Basic basshorn design questions

[jwc]

Come to think of it, I think I will do a big straight horn on paper with the 3 x 13 slot and throat of 78 sq in or 503.22 sq cm.

Dana, If I want a Horn that isn't a corner horn with a cutoff at 45Hz, will the folded horn be huge? I guess that is relative.

jc

[DrWho]

45Hz? That's sounding awfully like the Jubilee bass bin. Just curious, what performance did you find lacking in the Jubilee that you're hoping to improve upon? Or why do you feel the need to move to a single driver? The way I see it you're going to lose HF extension by going this route.

[D-MAN]

Come to think of it, I think I will do a big straight horn on paper with the 3 x 13 slot and throat of 78 sq in or 503.22 sq cm.

Dana, If I want a Horn that isn't a corner horn with a cutoff at 45Hz, will the folded horn be huge? I guess that is relative.

jc

Here's the deal - the Klipsch Heritage horns all use the 39 sq. in slot feeding a 78 sq. in throat. That means that the acoustic resistance is very high AT the SLOT, but then relaxes somewhat for the rest of the horn path which is larger in cross-section at the throat. Using a 78" throat (and the K33E or equiv) will make the horn channels 3" deep x whatever the expansion dictates. In a Jubilee format, the footprint will be larger than using 2 x smaller throat sizes. Which one you choose is up to you.

If you use a driver with a narrow-slot requirement and a matching 1:1 throat size, you could keep the footprint size down to the Jubilee size to a degree, same size mouth, etc. Yes, the horn cabinet could be shorter in height to compensate, but the channels would be narrower (or as-narrow as the "real" Jubilee), too.

If you are comfortable with the larger footprint, then why not go with 2 x 15" drivers?

1/4 space placement (along a wall/floor intersection) is going to be larger than a corner horn, of course. Free-standing on the floor is even larger (mouth size and horn length increases dramatically). The corner design is therefore the smallest in all dimensions that you can have for a given Fc.

[jwc]

Dana. I follow you. I couldn't figure out a way to make a one 15" driver w/o having a big footprint and being short. Unless of course I Folded the horn vertically instead of horizontally.

I have no problem using two drivers necessarily but I would like to be able to use Bob's woofer. With this, I was assuming keeping the 3 x 13 slot and I have a good bit of experience at this point making low pass filters with that woofer and K33's. From what you just stated, that may give me a huge cabinet.

This may sound silly to you.

At any rate. Yes, I can build a two 15" woofer in a "style" like a Jubilee. That mey give a better shape. I don't wan't ports. I was readind the AES Jubilee article again last night. I wasn't too excited about the "dead space" at the first 90 degree turn like the La scala but I may need to do it this way to prevent the cabinet from being over 45" wide.

So tell me at 1/4 space placement, what is a good Fc to shoot for? The lower the better for me. I'm not necessarily worried about HF extension. I know this is going about this with a different approach than you would.

Dana, I have been using software to calculate the cross-sectional area of a horn at certain lengths down the horn from the throat to mouth. Is this bad? You quoted another means of doing it with a calculator and an article reference.

Also, one last thing. Set me straight on this. Say for example I am trying to calculate the horn height at length 1" from the throat of "ONE SIDE" of the La Scala. Lets say we know the horn would have to be a cross sectional area of 81 sq inches at that location.

3" (depth) X Height = 81 sq inches. Therefore the height of the horn ON ONE SIDE would be 27 inches and the depth would be 3 inches. Is this correct?

Also, is the calculations for each split horn based off a throat of 78 sq inches in the la scala?

Thanks man.

[D-MAN]

1/4 space, 50Hz Fc = 1175 sq. in. mouth size (Edgar's Showhorn). Download the article from ww.volvotreter.de and read it thoroughly before making any decisions...

Also, the Turbosound 50Hz horn (Melhart patent) is a winner for its simplicity and fairly good response.

The Electrovoice "Eliminator" is another 50Hz horn. So is the University "Classic".

None of the above are "small".

[jwc]

I have the the showhorn article. Read it a few days ago. So could I use the same cacluations but on a split horn like a la scala. I'll read it again tonight.

[D-MAN]

The calculations are exactly the same for a bifurcated horn path or a unitary path horn. Of course, the bifurcated value is 1/2 the total value per side, but added together, the results are exactly the same...

The LS is a two-flare rate horn. It is a 60Hz at the throat and a 125Hz flare rate in two sections and its also bifurcated at the throat which seems add to the confusion. The target overall Fc is 70Hz, per PWK. See the 1965 LS paper posted originally by Gil in the Tech section.

DM

[jwc]

Found the 1965 LS article. Not a lot of info there....read it.

Skimmed over the Showhorn article again. Now his listed 50Hz horn expansion is for a M=0.6 (as opposed to pure exponential) with a mouth that is 40 sq inches. Wasn't this on a 1/8 size horn to give it a small mouth of 725 sq inches? Isn't the la scala mouth 2304 inches?

At any rate. Just messed around with some numbers and drawings again to see what that initial angle of the "ramp" or wings would be at the initial start of the horn. Now I did what you said and basically divided the cross sectional area by two in order to work on one side of the horn. Now I kept the horn as M=0.6 except 1/4 size for a 50Hz horn with a throat of 78 sq inches. Length of the horn was estimated at 72.5 inches.

Again...gonna make for a very wide bass bin....very wide in fact.

Appreciate your help. Pretty sure I can do this except worried about the shape. I thank you that I have now figured out the throat and how to calculate the area at a certain point on one side of a split horn.

I think keeping the throat at 78 sq inches with dual driver will create a "monster". I get your point now. Smaller throat makes a big difference.

To make one driver work with a split-folded horn, I would have to make the initial part of the horn split in the vertical plane first and then have both horns travel back to a common chamber and then flare out from there horizontally. Heck...I might as well build a Khorn with false corners!

man

[WMcD]

I don't quite know what the calculation problem might be.

Attached is a spreadsheet I made up which should help you. You don't have to know how to make a spreadsheet and it is not too difficult to use. Note the fields that are input. These are where you put in numbers.

You will have to decide what units you are using. This is determined by the value of c, which is the speed of sound.

The first column is distance down the horn. Leave that alone unless you know what you're doing. People familiar with spreadsheets will see that the numbers are generated by just adding 1 to the value above.

The second column is a calculation of the area based on the typical exponential equation.

You can copy the last values and paste down to make more entries.

There are two other little utilities.

The first determines Fc if you start with the length in which area doubles.

The second addresses the situation where you have areas at two spots along the horn. Usually this is the mouth and throat but does not have to be. You also need the distance between the two. Usually this is total horn length. The output is calculated Fc based on the exponential equation.

I expect you and others will have some fun. I'd be pleased to answer questions.

Gil

Exponential Horn Spreadsheet.zip

[ajsons]

JC,

My vote is for Dana's V2.!! It's a lot SIMPLER to build. We know that some design elements of the Khorn needs to be improved, altered or modified. The V2 has already done those.

I have some horn designs of my own, but if I have to build somebody else's design, it will be the V2.

Check Flemming's.

http://forums.klipsch.com/forums/thread/743652.aspx

[jwc]

Thanks Gil. I will play with that some.

I have seen that thread before and Dana has sent me plans of another horn. Definately a talented guy.

Gonna ponder on this DIY some more.

jc

[jorjen]

Did Flemming ever figure out his problem in the 150 - 400 hz region?

Good intel here fellas. I am really enjoying this thread and trying to learn this stuff myself. I love your enthusiasm JC. By the way, did you get my PM/mail on the bendable ply?

[WMcD]

I'll give you some free advice. It is worth every penny. OTOH I've built a lot of bass horns over the years.

The KHorn is a real bear to cut. Assembly is not too bad but getting oddball angles right can be discouraging.

Build a single LaScala or Belle first. This is somewhat in keeping with the folks who grind mirrors for telescopes. If you want to grind a 6 inch mirror, it is better to grind a 3 inch mirror first, just to get the experience. Making a 3 inch, then a 6 inch is faster than starting on a 6 inch.

Then build a pair of Jubilee. As DMan has pointed out, the Jubilee is sort of like stacked LS with extra expansion. You can use the single earlier speaker as a center channel.

I'm a big believer in making full scale drawings on graph paper. When I made the 15 inch Jubilee as seen in "The Caves" I bought a roll of 48 inch wide graph paper. I've still got most of it. I could send you a length for your project.

The offer is open to others here too. But serious builders only, please. The cost is a beer at the next Pilgrimage and a promise to post pictures of your work.

Gil

[jwc]

Gil I may take you up on the beer offer as I am always looking for some excuse to drink.

I too am piddling with the graph paper. Like it. I've read your "caves" post a few times as well as the Jubilee AES. I might bug you one day on more details with that beer.

Jorden. Got your email. Thanks. I will ask you again more of this bendable plywood later. And a special thanks for encouraging me to reread that Edgar Midrange horn article. It is very good and easy to understand.

jc

[ajsons]

Did Flemming ever figure out his problem in the 150 - 400 hz region?

Good intel here fellas. I am really enjoying this thread and trying to learn this stuff myself. I love your enthusiasm JC. By the way, did you get my PM/mail on the bendable ply?

Flemming sent me an email and said that it wasn't a "booming" but more of an increase in loudness somewhere in the 150-200hz range. He was using 10 sec test tones. He thinks it is more from room resonances, and not from the V2.

[D-MAN]

Yes, he said he used a passive notch filter at 400Hz to tame the response down by -4 db and he said he's quite happy now. Since I do not have the same drivers as him, and I certainly don't have any booming, I figure it's a driver-and/or-room related issue.

He also has stone floors. I think that its a combination of the room and JBL J-145. I feel safe in assuming that the reported +4db rise at 400Hz and Flemming choosing to crossover by ear at 750Hz means that the driver in question clearly has a rising response curve, that is, it gets louder as it goes up in frequency. That may be part of the problem.

Evidently, he is quite good at figuring out the electronics needed to accomplish whatever he wants to do with the networks. He designed his own from scratch. He said he was an engineer...

He's now working on a Smith horn design for his midrange.

DM

[D-MAN]

Skimmed over the Showhorn article again. Now his listed 50Hz horn expansion is for a M=0.6 (as opposed to pure exponential) with a mouth that is 40 sq inches. Wasn't this on a 1/8 size horn to give it a small mouth of 725 sq inches? Isn't the la scala mouth 2304 inches?

The reasoning behind an M < 1 (exponential/hyberbolic) flare rate is from several sources, such as Salmon's original Hypex patent, and Marshall Leach's first paper (actually a correction by Leach thereof) on horn design. It allows for "more accurate" frequency annulling of the back chamber, something which is "less accurate" for a pure exponential flare rate of specific length. This is particularily important with back-loaded horns, but is also applicable to front-loaded horns, however, it is generally accepted that it is not as critical for the operation of the driver as in a back-loaded configuration.

The math doesn't work out as well for an pure exponential curve, and I'll leave it at that!

You'll note in the "Show Horn" article that Edgar does the annulling "manually" by experimentation rather than calculation alone. That speaks volumes, don't it?!

The mouth on the LS is about 4 sq. feet (24x24" or 576 sq. in.) pretty close to the Khorn mouth exit size. However, since it is a 70Hz (nominal) Fc horn, it's smaller in mouth area than the 50Hz Fc "Show Horn", of course. It is also not intentionally designed for 1/8th space as is the show horn.

It should be noted that none of the Heritage horns are completely annulled (by today's standards, anyway) and that PWK preferred (as derived from the "Little Bxstard or Valerie" patent) to slightly undersize his back chambers rather than have them completely annulled. This allows for a more-gradual falloff than if completely annulled.

He also chose driver with a lower Fs than horn Fc, where Edgar recommends driver with a higher Fs than the horn Fc and then annulls the back chambers. In the later case, the driver will fall off more rapidly below the horn's Fc than the non-completely annulled driver will.

DM

[jwc]

I want to thank everyone for helping me with my basic questions.

I finished of an exponential horn on graph paper that was a 56Hz cutoff, 1/4 wavelength, with one woofer. It was drawn out down to a centimeter.

I'm not gonna build it because it is very wide.

At any rate, the thread was there to help me understand a few things and I feel much more solid on the subject.

Will hold off on any build right now as I learn a few more things.

jc