lindee Posted April 24, 2002 Share Posted April 24, 2002 Is this workable? I've got two 18" drivers I'm planning to use for subs. Would scaling the Classic up to size work or should I go with a vented alignment?? Thanks for any info. Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted April 24, 2002 Share Posted April 24, 2002 uh, okay... Which of the many speakers listed as "classic" are we talking about? ------------------ Music is art Audio is engineering Ray's Music System Quote Link to comment Share on other sites More sharing options...
lindee Posted April 24, 2002 Author Share Posted April 24, 2002 Sorry about that, had started this under the thread for Q mans University Classic and thought I'd get more responses here. Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
djk Posted April 25, 2002 Share Posted April 25, 2002 What are the TS parameters for the 18" drivers? Quote Link to comment Share on other sites More sharing options...
lindee Posted April 25, 2002 Author Share Posted April 25, 2002 The numbers are: Fs is 28.1025 Hertz Qts is 0.3330 cone area is 0.1359 m^2 Qes is 0.3453 Vas is 22.1692 cubic feet Qms is 9.3576 Vas is 628.0218 litres Re is 5.5129 ohms Rm is 154.9145 ohms R1 is 29.2237 ohms Voice Coil Inductance Le is 2.8015 mH Efficiency is 97.89 dB 1w/1m BL is 19.32 Tesla meters Cm is 242.221 microns/Newton Mm is 132.4525 grams Rm (mechanical) is 2.499 mechanical ohms (Ns/m) The vented box I have worked out is 14 cuft (each) tuned to 22hz which gives an F3 of 51.8 F10 around 21/22, I figured with room gain that would put me back nearly flat to 25hz. Does that all seem to jive or am I off my rocker? Thanks, Eric Forgot this part, the Xmax is 6mm. Eric ------------------ Where does this connect? This message has been edited by lindee on 04-26-2002 at 12:35 PM Quote Link to comment Share on other sites More sharing options...
lindee Posted April 27, 2002 Author Share Posted April 27, 2002 Anyone? ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 27, 2002 Share Posted April 27, 2002 Sorry for the silence. I don't know about ported boxes. My initial impression is that the units should do pretty well as a horn driver. One issue is to calculate the throat size which the driver "likes". This is dictated by the TS parameters. My recall is that it is 2*pi*Qts*Vas*Fs/c = throat area. The only tricky part is that the c is the velocity of sound. So convert the Vas to cubic inches and use c of 13500 inches per second. Then the answer will be in square inches. Note in the equation this results in inches^3/inches^1 and you wind up with inches^2. That is to say, square inches. You should get an answer around 100 square inches. I'll assume you plan to scale up the University. The first issue will be that it will have to be scaled up by a factor of 18/15 to get the driver to physically fit in the horn and back chamber combination. In doing so, you'll be scaling up the throat of the horn. This may or may not wind up being the size called for by the TS parameters. If the throat of the scaled up horn is smaller than called for, you can scale up a bit more to match. My guess is that the scaled up horn will not get as low as 20 Hz. None the less, it may be a very worthwhile experiment. If you need more questions answered, I'd be happy to give advice. NOTE EDIT: Originally I forgot the 2*PI Gil This message has been edited by William F. Gil McDermott on 04-30-2002 at 06:38 PM Quote Link to comment Share on other sites More sharing options...
lindee Posted April 28, 2002 Author Share Posted April 28, 2002 Gil, Thanks for the info, I had thought about using a Patrician IV or a scaled up version of an Imperial build in style for the sub duties, but the Pats need corners, which are already spoken for by Khorns, and putting them at the floor/wall junction would just turn them into a jungle jim for the boys (2,4,and 6), and the Imperials would scale to an obscenely large cabinet (78x45x30). Thats why I thought about using the University cabinet, not exactly petite, but still sized within reason, and not needing a corner I can use them along a wall. If I can get down into the mid to upper 20's and still have everything hornloaded, I'd be very happy. Again, thanks for your input. This project will probably get the evil eye, but I think I can sell it. Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 30, 2002 Share Posted April 30, 2002 Please note I edited my post above to include a factor of 2*pi. Sorry, Gil Quote Link to comment Share on other sites More sharing options...
lindee Posted May 1, 2002 Author Share Posted May 1, 2002 Gil, Horn loading these will raise the impedance to 16 ohms correct? So hooking them up parallel will get me back to 8 and the corresponding increase in output, or is there more involved because of the horn loading? Thanks, Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
WMcD Posted May 2, 2002 Share Posted May 2, 2002 I did some math. Whoops; another tutorial. Please excuse my pedantic nature when I get wound up. Some people seem to like it. It is difficult to speak to people with different levels of technology under their belt. The Vas in cubic inches for the 18 inch driver is 38,305 by conversion of units. But let me digress. The Keele equation for the throat area is St=2*pi*Fs*Qts*Vas/c Now these are Thiele-Small parameters. There a link published on another thread which would lead one to the belief that Thiele and Small came up with the equation. Not so. D.B. Don Keele published it in "Low-Frequency Horn Design Using Thiele/Small Driver Parameters." AES preprint 1250 (1977). His employer at the time is listed as Klipsch & Associates, Inc. Bruce Edgar later published articles using the Qes parameter rather than the Qts (crediting Keele). They are usually very close in value so it hardly makes a difference. And Keele says so too, one of his assumptions. However, I looked into it more closely. Mr. Keele's paper shows that the equation is a conversion of one originally published in E.C. Wente, A.L. Thuras, "Auditory Perspective - Loud Speakers and Microphones," Trans. Am. Ins. Elect. Eng., vol 53 pp 17-24 (Jan 1934). I don't have it here, so excuse any memory glitch. Now that is interesting for two reasons. First, folks will recognize this as being included in The Klipsch Papers. Second, it is referenced in patents to Klipsch on how to calculate throat area for a driver. The W/E equation is St= P*c*Re*Sd^2/B^2*l^2 (if n=1) That P is the density of air (rho?). c is velocity. The n is comes into play if the amp impedance is high, but with modern amps with close to zero internal impedance, n = 1. Sd is area of the diaphragm. If you look at the article, you have to do some algebra to even get to that form. My recall is that the W/E article says they are neglecting losses in the driver. I looked at the conversion math years ago, sort of backwards, and found that if one uses Qes, you wind up with the W/T equation. This makes sense because Qes does indeed ignore driver mechanical loses. So Edgar (using Qes) honored the W/T origin. It might, might, be that Keele's equation is more accurate because it contemplates the small driver loss. I had a bit of an insight from the exercise. We should well wonder why resonant frequecy, Q, and compliance have anything to do with optimum throat size. Actually they don't, directly. These are parameters which can be measured with a voltmeter and tone generator if you have a driver to test. Which by the way is what makes them so handy. T-S use these to allow calculation of box response. Rather, if you can measure the T-S parameters, or get them from a manufacturer, and plug them into the equation, you are actually mimicing the W/T equation in a round-about way. It is complicated but you can appreciate that Q is affected by Vas (spring), Fs is affected by Vas, etc. There is a lot of cancellation of units going on. I can give you the big paper and pencil equation if you're interested. The bottom line is that when we look at the W/T equation, we see the optimum throat size of the horn relies on Re (voice coil resistance) and B (magnetic field strenght) and l (length of wire in the field). It is all about the strength of the motor. The bottom line is that the effecive resistance of the bass horn throat load (set by its area and motor strength) has to equal the voice coil resistance. That is "impedance matching" leading to optimum efficency. But, going back to the problem at hand. I calculate (from T/S parameters) for the 18 inch driver: St = 2*pi*281*0.33*38380/13500 = 166.8 square inches. Let's call that 160 inches square. Let's assume the Classic in its original size had a throat area of 80 inches square. I don't know what is it, but that is probably close. If we scale up a Classic bass unit in linear dimensions by a factor of square root of 2 = 1.414, then the size of the throat is doubled. And this is the result we want. Note, if we made all linear dimensions twice as big, we'd wind up with a throat size four times as big. This scale up should result in better bass response than the original. So the project could be very worthwhile in view of simplicity. Regards, Gil Quote Link to comment Share on other sites More sharing options...
lindee Posted May 6, 2002 Author Share Posted May 6, 2002 Math was never my forte, but let me see if I understand, 'cos, for me, that was a brainfull... Scale all dimensions by 1.414, not 1.2, right? If 1.414 is correct then the mouth comes to @ 8.5x18.375. Would I be able to modify the dimensions to 10x16 to maintain the 160 sq in., or leave as is, but only taking the width to edge of the gasket on the speaker frame? About 17.5". Thanks, Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
WMcD Posted May 8, 2002 Share Posted May 8, 2002 Yes, I should have thought about the woofer cut out problem. I ran into it myself. You're absolutely right about using a 16 x 10. But watch even that. The diagonal measurement is more than 18 inches. So you're going to have to cheat a little bit by rounding off the diagonal. Hard to describe. Draw a 16 x 10 rectangle and mark its center. Then at that center draw a 16 inch diameter circle. You'll see the rounded off long dimension allows for a good seal and doesn't reduce the area by much at all. For all the complicated math, a throat size or restriction which is off by 10 or 20 percent is not going to hurt performance. Regards, Gil Quote Link to comment Share on other sites More sharing options...
WMcD Posted May 8, 2002 Share Posted May 8, 2002 I looked at the impedance curves of the K-Horn published in Audio. The impedance of the bass unit varies about 5 and 7 ohms in most places. One figure I saw on the K-33 is that the voice coil resistance is 3.2 ohms, or so. Therefore, it looks like we are getting a doubling due to horn loading. The specification on your units show an Re of 5.5 ohms. Assume the use of the horn doubles that to 11 ohms. Then wiring in parallel brings it back down to 5.5 ohms. It seems okay. However, I have some reservation about the fact that if you look at just the parallel Re, it is down to 2.75 ohms. A driving amp may see that at very low frequencies where the horn doesn't present an acoustic load. That might be bad for an amplifier. It might well be better to wire in series. Gil Quote Link to comment Share on other sites More sharing options...
Jim Cornell Posted May 8, 2002 Share Posted May 8, 2002 Indee I modified an 18inch Crate sub professional with the RP-3 using the Crate box, i thought it was an EV but i might of been wrong! The power rating on the 18 is 600 watts RMS, and the amp is only 110 watts! Nothing smoked yet, it seems to run ok, this one sub thunders the house with bass! I havent had low end in the house, like this, even with 4 cornwalls, with this sub mod! Idependence day was a new expereience! Outlaw 1050 Chorus 1 front Chorus 1 rear Academy center Klf-C7 rear center Crate 18inch sub with RP-3 amp RS3-2s doing nothing still caint hear them Harman Kardon CD Zenith DVD Sony 27 inch trinitron flatscreen TV Regards Jim This message has been edited by Jim Cornell on 05-08-2002 at 08:13 AM Quote Link to comment Share on other sites More sharing options...
lindee Posted May 8, 2002 Author Share Posted May 8, 2002 Gil, It would never have caught my attention about the impedance going back to "normal" in absence of the horn load. You're input has been highly informative, anything else you might want to share will be greatly appreciated, I'm all ears. Jim, Sounds like you're cracking some plaster and loving it. Is that Crate similar in design to University? What would be your guess on low end response of your sub? Thanks fellas, Eric ------------------ Where does this connect? Quote Link to comment Share on other sites More sharing options...
Q-Man Posted May 8, 2002 Share Posted May 8, 2002 I think you can try a 9"x16" slot for an 18" woofer. Scaling up the Classic will give you a larger mouth, and the larger the mouth the lower the frequency. But,with a larger mouth I believe the horn expansion rate must also change to match the mouth size. This won't be accomplished by just scaling up the Classic. You need to calculate a new horn length and expansion rate to match the mouth size. The horn length must now be longer and expand slower. Q. ------------------ Q-Man Quote Link to comment Share on other sites More sharing options...
Jim Cornell Posted May 8, 2002 Share Posted May 8, 2002 I think this Crate woofer is an EV product but i caint prove it, i have the RP-3 emblem on the front, because its powered by the RP-3 amp! Low end id say it pulls around 28Hz, down to 18 HZ! 18hZ CAINT BE HEARD, BUT ID SAY ITS GIONG DOWN THAT FAR! Dam laptop! This is a bass guitar speaker modified for home theater use! Regards Jim Quote Link to comment Share on other sites More sharing options...
WMcD Posted May 9, 2002 Share Posted May 9, 2002 Qman brought up an old subject in my mind and I revisted the math. Specifically, is it legit to simply scale up a design in view of mouth size and flare rate? It looks to me that scaling up lowers the flare rate. This is good because we want that for lower bass. The mouth size scales up too. That is good because without a bigger mouth, the increased flare rate wouldn't help too much. Some years ago I wondered whether back chamber volume would scale up, and found it does. Gil Quote Link to comment Share on other sites More sharing options...
lindee Posted May 9, 2002 Author Share Posted May 9, 2002 Just realized, if I build this, it won't fit thru the door to the basement. I'm going to have to make it so it can be disassembled, then cut it and build it in place. I'd hate to have to leave it behind if we move. And right when I was getting all excited, well at least my shorts are a comfortable fit again! Eric ------------------ There is no substitute for cubic inches? Quote Link to comment Share on other sites More sharing options...
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