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In Reply to: Re: On axis SPL -VS- acoustic power response posted by John Sheerin on July 28, 2003 at 16:03:37:
Complicated, but it works. I've used the same basic flair configuration in all my DR horns, going back some three years plus. They all have appeared in audioXpress magazine.
Follow Ups:
I was just trying to take you up on your suggestion to model your horn. If you'd like to provide more details, I can do that and then maybe an intelligent discussion can take place where both sides know the specifics of what you're talking about.Otherwise, I can speculate that you are using the driver way into cone breakup which Leach and McBean's HR don't account for. This would lead to a deterioration in sound quality.
Or, perhaps I could speculate that McBean's HR and Leach's model are not appropriate for modeling your construction - they do not allow modeling what you hint at. So it's no suprise that their predictions do not fit with what you measure. If this is the case, you basically put garbage into the equations. This does not make either approach to modeling a horn wrong, just too restricted for what you need. I have a similar situation where neither approach comes close enough to modeling what I'm building. This has led me to try writing my own simulation program.
So are you basically building something like Olson describes in sec 5.30 of Acoustical Engineering?
John
Yes, I use his multiple flair, sort of. I start with a rapid flair, go to a slow flair, finish with medium flair. As far as predictions go the McBean program is within spitting distance as far as the low end goes, but is way off on the high end, two octaves on average, and his program is for straight horns at that. I'm not concerned over the modeling aspect per se- the horns do what I want them to, that's all I care about. The point I'm trying to make relates to the original question of this thread, can a folded 15 work to 650 Hz? The answer is yes, absolutely. The problem lies in that so many will do as one poster said, assume that it can't be done because they accept without question Keele's Fh(m)equation. There are too many people getting results that Fh(m) cannot reconcile. It's time to re-examine the whole thing.
Bill,
I never paid much attention to what McBean’s program showed for the high frequency roll off. I don’t even bother using it anymore. I agree with you that that part of the program is off. However, mass roll off is real and very much so a problem with horns. A driver only has a finite amount of motor strength. Physics states the amount of energy required to accelerate an object is its mass X velocity^2. Since mass and energy are constants, it is obvious that once a certain velocity or frequency is reached, response has to fall off. Saying that mass roll off does not exist is like saying a 3000lb. car with a 10hp engine can do 1500mph, its just not going to happen. There is not enough energy to accelerate it to that point, nor to maintain it there even if it could reach 1500mph.One thing I see people confuse is what portion of the measured response is from horn loading (i.e. power response) and what part is from directivity. Any usable response above mass roll off is due to bouncing the high frequencies around the reflectors and the directivity of the horn. (This in part should reconcile why others are getting higher measurements than Fhm) This is because once you go higher in frequency than mass roll off, the driver is incapable of accelerating the cone fast enough to form compression in the horn throat. Without compression we have no horn gain effect; it just becomes a very directional direct radiator. Is it possible that with your multi flare rate horn (“rubber throat” as Klipsch would call it) you have some how made the directivity so tight that it measures higher? I don’t know; I just know there is mathematical or physical explanation for your reported measurements. I think this is what Tom was kindly trying to hint at.
Two things that are quite easy to see in manufacture’s graphs are mass roll off and voice coil roll off. Mass roll off is (2 X Fs)/Qes and voice coil roll off is Re/(Pi X Le). A good place to see this is here: http://www.bcspeakers.com/compproducts/speakers/8pe21.htm
If you click on the Graph tab it is easy to see the woofer’s response stops climbing and levels out right around mass roll off (875Hz), and that the high frequency response rolls off at the voice coil roll off point (3.5Khz). This isn’t just true for the B&C woofers, you can see the same things in the data sheets from EV, JBL, Eminence, etc… Its not magic, its just pure, simple, real math and physics.
I don’t blindly accept Keele’s formulas. When I first started building horns I challenged every darn thing that had been written about horns. Well, guess what, there is a reason why we still use their formulas. Its because they are the only universal tool we have to represent what is going on in a horn. In addition, I find them damn accurate; that is if one knows how to interpret their results. About the only thing that needs re-examined is the typical DIYer measurement techniques and test equipment. I am very fortunate to work for a company that has a large amount of high quality test equipment that gets calibrated to NIST standards every 6 months. We can re-examine other things too, but I really don’t think anyone is going to rewrite the book on physics any time soon.
and I've done what I've done. He based his written works on the results of the cabinets he built, as have I. As to the car analogy, maybe not on earth, but a ten HP engine would be enough to accelerate a vehicle to quite a few thousand miles per hour in space, where neither the constraints of friction or gravity would have to be overcome. Point being: For every rule there is always an exception.A driver does have a finite motor strength. But excursion, and the force required to get it, of a cone drops by a factor of four as frequency doubles. Drivers eventually 'run out of steam' at high frequencies as the impedance rises and as the mass of the cone becomes too great to sustain high frequency response. But there are ways around everything. See: Whizzer Cone.
The Klipsch 'rubber throat' was his discovery that reducing the area of a throat plate enhanced low frequency response by turning the volume between the cone and the throat plate into a tuned chamber that acted as a low pass filter. It also can improve high-frequency loading. I use both of those factors in my horns.
On the directivity issue, my latest mid-bass horn measures down 4dB at 45 degrees off axis at 1.6 kHz, which for a ten inch driver isn't half bad in a baffle. I'll certainly take it in a horn, folded or straight. Does 'mass rolloff' exist? Undoubtably. Is its frequency derived from the formula 2Fs/Qes? Absolutely not, at least not to the extent that it affects the performance and usefulness of a horn as much as many designers believe it to. While it's true that the total power may be falling, as long as you're getting no more than 6dB deviation between on-axis and 45 degrees off-axis response then the frequency range is considered at least usable, and in many cases pretty damn good.
Re-writing the book on Physics is a continuous process. When I went to high-school, sometime not long after the Dark Ages, our physics texts told us that the smallest particle was the electron. Now we're looking for Dark Matter? Not long before that it was held that travel beyond the speed of sound was not possible. Mr.Yeager put an end to that myth in fine fashion. Today travel at light speed seems impossible, but maybe only because Zephraim Cochrane hasn't been born yet. Newton and Einstein still don't know which of them was right, and in the end the answer may be neither.
Not so many years ago a group of NASA scientists undertook a detailed analysis of the common Honey Bee. After months of work, thousands of calculations on the Cray, and more than a few dollars expended, they decried that according to the Laws of Aerodynamics and Physics it was simply impossible for a Honey Bee to fly. Somehow the Honey Bees never got the message. However, a strange phenomenon occurred. Not long after NASA published the results of their study, entymologists around Cape Canaveral noted an unusual rise in the incidence of NASA employees being stung on the ass by Honey Bees flying past.
I don't care for being stung on the ass so much, so rather than be bound by the Laws of Physics I'd far prefer to rewrite them.
Hi BillThe fact that exteneded high frequency response in horn loaded cone drivers is possible is certainly a given in my experience. My horn laoded EV 15B's can reach right up into the bottom of the tweeter territory, but it's a rocky road up there (the big 4" dust cap becomes a seperate sub system with it's own artifacts), and not really hi-fi IMHO, and with good midrange compression drivers available, why bother (just MHO again). Now there are ways around this of course, the phase plug comes to mind, but with those comp. drivers handy... Another way is with E.Q., which is currently out of fashion in hi-fi, but is still nearly a necessity in pro-sound. I remember as if it was yesterday the day I gave up graphic equalizers. Back in the late 80's a golden eared friend (opera singer) said "what's that distortion?" while listening to my rig. Removing the graphic eq. removed the distortion, and I never went back. All of this does not preclude a clever person getting all of this stuff to work (phase plug and or eq. to iron out the lumpiness), but it just has'nt for me, and I would be pleasantly surprised at anyone demonstrating a working hi-fi version that can match a good midrange comp. driver. But hey, stranger things have happened in audio.
Newton's physics work well enough for the everyday world we live in, but Einstein demonstrated that well enough is not good enough for describing the big (or very little) picture of the universe. The next step apparently came in the mid 90's when Edward Witten (of the Institute for Advanced Studies at Princeton, Einsteins's last employer) introduced M Theory, which tied together the then 5 disparate fragments of Super String Theory, and literlly hundreds of scientific papers by many physicists followed. M theory is apparently the end of the road for experimental physics as we know it, the energy levels needed to prove it would be on the level of the big bang itself, and entirely not likely in our lifetimes. So M Theory seems destined to be only a theory, but nontheless has mown down some of the big problems (theoretically at least) that Einstein could'nt. Interestingly for us here, M theory prestents a vibrational model of sub atomic reality.
Now the speed of light. While this is apparently a given speed limit of the universe for anything with mass, speed is figured with mass (and the energy needed to accelarated it) multiplied by space/time (
Einstein). While the maximum speed of light is apparently non negotiable, both space and time are entirely negotiable and quite rubbery acording to Einstein. Space and time, having no mass, can expand and contract much faster than the speed of light without breaking any of Einsteins's rules. Now gimme a big enough quantum shock wave and... BTW I like the original Zephraim Cochran played by Glenn Corbett rather than the hippie version from that last movie. He seemed like he could blow a hole in space/time.Now those bees. I've heard this story many times since the 60's, and the conclusions were based on the assumptions that the motive power of the bees wings were similar to our muscles and therefore the bee did'nt have enough horse power to take off with it's wing size, as we could'nt become airborn with a proportional set of wings. It turned out after further studies that the mechanism powering the bees wings was not at all like our muscles, and involved a much more primative and efficient chemical reaction. The problem for the bees is that the chemical reaction does'nt work below about 60 degrees. It's still a good story illustrating the limits of our science though.
Paul
well, since my stuff is all pro-sound oriented the not-really hi-fi thing is a given. I pretty much don't use fifteens anyway, as I can get all I need from tens and twelves, but once you horn load the driver characteristics become swamped by the horn, especially when it comes to what really limits HF response/dispersion, the size of the radiating plane. As to EQ's, on the pro touring circuit today the level of sophistication in the booth is mind-boggling. At our 6,000 seat venue it's the rare act that comes in with a mixing console that costs less than $150,000, with enough computing power to calculate a flight to Venus. We had the 'REO, Styx, Journey' show two nights ago and their video projection system alone carried a million-$ plus price tag.The biggest advantage to my designs for the pro market is the elimination of the separate midrange driver. In hi-fi use that's not necessarily a big advantage, but for the pro it can be literally huge. Cabinet size is greatly reduced, while the efficiency/size ratio is enhanced, as the entire frontal area and internal volume of the box, save the small tweeter footprint, can be devoted to the mid-bass driver/rear chamber/horn. Not a big deal in the home necessarily, but a very big deal if you have to carry a load of cabinetry, be it in one pickup or in two semis, to every gig. The space/dollar savings are further enhanced as formerly three-way systems are reduced to two-way, cutting power amp channel requirements by 1/3, which also carries over to less cabling, simplified set-ups, and an overall reduction in the cartage of at least 20%. For a bar band that means making it easier to set up and tear down every night, while for concert touring a 20% cartage reduction can add up to millions in annual savings for a large contractor, from not only reduced expenses of vehicles/fuel etc. but also reduced labor costs/motel bills/food expense/per diem, as you don't need as large a crew. Going back to 'REO,Styx,Journey', the crew for that show numbers over thirty, not counting the lighting crew.
I liked Corbett better too. I found it hard to accept a zoned-out Stretch Cunningham inventing warp-drive.
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