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jsg mashed View Drop Down
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Points: 305 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 6:49pm
OK, so he's feeding the rear cone output through two cascaded resonators.
 
I can believe that this could make it easier to meet port area requirements for the final output port without them being insanely long - the same thing happens in bandpasses with cascaded resonators.
 


Edited by jsg mashed - 28 March 2008 at 7:00pm
...because Good is Dumb.
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josh View Drop Down
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Sorry as a side note, how do you work out the optimum area that a port should be, is it something to do with the size of the chamber?
 
thanks
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Points: 2744 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tb_mike Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2008 at 2:37am
Originally posted by josh josh wrote:

Sorry as a side note, how do you work out the optimum area that a port should be, is it something to do with the size of the chamber?
 
thanks


http://www.diysubwoofers.org/prt/
You can see it depends on area,and volume of the enclosure.


Quote Port Length
The port length required to tune a volume of air to a specific frequency can be calculated by using the following equation:

   Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

where,

    Dv = port diameter (cm)
    Fb = tuning frequency (Hz)
    Vb = net volume (litres)
    Lv = length of each port (cm)
    Np = number of ports
     k = end correction (normally 0.732)
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jsg mashed View Drop Down
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Points: 305 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2008 at 1:35pm
Originally posted by tb_mike tb_mike wrote:

Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)
 
That formula determines port length given a certain area. To actually choose the area, the usual rule is to keep velocity less than 5% of the speed of sound. Some modelling programs give port velocity.
 
...because Good is Dumb.
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Jake_Fielder View Drop Down
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Rog said that the chamber behind each of the drivers is ~20L and with the port area he choose the ports would need to be 4.5meters long!!!!!
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jsg mashed View Drop Down
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Points: 305 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 10:57am
Originally posted by Jake_Fielder Jake_Fielder wrote:

Rog said that the chamber behind each of the drivers is ~20L and with the port area he choose the ports would need to be 4.5meters long!!!!!
 
Yup, so that's a big area and a small chamber, and presumably a lowish tuning freqeuncy, making for a long port.
 
...because Good is Dumb.
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Jake_Fielder View Drop Down
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Points: 4231 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 11:01am
Yeah, i optomisically thought i could grasp how that theory worked and apply it to a design of mine to free up space taken up by a port and give me more room for horn length.
 
Does anyone know where i can read up about this, or should i give up and just prototype what i have so far?
 
Cheers
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adambomb View Drop Down
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Points: 3215 		Post Options Post Options   Thanks (0) Thanks(0)   Quote adambomb Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 11:59am
he also said it works like "blowing accross the top of a bottle"
 
I have already sketched this.. I'm pretty sure I have a rough idea of the inards... no I'm not posting my ideas.
www.freespeakerplans.com
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Jake_Fielder View Drop Down
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Points: 4231 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 12:04pm
Yeah, i already know the general layout, its not like i could even start trying to work out the plans for Rogs cab, and i dont want to.
 
Im just interested in replacing a long port with a smaller chamber, in a different design.
But i think its probably more trouble than its worth (unless Rog wants to lend me his brain for a weekend)
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Ha ha,
 
To do you're heads in a bit more the port tuning frequency is sub 30Hz, so <30Hz.
 
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Jake_Fielder View Drop Down
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Points: 4231 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 2:54pm
I give in, im going to build my prototype cab how it is, I think im being too optomistic! im not even sure that this "Rog effect" chamber would benefit me anyway.
 
My Design (its almost the same as the one i posted on this thread but designed around the E18-600A, but with a folded portErmm) if you're interested is a horn with a ported rear chamber, Tuned to something like 35Hz although i dont recall exactly, i havent looked at it for a while, i need to save up!


Edited by Jake_Fielder - 31 March 2008 at 2:55pm
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Jake_Fielder View Drop Down
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Points: 4231 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 31 March 2008 at 4:54pm
@JSG Back on the bandpass bandwagon again, just re-reading this thread again, im gonna start a new thread in a bit with all this stuff set out nicely and i'll cover the basics of band pass for referance for other people.
 
you say that the driver is 2 orders (in a sealed chamber or not), every chamber and port added is 2 more orders, the rear chamber is included in the drivers suspention until its ported, adding two more orders.
 
So can you not get odd numbers? i assume the 2 orders come from the mass of the port and the "suspention" of the chamber, so what ever hapens you cant add just one? or am i wrong.?
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