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jwc

Bass horn ideas again. A possible build. Need criticism.

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I never thought of that one. Didn't see it coming. I tried to find the specs on the Fane at one time and couldn't get all the info. See again it is "somewhat" like a wide La Scala on its side. Should be an easy build although the dog house on these look difficult.

It's throat area does loook "kinder" for lack of better words. With that gradual taper and the horn bing split at the throat....how do you calculate the throat area?

My weakest understanding so far has been the throat and what area you use to calculate the horn when slpit. Seems to work differently with different designs.

By the way...do you know the size of the slot openings on the jubilee and what the total area is of the throat?

jc

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JC

You can put the throat flare on the cabinet shell, this simplifies the doghouse build, but, does not allow the woofer access to the volume created by the flare chamber. I like putting on the cabinet shell, since it also adds strength to the cabinet face getting the initial sound blows by the driver.

As far as calculations, can't help you there. There are a few folks who have posted some real good modeling software results, maybe they will chime in.

Throat dynamics are complicated. Following a time-tested models helps.

I don't think anyone really knows the internals of the jubilee. The fact that Klipsch allows our post with our speculations, tells me, we are probably not even close.

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you will never amount to anything. 

jacksonbart

?

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These have been great ideas so far. They are really helping me. Sometimes a fresh thought opens my mind to many other things.

I must say that the calculations part has been making pretty good sense to me. I actually have made about 4-5 of these horns on paper but the size/shape is just not there. These were all based off the same throat size.

Let me ask you this to back up a sec. Now are you still saying the sketch of my horn will still cause problems with the upper frequencies eventhough I will have the 45 degree "fillets" at the first and second turn. It is already calculated and drawn that way to put them there.

To further clear something up for me is how the Jubilee gets by with the 90 degree turn then the 180 degree turn. Now granted, that 180 degree is not a "squared off' 180 but it is still a wave of sound that has to travel in the opposite direction.

jc

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The Jubilee tailboard arrangement is designed to reflect the waveform around the turn, from one reflecting wall to another using the opposite of the incident angle.

This is one way to retain the phase and retain the higher frequencies. The rule of thumb is that the width of the channel will pass the frequencies that are 1/6th the wavelength of the highest frequency [to be passed] (Kellogg). This forms the upper band limit on the horn in the physical sense.

Reflectors only effect the higher of the frequencies being passed. Low frequencies (300Hz and below) will tend to pass through rather uneffected.

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jwcullison

I think D-Man addressed the how's on the Jubilee 180. Only thing I would add, is that you note, that the horn path expands thru it's length as well. D-Man's 300hz assessment is right on the money.

Back to your question about your inital drawing, which I indicated had a lot of +'s. If you were to modify the horn path so that it expands thru it's length, taper either the cabinet shell inside face or the doghouse horn exit face, use the 45 degree fillets, and chop off your corners, you would be addressing the w-bin issues.

The extent that these issues are important has a lot to do with your intended footprint for the cab's and your implementation and selection of drivers and horns. I realize thus far, the system aspect was consider further down the road, but no sense in trying to get the cabs to reach 500hz, if your going to use a university cobra-flex III mid horn with an atlas PD5HV driver combo which has a cut off below 300hz. Likewise, if youre going to use an altec 902 with an altec 511b, then mitigating w-bin issues has a greater priority.

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Very well. Good food for thought.

So I could maybe change the splitter at the throat to match the "fillet" at the first turn.

One thing I must be missing here.

"Only thing I would add, is that you note, that the horn path expands thru it's length as well"

My schematic does have the horn expanding through it's entire length...I thought. The "straight path" with parallel panels has a vertically expanding column w/in it. Not drawn. there are "ramps' there just like at the throat.

Isn't that "expanding"?

jc

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jwcullison

I looked at your drawing again. You have two 90 degree turns indicated which would not be possible if the horn expanded thru it's length.

Now maybe I should really say widen thru its length, as in the diagrams I posted.

Also, are you saying your going to include horizontal ramps that gradually expand thru the horn length? The ramps will exist gradually from start to finish? I have not posted a diagram depicting this.

I have gotten bad feed back from folks on ramps that follow the entire horn length and expand horizontally. I personally can't image why it would not work and my give it a try someday. Maybe D-man can chime in on this.

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The main reason for that is that the non-expanding walls stay parallel too long, which allows for standing waves to form between the parallel walls dictated by wavelength and sub-multiples of wavelength.

In general anything parallel is bad for horns, including the back chamber wall, top/bottom, etc. Unfortunately, that increases the complexity, of course.

Short distances are ok and that generally means its ok at the throat, like the LS/Belle/Klipschorn throat(s).

DM

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Ok, maybe this will make my point. Notice with this motorboard showing the first flare from the throat on one side. Notice that the flare doesn't reach the top of the motorboard/cabinet. This flare goes to the first 90 degree turn. The height of the horn as it reaches the first turn is only 18.75 inches.

post-16499-13819304668994_thumb.jpg

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Now if you look at the horn on one side after the first 90 degree turn (with a 45 degree fillet), you will see that the horn will get taller while keeping the same width. So the height of the horn here goes from 18.75 inches up to 39 5/8 inches. Now I'm to the back of the cabinet before the next turn. The horn will no longer get taller but will get wider to continue the exponential flare.

post-16499-13819304669474_thumb.jpg

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Dana. I read you post after I posted the images. It seems to me that many horns keep 2 of the 4 sides in parallel for simplicity. This of course doesn't mean it's right. Eventhough you say the la scala does it at the throat....but doesn't it do it after the first 90 degree turn. The top and bottom of the horn/cabinet is parallel. Right?

jc

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jwcullison

OK, I follow your plan.

I think you have all the info, reviewed it, and came out with the best compromise for the given foot print you are looking for.

It would be great if someone can run this thru some modeling software.

Fall back option if it does not cut off high enough is a lower cutoff mid driver/horn arrangement.

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If I may throw in a thought I've been noodling with. It is that single driver bass horns were necessary in the past. Now things have changed.

Consider that except for the MCM and Jubilee, and one EV bass bin (newer ones), the popular designs (older ones) use a single woofer. That seems to be the starting point for most designs. It (single driver) might be a compromised one in view of cheap drivers these days. We've been "thinking inside the box" by following old constraints, which have changed.

I was very taken by PWK's description of possible bass drivers in the late '40s, when he described them. Costs ranged from $50 to $120. Translated to today, you can probably multiply by 10 or 20. Someone can work the CPI. Yikes. We're not designing for $1000 or $2000 drivers, but they were. Perhaps they'd do it differently, back then, at modern prices.

This cost item may well have driven the single woofer design to the exclusion of dual driver designs in the old days.

Consider that the original Hartsfield patent shows the use of an 8 inch driver (relatively cheap) which could be upgraded to a 15 (?) inch. The use of the 8 inch required an intricate extension back to the driver. The original Hartsfield was very complex. The second version was still very complex but perhaps a little less.

This probably also shows some cost relation between the bass driver and skilled woodworking necessary to make the resulting single driver bass horn work. But now drivers are much less expensive and as home builders, we have poorer skills and our time is worth more. So these important factors have flipped the other way in these days.

The other factor is that some of the folding issues which create high frequency losses arise because of a single driver. In just about all the designs, the woofer looks into some sort of a rectangle to get a good start. With two drivers we're able to make a longer slot. Or at least two rectangles in a row to get the same effect.

The MCM uses two drivers and this allows for one 180 degree turn in one plane. Consider what we see in the AES paper for the Jubilee. The prototype which flubbed probably used two drivers to form two rectangles in a row even if it not described. Same idea.

As an aside, one design issue in the K-5 is to get the initial flare down to a long slot as soon as possible before the rest of the horn. In fuzzy thinking, this the same issue as the bass horn.

Basically, two drivers solve issues of HF response and "buildability".

My conclusion is that we've all been sort of "thinking inside the box" and following the single driver theory. The fellows in the old days had to use a single driver simply because the drivers were so expensive.

The Jubilee is a success because of the use of two drivers. It makes the one plane folding possible as well as simplified woodworking.

So if you want a proven design with a small volume, why not a 2/3 scale "Jubilee". (I want to honor the trademark. Therefore the quotes.) You could use the plans which have been floating around, use 8 inch drivers and 1/2 inch ply. You'd also be a participant in the developing Jubilee by homebuilders project.

Best,

Gil

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That all makes very good sense. Dana on several occasions had tried to get me to switch to the two driver option. I see how it allows for the easier build and nice shape. I already have my dbb's (dual k33) which have duplicated Cornwall bass bins. The drivers are in parallel and I have caught a lotta concerning comments on the possible low impedance.

I have looked at the Jubilee plans foating around. I guess I could just do the same type build like you did with the 15" drivers. Beautiful thread by the way.

I will have to give that some thought. I will probably get caught up in the throat calculation.

From my understanding, the throat is considered starting at the top of the first rectangle slot to the bottom of the the bottom slot. In between the two slots, you could put a "bar" or rubber throat or "flare it" between the two slots.

On your cabinet, were you even concerned of the flare from the slot openings to the first 90 degree turn? Since you already knew the hieght of the motorboard, did you just make the flares go to the "top corners" of the motorboard?

jc

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you will never amount to anything.

jacksonbart ?

Sorry, thought you asked for some criticism.

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JC,

I'm not quite sure what the question is. The Professor's photos show what is there.

The Caves project has kind of bogged down. I'll get back to it. The issue is that I have to get the LMS system set up, run curves on the Belle and Quartets as a base line, move the couches, maybe put up the eight polycyliners on the wall, and make the whole measurements "scientific". Mike C says I have to get all or part of this out into Lincoln Park for tests in the free field. Grr. Then, I have to work for a living, too. Smile.

If I may say, Roy and Paul in the AES paper injected some confusion on the rubber throat issues and what is the effective horn flare. Too much to describe here.

I did look at the expansions in the Jubilee very closely. It is fairly implied that the footprint of the KHorn had to be honored in their design. It necessitated a first rapid flare.

In my alternative, the first flare is more in keeping with the expansion rate in the rest of bass horn. This arises because of the larger drivers and resulting throat, and the three inch horizontal "plug" or stretched structure. The Professor was talking about it.

I think your question is whether I just did this in the first flare because it fitted, or was there a studied intent. Actually, I looked at it and discovered that it worked in the math.

My alternative design maps fairly well to a classic 29 Hz exponential horn. No rubber throat. No mystic restrictor plate.

Gil

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jwcullison

Getting dual k-33's to spec out to the impedance of a single k-33 is an easy fix. There are two companies that make a high power autoformer that can be used to accomplish this. Price is around 52 bucks per cabinet. Insertion loss is only .6 db.

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