volvotreter Posted August 16, 2000 Share Posted August 16, 2000 Hi there! I got a cornerhorn for use as subwoofer. now I'am planning to built some La Scalas Since there is no need for response below 80Hz, I'am thinking to scale them down by 1.25 to utilize a 12" woofer. Any experiences or sugestions out there? Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 16, 2000 Share Posted August 16, 2000 Nice project. I'm thinking about a 66% scale down along the same lines. It is annoying that the THX, Dolby spec for "small" calls for 80 Hz. That is in the ballpark for your project, and a bit low for mine. The present hand wringing here is to find a suitable bass driver. I think we're on the same wavelength. If you have a suitable sub, and the HT system is set to "small", it should be possible to adopt the LaScala design for the mains and surround. Share your thoughts. Gil 1 Quote Link to comment Share on other sites More sharing options...
Klewless Posted August 17, 2000 Share Posted August 17, 2000 Guys, Search this board for "runt". There is a picture of it which looks a lot like what you are discussing. I have no clue as to what the "runt" is all about. ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
pzannucci Posted August 17, 2000 Share Posted August 17, 2000 If you are going to make something smaller than a La Scala bass section, it can also be shorter in length due to the higher frequency. Also your growth rate will be even faster. I once rebuilt my old Frazier 12" woofer from a Mark 5a into what was called a Dixielander (by Frazier) bass enclosure. It only contained one fold and was about 20" by 20". Fairly easy to build. If you can find some info on that type of build, it might also suit you since you did not have any large panels to resonate due to the fully supported bass section, unlike the La Scala design. Peter Z. Quote Link to comment Share on other sites More sharing options...
volvotreter Posted August 17, 2000 Author Share Posted August 17, 2000 Originally posted by William F. Gil McDermott: Nice project. I'm thinking about a 66% scale down along the same lines. Hmm... what brings you to 66%? Wanna use it for a 10" speaker? Quote Link to comment Share on other sites More sharing options...
KGeist Posted August 21, 2000 Share Posted August 21, 2000 I could be mistaken, but I believe that (horn) flare rate scales with linear dimension. Therefore a 20% reduction in size would translate to a 20% higher cut-off. Assuming that the La Scala flare is around 55 Hz (I'm guessing, but this should be about right), a 20% smaller enclosure would be about 69 Hz. Kerry Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 28, 2000 Share Posted August 28, 2000 Kerry, My calculations agree with yours, the expansion does "scale." I think that is also true of back chamber volume, but I'm gonna look at it again on paper to be sure. I've been assuming that the LaScala flare doubles every 12 inches, which gives an Fc of 61 Hz or so. Regards, Gil 1 Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 28, 2000 Share Posted August 28, 2000 Volvo, The figure of 66% makes some sense to me. 3/4 inch plywood scales down to 1/2 inch. And the 15 inch driver scales down to 10 inch, as you point out. Also, with the 66 % reduced linear dimensions, we are talking about something reasonable in bulk. Five of these are under construction. I owe all you folk some photos and curves. Maybe in a month or so. Making a matching midrange out of plywood was no small problem. Picking a bass driver has been a real problem. I noticed that the drivers used by Klipsch tend to be ones suitable for a larger throat and thus are looking into a smallish throat. Also Klipsch seem to stick to a 97 dB output. By Keele's parameters, the high frequency limit is low, but Keele doesn't account for the effect of the back chamber, which increases the Fs of the system. Naturally, the proof of the pudding is in the eating, and the outcome here has to be measured. I'll keep you advised. Gil 1 Quote Link to comment Share on other sites More sharing options...
KGeist Posted August 28, 2000 Share Posted August 28, 2000 Gil, Volume scales with the cube of linear dimension, therefore a 34% (66% scale) reduction in linear dimension translates to 71% reduction in internal volume (.66x.66x.66=.29). This, most importantly, applies to back air chambers and would suggests that an appropriate woofer would have approximately 1/4 the Vas of the La Scala woofer (K-33-E). BTW, area scales with the square of linear dimension, In this case, areas such as horn throat and mouth area are reduced by 56% (.66x.66=.44). Kerry Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 29, 2000 Share Posted August 29, 2000 Kerry, I wanted to check the calculations on the back chamber volume. PWK says it is 2.9 x throat area x length to double. So, the scaling factor shows up three times in the equation and the back chamber does scale. Just as you say. Gil 1 Quote Link to comment Share on other sites More sharing options...
Klewless Posted August 29, 2000 Share Posted August 29, 2000 Compression chamber volume ?? I have seen that formula in several places and it seems it was always applied to exponential expansions. Would it be different for hyperbolic or conical or tractrix? Just wondering..... ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
djk Posted September 3, 2000 Share Posted September 3, 2000 For half space loading(on the floor)the sides of the mouth need to be a 1/4 wave long.The mouth size of the LaScala is good for about 128hz.Olson suggests that the taper rate be set about 1/3 octave lower than this(ie about 100hz).The taper rate of a LaScala would seem to be 8"(ie 100hz)average,ignoring the short non tapering segment.Measuring a LaScala in true half space it peaks at 125hz on a 1/3rd octave RTA and is down about 10dB in the 50hz band.This is consistent with the Klipsch spec of a 10dB envelope(+/- 5dB) from 45hz to 17khz.In PWK's article "A Low Frequency Horn of Small Dimensions"(JAES vol 13,#2 137~144)he cites Olson in describing a 100hz horn with a 25" mouth and a 8" taper rate.He then goes on to describe the K-horn as being a multiple taper 8"(100hz)changing to a 16" taper(47hz).He then states "The cut-off of the horn is 47 cycles and the computations show poor performance below 55 cycles".This is consistent with the Klipsch spec of a 10dB envelope(+/- 5dB)from 35hz to 17khz.If you need actual horn loading to 80hz you need to scale UP the dimensions of the LaScala,not make it smaller.PS,the THX approved 500hz high frequency horns from JBL have 32"x32" mouths and the EV and Altec horns are even larger. Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 4, 2000 Share Posted September 4, 2000 Dear Klewless: The PWK calculation for the back chamber is for the exponential horn. Also, it assumes an infinite horn. In later patent specifications he points out that the chamber for a finite horn might have to be smaller. This is because the mass load from the finite horn is higher. Thus there is more "reactance" to annul. Also, Don Keele has pointed out that the compliance of the driver has to be taken into account. The driver has its own spring-e-ness. (Sp?) Overall, the calculations are starting points from which to experiment. Text book calculations show that other "families" of horn expansions, like hyperbolic, exhibit other levels of mass reactions. In fact, the exponential is a subset of the hyperbolic. Again, it is difficult to generalize what will actually show up in practice and what is optimum. One important point is that we ARE dealing with the type of bass horn which uses a back chamber. Not all do. The VoT types have a bass reflex chamber. However, it seems that PWK is a fan of the sealed chamber. The people at Jensen reached similar conclusions about its merits. From what we are listening too, there is not much room for argument. This is PWK's design choice. He does it well. Gil 1 Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 4, 2000 Share Posted September 4, 2000 Dear djk, Thanks for your remarks. All input is welcome. But, gee, you seem to reach some harsh conclusions in a brusk way. I don't take issue with the citations to literature. They say what they say. However. . . . Measurements reveal better than you imply. There is reason for this. A lot of PWK's work has been to work engineering tradeoffs in mouth size. And getting good bass response out of speaker of reasonable size is the goal. The most analytical study of mouth size IMHO is from D.B. Keele in his AES paper on optimal mouth size. He points out that bigger is not necessarially better. And, from his paper, if you look at the numbers for the "optimum" bass near cut off, the Klipsch family of horn loaded woofers are not quite optimum. None the less. In rooms, the mouth load is better than in half space. In a corner, there is a respectable match; even at a wall floor boundry, it ain't half bad. If you look at the reflection coefficents for corner placement, we're in the ball park. An early patent by Thuras on the WE 555 driver has something to say on this also. Essentially, a good choice of driver and reactance anuling back chamber can make things work better than a simple look at mouth size would indicate. You cite to PWK's paper on the early K-Horn. That was his EARLY work and impressions. In my read, it does not support a conclusion that the modern K-Horn or LaScala are dullards in the low end. Measured specs are to the contrary. PWK's AES paper on the prototype of the LaScala showed otherwise. Specs on the K-Horn are otherwise. Regarding the K-Horn, Heyster's review in Audio magazine shows it has good response to the high 30's. The bottom line is that PKW's designs are the result of a thoughtful analysis of mouth loading, the affect of the finite horn, and careful selection of the driver. Put together, it all works very, very well. It is all based on sound engineering and measured results. Mr. Olsen never said that K-Horns or LaScalas don't work as advertised. The bottom line is that K-Horns and LaScala's do work well (1) below Fc and (2) despite having small mouth dimensions. Gil 2 Quote Link to comment Share on other sites More sharing options...
JamesS Posted June 7, 2020 Share Posted June 7, 2020 Has anyone put a set of drawings together for this Scale down La Scala for 12" woofer Quote Link to comment Share on other sites More sharing options...
JamesS Posted June 7, 2020 Share Posted June 7, 2020 On 8/16/2000 at 10:59 AM, volvotreter said: Hi there! I got a cornerhorn for use as subwoofer. now I'am planning to built some La Scalas Since there is no need for response below 80Hz, I'am thinking to scale them down by 1.25 to utilize a 12" woofer. Any experiences or sugestions out there? Did you have succes with this project? Quote Link to comment Share on other sites More sharing options...
moray james Posted June 8, 2020 Share Posted June 8, 2020 3 hours ago, JamesS said: Did you have succes with this project? try asking here. http://wp.volvotreter.de/ 1 Quote Link to comment Share on other sites More sharing options...
JamesS Posted June 8, 2020 Share Posted June 8, 2020 On 8/16/2000 at 10:59 AM, volvotreter said: Hi there! I got a cornerhorn for use as subwoofer. now I'am planning to built some La Scalas Since there is no need for response below 80Hz, I'am thinking to scale them down by 1.25 to utilize a 12" woofer. Any experiences or sugestions out there? Did you have succes with this project? Quote Link to comment Share on other sites More sharing options...
JamesS Posted June 8, 2020 Share Posted June 8, 2020 Thank you! I found exactly what I was looking for on the website, under the plans tab. So now I need to seek a perfect 10" woofer and crossover. Quote Link to comment Share on other sites More sharing options...
JamesS Posted June 8, 2020 Share Posted June 8, 2020 Frequency Response 22 - 120 Hz ? Quote Link to comment Share on other sites More sharing options...
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