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Old 1st November 2009, 08:51 PM   #31
Wizard of Kelts
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Let me check to see if I still have the article. Reasonably certain I still do. If I do, I should be able to get some jpg's of the pages over to you in a couple of days. I don't do pdf's, but getting jpg's of the pages is the equivalent of somebody using a copy machine to make a copy for you. Still interested?
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Old 26th July 2013, 02:46 PM   #32
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Hi

Very interesting concept!
I am tempted...

Has anyone else tried it out?
Any experience would be helpful. In particular I still don't really understand how the perforated covering should look like (material, geometry?).

Maybe a good starting point would be to build a subwoofer? It could be used only below the half wavelength point which would make things a lot easier. E.g. no perforated cover necessary.
It could be placed in front of the listening position, directed at the listener.
Or maybe two such subwoofers at the front speaker positions?

Oliver
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Old 26th July 2013, 09:48 PM   #33
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2nd order gradient bass is not very useful in real terms. First of all, aside from the driver eq, a boost of 12dB per octave is necessary to achieve flat response in the gradient region. Second, the idea that there is directional control in an acoustically small room is incorrect. As always, in an acoustically small room low frequency response is controled by room modes. Third, driver excursion, once eaulaized to flat response, increases at 24dB/octave leading to excessive excursion if asked to opeate over any significant frequency range.
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Old 27th July 2013, 10:37 AM   #34
Elias is offline Elias  Finland
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There was a second order cardioid DIY speaker published in Finland in early 1990's. It was second order cardioid in the freq range of 100-400 Hz, if I remember correctly. It had two groups of 4 pcs of 8" seas elements, and the back group was delayed in order to cancel the back wave.

The most right in the picture. However can only see the front group clearly from it.
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Old 27th July 2013, 11:39 AM   #35
Elias is offline Elias  Finland
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HA ! I posted the same thing twice, last time more than 10 years ago ! Damn my memory is poor

This is the speaker:

Quote:
Originally Posted by Elias View Post
Hello!

There have been at least one second-order gradient construction that I'm avare of. It was published in "Hifi", a hifi magazine here in Finland in the early 90's and also in the book called "Rakenna Hifikaiuttimet" by Pekka Tuomela, 2nd corrected print, Tecnopress 1993, ISBN:951-832-034-9.

The book is in finnish, if that makes sense to you

The loudspeaker was called Hifi-C1. The second-order gradient principle was employed in the 100-400Hz range by using 4+4 Seas P21REX elements, 4 in front group and 4 in the rear. These elements were placed in square around midranges and tweeter.
Other elements were Philips RT8 ribbon tweeter >4kHz, 2* Seas MP14RCY 400Hz-4kHz placed below and above the tweeter, and cardioid bass < 100Hz using 2* Seas P21REX and 2* Seas P17REX. Filters were passive.

From the looks of the book it sure looks an impressive idea for a loudspeaker! It was said have been used as a reference speaker in the mentioned Hifi magasine tests. I have never heard the speaker, though.

Also, it is stated in the book that the author made also design of the second-order cardioid speaker for a commercial manufacturer, but I have no info about that.

Yes, it is a rare consept that I would like to see used more often. Actually, I've had the second-order cardioid concept on my mind when thinking what kind of speakers to build, but I've neglected the idea as too expensive to realise at home.


-Elias
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Old 29th July 2013, 09:57 AM   #36
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Quote:
Originally Posted by john k... View Post
2nd order gradient bass is not very useful in real terms. First of all, aside from the driver eq, a boost of 12dB per octave is necessary to achieve flat response in the gradient region.
Hello John

Using an 18" driver the amplitude falls off at 12 dB/octave below 370 Hz. When we want to use it down to 20 Hz a boost of 48 dB is necessary. This is indeed heavy...

Quote:
Second, the idea that there is directional control in an acoustically small room is incorrect. As always, in an acoustically small room low frequency response is controled by room modes.
A second order gradient can only excite room modes at velocity antinodes. And it can only excite them in one direction.
When it is placed in a velocity node corresponding to its orientation, no (axial) modes are excited at all meaning the behaviour is more like in free space. Apart from the increased power requirements I consider this an advantage.

Quote:
Third, driver excursion, once eaulaized to flat response, increases at 24dB/octave leading to excessive excursion if asked to opeate over any significant frequency range.
This is a challenge. Still, large drivers have essentially zero excursion at higher frequencies. Multiple drivers could be used. Maybe 21" drivers?

Best,
Oliver
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Old 29th July 2013, 10:04 AM   #37
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Hi Elias

Quote:
Originally Posted by Elias View Post
There was a second order cardioid DIY speaker published in Finland in early 1990's. It was second order cardioid in the freq range of 100-400 Hz, if I remember correctly. It had two groups of 4 pcs of 8" seas elements, and the back group was delayed in order to cancel the back wave.

The most right in the picture. However can only see the front group clearly from it.
Thanks for the picture!

The idea to use a different mechanism in the lowest frequency band is good. Maybe the driver to the front could simply be used as a dipole there. It only falls off at 6 dB/octave
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