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jwc

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

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jwcullison

Yes thats the before scaled down version. Time lines for an additional room will dictate the full size or scaled down model.

Yes stacking horn sections like floors. 3 story building scheme.

Slot for the drone will be on a removeable baffle. Thinking the smaller size is what I will wind up with, but want to be able to have a choice of a throat as large as the other two.

Goal of the drone is to add 1.5 to 3db from the tuned point and at a range of half an octave above and below, rolling off at 18 db per octave. The drone gimick is loosing favor to adding a third woofer or a push pull woofer. Issue is the marginal improvement gained by a passive radiator relative to other options and the narrow range passive radiators operate at. That jubilee cab is just not a deep enough kicker in my view to add a passive radiator. I'm going to try it. But I don't think it will stay in there.

I was out in the garage making some practice cuts with my new table saw and my panel saw both of which have been upgraded with a very sharp "diablo" titanium carbide blade. The thing cuts 3/4 11ply birch like it was butter. Barely feel it hitting the wood. And the cut is so smooth it will need little sanding.

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Now I have some more questions about the throat and the initial flare. Now, I plotted the flare using the total height of the cabinet of 36.5 inches (almost 37) with the slots 5 x 9 inches. I basically sketched the top half of the motorboard with the slot placed right in the middle. Now drawing in a flare to make it fit, I backwards calculated out the initial flare with this setup as being 68 Hz Fc. If you look at the line that would make a flare a lower cutoff of 40Hz Fc, it wouldnt line up. The cabinet height would be too short as expected.

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So, if I were to go the route of stacking 2 horns as SpkrF is doing with the height and slot that has been mentioned here. This is what you get with no drone. This leads me into my next point.

Now in the AES paper, the initial flare has an Fc of 97Hz. The second flare is Fc of 35Hz, and the third flare Fc of 40Hz. Now they quoted the initial flare as something they didnt want to change as it would 1) require the height of the cabinet to be too tall and 2) would have to make changes to the other portions of the horn (paraphrased). They could have changed the size of the throat but they mentioned twice that the throat of 0.0029 m2 (45 sq inches) was needed to MAXIMIZE MIDBAND EFFICIENCY.

Now we are getting deep into perfection here so please dont be annoyed. It will take some time and money to do this and I want to go in it w/o the regret of not asking enough questions.

So here goes.

1) Can yall think of any compromise by having the initial flare rate lower than 97. I cant think of one.

2) More seriousand Im worried. We have our suggested throat on this thread of 90 sq inches. The paper is pretty firm on the importance of 45 sq inches. There are some other diagrams cloned that have the slots at 3.75 x 6 inches. These are with the same depth of the initial flare and the same splitter.

3) Please explain this MAXIMIZE MIDBAND EFFICIENCY

Now my point is not to find something wrong with the suggestions. I just want to understand potential compromises.

The help is always appreciated

The attached image is the one I drew out tonight.

jc

post-16499-13819304818888_thumb.jpg

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Here are the two slot/throat options w/o a drone I have seen on this forum. I am understanding that the depth of the initial flare on both options was 2.5 inches deep. One has a throat of 45 sq inches and the other is 90 sq inches. It would seem to me that the "left" one would be like the one in the AES paper with smaller slots, smaller throat and higher initial flare. I hope I am not missing something that will make me look really stupid.

post-16499-13819304819508_thumb.jpg

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Guest " "

Assuming a 5 * 9 motorboard opening for the driver

Driver one, Throat A, right turn opening = 2.5 * 9 = 22.5

Driver one, Throat B, left turn opening = 2.5 * 9 = 22.5

Total of the driver one above = 45

Driver two, Throat A, right turn opening = 2.5 * 9 = 22.5

Driver two, Throat B, left turn opening = 2.5 * 9 = 22.5

Total of the driver two above = 45

Total of both drivers 45+45=90

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speakerfritz,

That is exactly how I am percieving the slots with the 5 x 9 opening. A total of 90 sq inches.

What I am concerned about is that the AES paper wanting a throat of 45 sq inches total. Unless I am reading it wrong. That is why I was thinking the motorboard to the "left" may be similar to the AES paper. Am I still missing the boat here?

jc

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Assuming a 3.75 * 6 motorboard opening for the driver

Driver one, Throat A, right turn opening = 1.875 * 6 = 11.25

Driver one, Throat B, left turn opening = 1.875 * 6 = 11.25

Total of the driver one above = 22.5

Driver two, Throat A, right turn opening = 1.875 * 6 = 11.25

Driver two, Throat B, left turn opening = 1.875 * 6 = 11.25

Total of the driver two above = 22.5

Total of both drivers 22.5+22.5=45

post-16499-13819304820258_thumb.jpg

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jwcullison

This is a version of the 3X13 vs the 6X13 Khorn throat debate.

The specs on 3X13 K-horn throat show it boost bass at the expense of mid-bass.

The specs on 6X13 k-horn throat show it boost mid bass at the expense of lower bass.

You have discovered why I want to make adjustable throats.

My speaker building water stick tells me that 45 will be good for the drone due to the narrow bandwidth the drone operates at.

My speaker building water stick thinks 90 is good for the drivers.

Maybe thats why we need a drone.

If your not going to use a drone, you might need one of each throat size.

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Sounds like I should make it 5 x 9. Make woofer mounting plates in which I could add a "template" to shrink the slot down to 3.75 x 6. The problem is with the change in height of the slot. If I change it, then my ramps won't line up. Maybe this is why you have the height the same and the horizontal as a changing option.

Man. This will be tough.

What is meant by "maximize the midband efficiency" stated in the article along with the reason for the 45 sq in throat. This seems to contradict the reasoning in your last post. I have only a guess at what it means.

Again...not to make argument here. Just trying to understand.

I want to make it clear that I'm not too concerned with my build being able to make it out to 1500Hz like in the article. I seriously could be very happy with 500Hz as long as the lower Hz is good. I could manage if it went to 350Hz.....but that would defeat doing a build this way.

Thanks

jc

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hey jw,

let's see, maximum bandwidth efficiency...some of don keele's equationss call for a bandwidth product that points to a throat area that would maximize the efficiency of the horn using the driver parameters, kinda of like tuning a vented box. if you make the throat area too small, you increase effieciency that translates into spl over a small bandwidth, make it too large, and efficiency decreases and bandwidth increases. using the equation balances parameters to get most efficiency over the most bandwidth.

by the way, when i was laying out the jub, i was designing one horn that i mirrored to make two drivers and two horns. so it might help if you think of this in terms of laying out one horn for one driver and then just "stack" another horn on top.

hope this helps.

roy

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jwcullison

Yes the reasoning behind the switch to 3x13, then back to 6x13, then back to 3x13 contradict specs for a throat that say smaller is wider bandwidth.

My experience with k-horn throats line up with the notion that the smaller 3x13 throat had better bass response than the 6X13 throat which had better mid bass response.

Intrestingly, there was also a run of the 3X13 throat with rasied and beveled inside edges that tapered off, kinda like the bevel inside the dog house shell that we passed some diagrams about to prevent wave bounce back.

Question about the flares. If the production Jubilee has a drone, then the flares would not be as steep as yor diagram indicates.

Back to the next steps. Mabe I'll do a dry run using two one section Jubilee horns for just one driver with one of each throat size. Then do an A/B test and evaluate pros and cons. I was planning on one section with a smaller throat than the other two anyway so it wouldn't be throw away work.

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Roy, thanks.

I hear ya. Only trial and error on my part will resolve some of this as I am using drivers that you probably didn't in your article.

Making the horn for one driver then stacking them. Speakerfritz has got me thinking this way now. If your article was calling "throat" for one driver is one thing or is it the throat "after the stacking".

Again...may all come down to my driver issue as well and experimenting with it.

Thanks for the input.

jc

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You plug anything into WinISD yet JW? I'm not sure if I answered your question earlier...yes it is free. I won't vouch for its accuracy, but the program will certainly show you the effects of changing the size of the throat.

And did you already purchase the drivers? You might wanna check out the Eminence Lab-12:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-570

Its T/S parameters are optimized for horn-loaded configurations...and more importantly (for you) I think you'll get a bit more bass from it as well - though that usually means some sacrifices in the top end.

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I am surprised to hear this, but will take it as good news.

We will need to add some mass to the radiator.

Adding mass lowers the tuning point. What is the effective volume behind the drivers in the Jubilee anyway? I couldnt' find the specs anywhere.

Keep in mind that the drone also causes the active driver to drop off

faster too...so you can't just throw the drone in at any frequency and

expect it to not affect the response below its operating bandwidth. I

wouldn't aim for a tuning any higher than 45Hz when looking at the

response plot Roy provided.

Also keep in mind that the resultant output is not just the sealed

response of the driver + the output of the drone. The drone/driver

relationship also causes the driver to have more output above the

tuning point as well (different acoustical impedance behind the driver).

In a passive radiator situation, it is better to aim for a tuning that

is too high because mass can always be added to lower the tuning point.

You can't really raise the tuning of a drone without rebuilding it (or

somehow removing mass).

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DrWho

I'll give you some internals late this morning.

The radiator from PE recomends half a gram to start, so assumption is there will be some weight to remove,

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Guest " "

DrWho,

Thanks for your input. internal volume of the Jubilee cab is 2.98. Below are misc current assumptions, subject to change, as our thinking about drones gets less fuzzy.

"Adding mass lowers the tuning point. "

Yes. Cone becomes heavier, operating ceiling of the drone drops.

"What is the effective volume behind the drivers in the Jubilee anyway? "

2.98 cubic feet

"Keep in mind that the drone also causes the active driver to drop off

Faster too...so you can't just throw the drone in at any frequency and

Expect it to not affect the response below its operating bandwidth."

Thats the tricky part. The drone only has a range of one octave. The center of which is the tuned frequency. Beyond that, there is a roll off at 18 db per octave.

" I wouldn't aim for a tuning any higher than 45Hz when looking at the

Response plots Roy provided."

Assuming our driver/enclosure values are consistent with a usable frequency of 45hz. The drone tuning point should be 60hz. Setting at 45hz would result in only half a drone. AT 45hz the drone would add value from 45hz to 60hz. At 45hz, I dont think that the drone would help from 45hz down to 30hz. The jubilee cab seems to have a bottom end of 40hz.

"Also keep in mind that the resultant output is not just the sealed

Response of the driver + the output of the drone. The drone/driver

Relationship also causes the driver to have more output above the

Tuning point as well (different acoustical impedance behind the driver)."

Yes. Half an octave above the tuning point and half an octave below the tuning point.

"In a passive radiator situation, it is better to aim for a tuning that

Is too high because mass can always be added to lower the tuning point."

If the drone is pre-loaded with half a gram of mass. We can shoot for 60hz and add/subtract from there.

"You can't really raise the tuning of a drone without rebuilding it (or

Somehow removing mass."

The PE drone specifies half a gram of mass. My assumptions are that that half a gram was used to get the published specs.

""And did you already purchase the drivers? You might wanna check out the Eminence Lab-12:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-570

Its T/S parameters are optimized for horn-loaded configurations...and more importantly (for you) I think you'll get a bit more bass from it as well - though that usually means some sacrifices in the top end.""

I got excited when I saw the response graph. The upper range appeared to reach 1K, then drop off sharply. Bubble burst pretty quickly. The impedance at 1k is 16 ohms. Due to the drivers rapidly climbing impedance above 125 hz, the effective rave for the drive is indicated at 25hz - 125 hz.

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Mike. I haven't done any of the modeling in WinISD like I have with bass reflex stuff. Frankly, I'm not sure I know how. I haven't even investigated it. May need to piddle with it.

I had noticed the Labgen12 woofer before. I had "assumed" it would only work well for a subwoofer and never gave it much thought past there.

So speakerfritz. Sounds like with all the above info in this thread, the unknowns have pretty much been identified and ideas of how to complete the project are there.

I will now need to look into the complicated cuts of the horn walls. I no longer make the large cuts with a table saw as I have some disability insurance issues. Therefore, I lately have farmed out the large panels to a local cabinet guy and I do the small cuts and assembly. Wil need to run down and show him some diagrams to see if he is up to the task.

jc

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Jc, the throat area is 90 sq. inched TOTAL, each opening being 45 sq. inches.

The article was referring to a single opening.

This is easily understood in that you simply cannot fit a 40Hz Fc horn (properly) in the path length of the Jubilee using a 45 sq. in throat. Ain't physically possible to have it work properly.

Smaller throats naturally mean longer pathlengths! The correct mouth size ALWAYS remains unchanged.

Are you using the 37.5" overall height of the cabinet, which means (using 3/4" ply) that the inside channel height would be 36" even?

If so, then in reallity, you cannot screw up the throat. The measurements all work out no matter what you do!

Here's the skinny:

1) the outside full-height channels (at the throat section exit) are 36x2.5x2 = 180 sq. inches total

2) the 2 throat cavity openings of 9x5x2 = 90 sq. inches

the throat area is clearly DOUBLED in size at the outside channels giving an exponential doubling length of approx 9" (measured center-of-channel) for a 97Hz flare rate.

Providing you have 9" of horizontal travel available. Looks entirely possible to me from looking at the plans previously posted.

SO As long as you maintain a path with an EVEN expansion between the two points, you really CANNOT screw it up! It's already fixed in stone!

Like I said previously, all the important horn parameters and calculations are already done for you!

Remember to select a driver that will APPRECIATE a 45 sq. in. opening, certainly not all will! I would question the low efficiency rating on the previously posted subwoofer as being appropriate in a Jubilee application. I also don't like rubber or foam surrounds - they are too sloppy for horns, IMO, but that's just me. Also you won't need that kind of excessive excursion, which is better for a subwoofer application, I think. Q is also a bit high for my taste, too. Beware!

DM

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Well there you go. It makes sense. I didn't realize that the paper was refering to the throat of one driver. It all adds up now.

The image with the smaller throat has been circulated on this forum and it further lead to my confusion.

So a 36 inch total internal height. However, I think 36.5 came out a little closer when I was adding it up at one time. But not much difference in 0.25 inches per horn.

I was still just planning on using the Kappa Pro 12 " cast frame driver.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-424

What is this "Cloth accordian surround" on this woofer.

I hope the 5 x 9 cutout won't be too much at the corners causing the surrounds of the woofer to be exposed. Not sure how to explain that. Looks like BFD got away with squared off corners.

Looks like its getting close to production time.

jc

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Guest " "

The accordian surround is the same type used on the k-33, k-43, etc.

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Well there you go.  It makes sense.  I didn't realize that the paper was refering to the throat of one driver.  It all adds up now.

The image with the smaller throat has been circulated on this forum and it further lead to my confusion.

So a 36 inch total internal height.  However, I think 36.5 came out a little closer when I was adding it up at one time.  But not much difference in 0.25 inches per horn.

I was still just planning on using the Kappa Pro 12 " cast frame driver.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-424

What is this "Cloth accordian surround" on this woofer.

I hope the 5 x 9 cutout won't be too much at the corners causing the surrounds of the woofer to be exposed.  Not sure how to explain that.  Looks like BFD got away with squared off corners.

Looks like its getting close to production time.

jc

 

jc,

Have you bought the Kappa Pro-12As yet? I might be able to save you some money on them.

Bob

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