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JF Vented Horn (P-audio E18-600a)
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Jake_Fielder View Drop Down
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Joined: 08 October 2007
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    Posted: 04 April 2008 at 10:14am
Ok, im have a final design for a ported horn, im going to prototype it in about a month, if anyone knows of any reason i should re-design this or scrap it let them speak now or forever hold their peace!
 
The design looks a little like this: But picture the port folded so you can get the driver out of the top, (outer dimentions will be something like 818mm x 636mm x 636mm) 
 
The mouth is 3600cm2 not 4800 as the diagram states.
 
 
Input Parameters:
 
Sensitivity 1w/1m: (bear in mind the idea is to EQ the tuning freq up (37Hz) as there is V low excursion at this point)
 
Driver excursion plot at 700w - probably the most i'll put through these....
 
I know the xmax isnt rated at 10mm, but i've been talking about this before and i was thinking of giving it a try anyway....
 
Heres the little fellas!:


Edited by Jake_Fielder - 08 April 2008 at 3:39pm
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jethrocker View Drop Down
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Points: 1942 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jethrocker Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2008 at 10:32am
Just wondering when looking at the plots how the eq will work out. The problem is in order to get a flat response down to the port tuning frequency you're going to need to apply boost from just under 37 up to about 55Hz...this is taking you into the area of peak excursion above the tuning frequency, so your excursion might be worse than predicted. It's always said HR excursion plots are exaggerated, but I'm never sure by how much, I'm guessing it's not likely to be worse overall in reality than the 11mm on the plot.
You're other option is to eq with a bit of a dip around 55Hz, might give you higher overall safe output, but also a particular sound, which might be what you want..
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Jake_Fielder View Drop Down
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Yes, i think there will be a dip, i'll just find what i wrote about it before... i also think i drew a pic of what it might look like.....

 
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Jake_Fielder View Drop Down
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This is what i predicted it may look like:
 
Obviously when i prototype it i will work out the best EQ to get the plot as flat and low as possible without increacing excursion beyond the highest it is now.
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Jake_Fielder View Drop Down
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Originally posted by ME! ME! wrote:

As far as the predicted plot goes, atm its looking like for 1w @1m 103dB +/-2 from 52Hz-225Hz. The tuning frequency of the port is 37Hz and the idea is that at the tuning frequency i can give the eq a massive boost without risk of over excursion, hopfully bringing 37Hz up to the same sensitivity as the rest of the usable bandwidth. With a highpass filter just below the tuning frequency (like 34/35).
 
Of course it could end up nothing like how i want it, and the prototype could be a bag of wank. Only one way to find out though!
 
I dont know how the EQing will work, hopefully it will be as expected, I do think there will be a slight dip in the response after eq between the horn drop off to the tuning freq (i'll draw a pic) this wont be able to be EQd out as the driver will move to far (thats my guess).
 
That about it! I'll have to wait a while (for money) then i'll prototype. i'll make four or eight if its good, the idea is its 1 way, bass and kick in one, it should play high(ish) as its not too folded, and also down to ~35Hz (i hope) Its also not too big and reasonably efficient, so if it all works out i'll be well chuffed!
 
Thats what i thought originally, and i know its a risky buisness, but if this works and has a reasonable flatish output from 35-180 with a bit of EQ and sound half decent then it'll be a great result for a single cab of that size....
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darkmatter View Drop Down
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Points: 2419 		Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2008 at 1:19pm
Will using eq affect the phase around that point, or is that not something you really need to worry about?
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Jake_Fielder View Drop Down
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I'm not sure, if it did affect the phase what would happen?
 
i was just going to use delay to match the top frequency ~Hz to what ever mid tops i use, then not worry about what happens bellow the crossover point. I haven't prototyped any of my designs yet so i don't know if I'm doing it right,
 
I think that the tuning of this cab will be different to whats been predicted, so 'I'll just have to work it out after i build it, i defiantly don't want to eq the wrong bit! IE anywhere thats not the tuning frequency!
 
Deaddriver!
 
 
 
Come to think of it, this design is also a parallel 6th order bandpass with a flared port.
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darkmatter View Drop Down
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Originally posted by Jake_Fielder Jake_Fielder wrote:

I'm not sure, if it did affect the phase what would happen?
 


no idea i was hoping you could tell meEmbarrassed

i guess i was just wondering whether you'd effectively be changing the group delay by having to eq the signal that goes into the cab. but im probably worrying about nothing as the difference would no doubt be imperceptible - people like scoops so...

yeah would kind of destroy the point in going for a good value driver if you have to go through 4 just finding the eq point lolLOL
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Jake_Fielder View Drop Down
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When i build it im going to put a tone from a signal generator through an amp (about 200w) and go up and down until i find the tuning point (where the driver moves least), then EQ the hell out of it at that point!!
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Jake_Fielder View Drop Down
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Originally posted by darkmatter darkmatter wrote:


no idea i was hoping you could tell meEmbarrassed
As far as i know, using any EQ or limiter or crossover will shift the phase slightly, depending on what type of filter is used...
Originally posted by darkmatter darkmatter wrote:


yeah would kind of destroy the point in going for a good value driver if you have to go through 4 just finding the eq point lolLOL
Ha, yep, im gonna have to be careful, Hopefully once i have done all the complicated stuff i can draw up a design that anyone can use, as a simple buget speaker, with a good frequency range! (fingers crossed!)


Edited by Jake_Fielder - 26 August 2009 at 6:03pm
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Disco Stu View Drop Down
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Hi Jake I would be tempted to do a couple of things to try and even out the cone loading, as I remember the E18 driver has quite a thin cone.

1) Reverse the driver to aid heat escaping
2) Mount the driver parallel to the back wall of the cab if possible to prevent some uneven stresses caused by one side of the cone being closer to a surface than the other.

Stu
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Jake_Fielder View Drop Down
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Joined: 08 October 2007
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Points: 4236 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 07 April 2008 at 10:14am

The loading will be better than the pic i put up, i have since drawn it out to scale and it looks much better, the chamber in front of the driver is almost symetrical (in 2d) and the port is folded in such a way that the rear chamber isnt too bad.

I thought as its ported it would be better that way round? especially at the tuning freq, as all the air is moving through the port, but i would have thought that above the tuning freq the horn side was cooler....? what do you think?
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