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Idle Scoop Thinking |
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tweeter box 
Old Croc 
Joined: 21 October 2007 Location: United Kingdom Status: Offline Points: 6784 |
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 Posted: 05 February 2008 at 6:53pm |
 The full size version!
 Edited by tweeter box - 05 February 2008 at 7:19pm |
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Jake_Fielder
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Joined: 08 October 2007 Status: Offline Points: 4231 |
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Posted: 05 February 2008 at 7:30pm |
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I just did scale modles of the HOG unraveled and my design on page one of this thread....
Stapiers does look slightly better.....
 ahaha |
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Jake_Fielder
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Posted: 05 February 2008 at 7:37pm |
The Horn expantion rate isnt constant... ie, the horn path gets bigger and smaller, i'll do a drawing of the horn as if it was straightened out...
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Jake_Fielder
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Posted: 05 February 2008 at 8:47pm |
If you look, your horn path doesnt always expand and the corners are a bit dodgy, i'll see if i can tidy it up a bit....
Also if you angle the baffle downwards then you get a bigger mouth and the cab can drop lower.
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jethrocker
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Joined: 07 June 2006 Location: Chiapas, Mexico Status: Offline Points: 1942 |
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Posted: 06 February 2008 at 2:08am |
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Actually Jake another of my sketches made around the time I was was thinking about the one you posted was basically the same as yours, but I also found that in this layout it was impossible to get a good expansion in the first couple of flare sections without the box getting ridiculously deep..like 1m plus... i think that was what led to the sketch you posted with the horizontal folds, same horn length more or less but much better expansion.
With regard to your question as to the downside of the long barely expanding section I think as mentioned in another post above this could end up sounding just like a very long narrow port, ie, very muddy. |
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jethrocker
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Joined: 07 June 2006 Location: Chiapas, Mexico Status: Offline Points: 1942 |
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Posted: 06 February 2008 at 3:21am |
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While I'm here I'll post a few of my old sketches made around the same time..
First up, ridiculous double hog drawn just for the sake of amusement, just because it looks so damn heavy, in all senses of the word... Totally impractical, horn expansion in this one is also completely off and mouth size would be nowhere near enough for the two drivers and long horn paths..  Next two are a mini based on the sketch you referenced...Again just a layout idea and never modelled..   last one not really relevant to your thread but I'll put it here anyway, this was meant to be a simple scoop layout, based on the super but cheaper to build, uses a shelf at the first fold to lengthen horn a little and tighten the throat, depth of cab could be adjusted to suit required throat/chamber dims.  |
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mykey
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Joined: 18 August 2005 Location: UK/Indonesia Status: Offline Points: 9680 |
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Posted: 06 February 2008 at 4:07am |
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I like the first two Jethrocker, I have a similar drawing to the second one
what would the horn lengths be??
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jethrocker
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Posted: 06 February 2008 at 7:26am |
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A quick check with the cable from my headphones says the mini is getting on for 2.5 metres..
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mykey
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Joined: 18 August 2005 Location: UK/Indonesia Status: Offline Points: 9680 |
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Posted: 06 February 2008 at 7:55am |
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thats weird! my chewing gum says 2.3
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Jake_Fielder
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Posted: 06 February 2008 at 8:40am |
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Cheers for the input jethro. Those are some nice looking scoop ideas, Its so difficult fitting the horn length you want and the expantion rate you want inside the outer dimentions you want!! Is there any way to tell if an expantion rate is to slow? or does it come down to experiance?
I didnt think the horn path/expantion on my first diagram was vastly different to the hog, but when i unravelled them it showed up how poor the expantion rate was on my design!!
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tommysb
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Joined: 24 April 2006 Location: Finland Status: Offline Points: 1036 |
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Posted: 06 February 2008 at 10:41am |
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You want the expansion of the scoop to be exponential ideally (probably) to get horn loading on the driver. THink of the scoop as a rear loaded horn/transimission line. This is how it works in my mind anyway.....
SO you want the horn to be tuned to the lowest frequeny you want to produce. the rate at which the horn expands affects the tuning frequency. If you look at some of the expansion rates, you have a very slow expansion at first (exponential). THis will help you keep your narrow throat.
If you're trying to achieve a 30Hz cutoff with a front loaded horn then the maths says you need a massive mouth to get fully horn loaded at those frequencies. Luckily, with a scoop, you have a couple of other factors coming into play.
You have the front radiating part of the output. In something like the hog/dubsub you also have the rear wave affecting the front of the driver, i think, in a similar way to how 'tapped horns' work. And for wavelengths where the rear horn isn't affectively loaded by the horn, you have a wave reflected back which affects the speaker, either interfering destructively/constructively.
But back to your initial 'flare rate'. Look at Staiper's cross section. THat looks like an exponential flare. If you're not sure about tuning it, go into hornresp and play around with the different horn lengths required for different flare 'cutoff' frequencies, for different throat sizes. Then look at the schematic diagram, if you want a visual representation of how quickly the horn is expanding.
THis should help with trying to determine a 'sensible' flare rate.
I mhave manages to fit 4m of horn into a box about 60cmx80cmx30cm, but it is a bit of a specialised case, being used for a home theatre sub. It is also using a 10" driver, so the throat can be very small in cross section (maybe 150cm^2 at the start), and using a very small mouth, as I would like it to act like a transmission line, (a bit), so it doesn't need to have a large mouth in the same way a scoop does.
It isn't finished yet so no idea if it works...... Just sharing my thoughts about how you work this out with you!
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tweeter box
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Joined: 21 October 2007 Location: United Kingdom Status: Offline Points: 6784 |
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Posted: 06 February 2008 at 11:47am |
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Aaaaaahh i get what you mean about the expansion rate thingy now!
Ok gonna work some more on the design!
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tweeter box wrote: