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jwc

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

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Super. Now that is simplicity. Makes for simple construction.

Non ported I assume.

Now what I know with the AES paper and what you have provided, I can visualize the build. thanks Dana.

Now I would just need to figure out the flare/ramps to the first turn. This would also have an impact on how far apart exactly the slots are from each other. I think I would need to reread the AES paper again and figure that one out. The throat from your suggestion is slightly different size. I like it.

If you feel solid on how to do a port...throw it out there.

Man..this is coming together.

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Here's the deal with the initial throat expansion ...

1) it is so short that virtually any configuration will work, as long as it is sealed (air tight). I actually don't think that it can be screwed up - its too short of a run in a restricted space, as long as you stay symetrical. The throat layout needs vertically oriented openings, of course. I would say the MINUMUM vertical dim. is 9" to a MAXIMUM of 10-1/2". The MAX width of each opening is dictated by the depth of the throat channel at the throat which is approx. 2.5", so 2.5+2.5 (bifurcated) = 5" maximum width, or you will increase the chance of overloading the throat, increasing distortion. If you are going for a central port, then you will want to use the shorter vertical dimension in order to make room, of course.

2) If you want a slower expansion rate at the throat, increase the long dimension of the opening to 10.5" max. the flare of the channels will magically follow. Will it hurt anything? NO. There is not a whole lot of difference in 1.5" per opening of vertical difference and about 6 sq. inches of overall area per driver. 6 sq. inches ain't nothin.

Whether you want the largest throat opening depends on the driver you choose... however, the 45 sq. in is a good safe bet. Do not go much smaller than about 30 sq. inches each opening. So the safe bet on largest size openings are 55 sq. in. each (total 110 sq. in.) to a minimum of 27 sq. in. each (total 54 sq. in.).

3) keep it simple. Where BigD's throat configuration is admitedly the "Cadillac of throat layouts", Klipsch typically uses a simpler and somewhat less elegant approach. Both work. You're the builder, so you decide.

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re the port...

First of all, the length of the port would be easily adjustable so with

a little measuring equipment or good ears you could dial it in after

it's all built.

To get an idea of where to start, I would model the driver(s) just like

you would a normal vented enclosure. Then taking into account the

transfer function of the horn (isn't it an 18dB/octave drop-off below

the Fc?) aim for a low Q system response. WinISD should be pretty

effective at modelling this. When you drop this port into the actual

horn the actual tuning will be effectively lowered - which will be a

good thing because shortening a port to bring the tuning back up is

easier than making it longer.

So what's wrong with this approach? It totally ignores the complex

acoustical impedance at the throat of the horn, which should definetly

affect the behavior of the port. The port is also going to change the

rear-loading on the driver, which is a big part in the behavior of the

driver on the horn. A low Q tuning should help avoid this problem.

Speaking of increased low frequency extension, here are a couple links that I found rather interesting:

http://www.danleysoundlabs.com/pdf/danley_tapped.pdf

http://www.quarter-wave.com/

If I understand correctly, the tapped design is basically a quarter wave transmission line mixed with a horn?

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Here is a hand drawing (just got a mac, and no cad software yet).

While the two drivers and drone will share the same woofer chamber, their exit paths will be independent.

Drone throat will be smaller than driver's throat using an insert, for tweaking purposes.

post-22082-13819304798198_thumb.jpg

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I have no excuse at this point. With all this info.....I have to do it.

What drone do I need to get to match the two Kappa pro 12's?

With that drone in there, I will have very little option on the flares anyway.

jc

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Roy, ANOTHER ported horn patent, this one ports mid-way in horn channel proper.

DM

post-13458-13819304802028_thumb.jpg

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I have no excuse at this point. With all this info.....I have to do it.

What drone do I need to get to match the two Kappa pro 12's?

With that drone in there, I will have very little option on the flares anyway.

jc

That I don't know, but it seems to me that you'll need a drone rather than a port, because I don't think the Jubilee has enough available Vb to effectively resonate (Fr) low enough for a port tuned below the horn's overall Fc of 40Hz. It presumably can, however, resonate above that. Depends on the driver(s), of course. Perhaps that's a better question for Roy.

DM

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D-man

I might scale this down to reduce the footprint. If so, the passive radiator may be a moot point if the associated shift to the xover frequency of the sub woofer is above the tuned frequency of the passive radiator. If that turns out to be the case, will put three drivers in there and use an autoformer to bring the impedance back up.

jwcullison

Passive radiator

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-496

I'm going to put mine on the bottom. My thinking is that you would not put a sub woofer 18 inches off the floor, so putting it in the middle position would be self-defeating.

Also am going to have independent exit paths. I realize this will triple my cuts, but I have a panel saw, and can pre-set it for vertical cuts as well as being able to turn the saw 90 degrees to make horizontal cuts.

I'm also thinking along the lines of the 3X13 vs the 6X13 debate and want to make my drone position opening scalable to any size between 2.4 X 10.4 and 4.8 X 10.4.

Past experience with passive radiators tells me the tighter the internal volume, the narrower they perform from a reduced ceiling perspective. These radiators have a matrix that computes their value-added based on the same factors used to compute ported tube specifics.

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The position (inside the horn) of the passive in the horn throat won't matter. It won't have any effect below the Fc of the horn either. Don't expect it to go lower in LF extension, that is not what it will do per se, it will just do a little LF "reinforcement" of what you normally would get with the non-ported dual driver version. That is, it won't fall off as rapidly due to the "boost" at the tuned resonant frequency, but it will still fall off below Fc as dictated by the horn itself. For a fictional example, the 40 Hz Fc horn will pass 32 Hz, but that will be at

-5db to -9db (?) for a Fc of 40Hz, (example). Tuning the port at 32 Hz will increase the output at 32Hz to -2db to -6db below Fc, (maybe as high as +5db overall if tuned inside the horn bandwidth) etc. Still rolling off, just got a bump at 32Hz due to the reflex port. Horns rolloff much faster below Fc than a BR cab. This is when the port is in a horn. The benefit is that the horn is a wider bandwidth device than a tuned port by itself, the drawback is that for frequencies below Fc, the horn actually takes away efficiency, instead of adding it. However, I should add less falloff will be perceived as being louder, off course, so perhaps I shouldn't say it doesn't add LF extension, if you look at it that way.

From all this, I would think that you would want to tune for just below the horn overall Fc, not well below like a BR box. At least that's my figuring.

Unless you are talking about a direct vent from the back chamber to the outside, (frontally vented through the front panel) is that what you mean? In that case, I would agree on the bottom position, THAT could be tuned as a sub, all things being equal.

But I'm confused because that isn't what you've drawn.

Dana

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D-Man

Maybe.

Issue I am thinking about in reguards to the location and placement of the passive radiator has to do with two factors in my mind.

The first is the value-add that the passive radiator will have based on how it is tuned. Typically this is 1/4 of an octave above and below the its resonace frequency and drops off pretty steeply at approx 18 db per octave. So lets's assume we can tune to add 1.5 db at 80 HZ for now with an 18 db rolloff in both directions.

The second issue has to do with human perceptions. Most folks percieve bass response to be more exciting when it is generated at floor level. As you raise the bass generator off the floor, say 12 - 18 inches, it is not percieved as loud. Not sure why. Maybe has something to do with running away from elephants during the caveman days.

Since my version has three seperate exit paths, I am thinking that the drone, which in our example is tuned at 80hz, will sound louder in the lower exit path, as opposed to the middle or top.

The actual frequency that the drone is tuned to has to due with the volume of the cab, playing around with wieghts that attach to the radiator and the resonace frequencies of the woofers as well as the radiator.

The parts express drone can be tuned to 16hz in a 5 cubic foot enclosure, assuming it's woofer partner can go down that low.

Unfortunately, we do not have 5 cubic feet in our concept model.

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SF, you only need to keep the port channel separate for the time it takes for soundwaves to travel the distance required for maintaining the proper phase relationship before "mixing". The throat area should be enough - what you've drawn would be correct for this.

Still, the vertical position of the passive/port won't matter. No effect.

Ok, bottom position is good for fiddling, which you will probably be doing with alternate slots, etc., but that is a matter of convenience, not sound.

The way the horn mouth works, it isn't like you think. It presents a vibrating sheet of air to the atmosphere, like a sheet of cellophane sealing the opening(s). The vibration is equal top-to-bottom and side-to-side, like a drum head. The whole mouth area vibrates evenly (more or less). If it doesn't then there is a problem.

Tuning the Vb for the reflex port below Fc will un-annull the front-loaded horn(s) and require some thought. That is a difficult balance.

I'm just pointing out things - not trying to talk you out of it! It's a learning experience, and you are going to teach! Post your experiences.

DM

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D-Man

Ok, sonds good, thanks for all the input.

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Roy, another ported-throat patent!

DM

dman,

going to have to change your board name to pman for patent man!! got the number at work, emailed my boss and an hour later, had the patent..... couldn't believe....i didn't know whether to email or call him so i emailed him and said.....

WHAT TOOK YOU SO LONG!!!! :)

interesting but not much thought given to manifolding the different acoustic sources but it is going into my vented horn folder. keep them coming.

thanks,

roy

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When the speaker is coupled to the floor, the cabinet vibrations in turn vibrate the floor which will act as a huge diaphragm (that doesn't need to move very much to produce SPL). A sort of "floor shock" if I can steal a term from Colter. Another possible factor is you start running into boundary gain cancellations:

http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

Btw, I get a tuning of 24Hz in a 5 cubic foot cabinet and 30Hz in a 2.5 cubic foot cabinet for that particular passive radiator using WinISD (without adding mass).

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DrWho

""Btw, I get a tuning of 24Hz in a 5 cubic foot cabinet and 30Hz in a 2.5 cubic foot cabinet for that particular passive radiator using WinISD (without adding mass)."""

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

We will need to add some mass to the radiator. There's not much action in a jubilee cab at 30hz. At a -18 db per octave roll off for the radiator, it would not add to much value at 45 - 60 hz. It certainly would not add anything from 15hz - 30hz. These radiators don't add much, 1.5 to 3db and they have a very narrow band, +- half an octave.

I was thinking we would not want to tune initially to less than 45hz. This would put the range of the radiator from 30hz - 60hz.

i expected to wind up at 60hz, putting the radiators range to 45hz - 75hz. More in line with the Jubilee cab lower end. Assuming that the cab exit path was the limitation and not the enclosure internal volume.

There will probally be both mass changes and throat mouth opening tweaks needed before all the saw dust settles.

My speaker building water stick tells me that we probally would get more mid-bass and bass if we went push-pull using the third position rather than going the passive radiator route. Provided there were seperate exit paths, common enclosure, and we use an autoformer to keep the impedance on target.

The hole will be there so testing both will be an option.

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Guys, with the drone. The cabinet may need to be a little taller. Maybe just over 37".

Dayton Drone 12-3/8
E. Kappa Pro 12.38
E. Kappa Pro 12.38

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jwcullison

A little taller in my case.

.75 horizontal top plate (top of cab)

12.5 inches kappa pro

.75 1st horizontal baffle

12.5 inches kappa pro

.75 2nd horizontal baffle

12.5 inches drone

.75 horizontal bottom plate (bottom of cab)

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wow. That's externally 41.5 inches tall w/o the top and bottom panels to cover the woofer access chamber. That will add 1 1/2 more inches.

So much for scaling down. But it sounds good.

Now to keep all the horns seperate for each driver and drone, are you basically "stacking" three horns. So with what you are calling "horizontal baffle", is this a large panel of 3/4 inch that will be just like the "bottom plate and top plate"?

One other thing. How will you make the slot opening for the drone "adjustable". That might be hard for me to visualize w/o a drawing. Will you just mount the drone on a square panel with a throat that is removable?.

I'm kinda wondering if the drone will make that much difference either. The kappa pro' s have an Fs of 37Hz and the Horn has a 40Hz cutoff. Will the goal be for the drone just to add a boost of dB just under 40Hz?

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