Cardioid using aperiodic ports (Fulcrum Acoustics) |
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3749 |
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Posted: 25 July 2017 at 8:06pm |
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hey all
really interested in this kind of thing...... Using aperiodic ports at the rear of the speaker to create passive cardioid dispersion. Anyone any links with more info to see exactly how this is done? Forgetting about the cardioid aspect for a bit, as I understood it these kinds of "vents" lowered the impedance spikes of cabs and made them perform more like sealed boxes or infinite baffles, by giving a restive "air leak". But a sealed box doesn't have the greatest bass response obviously. So does that mean if I was doing a sub version, I'd really need to have traditional ports as well as the vents to get the driver to play low enough? Or would just adding a very large vent area be enough to accomplish the amount of tuning that a port would otherwise create? K
Edited by kevinmcdonough - 25 July 2017 at 8:28pm |
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bob4
Old Croc Joined: 29 February 2004 Location: Finland/Germany Status: Offline Points: 1842 |
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Afaik geithain uses the same method in their studio monitors
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3749 |
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Dave Gunness himself (designer, and made famous with Gunness Focusing among other things) was kind enough to reply to the same questions I posted on another forum. His reply below, for anyone who's interested....
Edited by kevinmcdonough - 06 August 2017 at 3:36pm |
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Crashpc
Registered User Joined: 26 February 2008 Location: Czech Republic Status: Offline Points: 463 |
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Doesn't sound right to me. Like saying A, not B... Aperiodic ports were here for ages with us. And for sure these have different performance. But connecting it with boasting about directivity alone is rather a long shot. Quite a drag in my eyes.
Edited by Crashpc - 06 August 2017 at 4:43pm |
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Nikon and Canon people should not be married to each other. Why did you let this happen?
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3749 |
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Well he wasn't saying that the ports were aperiodic, someone else had described to me that that was how they worked. However as he replied in his message, his ports are somewhere in between, not purely traditional ports or purely aperiodic ones.
And its more the fact that they are set up in a particuluar way at the rear of the cab, so their radiation cancels with the cone sound and creates the cardioid aspect. Kev |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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not sure if this is the same idea taken to the extreme of having the entire back of the cabinet open with an acoustic resistor in series with the volume compliance:
http://www.linkwitzlab.com/frontiers.htm#A are the vortex vents used by seventies-trousers an aperiodic port too? |
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toastyghost
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I trust Dave’s data very much. Even if I disagree with some Of his methods in principle I can’t deny the results. Also careful not to use the word vortex in relation to ports eh? Oh sh... |
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snowflake
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what's the effect of making the box out of thin but well damped wood instead of thick, stiff wood. surely this would damp the q of the box in a similar way to introducing resistance in the port and also dramatically reduce the weight...
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MattStolton
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My first thoughts too!
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Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains" |
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Hemisphere
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Lots of interesting talk here ie: http://techtalk.parts-express.com/forum/tech-talk-forum/66622-bbc-style-thin-walled-cabinets-vs-tight-bass And an ongoing thread in the Diyaudio Full Range section front page.
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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very interesting, thanks |
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Timo Beckman
Registered User Joined: 09 August 2011 Location: Netherlands Status: Offline Points: 197 |
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You guy's might find this interesting?
After this one there's a gradient sub array (https://timobeckmangeluid.wordpress.com/2017/08/17/gradient-sub-array-or-reversed-end-fired-sub-array/) with the same subs (back sub delayed to the front sub and after the phase alignment reverse polarity) . I hope to find the time to do a measurement on 1 Fulcrum CS121 at Thursday / Friday if the weather allows it. That will show the difference between the front and back in level..... Edited by Timo Beckman - 17 August 2017 at 3:35pm |
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The sound will be as good as the band play's
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