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adambomb 
Old Croc 
Joined: 10 April 2006 Location: United Kingdom Status: Offline Points: 3215 |
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 Posted: 15 April 2008 at 1:04pm |
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I would guess the bottom impedence hump is the low port tuning.. I think Rog said it was tuned below 20hz... looks like about 13 or 14hz to me.... must be some kick ass driver you have in there.
Alos have to say.. congrats man you must be chuffed with the results... I am soo looking forward to hearing these. Edited by adambomb - 15 April 2008 at 1:05pm |
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JaKe
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Joined: 14 September 2007 Location: N.E. Wales Status: Offline Points: 684 |
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Posted: 15 April 2008 at 1:19pm |
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Jake_Fielder
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Joined: 08 October 2007 Status: Offline Points: 4231 |
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Posted: 15 April 2008 at 1:22pm |
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Nope, im pretty sure that the first peak in impedance is the drivers resonance. the driver may have an Fs of 30Hz say, but once there is an airload either side of it the resonance drops down (its like adding mass to the drivers cone). The tuning frequency is between the two lowest peaks.
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Jake_Fielder
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Posted: 15 April 2008 at 1:27pm |
Thats what im thinking! its an incredible output for a port, usually you cant make the ports match the horn output, im amazed!
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FarmerWardy
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Joined: 05 April 2004 Location: United Kingdom Status: Offline Points: 647 |
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Posted: 15 April 2008 at 1:34pm |
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these things really do make me smile.
the thing that amazes me most is the amount of kick you get from something that goes so dam low. iv now forgotten what they sound like, but im sure the next time i hear it i will be just as amazed. |
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ceharden
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Joined: 05 June 2005 Location: Southampton Status: Offline Points: 11692 |
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Posted: 15 April 2008 at 1:53pm |
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There isn't an impedance peak for the driver at resonance because this is swamped by the port. Take a closed box, it has one impedance peak. For a reflex say you tune the port the same as the driver resonance, what you get are two peaks, one either side of the tuning frequency.
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Jake_Fielder
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Posted: 15 April 2008 at 2:17pm |
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All i know is that a driver on its own has a resonant frequency, and i thought that when you added a chamber with a port it added another impedance spike slightly above the tuning frequency, i thought the closer the tuning is to the drivers Fs the lower it moved it, also the higher you tuned the port the higher up in frequency the spike was, i also noticed as you tune the port higher and higher the spike gets smaller and smaller. But are you saying that by adding a chamber and port the drivers Fs is now not important, and you just get an impedance spike either side of the ports tuning frequency?
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JaKe
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Joined: 14 September 2007 Location: N.E. Wales Status: Offline Points: 684 |
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Posted: 15 April 2008 at 3:04pm |
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A loudspeaker in free air has one impedance spike at resonance (Fs), when you put it in a ported box tuned around the Fs it will damp the impedance spike but not completely leaving an undamped area either side of Fs.
If you move the tuning above Fs the lower spike will be larger than the upper spike, if you tune below Fs then the opposite will happen. You could then put another vented box on the other side of the driver and tune that to the upper peak say and you would now have three peaks, all smaller than the Fs. Looking at the plots the GD is very low at F3 and also the impedance spikes are small distortion is decent too. Damn. JaKe Edited by JaKe - 15 April 2008 at 3:08pm |
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ArKs
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Joined: 23 January 2006 Location: United Kingdom Status: Offline Points: 6 |
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Posted: 15 April 2008 at 5:54pm |
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Just played with Win-ISD - you can get a very similar impedance graph shape by using an 18XB in a 6th order bandpass cabinet with one side in a 140l box tuned to 30Hz and the other in a small 13l box tuned to 185Hz, but with the 110Hz spike missing which would be due the horn loading? Lowest spike looks like damped Fs, then 50Hz spike dictated by 30Hz tuning and 230Hz spike due tuning of small chamber.
I notice this in Pro Sound News this month which uses an interesting alignment:
which looks like a 6th order bandpass with a horn loaded front chamber, and large vented rear chamber?
Rich Edited by ArKs - 15 April 2008 at 6:09pm |
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chilli
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Joined: 28 July 2004 Location: United Kingdom Status: Offline Points: 1676 |
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Posted: 15 April 2008 at 6:22pm |
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jesus! who styled that?
thats one ugly bassbin  |
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Money can't buy you happiness, but it can allow you to be miserable in comfort.
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Jake_Fielder
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Posted: 15 April 2008 at 9:50pm |
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I wonder what the 4th (smallest) impeadiance peak means?
Also i was racking my brain to remember what the plot looked similar to...
... then i realised i was thinking about this! I know its not very similar but there are certain characteristics that i recognised,
@Rog, do you take your plots in a warehouse 26 meters wide by any chance?
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adambomb
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Joined: 10 April 2006 Location: United Kingdom Status: Offline Points: 3215 |
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Posted: 15 April 2008 at 10:41pm |
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I'll get me coat.
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adambomb wrote: