Cardioid using aperiodic ports (Fulcrum Acoustics)
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Topic: Cardioid using aperiodic ports (Fulcrum Acoustics)
Posted By: kevinmcdonough
Subject: Cardioid using aperiodic ports (Fulcrum Acoustics)
Date Posted: 25 July 2017 at 8:06pm
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hey all really interested in this kind of thing...... http://www.audioxpress.com/article/fulcrum-acoustic-unveils-new-ccx-subcardioid-coaxial-loudspeaker" rel="nofollow - http://www.audioxpress.com/article/fulcrum-acoustic-unveils-new-ccx-subcardioid-coaxial-loudspeaker http://www.fulcrum-acoustic.com/products/cardioid-subwoofers/" rel="nofollow - http://www.fulcrum-acoustic.com/products/cardioid-subwoofers/ 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
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Replies:
Posted By: bob4
Date Posted: 06 August 2017 at 12:31am
| Afaik geithain uses the same method in their studio monitors |
Posted By: kevinmcdonough
Date Posted: 06 August 2017 at 3:35pm
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....
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The difference between an "aperiodic port" design and our passive cardioids is the acoustical mass of the ports and the amount of resistance. The acoustical mass in our passive cardioids puts a second-order low-pass filter a little below the frequency below which we want cardioid behavior. The resistance is just enough to damp the helmholtz resonance to "slightly underdamped" (Q of about 1). An aperiodic port design has almost no acoustical mass and is dominated by resistance, so there is essentially no helmholtz resonance and the resulting first-order low-pass corner is well above the passband; so it operates simply as a resistive leak that damps the sealed box resonance. If you look at the impedance of our passive cardioid subs, you'll see a trace of the double peaks of a ported box, but the dip between them doesn't go nearly as low. That's the effect of the port resistance.There is still significant reduction of excursion around the helmholtz frequency, and the summation of the rear radiation and front radiation increases the output over about 1 1/2 octaves. If you try to stretch the cardioid behavior beyond 1 1/2 octave, there will be a penalty in low frequency extension and maximum output.Posted By: Crashpc
Date Posted: 06 August 2017 at 4:40pm
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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. ------------- Nikon and Canon people should not be married to each other. Why did you let this happen? |
Posted By: kevinmcdonough
Date Posted: 06 August 2017 at 4:52pm
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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 |
Posted By: snowflake
Date Posted: 06 August 2017 at 9:32pm
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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" rel="nofollow - http://www.linkwitzlab.com/frontiers.htm#A are the vortex vents used by seventies-trousers an aperiodic port too? |
Posted By: toastyghost
Date Posted: 07 August 2017 at 4:32am
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... |
Posted By: snowflake
Date Posted: 07 August 2017 at 5:09pm
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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... |
Posted By: MattStolton
Date Posted: 07 August 2017 at 5:48pm
My first thoughts too!  ------------- Matt Stolton - Technical Director (!!!) - http://www.wildingsound.co.uk" rel="nofollow - Wilding Sound Ltd "Sparkius metiretur vestra" - "Meter Your Mains" |
Posted By: Hemisphere
Date Posted: 07 August 2017 at 6:50pm
Lots of interesting talk here ie: http://techtalk.parts-express.com/forum/tech-talk-forum/66622-bbc-style-thin-walled-cabinets-vs-tight-bass" rel="nofollow - 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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Posted By: snowflake
Date Posted: 08 August 2017 at 1:06pm
very interesting, thanks |
Posted By: Timo Beckman
Date Posted: 13 August 2017 at 10:46pm
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You guy's might find this interesting? https://timobeckmangeluid.wordpress.com/2017/08/13/end-fired-sub-array-with-2-fulcrum-acoustic-cs121-passive-cardioid-subs/" rel="nofollow - https://timobeckmangeluid.wordpress.com/2017/08/13/end-fired-sub-array-with-2-fulcrum-acoustic-cs121-passive-cardioid-subs/ 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/" rel="nofollow - 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..... https://timobeckmangeluid.files.wordpress.com/2017/08/img_1660.jpg?w=2000" rel="nofollow - https://timobeckmangeluid.files.wordpress.com/2017/08/img_1660.jpg?w=2000  ------------- The sound will be as good as the band play's |
Posted By: Timo Beckman
Date Posted: 19 August 2017 at 8:41pm
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I did a post on the difference between a "omni" and a "passive cardioid" sub. https://timobeckmangeluid.wordpress.com/2017/08/19/omni-vs-passive-cardioid/" rel="nofollow - https://timobeckmangeluid.wordpress.com/2017/08/19/omni-vs-passive-cardioid/ ------------- The sound will be as good as the band play's |
Posted By: Timo Beckman
Date Posted: 24 March 2018 at 12:22am
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I did a new post on a new model from Fulcrum Acoustic The CCX1295 is a passive mid-high speaker passive cardioid response @ the back. http://timobeckmangeluid.wordpress.com/2018/03/23/measuring-the-fulcrum-acoustic-ccx1295-passive-cardioid/" rel="nofollow - http://timobeckmangeluid.wordpress.com/2018/03/23/measuring-the-fulcrum-acoustic-ccx1295-passive-cardioid/ ------------- The sound will be as good as the band play's |