Jubilee - D.I.Y. drawing project (work in progress)

[Neandertal]

Hello,

I have decided to invest time and thought in producing an engineered set of Jubilee drawings. My hope is to reverse engineer a design which matches the original designed by PWK and that can be built by us "handy" types.

The attached file is my best attempt to reproduce the Jubilee as found in the .pdf files previously posted on this site. Using the J.A.E.S. document imported into AutoCad I traced the .pdf print. I "best" interpreted the slightly distorted lines, made all intersections square where appropriate, set all boards at exactly 3/4" thick, ect.... The intent was to best be able to see what the J.A.E.S. drawing had to offer. The drawing was then scaled to match the .540m front width as stated in the body of the article.

I hope to dirive from the fellow members of this forum help and suggestions to allow us to come up with enough data to generate a set of plans that will allow us to build the Jubille.

The following drawings are a work in progess.

Thanks,

Bert

[Neandertal]

This is the same modified tracing of the J.A.E.S. drawing with throat paths measured for length and the A,B,C,& D evaluation points calculated. This was done to compare how the .pdf drawing matched the engineered values provided. To be considered in this evaluation was: 1) How accurate the original drawing was for the published paper and: 2) How much distortion had been introduced in transfer to the article formating, publication, .pdf scanning, ect...

I admitt I was surprised at how well the tracing matched the published numbers with no adjustments beyond those previously mentioned.

Any forum member who know how to directly post these drawings into the body of this thread are asked to do so. I do not know how and personally hate to have to open the attachments and then try to read the subject text.

Bert

[customsteve01]

PDF.gif

speced.gif

I left them big so the numbers could be easily read.....

Looks interesting................

Steve

[D-MAN]

Good job, Bert.

The Jubilee throat is designated as being .029 Sq. M, so in inches it is 44.95 inches (let's call it 45 sq. in).

That would make the throat 10" x 4.5", entirely appropriate for a 12" driver.

However, is the "throat" specified that of 1 driver or both?

I think it is 45 sq. in. for EACH driver, for a total throat area of about 90 sq. inches (the Khorn, Belle and LS are 78 sq. in. for a single 15" driver). This would make sense for the specified dimensions of the horn channels following to the throat channels.

DM

[Neandertal]

O.K....here is where it gets fun. I have now adjusted, pulled, twisted, shrunk, expanded little bits of the pdf tracing to BEST match the publish data. I did have to assume some things to do this. Now we are at the point to make suggestions or corrections. I would like to list the points where assumptions had to be made:

1) Height of the LF bin: From the published data and the conversion from metric to english I have set the bin height at 38" exterior and 36.5" interior. The back volume is dead-on for these numbers. I believe this confirms the "doghouse" is correct in size and proportions.

2) Point A: A real guess here. Need height of trhroat opening and width (location may also be an issue and will talked about it in the motor board drawing). To keep the A-B distance as correct as possible, I need to keep the throat vertically narrow. Even as shown the lenght is slightly short. The shown area for A is correct only if one assumes both throats togther, both sides (halves) together, and a 6" tall opening. I do not like these assumptions (and yes, I do know what happens when you assume something). We need a wider throat but this kills the A-B length unless the A-B path is not measured horizontal?...hummm?....hence motor board questions later.

3) A-B length is a little short (see above).

4) Point B: Point B is a dead-on match if one assumes that the measured point in an average of the entering path width and the leaving width. Since the A-B path is flared along the motor board face (as in the LaScalla), the beginning of the B-C path could and should be wider (no more vertical occuring flare). An assumption yes...but it calculates perfect and does follow the pdf tracing quide.

5) Point B reflector: I have the reflector sized at 2-1/2" as per the A-B path width to better match the previous postings that suggest that 45 degree reflectors should be full width. I agree with this engineering. If one overcomes the belief that the corner is now contricted by the larger reflector, it should work much better. Need to remember that the sound waves are pressure waves reflected by the angle and not waterlike flow through the corner. Not restricted but reflected.

6) Point C: No real problems here....followed the pdf tracing and adjusted a few millimeters here or there to make the numbers match.

7) Point D: Numbers end up real close. Total length will be a better match if the A_B distance can be extended.

All calculations have been measured in the CAD program at the shown micro measurements. I have then made the adjustments to carpentry units measured at 1/16" accuracy. (As close as most of us really cut the projects we build.) These can be posted at 1/32" measurements if any should want them that accurate.

Next... the real problems begin.

Bert

[D-MAN]

See my previous post on the throat area.

Some additional thoughts about throat cavity openings (or slots). The slot size is not required to be the same size as the throat cross-sectional area.

This is made particularily difficult because PWK and Delgato specifically left this ambiguous in the AES article. That fact that the throat size is specified as being .029 sq. meters which gives me some pause in determining exactly what the term "throat" refers to.

In the strictest sense, the throat proper is the area of the horn that is the narrowest in dimensions or embodies the smallest cross-sectional area. The term throat is often used to describe the actual cavity opening into the horn throat as previously described as well. PWK has used the term to describe both particulars in his '45 patent for the Klipschorn, however, in the patent, both were sized exactly the same for a 1:1 correspondence. SO this is easily understood. It is not quite the same when talking about the Khorn and its kin, as the K33E slot is NOT the same size as the horn throat area. But the Jubilee is not using the K33E, so with that in mind, the term throat should be regarded as being separate from the slot cavity when talking about the Jubilee (although it is most likely a 1:1 ratio, and therefore may BE the same as with the patent), I prefer to regard them as separate as it is less ambiguous and as a difference is not indicated in the article.

{edit} Let me preface slot "size" as being consistant with at least one dimension of the respective throat cross-section dimensions. In most horns and all of PWK's designs, the "consistant dimension" being the longest dimension.

When the throat cavity opening (or slot) is NOT the same size as the throat area cross-section of the respective horn, it is acting as a low-pass filter, also called an acoustic filter. This filter is usually a rectangular slot sized to follow the overall dimensions of the throat proportions, although usually sized smaller. The general rule of thumb on the slot size is that the wider, the higher the frequencies will be passed, and the higher the mid-range crossover point can be. In the case of anything using the K33E as a horn driver, the slot is approx. 1/2 as wide as the throat area cross-section to restrict the passage of higher bass frequencies. In the case of the Jubilee, this would not be the case, as the passage of higher frequencies would be desirable, in particular for use as a two-way.

Being no particular reason to restrict the passage of higher bass frequencies in the Jubilee, I would estimate that the slot(s) employed are equal in area to the throat area cross-section, that is, a 1:1 relation.

However, as defined by the article, the Jubilee throat area being resolved to 45 sq. inches, is entirely too small to extrapolate a mouth size of approx. 4 sq. feet in the distance of travel that the horn embodies, including the "rubber throat" section and the different expansion rates of the subsequent horn channels, being 35 and 40 Hz exponential rates, respectively.

I therefore conclude that the throat area proper is cited as being applicable to a single driver only, and that the value is to actually be doubled.

If in fact, I am wrong in my assessment, the value of 45 sq. in. for the throat/slot would have to be revised to 2 slots with dimensions as 2-1/4" wide by 10" tall. This would inhibit the transmission of higher bass frequencies

through the throat which would reduce efficiency and lower the crossover point, both of which are not what the Jubilee is known for. So this further convinces me of the correctness of my assessment.

If the throat splitter devides the slot in half, each side of the slot being an equal area to the respective throat channel area (one side of the bifurcation) at the side of the splitter, then, again the slot should be 2-1/4 x 2 (or 4-1/2") wide by 10" to equal 45 sq. in.

DM

[Neandertal]

Here is the fun part...how to get two 12" speakers and a x" drone in the motor board. The atached drawing show the most "simple" way of placing two speakers only. This would be correct for a LaScalla type placement. Problem is... no drone. Also note that the point A to B distance is short compared to published values.

If one makes room for the drone..the two drivers must move to the top and bottom of the housing. A-B path will distort but will become longer. The A point throat can become larger and better sized. Will draw up a three port idea when you folks help out with possible suggestions.

Need to know....

How large is the drone?

Does it have open air path to the main bass outlet path? (or does it open only into an area 2-1/2" wide as trapped by the flare pathes formed by the two drivers?) Also...where, what, why, when, how do we get info on what the drone is and how we may btain one?

I would like to see some horizontal (along sound path) bracing between the doghouse and the inner "wall". I know that there are two braces between the inner and outer "walls" of the final outlet path. A single 3/4" plywood brace in the middle of the LF bin would be great if we knew what the drone was doing.

Input and comments from you folks may yet allow us to see and hear a live Jubilee. I will do the drawings as per group input on this forum. Someone needs to track down hardware and x-over details.

Bert

[Marvel]

Be nice to make them fit though. Right click and choose "view image" for full size.

speced.gif

[customsteve01]

When I right click there is no option for viewing full size. I resized them at first but couldn't read the numbers thats why I left them alone.

I really would like to hear one of these if someone builds them.

Steve

[D-MAN]

On choosing throat cavity opening dimensions, one point being:

In designing the throat area the 2-1/4 or whatever depth that the throat channel uses should be reflected in the slot opening. It is also accepted practice that the slot proportions follow as much as possible the proportions of the respective throat to prevent reflections caused by discontinuities that would effect the throat impedance.

i.e., a throat channel of 2-1/2" the slot should be twice that in a bifurcated horn. The HEIGHT of the slot is determined by the diameter of the driver employed, usually being approximately the diameter of the cone without the surround. Examples: 13 in. for 15" driver, 10" for 12", 6-1/2 for 8", etc.

A smaller rectangular slot than the throat proportions for instance, the 6x4.5 slot described previously, would act as an acoustic filter, being smaller than and not proportioned to the throat proportions, causing a discontinuity in the throat passageway and is rather drastically undersized for the driver employed, being more correctly sized for an 8" driver rather than a 12" one. This would not give optimum performance, would restrict the passage of upper frequencies and reduce efficiency by raising the reactance at the throat.

DM

[Neandertal]

D-man...thanks for looking and input. I hear what you say on the 10" vertical opening for the 12" driver. Unless someone else has a better idea I will assume that the 10" vertical component will be now accepted "standard". I will be making new drawings (I am sure many new drawings) when WE come up wth a better understanding of how the motor board looks.

This is going to be interesting.....

Bert

[sunnysal]

I look forward to this evening when more people have a chance to review these docs and opin. this IS going to be fun! tony

[D-MAN]

If I was building a set, that's the size I would use.

BTW, it could be between 37-1/2 (a size that PWK especially liked) and 38-3/4" tall which is what (if I remember correctly) is what the stated height works out to. I suppose that depends on the thickness of the wood employed, etc.

If it was me I would go with vertical sides being 37" tall and with over-placed top and bottoms of 3/4" thickness amounting to the 38-1/2" overall height. This is entirely subjective, though... I missed any reference in the article that specified whether it was the overall height of the cabinet, or it refered to the internal vertical dimension of the horn channels, so I assume it means the overall height of the cabinet.

I agree that there should be some horizontal bracing employed in at least the outermost horn channels, and preferably in the inside (exponential) channels as well.

The 90 deg. more-or-less non-expanding channels would be the last on my list for bracing, as the joints occur fairly close to each other, which automatically add some structural integrity to that portion of the horn.

DM

[Marvel]

customsteve,

You must be using Internet Explorer. With Firefox, you can right click on the image and then go to view image. I actually just placed html to resize the graphic on the fly. They are the same uploads as the big pictures. You can right click and save it to your pc for viewing later, and the saved image will be the larger ones.

Nice drawings.

D-Man - I'm still working on those of yours. Had some unexpected things come up, and it's slowing me down. Sigh!

Marvel

[D-MAN]

Tony, as I said, I'm estimating; only the commercial Jubilee owners really know for sure!

But I'm basing my guesses on some pretty sound information, at least enough that I would be comfortable building them as I described.

DM

[sunnysal]

so far d-man I would say your observations are spot-on! especially your estimates of throat area and dimensions...regards, tony

[WMcD]

I don't have the article here.

I would counsel that there is no need to get too persnicity about the opening in the motor board and the two ducts they feed. 10 percent means nothing. Of course everything has to fit together.

Using appoximate numbers . . . the total throat size for each driver is 50 square inches. 5 x 10 is an appoximate openning to feed the two approximate 2.5 x 10 ducts which each driver feeds.

There are some other construction issues though.

One is that a rectangular openning in the motor board is such that the corners of the cut out get very close to the edge of the driver and its front seal via the gasket, at least in my designs using 15 inch drivers.

Hard to descibe. I make the cutout with a bit of a V on the bottom and a ^ at the top. This is just to not intrude on the seal. Some EV designs use a curve. Same effect.

The other potential issue is the excursion of the diaphragm when mounted to the motor board. One good fellow on the forum pointed this out years ago. I thought he was being too cautious but I took it to heart.

It may be that the K-33 woofer has an extra thick gasket so that the diaphragm excusion can't hit the motor board. I was using a Pyramid unit in the home made K-Horn. Therefore I used some hardboard to make a spacer in all my bass horns. It is a pain in the neck but it is one less thing to worry about.

= = = = =

You will also have to start thinking about the construction of the hatches on either end of the dog house, how to attach the motor board with drivers to the rest of the bass horn, etc.

Gil

[greg928gts]

This is a great thread, and one which I will be watching intently.

Greg

[bigdnfay]

Bret,

VERY NICE WORK! I KNOW you spent several hours on this project.

I put together a model about a month ago to get all the angles and lengths of the various parts needed. I calculated the throat opening to be 10 3/4 x 4 3/4. The 10 3/4 is the diameter of the woofers I bought for this project. the 4 3/4 is twice the height of the first leg which I calculate as being 2 3/8. On the model I plan to keep it at that height/width until the second turn up the doghouse. From what I can tell, your drawings are close to what I came up with. I'll sit down with your drawings this weekend and do a comparison.

I'm taking a week off near the end of April to build these babies. All my parts have arrived and I'm ready to go.

Don't you just love coming home and finding boxes on the front porch...Boys with Toys!

Big D

[formica]

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On 3/29/2005 10:00:03 PM greg928s4 wrote:

This is a great thread, and one which I will be watching intently.

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Ditto... almost missed it here in the 2-channel forum, esp given the previous posts in Updates and Modifications.

Rob