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

[D-MAN]

Lots of people get a little twitchy when it comes to horn throats. The bottom line is that is DOESN'T MATTER if the surround is exposed or not. Semi-rounded ends or square ends of the opening don't matter.

It's the cross-section that matters in total area size. The shape of the opening in theory should match the structure of the horn channels its feeding. There is some leeway however.

Overall Cabinet Height:

The Jubilee paper refers to the overall height of the cabinet as .964 meters which is 37.5 inches. This dimension is familiar as it is exactly the same height as the Khorn internal channels. Therefore, I assumed that PWK would stay with that dimension for the inside of the Jubilee, as he historically tended to stay with previously determined values in his designs, and since the Khorn also has the same overall Fc as the Jubilee, and that the 37.5 dimension is particular to the 38 Hz overall Fc, mathematically speaking.

That means that there is some historical evidence towards an internal channel height of 37.5 inches as well, which BTW is exactly what I used in my horn design, which also has the same Fc as both Klipsch units. In doing so, I found that there are certain aspects of the horn channels that flow along with that particular value, which is why I think that PWK would tend to stay with it.

There is absolutely no reason, however, to worry about the difference in internal channel dimensions of only an inch and a half. It will work fine either way.

When considering the benefits of one over the other, it may be better to actually have a slightly larger mouth using the taller of the two choices.

The difference however, will be very, very slight, about 22 sq. inches total difference at the terminal exit, which is extremely small, somewhat akin to having tall floor mouldings, etc.

Point I'm making is that I'd go with the 37.5 INTERNAL channel height, if it were me. I guarantee it to be satisfactory.

DM

[Guest " "]

http://www.partsexpress.com/resources/indexes/sb_guide.html

Here is a nice link from PE that has all their woofers listed in spreadsheet form, with specs going across from left to right.

[DrWho]

Assuming you get the same response plot as indicated in the Jub versus

Khorn thread with your eminence drivers, this is the kind of responses

you're looking at with "porting" the cabinet.

The first yellow plot is the behavior of the driver in a sealed cabinet

with the transfer function of the horn implemented. The next few plots

can be seen by looking up above at the driver parameter boxes. The

white line is actually a passive radiator (the one I link to below)

Note how the response even 2 octaves above the tuning point is affected by 1dB.

And just to reiterate, these plots are ignoring the different

acoustical impedance on the other side of the passive radiator (the

horn side). One part of me wants to say the tuning will end up going

lower because the force function will appear to have more mass present

(since it's harder to move air down the throat of a horn than in free

space). But at the same time more damping results in the tuning going

higher as well. Who knows, maybe everything will just average out?

And this is the PR that results in a 35Hz tuning in a 3 cubic foot box:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-192

Been trying to look for something that goes higher, but I'm not finding

anything...not to mention a port would be much cheaper, more efficient

(1dB) and work over a wider bandwidth.

[Guest " "]

DrWho <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Thanks for looking into this.

What a coincidence. We have 2.98 cubic feet and the PR from parts express will tune to 35hz in a 3.0 cubic feet enclosure.

How much more/less volume do you think we will need to tune to 45hz? Maybe we can make the thing deeper/narrower.

Also, would it help any if there were three drivers in it. I could mount the drone on top and have the horn exit path for the drone wrap around the back and come out the bottom front. Drone horn lenth would be about 5ft if I used this approach.

[DrWho]

2 of those PR's would result in a 45Hz tuning. And I would not recommend changing the volume of the rear chamber at all.

Perhaps have the PR's exit at the angled part of the rear chamber into the side of the expansion? The concern there is you run into "tapped horn" limitations and will have to deal with phasing issues...but who knows, maybe those peaks from 100-200Hz could be reduced a bit in the process? The center of the PR to mouth of the driver would be about 20"? and about 34" from the mouth? That actually puts it right in the position to be effective at those frequencies...now I wanna chop one up and find out.

[Guest " "]

Oh, then it is a done deal. .

I'll put two in there.

The first in the third driver position.

The second underneath the cab where the dog house access panel is. I'll just have to raise the cab about 2.5 inches. This drone would not be horn loaded.

or

I could also put it on the top access panel. I would need to build a channel for it that wraps around the top, down the back, and back to the front from underneath the cab. That would allow it to be horn loaded.

2 drones will tune to 45hz, plus a half octave up and down will give me a 30hz jubilee cab. Thats a half an octave more than I expected.

Thanks for your help.

[jwc]

Dana.

Yes. 0.964 meters which is 37.95 inches exactly. Not sure if this was quoted as internal or external height. I do know the bass bin with risers and feet was about 40 inches.

I think the 37.5 interanl is a good starting point. However, if you look at the top view that has been posted, the calculated area at Points B,C,D will be slightly more than what is quoted in the paper. But I think this is "OK".

I am going to build cabinets for each driver and stack them. That way I don't have to make the "braces" for the final flare. Will use 3/4 panels. However, the top of one cabinet and the bottom of another will be 3/8 inch. Then I will stack with the 3/8" panels together to make 3/4 inch. Can glue and screw later if needed.

Therefore for each driver, the internal height of its horn will be 18 3/4 inches. Total internal height 37.5. Therefore, the total height of the bass bin will be 39 3/4 w/o the risers. There is 3/4 inch in there that will be the "brace" between the two.

Mike.

Nice work. I saved that plot as a reference. Will see later if I can figure out how you did it with that software. Question: That Kappa pro 12" driver you modeled is the CAST FRAME version isn't it?

jc

[Guest " "]

jwcullison

Looks like your ready to go wood and parts shopping.

Good move on the stacking approach. How many stack's?

I am going to use three. Since I'll be using drones, I'm going to cut thru all the floors so that all the drivers and drone share the same internal volume. Probally use wing nuts on the end wings to keep the floors together. May even run some threaded rebar down the middle and bolt there as well.

[jwc]

No drone on the first one. Will stack two cabinets. The attached image is the top view of just one stack with internal height of 18 3/4". Please proof read.

jc

[Guest " "]

looks fine to me.

I know what the front view will be from your previous 2 driver post.

The expansion gap of 2.5 between the first 90 and the 45 degree fillet is there. Thats expanding from the 2.5 before the turn and the 2.75 after the turn.

Everything else is straight forward.

The volume of 1 independent cab is approx 1.74 cubic feet if you do not connect them both together and 2.98 cubic feet for both if you do connect them.

[DrWho]

Mike.

Nice work. I saved that plot as a reference. Will see later if I can figure out how you did it with that software. Question: That Kappa pro 12" driver you modeled is the CAST FRAME version isn't it?

I dunno...I just forced the transfer function of the sealed cabinet to that of the posted response plot of the Jubilee. I could have used any driver really. The effects of the porting/passive would be the same.

[DrWho]

Here is the set of EQ's I used to achieve the transfer function of the horn. You'll notice the green one is scrolled up all the way, and the blue one is scrolled down all the way. The only thing to ignore is the very last adjustment on the blue side...

I wanted to post these graphs to show the effects of a little EQ on the bass bin (which would easily be implemented with a typical active crossover). It's just -6dB at 137Hz with a Q of 1. The green chart shows the effects on the original Jubilee (+-3dB from 40Hz - 1.3kHz). The blue chart shows the possible output with a 45Hz tuning (+-3dB from 35Hz - 1.3kHz).

JW, if you want I can send you the WinISD file so that you don't have to plug it in manually.

[jwc]

Guys. So far. I've got good news. I have drawn out the top view of what I have been posting. This is to actual scale on large graph paper. I am to the back of the horn.

Now I did make a few modifications of what someone earlier had put together. This is shown on a few posts back. So far it is perfect. By tomorrow night, I will have the entire thing drawn out to scale to verify. This will make the build easier. Will be able to provide absolutely all lengths and angles. Including those awkward pieces at the back.

The two Kappa pro 12A cast frame drivers are on the way.

jc

[Guest " "]

I was wondering what you were up to.

[Guest " "]

fyi

J_Box_Dwg_p1.pdf

[Guest " "]

fyi

J_Box_Dwg_p2.pdf

[Guest " "]

previously posted on a different thread

KPTKHJKPT402K69A.pdf

[jwc]

Yes I have that file. It is a little different than the "top view" I have been posting. I just want to do it from scratch to prove to myself the calculations are right.

You started cutting?

[D-MAN]

I just wanted to say that in the "old" top-view above which shows the non-expanding portion of the side channels at 2.75" width is not technically correct - should be 2.5", same as front channel width. The rest looks good.

That's it.

DM

[jwc]

Well, then I need to start over then. Just so it gets done right. Now at point "B", I assume it will have to be greater than 2.5 inches to get the correct volume.

It was interesting that last night I was noticing that the "fillet" at the first turn wasn't as wide as I thought it would be. In fact, it came out much smaller than the "splitter". I assume this thread is in favor of the same size fillet as the splitter to prvent loss of the high end. Does this make sense?

jc