel. Rob Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted February 17, 2005 Share Posted February 17, 2005 I think slotted ports are less suseptible to port noise than tubes unless they are nicely flared. To me the Cornwall's overall frequency response is closest to the Klipschorn than the La Scala/Belle. When I went from La Scala's to Cornwalls in the rear it seemed to be a much better seamless match. Now that I have Khorns back there I have a true seamless match, plus I also have Cornwalls back there. I chose a La Scala for center since it's HF performance is closest to the Khorn. Quote Link to comment Share on other sites More sharing options...
jdm56 Posted February 17, 2005 Author Share Posted February 17, 2005 ---------------- On 2/17/2005 10:31:46 AM formica wrote: Actually it's the "port's" resonant frequency. The cabinet (the sides of the enclosure) ideally resonate entirely outside of the audible range... but that is the gist of it. ---------------- I may be off, but even MORE correctly (I think) it is the resonant frequency of the ~air~ in the port , or in the box. Right? That's probably what you meant anyway. BTW, thanks guys for shedding some light on this for me. Quote Link to comment Share on other sites More sharing options...
jtkinney Posted February 17, 2005 Share Posted February 17, 2005 JDM, The Cornwall does have a tube of sorts. Here is a drawing from the Updates & Modification page by JimE (gotta give credit where credit is due). There is a shelf the width of the box below the woofer and above the ports. I don't have the equations to calculate the tuning freq, but the dimensions are 2.375 tall x 23.875 wide x 9.5 long. The ports are 2.1875 tall and 6.875 or 10.5 wide (depending on 2 or 3 ports). He also shows a 4 port version with 2.25 x 4.75 wide ports. Quote Link to comment Share on other sites More sharing options...
formica Posted February 17, 2005 Share Posted February 17, 2005 ---------------- On 2/17/2005 11:02:42 AM jdm56 wrote: I may be off, but even MORE correctly (I think) it is the resonant frequency of the ~air~ in the port ... ---------------- That is correct... it is the air within the port/vent. Quote Link to comment Share on other sites More sharing options...
DRBILL Posted February 17, 2005 Share Posted February 17, 2005 If you would like to see some really interesting research, check out the work of William E. Haskell at Estey Organ Company c. 1900. He discovered that by inserting a tube, closed at the top and open at the bottom, into an open organ pipe, the fundamental frequency of the pipe was halved. Thus, an 8' pipe could produce the frequency of a 16' pipe. These were frequently used when space was at a premium. Physicists still argue about the explanation. I am surprised that some application of this was never tried in speaker enclosure design. This might have been the "miniature 32 foot wave-length" that PWK so longed for. DR BILL Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted February 17, 2005 Share Posted February 17, 2005 ---------------- On 2/17/2005 1:24:35 PM jtkinney wrote: JDM, The Cornwall does have a tube of sorts. Here is a drawing from the Updates & Modification page by JimE (gotta give credit where credit is due). There is a shelf the width of the box below the woofer and above the ports. I don't have the equations to calculate the tuning freq, but the dimensions are 2.375 tall x 23.875 wide x 9.5 long. The ports are 2.1875 tall and 6.875 or 10.5 wide (depending on 2 or 3 ports). He also shows a 4 port version with 2.25 x 4.75 wide ports. ---------------- That's why we should always refer to the port VOLUME, not port AREA, think of the air in the port as a piston, it has three dimensions. Michael Quote Link to comment Share on other sites More sharing options...
WMcD Posted February 17, 2005 Share Posted February 17, 2005 It my recall that T-S parameters came into common use in the mid-1970s. As a result, T-S parameters have been published by driver manufacturers since that time. OTOH, if the model dropped out of production before then, the manufacturer would not have published T-S parameters. All we have is the results of measurements by users. I've gone into this before but . . . the resonance is between the mass of air in the vent and the spring created by the air in the box. The B3 (?) alignment puts the resonance at a frequency equal to the driver's free air resonance. You can see a bit of this in the electrical impedance. There is not a single hump as you see with a closed box. Rather there is a hump with a valley in the center . . . and the result is two peaks, one above and one below where the hump would be maximum. The valley is caused by the woofer having a good air load on it because it is pumping air through the port. At the same time, driver excursion is very much reduced. One other interesting thing is that the electrical impedance at the valley bottom is the D.C. voice coil resistance. Gil Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted February 17, 2005 Share Posted February 17, 2005 Gil said: "You can see a bit of this in the electrical impedance. There is not a single hump as you see with a closed box. Rather there is a hump with a valley in the center . . . and the result is two peaks, one above and one below where the hump would be maximum. The valley is caused by the woofer having a good air load on it because it is pumping air through the port. At the same time, driver excursion is very much reduced." Thanks Gil, that's what I was trying to say in my first post: "They seem to rather enjoy the Cornwall sound. From the Frequency curve supplied with the CWII tear sheet, there is a distinct hump at 45 Hz, a boader one from 70-90 and a dip at about 52. From my understanding, this dip is the 'resonant frequency' that would be a severe spike in the reponse of a 'free air' speaker, but is tamed by the cabinet volume." Okay I got it wrong, it's the port that tames the resonance hump into two smaller ones... It always sounds so much better coming from the master! Thanks Gil. Michael Quote Link to comment Share on other sites More sharing options...
Klewless Posted February 17, 2005 Share Posted February 17, 2005 The development of the Cornwall is in the package of papers people have from Klipsch. Perhaps we can get Gil to post that one for our Weekly Reader session (does anyone remember "Weekly Reader"?). If I am not mistaken, Paul said he allowed the bass to drop off in the Cornwall because it got too boomy, esp with the plucked viola. Somebody informed Paul that a 12" in the Cornwall box would give ruler flat response to 20 Hz! But Paul said he would also suffer a loss of 3 db. Quote Link to comment Share on other sites More sharing options...
formica Posted February 18, 2005 Share Posted February 18, 2005 Actually I believe Gil was referring to the impedance plot... ---------------- On 2/17/2005 8:00:19 PM William F. Gil McDermott wrote: You can see a bit of this in the electrical impedance. ---------------- where the impedance will drop to it's lowest level at the port's tuning frequency. If properly designed, the FR curve won't have this same feature. BTW... I used the impedance drop to verify the tuning of my current AV15 sub. Rob Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted February 18, 2005 Share Posted February 18, 2005 i'll just keep quiet then 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.